Somatostatin-containing Neurons Research Articles

A hypothalamic dopamine locus for psychostimulant-induced hyperlocomotion in mice

The lateral septum (LS) has been implicated in the regulation of locomotion. Nevertheless, the neurons synchronizing LS activity with the brain’s clock in the suprachiasmatic nucleus (SCN) remain unknown. By interrogating the molecular, anatomical and physiological heterogeneity of dopamine neurons of the periventricular nucleus (PeVN; A14 catecholaminergic group), we find that Th+/Dat1+ cells from its anterior subdivision innervate the LS in mice. These dopamine neurons receive dense neuropeptidergic innervation from the SCN. Reciprocal viral tracing in combination with optogenetic stimulation ex vivo identified somatostatin-containing neurons in the LS as preferred synaptic targets of extrahypothalamic A14 efferents. In vivo chemogenetic manipulation of anterior A14 neurons impacted locomotion. Moreover, chemogenetic inhibition of dopamine output from the anterior PeVN normalized amphetamine-induced hyperlocomotion, particularly during sedentary periods. Cumulatively, our findings identify a hypothalamic locus for the diurnal control of locomotion and pinpoint a midbrain-independent cellular target of psychostimulants.

Somatostatin and Somatostatin-Containing Neurons in Shaping Neuronal Activity and Plasticity.

Since its discovery over four decades ago, somatostatin (SOM) receives growing scientific and clinical interest. Being localized in the nervous system in a subset of interneurons somatostatin acts as a neurotransmitter or neuromodulator and its role in the fine-tuning of neuronal activity and involvement in synaptic plasticity and memory formation are widely recognized in the recent literature. Combining transgenic animals with electrophysiological, anatomical and molecular methods allowed to characterize several subpopulations of somatostatin-containing interneurons possessing specific anatomical and physiological features engaged in controlling the output of cortical excitatory neurons. Special characteristic and connectivity of somatostatin-containing neurons set them up as significant players in shaping activity and plasticity of the nervous system. However, somatostatin is not just a marker of particular interneuronal subpopulation. Somatostatin itself acts pre- and postsynaptically, modulating excitability and neuronal responses. In the present review, we combine the knowledge regarding somatostatin and somatostatin-containing interneurons, trying to incorporate it into the current view concerning the role of the somatostatinergic system in cortical plasticity.

Cortical inhibitory neuron disturbances in schizophrenia: role of the ontogenetic transcription factor Lhx6.

Disturbances in parvalbumin- and somatostatin-containing neurons, including deficits in the gamma-aminobutyric acid (GABA)-synthesizing enzyme GAD67 in the prefrontal cortex (PFC) in schizophrenia, may be related to disrupted pre- and/or postnatal development. Deficits in the transcription factor Lhx6, which regulates parvalbumin and somatostatin neuron development, are associated with GAD67 deficits in schizophrenia. Therefore, we investigated the potential pre- and postnatal roles of Lhx6 in GABA-related disturbances using qPCR and/or in situ hybridization to quantify PFC levels of (1) Lhx6 mRNA in a new cohort of schizophrenia subjects; (2) Lhx6 mRNA in monkeys across postnatal development; (3) GABA-related mRNAs in Lhx6 heterozygous (Lhx6+/−) mice, which model Lhx6 deficits in schizophrenia; and (4) Lhx6 mRNA in GAD67+/− mice, which model GAD67 deficits in schizophrenia. Lhx6 mRNA levels were lower (−15%) in schizophrenia and correlated with lower GAD67 mRNA levels. In addition, Lhx6 mRNA levels declined 24% from the perinatal to prepubertal periods then stabilized in monkeys. Finally, GAD67, parvalbumin, and somatostatin mRNAs were not altered in Lhx6+/− mice, and Lhx6 mRNA was not altered in GAD67+/− mice. These data suggest that PFC Lhx6 and GAD67 mRNA deficits are common components of GABA neuron pathology in schizophrenia. An excessive early postnatal decline in Lhx6 mRNA might contribute to Lhx6 mRNA deficits in schizophrenia. However, a partial loss of Lhx6 is not sufficient in isolation to produce deficits in GAD67 mRNA and vice versa, suggesting that the concurrence of Lhx6 and GAD67 mRNA deficits in schizophrenia may instead be the consequence of a common upstream factor.

The claustrum of the bottlenose dolphin Tursiops truncatus (Montagu 1821).

The mammalian claustrum is involved in processing sensory information from the environment. The claustrum is reciprocally connected to the visual cortex and these projections, at least in carnivores, display a clear retinotopic distribution. The visual cortex of dolphins occupies a position strikingly different from that of land mammals. Whether the reshaping of the functional areas of the cortex of cetaceans involves also modifications of the claustral projections remains hitherto unanswered. The present topographic and immunohistochemical study is based on the brains of eight bottlenose dolphins and a wide array of antisera against: calcium-binding proteins (CBPs) parvalbumin (PV), calretinin (CR), and calbindin (CB); somatostatin (SOM); neuropeptide Y (NPY); and the potential claustral marker Gng2. Our observations confirmed the general topography of the mammalian claustrum also in the bottlenose dolphin, although (a) the reduction of the piriform lobe modifies the ventral relationships of the claustrum with the cortex, and (b) the rotation of the telencephalon along the transverse axis, accompanied by the reduction of the antero-posterior length of the brain, apparently moves the claustrum more rostrally. We observed a strong presence of CR-immunoreactive (-ir) neurons and fibers, a diffuse but weak expression of CB-ir elements and virtually no PV immunostaining. This latter finding agrees with studies that report that PV-ir elements are rare in the visual cortex of the same species. NPY- and somatostatin-containing neurons were evident, while the potential claustral markers Gng2 was not identified in the sections, but no explanation for its absence is currently available. Although no data are available on the projections to and from the claustrum in cetaceans, our results suggest that its neurochemical organization is compatible with the presence of noteworthy cortical inputs and outputs and a persistent role in the general processing of the relative information.

A Novel Pathway Regulates Thyroid Hormone Availability in Rat and Human Hypothalamic Neurosecretory Neurons

Hypothalamic neurosecretory systems are fundamental regulatory circuits influenced by thyroid hormone. Monocarboxylate-transporter-8 (MCT8)-mediated uptake of thyroid hormone followed by type 3 deiodinase (D3)-catalyzed inactivation represent limiting regulatory factors of neuronal T3 availability. In the present study we addressed the localization and subcellular distribution of D3 and MCT8 in neurosecretory neurons and addressed D3 function in their axons. Intense D3-immunoreactivity was observed in axon varicosities in the external zone of the rat median eminence and the neurohaemal zone of the human infundibulum containing axon terminals of hypophysiotropic parvocellular neurons. Immuno-electronmicroscopy localized D3 to dense-core vesicles in hypophysiotropic axon varicosities. N-STORM-superresolution-microscopy detected the active center containing C-terminus of D3 at the outer surface of these organelles. Double-labeling immunofluorescent confocal microscopy revealed that D3 is present in the majority of GnRH, CRH and GHRH axons but only in a minority of TRH axons, while absent from somatostatin-containing neurons. Bimolecular-Fluorescence-Complementation identified D3 homodimers, a prerequisite for D3 activity, in processes of GT1-7 cells. Furthermore, T3-inducible D3 catalytic activity was detected in the rat median eminence. Triple-labeling immunofluorescence and immuno-electronmicroscopy revealed the presence of MCT8 on the surface of the vast majority of all types of hypophysiotropic terminals. The presence of MCT8 was also demonstrated on the axon terminals in the neurohaemal zone of the human infundibulum. The unexpected role of hypophysiotropic axons in fine-tuned regulation of T3 availability in these cells via MCT8-mediated transport and D3-catalyzed inactivation may represent a novel regulatory core mechanism for metabolism, growth, stress and reproduction in rodents and humans.

Abstract 472: Calcium Current by Somatostatin Leads to Vasoconstriction in Rabbit Cerebral Artery

Somatostatin-containing neurons have a widespread distribution in the central nervous system. Moreover, the level of somatostatin in bloody cerebrospinal fluid and plasma is elevated patients with stroke. However, there is little evidence to support that somatostatin is a possible factor of vasopasm after stroke. This experiment was to undertaken to evaluate the effects of somatostatin on Ca 2+ currents using the whole-cell voltage-clamp techniques and on Ca 2+ transients using whole-cell fluorescence in cerebral arteries of the rabbit. During rectangular pulses, both peak and steady-state Ca 2+ currents were significantly increased by the application of somatostatin. Somatostatin had little effect on the steady-state activation kinetics, however, significant effect on the time constants for current decay. τ increased monotonically with voltage and was slightly slower in somatostatin-treated cells between 0 and +30 mV. The half maximal concentration of somatostatin was 8.5±1.3 pM in dose-response relation. Moreover, Ca 2+ transients by somatostatin were significantly increased in cells. From these results, the activation of Ca 2+ currents by somatostatin could be involved in pathogenesis of vasospasm after stroke.

Hub GABA Neurons Mediate Gamma-Frequency Oscillations at Ictal-like Event Onset in the Immature Hippocampus

Gamma-frequency oscillations (GFOs, >40Hz) are a general network signature at seizure onset at all stages of development, with possible deleterious consequences in the immature brain. At early developmental stages, the simultaneous occurrence of GFOs in different brain regions suggests the existence of a long-ranging synchronizing mechanism at seizure onset. Here, we show that hippocamposeptal (HS) neurons, which are GABA long-range projection neurons, are mandatory to drive the firing of hippocampal interneurons in a high-frequency regime at the onset of epileptiform discharges in the intact, immature septohippocampal formation. The synchronized firing of interneurons in turn produces GFOs, which are abolished after the elimination of a small number of HS neurons. Because they provide the necessary fast conduit for pacing large neuronal populations and display intra- and extrahippocampal long-range projections, HS neurons appear to belong to the class of hub cells that play a crucial role in the synchronization of developing networks.

A “Growing” Realization

Activation of the somatotropic and gonadotropic axes are well-documented phenomena in the temporal sequence of human development. An increase in GHRH and a decrease in somatostatin from neurons in the hypothalamus have the net action of increasing GH secretion from the anterior pituitary. The increase in GnRH from the GnRH-containing neurons of the hypothalamus also acts at the anterior pituitary to stimulate release of the gonadotropins LH and FSH. The release of GH stimulates production of IGF-I from its target tissues such as bone, muscle, and liver. Likewise, gonadotropins act on the gonad and support steroidogenesis. Working in tandem, GH and the gonadotropins account for the somatic and physiological changes that we collectively recognize as puberty (see Ref. 1 for review). Numerous studies have focused on the causal link between somatic growth and puberty. The mechanisms that activate GnRH neurons and, thus, underlie the pubertal increase in GnRH secretion are unknown. However, the so-called somatometer hypothesis proposed that some aspect of growth served as a signal to the brain that activation of GnRH neurons was appropriate. This central growth-tracking device would be one that responded to growth-related cues from the periphery and by some undefined mechanism induce GnRH release. Notwithstanding the somatometer hypothesis, the link between growth and sexual maturation is perhaps best exemplified by the interaction between somatic growth and gonadal steroids. For instance, rising levels of gonadal steroids are implicated in the increase in GH release from the pituitary around the time of puberty. Likewise, androgens are reported to stimulate IGF-I production in bone and muscle and, thus, account at least in part for the changes in body composition and linear growth during adolescence. Accordingly, the dominant component of the link between somatic growth and sexual maturation has been outside the hypothalamus (Fig. 1). Fig. 1. Do somatostatin-containing neurons compose the pubertal somatostat? Somatostatin robustly inhibits activity of GnRH neurons at a dendritic site and inhibits GH secretion at the anterior pituitary. Thus, a decrease in activity of somatostatin neurons would ... The work of Koyama et al. (2) in this month's Endocrinology solidifies a common hypothalamic link for the control of growth and sexual maturation. Interestingly, this is a direct mechanism for the control of the output of GnRH neurons. Using a combination of anatomical and electrophysiological approaches, they show that GnRH neurons and somatostatin neurons are closely associated in the organum vasculosum of the lamina terminalis of the rat, a finding that is consistent with an earlier finding in mice (3). Moreover, both studies indicate that somatostatin, which is inhibitory to GH secretion from the anterior pituitary, is also strongly inhibitory in GnRH neurons in the hypothalamus (Fig. 1). Of particular interest was the observation derived from studying responses to somatostatin in both GnRH neurons in slices and isolated GnRH somata from the same rat model. Using this approach, the authors demonstrate that the hyperpolarizing influence of somatostatin was lost in isolated GnRH somata, indicating that the dendrites of GnRH neurons are the most likely site of action of somatostatin. Although the present study focused on GnRH neurons in adult animals, the direct inhibition of GnRH neuronal activity by somatostatin represents a potential shift of the current paradigm of growth and sexual maturation. Instead of somatic growth altering GnRH secretion, these present data suggest that factors controlling GH secretion might also directly regulate GnRH secretion. Specifically, it suggests whatever physiological cues unleash GH secretion by decreasing somatostatin release would also dramatically reduce inhibition of GnRH neurons. Based on the electrophysiological studies, the reversal potential of somatostatin was about −65 mV. This voltage is substantially below reported spike thresholds in GnRH neurons (see Table 1 in Ref. 4). Moreover, the change in conductance in response to somatostatin application was relatively large. Thus, somatostatin would strongly curtail depolarization of GnRH neurons, both through its direct actions and via the reduction in membrane resistance due to the opening of large conductances. In most species, the distribution of the somatostatin neurons is similar. Most somatostatin neurons in the periventricular area innervate the external layer of the median eminence and are therefore poised to regulate GH secretion. However, additional somatostatin fibers are found in the regions that contain GnRH neurons (5). Thus, the question remains as to the origin of the somatostatin fibers that interact with GnRH neurons. This consideration notwithstanding, given the striking potency of somatostatin in inhibition of GnRH neurons, it would not be surprising if somatostatin were a major contributor to the presumed quiescence of GnRH neurons in prepubertal animals.

Neurochemical investigations on parathyroid hormone 2 receptor-immunoreactive neurons in the human and macaque hypothalamus and brainstem

Event Abstract Back to Event Neurochemical investigations on parathyroid hormone 2 receptor-immunoreactive neurons in the human and macaque hypothalamus and brainstem Attila G. Bagó1, 2*, Dimitrov Eugene3, Richard Saunders4, Laszlo Seress5, Miklos Palkovits1, 2, Ted B. Usdin3 and Arpad Dobolyi1, 2 1 HAS - Semmelweis University, Neuromorphological and Neuroendocrine Research Laboratory, Department Anatomy, Histology and Embryology, Hungary 2 National Institute of Neurosurgery, Hungary 3 National Institute of Mental Health, Section on Fundamental Neuroscience, United States 4 National Institute of Mental Health, Laboratory of Neuropsychology, United States 5 University of Pécs, Central Electron Microscopic Laboratory, Hungary Parathyroid hormone receptor 2 (PTH2R) and its ligand, tuberoinfundibular peptide of 39 residues (TIP39) constitute a neuromodulator system implicated in endocrine and nociceptive regulations. We described the presence and distribution of the PTH2R and TIP39 in macaque and human brain. In situ hybridization histochemistry showed TIP39 mRNA only in the thalamic subparafascicular area and the pontine medial paralemniscal nucleus. In contrast, high levels of PTH2R expression were identified in a variety of hypothalamic and brainstem areas in macaque, which correlated well with RT-PCR data in human. Immunohistochemically, a widespread distribution of PTH2R-immunoreactive fibers was described in human, including dense fiber networks in the medial preoptic area, hypothalamic paraventricular, periventricular and infundibular (arcuate) nuclei, lateral hypothalamic area, median eminence, periaqueductal gray, lateral parabrachial nucleus, nucleus of the solitary tract, sensory trigeminal, and medullary dorsal reticular nuclei. Co-localization of PTH2R immunoreactivity with vesicular glutamate transporter 2 suggested that PTH2R terminals are glutamatergic. In addition, PTH2R co-localized with somatostatin in neuronal cell bodies in the hypothalamic periventricular nucleus as well as in fibers located in the median eminence suggesting that TIP39 may directly influence hypophysiotropic somatostatin-containing neurons. In contrast, numerous PTH2R-containing terminals closely appose corticotropin releasing-hormone containing neurons suggesting a presynaptic action of TIP39 on terminals innervating these cells. The results support that TIP39 and the PTH2R are expressed in the brain of primates and this peptide neuromodulator system is able to influence target neurons with different mechanisms. The work was supported by the Bolyai Fellowship of the HAS, NKTH-OTKA K67646 and NFM-OTKA NNF78219 for AD, OTKA NK72929 for MP, and NIMH Intramural Research Program for TBU. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Homeostatic and neuroendocrine systems Citation: Bagó AG, Eugene D, Saunders R, Seress L, Palkovits M, Usdin TB and Dobolyi A (2010). Neurochemical investigations on parathyroid hormone 2 receptor-immunoreactive neurons in the human and macaque hypothalamus and brainstem. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00076 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 21 Apr 2010; Published Online: 21 Apr 2010. * Correspondence: Attila G Bagó, HAS - Semmelweis University, Neuromorphological and Neuroendocrine Research Laboratory, Department Anatomy, Histology and Embryology, Budapest, Hungary, bagoatt@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Attila G Bagó Dimitrov Eugene Richard Saunders Laszlo Seress Miklos Palkovits Ted B Usdin Arpad Dobolyi Google Attila G Bagó Dimitrov Eugene Richard Saunders Laszlo Seress Miklos Palkovits Ted B Usdin Arpad Dobolyi Google Scholar Attila G Bagó Dimitrov Eugene Richard Saunders Laszlo Seress Miklos Palkovits Ted B Usdin Arpad Dobolyi PubMed Attila G Bagó Dimitrov Eugene Richard Saunders Laszlo Seress Miklos Palkovits Ted B Usdin Arpad Dobolyi Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Neuronal localization of 5-HT type 2A receptor immunoreactivity in the rat basolateral amygdala

Although it is well established that there are alterations in type 2A 5-HT receptors (5-HT 2ARs) in the basolateral nuclear complex of the amygdala (BLC) in several neuropsychiatric disorders, very little is known about the neuronal localization of these receptors in this brain region. Single-labeling and dual-labeling immunohistochemical techniques were utilized in the rat to address this question. Three different 5-HT 2AR antibodies were used, each producing distinct but overlapping patterns of immunostaining. Two of three 5-HT 2AR antibodies mainly stained pyramidal projection neurons in the BLC. The third antibody only stained pyramidal cells in the dorsolateral subdivision of the lateral amygdalar nucleus. With one of the antibodies, the most intensely stained neurons were a population of large nonpyramidal neurons whose morphology and distribution closely resembled those shown in previous studies to project to the mediodorsal thalamic nucleus (MD). This was confirmed in the present study using a technique that combined 5-HT 2AR immunohistochemistry with fluorogold retrograde tract-tracing. Two of three 5-HT 2AR antibodies stained large numbers of parvalbumin-containing interneurons in the BLC. One of these two antibodies also stained a subpopulation of somatostatin-containing neurons. None of the 5-HT 2AR antibodies stained significant numbers of the other two main interneuronal subpopulations, the large cholecystokinin-positive neurons or the small interneurons that exhibit extensive colocalization of calretinin and cholecystokinin. Since each of the three antibodies was raised against a distinct immunizing antigen, they may recognize different conformations of 5-HT 2AR in different neuronal domains. The expression of 5-HT 2ARs in pyramidal cells and parvalbumin-positive interneurons in the BLC is consistent with the results of previous electrophysiological studies, and suggests that 5-HT may produce excitation of several neuronal populations in the BLC via 5-HT 2ARs.

Glutamatergic innervation of growth hormone-releasing hormone-containing neurons in the hypothalamic arcuate nucleus and somatostatin-containing neurons in the anterior periventricular nucleus of the rat

Growth hormone-releasing hormone (GHRH) and somatostatin are the two main hypothalamic neurohormones, which stimulate or inhibit directly hypophysial growth hormone (GH) release. Majority of the GHRH neurons projecting to the median eminence is situated in the arcuate nucleus and the somatostatin neurons in the anterior periventricular nucleus. Data suggest that the excitatory amino acid glutamate may play an important role in the control of hypothalamic neuroendocrine neurons and processes including the control of GH. There is a dense plexus of glutamatergic fibres in the hypothalamic arcuate and anterior periventricular nucleus. The aim of the present studies was to examine the relationship of these fibres to the GHRH neurons in the arcuate nucleus and to somatostatin neurons in the anterior periventricular nucleus. Double-labelling immuno-electron microscopy was used. Glutamatergic structures were identified by the presence of vesicular glutamate transporter 2 (VGluT2) (a selective marker of glutamatergic elements) immunoreactivity. A significant number of VGluT2-immunoreactive boutons was observed to make asymmetric type of synapses with GHRH-immunostained nerve cells in the arcuate and with somatostatin neurons in the anterior periventricular nucleus. A subpopulation of somatostatin-immunoreactive neurons displayed also VGluT2 immunoreactivity. Our findings provide direct neuromorphological evidence for the view that the action of glutamate on GH release is exerted, at least partly, directly on GHRH and somatostatin neurons releasing these neurohormones into the hypophysial portal blood.

Loss of interneurons innervating pyramidal cell dendrites and axon initial segments in the CA1 region of the hippocampus following pilocarpine-induced seizures.

In the pilocarpine model of chronic limbic seizures, vulnerability of GABAergic interneurons to excitotoxic damage has been reported in the hippocampal CA1 region. However, little is known about the specific types of interneurons that degenerate in this region. In order to characterize these interneurons, we performed quantitative analyses of the different populations of GABAergic neurons labeled for their peptide or calcium-binding protein content. Our data demonstrate that the decrease in the number of GAD mRNA-containing neurons in the stratum oriens of CA1 in pilocarpine-treated rats involved two subpopulations of GABAergic interneurons: interneurons labeled for somatostatin only (O-LM and bistratified cells) and interneurons labeled for parvalbumin only (basket and axo-axonic cells). Stratum oriens interneurons labeled for somatostatin/calbindin or somatostatin/parvalbumin were preserved. The decrease in number of somatostatin- and parvalbumin-containing neurons was observed as early as 72 hours after the sustained seizures induced by pilocarpine injection. Many degenerating cell bodies in the stratum oriens and degenerating axon terminals in the stratum lacunosum-moleculare were observed at 1 and 2 weeks after injection. In addition, the synaptic coverage of the axon initial segment of CA1 pyramidal cells was significantly decreased in pilocarpine-treated animals. These results indicate that the loss of somatostatin-containing neurons corresponds preferentially to the degeneration of interneurons with an axon projecting to stratum lacunosum-moleculare (O-LM cells) and suggest that the death of these neurons is mainly responsible for the deficit of dendritic inhibition reported in this region. We demonstrate that the loss of parvalbumin-containing neurons corresponds to the death of axo-axonic cells, suggesting that perisomatic inhibition and mechanisms controlling action potential generation are also impaired in this model.

The proprotein convertase PC2 is involved in the maturation of prosomatostatin to somatostatin-14 but not in the somatostatin deficit in Alzheimer's disease

A somatostatin deficit occurs in the cerebral cortex of Alzheimer's disease patients without a major loss in somatostatin-containing neurons. This deficit could be related to a reduction in the rate of proteolytic processing of peptide precursors. Since the two proprotein convertases (PC)1 and PC2 are responsible for the processing of neuropeptide precursors directed to the regulated secretory pathway, we examined whether they are involved first in the proteolytic processing of prosomatostatin in mouse and human brain and secondly in somatostatin defect associated with Alzheimer's disease. By size exclusion chromatography, the cleavage of prosomatostatin to somatostatin-14 is almost totally abolished in the cortex of PC2 null mice, while the proportions of prosomatostatin and somatostatin-28 are increased. By immunohistochemistry, PC1 and PC2 were localized in many neuronal elements in human frontal and temporal cortex. The convertases levels were quantified by Western blot, as well as the protein 7B2 which is required for the production of active PC2. No significant change in PC1 levels was observed in Alzheimer's disease. In contrast, a marked decrease in the ratio of the PC2 precursor to the total enzymatic pool was observed in the frontal cortex of Alzheimer patients. This decrease coincides with an increase in the binding protein 7B2. However, the content and enzymatic activity of the PC2 mature form were similar in Alzheimer patients and controls. Therefore, the cortical somatostatin defect is not due to convertase alteration occuring during Alzheimer's disease. Further studies will be needed to assess the mechanisms involved in somatostatin deficiency in Alzheimer's disease.

Substance P and nitric oxide signaling in cerebral cortex: anatomical evidence for reciprocal signaling between two classes of interneurons.

Parvalbumin-containing fast-spiking interneurons in the cerebral cortex exhibit widespread electrical coupling, as do somatostatin-containing low-threshold spiking interneurons. Besides the classical neurotransmitter gamma-aminobutyric acid, these cortical interneurons may also release various neuropeptides including substance P (SP), as well as the freely diffusible messenger nitric oxide (NO). To investigate whether these two networks of interneurons might interact via these nonclassical messengers, we performed immunocytochemistry for SP and NO signaling pathways in rat somatic sensory cortex. SP was found in a subset of parvalbumin-positive cells concentrated in layers IV and V, whereas its receptor, NK1, was found in a subset of somatostatin-containing neurons (and also, at much lower levels, in a disjoint subset of parvalbumin-containing neurons). Only 4% of SP-containing axon terminals were apposed to NK1-positive dendrites, suggesting that in the cerebral cortex, SP may act predominantly as a paracrine neuromediator. Nitric oxide synthase-I (NOS-I), the synthetic enzyme for NO, was found almost exclusively in NK1-positive neurons; 95% of intensely somatostatin/NK1-positive neurons were also positive for NOS-I, and 94% of NOS-positive neurons were also positive for NK1. Immunoreactivity for soluble guanylyl cyclase (the NO receptor) was at high levels in the apical dendrites of layer V pyramidal neurons and in parvalbumin/SP-positive neurons. These data point to a novel reciprocal chemical interaction between two inhibitory networks in the rat neocortex.

Dentate hilar mossy cells and somatostatin-containing neurons are immunoreactive for the α8 integrin subunit: characterization in normal and kainic acid-treated rats

Integrins are heterodimeric cell surface receptors composed of different α and β subunits that mediate cell–cell and cell–extracellular matrix interactions. They have been implicated in the regulation of neuronal migration, differentiation, process outgrowth, and plasticity. The α8 integrin subunit associates exclusively with the β1 subunit to form a receptor (α8β1) for fibronectin, vitronectin, tenascin, and osteopontin. In a previous study, we demonstrated that hippocampal dentate hilar neurons are immunoreactive for α8. The present study identifies the major types of α8-immunoreactive hilar neurons and characterizes the effects of kainic acid-induced seizures on α8-immunoreactivity in these cells. Examination of the hilus in normal rats revealed α8-immunoreactivity in the somatodendritic compartments of large hilar neurons identified as mossy cells, including a subset of dendritic thorny excrescences that were contacted by large mossy fiber terminals. α8-immunoreactivity also was found in approximately 71% of somatostatin-containing hilar cells. Kainic acid-induced seizures dramatically and rapidly altered the levels and distribution of α8-immunoreactivity in hilar neurons. After 1.5 h of seizures, α8-immunoreactivity in their dendrites was reduced greatly. One day after kainic acid treatment, labeling was diminished throughout the somatodendritic compartments of most hilar cells. This decrease appeared to be transient, since α8 labeling returned to normal levels in surviving hilar neurons within 2 weeks of treatment. In addition, many α8-immunoreactive hilar neurons, particularly in caudal dentate regions, were lost 3–5 weeks after kainic acid treatment. Our findings suggest that α8β1 may mediate adhesive interactions of the dendritic processes of mossy cells and somatostatin-containing hilar neurons with other cellular elements or with extracellular matrix components. They also suggest that α8 may be susceptible to activity-dependent proteolysis that could modulate its function in the somatodendritic compartment of these cells.

Localization of long-form leptin receptor in the somatostatin-containing neurons in the sheep hypothalamus

Reduction in the adiposity or dietary restriction increases plasma growth hormone (GH) concentrations, and in sheep this appears to be due, at least in part, to a reduction in the concentrations of somatostatin (SRIF) in hypophyseal portal blood. Leptin is a hormone secreted by the adipocytes and it is possible that the effects of altered adiposity or fasting on GH secretion could be due to regulation of SRIF neurons by leptin. To ascertain the extent to which leptin may act on these neurons, we have used immunohistochemistry to examine co-localization of long-form of the leptin receptor (OB-Rb) and SRIF in the sheep hypothalamus. In the hypothalamic periventricular area (PeriV), 44.5±10% of SRIF cells were found to co-stain for OB-Rb. In the dorsomedial hypothalamic, ventromedial hypothalamic and arcuate nuclei, 100% of SRIF immunoreactive neurons expressed OB-Rb. These findings provide a basis for the direct action of leptin on SRIF neurons. Thus, it is possible that leptin stimulates the secretion of SRIF in relatively obese individuals. The significance of the lower number of SRIF cells in the PeriV co-localizing OB-Rb expression is not clear at present.

Social Status Controls Somatostatin Neuron Size and Growth

Many animal species show flexible behavioral responses to environmental and social changes. Such responses typically require changes in the neural substrate responsible for particular behavioral states. We have shown previously in the African cichlid fish, Haplochromis burtoni, that changes in social status, including events such as losing or winning a territorial encounter, result in changes in somatic growth rate. Here we demonstrate for the first time that changes in social status cause changes in the size of neurons involved in the control of growth. Specifically, somatostatin-containing neurons in the hypothalamus of H. burtoni increase up to threefold in volume in dominant and socially descending animals compared with cell sizes in subordinate and socially ascending fish. Because somatostatin is known to be an inhibitor of growth hormone release, the differences in cell size suggest a possible mechanism to account for the more rapid growth rates of subordinate and socially ascending animals compared with those of dominant or socially descending fish. These results reveal possible mechanisms responsible for socially induced physiological plasticity that allow animals to shift resources from reproduction to growth or vice versa depending on the social context.

Brain somatostatin: a candidate inhibitory role in seizures and epileptogenesis

Recent evidence shows that neuropeptide expression in the CNS is markedly affected by seizure activity, particularly in the limbic system. Changes in neuropeptides in specific neuronal populations depend on the type and intensity of seizures and on their chronic sequelae (i.e. neurodegeneration and spontaneous convulsions). This paper reviews the effects of seizures on somatostatin-containing neurons, somatostatin mRNA and immunoreactivity, the release of this peptide and its receptor subtypes in the CNS. Differences between kindling and status epilepticus in rats are emphasized and discussed in the light of an inhibitory role of somatostatin on hippocampal excitability. Pharmacological studies show that somatostatin affects electrophysiological properties of neurons, modulates classical neurotransmission and has anticonvulsant properties in experimental models of seizures. This peptidergic system may be an interesting target for pharmacological attempts to control pathological hyperactivity in neurons, thus providing new directions for the development of novel anticonvulsant treatments.

Pathway-specific expression of PKC and PKA in sympathetic neurons

We used multiple-labelling immunofluorescence, intracellular dye injection, electrophysiological recording and confocal microscopy to examine the expression of immunoreactivity to protein kinase C (PKC) and protein kinase A (PKA) in sympathetic ganglia of guinea-pigs. PKCalpha and PKCgamma were widespread in vasoconstrictor and pilomotor neurons. High levels of PKA RIIalpha and RIIbeta were restricted to neurons that lacked significant expression of PKC, including somatostatin-containing neurons projecting to the gut, and non-noradrenergic vasodilator neurons. In coeliac ganglia, most neurons with PKC contained neuropeptide Y and displayed phasic patterns of action potential firing, often with a long after-hyperpolarization. Tonically firing neurons lacked both neuropeptide Y and PKC. These results show remarkably pathway-specific expression of protein kinases in functionally identified populations of sympathetic neurons.

Tetanus toxin-enhanced GABA immunoreactivity in living neurons.

Analysis of the connectivity between different neuronal cell types is dependent on an appreciation of their dendritic and axonal arborizations. A detailed study of the dendrites and axons of GABAergic neurons has been thwarted by the lack of a suitable technique for enhancing GABA immunoreactivity. This article describes a procedure using tetanus toxin which, when applied to organotypic hippocampal cultures, considerably enhances the immunoreactivity in the dendrites and axons of the GABA- and somatostatin-containing neurons and clearly demonstrates the co-localization of GABA and somatostatin immunoreactivities in the same neuron. Tetanus toxin was applied to the culture medium on Day 14 for a 24-hr period and the cultures were fixed at the end of Day 18. Tetanus toxin-treated cultures (n = 30) or untreated cultures (n = 40) were incubated for either GABA or somatostatin immunoreactivity. Tetanus toxin-treated cultures used for co-localization studies (n = 20) were incubated for both GABA and somatostatin immunoreactivity.