Discrete Neuronal Populations Research Articles

Intrinsic neurons in the human ovary.

Mammalian ovarian function is regulated by both hormonal inputs and direct neural influences. Recent studies have shown that, in addition to the extrinsic innervation, the ovaries of nonhuman primates and a strain of rats contain a discrete population of intrinsic neurons. In the present study, we used histological and immunohistochemical approaches to identify the presence of neuronal cell bodies in the fetal and neonatal human ovary. Neurons containing neurofilament immunoreactivity were detected in the hilum and medulla of the ovary at all ages studied, ranging from 24 weeks of gestation to 10 months of postnatal age. Most of them coexpressed the low affinity neurotrophin receptor (p75NTR), and some were catecholaminergic, as determined by their content of immunoreactive tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. The presence of intrinsic neurons in the human ovary, similar to those previously found in other species, indicates that they may be engaged in regulating common, phylogenetically conserved, ovarian functions. It also raises the possibility that their dysfunction may contribute to the manifestation of particular ovarian pathologies.

Contrasting Localizations of MALS/LIN-7 PDZ Proteins in Brain and Molecular Compensation in Knockout Mice

Proteins containing PDZ (postsynaptic density-95, discs large, zonula occludens) domains play a general role in recruiting receptors and enzymes to specific synaptic sites. In Caenorhabditis elegans, a complex of three PDZ proteins, LIN-2/7/10, mediates basolateral targeting of a receptor tyrosine kinase. Homologs of these LIN proteins have also been identified in higher organisms, and here we analyze the MALS/Veli (mammalian LIN-7/vertebrate homolog of LIN-7) proteins in brain. Immunohistochemical staining and in situ hybridization show that MALS occur differentially in discrete populations of neurons throughout the brain. Most neurons express only one MALS protein, although some cells contain two or even all three MALS isoforms. At the subcellular level, MALS proteins are found in both dendritic and axonal locations, suggesting that they may regulate processes at both pre- and postsynaptic sites. Targeted disruption of MALS-1 and MALS-2 does not yield a detectable phenotype, and hippocampal synaptic function and plasticity are intact in the MALS-1/2 double knockouts. Interestingly, MALS-3 protein is dramatically induced in the MALS-1/2 double knockouts, implying that dynamic changes in protein expression may play an important regulatory role for this family of synaptic PDZ proteins.

Hippocampal dependent learning ability correlates with N-methyl-D-aspartate (NMDA) receptor levels in CA3 neurons of young and aged rats.

Hippocampal N-methyl-D-Aspartate (NMDA) receptors mediate mechanisms of cellular plasticity critical for spatial learning in rats. The present study examined the relationship between spatial learning and NMDA receptor expression in discrete neuronal populations, as well as the degree to which putative age-related changes in NMDA receptors are coupled to the effects of normal aging on spatial learning. Young and aged Long-Evans rats were tested in a Morris water maze task that depends on the integrity of the hippocampus. Levels of NR1, the obligatory subunit for a functional NMDA receptor, were subsequently quantified both biochemically by Western blot in whole homogenized hippocampus, and immunocytochemically by using a high-resolution confocal laser scanning microscopy method. The latter approach allowed comprehensive, regional analysis of discrete elements of excitatory hippocampal circuitry. Neither method revealed global changes, nor were there region-specific differences in hippocampal NR1 levels between young and aged animals. However, across all subjects, individual differences in spatial learning ability correlated with NR1 immunofluorescence levels selectively in CA3 neurons of the hippocampus. Parallel confocal microscopic analysis of the GluR2 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptor failed to reveal reliable differences as a function of age or spatial learning ability. This analysis linking age, performance, and NR1 levels demonstrates that although dendritic NR1 is generally preserved in the aged rat hippocampus, levels of this receptor subunit in selective elements of hippocampal circuitry are linked to spatial learning. These findings suggest that NMDA receptor abundance in CA3 bears a critical relationship to learning mediated by the hippocampus throughout the life span.

Induction of ependymal, glial, and neuronal transactivation by intraventricular administration of the SGLT1 Na+-D-glucose cotransporter inhibitor phlorizin.

Reports that food intake is stimulated by intracerebroventricular (i.c.v.) administration of the SGLT1 Na+-D-glucose cotransport inhibitor, phlorizin, suggest that decreased central glucose uptake is a stimulus for compensatory motor activity underlying restoration of energy imbalance. In order to identify central cell populations that are functionally responsive to decreased SGLT1 function in the brain, the present study utilized immunocytochemical techniques to demonstrate cellular expression of the inducible activator protein-1 transcription factor, Fos, following i.c.v. delivery of phlorizin. Groups of adult male rats were treated with phlorizin at a dose of 10, 50, or 250 microg/animal, then sacrificed 2 hr later by transcardial perfusion. Ependymal expression of Fos-immunoreactivity (-ir) was observed throughout most of the cerebroventricular system, except the medullary fourth ventricle, at each dose examined. Higher doses of the transport inhibitor elicited immunostaining of periventricular glia, characterized by cytoplasmic glial fibrillary acidic protein-ir, underlying the lateral, third, and rostral fourth ventricles and cerebral aqueduct. These doses also resulted in the transcriptional activation of neurons in discrete brain sites, including the rostral medial preoptic area, median preoptic n., preoptic and hypothalamic periventricular n., subfornical organ, thalamic medial habenular and paraventricular n., hypothalamic paraventricular, ventromedial, and arcuate n., and n. of the solitary tract. These results show that nonexcitable cells located throughout much of the central neuroaxis and discrete populations of neurons in the brain are genomically responsive to pharmacological inhibition of central SGLT1 function. Evidence for the functional responsiveness of these cell types to manipulation of energy-dependent glucose transport suggests that cellular uptake of this metabolic fuel may serve as an indicator of central energy substrate availability, and that alterations in glucose uptake via this specific mechanism may be the source of regulatory signals involved in the maintenance of energy homeostasis.

Synergistic transcriptional activation by Sox10 and Sp1 family members

Neuronal nicotinic acetylcholine receptors (nAChR) are expressed at specific times during development and in discrete neuronal populations. Transcriptional regulation of the receptor genes clearly plays a key role in the molecular pathway underlying the expression of these critical synaptic components. In an effort to understand this regulation, we focus upon the genes encoding three receptor subunits: α3, α5 and β4. These subunits are genomically clustered and constitute the predominant nAChR subtype expressed in the peripheral nervous system. We and others demonstrated that the general transcription factors, Sp1 and Sp3, can transactivate the promoter of each subunit gene. Further, we showed that the regulatory factor Sox10 transactivates the α3 and β4 promoters and does so in a cell-type-specific manner. Interestingly, the Sp- and Sox10-binding sites on the β4 promoter are located immediately adjacent to each other, raising the possibility that the two sets of factors functionally interact to regulate receptor gene expression. Consistent with this hypothesis, we demonstrated that the proteins can directly interact. Here, we extend these observations and show that Sox10 and the Sp factors functionally interact, leading to synergistic transcriptional activation in a cholinergic cell line. Finally, evidence for the existence of cell-type-specific co-regulators for Sp1 and Sox10 is presented.

Role of nitric oxide in the control of the hypothalamic-pituitary-adrenocortical axis.

The gaseous radical nitric oxide (NO) is catalyzed by conversion of L-arginine to L-citrulline by one cytokine inducible form (iNOS), which becomes active only within hours after the inducing event, and by two constitutively expressed forms, endothelial (eNOS) and neuronal (nNOS), which are regulated by the cytosolic concentration of free Ca2+. Brain nNOS is physiologically present in discrete populations of neurons, which are all excited by glutamate via the ionotropic N-methyl-D-aspartate (NMDA) receptor, which controls a Ca2+ channel. After its diffusion into the extraneuronal space, NO may activate in neurons, which as a rule do not stain for NOS, soluble guanylyl cyclase and formation of cGMP as an intracellular messenger. Beyond that, NO is important as a feedback regulator of glutamatergic excitation. NO as a nitrosylating agent enhances disulfide bonding of vicinal sulfhydryl (thiol) groups of the redox modulatory site of the NMDA receptor complex and thereby down-regulates its Ca2+ channel activity. Histochemical studies have revealed the presence of a large number of NOS containing neurons in the magnocellular and parvocellular subdivisions of hypothalamic nuclei. Numerous studies conform to the view that NO participates in the control of many different neurosecretory processes, especially of the corticotropin-releasing hormone (CRH) neurosecretory system. The redox-modulatory site of the NMDA receptor appears, therefore, as a critical structure in the control of the hypothalamic-pituitary-adrenocortical (HPA) axis. Moreover, glucocorticoids augment neuronal excitotoxicity by increasing the expression of glutamate receptors and inhibition of glutamate reuptake. In attempting to explain the many conflicting results obtained in studies with NO, it may be worthwhile to consider that the actual redox-environment of distinct loci of the brain may determine the final function of NO, acting either as a transmitter or neuromodulator or, in the worst case, causing neurodestruction. It seems likely that any kind of stress by altering the ratio of reduced vs oxidized thiols within the central nervous system influences neuronal excitability, with NO working either as an amplifier or as a feedback regulator of neuronal excitation or inhibition, which may alter acutely or chronically, among others, the homeostasis of a given neurosecretory system.

The X-gal caution in neural transplantation studies.

Cell transplantation into host brain requires a reliable cell marker to trace lineage and location of grafted cells in host tissue. The lacZ gene encodes the bacterial (E. coli) enzyme beta-galactosidase (beta-gal) and is commonly visualized as a blue intracellular precipitate following its incubation with a substrate, "X gal," in an oxidation reaction. LacZ is the "reporter gene" most commonly employed to follow gene expression in neural tissue or to track the fate of transplanted exogenous cells. If the reaction is not performed carefully-with adequate optimization and individualization of various parameters (e.g.. pH, concentration of reagents, addition of chelators, composition of fixatives) and the establishment of various controls--then misleading nonspecific background X-gal positivity can result, leading to the misidentification of cells. Some of this background results from endogenous nonbacterial beta-gal activity in discrete populations of neurons in the mammalian brain; some results from an excessive oxidation reaction. Surprisingly, few articles have empha sized how to recognize and to eliminate these potential confounding artifacts in order to maximize the utility and credibility of this histochemical technique as a cell marker. We briefly review the phenomenon in general, discuss a specific case that illustrates how an insufficiently scrutinized X-gal positivity can be a pitfall in cell transplantation studies, and then provide recommendations for optimizing the specificity and reliability of this histochemical reaction for discerning E. coli beta-gal activity.

Castration rapidly decreases hypothalamic γ-aminobutyric acidergic neuronal activity in both male and female rats

The postcastration LH response is greater and somewhat more rapid in male than female rats. We have previously demonstrated that hypothalamic γ-aminobutyric acid (GABA)ergic neuronal activity decreases following gonadectomy in male rats. To investigate whether these same hypothalamic GABA neurons decrease their activity postcastration in female rats, and whether more rapid and or greater postcastration decreases occur in male rats, we determined the timing and magnitude of the postcastration decreases in GABA turnover which are associated with the sexually dimorphic postcastration LH response. Adult male and 4-day cycling female rats were castrated between 0800 and 1000 h (females ovariectomized on diestrus day 1). Serum LH levels increased significantly by 12 h postcastration in both males and females with the magnitude of the increases being 6.2-fold in males and 2.8-fold in females. GABA turnover was determined in 16 microdissected brain structures by the GABA transaminase inhibition method at 0 h (sham-operated controls), 6 h, 12 h and 1, 2, 4 and 6 days postcastration. In male rats, in the diagonal band of Broca at the level of the organum vasculosum of the lamina terminalis [DBB(ovlt)], the rate of GABA turnover decreased significantly already by 6 h postcastration compared with the 0 h controls, and remained suppressed through 6 days. This rapid down regulation of DBB(ovlt) GABAergic neurons also occurred in female rats, however, the duration of the decrease was not as prolonged as in male rats. Similar changes occurred in the tuberoinfundibular GABAergic (TIGA) neurons projecting to the median eminence in both males and females. Down regulation of these GABAergic neurons precedes or is coincident with increased postcastration LH secretion in both sexes, and the duration of the decreases is consistent with the less robust postcastration LH response in female rats. In addition, the rate of GABA turnover decreased after castration in the interstitial (bed) nucleus of the stria terminalis, ventral aspect (INSTv), the medial preoptic nucleus, dorsomedial aspect (MPNdm) and the ventromedial nucleus, ventrolateral aspect (VMNvl) in male rats, and in the INSTv and VMNvl of female rats, while there was no effect of castration in other hypothalamic regions or control structures. The result in the female VMNvl is consistent with reports that GABA facilitates lordosis behavior in this hypothalamic structure. These findings are consistent with the hypothesis that discrete hypothalamic populations of sex steroid-sensitive GABAergic neurons mediate the postcastration LH responses in both male and female rats, and may underlie other sexually dimorphic adult phenotypes such as sex behavior.

GATA2 is required for the generation of V2 interneurons.

During embryogenesis, transcription factor GATA2 is expressed in a variety of distinct cell types, and earlier experiments showed that GATA2 is a vital regulator of both hematopoiesis and urogenital development. Despite the fact that GATA2 is expressed early and abundantly in the nervous system, there has been no demonstration of its direct participation in neurogenesis. We show here that GATA2 is expressed in the ventral spinal cord exclusively in newly generated V2 interneurons, suggesting that GATA2 might be required for the generation of this discrete neuronal population. Proof for this hypothesis was provided by showing that the number of cells expressing V2 neuronal markers was drastically diminished in gata2 null mutant embryos. The tissue-specific enhancer that directs gata2 transcription specifically in V2 neurons was localized to a 190 bp intragenic element lying within gata2 intron 5, and this element is both necessary and sufficient to confer GATA2 spinal cord expression. The identification of a V2-specific enhancer should allow fundamental new insight into the genetic hierarchy of regulatory events that govern neurogenesis in a well-defined cell lineage.

Defects of Tyrosine Hydroxylase-Immunoreactive Neurons in the Brains of Mice Lacking the Transcription Factor Pax6

In the CNS, the lack of the transcription factor Pax6 has been associated with early defects in cell proliferation, cell specification, and axonal pathfinding of discrete neuronal populations. In this study, we show that Pax6 is expressed in discrete catecholaminergic neuronal populations of the developing ventral thalamus, hypothalamus, and telencephalon. In mice lacking Pax6, these catecholaminergic populations develop abnormally: those in the telencephalon are reduced in cell number or absent, whereas those in the ventral thalamus and hypothalamus are greatly displaced and densely packed. Catecholaminergic neurons of the substantia nigra (SN) and the ventral tegmental area (VTA) do not express Pax6 protein. Nevertheless, mice lacking Pax6 display an altered pathfinding of SN-VTA projections: instead of following the route of the medial forebrain bundle ventrally, most of the SN-VTA projections are deflected dorsorostrally at the pretectal-dorsal thalamic transition zone and in the dorsal thalamic alar plate. Moreover, some catecholaminergic neurons are displaced dorsally to an ectopic location at the pretectal-dorsal thalamic transition zone. Interestingly, from the pretectal-dorsal thalamic to the dorsal thalamic-ventral thalamic transition zones, mice lacking Pax6 display an ectopic ventral to dorsal expansion of the chemorepellant/chemoattractive molecule, Netrin-1. This may be responsible for both the altered pathway of catecholaminergic fibers and the ectopic location of catecholaminergic neurons in this region.

Cloning and cerebral expression of the guinea pig histamine H3 receptor: evidence for two isoforms.

We cloned the full length guinea pig H3 receptor cDNA using RT-PCR amplification with primers from the human receptor and templates from brain areas. Evidence was obtained for two isoforms, designated H3L and H3S, differing by a 30 amino acid stretch within the third cytosolic loop, presumably generated by alternative splicing. In situ hybridization using a selective cRNA probe showed the gene transcripts to be highly expressed in discrete neuronal populations, e.g. pyramidal cells in the cerebral cortex or cerebellar Purkinje cells, in some instances already known to express other histamine receptor subtypes.

Poly(ADP-ribosyl)ation basally activated by DNA strand breaks reflects glutamate-nitric oxide neurotransmission.

Poly(ADP-ribose) polymerase (PARP) transfers ADP ribose groups from NAD(+) to nuclear proteins after activation by DNA strand breaks. PARP overactivation by massive DNA damage causes cell death via NAD(+) and ATP depletion. Heretofore, PARP has been thought to be inactive under basal physiologic conditions. We now report high basal levels of PARP activity and DNA strand breaks in discrete neuronal populations of the brain, in ventricular ependymal and subependymal cells and in peripheral tissues. In some peripheral tissues, such as skeletal muscle, spleen, heart, and kidney, PARP activity is reduced only partially in mice with PARP-1 gene deletion (PARP-1(-/-)), implicating activity of alternative forms of PARP. Glutamate neurotransmission involving N-methyl-d-aspartate (NMDA) receptors and neuronal nitric oxide synthase (nNOS) activity in part mediates neuronal DNA strand breaks and PARP activity, which are diminished by NMDA antagonists and NOS inhibitors and also diminished in mice with targeted deletion of nNOS gene (nNOS(-/-)). An increase in NAD(+) levels after treatment with NMDA antagonists or NOS inhibitors, as well as in nNOS(-/-) mice, indicates that basal glutamate-PARP activity regulates neuronal energy dynamics.

Unraveling the mechanism for respiratory rhythm generation.

Breathing is generated by a neuronal network located within the caudal brainstem. One area of particular significance for respiratory rhythm generation is the pre-Bötzinger (preBotC) complex in the ventrolateral medulla. An important step towards understanding the cellular and network basis by which neurons within this region generate the respiratory rhythm was made in a recent study by Koshiya and Smith.(1) Using simultaneous image analysis and electrophysiological techniques these authors identified a discrete population of synaptically-coupled pacemaker neurons within the preBotC. They postulated that these neurons constitute the minimal essential network component (kernel) for generating the respiratory rhythm. BioEssays 22:6-9, 2000.

Neurotrophin receptors in the somatosensory cortex of the mature rat: co-localization of p75, trk, isoforms and c- neu

Trk immunoreactivity is expressed by a discrete population of cortical neurons, primarily those with cell bodies in layer Vb and dendrites in supragranular cortex. We tested the hypothesis that neurons co-express multiple isoforms of trk receptors. The distribution of neurons expressing specific high affinity neurotrophin receptors was determined immunohistochemically. Multiple antibodies directed against each trk isoform and an antibody directed against an epitope shared by all three trk isoforms were used. The distribution of neurons expressing each of the three receptors was virtually identical. Each anti- trk antibody primarily labeled neurons with cell bodies in layer V. More than one-third of layer V neurons was positive for a high affinity trk receptor. Few immunoreactive somata (1%–5%) were in the other layers. In addition, the neuropil in the supragranular laminae was immunopositive for each trk isoform. Recent data show that layer V neurons in the mature somatosensory cortex express the tyrosine kinase receptor c- erbB2, also known as c- neu. Immunofluorescence double labeling shows that ∼80% of the c- neu-immunolabeled neurons in layer V co-expressed pan- trk immunoreactivity and two-thirds of all c- neu-positive neurons expressed a specific trk isoform. We concluded from these data that there is significant co-expression of trk isoforms in layer V neurons. In summary, trkA, trkB, trkC, and c- neu were primarily expressed by cortical projection neurons in layer V and co-expression among these receptors was common. This implies that cortical growth factor systems are redundant and that cortical neurons are responsive to more than one growth factor.

Quantitative α-Ketoglutarate Dehydrogenase Activity Staining in Brain Sections and in Cultured Cells

The activity of a key mitochondrial enzyme, the α-ketoglutarate dehydrogenase complex (KGDHC), declines in the brains of patients with neurodegenerative diseases such as Alzheimer's disease, as well as in thiamine-deficient (TD) animals. The decreased activity often occurs without a reduction in enzyme protein, which negates the use of immunocytochemistry to study cellular or regional changes in enzyme activity within the brain. To overcome this limitation, an activity staining method using nitroblue tetrazolium was developed. The histochemical activity staining was standardized in cultured cells. The assay was linear with time and was highly specific for KGDHC. The dark-blue reaction product (formazan) formed a pattern that was consistent with mitochondrial localization. Treatment of the cultured cells with both reversible and irreversible inhibitors decreased formazan production, whereas conventional enzyme assays on cell lysates only revealed loss of KGDHC activity with irreversible inhibitors. The activity staining was also linear with time and highly specific for KGDHC activity in mouse brain sections. Staining occurred throughout the brain, and discrete neuronal populations exhibited particularly intense staining. The pattern of staining differed markedly from the distribution of KGDHC protein by immunocytochemistry. Generalized decreases in the intensity of activity staining that occurred in the TD brains compared to controls were comparable with the loss of KGDHC activity by conventional enzyme assay. Thus, the present study introduces a new histochemical method to measure KGDHC activity at the cellular and regional level, which will be useful to determine changes of in situ enzyme activity.

Parieto-frontal coding of reaching: an integrated framework.

In the last few years, anatomical and physiological studies have provided new insights into the organization of the parieto-frontal network underlying visually guided arm-reaching movements in at least three domains. (1) Network architecture. It has been shown that the different classes of neurons encoding information relevant to reaching are not confined within individual cortical areas, but are common to different areas, which are generally linked by reciprocal association connections. (2) Representation of information. There is evidence suggesting that reach-related populations of neurons do not encode relevant parameters within pure sensory or motor "reference frames", but rather combine them within hybrid dimensions. (3) Visuomotor transformation. It has been proposed that the computation of motor commands for reaching occurs as a simultaneous recruitment of discrete populations of neurons sharing similar properties in different cortical areas, rather than as a serial process from vision to movement, engaging different areas at different times. The goal of this paper was to link experimental (neurophysiological and neuroanatomical) and computational aspects within an integrated framework to illustrate how different neuronal populations in the parieto-frontal network operate a collective and distributed computation for reaching. In this framework, all dynamic (tuning, combinatorial, computational) properties of units are determined by their location relative to three main functional axes of the network, the visual-to-somatic, position-direction, and sensory-motor axis. The visual-to-somatic axis is defined by gradients of activity symmetrical to the central sulcus and distributed over both frontal and parietal cortices. At least four sets of reach-related signals (retinal, gaze, arm position/movement direction, muscle output) are represented along this axis. This architecture defines informational domains where neurons combine different inputs. The position-direction axis is identified by the regular distribution of information over large populations of neurons processing both positional and directional signals (concerning the arm, gaze, visual stimuli, etc.) Therefore, the activity of gaze- and arm-related neurons can represent virtual three-dimensional (3D) pathways for gaze shifts or hand movement. Virtual 3D pathways are thus defined by a combination of directional and positional information. The sensory-motor axis is defined by neurons displaying different temporal relationships with the different reach-related signals, such as target presentation, preparation for intended arm movement, onset of movements, etc. These properties reflect the computation performed by local networks, which are formed by two types of processing units: matching and condition units. Matching units relate different neural representations of virtual 3D pathways for gaze or hand, and can predict motor commands and their sensory consequences. Depending on the units involved, different matching operations can be learned in the network, resulting in the acquisition of different visuo-motor transformations, such as those underlying reaching to foveated targets, reaching to extrafoveal targets, and visual tracking of hand movement trajectory. Condition units link these matching operations to reinforcement contingencies and therefore can shape the collective neural recruitment along the three axes of the network. This will result in a progressive match of retinal, gaze, arm, and muscle signals suitable for moving the hand toward the target.

Localization of the olfactory cyclic nucleotide-gated channel subunit 1 in normal, embryonic and regenerating olfactory epithelium

The spatial and temporal expression of subunit 1 of the olfactory cyclic nucleotide-gated channel was investigated using affinity-purified anti-fusion protein antibodies. Immunoreactivity was most prominent in the ciliary layer of the olfactory epithelium, but high protein expression was also seen along the entire length of olfactory receptor neuronal axons to the level of the glomeruli. Electron microscopy showed that the long, thin distal compartments of olfactory cilia labeled more prominently than their thicker proximal segments. This was true as soon as these distal parts began to develop. Using light microscopy, developmental expression of olfactory cyclic nucleotide-gated channel subunit 1 could be detected in discrete populations of olfactory receptor neurons by embryonic day 14. Other signaling molecules are expressed either later (G olf) or only at the level of the epithelial surface and not in axons (adenylyl cyclase type III). Following unilateral lesions of the olfactory bulb, olfactory cyclic nucleotide-gated channel subunit 1 immunoreactivity was present early and throughout developing olfactory receptor neurons; adenylyl cyclase type III immunoreactivity, in contrast, was detectable only later, and again present only in the cilial layer. These results support the hypothesis that this subunit of the olfactory cyclic nucleotide-gated channel may be involved in olfactory axon guidance, in addition to its well-described role in olfactory signal transduction.

Animal models of nonconvulsive status epilepticus.

Nonconvulsive status epilepticus includes three clinical situations: complex partial status epilepticus; absence status epilepticus: and obtundation in the presence of electrographic status epilepticus. Animal models that provide information helpful to clinical management exist for both complex partial and absence status epilepticus. In models of complex partial status epilepticus (pilocarpine, kainic acid, and various protocols using electrical stimulation), neuronal damage in discrete neuronal populations follows an episode of status epilepticus. Hippocampal populations are particularly susceptible to neuropathologic sequelae. Although it is difficult in some cases to distinguish whether the inducing agent or the status epilepticus causes neuropathology, the similar patterns of damage caused by different inducing stimuli provide converging lines of evidence suggesting that the neuropathologic consequences stem at least in part from status epilepticus. In models of absence status epilepticus (genetic mutants, pentylenetetrazole), there is relatively scarce neuropathology that can be attributed directly to status epilepticus. Together these data from animal models suggest that neuropathologic consequences from complex partial status epilepticus may be more severe than those from absence status epilepticus. If these findings translate to patients, then nonconvulsive status epilepticus of the complex partial type should be managed more aggressively than nonconvulsive status epilepticus of the absence type.

Neural representation of the taste of NaCl and KCl in gustatory neurons of the hamster solitary nucleus.

NaCl and KCl are monovalent salts that can be discriminated behaviorally by hamsters on the basis of their tastes. We examined the effects of the passive Na+ channel blocker amiloride on responses to both of these salts in 34 taste-responsive neurons of the nucleus of the solitary tract (NST) in the hamster. The effects of amiloride were assessed with two different, commonly employed stimulus protocols. Additionally, concentration-response functions for each salt were measured in 37 neurons. Cells were characterized by their best response to (in M) 0. 03 NaCl, 0.1 sucrose, 0.003 HCl, 0.001 quinine hydrochloride, and 0. 1 KCl. In neurons classified as NaCl-best, amiloride reversibly blocked responses to both NaCl and KCl. In neurons classified as HCl-best, amiloride had no effect on either stimulus. In sucrose-best neurons, amiloride blocked the response to NaCl but not KCl. These results support the hypothesis that both salts are transduced by at least two different receptor mechanisms. In the NST, information arising from these different inputs is maintained in discrete populations of neurons. In addition to differences in amiloride sensitivity, the cell types also differed in their responses to the salts across concentration. At midrange salt concentrations, NaCl-best neurons were far more responsive to NaCl than KCl, whereas HCl- and sucrose-best neurons responded equivalently to the two salts at all concentrations. Because NaCl- and HCl-best cells cannot by themselves distinguish NaCl from KCl, it is the relative activity across these cell types that comprises the code for taste discrimination.

Trk-neurotrophin receptor-like immunoreactivity in the gut of teleost species.

Neurotrophins, acting through their high-affinity signal-transducing Trk receptors, are involved in the development, differentiation and maintenance of discrete neuron populations in the higher vertebrates. Furthermore, the presence of Trk receptors in some non-neuronal tissues, including the endocrine cells of the gut, could indicate an involvement of neurotrophins also in these tissues. Recently, neurotrophins and neurotrophin receptor proteins have been identified in the lower vertebrates and invertebrates, whose amino acid sequences are highly homologous with those found in mammals. The present study investigates the occurrence and distribution of Trk-like proteins in the neurons and gut endocrine cells in five species of teleost. Single and double immunolabeling was carried out on fresh and paraffin-embedded tissue using commercially available antibodies against sequences of the intracytoplasmic domain of the mammalian Trk. Western-blot analysis, carried out on samples of stomach and intestine of bass, identified proteins whose estimated molecular masses (140 kDa, 145 kDa and 143-145 kDa) were similar to those reported for full-length TrkA, TrkB and TrkC in the higher vertebrates. TrkA-like immunoreactivity was found in the enteric nervous system plexuses of three fish species. Trk-like immunoreactivity was observed in the endocrine cells as follows: sparse TrkA-like immunoreactive endocrine cells were detected only in the intestine: TrkB-like immunoreactive cells were detected only in the stomach; and TrkC-like immunoreactive cells were found both in the intestine of the carp and in the stomach of the bass, where they also showed TrkB-like immunoreactivity. These findings confirm the occurrence and distribution of Trk-like proteins in teleosts. These proteins are closely related to the Trk neurotrophin receptors of mammals. The functional significance of Trk-like proteins in both neuronal and non-neuronal cells of teleosts is still not clear.