bluuebunny/crossref_metadata_2025 huggingface dataset:
Putative pre- and postsynaptic ATP-sensitive potassium channels in the rat substantia nigra in vitro
Authors: Watts AE , Hicks GA , Henderson G
Published: April 2018

Pre- and postsynaptic adenosine 5′-triphosphate-sensitive potassium (ATP-K+) currents were studied using whole-cell recordings from substantia nigra zona compacta “principal” neurons in midbrain slices. The GABAA and GABAB receptor-mediated synaptic potentials were unaffected by the ATP-K+ channel inhibitor glibenclamide (30 microM) or by the opener diazoxide (500 microM), indicating that ATP-K+ channels on GABA-ergic terminals are not active, nor can they be activated pharmacologically, under control conditions. However, application of a glucose-free solution to reduce intracellular ATP levels caused a reduction of the GABAB IPSP in all neurons. This was substantially reversed by the sulfonylurea inhibitor tolbutamide (300 microM) in 50% of the neurons tested. The reduction of the GABAB IPSP was a presynaptic effect since postsynaptic hyperpolarizations induced by the GABAB receptor agonist baclofen (10 microM) were unaffected by glucose- free solutions. Diazoxide (500 microM) induced a slowly developing hyperpolarization or outward current in 64% of principal neurons, which was tolbutamide- (100–300 microM) or glibenclamide- (30 microM) sensitive. In contrast, the GABAB receptor agonist baclofen (30 microM) induced a rapid hyperpolarization or outward current in all neurons tested that was unaffected by tolbutamide (300 microM). Although both the diazoxide-induced current and the baclofen-induced current were inhibited by Ba2+ (300 microM), the currents elicited by diazoxide and baclofen summated. The reversal potential for the diazoxide-induced current was also less negative than that for baclofen, which was close to EK. In the presence of intracellular cesium, diazoxide induced a tolbutamide-sensitive inward current in a proportion of neurons, indicating that it has other actions in addition to activating a potassium current. Our results suggest that functional ATP-K+ channels exist both pre- and postsynaptically in the SN, where they modulate the activity of principal neurons. They are different to the potassium channels activated by the GABAB receptor agonist baclofen.
A novel metabotropic glutamate receptor expressed in the retina and olfactory bulb
Authors: Duvoisin RM , Zhang C , Ramonell K
Published: April 2018

A novel metabotropic glutamate receptor, mGluR8, was identified by screening a mouse retina cDNA library. This receptor is most related to mGluR4, mGluR7, and mGluR6 (74%, 74%, and 70% identical amino acid residues, respectively). Similar to these receptors, stimulation by L- glutamate or L-2-amino-4-phosphonobutyrate (L-APB) of Chinese hamster ovary (CHO) cells stably transfected with mGluR8 result in the inhibition of forskolin-stimulated adenylyl cyclase. In situ hybridization studies revealed a strong expression of the mGluR8 gene in the olfactory bulb, accessory olfactory bulb, and mammillary body. A weaker expression was found in the retina, and in scattered cells in the cortex and hindbrain. During development, the distribution of mGluR8 expression was more widespread. These results extend the diversity of metabotropic glutamate receptors in the CNS. Because at least two APB receptors are expressed in the retina, the use of this drug to block selectively the ON pathway needs to be reconsidered. The pharmacology and expression of mGluR8 in mitral/tufted cells suggest it could be a presynaptic receptor modulating glutamate release by these cells at their axon terminals in the entorhinal cortex.
cGMP inhibits L-type Ca2+ channel currents through protein phosphorylation in rat pinealocytes
Authors: Chik CL , Liu QY , Li B , Karpinski E , Ho AK
Published: April 2018

In this study, the effect of cGMP on the dihydropyridine-sensitive (L- type) Ca2+ current was investigated using the whole cell version of the patch-clamp technique in rat pinealocytes. Dibutyryl-cGMP (1 x 10(-4) M) induced a pronounced inhibition of the L-type Ca2+ channel current. The dibutyryl-cGMP effect was concentration dependent. Elevation of cGMP by nitroprusside had a similar inhibitory action on the L-type Ca2+ channel current. Norepinephrine, which increased cGMP in rat pinealocytes, also inhibited this current. The action of cGMP was independent of cAMP elevation since the cAMP antagonist, Rp-cAMPs, had no effect on the inhibitory action of dibutyryl-cGMP. The involvement of cyclic GMP-dependent protein kinase was suggested by the blocking action of two protein kinase inhibitors, (1-(5-isoquinolinesulfonyl)-2- methylpiperazine (H7) and N-(2-guanidinoethyl)-5- isoquinolinesulfonamide (HA1004), on the dibutyryl-cGMP effect on the L- type Ca2+ channel current. Taken together, these results suggest that (1) cGMP modulates L-type Ca2+ channel currents in rat pinealocytes, causing inhibition of this current; (2) the action of cGMP appears to be independent of cAMP elevation; and (3) phosphorylation by cGMP- dependent protein kinase may be involved.
TOPA quinone, a kainate-like agonist and excitotoxin is generated by a catecholaminergic cell line
Authors: Newcomer TA , Rosenberg PA , Aizenman E
Published: April 2018

The quinone derivative of 2,4,5-trihydroxyphenylalanine (TOPA) is a selective non-NMDA agonist and excitotoxin. While 3,4- dihydroxyphenylalanine (DOPA)-containing physiological solutions have been shown to generate TOPA and TOPA quinone (TOPA compounds), there have been no previous reports demonstrating the formation of this toxin in biological preparations. Here, using a pheochromocytoma catecholaminergic clonal cell line (PC12), we have identified TOPA compounds as by-products of catecholamine synthesis. PC12 cells incubated for 45 min with 30 microM tyrosine as a catecholamine precursor produced 1.0 +/- 0.2 pmol/10(6) cells of total TOPA compounds. The formation of these compounds could be enhanced nearly twofold when the cells were stimulated with 56 mM KCl. Moreover, the addition of a DOPA decarboxylase inhibitor (30 microM NSD-1015) increased the formation of TOPA compounds in both the unstimulated and stimulated conditions to a maximum of 5.5 +/- 0.7 pmol/10(6) cells after a 45 min incubation. A time-course analysis revealed that DOPA production above baseline levels coincided with the detectable generation of TOPA compounds. Finally, we observed an inhibition of TOPA compounds formation by 100 microM reduced glutathione, suggesting that these catecholamine products are formed from the extracellular autoxidation of DOPA. We propose that TOPA quinone may be an underestimated component of catecholamine toxicity that could be partly responsible for the demise of neurons in several neurodegenerative disorders, including Parkinson's and Huntington's disease. In addition, TOPA quinone may represent the first identified selective non-NMDA agonist that may be synthesized in the brain.
Presynaptic influence on the time course of fast excitatory synaptic currents in cultured hippocampal cells
Authors: Mennerick S , Zorumski CF
Published: April 2018

Since the lifetime of synaptically released glutamate is thought to be very brief, reflecting diffusion and glutamate uptake, the decay of synaptic currents is thought to represent the average elementary lifetime of a receptor channel bound only once by transmitter molecules. We show here that the decay of evoked non-NMDA synaptic currents can reflect presynaptic factors, in particular, the prolonged action of transmitter at postsynaptic receptors under conditions of enhanced transmitter release. We show that diffusion, high-affinity glutamate uptake, and non-NMDA receptor desensitization are insufficiently rapid to limit the decays of evoked synaptic currents to those of miniature synaptic currents in microcultures of rat hippocampal cells. Our results are consistent with recent studies suggesting that during evoked release, multiple glutamate quanta can interact with overlapping postsynaptic receptor domains.
Entorhinal-hippocampal connections and object memory in the rat: acquisition versus retention
Authors: Vnek N , Gleason TC , Kromer LF , Rothblat LA
Published: April 2018

Investigations of the neurobiology of memory using experimental animals have modeled many of the characteristic features of amnesia seen in human clinical populations. To examine long-term memory, however, animal models of amnesia often employ extended measures of acquisition, which stand in contrast to the retention measures used with humans. To determine the role of entorhinal-hippocampal circuitry on both information acquisition and long-term retention, rats with bilateral transections of the angular bundle were trained on three object discrimination problems and then retrained two weeks later to measure retention. Animals with discrete lesions of the angular bundle, which disrupted perforant path connections from the entorhinal cortex to the hippocampus and efferent hippocampal-cortical projections, acquired the object discrimination problems normally but showed a marked deficit in retention. These findings are important because they indicate that the role of entorhinal-hippocampal connections may be limited to maintaining some types of information (e.g., single object discriminations) for retention. This dissociation, moreover, suggests that behavioral paradigms that include a measure of retention may be particularly important for characterizing the mnemonic functions of the hippocampal/parahippocampal region.
Excitotoxic activation of the NMDA receptor results in inhibition of calcium/calmodulin kinase II activity in cultured hippocampal neurons
Authors: Churn SB , Limbrick D , Sombati S , DeLorenzo RJ
Published: April 2018

Neurotoxic effects of excitatory amino acids have been implicated in various neurological disorders, and have been utilized for excitotoxic models of delayed neuronal cell death. The excitotoxic glutamate- induced, delayed neuronal cell death also results in inhibition of calcium/calmodulin-dependent kinase II (CaM kinase II). In this report, we characterized the glutamate-induced inhibition of CaM kinase II in relation to loss of intracellular calcium regulation and delayed neuronal cell death. Glutamate (500 microM for 10 min), but not KCl (50 mM), exposure resulted in a significant inhibition of CaM kinase II activity. The inhibition of CaM kinase II activity was observed immediately following excitotoxic glutamate exposure and present at every time point measured. Glutamate-induced inhibition of kinase activity and delayed neuronal cell death was dependent upon both the activation of the NMDA glutamate receptor subtype and the presence of extracellular calcium. The relationship between inhibition of CaM kinase II activity and loss of intracellular calcium regulation was also examined. Experimental conditions which resulted in significant neuronal cell death and inhibition of CaM kinase II activity also resulted in a long-term loss of intracellular calcium regulation. Thus, inhibition of CaM kinase II activity occurred under experimental conditions which resulted in loss of neuronal viability and loss of neuronal calcium regulation. Since the glutamate-induced inhibition of CaM kinase II activity preceded neuronal cell death, the data support the hypothesis that inhibition of CaM kinase II activity may play a significant role in excitotoxicity-dependent, delayed neuronal cell death.
Functional analysis of human MT and related visual cortical areas using magnetic resonance imaging
Authors: Tootell RB , Reppas JB , Kwong KK , Malach R , Born RT , Brady TJ , Rosen BR , Belliveau JW
Published: April 2018

Using noninvasive functional magnetic resonance imaging (fMRI) technique, we analyzed the responses in human area MT with regard to visual motion, color, and luminance contrast sensitivity, and retinotopy. As in previous PET studies, we found that area MT responded selectively to moving (compared to stationary) stimuli. The location of human MT in the present fMRI results is consistent with that of MT in earlier PET and anatomical studies. In addition we found that area MT has a much higher contrast sensitivity than that in several other areas, including primary visual cortex (V1). Functional MRI half- amplitudes in V1 and MT occurred at approximately 15% and 1% luminance contrast, respectively. High sensitivity to contrast and motion in MT have been closely associated with magnocellular stream specialization in nonhuman primates. Human psychophysics indicates that visual motion appears to diminish when moving color-varying stimuli are equated in luminance. Electrophysiological results from macaque MT suggest that the human percept could be due to decreases in firing of area MT cells at equiluminance. We show here that fMRI activity in human MT does in fact decrease at and near individually measured equiluminance. Tests with visuotopically restricted stimuli in each hemifield produced spatial variations in fMRI activity consistent with retinotopy in human homologs of macaque areas V1, V2, V3, and VP. Such activity in area MT appeared much less retinotopic, as in macaque. However, it was possible to measure the interhemispheric spread of fMRI activity in human MT (half amplitude activation across the vertical meridian = approximately 15 degrees).
Interactions between segmental homologs and between isoneuronal branches guide the formation of sensory terminal fields
Authors: Gan WB , Macagno ER
Published: April 2018

Process outgrowth and peripheral field innervation by an identified mechanosensory neuron were examined in the intact embryonic leech. The dorsal pressure-sensitive (PD) neurons of the leech CNS are found as bilateral pairs in every segmental ganglion, and are amenable to study at early ages in intact embryos. Each PD has one major axonal projection that putatively pioneers the nerve to the dorsal body wall and branches extensively in its own segment, and two minor projections that innervate, via neighboring ganglia, smaller areas in adjacent segments. We found that adjacent embryonic PD cells form overlapping terminal fields in the body wall, but that the extent of overlap was governed by inhibitory interactions among these fields. When one PD neuron was ablated, the adjacent PD cell changed its peripheral arborization by (1) its major axon producing more filopodia and extending longer side branches toward the ablated cell and (2) its minor axon producing a large arbor in the operated segment. Interestingly, although growth was biased toward the side of the ablated neuron, reduced outgrowth of the PD cell was found on the side away from the ablation, while the total extent of arborization of the PD cell kept relatively constant. Further, we found that axotomy of the major PD projection resulted in extensive outgrowth of its minor projections. These results suggest that a single PD neuron has a limited capacity for growth, each of its branches growing at the expense of the others, and that inhibitory interactions between neighboring PD neurons influence the extent and direction of that growth.
Noxious thermal and chemical stimulation induce increases in 3H-phorbol 12,13-dibutyrate binding in spinal cord dorsal horn as well as persistent pain and hyperalgesia, which is reduced by inhibition of protein kinase C
Authors: Yashpal K , Pitcher GM , Parent A , Quirion R , Coderre TJ
Published: April 2018

We have previously suggested that protein kinase C (PKC) contributes to persistent pain in the formalin test. This study compared the effects of pharmacological inhibition of PKC with either GF 109203X or chelerythrine on persistent pain following noxious chemical stimulation with its effects on mechanical hyperalgesia, which develops in the hindpaw contralateral to an injury produced by noxious thermal stimulation. Furthermore, we have assessed changes in membrane- associated PKC in spinal cord in response to both noxious chemical and thermal stimulation. Nociceptive responses, to a hindpaw injection of 50 microliters of 2.5% formalin, and flexion reflex thresholds, to mechanical stimulation (Randall-Selitto test) in the hindpaw contralateral to a thermal injury (15 sec immersion in water at 55 degrees C), were assessed following intrathecal injection of PKC inhibitors (GF 109203X or chelerythrine). Changes in the levels of membrane-associated PKC, as assayed by quantitative autoradiography of the specific binding of 3H-phorbol-12,13-dibutyrate (3H-PDBu) in spinal cord sections, were assessed in rats after noxious chemical (50 microliters of 5.0% formalin) and noxious thermal (90 sec immersion in water at 55 degrees C) stimulation. Inhibitors of PKC (GF 109203X, chelerythrine), produced significant reductions of nociceptive responses to 2.5% formalin, as well as a significant reduction in the mechanical hyperalgesia in the hindpaw contralateral to a thermal injury. In addition, both noxious chemical and thermal stimulation produced significant increases in specific 3H-PDBu binding in the dorsal horn of the lumbar spinal cord, likely reflecting alterations in membrane-associated PKC. The results provide both pharmacological and anatomical evidence that persistent pain produced by chemical stimulation with formalin and mechanical hyperalgesia in the hindpaw contralateral to a thermal injury are influenced by the translocation and activation of PKC in spinal cord dorsal horn neurons.
The density and distribution of serotonergic appositions onto identified neurons in the rat rostral ventromedial medulla
Authors: Potrebic SB , Mason P , Fields HL
Published: April 2018

Neurons in the rostral ventromedial medulla (RVM) contribute to the modulation of nociceptive transmission and to the analgesic effects of opioids. The RVM contains serotonergic terminal arbors, serotonergic neurons and several types of serotonin (5-HT) receptors. Limited evidence suggests that 5-HT acting within RVM decreases nociceptive responsiveness and contributes to opioid analgesia. The present study examines the density and distribution of serotonergic afferents onto physiologically identified neurons in the RVM. In anesthetized rats, RVM neurons were characterized by their response to noxious stimulation as either on (excited), off (inhibited) or neutral (unaffected) cells. Tissue containing intracellularly labeled RVM neurons was processed for 5-HT immunocytochemistry. Five off, five on, and three serotonergic neutral cells were examined with the confocal microscope for appositions between 5-HT immunoreactive (5-HT-IR) processes and intracellularly labeled processes. Serotonergic neutral cells had the highest density of 5-HT-IR appositions. The density of 5-HT-IR appositions onto off cells was slightly lower. On cells demonstrated the lowest density of 5-HT-IR appositions. These results indicate that 5-HT contributes to nociceptive modulation by direct actions on the activity of RVM cells. Because the RVM has several sources of serotonergic input and a number of different 5-HT receptor subtypes, further understanding of the role of RVM 5-HT afferents will require pharmacological studies to determine the action of 5-HT on each cell class and anatomical studies to determine the brainstem origin of serotonergic input to each cell class.
Evidence for large-scale astrocyte death in the developing cerebellum
Authors: Krueger BK , Burne JF , Raff MC
Published: April 2018

There is increasing evidence that some glial cells die during normal vertebrate development, but the extent of the death and the types of glial cells that die remain uncertain. We have analyzed pyknotic cells in the developing postnatal rat cerebellum. During the first postnatal week, the majority of pyknotic cells are in the developing white matter where their number peaks at about postnatal day 7 (P7) and then declines sharply. Pyknotic cells in the internal granule cell layer peak at P10, while those in the molecular and external granule cell layers peak later. Both electron microscopy and in situ end labeling of DNA catalyzed by terminal deoxynucleotidyl transferase confirm that the pyknotic cells are undergoing apoptosis. Immunohistochemical staining suggests that 50–70% of the pyknotic cells in the white matter and internal granule cell layer are astrocytes. We estimate that at P7, as many as 50% of the white matter cells die and, of these, more than half appear to be astrocytes.
Integrin-cytoskeletal interactions in neuronal growth cones
Authors: Schmidt CE , Dai J , Lauffenburger DA , Sheetz MP , Horwitz AF
Published: April 2018

Development of the nervous system requires that neuronal growth cones, in coordination with growing axons, migrate along precise paths defined by specific extracellular matrix cues until they encounter their targets. Laminin promotes growth cone migration through receptors such as the integrins, but the underlying physical mechanism is poorly understood. We have investigated the cytoskeletal associations and surface dynamics of endogenous beta 1 integrins in chick dorsal root ganglion growth cones migrating on laminin. A single-beam optical gradient trap was used to place 0.5-micron-diameter polystyrene beads conjugated with anti-beta 1 integrin monoclonal antibodies at desired locations on the growth cone surface. We found a substantial increase in the stable attachment of these beads, with subsequent slow rearward motion, on the front periphery of the growth cone compared to the base. The surface dynamics of smaller aggregates of integrin were explored by monitoring the temporal and spatial displacements of 40-nm-diameter gold particles coated with anti-beta 1 integrin antibodies. The small particles were transported preferentially to the growth cone periphery by brief directed excursions interspersed with periods of diffusion. In addition, the leading edge of the growth cone was supported to a greater extent by an actin-dependent cytoskeleton that resisted mechanical tether formation. Such a regional differentiation of the growth cone has not been documented previously and has implications for the mechanism of growth cone migration and guidance.
Osmotic responsiveness and cross talk involving oxytocin, but not vasopressin or amino acids, between the supraoptic nuclei in virgin and lactating rats
Authors: Neumann I , Landgraf R , Bauce L , Pittman QJ
Published: April 2018

Lactation is associated with complex changes of the hypothalamo- neurohypophysial system, and oxytocin released within the hypothalamic supraoptic (SON) and paraventricular nuclei may serve as a signal of communication between the magnocellular nuclei in lactating rats. In the first study, the intranuclear and peripheral release patterns of oxytocin and vasopressin in response to intraperitoneal hypertonic saline were studied in virgin and lactating rats to determine if the reduced osmoresponsiveness of the oxytocinergic and vasopressinergic systems during lactation is reflected by reduced release not only into blood, but also within the SON. Simultaneous microdialysis was performed within the SON and the jugular vein before and up to 6 hr after peripheral osmotic stimulation (3.0 M NaCl, 0.6 ml/100 gm body weight, i.p.). There was an immediate increase in secretion of both oxytocin and vasopressin into blood, whereas peptide release within the SON was delayed and peaked after 4–5 hr. Peripheral release of both peptides was significantly reduced in lactating animals, whereas within the SON release of oxytocin, but not vasopressin, was significantly reduced during lactation. In the second study, cross talk between the SONs--another phenomenon which seems to be characteristic for lactation- -was studied. Microdialysis of one SON with hypertonic perfusion medium (with 1 M NaCl) significantly increased the release of oxytocin, vasopressin, and various amino acids (aspartate, glutamate, serine, glutamine, gamma amino butyric acid, and arginine) within the ipsilateral SON. In contrast to virgin female and male animals, this unilateral stimulation of the SON resulted in a transiently increased release of oxytocin in the contralateral SON of lactating rats. The release of vasopressin and amino acids within the contralateral SON of lactating rats remained unchanged, indicating specific activation of contralateral oxytocinergic neurons.
Women have greater density of neurons in posterior temporal cortex
Authors: Witelson SF , Glezer II , Kigar DL
Published: April 2018

Cytoarchitectonic area TA1 (von Economo) in the cortex of the planum temporale within the Sylvian fissure, which is auditory association cortex and documented to be part of the neural substrate of language functions, was studied quantitatively in the brain specimens of five women and four men (mean age of 50 year). All cases were documented to be medically and cognitively normal, and consistently right-handed. We investigated the possibility that the difference in brain size between men and women is reflected in differences in the numerical density of neurons in area TA1, an area associated with morphologic and psychological sex differences. Neuron counts were made directly through cell differentiation under the microscope from Nissl-stained sections. Cortical depth, the number of neurons through the depth of cortex under 1 mm2 of cortical surface (Nc), and the number of neurons per unit volume (Nv) were obtained for the total cortex and for each of the six layers in each hemisphere. For total cortex in both hemispheres, depth and Nc were similar, but Nv was greater by 11% in women, with no overlap of scores between the sexes. The sex difference in Nv was attributable to layers II and IV; in contrast, Nv did not differ between the sexes in layers III, V, and VI. This is the first report of such a sex difference in human cortex. The results suggest that the cortical functional unit has a different ratio of input and output components in men and women which could have implications for the sex differences in cognition and behavior. Due to the small sample size and the homogeneity of the cases studied, generalizability of the results requires replication by other studies. In addition, cytoarchitectonic mapping indicated that area TA1 also occurs in the vertical posterior wall of the Sylvian fissure, providing evidence that anatomical definition of the planum temporale should include the posterior vertical wall of the superior temporal gyrus.
Interleukin-1 beta attenuates excitatory amino acid-induced neurodegeneration in vitro: involvement of nerve growth factor
Authors: Strijbos PJ , Rothwell NJ
Published: April 2018

Certain cytokines have been reported to exert neurotrophic actions in vivo and in vitro. In the present study, we investigated the possible neuroprotective actions of the cytokine human recombinant interleukin-1 beta (hrIL-1 beta) against excitatory amino acid (EAA)-induced neurodegeneration in cultured primary cortical neurons. Brief (15 min) exposure of cultures to submaximal concentrations of glutamate, NMDA, AMPA, or kainate caused extensive neuronal death (approximately 70% of all neurons). Neuronal damage induced by the EAAs was significantly reduced (up to 70%) by pretreatment with 500 ng/ml (6.5 x 10(3) U/ml) hrIL-1 beta for 24 hr. The neuroprotective effect of hrIL-1 beta was reversed by coapplication of an IL-1 receptor antagonist (IL-1ra, 50 micrograms/ml). Neuroprotective actions of hrIL-1 beta were also reduced by administration of a neutralizing monoclonal antibody to NGF (65% inhibition). In concordance, the neurotoxic actions of EAAs were significantly reduced (by 40%) after pretreatment with NGF (100 ng/ml for 48 hr). Furthermore, an additive neuroprotective effect of approximately 75% was observed when cultures were exposed to a combination of hrIL-1 beta and NGF. In contrast, exposure of cultures to high concentrations hrIL-1 beta alone (100 micrograms/ml, 1.3 x 10(6) U/ml) for periods up to 72 hr resulted in neurotoxicity, which was reversed by IL-1ra (1 mg/ml). These findings suggest that hrIL-1 beta can limit EAA-induced neuronal damage. These effects appear to be may be mediated, at least in part, via NGF. These findings may be relevant to the understanding of neurodegenerative diseases.
Contribution of the circadian pacemaker and the sleep homeostat to sleep propensity, sleep structure, electroencephalographic slow waves, and sleep spindle activity in humans
Authors: Dijk DJ , Czeisler CA
Published: April 2018

The role of the endogenous circadian pacemaker in the timing of the sleep-wake cycle and the regulation of the internal structure of sleep, including REM sleep, EEG slow-wave (0.75–4.5 Hz) and sleep spindle activity (12.75–15.0 Hz) was investigated. Eight men lived in an environment free of time cues for 33–36 d and were scheduled to a 28 hr rest-activity cycle so that sleep episodes (9.33 hr each) occurred at all phases of the endogenous circadian cycle and variations in wakefulness preceding sleep were minimized. The crest of the robust circadian rhythm of REM sleep, which was observed throughout the sleep episode, was positioned shortly after the minimum of the core body temperature rhythm. Furthermore, a sleep-dependent increase of REM sleep was present, which, interacting with the circadian modulation, resulted in highest values of REM sleep when the end of scheduled sleep episodes coincided with habitual wake-time. Slow-wave activity decreased and sleep spindle activity increased in the course of all sleep episodes. Slow-wave activity in non-REM sleep exhibited a low amplitude circadian modulation which did not parallel the circadian rhythm of sleep propensity. Sleep spindle activity showed a marked endogenous circadian rhythm; its crest coincident with the beginning of the habitual sleep episode. Analyses of the (nonadditive) interaction of the circadian and sleep-dependent components of sleep propensity and sleep structure revealed that the phase relation between the sleep-wake cycle and the circadian pacemaker during entrainment promotes the consolidation of sleep and wakefulness and facilitates the transitions between these vigilance states.
Dopaminergic microtransplants into the substantia nigra of neonatal rats with bilateral 6-OHDA lesions. II. Transplant-induced behavioral recovery
Authors: Nikkhah G , Cunningham MG , McKay R , Bjorklund A
Published: April 2018

Transplants of fetal ventral mesencephalic (VM) dopamine neurons implanted into the substantia nigra in 6-hydroxy-dopamine (6-OHDA)- lesioned neonatal pups establish axonal connections with the denervated caudate putamen (Nikkhah et al., 1995). In the present study, we have explored the functional capabilities of these animals after they reached adulthood on a battery of spontaneous and drug-induced behavioral tasks. The results demonstrate that unilateral intranigral VM grafts in bilaterally lesioned neonates induce a marked bias in spontaneous- and stress-induced rotation contralateral to the implant not present in the lesion-only controls. Amphetamine and apomorphine induced vigorous contra- and ipsilateral rotation, respectively. Moreover, grafted animals achieved 75% of the performance level in contralateral skilled forelimb use when compared to normal controls, which was significantly above lesion-only animals (50% of normal). Spontaneous nocturnal locomotor activity was elevated 2.2-fold in the grafted animals. Sensorimotor orientation and disengage behavior was spared by the neonatal dopamine lesion and unaffected by the grafts. The level of functional restoration seen in the present study was more extensive than reported previously in neonatally 6-OHDA-lesioned rats where the VM grafts were implanted ectopically into the striatum. However, functional recovery remained incomplete also after intranigral graft placement compared to normal intact animals. The present approach should provide a new promising avenue for the continued exploration of the mechanisms involved in functional recovery and structural repair in the damaged nigrostriatal system.
L-glutamate-induced responses and cGMP-activated channels in three subtypes of retinal bipolar cells dissociated from the cat
Authors: de la Villa P , Kurahashi T , Kaneko A
Published: April 2018

Effects of L-glutamate (Glu), the neurotransmitter released by photoreceptors, on isolated cat bipolar cells were examined. Membrane currents of bipolar cells were recorded by the patch-clamp technique in a conventional whole-cell recording configuration using pipettes containing 1 mM cGMP, which has been known to activate a cationic current sensitive to Glu in ON-type bipolar cells. ON-type bipolar cells (depolarized by light in in situ) and OFF-type bipolar cells (hyperpolarized by light) were identified by their response polarity to Glu. When the whole-cell configuration was established, ON-type bipolar cells showed a steady inward current which was suppressed by Glu, consistent with the response polarity observed in in situ recordings. In contrast, OFF-type cells did not show a steady current during the recordings. However, they responded to Glu with an increase in cationic conductance. Among recorded cells, rod-driven bipolar cells were identified by their immunoreactivity to anti-protein kinase C (PKC-IR) antibody. Examination of PKC-IR revealed that ON-type bipolar cells included both rod- and cone-driven bipolar cells, while OFF-type cells were all cone-driven bipolar cells. The cGMP-activated current observed in ON-type cells was accompanied by a change in the current fluctuation due to the opening and closing of underlying channels. Fluctuation analysis gave a unitary conductance value of 13 pS. In half of the cells examined, maximum open probability reached almost 100%. The cGMP- activated channel in bipolar cells seems novel, fundamentally different from those found in photoreceptor cells or olfactory receptor cells.
Increased expression of c-jun, junB, AP-1, and preproenkephalin mRNA in rat striatum following a single injection of caffeine
Authors: Svenningsson P , Strom A , Johansson B , Fredholm BB
Published: April 2018

The effect of a single injection of caffeine on the expression of c- fos, c-jun, junB, and junD, on activator protein 1 (AP-1) and on the levels of preproenkephalin mRNA in rat striatum was studied. Male rats were given caffeine (25 mg/kg, 50 mg/kg, or 100 mg/kg, i.p.) and sacrificed at different times (0.5, 1, 2, 4, or 8 hr) after administration. By using in situ hybridization of adjacent sections we found a rapid, transient, and dose-dependent increase of c-fos, c-jun, and junB by caffeine in striatum, especially in the lateral part. The induction peaked after 1 hr, but persisted for 2 hr, and in the case of junB for 4 hr. No induction of junD was found. A strong induction of junB, a weak induction of c-fos and c-jun, but not of junD, was seen in nucleus accumbens. Furthermore, by using gel shift assay we found an induction of AP-1 by caffeine (100 mg/kg) in striatum, which peaked 2 hr after administration and was clearly increased after 4 hr. c-Fos, c- Jun, and JunB proteins were components of the AP-1. There was also a dose-dependent induction of preproenkephalin mRNA, which was most pronounced in the lateral and caudal part of striatum; the level peaked 4 hr after injection and was still significantly increased after 8 hr. In a complementary study we could not find increased binding to the AP- 1-like site in the 5′-flanking sequence of proenkephalin following caffeine treatment. The data show that a single dose of caffeine induces a temporally and spatially characteristic pattern of c-fos, c- jun, and junB induction, followed by changes in AP-1 and preproenkephalin mRNA. Thus, a single dose of caffeine causes changes in gene transcription in the brain that may be related to the adaptive changes that occur after caffeine administration. However, a direct causal link between the immediate early genes and enkephalin could not be proven.
Electrogenic Na-Ca exchange clears Ca2+ loads from retinal amacrine cells in culture
Authors: Gleason E , Borges S , Wilson M
Published: April 2018

Calcium influx into cultured retinal amacrine cells is followed by a small, slow, inward current that we show here results from the operation of electrogenic Na-Ca exchange. The activity of the exchanger is shown to correlate with the magnitude of the Ca2+ load and to depend on both the Ca2+ and Na+ gradients. Li+ is unable to substitute for Na+ and in the absence of Na+, slow tail currents are almost entirely suppressed. A rapid change in [K+]o does not affect the activity of the exchanger, suggesting that only Na+ and Ca2+ are transported. The ratio of charge entering as Ca2+ current to the charge entering as exchange current is highly variable between cells. We suggest that variability results from a variable fraction of Ca2+ load, we estimate typically 40%, being removed by a process other than Na-Ca exchange. This process is likely to involve internal buffering or sequestration since inhibition of the plasmalemmal Ca(2+)-ATPase does not increase the fraction of Ca2+ expelled by the exchanger. Ca2+ loading performed in the absence of Na+o generates smaller exchange charge the longer the delay in returning Na+o to the neuron. About 30% of exchange charge is lost for a delay of 1 sec.
Induced and spontaneous neuritogenesis are associated with enhanced expression of ganglioside GM1 in the nuclear membrane
Authors: Wu G , Lu ZH , Ledeen RW
Published: April 2018

Neuro-2a neuroblastoma cells can be stimulated to extend neurites with a number of agents, one of which, neuraminidase, induces terminal differentiation by a mechanism involving enhanced Ca2+ influx. Permeabilization of such differentiated cells with saponin and treatment with cholera toxin B subunit linked to horseradish peroxidase revealed intense staining of the nuclear membrane, indicating the presence of GM1 ganglioside. Unstimulated cells had barely detectable levels of nuclear GM1. Nuclei isolated by sucrose density gradient centrifugation similarly showed intense staining with fluorescently labeled cholera toxin B subunit, in contrast to nuclei from undifferentiated controls. Treatment with chloroform-methanol removed most of the fluorogenic material. Chemical analysis of such nuclei from neuraminidase-treated cells confirmed significant elevation of GM1 above control levels, along with virtual absence of markers for plasma membrane and Golgi apparatus. Cerebellar granule cells from neonatal rats revealed a similar phenomenon following spontaneous neurite outgrowth in culture.
Damage limited to the hippocampal region produces long-lasting memory impairment in monkeys
Authors: Alvarez P , Zola-Morgan S , Squire LR
Published: April 2018

Research in humans and monkeys has demonstrated a system of anatomically related structures in the medial temporal lobe that is important for memory function. This system is comprised of the hippocampal region (i.e., the dentate gyrus, hippocampus proper and subicular complex) and the entorhinal, perirhinal, and parahippocampal cortices. While the hippocampal region has long been thought to be important in memory, there are few systematic studies in primates of the effects on memory of damage limited to the hippocampal region. We have used magnetic resonance imaging techniques, together with a stereotaxic approach, to produce bilateral lesions limited to the hippocampal region (the H lesion). Damage to the adjacent perirhinal, entorhinal, and parahippocampal cortex was minimal. Monkeys with the H lesion exhibited significant and long-lasting impairment on the delayed non-matching to sample task. At the same time, on this and other amnesia-sensitive tasks, monkeys with the H lesion performed better overall than monkeys with lesions of the hippocampal region that also included damage to the adjacent entorhinal and parahippocampal cortices (the H+ lesion). These findings show that, first, the hippocampal region itself is essential for normal memory function; and second, the adjacent entorhinal and parahippocampal cortices, either alone or in combination, are also an essential component of the medial temporal lobe memory system.
Forelimb akinesia in the rat Parkinson model: differential effects of dopamine agonists and nigral transplants as assessed by a new stepping test
Authors: Olsson M , Nikkhah G , Bentlage C , Bjorklund A
Published: April 2018

Methods for the assessment of akinesia in the unilateral rat Parkinson model have so far been lacking. The experiments reported here evaluate the usefulness of a new “stepping test” to monitor forelimb akinesia in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the mesencephalic dopamine (DA) system, and to assess the ability of DA- receptor agonists and fetal DA neuron transplants to reverse these deficits. The 6-OHDA lesion induced marked and long-lasting impairments in the initiation of stepping movements with the contralateral paw. Systemic injections of low doses (chosen to be subthreshold for induction of rotation) of the mixed D1 and D2 receptor agonist apomorphine, the D1-selective agonist SKF 38393, and to a lesser extent also the D2-selective agonist quinpirole were effective in reversing these deficits. Similar effects was seen after a subrotational dose of L-dopa, whereas amphetamine had no effect. Fetal nigral transplants, implanted as multiple deposits in the ipsilateral caudate-putamen and substantia nigra, restored initiation of stepping to a similar degree as the DA agonists. Nigral grafts placed in substantia nigra alone were also effective, although the improvement was less pronounced. Apomorphine, at a dose effective in the lesion-only animals, had no additive effect in the grafted rats, whereas amphetamine appeared to further improve stepping in the rats with intranigral transplants. Identical experiments were performed on skilled forelimb use in the so- called staircase test. Interestingly, neither the DA agonist drugs nor the nigral transplants had any effects on the lesion induced deficits in this more complex task. The results show that forelimb stepping is a highly useful test to monitor lesion-/and transplant-induced changes in forelimb akinesia, a behavioral parameter that may be analogous to limb akinesia and gait problems seen in patients with Parkinson's disease.
Relationships between dendritic fields and functional architecture in striate cortex of normal and visually deprived cats
Authors: Kossel A , Lowel S , Bolz J
Published: April 2018

We examined relationships between the pattern of geniculocortical innervation and the dendritic fields of cells in layer 4 of in cat primary visual cortex. Experiments were performed on normal animals and on cats in which the geniculocortical projection was altered by monocular deprivation or by the induction of divergent squint during the critical period. Thalamic afferents providing the input from the contralateral eye were anterogradely labeled by injecting the fluorescent tracer Dil into lamina A of the lateral geniculate nucleus. Intracellular staining with Lucifer yellow in slice preparations allowed simultaneous visualization of the morphology of individual cells and the thalamic afferents. Our results demonstrate that spiny stellate cells close to the upper and lower margin of the geniculocortical input have highly asymmetric dendritic fields, and thereby confine their dendrites to the termination zone of these afferents. This effect was specific for the cell class; it was not observed in pyramidal neurons. These dendritic asymmetries perpendicular to the laminar borders of spiny stellate cells were not altered by monocular deprivation or strabismus. In contrast, visual deprivation strongly influenced the dendritic arbors of spiny stellate cells near the borders between adjacent ocular dominance columns. In normal animals, the dendrites of cells near columnar borders remained preferentially within one column. These dendritic asymmetries became much more pronounced in strabismic animals. Monocular deprivation weakened the influence of the columnar borders on dendritic fields. Spiny stellate cells within the columns of the open eye exhibited a slight tendency to confine their dendrites to these columns. Cells in the columns of the deprived eye showed the opposite effect; they extended their dendrites preferentially into the adjacent columns of the open eye. These results demonstrate that the segregation of geniculocortical afferents into ocular dominance columns and its perturbation by manipulation of the visual input plays an important role in defining the morphology of cortical target cells. Thus, activity-dependent structural changes not only occur at the level of the presynaptic terminals, but also at the level of the postsynaptic target cells, and thereby contribute to build up the functional architecture of the cortex.
Modulation of the inactivation of voltage-dependent potassium channels by cAMP
Authors: Chung S , Kaczmarek LK
Published: April 2018

Modulation of voltage-dependent potassium currents can alter the shape and timing of action potentials, thereby altering neurotransmitter release. To examine the effect of a cAMP analog on potassium currents in metabolically intact cells, perforated-patch and cell-attached patch recordings were carried out using the GH4C1 pituitary cell line. A major component of voltage-dependent potassium current in these cells inactivates slowly, with a time constant of several seconds. Application of dibutyryl cAMP decreased this current at voltages positive to -10 mV and increased the rate of inactivation by approximately twofold. Single channel recordings revealed two channel types whose voltage dependence and kinetics of inactivation match those of the macroscopic current. One of these, the smaller conductance (7.5 pS) channel, was sensitive to the cAMP analog, which decreased the latency of the channel to enter a long-lasting inactivated state. Ensemble averages of the activity of this channel showed that, consistent with its effect on the macroscopic current, dibutyryl cAMP increased its rate of inactivation. Somatostatin, an agent that is known to activate a serine/threonine phosphatase in these cells, completely reversed the effect of dibutyryl cAMP on the channel, while the cyclic GMP analog, dibutyryl cyclic GMP was without effect. In contrast, the rate of inactivation of the larger conductance (approximately 19 pS) channel was not accelerated by dibutyryl cAMP. These studies indicate that different channel subtypes expressed in a single cell respond differently to elevations of cAMP, and suggest that the overall response of potassium currents to second messengers may be determined by the ratio of different channel subtypes.
Cutaneous and muscle afferents: interactions with potential targets in vitro
Authors: Woodbury CJ , Scott SA
Published: April 2018

Previous studies suggest that cutaneous and muscle afferents use different environmental cues in growing to their peripheral targets. As a first approach to learning whether these earlier observations reflect differences in the behavior of individual growth cones, trigeminal cutaneous and muscle afferents of embryonic day 10 chicks were cocultured with explants of epidermis or dermis or with myotubes, and interactions of their growth cones with these potential targets were followed with time lapse video microscopy. Cutaneous and muscle afferents differed in their response to all three targets. In birds, few cutaneous afferents innervate epidermis. Accordingly, most cutaneous neurites retracted within minutes of touching an epidermal cell. In contrast, most muscle afferents stopped growing but remained in contact with epidermis for as long as they were observed (> 1 hr). Further, most cutaneous afferents grew readily across explants of dermis, their normal target, at rates comparable to their growth on the substrate. In contrast, most muscle afferents advanced only poorly on dermis. Finally, most cutaneous afferents grew readily across myotubes, the normal targets of muscle afferents. In contrast, few muscle afferents grew across myotubes; most either retracted or changed course and grew along the myotube. Overall, muscle afferents stayed in contact with myotubes longer than cutaneous afferents. These cell-type-specific responses reflect in large part the patterns of cutaneous and muscle afferent growth in vivo. Further studies are required to determine whether these observed differences between the behavior of regenerating cutaneous and muscle afferent growth cones could potentially play a role in the selection of targets or pathways during embryonic development.