bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical recordings of the cortical response to whisker stimulation before and after the addition of an epileptogenic agent
Authors: London JA , Cohen LB , Wu JY
Published: March 2018

Optical recording methods using voltage-sensitive dyes were used to monitor activity in rat somatosensory cortex. We measured evoked signals in response to whisker stimulation before (control) and after the addition of the epileptogenic agent, bicuculline, and also detected spontaneous interictal events that occurred after bicuculline. Bicuculline led to an increase in the size, duration, cortical extent, and, surprisingly, the latency of the evoked responses. These enhanced evoked responses appeared to originate in the region of the control response and propagate outward. In contrast, the spontaneous signals appeared to originate at random cortical positions and had a more variable cortical extent. A transition signal measured just after the addition of bicuculline was larger than the control response but localized and rapid in time course. In most cases, there was a good correlation between the optical recordings and field potential measurements made with a ball electrode on the cortical surface, but there were occasional instances where the optical signal disappeared while the ball electrode signal was unchanged.
HA-966 antagonizes N-methyl-D-aspartate receptors through a selective interaction with the glycine modulatory site
Authors: Foster AC , Kemp JA
Published: March 2018

3-Amino-1-hydroxypyrrolid-2-one (HA-966) has been known for several years as an excitatory amino acid antagonist, acting principally at the N-methyl-D-aspartate (NMDA) receptor subtype. We report here that HA- 966 blocks NMDA responses through a selective interaction with the glycine modulatory site present within the receptor complex. In radioligand binding experiments, HA-966 inhibited strychnine- insensitive 3H-glycine binding to rat cerebral cortex synaptic plasma membranes with an IC50 of 17.5 microM. At concentrations up to 1 mM, HA- 966 caused minimal inhibition of radioligand binding to the transmitter recognition sites of the NMDA, quisqualate, or kainate receptor subtypes and was similarly inactive against the binding of 3H- strychnine to rat spinal cord/brain stem membranes. In electrophysiological experiments, HA-966 produced a selective block of NMDA responses in a rat cortical slice preparation. The degree of antagonism caused by HA-966 was maximal at 250 microM and was not increased further by raising the HA-966 concentration. Both glycine (1 mM) and D-serine (100 microM) reversed the antagonism of NMDA responses caused by HA-966. In patch-clamp experiments using rat cortical neurons in culture, HA-966 blocked the potentiation of NMDA responses by glycine but had little effect on basal NMDA responses themselves. This profile of antagonism differs from that observed with 7- chlorokynurenate, another recently discovered antagonist of the glycine site on the NMDA receptor (Kemp et al., 1988) and may indicate that glycine antagonists of differing efficacies can exist. Previous experiments with HA-966 may now be interpreted to suggest that activation of the glycine site on the NMDA receptor occurs in vivo and is important for the participation of NMDA receptors in synaptic transmission.
Subcellular localization of benzodiazepine/GABAA receptors in the cerebellum of rat, cat, and monkey using monoclonal antibodies
Authors: Somogyi P , Takagi H , Richards JG , Mohler H
Published: March 2018

Two monoclonal antibodies, bd-17 and bd-24, specific for the beta- and alpha-subunit of the GABAA/benzodiazepine receptor/chloride channel complex, respectively, were used to determine the subcellular distribution of immunoreactivity in the cerebellum by electron microscopy. The 2 antibodies showed similar antigen distribution on the plasma membrane (except in the rat; bd-24 does not recognize the rat antigen), but intracellular immunoreactivity was more prevalent for the alpha-subunit. The plasma membrane of all neuronal types was immunopositive. The degree of immunoreactivity varied greatly between different types of cell, but it was stereotyped among individual cells of the same type. Granule cells showed the strongest immunoreactivity, not only on their dendrites which receive synapses from GABA-containing Golgi cell terminals, but also on their somata which do not receive synapses. Stellate and basket cells were somewhat weaker in immunoreactivity. Purkinje cells were only weakly positive on their somatic membrane but stronger on their dendritic shafts and spines. Golgi cells showed negligible if any immunoreactivity. Neurons of the deep cerebellar nuclei were strongly immunopositive along their plasma membrane. Immunoreactivity was strong in cisternae of the endoplasmic reticulum and in the Golgi saccules of stellate and basket cells, variable in Purkinje cells, while granule cells were rarely immunoreactive intracellularly. It is suggested that these differences reflect differences in the turnover of the receptor complex in the different cell types. The synaptic clefts established by boutons of the GABAergic stellate, basket, and Golgi cells were immunopositive, as were many synapses in the deep cerebellar nuclei. However, immunoreactivity was also present along the nonjunctional plasma membrane, and it was concluded that this reflected the distribution of the antigen. The synaptic clefts at the presumed glutamate-releasing parallel and mossy fiber terminals were almost always immunonegative. No immunoreactivity was detected on axons, nerve terminals, or glial cells. The results demonstrate that different neuronal types express the GABAA/benzodiazepine receptor/chloride channel complex to different degrees. The distribution of the receptor complex suggests that the cellular topography of GABAergic influence is not governed by the precise spatial arrangement of the receptors but by the precise placement of the GABA-releasing terminals, a characteristic of the cerebellar circuit.
Rapid remodeling of sensory endings in the corneas of living mice
Authors: Harris LW , Purves D
Published: March 2018

The terminals of trigeminal neurons were followed over time in the corneas of living mice by repeated staining with a nontoxic fluorescent dye. The purpose of these observations was to evaluate remodeling of sensory nerve endings in an adult mammal. Video images of topically stained nerve endings within particular corneal regions were recorded initially, and then again after intervals ranging from 4 hr to 30 d. Comparison of the 2 sets of images showed that sensory endings in the corneal epithelium undergo continual rearrangement under normal circumstances. Substantial changes in terminal configuration occurred over periods as brief as a day.
Selective elimination of axons extended by developing cortical neurons is dependent on regional locale: experiments utilizing fetal cortical transplants
Authors: O'Leary DD , Stanfield BB
Published: March 2018

In adult rats, cortical neurons that extend an exon through the pyramidal tract (a major subcortical efferent projection of the neocortex) are limited to layer V of about the rostral two-thirds of the neocortex. In neonates, however, pyramidal tract neurons are distributed throughout the neocortex, but all of those found in certain areas, such as the posterior occipital region (including primary visual cortex) selectively lose their pyramidal tract axon (Stanfield et al., 1982) yet maintain axon collaterals to other subcortical targets (O'Leary and Stanfield, 1985). To determine if the regional location of a developing pyramidal tract neuron critically influences the maintenance or elimination of the axon collaterals it initially extends, pieces of cortex from embryonic day 17 (E17) rat fetuses (exposed to 3H-thymidine on E15) were transplanted heterotopically into the cortex of newborn (PO) rats; rostral cortex was placed into the posterior occipital region (R----O), or posterior occipital cortex into a rostral cortical locale (O----R). The retrograde tracers Fast blue (FB) and Diamidino yellow (DY) were used to assay for the presence of specific populations of cortical projection neurons within the autoradiographically identified transplants. In terms of the extension and maintenance of pyramidal tract axons, the transplanted neurons behave like the host neurons of the recipient cortical region rather than like those of their site of origin. At P40, following FB injections into the pyramidal decussation on P34, pyramidal tract neurons are labeled within the O----R transplants, but none can be labeled within R----O transplants, although in the same R----O cases transplanted neurons are labeled by an injection of DY in the superior colliculus. However, at P13 pyramidal tract neurons can be identified within the R----O transplants, as well as in the host occipital cortex, following injections made on P9, a period when the distribution of pyramidal tract neurons in normal rats is widespread (Stanfield and O'Leary, 1985b). In a second series of host rats, on P34 FB was injected in the pyramidal decussation of the O----R cases, or in the superior colliculus of the R----O cases, and in both groups DY was injected into the region of contralateral cortex homotopic for the new location of the transplant. On P40, in both the O----R and R----O transplants, many neurons singly labeled with FB or DY are found, but no double dye-labeled cells are seen.(ABSTRACT TRUNCATED AT 400 WORDS)
Spinal cord segments containing key elements of the central pattern generators for three forms of scratch reflex in the turtle
Authors: Mortin LI , Stein PS
Published: March 2018

The immobilized, low-spinal turtle produces 3 forms of the fictive scratch reflex in response to tactile stimulation of specific sites on its body surface (Robertson et al., 1985). We used complete transections of the spinal cord at different rostrocaudal levels to reveal the minimum length of spinal cord sufficient to produce each scratch form. Additional transections revealed the progressive loss of elements of the motor pattern and the eventual loss of rhythmogenesis. We have identified, therefore, spinal cord segments containing key elements of each scratch form's central pattern generator (CPG). The turtle spinal cord consists of 8 cervical segments (C1-C8), 10 dorsal segments (D1-D10), 2 sacral segments (S1, S2) and about 16 caudal segments (Ca1-Ca16; Kusuma et al., 1979). The cell bodies of motor neurons innervating the hindlimb muscles are located in the hindlimb enlargement, segments D8-S2 (Ruigrok and Crowe, 1984). The receptive field for the rostral scratch is innervated by segments D3-D6; the pocket scratch receptive field is innervated by segments D6-D8; the caudal scratch receptive field is innervated by segments S2, Ca1, and more caudal segments (Mortin and Stein, 1985). A rostral scratch motor pattern could be produced with as few as 5 or 6 segments, i.e., segments D5-D9 or D3-D8. The anterior 3 segments of the hindlimb enlargement, D8-D10, could produce a pocket scratch motor pattern. A single segment, either D7 or D8, is capable of rhythmogenesis in response to stimulation of sites in its part of the pocket receptive field. A caudal scratch motor pattern could be produced by D8-End (the hindlimb enlargement and more caudal segments). The posterior 40–80% of the hindlimb enlargement is not necessary for the production of a rostral or pocket motor pattern. The anterior segment of the enlargement is necessary for the production of a normal caudal scratch motor pattern. Key elements of the CPG for each of the 3 scratch forms reside in segments D7-D10. The pattern-generating capacity of the anterior half of the hindlimb enlargement is greater than the posterior half; such an asymmetric distribution of pattern-generating elements in the enlargement of the spinal cord has been described for cat scratching (Deliagina et al., 1983). These results are consistent with the hypothesis that the CPGs producing different motor patterns for the hindlimb share neuronal elements (Grillner, 1981; Robertson et al., 1985; Currie and Stein, 1988, 1989).
Spontaneous and beta-adrenergic receptor-mediated taurine release from astroglial cells are independent of manipulations of intracellular calcium
Authors: Shain W , Connor JA , Madelian V , Martin DL
Published: March 2018

Stimulation of beta-adrenergic receptors on LRM55 astroglial cells results in cAMP-dependent release of taurine. We have previously demonstrated that extracellular Ca2+ is not required for either spontaneous or receptor-mediated taurine release (Martin et al., 1988b). In the present series of experiments we investigated the relationship between changes in intracellular free Ca2+ ([Ca2+]i) and taurine release. [Ca2+]i was measured using the fluorescent probe fura- 2 and was manipulated by changing the concentration of Ca2+ in the incubation medium and by using the Ca2+ ionophore ionomycin. [Ca2+]i was reduced from 150 +/- 95 nM (n = 46) in control medium (containing 1.1 mM CaCl2) to 46 +/- 10 nM (n = 43) in saline containing no CaCl2 and 10 microM EGTA. [Ca2+]i was rapidly elevated to greater than or equal to 1 microM in medium containing 100 microM CaCl2 and 10 microM ionomycin. Taurine release, either spontaneous or stimulated by isoproterenol, was not significantly affected by these manipulations of [Ca2+]i. [Ca2+]i did not change when cells were stimulated with 100 nM isoproterenol in either control saline containing 1.1 mM CaCl2 or in CaCl2-free saline containing 10 microM EGTA. Other secretogogs (serotonin and ethanol) did not cause changes in [Ca2+]i. These data indicate that neither spontaneous or receptor-mediated taurine release from astroglial cells is Ca2+ dependent. However, when cells were preloaded with Ca2+, allowed to recover briefly, and then stimulated with isoproterenol, it was possible to demonstrate transient increases in Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Place cells and silent cells in the hippocampus of freely-behaving rats
Authors: Thompson LT , Best PJ
Published: March 2018

In the present study, nearly two-thirds of all hippocampal pyramidal units isolated under barbiturate anesthesia, which maximizes these cell's activity, were behaviorally silent. These “silent cells” showed no spontaneous firing activity in the awake, freely-behaving rat. Both reanesthetization and antidromic stimulation, however, activated these silent cells. More than 92% of the remaining spontaneously active hippocampal pyramidal cells recorded from freely-behaving rats were place cells; i.e., they exhibited spatially specific changes in firing activity in at least one environment. The firing rates of these place cells varied depending on the animal's location in this environment. Interestingly many of these place cells displayed low or no spontaneous activity and no spatial specificity in other, dissimilar environments; i.e., their lack of firing in some spatial environments mirrored the behavioral silence of the more numerous silent cells reported here. In complex information processing, such as the processing of spatial information by the hippocampus demonstrated here, neural silence may be as important a signal as neural activity.
Selective distribution of the 57 kDa neural intermediate filament protein in the rat CNS
Authors: Brody BA , Ley CA , Parysek LM
Published: March 2018

In order to determine the CNS distribution of the 57 kDa neural intermediate filament protein (NIFP), a specific antiserum was used in immunofluorescence studies on serial sections taken from each spinal cord level and at 300-microns intervals through the rat brain. The labeling pattern was recorded onto camera lucida tracings of adjacent sections stained with hematoxylin and eosin/luxol fast blue. Three major immunolocalization patterns were revealed. (1) Both large-caliber and fine-caliber axons of optic and all brain stem cranial nerves and their tracts except for the auditory portion of the VIIIth nerve. (2) An extensive array of fine-caliber fibers in the cerebellar white matter and brain stem with region-specific variation in pattern and density. Prominent among the regions with dense arrays of labeled processes were selective cerebellar afferent systems, particularly olivocerebellar fibers, visual afferents arising in the retina, and selective regions of reticular formation. In contrast to the brain stem, the telencephalon contained rare label. (3) Filamentous labeling of neuronal cytokarya in sensory ganglia and a small number of CNS nuclear groups, including all autonomic nuclei and the cholinergic pontine nuclei. On sections of selected CNS regions, distribution patterns of the 57 kDa NIFP were correlated to results obtained by in situ hybridization of a cDNA probe for the 57 kDa NIFP. The data suggest the possible existence of neuronal IF proteins specifically related to selective anatomic and/or neurotransmitter systems.
Cholecystokinin-like peptide is a modulator of a crustacean central pattern generator
Authors: Turrigiano GG , Selverston AI
Published: March 2018

The presence, release, and physiological effects of a cholecystokinin(CCK)-like peptide within the stomatogastric ganglion (STG) of the lobster, Panulirus interruptus, are described. Indirect immunofluorescence with 2 antisera raised against CCK8 was used to determine the distribution of CCK-like immunoreactivity (CCKLI) in the stomatogastric nervous system. CCKLI was demonstrated in the input nerve and the neuropil of the STG and in neuropil and somata in the commissural ganglia (CGs), brain, and eyestalks. None of the somata within the STG displayed CCKLI. The cross-reactivities of the CCK antisera with several peptides were determined using either a radioimmunoassay or an immunoblot assay; the antisera recognized peptides homologous to CCK but did not cross-react significantly with several unrelated peptides. The STG contains 2 central pattern generators (CPGs), the pyloric and the gastric mill CPGs. Bath application of CCK8 to the STG had modulatory effects on both CPGs, which were dose dependent and reversible. CCK increased the spike frequencies and number of spikes per burst of the pyloric rhythm but had little effect on the period. CCK increased the period of the gastric rhythm and produced changes in the spike frequencies, burst lengths, and phases of gastric units. High concentrations of peptide were needed to produce these effects (10(-6) to 10(-4) M). Finally, stimulation of the stomatogastric nerve (stn), which contains fibers immunoreactive to CCK, produced calcium-dependent release of CCK molar equivalents (CCKE) into the STG. The stn was electrically stimulated and the superfusate around the ganglion was collected and assayed for CCKE using a radioimmunoassay. Stimulation produced the release of 37.1 +/- 7.1 fmol (mean +/- SEM), compared to 13.7 +/- 4.9 fmol for unstimulated controls and 4.9 +/- 2.9 fmol in the absence of calcium. These data suggest that a CCK-like peptide is an endogenous modulator of the stomatogastric ganglion of P. interruptus.
Release of vasoactive intestinal peptide in mouse cerebral cortex: evidence for a role of arachidonic acid metabolites
Authors: Martin JL , Magistretti PJ
Published: March 2018

In rodent cerebral cortex, vasoactive intestinal peptide (VIP) is contained in a homogeneous population of radially oriented bipolar interneurons. We have observed that 4-aminopyridine (4-AP), a K+- channel blocker, promotes a concentration- and Ca2+-dependent release of VIP from mouse cerebral cortical slices, with a significant effect already observed at 50 microM. Over 70% of VIP release elicited by 4-AP is blocked by 2 microM tetrodotoxin (TTX). Mepacrine, an inhibitor of phospholipase A2 (PLA2) activity and hence of arachidonic acid (AA) formation from membrane phospholipids, markedly inhibits (IC50 of approximately 15 microM) the release of VIP evoked by 4-AP. The inhibitory effect of mepacrine is not additive to that of TTX, thus indicating an involvement of PLA2 activation in the TTX-sensitive component of the 4-AP-evoked release. As a corollary, melittin (0.1–10 micrograms/ml), a PLA2 activator, promotes VIP release. Inhibition of AA metabolites of the lipoxygenase pathway by nordihydroguaiaretic acid, 5,8,11,14-eicosatetranoic acid, and caffeic acid results in a concentration-dependent inhibition of VIP release evoked by 4-AP. This set of observations indicates for the first time that the formation of AA metabolites of the lipoxygenase pathway plays a role in the release of a peptide in the mammalian CNS. Furthermore, these observations together with the previously reported potentiation by prostaglandins of the increase in cyclic AMP elicited by VIP in mouse cerebral cortex (Schaad et al., 1987) indicate that AA metabolites may act at both the presynaptic (lipoxygenase metabolites) and the postsynaptic (cyclooxygenase metabolites) levels to increase the “throughput” or “strength” of VIP-containing circuits in the rodent neocortex.
Glutamate decarboxylase-immunoreactive neurons are preserved in human epileptic hippocampus
Authors: Babb TL , Pretorius JK , Kupfer WR , Crandall PH
Published: March 2018

The present study was designed to determine whether inhibitory neurons in human epileptic hippocampus are reduced in number, which could reduce inhibition on principal cells and thereby be a basis for seizure susceptibility. We studied the distribution of GABA neurons and puncta by using glutamate decarboxylase (GAD) immunocytochemistry (ICC) together with Nissl stains. Using quantitative comparisons of GAD- immunoreactive (GAD-IR) neurons and puncta in human epileptic hippocampus and in the normal monkey hippocampus, we found that GAD-IR neurons and puncta are relatively unaffected by the hippocampal sclerosis typical of hippocampal epilepsy where 50–90% of principal (non-GAD-IR) cells are lost. GAD-IR neurons and puncta were not significantly decreased compared with normal monkey. In 6 patients, prior in vivo electrophysiology demonstrated that the anterior hippocampus generated all seizures. The anterior and posterior hippocampus were processed simultaneously, and the counts of hippocampal GAD-IR neurons were numerically greater in anterior than in the posterior hippocampus, where no seizures were initiated. These results indicate that GABA neurons are intact in sclerotic and epileptogenic hippocampus. Computerized image analysis of puncta densities in fascia dentata, Ammon's horn, and subicular complex in epileptic hippocampi (n = 7) were not different from puncta densities in the same regions in normal monkey (n = 2). Hence, despite the significant loss of principal cells (50–90% loss) GABA terminals (GAD- IR puncta) were normal, which suggests GABA hyperinnervation of the remnant pyramidal cells and/or dendrites in human epileptic hippocampus. The apparent increase in puncta ranged from 2 (fascia dentata) to 3.3 (CA1) times normal puncta densities. These findings would suggest increased inhibition and less excitability; however, those regions were epileptogenic. We suggest that GABA terminal sprouting or hyperinnervation of the few remnant projection cells may serve to synchronize their membrane potentials so that subsequent excitatory inputs will trigger a larger population of neurons for seizure onset in the hippocampus and propagation out to undamaged regions of subiculum and neocortex.
Specificity of circadian function in transplants of the fetal suprachiasmatic nucleus
Authors: Earnest DJ , Sladek CD , Gash DM , Wiegand SJ
Published: March 2018

Fetal tissues obtained from specific regions of the developing hypothalamus were transplanted to determine whether the precursor neurons of the suprachiasmatic nucleus (SCN) can be distinguished from those of the presumptive paraventricular nucleus (PVN) on the basis of the functional capacity to generate circadian rhythms. The presumptive SCN, the PVN, and a portion of the neocortical primordium were dissected from the developing forebrains of normal Long-Evans fetuses, separated, and selectively transplanted into the periventricular-third ventricle region of adult, vasopressin (VP)-deficient Brattleboro rats. In host animals that received grafts containing the precursor population of SCN neurons, the temporal profile of VP levels in the cerebrospinal fluid (CSF) oscillated with a circadian periodicity in a manner similar to that observed in normal Long-Evans rats. CSF collected serially from animals with grafts of the presumptive PVN also contained VP, but no circadian variation was manifested in peptide levels. VP was undetectable in CSF samples obtained from Brattleboro rats with cortical grafts. In association with their circadian functional capacity, grafts of the SCN primordium were characterized by clusters of parvicellular neurons immunopositive for VP or vasoactive intestinal polypeptide (VIP) that resembled the cell groups of the in situ SCN. In contrast, transplants of the presumptive PVN did not contain neurons immunoreactive for VIP, and the VP neurons in these grafts resembled the neurosecretory cells of the PVN.(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence for glycine as an inhibitory neurotransmitter of vestibular, reticular, and prepositus hypoglossi neurons that project to the cat abducens nucleus
Authors: Spencer RF , Wenthold RJ , Baker R
Published: March 2018

The localization and distribution of brain-stem afferent neurons to the cat abducens nucleus has been examined by high-affinity uptake and retrograde transport of 3H-glycine. Injections of 3H-glycine selectively labeled (by autoradiography) only neurons located predominantly in the ipsilateral medial vestibular and contralateral prepositus hypoglossi nuclei, and in the contralateral dorsomedial reticular formation, the latter corresponding to the location of inhibitory burst neurons. The specificity of uptake and retrograde transport of 3H-glycine was indicated by the absence of labeling of the dorsomedial medullary reticular neurons ipsilateral and in close proximity to the injection site, where local uptake by diffusion could have occurred. The selectivity of uptake and transport was demonstrated by the absence of retrograde labeling following injections of 3H-GABA or 3H-leucine into the abducens nucleus. The immunohistochemical localization of glycine and GABA revealed a differential distribution of the 2 inhibitory neurotransmitter candidates in the extraocular motor nuclei. Glycine-immunoreactive staining of synaptic endings in the abducens nucleus was dense with a widespread soma-dendritic distribution but was sparse in the trochlear and oculomotor nuclei. By contrast, GABA-immunoreactive staining within the oculomotor and trochlear nuclei was associated with synaptic endings that were particularly prominent on the somata of motoneurons. GABA- immunoreactive staining in the abducens nucleus, however, was sparse. These differences between glycine- and GABA-immunoreactive staining in the extraocular motor nuclei were correlated with differences in the immunoreactivity of axons in the descending (glycine) and ascending (GABA) limbs of the medial longitudinal fasciculus. Glycine- immunoreactive neurons, furthermore, were observed in the same locations as neurons that were labeled autoradiographically by retrograde transport of 3H-glycine from the abducens nucleus. Electrophysiological recordings from abducens motoneurons and internuclear neurons revealed a marked reduction in the slow positivity of the orthodromic extracellular potential elicited by ipsilateral vestibular nerve stimulation following systemic administration of strychnine, an antagonist of glycine. Intracellular recordings demonstrated that the vestibular-evoked disynaptic inhibitory postsynaptic potentials in abducens neurons were effectively blocked by strychnine but were unaffected by picrotoxin, an antagonist of GABA.(ABSTRACT TRUNCATED AT 400 WORDS)
Spatial and behavioral correlates of hippocampal neuronal activity
Authors: Wiener SI , Paul CA , Eichenbaum H
Published: March 2018

The firing rate of hippocampal neurons in rats was related both to spatial location and to multiple behavioral variables as rats performed 2 kinds of tasks that rely on hippocampal function: a spatial navigation task similar in performance demands to the radial-arm maze task and a simultaneous cue odor-discrimination task. In the place task, most cells had distinct single or multiple place fields, that is, neurons increased firing when the rat was in a particular location or locations. However, in most of these cells, firing rate also varied systematically in relation to behavioral variables, including the speed, direction, and turning angle of the rat as it moved through the place field. In addition, the activity of most cells was time-locked to task-relevant approach movements. In the odor task, most cells fired as the rat sampled discriminative cues or when it executed specific, task- relevant approach movements. Some cells fired selectively in relation to which odors were presented, the configuration of odor cues, the locus of the response, or a combination of these variables. Many cells with spatial correlates in the place task also had striking behavioral correlates when rats performed the odor task in the same environment, and the locus of the increased firing associated with behavior in the odor task was not the same as the place field in the place task. Thus, while the complex stimuli that compose spatial cues are reflected in hippocampal neuronal activity, hippocampal processing is not limited to the representation of spatial location. Rather, the domain of hippocampal representation includes both spatial and nonspatial relations among multiple cues and the actions directed in relation to these cues, across cue modalities, and across behavioral paradigms.
Regulation of muscarinic receptors in hippocampus following cholinergic denervation and reinnervation by septal and striatal transplants
Authors: Joyce JN , Gibbs RB , Cotman CW , Marshall JF
Published: March 2018

The regulation of hippocampal muscarinic M1 and M2 receptors was studied by autoradiographic methods following cholinergic denervation and reinnervation from embryonic septal transplant. In young adult male rats the density of M1 sites, labeled either with 3H-pirenzepine (PZ) or 3H-N-methylscopolamine (NMS, in the presence of excess carbachol), exceeded by 4- to 5-fold the density of M2 sites, labeled with 3H-NMS in the presence of excess PZ. Both receptors appeared to be densest in hippocampal regions lowest in acetylcholinesterase or 3H-hemicholinium- 3 binding. The distribution of M1 receptors did differ from the distribution of M2 receptors within subregions of the hippocampus. Along the mediolateral axis from the subiculum to the lateral CA 1, the density of M1 receptors is uniform, but the density of M2 receptors decreases. Also apparent is the relatively small difference in density between the CA1 and dentate gyrus for M1 receptors but a significantly greater difference for M2 receptors. However, the response of M1 and M2 receptors to long-term cholinergic denervation following fimbriafornix transection of the septal cholinergic input and to cholinergic innervation by embryonic septal transplants was similar. Long-term denervation (40–60 d) resulted in a 30–60% increase in both M1 and M2 receptors within regions of the hippocampal formation. Receptor levels were reduced to normal in regions innervated by septal transplants. For both receptors, the changes in the density of sites were due to alterations in the Bmax and not the Kd for the radioligands. The specificity of this regulation is supported by the evidence that (1) the degree and topography of the normalization of muscarinic receptor density was entirely dependent on the degree and pattern of cholinergic reinnervation by the fibers of the septal transplant, (2) cholinergic fiber reinnervation by embryonic striatal grafts also down-regulated the density of M1 and M2 receptors, and (3) successfully surviving transplants (e.g., cerebellar and striatal) that did not provide innervation to the hippocampus did not induce down-regulation of muscarinic receptors. Changes in the density of sites were not related to changes in the width of the hippocampus following denervation and reinnervation. The data support the view that the majority of M1 and M2 receptors are located postsynaptically on neurons within the hippocampus and not presynaptically on cholinergic fibers.
Ca2+ and Na+ currents in developing skeletal myoblasts are expressed in a sequential program: reversible suppression by transforming growth factor beta-1, an inhibitor of the myogenic pathway
Authors: Caffrey JM , Brown AM , Schneider MD
Published: March 2018

We have analyzed the biophysical and developmental properties of Ca2+ and Na+ currents in C2 muscle cells, whose morphological and biochemical phenotype closely resembles differentiated skeletal muscle. Both fused and unfused C2 myocytes possessed: (1) membrane capacitance consistent with the presence of complex sarcotubular invaginations, (2) tetrodotoxin-sensitive Na+ channels, and (3) “fast” and “slow” Ca2+ channels that inactivated at holding potentials of -40 and -20 mV, respectively. Thus, the passive electrical properties, Na+ currents, and Ca2+ currents expressed in C2 cells each differed from those found in the nonfusing muscle cell line, BC3H1, and corresponded more precisely to characteristic findings observed in skeletal muscle fibers. In further contrast to BC3H1 cells, C2 muscle also expressed “transient” Ca2+ channels similar to those reported in embryonic or neonatal skeletal muscle, which were detected within 12–24 hr of mitogen withdrawal, up to 60 hr before appearance of “fast” and “slow” currents. Na+ channels also were induced 12–24 hr after mitogen withdrawal. Unlike the “fast” and “slow” Ca2+ currents, which were maximally expressed at 8–14 d of serum withdrawal, “transient” Ca2+ channels became down-regulated upon prolonged differentiation (as found in postnatal skeletal muscle in vivo) and were no longer expressed at 14 d. Despite their divergent kinetic and developmental properties, all components of Ca2+ and Na+ current in C2 myocytes were suppressed reversibly in the presence of transforming growth factor beta-1, a purified growth factor that inhibits the myogenic phenotype. The results indicate that fusion is not essential for skeletal myoblasts to produce developmentally regulated voltage-gated channels that resemble those of intact muscle and demonstrate that the formation of diverse Ca2+ and Na+ channels can be mediated by a single peptide that affects the myogenic pathway.
Differentiation of 5-hydroxytryptamine2 receptor subtypes using 125I-R- (-)2,5-dimethoxy-4-iodo-phenylisopropylamine and 3H-ketanserin
Authors: McKenna DJ , Peroutka SJ
Published: March 2018

The radioligand binding characteristics of 125I-R-(-)4-iodo-2,5- dimethoxyphenylisopropylamine [125I-R-(-)DOI] and 3H-ketanserin were compared in rat and bovine cortical membranes. In rat cortex, 125I-R-(- )DOI labels a relatively low density of binding sites (Bmax = 2.5 +/- 0.2 pmol/gm tissue) with high affinity (KD = 0.63 +/- 0.09 nM). In bovine cortex, specific binding of 125I-R-(-)DOI represents less than 20% of total binding at radioligand concentrations above 0.6 nM, and, therefore, the data cannot be analyzed adequately by Scatchard transformation. By contrast, 3H-ketanserin displays saturable, specific high-affinity binding in both rat cortex (KD = 1.0 +/- 0.1 nM; Bmax = 11 +/- 0.4 pmol/gm tissue) and bovine cortex (KD = 1.2 +/- 0.2 nM; Bmax = 5.3 +/- 0.4 pmol/gm tissue). Ki values for 30 drugs were determined for 125I-R-(-)DOI-labeled sites in rat cortex and 3H-ketanserin-labeled sites in bovine cortex. 5-Hydroxytryptamine (5-HT) displays 250-fold higher selectivity for the 125I-R-(-)DOI-labeled sites (Ki = 3.0 +/- 0.7 nM) than for the 3H-ketanserin-labeled sites (Ki = 750 +/- 50 nM). Structural congeners of R-(-)DOI display 80- to 160-fold higher affinity for the 125I-R-(-)DOI binding site than for the 3H-ketanserin- labeled binding site. d-LSD and putative 5-HT2 antagonists are approximately equipotent at both sites. Significant correlations were found between drug affinities for 125I-R-(-)DOI-labeled sites in rat cortex and putative 5-HT2A sites labeled previously by 77Br-R-(-)DOB (r = 0.93, p less than 0.01), putative 5-HT2B sites labeled by 3H- ketanserin in bovine cortex (r = 0.63, p less than 0.01), and 5-HT1C binding sites that have been characterized by other investigators (r = 0.78, p less than 0.01). No significant correlations were found between drug affinities for 125I-R-(-)DOI-labeled sites in rat cortex and 5- HT1A, 5-HT1B, 5-HT1D, or 5-HT3 sites, as determined by previous investigators. We conclude that 125I-R-(-)DOI labels a novel 5-HT binding site subtype (tentatively designated the 5-HT2A binding site) that is present in rat cortex but is either absent or minimally present in bovine cortex. By contrast, 3H-ketanserin labels both the putative 5- HT2A site in rat cortex as well as a separate, distinct recognition site that is present in both rat and bovine cortex, tentatively designated the 5-HT2B site.
Restraint-stress-induced changes in exploratory behavior appear to be mediated by norepinephrine-stimulated release of CRF
Authors: Berridge CW , Dunn AJ
Published: March 2018

Exploratory behavior, measured by the time an animal spends investigating objects in a novel environment, has been shown to be sensitive to prior exposure of the animal to stressors. Using this paradigm, it was demonstrated previously that both corticotropin- releasing factor (CRF) and the alpha 2-adrenoreceptor antagonist, idazoxan, elicited stress-like decreases in exploratory behavior. Because an activation of cerebral noradrenergic systems is observed during stress, following intracerebroventricular (i.c.v.) administration of CRF, or following peripheral administration of idazoxan, the involvement of noradrenergic systems in the behavioral effect of restraint and CRF was examined. Inhibition of norepinephrine (NE) release using the alpha 2-agonist clonidine (25 micrograms/kg, i.p.) or the noradrenergic-selective neurotoxin DSP-4 antagonized the restraint-induced decrease in exploratory behavior. The combination of these 2 treatments completely prevented this effect of restraint. The alpha 1-receptor antagonist prazosin (200 micrograms/kg) also prevented the behavioral effect of restraint, whereas the alpha 1-agonist phenylephrine (50 or 100 ng, i.c.v.) decreased exploratory behavior. None of these treatments consistently altered locomotor activity as measured by the number of entries into the different compartments or the number of rears. These results implicate noradrenergic systems in the stress-related changes in this behavior, consistent with our parallel measures on the production of NE catabolites. Thus, both CRF and noradrenergic systems appear to be involved in the effect of restraint on exploratory behavior in this task. Neither DSP-4 nor prazosin had any effect on the CRF-induced decrease in exploratory behavior. However, the CRF antagonist alpha-helical CRF (20 micrograms, i.c.v.) reversed the decrease in exploratory behavior induced by phenylephrine. The most likely explanation is that the 2 systems act in tandem such that noradrenergic systems regulate the release of brain CRF via an alpha 1-adrenoreceptor. This arrangement parallels that involved in the release of hypothalamic CRF to activate the pituitary- adrenal axis. The implications of these results for research on stress- related behaviors and for the etiology of depression are discussed.
A muscle-derived factor(s) induces expression of a catecholamine phenotype in neurons of cultured rat cerebral cortex
Authors: Iacovitti L , Evinger MJ , Joh TH , Reis DJ
Published: March 2018

We sought to determine the source of the signal(s) that promotes expression of the catecholamine (CA) enzyme tyrosine hydroxylase (TH) in cultured neurons of embryonic rat cerebral cortex, a tissue which is not thought to contain CA cells in vivo. Cortical neurons were cultured with their non-neuronal constituents and 48 hr later immunostained for TH. Fibroblasts or glia had no effects, however, blood vessels increased the numbers of TH neurons nearly 4-fold. Coculture with either perinatal aorta, skeletal or cardiac muscle, clonal muscle cell lines 1440 (smooth) and L6 (skeletal), conditioned media from L6 cells, or a soluble extract of L6 cells increased the number of TH neurons up to 20-fold. The induction of TH by muscle extract was (1) dose dependent; (2) paralleled by a proportional increase in the steady- state levels of TH mRNA; (3) greatly reduced by the RNA synthesis inhibitor alpha-amanitin or the protein synthesis inhibitor cycloheximide; and (4) unassociated with change in the survival of neurons in culture. The response was not replicated by treatment with other established neurotrophic substances, including NGF, EGF, FGF, PDGF, neuroleukin, insulin, pyruvate, KCI, adenosine, or inosine. We conclude that muscle contains a potentially novel substance, muscle- derived differentiation factor (MDF) that promotes differentiation but not survival of neurons of cerebral cortex by de novo synthesis of TH mRNA and TH protein. Thus, neurons of the CNS, as in periphery, may undergo phenotypic interconversion in response to biologically derived molecules in their environment.
Opiate influences on nucleus accumbens neuronal electrophysiology: dopamine and non-dopamine mechanisms
Authors: Hakan RL , Henriksen SJ
Published: March 2018

Single-unit recordings of nucleus accumbens septi (NAS) neurons in halothane-anesthetized rats revealed that microinfusions of morphine into the ventral tegmental area (VTA) primarily inhibited spontaneously active NAS units. These inhibitory effects were reversed by alpha- flupenthixol (s.c.), suggesting a role for dopamine (DA) in the observed opiate-induced effect. VTA opiate microinfusions also inhibited the evoked (driven) responses of silent cells (spontaneously inactive) in the NAS elicited by stimulation of hippocampal afferents to the NAS. In addition, this inhibition of driven response was reversed by naloxone (s.c.) but not by alpha-flupenthixol, implying a VTA-mediated non-DA mechanism. Morphine applied iontophoretically to cells within the NAS inhibited spontaneous activity but not fimbria- driven cellular activity, suggesting that the systemic effects of opiates on NAS activity can be mediated directly in the NAS as well as through VTA afferents. Moreover, since VTA-induced inhibition of fimbria-driven activity was reversed by systemic opiates, opiates also can exert effects through other, as yet unidentified NAS afferent systems.
Selective formation and modulation of electrical synapses between cultured Aplysia neurons
Authors: Carrow GM , Levitan IB
Published: March 2018

When dissociated neurons from the mollusc, Aplysia californica, are placed in primary cell culture, they form electrical synapses in a specific, yet alterable, manner. Pairs of neurons from the same ganglion (“homoganglionic” pairs) form electrical synapses with high coupling coefficients. This is due to relatively high macroscopic junctional conductance as determined directly by voltage clamping both neurons of each pair. By contrast, synapses between pairs of neurons from different ganglia (“heteroganglionic” pairs) exhibit lower coupling coefficients as a result of lower macroscopic junctional conductance. Both types of junction are nonrectifying, not gated by voltage, and resistant to uncoupling by octanol and heptanol. This dichotomy of synaptic efficacy is altered upon exposure of the neurons to the lectin, conacanavalin A (Con A). Acute treatment of heteroganglionic cell pairs with Con A increases their junctional conductance to the higher level characteristic of homoganglionic pairs within several hours. However, the higher junctional conductance of homoganglionic pairs is not modulated by Con A. The results presented here suggest that synaptic specificity among these regenerating neurons may be mediated at least in part by ganglion-specific cell-recognition molecules. Furthermore, these molecules may be, or may be linked to, lectin receptors that regulate gap junction channels.
Fibroblast growth factor and glutamate: opposing roles in the generation and degeneration of hippocampal neuroarchitecture
Authors: Mattson MP , Murrain M , Guthrie PB , Kater SB
Published: March 2018

Neuritic regression and cell death (neurodegeneration) are common features of both normal nervous system development and neurodegenerative disorders. Growth factors and excitatory amino acid neurotransmitters have been suggested independently to play roles in neurodegenerative processes. The present study investigated the combined effects of fibroblast growth factor (FGF) and glutamate on the development and degeneration of cultured hippocampal neurons. Consistent with previous data, we found that FGF, but not NGF, promoted neuronal survival and dendritic outgrowth. In contrast, a low level of glutamate (50 microM) caused a reduction in dendritic outgrowth, and high levels (100 microM-1 mM) reduced neuronal survival in a dose- dependent manner. When cultures were maintained in the presence of FGF, there was a striking reduction in neuronal death normally caused by 100– 500 microM glutamate. FGF raised the threshold for glutamate neurotoxicity. FGF also antagonized the outgrowth-inhibiting actions of glutamate. Measurements of intracellular calcium levels with fura-2 demonstrated a direct relationship between glutamate-induced rises in intracellular calcium and neurodegeneration. FGF reduced the glutamate- induced increases in intracellular calcium levels. However, when cultures were pretreated with the RNA synthesis inhibitor actinomycin D or with the protein synthesis inhibitor cycloheximide, FGF did not prevent glutamate-induced increases in intracellular calcium or neurodegeneration. Taken together, these results suggest that (1) interactions between growth factors and neurotransmitters may be important in brain development; (2) imbalances in these systems may lead to neurodegeneration; and (3) cellular calcium-regulating systems may be a common focus of growth factor and neurotransmitter actions.
Neural circuits mediating visual flight control in flies. I. Quantitative comparison of neural and behavioral response characteristics
Authors: Hausen K , Wehrhahn C
Published: March 2018

The motion-sensitive horizontal cells in the lobula plate of the fly are assumed to play a key role in the sensory control of yaw torque generated by the flying animal during course-stabilization maneuvers and the fixation of objects. This inference results from comparisons of electrophysiological data obtained from blowflies (Calliphora erythrocephala) and behavioral data obtained mainly from houseflies (Musca domestica) and fruitflies (Drosophila melanogaster). Apart from few exceptions, the compatibility of these physiological and behavioral data has not been critically tested. In the present study, the responses of the equatorial horizontal cell HSE of Calliphora and the yaw torque responses of Calliphora and Musca were recorded under identical visual stimulation with moving periodic gratings. The goal of the experiments was to obtain electrophysiological and behavioral data on Calliphora, on the one hand, and behavioral data on Calliphora and Musca, on the other hand, that allow direct comparisons between the physiological properties of the HSE and the visually induced torque responses in both species. The dependence of the HSE responses and the yaw torque responses on the direction, contrast frequency, and brightness of a moving periodic grating were evaluated quantitatively. The results of the electrophysiological recordings and torque measurements are in close agreement and thus represent strong evidence that the horizontal cells are, in fact, involved in yaw torque control in both species. Measurements of the cellular and behavioral responses as function of the stimulus position in the visual field, however, reveal differences between the spatial sensitivity of the horizontal cells and the sensory input to the motor system.(ABSTRACT TRUNCATED AT 250 WORDS)