bluuebunny/crossref_metadata_2025 huggingface dataset:
Submicrovillar tubules in distal segments of squid photoreceptors detected by rapid freezing
Authors: Walrond JP , Szuts EZ
Published: March 2018

Invertebrate phototransduction is believed to involve an inositol trisphosphate (InsP3)-mediated release of calcium from intracellular storage compartments. Although light-induced production of InsP3 has been demonstrated for squid retinas, morphological evidence for the presence of internal calcium stores has been lacking. Because squid retinas are about 1 mm thick and composed of densely packed receptor cells, conventional aldehyde fixatives may not penetrate rapidly enough to preserve subcellular organelles. To reduce the time for fixative penetration, receptor cells were isolated from intact retinas before fixation, but these techniques provided little improvement in the preservation of membrane-bound compartments. Alternatively, the distal ends of the receptors were ultra-rapidly frozen by dropping 1 mm2 pieces of intact retina against a liquid helium-cooled copper block. Electron micrographs of thick sections from rapidly frozen and freeze- substituted retinas showed elongated saccules oriented parallel to the long axis of the receptor cell and located about 40 nm from the microvillar openings. Freeze-fracture and etch views of rapidly frozen cells showed that the saccules are 130 nm diameter tubules and extend for at least several micrometers along the length of the receptor cell. We call these organelles submicrovillar tubules (SMT). The gap between the SMT and the plasma membrane contains a network of filaments that appear to be actin. Freeze-fracture and etch views of the rhabdomeres also indicate that adjacent microvilli are separated by a 6–8-nm-wide extracellular space along most of their length. This space is spanned by extracellular connections linking adjacent microvilli. The position and orientation of the SMT suggest that these organelles may serve the same function as the more voluminous and highly convoluted submicrovillar cisternae found in other invertebrates. The SMT is likely to be the intracellular compartment that stores and releases calcium as part of the InsP3-mediated light response.
Pre-oligodendrocytes from adult human CNS
Authors: Armstrong RC , Dorn HH , Kufta CV , Friedman E , Dubois-Dalcq ME
Published: March 2018

CNS remyelination and functional recovery often occur after experimental demyelination in adult rodents. This has been attributed to the ability of mature oligodendrocytes and/or their precursor cells to divide and regenerate in response to signals in demyelinating lesions. To determine whether oligodendrocyte precursor cells exist in the adult human CNS, we have cultured white matter from patients undergoing partial temporal lobe resection for intractable epilepsy. These cultures contained a population of process-bearing cells that expressed antigens recognized by the O4 monoclonal antibody, but these cells did not express galactocerebroside (a marker for oligodendrocytes), glial fibrillary acidic protein (a marker for astrocytes), or vimentin. Selective elimination of O4-positive (O4+) cells by complement-mediated lysis resulted in inhibition of oligodendrocyte development in vitro. Since O4+ cells have an antigenic phenotype reminiscent of the rat adult oligodendrocyte-type 2 astrocyte progenitor and appear to develop into oligodendrocytes rather than type 2 astrocytes with time in culture, we call them “pre-oligodendrocytes.” Neither pre-oligodendrocytes nor oligodendrocytes incorporated 3H- thymidine in response to rat astrocyte-conditioned medium, platelet- derived growth factor, insulin-like growth factor (IGF-1), or basic fibroblast growth factor (bFGF). However, IGF-1 increased the relative abundance of oligodendrocytes to pre-oligodendrocytes, while bFGF had the opposite effect. Cells with the antigenic phenotype of pre- oligodendrocytes were also identified in tissue prints of adult human white matter. We propose that, in human demyelinating diseases such as multiple sclerosis, pre-oligodendrocytes may divide and/or migrate in response to signals present in demyelinated lesions and thus facilitate remyelination.
IGF-I and IGF-II protect cultured hippocampal and septal neurons against calcium-mediated hypoglycemic damage
Authors: Cheng B , Mattson MP
Published: March 2018

Insulin and insulin-like growth factors I and II (IGF-I and IGF-II) have recently been shown to have biological activity in central neurons, but their normal functions and mechanisms of action in the brain are unknown. Since central neurons are particularly vulnerable to hypoglycemia that results from ischemia or other insults, we tested the hypothesis that growth factors can protect central neurons against hypoglycemic damage in vitro. IGF-I and IGF-II (3–100 ng/ml) each prevented glucose deprivation-induced neuronal damage in a dose- dependent manner in rat hippocampal and septal cell cultures. High concentrations of insulin (greater than 1 microgram/ml) also protected neurons against hypoglycemic damage. Epidermal growth factor did not protect against hypoglycemic damage. Both IGFs and insulin were effective when administered 24 hr before or immediately following the onset of glucose deprivation. Direct measurements of intraneuronal calcium levels and manipulations of calcium influx demonstrated that calcium influx and sustained elevations in intraneuronal calcium levels mediated the hypoglycemic damage. IGF-I and IGF-II each prevented the hypoglycemia-induced elevations of intraneuronal free calcium. Studies with excitatory amino acid receptor antagonists and calcium channel blockers indicated that NMDA receptors did, and L-type calcium channels did not, play a major role in hypoglycemic damage. Taken together, these findings indicate that IGFs can stabilize neuronal calcium homeostasis and thereby protect against hypoglycemic damage.
Depolarization increases vasoactive intestinal peptide- and substance P- like immunoreactivities in cultured neonatal and adult sympathetic neurons
Authors: Sun Y , Rao MS , Landis SC , Zigmond RE
Published: March 2018

We have utilized the favorable signal-to-noise ratios provided by whole- cell recording, combined with variance analysis, to determine the pre- or postsynaptic actions of a variety of manipulations on unitary EPSPs evoked by low-intensity stimulation of afferents to CA1 pyramidal neurons in slices of hippocampus. Estimates of quantal content (mcv) were determined by calculating the ratio of the squared average unitary EPSP amplitude (determined from 150–275 responses) to the variance of these responses (M2/sigma 2), while quantal amplitudes (qcv) were estimated by calculating the ratio of the response variance to average EPSP size (sigma 2/M). Estimates of mcv were highly correlated with those determined using the method of failures (mf). With paired stimulation (50 msec interpulse interval) there was a significant facilitation of the second unitary EPSP, accompanied by an increase in mcv, but not qcv, suggesting that this facilitation was of presynaptic origin. Superfusion of hippocampal slices with various concentrations of adenosine, the A1-selective adenosine receptor agonist cyclohexyladenosine, or the Ca2+ channel blocker cadmium significantly reduced average unitary EPSP amplitudes and mcv, without significantly altering qcv, suggesting a presynaptic locus for this inhibition. The 50% effective concentration for the apparent presynaptic action of adenosine on mcv in the present study (5.7 microM; 95% confidence limits = 4.2–7.7 microM) was significantly lower than its EC50 for reducing conventional, large EPSPs (33 microM; recorded with high- resistance microelectrodes), or extracellular field EPSPs (29 microM), as previously reported by this laboratory. The glutamate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) reduced average unitary EPSP amplitudes; in contrast to the above manipulations, it had no effect on mcv, but significantly altered qcv, which is consistent with its presumed postsynaptic mechanism of action. We conclude from these data that adenosine presynaptically reduces synaptic strength at Schaffer collateral-commissural synapses in the hippocampus by diminishing the number of quanta released, not by reducing the size of these individual quanta or postsynaptic sensitivity to excitatory neurotransmitter. These results suggest that the mechanism by which adenosine inhibits synaptic transmission in the hippocampus is similar, if not identical, to the mechanism by which it inhibits synaptic transmission at the neuromuscular junction.
Equivalent forgetting rates in long-term memory for diencephalic and medial temporal lobe amnesia
Authors: McKee RD , Squire LR
Published: March 2018

Amnesia can result from damage to either the midline diencephalon or the medial temporal lobe. An important related question has been whether these two forms of amnesia result in similar or different kinds of memory impairment. Earlier studies raised the possibility that differences might exist in the rate of forgetting within long-term memory, specifically, that the forgetting rate is normal in diencephalic amnesia but abnormally rapid in medial temporal lobe amnesia. In the present study, forgetting was studied in five amnesic patients with damage to the medial temporal lobe, six amnesic patients with damage to the diencephalon, and 10 normal subjects. One hundred twenty pictures were presented to the control subjects for 1 sec each and to the amnesic patients for 8 sec each. Retention was then tested after 10 min, 2 hr, and 30–32 hr using four different procedures for testing recognition memory. The different exposure times for the pictures succeeded in matching the performance scores of both groups of amnesic patients and the control subjects at the 10 min retention interval. Both groups of amnesic patients also performed similarly to control subjects at retention delays of 2 hr and 30–32 hr. In addition, performance was nearly identical, regardless whether recognition memory was assessed by asking subjects to select the new items or the old items. The findings emphasize the similarities between medial temporal lobe and diencephalic amnesia.
GABAergic inhibition of endogenous dopamine release measured in vivo with 11C-raclopride and positron emission tomography
Authors: Dewey SL , Smith GS , Logan J , Brodie JD , Yu DW , Ferrieri RA , King PT , MacGregor RR , Martin TP , Wolf AP
Published: March 2018

Extensive neuroanatomical, neurophysiological, and behavioral evidence demonstrates that GABAergic neurons inhibit endogenous dopamine release in the mammalian corpus striatum. Positron emission tomography (PET) studies in adult female baboons, using the dopamine D2-specific radiotracer 11C-raclopride, were undertaken to assess the utility of this imaging technique for measuring these dynamic interactions in vivo. 11C-raclopride binding was imaged prior to and following the administration of either gamma-vinyl-GABA (GVG), a specific suicide inhibitor of the GABA-catabolizing enzyme GABA transaminase, or lorazepam, a clinically prescribed benzodiazepine agonist. Striatal 11C- raclopride binding increased following both GVG and lorazepam administration. This increase exceeded the test/retest variability of 11C-raclopride binding observed in the same animals. These findings confirm that changes in endogenous dopamine concentrations resulting from drug-induced potentiation of GABAergic transmission can be measured with PET and 11C-raclopride. Finally, this new strategy for noninvasively evaluating the functional integrity of neurophysiologically linked transmitter systems with PET supports its use as an approach for assessing the multiple mechanisms of drug action and their consequences in the human brain.
A novel T-type current underlies prolonged Ca(2+)-dependent burst firing in GABAergic neurons of rat thalamic reticular nucleus
Authors: Huguenard JR , Prince DA
Published: March 2018

The inhibitory GABAergic projection of thalamic nucleus reticularis (nRt) neurons onto thalamocortical relay cells (TCs) is important in generating the normal thalamocortical rhythmicity of slow wave sleep, and may be a key element in the production of abnormal rhythms associated with absence epilepsy. Both TCs and nRt cells can generate prominent Ca(2+)-dependent low-threshold spikes, which evoke bursts of Na(+)-dependent fast spikes, and are influential in rhythm generation. Substantial differences in the pattern of burst firing in TCs versus nRt neurons led us to hypothesize that there are distinct forms of transient Ca2+ current (I(T)) underlying burst discharges in these two cell types. Using whole-cell voltage-clamp recordings, we analyzed I(T) in acutely isolated TCs and nRt neurons and found three key differences in biophysical properties. (1) The transient Ca2+ current in nRt neurons inactivated much more slowly than I(T) in TCs. This slow current is thus termed I(Ts). (2) The rate of inactivation for I(Ts) was nearly voltage independent. (3) Whole-cell I(Ts) amplitude was increased when Ba2+ was substituted for Ca2+ as the charge carrier. In addition, activation kinetics were slower for I(Ts) and the activation range was depolarized compared to that for I(T). Other properties of I(Ts) and I(T) were similar, including steady-state inactivation and sensitivities to blockade by divalent cations, amiloride, and antiepileptic drugs. Our findings demonstrate that subtypes of transient Ca2+ current are present in two different classes of thalamic neurons. The properties of I(Ts) lead to generation of long-duration calcium-dependent spike bursts in nRt cells. The resultant prolonged periods of GABA release onto TCs would play a critical role in maintaining rhythmicity by inducing TC hyperpolarization and promoting generation of low-threshold calcium spikes within relay nuclei.
Contribution of polysynaptic pathways in the mediation and plasticity of Aplysia gill and siphon withdrawal reflex: evidence for differential modulation
Authors: Trudeau LE , Castellucci VF
Published: March 2018

The gill and siphon withdrawal (GSW) reflex of Aplysia is centrally mediated by a monosynaptic and a polysynaptic pathway between sensory and motor neurons. The first objective of this article was to evaluate quantitatively the relative importance of these two components in the mediation of the GSW reflex. We have used an artificial sea water (ASW) solution containing a high concentration of divalent cations to raise the action potential threshold of the interneurons without affecting the monosynaptic component of the reflex (2:1 ASW). Compound EPSPs induced in gill or siphon motor neurons by direct stimulation of the siphon nerve or by tactile stimulation of the siphon skin were reduced by more than 75% in 2:1 ASW. These results indicate that interneurons intercalated between sensory and motor neurons are responsible for a considerable proportion of the afferent input to the motor neurons of the reflex. The second objective of this article was to compare the modulation of the monosynaptic and polysynaptic pathways. We have evaluated their respective contribution in sensitization of the GSW reflex by testing the effects of two neuromodulators of the reflex, 5- HT and small cardioactive peptide B (SCPB). We found that these two neuromodulators have a differential action on the two components of the GSW neuronal network. The polysynaptic pathway was more facilitated than the monosynaptic pathway by the neuropeptide SCPB. By contrast, 5- HT displayed an opposite selectivity. These results suggest that the polysynaptic component of the neuronal network underlying the GSW reflex is very important for its mediation. The data also indicate that the monosynaptic and polysynaptic components of the reflex can be differentially modulated. The diversity of modulatory actions at various sites of the GSW network should be relevant for learning- associated modifications in the intact animal.
Ectopic expression of ultraviolet-rhodopsins in the blue photoreceptor cells of Drosophila: visual physiology and photochemistry of transgenic animals
Authors: Feiler R , Bjornson R , Kirschfeld K , Mismer D , Rubin GM , Smith DP , Socolich M , Zuker CS
Published: March 2018

We have generated transgenic flies expressing R7 cell-specific opsins in the major class of photoreceptor cells of the Drosophila retina and characterized their spectral properties using high-resolution microspectrophotometry and sensitivity recordings. We show that the Rh3 and Rh4 opsin genes encode UV-sensitive opsins with similar spectral properties (lambda max = 345 nm and 375 nm), and that Rh3 corresponds to the R7p and R7marg class of visual pigments. We have also generated Rh3 and Rh4 isoform-specific antibodies and present an R7 cell map of the Drosophila retina. In a related set of experiments, we show that it is possible to coexpress two different visual pigments functionally in the same cell and produce photoreceptors that display the summed spectral response of the individual pigments. These findings open up the possibility of tuning an animal's visual behavior by targeted expression of combinations of opsin genes to selective types of photoreceptors.
Cyclic nucleotides mediate an odor-evoked potassium conductance in lobster olfactory receptor cells
Authors: Michel WC , Ache BW
Published: March 2018

Odors activate at least two distinct transduction pathways in lobster olfactory receptor cells that, respectively, excite and inhibit the cell. Data presented suggest that odors selectively activate the inhibitory conductance through the second messenger cAMP. Not all cells support both odor-evoked excitatory and inhibitory conductances; in the current investigation, about 50% of the cells tested were inhibited by odors. In the majority of cells that, as a group, support an inhibitory response to odor stimulation, activation of adenylate cyclase with forskolin or inhibition of phosphodiesterase activity with 3-isobutyl-1- methylxanthine (IBMX) elicits an outward current with a time course similar to that of odor-evoked outward currents. The membrane-permeant cyclic nucleotide analogs 8-Br-cAMP and 8-Br-cGMP have a similar effect. Forskolin and IBMX enhance the magnitude of odor-evoked outward currents when the drug and the odor are copresented to the cell. In contrast, these same drugs have little or no effect on cells that, as a group, fail to support an inhibitory response to odor stimulation. This study provides the first direct evidence implicating cAMP in olfactory transduction in an invertebrate and contrasts with similar studies in vertebrates that have implicated cAMP as a second messenger mediating excitation.
Noradrenergic inhibition of synaptic transmission between mitral and granule cells in mammalian olfactory bulb cultures
Authors: Trombley PQ , Shepherd GM
Published: March 2018

Noradrenergic modulation of the glutamatergic-GABAergic synapses between mitral/tufted (M/T) and granule cells has been implicated in some forms of olfactory learning (Brennan et al., 1990). Norepinephrine (NE) has been shown to disinhibit mitral cells (Jahr and Nicoll, 1982), but its site of action is not well defined. The effects of NE on synaptic transmission between monosynaptically coupled pairs of mitral and granule cells have been examined using primary culture and whole- cell recording techniques. Intracellular stimulation of M/T cells evoked dual-component EPSPs in granule cells consisting of both NMDA and AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid) receptor-mediated mechanisms. The EPSPs were reversibly inhibited by approximately 50% during application of 30 microM NE. NE had no effect, however, on the membrane current evoked by exogenous application of glutamate, indicating a presynaptic site of action. The effect of NE on EPSPs was mimicked by the alpha-adrenergic agonist clonidine but not by the beta-adrenergic agonist isoproterenol. NE had no significant effect on either accommodation or macroscopic currents in either M/T or granule cells. NE also inhibited spontaneous GABAergic IPSPs recorded in M/T cells, by a presynaptic alpha-adrenergic-mediated mechanism. These results support previous results suggesting a disinhibitory role for NE in the olfactory bulb. This action, however, is at least in part mediated by a reduction in mitral cell-mediated granule cell excitation.
Norepinephrine inhibits calcium currents and EPSPs via a G-protein- coupled mechanism in olfactory bulb neurons
Authors: Trombley PQ
Published: March 2018

The most pronounced effect of norepinephrine (NE) in the olfactory bulb is disinhibition of mitral/tufted (M/T) cells. Although it has been previously proposed that the effects of NE are mediated by a direct inhibitory action on granule cells, we have demonstrated that NE could exert it effects through inhibition of excitatory synaptic transmission from M/T cells to granule cells (Trombley and Shepherd, 1992). In order to define further the mechanism underlying NE-mediated inhibition of synaptic transmission, the effects of NE on calcium channel currents were examined using whole-cell recording techniques on bulb neurons in primary culture. NE inhibited high-threshold calcium currents at concentrations that were effective in reducing synaptic transmission. Clonidine, but not isoproterenol, mimicked the effects of NE on calcium currents, suggesting that the effects were mediated through activation of presynaptic alpha-adrenergic receptors. The effects of NE on calcium currents were irreversible in the presence of internal GTP-gamma S and prevented by preincubation with pertussis toxin, results that are consistent with a G-protein-coupled mechanism. Preincubation with pertussis toxin also prevented the effects of NE on synaptic transmission, suggesting that a similar G-protein couple mechanism mediates both effects. Intracellular dialysis with staurosporin or calcium buffering with EGTA did not prevent the effects of NE, suggesting that neither protein phosphorylation nor elevated intracellular calcium were required. These results suggest that NE may inhibit synaptic transmission in the olfactory bulb by reducing calcium currents via a G-protein-coupled alpha-adrenergic receptor.
Colocalization of NGF binding sites, trk mRNA, and low-affinity NGF receptor mRNA in primary sensory neurons: responses to injury and infusion of NGF
Authors: Verge VM , Merlio JP , Grondin J , Ernfors P , Persson H , Riopelle RJ , Hokfelt T , Richardson PM
Published: March 2018

The distributions of mRNAs for the protooncogene trk and the low- affinity NGF receptor (LNGFR) were studied by hybridization with oligonucleotide probes on sections of adult rat primary sensory and sympathetic ganglia. For comparison with high-affinity binding sites, adjacent sections were processed for NGF receptor radioautography. Among neurons in lumbar dorsal root ganglia and trigeminal ganglia, trk mRNA and NGF-binding sites were closely colocalized; this finding together with previous direct evidence in other cell types is taken to indicate that trk protein is an essential component of the high- affinity NGF receptor in adult sensory neurons. In lumbar dorsal root ganglia and trigeminal ganglia, abundant LNGFR mRNA was found in all neurons with strong 125I-NGF labeling and on additional neurons lacking high-affinity NGF-binding sites. The presence of abundant LNGFR in neurons with high-affinity receptors could be the cause and/or consequence of their ability to respond to NGF. Neurons with abundant LNGFR mRNA but few high-affinity NGF-binding sites may have receptors for other members of the neurotrophin family. In nodose ganglia, neurons with high concentrations of LNGFR mRNA greatly outnumbered the small percentage with abundant trk mRNA. Following intrathecal infusion of NGF to otherwise normal dorsal root ganglia, the concentrations of LNGFR mRNA but not those of trk mRNA and NGF-binding sites were increased in NGF-responsive neurons. The usual single normal pattern of frequency histograms of LNGFR labeling indices became bimodal in response to NGF. Concentrations of NGF-binding sites, LNGFR mRNA, and trk mRNA were all decreased by peripheral nerve transection and restored by exogenous NGF, the restoration being complete for LNGFR mRNA and partial for trk mRNA and NGF-binding sites. The data indicate that NGF can regulate both LNGFR and trk mRNAs but do not clarify the possible contribution of the LNGFR protein to high-affinity binding sites.
Neurochemical afferents controlling the activity of serotonergic neurons in the dorsal raphe nucleus: microiontophoretic studies in the awake cat
Authors: Levine ES , Jacobs BL
Published: March 2018

Serotonergic (5-HT) neurons of the brainstem dorsal raphe nucleus (DRN) have been implicated in a diversity of physiological and behavioral processes in vertebrates. However, despite extensive information about the intrinsic properties and the efferent projections of this neurochemical system, little information is available regarding the afferents that control its activity. This study investigated the neurotransmitters that regulate the activity of DRN-5-HT neurons under physiologically relevant conditions, by utilizing microiontophoresis in combination with single-unit recordings in the awake, head-restrained cat. This made it possible to examine the direct effects of neurotransmitters on DRN-5-HT neuronal activity, and, through the use of specific antagonists, to study the roles of these neurotransmitter inputs during physiological conditions that influence DRN-5-HT neuronal activity. The results indicate that (1) iontophoretic application of the GABA antagonist bicuculline reversed the typical suppression of neuronal activity seen during slow wave sleep, but had no effect on maintained activity during wakefulness. The suppression of neuronal activity during REM sleep was generally unaffected by application of bicuculline. This suggests a role for a GABAergic input to DRN-5-HT neurons in controlling some aspects of their state-dependent activity. (2) Iontophoretic application of the excitatory amino acid (EAA) antagonist kynurenic acid reduced the magnitude of the neuronal response evoked by phasic auditory stimuli, but had no effect on the spontaneous activity of these neurons, suggesting a role for an EAA input to the DRN in mediating the response to phasic sensory stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
The G-protein-coupled receptor kinases beta ARK1 and beta ARK2 are widely distributed at synapses in rat brain
Authors: Arriza JL , Dawson TM , Simerly RB , Martin LJ , Caron MG , Snyder SH , Lefkowitz RJ
Published: March 2018

The beta-adrenergic receptor kinase (beta ARK) phosphorylates the agonist-occupied beta-adrenergic receptor to promote rapid receptor uncoupling from Gs, thereby attenuating adenylyl cyclase activity. Beta ARK-mediated receptor desensitization may reflect a general molecular mechanism operative on many G-protein-coupled receptor systems and, particularly, synaptic neurotransmitter receptors. Two distinct cDNAs encoding beta ARK isozymes were isolated from rat brain and sequenced. The regional and cellular distributions of these two gene products, termed beta ARK1 and beta ARK2, were determined in brain by in situ hybridization and by immunohistochemistry at the light and electron microscopic levels. The beta ARK isozymes were found to be expressed primarily in neurons distributed throughout the CNS. Ultrastructurally, beta ARK1 and beta ARK2 immunoreactivities were present both in association with postsynaptic densities and, presynaptically, with axon terminals. The beta ARK isozymes have a regional and subcellular distribution consistent with a general role in the desensitization of synaptic receptors.
Alteration of long-lasting structural and functional effects of kainic acid in the hippocampus by brief treatment with phenobarbital
Authors: Sutula T , Cavazos J , Golarai G
Published: March 2018

Kainic acid, an analog of the excitatory amino acid L-glutamate, induces acute hyperexcitability and permanent structural alterations in the hippocampal formation of the adult rat. Administration of kainic acid is followed by acute seizures in hippocampal pathways, neuronal loss in CA3 and the hilus of the dentate gyrus, and reorganization of the synaptic connections of the mossy fiber pathway. Rats with these hippocampal structural alterations have increased susceptibility to kindling. To evaluate the role of the acute seizures and associated hippocampal structural alterations in the development of this long- lasting susceptibility, rats that received intraventricular kainic acid were cotreated with phenobarbital (60 mg/kg, s.c., once daily). Treatment with this dose for 5 d after administration of kainic acid suppressed acute seizure activity, protected against excitotoxic damage in the dentate gyrus, reduced mossy fiber sprouting, and completely abolished the increased susceptibility to kindling associated with kainic acid. Brief treatment with phenobarbital modified the pattern of damage and synaptic reorganization in the dentate gyrus in response to seizure-induced injury, and altered the long-lasting functional effects associated with hippocampal damage. As phenobarbital treatment did not protect against neuronal damage in CA3 or other regions of the hippocampus, the circuitry of the dentate gyrus was implicated as a locus of cellular alterations that influenced the development of kindling. These observations are evidence that pharmacological intervention can prevent the development of epilepsy in association with acquired structural lesions, and suggest that pharmacological modification of cellular responses to injury can favorably alter long- term functional effects of CNS damage.
Fibroblast growth factor differentially modulates the neurotransmitter phenotype of cultured sympathetic neurons
Authors: Zurn A
Published: March 2018

Fibroblast growth factors (FGFs) are multifunctional growth factors that increase the proliferation of mesoderm- and neuroectoderm-derived cells and promote neuronal survival and neurite outgrowth in various regions of the brain, yet the physiological role(s) they may play in nervous system function and/or development is unclear. The present report demonstrates, using a well-characterized system, avian sympathetic neurons in vitro, that acidic and basic FGFs increase ChAT but decrease tyrosine hydroxylase (TH) activity in these cells, without affecting neuronal growth and survival. Heparin, which binds to FGFs with a high affinity, potentiates the activity of FGF on ChAT, but not TH. The time course of FGF action on the neurotransmitter phenotype is slow since effects start to appear after 1–2 d only. FGFs may thus modulate the activities of ChAT and TH by differentially regulating the expression of the genes coding for these enzymes. In conclusion, this report provides evidence supporting the hypothesis that FGFs may play a role in regulating neurotransmitter expression in sympathetic neurons during development independently of any effect on neuronal survival.
Light-evoked expansion of subretinal space volume in the retina of the frog
Authors: Huang B , Karwoski CJ
Published: March 2018

The retina of the frog was superfused with a Ringer solution containing impermeant “probe” cations and anions. Light-evoked concentration changes in these probe ions were measured in the subretinal space (SRS) with ion-selective microelectrodes. A decrease in probe ion concentration was found, and several observations suggest that this is caused by a light-evoked expansion of the SRS. The probe ion decrease was not seen in the isolated retina; thus, the pigment epithelial (PE) cells are important for its generation. Pharmacological studies suggest that K+ channels in the PE cells are important--perhaps the PE cells shrink in response to the light-evoked decrease in SRS [K+]. The light- evoked decrease of SRS volume may be important in the understanding of SRS solute concentrations, retina-PE adhesivity, photoreceptor-PE cell interactions, and the interphotoreceptor matrix.
Promoter organization and activity of human monoamine oxidase (MAO) A and B genes
Authors: Zhu QS , Grimsby J , Chen K , Shih JC
Published: March 2018

Monoamine oxidase A and B (MAO A and B) play important roles in the metabolism of biogenic and dietary amines and are encoded by two genes derived from a common ancestral gene. The promoter regions for human MAO A and B genes have been characterized using a series of 5′ flanking sequences linked to a human growth hormone reporter gene. When these constructs were transfected into NIH3T3, SHSY-5Y, and COS7 cells, the maximal promoter activity for MAO A was found in a 0.14 kilobase (kb) PvuII/DraII fragment (A0.14) and in a 0.15 kb PstI/NaeI fragment (B0.15) for MAO B. Both fragments are GC-rich, contain potential Sp1 binding sites, and are in the region where the MAO A and B 5′ flanking sequences share the highest identity (approximately 60%). However, the organization of the transcription elements is distinctly different between these two promoters. Fragment A0.14 consists of three Sp1 elements, all in reversed orientations, and lacks a TATA box. Two of the Sp1 sites are located within the downstream 90 base pair (bp) direct repeat, and the third is located at the 3′ end of the upstream 90 bp direct repeat. Fragment B0.15 contains an Sp1-CACCC-Sp1-TATA structure; deletion of any of these elements reduced promoter activity. Additional Sp1 sites, CACCC elements, CCAAT boxes, and direct repeats (four 30 bp direct repeats in MAO A and two 29 bp direct repeats in MAO B) are found in farther-upstream sequences of both genes (1.27 kb for MAO A and mostly in 0.2 kb for MAO B). Inclusion of these sequences decreased promoter activity. The different promoter organization of MAO A and B genes provides the basis for their different tissue- and cell- specific expression.
Equipotentiality of thalamo-amygdala and thalamo-cortico-amygdala circuits in auditory fear conditioning
Authors: Romanski LM , LeDoux JE
Published: March 2018

The goal of the present study was to examine the contribution of thalamo-amygdala and thalamo-cortico-amygdala projections to fear conditioning. Lesions were used to destroy either the thalamo-cortico- amygdala projection, the thalamo-amygdala projection, or both projections, and the effects of such lesions on the acquisition of conditioned fear responses (changes in arterial pressure and freezing behavior) to a tone paired with footshock were measured. In each group of animals examined, a large lesion of the acoustic thalamus, including all nuclei of the medial geniculate body and adjacent portions of the posterior thalamus, was made on one side of the brain to block auditory transmission to the forebrain at the level of the thalamus on that side. In this way, experimental lesions could be made on the contralateral side of the brain. Thus, animals with thalamo-amygdala pathway lesions received a large lesion of the acoustic thalamus on one side. Contralaterally, only the nuclei that project to the amygdala (the medial division of the medial geniculate body, the posterior intralaminar nucleus, and the suprageniculate nucleus) were selectively destroyed, leaving much of the thalamo-cortico-amygdala projection intact. For thalamo-cortico-amygdala pathway lesions, the acoustic thalamus was destroyed on one side and temporal and perirhinal cortices were ablated contralaterally. In these animals, thalamo-amygdala projections were intact on the side of the cortical lesion. Destruction of either pathway alone had no effect on auditory fear conditioning. However, combined lesions of the two sensory pathways disrupted conditioning.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibitory influence of the dorsal nucleus of the lateral lemniscus on binaural responses in the rat's inferior colliculus
Authors: Li L , Kelly JB
Published: March 2018

The contribution of the dorsal nucleus of the lateral lemniscus (DNLL) to binaural processing was examined by recording single-unit activity in the rat's inferior colliculus before, during, and after a reversible block of the excitatory activity in DNLL by local injection of kynurenic acid. Recordings were made from the central nucleus of the inferior colliculus with glass micropipettes filled with 3 M sodium acetate. Kynurenic acid (2 mM in Locke's solution) was injected into the DNLL through one side of a double-barreled glass pipette. The other side of the pipette was filled with Locke's solution for making control injections and recording neural activity. Pressure injection of 0.7–2.0 microliter of kynurenic acid resulted in the complete cessation of tone- evoked responses in DNLL for periods of 45 min to 1 hr. Tone bursts were delivered separately to the two ears through headphones fitted to the external auditory meatus. Binaural responses in the inferior colliculus were determined by comparing the effects of monaural and binaural stimulation. Attention was focused on neurons that were excited by contralateral stimulation and inhibited by ipsilateral stimulation. Interaural intensity difference (IID) functions were generated by holding contralateral sound pressure constant at 10 dB above threshold while increasing ipsilateral sound pressure level. Prior to kynurenic acid injection, ipsilateral stimulation caused a pronounced suppression of contralaterally evoked single-unit activity. Unilateral injection of kynurenic acid into DNLL reduced the strength of binaural suppression in the contralateral inferior colliculus. In every cell tested, the IID curve in inferior colliculus was shifted following contralateral DNLL injection. The IID curve returned to normal after recovery of neural activity in DNLL. In contrast, no effect was seen in the inferior colliculus ipsilateral to the kynurenic acid injection. The injection of Locke's solution into DNLL had no effect on IID curves in the inferior colliculus. These data suggest that the DNLL plays a role in binaural processing through an inhibitory influence on responses in the contralateral inferior colliculus.
Neuronal activity in monkey ventral striatum related to the expectation of reward
Authors: Schultz W , Apicella P , Scarnati E , Ljungberg T
Published: March 2018

Projections from cortical and subcortical limbic structures to the basal ganglia are predominantly directed to the ventral striatum. The present study investigated how the expectation of external events with behavioral significance is reflected in the activity of ventral striatal neurons. A total of 420 neurons were studied in macaque monkeys performing in a delayed go-no-go task. Lights of different colors instructed the animal to do an arm-reaching movement or refrain from moving, respectively, when a trigger light was illuminated a few seconds later. Task performance was reinforced by liquid reward in both situations. A total of 60 ventral striatal neurons showed sustained increases of activity before the occurrence of individual task events. In 43 of these neurons, activations specifically preceded the delivery of reward, independent of the movement or no-movement reaction. In a series of additional tests, these activations were time locked to the subsequent reward, disappeared within a few trials when reward was omitted, and were temporally unrelated to mouth movements. Changes in the appetitive value of the reward liquid modified the magnitude of activations, suggesting a possible relationship to the hedonic properties of the expected event. Activations also occurred when reward was delivered in a predictable manner outside of any behavioral task. These data suggest that neurons in the ventral striatum are activated during states of expectation of individual environmental events that are predictable to the subject through its past experience. The prevalence of activations related to the expectation of reward suggests that ventral striatal neurons have access to central representations of reward and thereby participate in the processing of information underlying the motivational control of goal-directed behavior.
The expression of nicotinic acetylcholine receptors by PC12 cells treated with NGF
Authors: Rogers SW , Mandelzys A , Deneris ES , Cooper E , Heinemann S
Published: March 2018

The expression of neuronal nicotinic ACh receptors (nAChRs) and the subunits that compose these receptors by PC12 cells exposed to NGF has been studied. The analysis of total RNA reveals that the neuronal nAChR subunits alpha 3, alpha S, beta 2, beta 3, and beta 4, but not alpha 2 and alpha 4, are expressed in our PC12 cells. Within 48 hr of adding NGF to cultures, the RNA corresponding to alpha 3, alpha 5, beta 3, and beta 4 is decreased, but the beta 2 RNA increases for up to 6 d after NGF treatment. To determine the influence of NGF treatment on subunit protein expression, subunit-specific antisera were prepared. Immunocytochemistry detected antigen for alpha 3, alpha 5, beta 2, beta 3, and beta 4 (but not alpha 2 and alpha 4) in both NGF-treated and nontreated PC12 cells. The expression of nAChR subunit proteins, as measured by direct binding of antibodies to PC12 cells, does not change subsequent to 6 d of treatment with NGF. Whole-cell recording of PC12 cells shows that both the individual cell current density and response to the agonist cytisine were not altered after 5–7 d in NGF. However, the number of cells exhibiting detectable ACh-induced currents doubled. These results indicate that NGF increases the number of PC12 cells expressing ACh-sensitive nAChR currents but the activation is not the result of altering the amounts of individual nAChR subunit proteins. These data, taken together with the decrease in most nAChR subunit RNAs (except beta 2), suggest that NGF regulation of nAChRs may be through a posttranscriptional mechanism.
Nerve growth factor (NGF) prevents the shift in ocular dominance distribution of visual cortical neurons in monocularly deprived rats
Authors: Maffei L , Berardi N , Domenici L , Parisi V , Pizzorusso T
Published: March 2018

The hypothesis that NGF could play a role in the plasticity of the developing mammalian visual cortex was tested in monocularly deprived (MD) rats. In particular, we have asked whether an exogenous supply of NGF could prevent the changes in ocular dominance distribution induced by monocular deprivation. Hooded rats were monocularly deprived for 1 month, starting at postnatal day 14 (P14), immediately before eye opening, by means of eyelid suture. In eight rats, only monocular deprivation was performed; in eight rats, monocular deprivation was combined with intraventricular injections of beta-NGF, and in three rats, with intraventricular injections of cytochrome C. Injections (2 microliters) were given every other day for a period of 1 month. Single neuron activity was recorded in the primary visual cortex of MD rats, MD rats treated with NGF, and MD rats treated with cytochrome C at the end of the deprivation period, and in normal rats of the same age. We found that monocular deprivation caused a striking change in the ocular dominance distribution of untreated MD rats, reducing binocular cells by a factor of two and increasing by a factor of eight the number of cells dominated by the nondeprived eye. In MD NGF-treated rats, the ocular dominance distribution was indistinguishable from the normal. Cytochrome C treatment was completely ineffective in preventing the ocular dominance shift induced by monocular deprivation. To test whether NGF affected cortical physiology or interfered with transmission of visual information, we evaluated in NGF-treated rats the spontaneous discharge and the orientation selectivity. We found these functional properties to be in the normal range. We conclude that NGF is effective in preventing the effects of monocular deprivation in the rat visual cortex and suggest that NGF is a crucial factor in the competitive processes leading to the stabilization of functional geniculocortical connections during the critical period.
Localization of acidic fibroblast growth factor in specific subcortical neuronal populations
Authors: Stock A , Kuzis K , Woodward WR , Nishi R , Eckenstein FP
Published: March 2018

The effects of fibroblast growth factors (FGFs) in vitro include the stimulation of mitogenesis in a variety of non-neuronal cell types and the promotion of the survival of various central and peripheral neuronal populations. The precise physiological role of FGFs in vivo is currently not known. As a step toward understanding the role of FGFs in the nervous system, the present study determined the distribution of acidic FGF (aFGF) in the rat CNS. The levels of aFGF in dissected areas of the nervous system were quantified using a biological assay method, and the cellular distribution of aFGF was determined in tissue sections using immunohistochemical methods. aFGF was found to be localized within specific neuronal populations in the CNS and was absent from non- neuronal cells. Neurons containing aFGF immunoreactivity included magnocellular neurons in the septal area and nucleus basalis; some additional defined neuronal groups in the subcortical telencephalon; specific neuronal populations in the hypothalamus, the thalamus, the substantia nigra, the reticular formation, and the pons; and motor and sensory neurons. Cerebral cortex and hippocampus contained only a very limited number of aFGF-immunoreactive neurons. A significant overlap of neuronal populations known to express the low-affinity NGF receptor (LNGFR) with populations containing aFGF immunoreactivity was also observed. These neuronal populations are known to be affected by neurodegenerative diseases, and the possible functional implications of the presence of aFGF and the LNGFR in these cells are discussed.
Cellular bases of neocortical activation: modulation of neural oscillations by the nucleus basalis and endogenous acetylcholine
Authors: Metherate R , Cox CL , Ashe JH
Published: March 2018

In the mammalian neocortex, the EEG reflects the state of behavioral arousal. The EEG undergoes a transformation, known as activation, during the transition from sleep to waking. Abundant evidence indicates the involvement of the neurotransmitter acetylcholine (ACh) in EEG activation; however, the cellular basis of this involvement remains unclear. We have used electrophysiological techniques with in vivo and in vitro preparations to demonstrate actions of endogenous ACh on neurons in auditory neocortex. In vivo stimulation of the nucleus basalis (NB), a primary source of neocortical ACh, (1) elicited EEG activation via cortical muscarinic receptors, (2) depolarized cortical neurons, and (3) produced a change in subthreshold membrane potential fluctuations from large-amplitude, slow (1–5 Hz) oscillations to low- amplitude, fast (20–40 Hz) oscillations. The NB-mediated change in pattern of membrane potential fluctuations resulted in a shift of spike discharge pattern from phasic to tonic. Stimulation of afferents in the in vitro neocortex elicited cholinergic actions on putative layer 5 pyramidal neurons. Acting via muscarinic receptors, endogenous ACh (1) reduced slow, rhythmic burst discharge and facilitated higher- frequency, single-spike discharge in burst-generating neurons, and (2) facilitated the appearance and magnitude of intrinsic membrane potential oscillations. These in vivo and in vitro observations suggest that neocortical activation results from muscarinic modulation of intrinsic neural oscillations and firing modes. Rhythmic-bursting pyramidal neurons in layer 5 may act as cortical pacemakers; if so, then modifying their discharge characteristics could alter local cortical networks. Larger, intercortical networks could also be modified, due to the widespread projections of NB neurons. Thus, NB cholinergic neurons may play a critical role in producing different states of neocortical function.