bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of metabotropic glutamate receptors differentially affects two classes of hippocampal interneurons and potentiates excitatory synaptic transmission
Authors: McBain CJ , DiChiara TJ , Kauer JA
Published: April 2018

Based on responses to metabotropic glutamate receptor (mGluR) activation, we have characterized two distinct classes of interneuron in stratum (st.) oriens of the CA1 region of hippocampus. One type of interneuron was strongly excited by 1S,3R-aminocyclopentane dicarboxylic acid (ACPD), responding with a large inward current accompanied by increased baseline noise and prominent current oscillations. A second interneuron population responded with a modest inward current with no changes in baseline noise. These two classes of responses persisted in the presence of tetrodotoxin and antagonists of ionotropic glutamate and GABA receptors, suggesting that the inward currents result from mGluRs on the interneurons themselves. The two physiologically defined cell types correspond to two distinct morphological cell types in st. oriens/alveus, distinguished by very different patterns of local axonal connections. Large oscillatory inward current responses were recorded predominantly from an interneuron type whose axons heavily innervated st. lacunosum. The more modest inward current response was generally found in interneurons whose axons innervated the somata and proximal dendrites of CA1 pyramidal neurons. These differences in physiology and local circuitry imply that activation of mGluRs in st. oriens will cause very strong excitation of interneurons synapsing in st. lacunosum, and weaker excitation of interneurons innervating pyramidal cells at the soma and proximal dendrites. These data suggest that each interneuron population has a specific role in hippocampal function, and that mGluR activation will affect the local circuit differently for each interneuron type. Metabotropic GluR activation also markedly enhanced the amplitudes of the evoked and spontaneous EPSCs received by all interneurons in the region, independent of changes in the postsynaptic holding current and with no change in the kinetics of the EPSC. In contrast to the enhancement of evoked and spontaneous EPSCs, miniature EPSCs recorded in the presence of tetrodotoxin were not increased. These data suggest that ACPD acts at a presynaptic site to potentiate the EPSC. Taken together, these results highlight an important modulatory role for metabotropic receptors located at sites both pre- and postsynaptic to CA1 st. oriens interneurons.
Requirement of polysialic acid for the migration of the O-2A glial progenitor cell from neurohypophyseal explants
Authors: Wang C , Rougon G , Kiss JZ
Published: April 2018

While the capacity of O-2A oligodendrocyte progenitors to migrate in cell culture and during in vivo myelin formation is well documented, little is known about factors that regulate the motility of these cells. Here, we report on an in vitro model that allowed us to evaluate the contribution of alpha 2–8 linked polysialic acid (PSA) to O-2A cell motility. Using explant cultures of newborn rat neurohypophysis, we observed that individual glial fibrillary acidic protein (GFAP)- positive cells rapidly disperse from the explants, and that cells of the O-2A lineage predominate in the migratory cell pool. Presumed O-2A progenitor cells had a round or bipolar morphology and presented both A2B5 and GFAP immunoreactivity. When cultured in medium containing 10% fetal calf serum, these cells differentiated into stellate-shaped, A2B5/GFAP-positive type 2 astrocytes. In serum-free medium most of them developed into O4/galactocerebroside-positive oligodendrocytes. O-2A lineage cells were found only in a specific developmental period extending from embryonic day 21 to postnatal day 3. A monoclonal antibody, which recognizes the alpha 2–8 linked PSA, characteristic of the embryonic form of NCAM, revealed immunoreactivity on the surface of O-2A progenitor cells, whereas mature oligodendrocytes, type 2, type 1 astrocytes as well as flat GFAP-negative cells were negative. Treatment of the explants with endoneuraminidase purified from phage K1, which specifically removes PSA from the surface of the cell, resulted in a complete blockade of the dispersion of O-2A lineage population from the explant. The effects of the enzymatic treatment were both selective and reversible: migration of GFAP-negative fibroblast-like cells that are normally PSA negative was not influenced, and upon removal of the enzyme, cells of the O-2A lineage were readily detectable in the migrating population. These results provide direct evidence that alpha 2–8 linked PSA contribute to the motility of O-2A, glial progenitor cells.
Differential effects on spatial navigation of immunotoxin-induced cholinergic lesions of the medial septal area and nucleus basalis magnocellularis
Authors: Berger-Sweeney J , Heckers S , Mesulam MM , Wiley RG , Lappi DA , Sharma M
Published: April 2018

The effects on anatomy and behavior of a ribosomal inactivating protein (saporin) coupled to a monoclonal antibody against the low-affinity NGF receptor (NGFr) were examined. In adult rats, NGFr is expressed predominantly in cholinergic neurons of the medial septal area (MSA), diagonal band nuclei, and nucleus basalis magnocellularis (nBM), but also in noncholinergic cerebellar Purkinje cells. Rats with immunotoxin injections to the MSA, nBM, and lateral ventricle were compared to controls on a spatial and cued reference memory task in the Morris maze. Toxin injections to the MSA slightly impaired the initial, but not asymptotic, phase of spatial navigation. Injections to the nBM impaired all phases of spatial navigation. Cued navigation, however, was not affected in either the MSA or nBM group. The ventricular injections severely affected spatial and cued navigation. Acetylcholinesterase (AChE) histochemistry and NGFr and choline acetyltransferase immunohistochemistry revealed a loss of (1) almost all NGFr-positive cholinergic neurons in the MSA and AChE fibers in hippocampus (MSA group); (2) almost all NGFr neurons in the nBM, some in the MSA, most AChE fibers in neocortex and some in the hippocampus (nBM group), and (3) almost all NGFr neurons in the MSA and nBM and their corresponding hippocampal and cortical AChE fibers (ventricular group). Cholinergic nBM projections to the amygdala were largely preserved in all groups. The amount of cholinergic fiber loss in the cortex correlated modestly, but significantly, with the severity of impairment of the asymptotic phase of performance of the spatial task. An unambiguous interpretation of the anatomical locus of behavioral deficits was not possible because of damage to cholinergic striatal interneurons (nBM group) and to noncholinergic cerebellar Purkinje cells (ventricular group). These data suggest that the cholinergic cortical system is critical to the performance of this spatial memory task. Cholinergic denervation of the hippocampus alone, however, is not sufficient to impair markedly performance of this task.
Regional differences in glial-derived factors that promote dendritic outgrowth from mouse cortical neurons in vitro
Authors: Le Roux PD , Reh TA
Published: April 2018

To determine whether glia from different CNS regions differ in their ability to support axons or dendrites, embryonic (E18) mouse cortical neurons were cocultured with early postnatal (P4) rat astroglial derived from cortex, retina, olfactory bulb, mesencephalon, striatum, and spinal cord. After 5 d in vitro, axon and dendrite outgrowth from isolated neurons was quantified with double-labeling immunohistochemical techniques. Whereas axonal growth was similar on the various monolayers, total primary dendritic outgrowth was nearly threefold greater on glia derived from the cortex, retina, and olfactory bulb than on glia derived from mesencephalon, striatum, or spinal cord. This effect was principally on the number of primary dendrites rather than the elongation of individual dendrites. Similar morphological differences were observed when cortical neurons were grown on polylysine in a noncontact coculture system with glia continuously conditioning the media. This selective promotion of dendrite growth was independent of neuron survival. These results indicate that there are regional differences in the ability of CNS glia to support dendritic growth and that this effect is due, in part, to release of a diffusable factor.
The developmental expression in rat of proteases furin, PC1, PC2, and carboxypeptidase E: implications for early maturation of proteolytic processing capacity
Authors: Zheng M , Streck RD , Scott RE , Seidah NG , Pintar JE
Published: April 2018

The genes encoding mammalian subtilisin-like endoproteases furin, PC1, and PC2 have been isolated and are implicated in endoproteolytic cleavage of precursor molecules, which is a key step in posttranslational maturation of proproteins and neuropeptide precursors. Following endoproteolytic cleavage, the carboxyl-terminal basic amino acid residues are removed by carboxypeptidase E (CPE). We have examined the expression of these genes during rat development by in situ hybridization and compared their expression patterns to those of potential substrates. In the primitive streak stage of embryogenesis (e7) furin is expressed in both endoderm and mesoderm. This overall expression pattern is maintained until e10, when a distinctly higher level of furin expression is observed in the heart and liver primordia. In mid- and late gestational stages furin is broadly expressed in the peripheral tissues, and, therefore, may contribute to the proteolytic processing of numerous fetal proproteins, such as the precursors for natriuretic factors in heart and IGF-II throughout the embryo. In contrast, the expressions of PC1 and PC2 are initiated much later (e13) and are mainly confined to the developing nervous system, but with distinct spatial distributions. At midgestational ages, PC1 mRNA is mainly expressed in the hypothalamus and peripheral ganglia, while PC2 is expressed not only in these tissues but also in the thalamus, midbrain, pons, medulla oblongata, cortical plate, and spinal cord. Besides neuropeptide precursor processing in the nervous system, PC1 and PC2 may also be involved in the proteolytic processing in additional regions as evidenced by the finding that both PC1 and PC2 mRNAs are expressed in the embryonic pituitary and pancreas. CPE mRNA is expressed in both neural tissues and some non-neural tissues. In the developing nervous system, the expression of CPE encompasses all the regions where PC1 and PC2 are expressed and in fact includes most brain regions as neurogenesis proceeds. CPE mRNA is also expressed in some peripheral tissues, such as the embryonic heart and cartilage primordia, and in some cases its expression overlaps with furin expression. Thus, CPE may functionally collaborate during development with the subtilisin family of endoproteases in the completion of proteolytic processing of neuropeptide precursors in the nervous system and proproteins in the peripheral tissues. In the pituitary, the endoproteolytic processing of polyfunctional precursor proopiomelanocortin (POMC) occurs in a developmentally regulated manner. We have shown that while PC2 mRNA is predominantly expressed in the intermediate lobe in the adult, we observed an increased expression of PC2 mRNA in developing rat anterior lobe, peaking at early postnatal stages.(ABSTRACT TRUNCATED AT 400 WORDS)
Selective coexpression of insulin receptor-related receptor (IRR) and TRK in NGF-sensitive neurons
Authors: Reinhardt RR , Chin E , Zhang B , Roth RA , Bondy CA
Published: April 2018

The insulin receptor-related receptor (IRR) has recently been identified as a member of the insulin receptor tyrosine kinase family; however, its endogenous ligand and biological function are still unknown. In contrast to the very widespread pattern of expression of the homologous insulin and IGF-I receptors, IRR demonstrates a very restricted cellular distribution. Using in situ hybridization and immunohistochemistry, we now show that the expression of this receptor is selectively concentrated in a subset of neurons where its appearance is closely associated with that of the NGF receptor TRK. IRR and TRK demonstrate synchronized patterns of coexpression in neural crest- derived sensory and sympathetic neurons and in non-neural crest basal forebrain and striatal neurons. Both appear early in the embryonic development of dorsal root and trigeminal neurons and somewhat later, near the time of birth, in sympathetic neurons. Expression of both IRR and TRK appears perinatally in basal forebrain neurons, reaching maximal levels about postnatal day 20. This association is highly selective, since TRK mRNA is not detected anywhere in the developing nervous system in the absence of coordinate IRR expression, and the same is true for IRR expression with respect to TRK. In the adult rat, the majority of TRK-positive sensory neurons still express IRR mRNA, and coexpression in sympathetic and forebrain neurons continues without evidence of diminution. These findings are consistent with a functional linkage of the IRR and TRK receptors in NGF-sensitive neurons.
Increased expression of the NG2 chondroitin-sulfate proteoglycan after brain injury
Authors: Levine JM
Published: April 2018

Injury to the adult mammalian CNS results in reactive changes among the glial cells surrounding the site of damage. Recently, an unusual class of glial cells has been identified within the intact adult rat cerebellum on the basis of the expression of the NG2 chondroitin- sulfate proteoglycan (Levine and Card, 1987). To determine whether the cells that express the NG2 proteoglycan show reactive changes after injury, small puncture lesions were made into the cerebelli of adult rats, and changes among astrocytes, microglia and NG2-positive cells were examined using immunohistochemical staining with cell type- specific marker antibodies. Beginning at 24 hr after lesion, NG2- positive cells immediately adjacent to the lesion site bound the anti- NG2 antibodies more heavily than cells within the undamaged areas of the cerebellum. This increase in anti-NG2 immunoreactivity was transient, reaching a maximum at 7 d postlesion and declining slowly thereafter. The increase in anti-NG2 immunoreactivity was accompanied by an increase in the levels of mRNA encoding the NG2 core protein as demonstrated by in situ hybridization. NG2-positive cells adjacent to the lesion site incorporated 3H-thymidine into their nuclei beginning at 24 hr postlesion and increased in number. Concurrent with these changes, microglia became activated and increased in number, monocytes invaded the damaged tissue, and an astrocytic scar formed. These observations demonstrate that the cells that express the NG2 proteoglycan are a reactive cell type that responds to brain injury. The increased expression of the NG2 chondroitin-sulfate proteoglycan may contribute to the failure of damaged CNS axons to regenerate successfully.
Mesencephalic type 1 astrocytes rescue dopaminergic neurons from death induced by serum deprivation
Authors: Takeshima T , Johnston JM , Commissiong JW
Published: April 2018

We have established a primary neuronal culture of the embryonic day 14 rat, ventral mesencephalic region, centered on the A8, A9, and A10 dopaminergic nuclei (approximately 1.0 mm3 of tissue). At 16 hr after plating on a substrate of poly-D-lysine, in a serum-free or serum- supplemented growth medium, using a microisland culturing method, 95% of the cells stained positive for neuron-specific enolase, 20% for tyrosine hydroxylase, and < 5% for vimentin. When the growth medium was supplemented with 10% fetal calf serum, the percentage of tyrosine hydroxylase-positive neurons increased significantly (p < 0.05) at the 7th and 10th days in culture, compared with the percentage present at 16 hr after plating. When cultured in a serum-free growth medium, the percentage of tyrosine hydroxylase-positive neurons decreased to < 5% and to 0% by the 5th and 7th days, respectively, while the percentage of GABA-IR neurons increased. The addition of serum to the serum-free culture rescued dopaminergic neurons from death induced by serum deprivation. The effect of serum was dependent both on the time of addition after plating, and on the percentage added. When the cells were plated in a serum-free medium, on a confluent, type 1 astrocyte monolayer, prepared from the ventral mesencephalon of the embryonic day 16 rat, the survival of dopaminergic neurons increased significantly (p < 0.01) at DIV5, versus survival after plating on poly-D-lysine. Conditioned medium prepared from the same mesencephalic type 1 astrocyte monolayer also rescued dopaminergic neurons from death. The rescue mediated by the astrocyte monolayer or the conditioned medium was not inhibited by the mitotic inhibitor cytosine arabino furanoside (1.0 microM). Type 1 astrocyte monolayers and conditioned media prepared from the striatum and cerebral cortex of the embryonic day 16 rat had weaker trophic effects than those mediated by mesencephalic glia. We conclude that serum deprivation causes the selective death of dopaminergic neurons in a primary culture of the rat E14 ventral mesencephalon. Type 1 astrocytes or the conditioned medium from type 1 astrocytes can rescue dopaminergic neurons from death induced by serum deprivation.(ABSTRACT TRUNCATED AT 400 WORDS)
Induction of c-fos expression in hypothalamic magnocellular neurons requires synaptic activation and not simply increased spike activity
Authors: Luckman SM , Dyball RE , Leng G
Published: April 2018

Magnocellular neurons of the hypothalamic supraoptic nucleus have been shown to express the immediate-early gene c-fos in a number of experimental and physiological circumstances. In each case the induction of the immediate-early gene followed the increase in the spike activity of the cells. Since an increase in the intracellular concentration of calcium following influx through voltage-sensitive calcium channels is a known stimulus for c-fos expression and since the action potentials of these neurons have a large calcium component, we hypothesized that c-fos induction in these neurons could be attributed to calcium influx during spike activity. In the present experiments we use extracellular recording and immunocytochemistry for Fos, the protein product of c-fos, to demonstrate the activation of the cells following intracerebroventricular administration of the muscarinic agonist, carbachol. Fos expression following carbachol injection was then compared with that induced by a similar number of antidromically evoked action potentials. Antidromic activation, unlike the activation induced by carbachol, did not lead to the induction of Fos. We conclude that Fos induction in these neurons requires receptor activation rather than spike activity.
Dopaminergic regulation of the serotonergic raphe-striatal pathway: microdialysis studies in freely moving rats
Authors: Ferre S , Cortes R , Artigas F
Published: April 2018

Morphological evidence demonstrates the existence of dopaminergic afferent pathways and dopamine (DA)-containing neurons in the dorsal raphe nucleus (DRN). In a recent report, a DA D2-like receptor-mediated regulation of serotonin (5-HT) extracellular concentration in DRN has been found. Given the existence of somatodendritic 5-HT1A autoreceptors in the DRN, changes of the extracellular concentration of 5-HT in the vicinity of cell bodies and dendrites may be relevant for the control of the activity of ascending serotonergic pathways. In the present brain microdialysis study we have used a chromatographic method (HPLC) enabling the simultaneous measurement of DA, 5-HT, and their main metabolites dihydroxyphenylacetic acid (DOPAC) and 5- hydroxyindoleacetic acid (5-HIAA). The presence of a neuronal pool of DA within the DRN was revealed by the local infusion of amphetamine (10 microM), which significantly increased the extracellular concentration of both amines. The local striatal infusion (10 microM) of the selective DA D1-like agonist SKF-38393, the selective DA D2-like agonist quinpirole (LY 171,555), or the nonselective DA agonist apomorphine markedly decreased DA and DOPAC extracellular concentrations and failed to modify 5-HT or 5-HIAA in the striatum, indicating the lack of terminal (striatal) control of 5-HT release by dopaminergic transmission. In contrast, the systemic administration of apomorphine (2.8 mumol/kg, s.c.) significantly increased the extracellular concentration of 5-HT in the DRN and decreased it in the striatum. The reduction of striatal 5-HT extracellular concentration was prevented by the previous administration of the selective 5-HT1A receptor antagonist WAY 100135 (17.6 mumol/kg, s.c.), which by itself did not change extracellular 5-HT in striatum.(ABSTRACT TRUNCATED AT 250 WORDS)
What happens if it changes color when it moves?: the nature of chromatic input to macaque visual area MT
Authors: Dobkins KR , Albright TD
Published: April 2018

Neurons in the middle temporal visual area (MT) of macaque cerebral cortex are highly selective for the direction of motion but not the color of a moving stimulus. Recent experiments have shown, however, that the directional selectivity of many MT neurons persists even when a moving stimulus is defined solely by chromatic variation (Charles and Logothetis, 1989; Saito et al., 1989; Dobkins and Albright, 1991 a, b; Movshon et al., 1991; Gegenfurtner et al., 1994). To illuminate the mechanisms by which area MT uses color as a cue for motion correspondence, we recorded from MT neurons while rhesus monkeys viewed an “apparent motion” stimulus in which red/green sine wave gratings underwent contrast reversal each time they were displaced in a particular direction. Under such conditions, correspondence based upon chromatically defined borders conflicts with correspondence based upon conservation of chromatic sign. When our heterochromatic stimuli possessed sufficient luminance modulation, MT neurons responded best to motion in the direction for which the sign of luminance (and chromatic) contrast was preserved. At isoluminance, however, two different chromatic influences were revealed. First, when stimuli underwent small spatial displacements, directional selectivity was elicited by movement of the stimulus in the direction of the nearest chromatically defined border, even though the sign of chromatic contrast at that border alternated over time. Under these conditions, MT neurons apparently exploited information about image borders defined by chromatic contrast while sacrificing information about the colors that make up those borders. By contrast, when chromatically defined borders provided only ambiguous information about direction of motion, MT neurons were capable of using information about the sign of chromatic contrast to detect direction of motion. The results from these experiments suggest the existence of a hybrid mechanism, one in which both signed and unsigned chromatic signals contribute to motion processing in visual area MT.
Cell-type-specific expression of catecholamine transporters in the rat brain
Authors: Lorang D , Amara SG , Simerly RB
Published: April 2018

The dopamine transporter (DAT) and norepinephrine transporter (NET) terminate catecholaminergic neurotransmission at synapses by high- affinity sodium-dependent reuptake into presynaptic terminals, and are the initial sites of action for drugs of abuse and antidepressants. In the present study, we used in situ hybridization combined with immunohistochemistry to study the distribution of DAT and NET mRNA in the adult rat brain. Cells were first immunolabeled with antisera directed against one of the catecholamine-synthetic enzymes, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), or phenylethanolamine-N-methyltransferase (PNMT), in order to identify dopaminergic, noradrenergic, or epinephrine-containing cells. The immunolabeled cells were subsequently assayed for their ability to express catecholamine transporter mRNAs by in situ hybridization using either a rat DAT or NET cRNA probe. All dopaminergic cell groups of the mesencephalon contained high levels of DAT mRNA but only the A12 and A13 dopaminergic cell groups of the diencephalon appear to express detectable levels of DAT. All norepinephrine-containing cell bodies in the brainstem (locus coeruleus and lateral tegmentum) appear to express NET mRNA. In contrast, epinephrine-containing cell bodies of the brainstem do not appear to express NET mRNA, which raises the possibility that epinephrine may utilize a transporter that is distinct from the other bioactive amines, or may act as an endocrine regulator that does not require rapid reuptake mechanisms. Moreover, the cell- type-specific expression of catecholamine transporters suggests that DAT and NET gene expression may be closely linked to cellular mechanisms that specify transmitter phenotype. The termination of neurotransmission is a critical component of neural signaling and depends on the rapid removal of neurotransmitters from the synaptic cleft. Pharmacological evidence indicates that the action of monoamines at the synapse is terminated predominantly by rapid reuptake into presynaptic nerve endings via neurotransmitter-specific, high-affinity, Na(+)-dependent membrane transporter proteins. The cDNAs encoding distinct transporter proteins for the monoamines dopamine, norepinephrine, and serotonin have been cloned, expressed, and characterized in a variety of heterologous systems (Blakely et al., 1991; Giros et al., 1991; Hoffman et al., 1991; Kilty et al., 1991; Pacholczyk et al., 1991; Shimada et al., 1991; Usdin et al., 1991). Although the monoamine transporters share a high degree of sequence homology, they are distinguished by their monoamine substrate specificities and by their differential sensitivities to a wide spectrum of transport antagonists. For example, pharmacological agents that potently inhibit norepinephrine and serotonin transport, such as desmethylimipramine and citalopram, have little effect on the activity of the dopamine transporter (Javitch et al., 1983).(ABSTRACT TRUNCATED AT 400 WORDS)
The NMDA glycine site antagonist (+)-HA-966 selectively regulates conditioned stress-induced metabolic activation of the mesoprefrontal cortical dopamine but not serotonin systems: a behavioral, neuroendocrine, and neurochemical study in the rat
Authors: Goldstein LE , Rasmusson AM , Bunney BS , Roth RH
Published: April 2018

Animals confronting threatening stimuli respond with a coordinated set of autonomic, neuroendocrine, neurochemical, and behavioral responses that constitute the stress response. The role of the NMDA receptor and its glycine modulatory site was investigated in a rat conditioned stress model. Behavioral, neuroendocrine, and neurochemical analyses were conducted. Regional dopamine (DA) and serotonin (5-HT) utilization was assessed by postmortem tissue measurements of metabolite-to-parent neurotransmitter ratios. Rats were conditioned to fear a tone previously paired with footshock. The following day, rats were systemically administered saline or the NMDA glycine site antagonist (+)-HA-966 before exposure to thirty minutes of conditioned stress. Conditioned stress resulted in a selective increase in medial prefrontal cortical DA and 5-HT utilization, elevation in serum corticosterone, and freezing behavior in control animals. The conditioned stress-induced increase in DA utilization in control animals was also detected in the lateral prefrontal cortex and nucleus accumbens, whereas DA utilization was not affected in the perirhinal or cingulate cortices, lateral-basolateral amygdaloid complex, anterior ventromedial caudatoputamen, or posterior dorsolateral caudatoputamen. Pretreatment with (+)-HA-966 at 15 mg/kg completely abolished the conditioned stress-induced increase in DA utilization in the medial and lateral prefrontal cortices. This effect was regionally specific since (+)-HA-966 pretreatment did not block increased DA utilization in the nucleus accumbens. This effect was also neurochemically specific since the stress-induced increase in 5-HT utilization in the medial prefrontal cortex was not affected by (+)-HA-966 pretreatment. Pretreatment with (+)-HA-966 did not affect stress-induced serum corticosterone elevation but did attenuate the freezing response. Control experiments demonstrated that (+)-HA-966 pretreatment did not (1) induce sedation, (2) interfere with habituation to a novel environment, (3) alter basal DA, 5-HT, or serum corticosterone levels, or (4) block acquisition of aversive memories. These data suggest that the NMDA receptor complex and associated glycine modulatory site may play an important role in the afferent control of the mesoprefrontal cortical DA system during conditioned stress. The relevance of these findings to schizophrenia and human anxiety disorders such as post- traumatic stress disorder are discussed.
Systemic interleukin-1 induces early and late patterns of c-fos mRNA expression in brain
Authors: Brady LS , Lynn AB , Herkenham M , Gottesfeld Z
Published: April 2018

This study was designed to examine the mechanisms by which systemic interleukin-1 affects neuroendocrine systems in the brain. Intraperitoneal injections of interleukin-1 beta (1.25 micrograms/rat) were administered to rats. One or three hours after injection, the expression levels of the immediate-early gene c-fos and of genes for several neuropeptides, receptors, and enzymes were examined by in situ hybridization histochemistry. In the brainstem at 1 hr, c-fos mRNA was elevated in the area postrema and nucleus of the solitary tract, but not in the locus coeruleus. At 3 hr, the c-fos mRNA levels had increased further in the nucleus of the solitary tract. Rostrally, elevations in c-fos mRNA levels were found in the hypothalamic and thalamic paraventricular nuclei, central nucleus of amygdala, bed nucleus of the stria terminalis, and medial preoptic area, peaking at 1 hr and diminishing at 3 hr. In addition, at 3 hr a new pattern of c-fos activity emerged--the arcuate nucleus and cells at the external margins throughout the brain now expressed c-fos mRNA. Corticotropin-releasing hormone mRNA levels were doubled in the paraventricular nucleus at 1 and 3 hr, concomitant with elevations in plasma adrenocorticotrophic hormone (ACTH) and corticosterone. Tyrosine hydroxylase mRNA levels in the brainstem did not change. The c-fos mRNA induction patterns reveal a temporally dynamic response to interleukin-1 administration. We propose that the early set of structures responding to interleukin-1 initiates the neuroendocrine response to cytokines. Coactivation of the area postrema and nucleus of the solitary tract may reflect entry into the brain and neural transduction of the peripheral signal. The late set--including the nucleus of the solitary tract, arcuate nucleus, and the brain's edge--may reflect cellular activation along the diffusion routes traveled by interleukin-1 or a bioactive transduction product, because the pattern of edge labeling is similar to the autoradiographic pattern of flow lf radiolabeled tracer substances in the cerebrospinal fluid. The late c-fos mRNA response to interleukin-1, therefore, may represent a demonstration of information transfer in the parasynaptic mode, also known as volume transmission.
omega-Conotoxin block of N-type calcium channels in frog and rat sympathetic neurons
Authors: Boland LM , Morrill JA , Bean BP
Published: April 2018

Block of N-type Ca channels by omega-conotoxin GVIA (CgTx) was studied in freshly dissociated bullfrog and rat sympathetic neurons. With 2–5 mM Ba as charge carrier, CgTx blocked almost all of the high-threshold Ca channel current recorded in the presence of nimodipine (3 microM) to block L-type Ca channels. Toxin block reversed slowly (time constant approximately 1 hr) in frog cells and even more slowly in rat cells. CgTx block was faster and more potent in rat cells than frog cells. The rate of block was proportional to CgTx concentration, consistent with 1:1 binding of CgTx to channels. When the external Ba concentration was increased, the development of block was slower, consistent with competition between CgTx and Ba for a binding site. The recovery from block was somewhat faster in higher external Ba. Some cells had significant current remaining in saturating concentrations of nimodipine and CgTx, especially with high Ba concentrations in the external solution. The current resistant to nimodipine and CgTx was activated at lower depolarizations than the CgTx-sensitive current and had faster activation and inactivation kinetics, but unlike low- threshold T-type current, the resistant current had rapidly decaying tail currents.
Gases as biological messengers: nitric oxide and carbon monoxide in the brain
Authors: Dawson TM , Snyder SH
Published: April 2018

In a remarkably brief period of time, NO and CO have been recognized as putative neurotransmitters. These two novel messenger molecules have greatly expanded the criteria for candidacy of a chemical for the status of neurotransmitter and our notions about how synaptic transmission takes place. The involvement of NO and CO in several important aspects of neuronal function suggests that agents affecting the synthesis, transactions, and disposition of these gases are bound to have clinical relevance.
Three novel types of voltage-dependent calcium channels in rat cerebellar neurons
Authors: Forti L , Tottene A , Moretti A , Pietrobon D
Published: April 2018

With the aim of characterizing the functional and pharmacological properties of the different voltage-dependent Ca2+ channels expressed in a given type of CNS neuron, we obtained single Ca2+ channel recordings from rat cerebellar granule cells in primary culture. Our data show that three novel classes of voltage-dependent Ca2+ channels are coexpressed in cerebellar granule cells. They are pharmacologically distinct from dihydropyridine-sensitive L-type and omega-conotoxin- sensitive N-type channels, and their functional properties are different from those of P- and T-type channels. The three novel 21 pS G1-, 15 pS G2-, and 20 pS G3-type Ca2+ channels have similar inactivation properties. They show complete steady-state inactivation at -40 mV and their single-channel average currents have both sustained and decaying components. They differ in activation threshold (-40 mV for G2, -30 mV for G3, and -10 mV for G1, with 90 mM Ba2+ as charge carrier), mean open time (1.2 msec for G2, 1 msec for G3, 0.8 msec for G1), and single-channel currents (at 0 mV: 0.5 pA for G2, 0.8 pA for G3, and 1.4 pA for G1). Together with the previously characterized multiple L-type Ca2+ channels (Forti and Pietrobon, 1993), G1-, G2-, and G3-type channels constitute the large majority of Ca2+ channels of cerebellar granule cells in culture. The low activation threshold of G2- type channels and their inactivation properties suggest that they might be native counterparts of the recently expressed rat brain clone rbE-II (Soong et al., 1993).
Receptive fields and dendritic structure of directionally selective retinal ganglion cells
Authors: Yang G , Masland RH
Published: April 2018

We studied the relationship between the receptive fields of directionally selective retinal ganglion cells and the dendritic arbors of the same cells. The cells were recorded from extracellularly under visual control and then injected with Lucifer yellow. The arbor of Lucifer-filled dendrites could then be directly compared with the properties of the receptive field. A large population of on-off directionally selective cells was injected and drawn. The directionally selective ganglion cells had bistratified receptive fields similar to those previously described by others in the central retina. In the periphery, the dendritic fields became larger, rounder, and sparser than centrally. The diameters of the dendrites were measured in living or lightly fixed retinas; they were found to be somewhat larger than previously estimated by electron microscopy. The local structure of the dendritic arbor bore no obvious relation to the directional properties of the cell. The receptive fields of most cells were centered symmetrically around their dendritic fields. For about 10% of the cells, however, the receptive field was displaced. The displacement was always toward the preferred direction, relative to the dendritic field. The meaning of these shifts is not clear. In both cases, the diameter of the receptive field exceeded the diameter of the dendritic field only slightly; in our sample, the diameters of the receptive fields averaged 6% larger than the dendritic fields. This means that the neurons afferent to the directionally selective ganglion cells must either have narrow dendritic fields or, if they are wide spreading, have dendrites that do not conduct effectively along their length. It also means that the observed spread of neurobiotin between DS ganglion cells (Vaney, 1991) must be due to a very few gap junctions, or to some mechanism other than a gap junction.
Apoptotic cell death induced by optic nerve lesion in the neonatal rat
Authors: Rabacchi SA , Bonfanti L , Liu XH , Maffei L
Published: April 2018

Cell death can be ascribed to one of two distinct modes of degeneration: apoptosis (programmed or active cell death) or necrosis (passive degeneration). While apoptosis is generally assumed to occur in physiological conditions such as normal development or tissue turnover, necrotic cell degeneration is induced in pathological situations. Here we report that also in a pathological situation, such as after axotomy in the CNS, apoptotic type of cell death comes into play: following intracranial transection of the optic nerve in the neonatal rat in vivo, retinal ganglion cells undergo an active, apoptotic cell death. In fact, the administration of protein synthesis inhibitors (actinomycin D and cycloheximide) prevents the appearance of pyknotic nuclei as well as of fragmented DNA of ganglion cells at 24 hr postlesion. Correspondingly, the number of surviving cells after actinomycin D and cycloheximide treatment is comparable to normal, unlesioned retinas. In addition, cycloheximide decreases the number of pyknotic ganglion cells during spontaneous cell death.
Switch in the expression of rat GABAA-receptor subtypes during postnatal development: an immunohistochemical study
Authors: Fritschy JM , Paysan J , Enna A , Mohler H
Published: April 2018

The involvement of GABA in neuronal differentiation and maturation precedes its role as inhibitory neurotransmitter in the brain. It was therefore investigated whether GABAA receptors mediating the actions of GABA in neonatal and adult brain can be distinguished by their molecular structure and cellular location. Immunohistochemistry with subunit-specific antibodies was employed to analyze changes in the distribution of GABAA-receptor subunits during postnatal development. In particular, subunit association patterns, as evidenced by colocalization of subunits within individual neurons, were analyzed by confocal laser microscopy. The subunits analyzed include the alpha 1- and alpha 2-subunits, which are associated with pharmacologically distinct GABAA-receptor subtypes, and the beta 2,3-subunits, which are a major constituent of GABAA receptors in both immature and adult rat brain. Each of these subunits exhibited age-dependent changes in their distribution, indicative of a differential maturation process. The alpha1-subunit immunoreactivity (-IR) was low at birth, restricted to a few areas, and increased dramatically during the first postnatal weeks. By contrast, the alpha 2-subunit-IR displayed a widespread distribution throughout the brain at birth, and disappeared from numerous areas soon after the appearance of the alpha 1-subunit. Double-immunofluorescence staining demonstrated the coexistence of both subunits in many individual neurons during a short time window, indicating that receptors containing the alpha 1-subunit gradually replace receptors containing the alpha 2-subunit in these cells. Staining for the beta 2,3-subunits was prominent and ubiquitous at every developmental age, indicating that these subunits are present in both neonatal and adult GABAA receptors. Indeed, double-immunofluorescence staining revealed an extensive colocalization of the alpha 2- and beta 2,3-subunits in neurons from neonatal rats, whereas the beta 2,3-subunits were associated with the alpha 1-subunit at later stages. Thus, the onset of alpha 1-subunit staining in maturing brain is indicative for the expression of a new, prevalent receptor subtype, presumably involved in synaptic inhibition. These findings demonstrate a switch in the subunit composition of GABAA receptors during postnatal development, suggesting the existence of molecularly distinct immature and adult forms of GABAA receptors in rat CNS.
Nuclear-encoded mitochondrial precursor protein: intramitochondrial delivery to dendrites and axon terminals of neurons and regulation by neuronal activity
Authors: Liu S , Wong-Riley M
Published: April 2018

Mitochondria contain hundreds of proteins, most of which are encoded by the nucleus. In neurons, distal dendrites and axon terminals can be separated from the nucleus by a great distance, and the mechanism by which precursor proteins reach distal neuronal processes is not well understood. While our previous study on cytochrome oxidase suggests a post-translational mechanism of delivery, it is not known whether precursor proteins reach their target processes before or after incorporation into mitochondria. In order to localize only precursor proteins and not the mature form of the subunit in neurons, we generated polyclonal antibodies against synthetic presequence polypeptides specific to nuclear-encoded subunit IV precursor protein of rat brain cytochrome oxidase. We found that the precursors were located not only in neuronal cell bodies, but also in dendrites and axon terminals. This indicates that the conversion of these precursors to their mature form is not confined to the cell body but occurs in dendrites and axons as well. At the electron microscopic level, an overwhelming majority of immunoreaction product was found within mitochondria, suggesting that precursor proteins are transported to neuronal processes mainly within mitochondria, and that their half- lives are much longer in neurons than in yeast and rat hepatocytes. The precursor pool was downregulated in the rat superior colliculus after monocular enucleation, indicating that precursor synthesis and/or degradation is regulated by neuronal functional activity. These results also suggest that local functional demands may play an important role in controlling the processing of precursors and the assembly of holoenzymes in dendrites and axon terminals. This allows neurons to regulate enzyme levels locally, precisely, and rapidly.
Expression of neuron-specific tubulin defines a novel population in the proliferative layers of the developing telencephalon
Authors: Menezes JR , Luskin MB
Published: April 2018

We have used a monoclonal antibody against the neuron-specific class III beta-tubulin (TuJ1; Lee et al., 1990b) to study the distribution and morphology of immature neurons in the proliferative ventricular and subventricular zones of the developing telencephalon. Mouse brains from embryonic day 12 (E12) to postnatal day 5 (P5) were fixed either with a non-cross-linking agent, HistoChoice, or with 4% paraformaldehyde, and processed for TuJ1 immunohistochemistry. TuJ1 immunoreactivity first appeared in the proliferative zones of the developing cerebral cortex at E13-E14 as the cortical plate was emerging. After E14, tangentially oriented TuJ1-positive cells were abundant at the interface between the ventricular and subventricular zones. This tangential pattern was less conspicuous in the developing striatum. Within the cortical and striatal ventricular zone TuJ1-positive cells were less numerous and displayed a variety of orientations and morphologies. Postnatally, after the period of neurogenesis has ended, TuJ1 immunoreactivity continued to increase in the subventricular zone and remained high until the last developmental stage examined (P5). Anti-MAP2, another neuron-specific marker, never labeled the cells of the ventricular and subventricular zones, pre- or postnatally. To determine the birthdates of TuJ1-positive cells in the cortical-ventricular and subventricular zones, brains were double labeled with TuJ1 and bromodeoxyuridine according to different pulse-chase schedules. TuJ1-positive cells were postmitotic and generated throughout the period of cortical neurogenesis. Collectively, the results suggest that TuJ1 immunoreactivity distinguishes two neuronal populations: those that remain for an indefinite period of time in the proliferative zones, and those that leave the proliferative zones soon after being generated. Although the fate of the TuJ1-positive cells that reside in the proliferative zones remains unclear, their tangentially aligned orientation and their distribution suggest that they migrate independent of radial glial fibers.
Ethanol directly modulates gating of a dihydropyridine-sensitive Ca2+ channel in neurohypophysial terminals
Authors: Wang X , Wang G , Lemos JR , Treistman SN
Published: April 2018

Ingestion of ethanol results in a decreased level of plasma vasopressin, which appears to be caused by inhibition of arginine vasopressin (AVP) release from the neurohypophysis. Activation of membrane voltage-gated Ca2+ channels plays an important role in triggering this neurohormone release. In this article, single-channel recordings are used to demonstrate that ethanol, at concentrations constituting legal intoxication, inhibits dihydropyridine-sensitive “L- type” Ca2+ channels in isolated nerve terminals of the rat neurohypophysis. Ethanol reduced the channel open probability in a concentration-dependent manner. To allow finer resolution of channel openings and to better characterize the mechanisms of ethanol action, Bay K 8644 was used to prolong the openings of L-type Ca2+ channels. In the presence of this dihydropyridine (DHP), the reduction of the channel open probability by concentrations of ethanol of 25 mM or higher could be determined to be due primarily, although not completely, to a shortening of the open duration of this L-channel. Channel conductance was unaffected by ethanol, even at high concentrations. These results are consistent with previous macroscopic data indicating that calcium channels in these peptidergic terminals are targets for ethanol action, and indicate that ethanol acts directly on the gating characteristics of the L-type channel. Furthermore, examination of open and closed state transitions, as well as Hill plot analysis, suggests that ethanol's effects on gating are consistent with the interaction of a single drug molecule with a single target site, possibly the L-channel itself.