CRF-containing neuron systems in the rat hypothalamus: retrograde tracing and immunohistochemical studies

Insulin synthesized in the paraventricular nucleus of the hypothalamus regulates pituitary growth hormone production

Evidence has mounted that insulin can be synthesized in various brain regions, including the hypothalamus. However, the distribution and functions of insulin-expressing cells in the hypothalamus remain elusive. Herein, we show that in the mouse hypothalamus, the perikarya of insulin-positive neurons are located in the paraventricular nucleus (PVN) and their axons project to the median eminence; these findings define parvocellular neurosecretory PVN insulin neurons. Contrary to corticotropin-releasing hormone expression, insulin expression in the PVN was inhibited by restraint stress (RS) in both adult and young mice. Acute RS–induced inhibition of PVN insulin expression in adult mice decreased both pituitary growth hormone (Gh) mRNA level and serum GH concentration, which were attenuated by overexpression of PVN insulin. Notably, PVN insulin knockdown or chronic RS in young mice hindered normal growth via the downregulation of GH gene expression and secretion, whereas PVN insulin overexpression in young mice prevented chronic RS–induced growth retardation by elevating GH production. Our results suggest that in both normal and stressful conditions, insulin synthesized in the parvocellular PVN neurons plays an important role in the regulation of pituitary GH production and body length, unveiling a physiological function of brain-derived insulin.

Insulin produced in the paraventricular nucleus regulates body length by modulating pituitary growth hormone expression and secretion under both normal and stress conditions.

Median and Dorsal Raphe Serotonergic Neurons Control Moderate Versus Compulsive Cocaine Intake

BACKGROUND

Reduced expression of the serotonin transporter (SERT) promotes anxiety and cocaine intake in both humans and rats. We tested the hypothesis that median raphe nucleus (MRN) and dorsal raphe nucleus (DRN) serotonergic projections differentially mediate these phenotypes.

METHODS

We used virally mediated RNA interference to locally downregulate SERT expression and compared the results with those of constitutive SERT knockout. Rats were allowed either short access (ShA) (1 hour) or long access (LgA) (6 hours) to cocaine self-administration to model moderate versus compulsive-like cocaine taking.

RESULTS

SERT knockdown in the MRN increased cocaine intake selectively under ShA conditions and, like ShA cocaine self-administration, reduced corticotropin-releasing factor (CRF) immunodensity in the paraventricular nucleus of the hypothalamus. In contrast, SERT knockdown in the DRN increased cocaine intake selectively under LgA conditions and, like LgA cocaine self-administration, reduced CRF immunodensity in the central nucleus of the amygdala. SERT knockdown in the MRN or DRN produced anxiety-like behavior, as did withdrawal from ShA or LgA cocaine self-administration. The phenotype of SERT knockout rats was a summation of the phenotypes generated by MRN- and DRN-specific SERT knockdown.

CONCLUSIONS

Our results highlight a differential role of serotonergic projections arising from the MRN and DRN in the regulation of cocaine intake. We propose that a cocaine-induced shift from MRN-driven serotonergic control of CRF levels in the hypothalamus to DRN-driven serotonergic control of CRF levels in the amygdala may contribute to the transition from moderate to compulsive intake of cocaine.

Gq Protein-Coupled Membrane-Initiated Estrogen Signaling Rapidly Excites Corticotropin-Releasing Hormone Neurons in the Hypothalamic Paraventricular Nucleus in Female Mice

CRH neurons in the hypothalamic paraventricular nucleus (PVN) play a central role in regulating the hypothalamus-pituitary-adrenal (HPA) axis and are directly influenced by 17β-estradiol (E2). Although compelling evidence has suggested the existence of membrane-associated estrogen receptors (mERs) in hypothalamic and other central nervous system neurons, it remains unknown whether E2 impacts CRH neuronal excitability through this mechanism. The purpose of the current study is to examine the existence and function of mER signaling in PVN CRH neurons. Whole-cell recordings were made from CRH neurons identified by Alexa Fluor 594 labeling and post hoc immunostaining in ovariectomized female mice. E2 (100nM) rapidly suppressed the M-current (a voltage-dependent K(+) current) and potentiated glutamatergic excitatory postsynaptic currents. The putative Gq-coupled mER (Gq-mER) characterized in hypothalamic proopiomelanocortin neurons initiates a phospholipase C-protein kinase C-protein kinase A pathway; therefore, we examined the involvement of this pathway using selective inhibitors. Indeed, the ER antagonist ICI 182780 and inhibitors of Gq-phospholipase C-protein kinase C-protein kinase A blocked E2's actions, suggesting dependence on the Gq-mER. Furthermore, STX, a selective ligand for the Gq-mER, mimicked E2's actions. Finally, to examine the in vivo effect of Gq-mER activation, E2 or STX injection increased c-fos expression in CRH neurons in the PVN, suggesting CRH neuronal activation. This corresponded to an increase in plasma corticosterone. We conclude that the Gq-mER plays a critical role in the rapid regulation of CRH neuronal activity and the HPA axis. Our findings provide a potential underlying mechanism for E2's involvement in the pathophysiology of HPA-associated mood disorders.

Dorsomedial hypothalamus CRF type 1 receptors selectively modulate inhibitory avoidance responses in the elevated T-maze

Corticotropin-releasing factor (CRF) plays a critical role in the mediation of physiological and behavioral responses to stressors. In the present study, we investigated the role played by the CRF system within the dorsomedial hypothalamus (DMH) in the modulation of anxiety- and panic-related responses. Male Wistar rats were administered into the DMH with CRF (125 and 250 ng/0.2 μl, experiment 1) or with the CRFR1 antagonist antalarmin (25 ng/0.2 μl, experiment 2) and 10 min later tested in the elevated T-maze (ETM) for inhibitory avoidance and escape measurements. In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. To further verify if the anxiogenic effects of CRF were mediated by CRFR1 activation, we also investigated the effects of the combined treatment with CRF (250 ng/0.2 μl) and antalarmin (25 ng/0.2 μl) (experiment 3). All animals were tested in an open field, immediately after the ETM, for locomotor activity assessment. Results showed that 250 ng/0.2μl of CRF facilitated ETM avoidance, an anxiogenic response. Antalarmin significantly decreased avoidance latencies, an anxiolytic effect, and was able to counteract the anxiogenic effects of CRF. None of the compounds administered altered escape responses or locomotor activity measurements. These results suggest that CRF in the DMH exerts anxiogenic effects by activating type 1 receptors, which might be of relevance to the physiopathology of generalized anxiety disorder.

Anatomical organization of the melanin-concentrating hormone peptide family in the mammalian brain

More than 20 years ago, melanin-concentrating hormone (MCH) and its peptide family members - neuropeptide EI (NEI) and neuropeptide GE (NGE) - were described in various species, including mammals (rodents, humans, and non-human primates). Since then, most studies have focused on the role of MCH as an orexigenic peptide, as well as on its participation in learning, spatial memory, neuroendocrine control, and sleep. It has been shown that MCH mRNA or the neuropeptide MCH are present in neurons of the prosencephalon, hypothalamus and brainstem. However, most of the neurons containing MCH/NEI are within the incerto-hypothalamic and lateral hypothalamic areas. In addition, the terminals of those neurons are distributed widely throughout the central nervous system. In this review, we will discuss the relationship between those territories and the roles played by MCH/NEI, as well as the importance of MCH receptor 1 in the respective terminal fields. Certain neurochemical features of MCH- and NEI-immunoreactive (MCH-ir and NEI-ir) neurons will also be discussed. The overarching theme is the anatomical organization of an inhibitory neuropeptide colocalized with an inhibitory neurotransmitter in integrative territories of the central nervous system, such as the IHy and LHA. Although these territories have connections to few brain regions, the regions to which they are connected are relevant, being responsible for the organization of motivated behaviors. All available information on this peptidergic system (anatomical, neurochemical, hodological, physiological, pharmacological and behavioral data) suggests that MCH is intimately involved in arousal and the initiation of motivated behaviors.

Lateral thinking about leptin: a review of leptin action via the lateral hypothalamus

The lateral hypothalamic area (LHA) was initially described as a "feeding center" but we are now beginning to understand that the LHA contributes to other aspects of physiology as well. Indeed, the best-characterized neuronal populations of the LHA (which contain melanin-concentrating hormone (MCH) or the hypocretins/orexins (OX)) are not strictly orexigenic, but also have roles in regulation of the autonomic and sympathetic nervous systems as well as in modulating motivated behavior. Leptin is an anorectic hormone that regulates energy homeostasis and the mesolimbic DA system (which transduces the wanting of food, drugs of abuse, and sex) in part, via actions at the LHA. At least three populations of LHA neurons are regulated by leptin: those containing MCH, OX or the long form of the leptin receptor, LepRb. The emerging picture of leptin interaction with these LHA populations suggests that the LHA is not merely regulating feeding, but is a crucial integrator of energy balance and motivated behavior.

Occlusion and brain function: mastication as a prevention of cognitive dysfunction

Research in animals and humans has shown that mastication maintains cognitive function in the hippocampus, a brain area important for learning and memory. Reduced mastication, an epidemiological risk factor for the development of dementia in humans, attenuates spatial memory and causes hippocampal neurons to deteriorate morphologically and functionally, especially in aged animals. Active mastication rescues the stress-attenuated hippocampal memory process in animals and attenuates the perception of stress in humans by suppressing endocrinological and autonomic stress responses. Active mastication further improves the performance of sustained cognitive tasks by increasing the activation of the hippocampus and the prefrontal cortex, the brain regions that are essential for cognitive processing. Abnormal mastication caused by experimental occlusal disharmony in animals produces chronic stress, which in turn suppresses spatial learning ability. The negative correlation between mastication and corticosteroids has raised the hypothesis that the suppression of the hypothalamic-pituitary-adrenal (HPA) axis by masticatory stimulation contributes, in part, to preserving cognitive functions associated with mastication. In the present review, we examine research pertaining to the mastication-induced amelioration of deficits in cognitive function, its possible relationship with the HPA axis, and the neuronal mechanisms that may be involved in this process in the hippocampus.

Comparison of the spatial distribution of seven types of neuroendocrine neurons in the rat paraventricular nucleus: toward a global 3D model

The paraventricular nucleus of the hypothalamus (PVH) coordinates neuroendocrine, autonomic, and behavioral responses to help maintain energy and body water balance. The rat paraventricular nucleus has three major divisions: descending with axonal projections to somatomotor-behavioral and autonomic circuitry, magnocellular neuroendocrine with projections directly to the posterior pituitary, and parvicellular neuroendocrine with projections to the median eminence for controlling anterior pituitary hormone secretion. The present work was undertaken to provide high-resolution mapping of spatial relationships among the two magnocellular neuroendocrine and five parvicellular neuroendocrine neuron types throughout the nucleus. Double immunohistochemical labeling for two neuron types combined with retrograde labeling to identify neuroendocrine neurons positively was used in individual sections spaced 45 mum apart, along with a grid transfer method for reducing plane of section artifacts when comparing staining pattern data between animals. The results indicate that whereas each neuroendocrine neuron phenotype displays a unique distribution pattern, there is extensive partial overlap in a complex pattern between small "hot spots" with a relatively high density of a particular neuron type and few if any other phenotypes. In addition, the distribution of non-neuroendocrine neurons staining with each of the markers (but not retrogradely labeled) was mapped and compared with each other and with the neuroendocrine neuron populations. This spatial organization raises important questions about the differential functional regulation of individual-and perhaps sets of-neuroendocrine motor neuron populations in the PVH by synaptic mechanisms and by less traditional mechanisms like dendritic neurotransmitter release and gap junctions within and between neuron types.

The functional neuroanatomy of corticotropin-releasing factor

Descriptions of the central distribution of corticotropin-releasing factor (CRF) have been taken as generally supporting the proposition that this neuropeptide is involved in the mediation of complementary neuroendocrine, autonomic and behavioural responses to stress. The hypothalamic paraventricular nucleus (PVN) is recognized as the principal source of CRF in hypophysial portal plasma; CRF mRNA and peptide expression in parvocellular neurosecretory neurons are regulated negatively by adrenal steroids and positively by many stressors. Consistent with the latter, the hypophysiotropic zone of the PVN receives a rich, and biochemically differentiated, afferent supply that provides visceral, somatic and special sensory systems with access to the 'CRF neuron'. Within the PVN, CRF is also expressed, and differentially regulated, in oxytocinergic magnocellular neurosecretory neurons and in autonomic-related projection neurons. CRF expression in at least some extrahypothalamic cell groups (olfactory bulb, Barrington's nucleus) is responsive to certain stressful stimuli, but not to perturbations of the steroid environment. Refinement of our understanding of the central distribution of CRF has been provided by the recognition that most CRF antisera cross-react with an amidated dipeptide encoded by the melanin-concentrating hormone precursor, and by the likelihood that some central sites of CRF peptide expression may be muted or masked by the presence of a CRF-binding protein (CRF-BP). The CRF-BP is expressed prominently in the telencephalon, where it is co-localized with CRF in some neurons, and in anterior pituitary corticotrophs.

Interleukin-6 and Nitric Oxide Synthase Expression in the Vasopressin and Corticotrophin-releasing Factor Systems of the Rat Hypothalamus

Nitric oxide synthase (NOS) and interleukin-6 (IL-6) are constitutively expressed in hypothalamic cells. However, phenotypic and functional aspects of these cells remain unknown. We have studied the expression pattern of these two molecules in hypothalamic cells expressing corticotropin-releasing factor (CRF) and arginin-vasopressin (AVP), two major regulatory peptides in the hypothalamus-pituitary system, using immunofluorescence, intracerebroventricular injection of colchicine, and the study in parallel of the labeling pattern of axons in the median eminence. Within AVP cells, we distinguished two different populations: large, intensely stained AVP cells coexpressing IL-6; and large, intensely stained AVP cells coexpressing IL-6 and NOS. Within the CRF cells, we distinguished three different populations: large, intensely stained CRF cells immunonegative for AVP, NOS, and IL-6; large cells weakly stained for CRF and AVP, immunopositive for NOS and immunonegative for IL-6; and small cells intensely stained for CRF and AVP and immunonegative for IL-6 and NOS. In addition, we also found AVP cells containing IL-6 in the suprachiasmatic nucleus. These results suggest that neuronal NOS and IL-6 may be involved in different modulatory processes in hypophysiotropic and non-hypophysiotropic cells.

Glutamatergic innervation of corticotropin-releasing hormone- and thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus of the rat

Glutamate plays a role in the central regulation of the hypothalamic-pituitary-adrenal (HPA) and thyroid (HPT) axes. Until the recent discovery of vesicular glutamate transporters (VGLUT1-3), there was no specific tool for the examination of the putative morphological relationship between the glutamatergic and the hypophysiotropic systems. Using antisera against VGLUT2, corticotropin-releasing hormone (CRH), and prothyrotropin-releasing hormone (proTRH) (178-199), we performed double-labeling immunocytochemistry at light and electron microscopic levels in order to study the glutamatergic innervation of the CRH- and TRH-synthesizing neurons in the hypothalamic paraventricular nucleus (PVN). Fine VGLUT2-immunoreactive (IR) axons very densely innervated the parvocellular subdivisions of the PVN. VGLUT2-IR axons established juxtapositions with all parvocellular CRH- and TRH-synthesizing neurons. The innervation was similarly intense in all parvocellular subdivisions of the PVN. At ultrastructural level, VGLUT2-IR terminals frequently established synapses with perikarya and dendrites of the CRH- and proTRH-IR neurons. These findings demonstrate that glutamatergic neurons directly innervate hypophysiotropic CRH and TRH neurons in the PVN and, therefore, support the hypothesis that the glutamate-induced activation of the HPA and HPT axes may be accomplished by a direct action of glutamate on hypophysiotropic CRH and TRH systems.

Differential qualitative and temporal changes in the response of the hypothalamus-pituitary-adrenal axis in rats after localized or total-body irradiation

Stress such as exposure to ionizing radiation is able to activate the hypothalamus-pituitary-adrenal axis. The present study sought to examine the effects of different configurations of a 10-Gy gamma irradiation in rats on the hypothalamus-pituitary-adrenal axis to understand the mechanism of negative feedback by glucocorticoids induced by ionizing radiation. Specifically, we determined adrenocorticotropin and corticosterone levels in plasma as well as corticotrophin-releasing factor expression in the paraventricular nucleus of the hypothalamus by in situ hybridization from 6 h to 4 days after total-body, abdominal or head irradiation. In this study, we found an activation of the hypothalamus-pituitary-adrenal axis after radiation exposure. Plasma adrenocorticotropin and corticosterone levels were significantly increased after total-body and abdominal irradiation 3 days after exposure, in parallel with decreased labeling of corticotrophin-releasing factor mRNA in the parvocellular region of the paraventricular nucleus of the hypothalamus. Our results suggest that ionizing radiation activates the neuroendocrine system to protect the organism from the occurrence of radiation-induced inflammation.

Studies on the neuroanatomical basis for stress-induced oestrogen-potentiated suppression of reproductive function: evidence against direct corticotropin-releasing hormone projections to the vicinity of luteinizing hormone-releasing hormone cell bodies in female rats

Various studies implicate corticotropin-releasing hormone (CRH) as a mediator for the inhibitory effects of stress on reproduction. This study was designed to elucidate the underlying neuroanatomy. The retrograde tracer cholera toxin was picospritzed into the vicinity of the luteinizing hormone-releasing hormone (LHRH) perikarya. CRH neurones were examined for the tracer in the medial preoptic nucleus (MPO), bed nucleus of the stria terminalis (BST), paraventricular nucleus (PVN), central amygdaloid nucleus (CeM), parabrachial nucleus (PB) and additional locations. Retrograde label was not detected in CRH neurones at any of these sites; nevertheless, in the MPO and PB, abundant retrogradely-labelled perikarya intermingled with CRH neurones. In the BST, CeM and PVN, sites containing major CRH cell populations, retrogradely-labelled cells were scarce or absent; however, retrograde labelling was found in adjacent regions: lateral septum, medial amygdaloid nucleus and areas bordering the PVN. Double-label in situ hybridization for the mRNAs for LHRH and the CRH type-1 receptor (CRH-R1) identified the receptor transcript at sites rostral and lateral to the LHRH neurones (in the vertical and horizontal limbs of the diagonal band) but not in the LHRH neurones. Given the ability of oestrogen to potentiate stress-induced suppression of LH release, the identification of CRH neurones immunoreactive for oestrogen receptor (ER) alpha in the MPO and for ER beta in the caudal PVN may be significant. In this context, it is also noteworthy that CRH neurones within the MPO and PB which are, respectively, immunopositive and immunonegative for ER alpha, lie within the vicinity of retrogradely-labelled cells. The present findings suggest that the means by which CRH may mediate inhibitory effects of stressors on LH release do not involve direct CRH projections to LHRH neurones; the indirect means for such regulation, and the sites at which oestrogen may potentiate the inhibitory response, remain to be established.

Blunted stress responses in delayed type hypersensitivity in mice lacking the neuronal isoform of nitric oxide synthase

Nitric oxide (NO) is implicated in inflammation and hypothalamic-pituitary responses to immune stimuli; however, the specific role of NO from neurons during stress-induced immune responses remains unspecified. We measured antigen-specific delayed-type-hypersensitivity (DTH) responses in the skin of wild-type (WT) and neuronal nitric oxide synthase knockout (nNOS(-/-)) mice at baseline and after 2 h of restraint. Baseline corticosterone concentrations were higher in nNOS(-/-) than WT mice. However, stress-induced increases in corticosterone were dampened in nNOS(-/-) mice, and restraint suppressed DTH only in WT animals. Furthermore, WT mice lost more body mass after stress, and exhibited more anxiety-like behavior in the open field, than nNOS(-/-) mice. Neuronal NO appears to be involved in the neuroendocrine-immune response to stress, perhaps via glucocorticoid regulation.

Evidence of melanin-concentrating hormone-containing neurons supplying both cortical and neuroendocrine projections

In the rat, melanin-concentrating hormone-containing projections are detected in the median eminence and in the neural lobe of the pituitary. After vascular injections of the retrograde tracers fluorogold or fastblue, melanin-concentrating hormone neurons are retrogradely labeled in the rostromedial zona incerta and adjacent perifornical region. These neurons may be the source of the melanin-concentrating hormone projections toward the median eminence and posterior pituitary, and may release their secretory products into the bloodstream. After fastblue injections in the cerebral cortex and vascular fluorogold injections, some melaninconcentrating hormone neurons contain both tracers, indicating that they send collaterals in the cerebral cortex and in the median eminence/posterior pituitary. No such collaterals have been described for the classical neuroendocrine systems. The melanin-concentrating hormone system is thought to play a role in arousal in correlation with specific goal oriented behaviors such as feeding or reproduction. Some MCH neurons may be involved in such functions by modulating directly cortical activity as well as being neuroendocrine.

Nicotine-induced inflammatory decreasing effect on passive skin arthus reaction in paraventricular nucleus-lesioned wistar rats

To evaluate the relationship between nicotine and immunological inflammation, we investigated the effects of nicotine on plasma extravasation of the passive skin Arthus reaction, elicited 4 hr after sensitizing skin with antiserum, and serum corticosterone levels in rats. Pretreatment with a single subcutaneous injection of nicotine (0.4 or 0.8 mg/kg) 30 or 60 min. before antigen challenge attenuated the passive skin Arthus reaction immunological inflammation. Serum corticosterone levels were dose-dependently increased 30 and 60 min. after nicotine administration. Both markers co-varied with a similar dose-response and time course after the nicotine-treatment. In addition, we also examined these nicotine-induced responses after bilateral lesions of the hypothalamic paraventricular nucleus; both the nicotine-induced suppression of immunological inflammation and the increased serum corticosterone levels were attenuated in bilateral paraventricular nucleus-lesioned animals. Moreover, the immunological inflammatory decreasing effects of a single subcutaneous injection of nicotine (0.4 mg/kg) were antagonized by intraperitoneal preinjection with mecamylamine (1.0 mg/kg; blocking the brain nicotinic acetylcholine receptors) as well as by subcutaneous preinjection with mifepristone (30 mg/kg; a glucocorticoid receptor antagonist) but not by intraperitoneal preinjection with hexamethonium (2.0 mg/kg; a peripheral nicotinic acetylcholine receptors antagonist). Finally, intraperitoneal preinjection with cycloheximide (2 mg/kg), a protein synthesis inhibitor, abolished both the inhibitory effect of nicotine (0.4 mg/kg) on the dye leakage and the elevation of blood corticosterone levels. These findings indicate that the nicotine-induced decreasing effect on immunological inflammatory response may be related to serum corticosterone levels elevated by an activation of the paraventricular nucleus through the brain nicotinic acetylcholine receptors.

Hypophysiotropic neurons of the paraventricular nucleus respond in spatially, temporally, and phenotypically differentiated manners to acute vs. repeated restraint stress: rapid publication

Hypothalamic-pituitary-adrenal (HPA) responses to stress are initiated by parvicellular neurosecretory neurons in the medial parvicellular (mp) part of the paraventricular hypothalamic nucleus (PVH), which express corticotropin-releasing factor (CRF), among other neuropeptides. We have used an approach guided by patterns of stress-induced Fos expression to explore the manner in which anatomically and phenotypically defined components of the mpPVH respond to acute vs. repeated restraint stress. Hormonal indices of HPA activation in animals exposed to the last of 14 daily repeated restraint sessions were significantly lower than those in rats receiving a single restraint episode. Although this habituation was paralleled by global decrements in activation patterns across all PVH compartments, clear spatial-temporal differences in recruitment profiles were noted between dorsal and ventral aspects of the mpPVH. Thus, acute restraint provoked a biphasic Fos induction, which occurred first within the mpPVH and in an adjoining population of somatostatinergic cells in the periventricular region and only later within other aspects of the PVH. By contrast, Fos responses of habituated animals were monophasic and focused decisively within a discrete ventral aspect of the mpPVH. The ventral population was identified as comprising neurons that express CRF and/or enkephalin and, to a lesser extent, growth hormone-releasing factor. These results indicate a lack of homogeneity among stress-responsive parvicellular neurosecretory neurons and suggest that distinct complements of CRF cells may be preferentially involved in initiating HPA responses to acute stress and sustaining them in the repeated condition.

The suprachiasmatic nucleus and intergeniculate leaflet of Arvicanthis niloticus, a diurnal murid rodent from East Africa

Little is known about the neural substrates controlling circadian rhythms in day-active compared to night-active mammals primarily because of the lack of a suitable diurnal rodent with which to address the issue. The murid rodent, Arvicanthis niloticus, was recently shown to exhibit a predominantly diurnal pattern of activity and body temperature, and may be suitable for research on the neural mechanisms underlying circadian rhythms. This paper describes, in A. niloticus, the anatomy of two neural structures that play important roles in the control of circadian rhythms, the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL). Immunohistochemical techniques were used to examine the distribution of neuroactive peptides in the SCN and IGL, and retinal projections to these structures were traced with anterograde transport of the beta subunit of cholera toxin. In A. niloticus, distinct subdivisions of the SCN contained cell bodies with immunoreactive (IR) vasopressin, vasoactive intestinal polypeptide, gastrin-releasing peptide, and corticotropin-releasing factor. The SCN did not contain cell bodies with met-enkephalin-IR and substance P-IR, but did contain fibers with substance P-IR and neuropeptide Y-IR. Retinal fibers were present throughout the SCN, but were most densely concentrated along its ventral edge, particularly in the contralateral SCN. Retinal fibers also extended to a variety of hypothalamic regions outside the SCN, including the supraoptic nucleus and the subparaventricular region. The IGL contained cells with neuropeptide Y-IR and enkephalin-IR cells. Retinal fibers projected to both the ipsilateral and contralateral IGL. The anatomy of the SCN and IGL were compared and contrasted with that previously described for other nocturnal and diurnal species.

Effects of nitric oxide on neuroendocrine function and behavior

Nitric oxide (NO) is an unusual chemical messenger. NO mediates blood vessel relaxation when produced by endothelial cells. When produced by macrophages, NO contributes to the cytotoxic function of these immune cells. NO also functions as a neurotransmitter and neuromodulator in the central and peripheral nervous systems. The effects on blood vessel tone and neuronal function form the basis for an important role of NO on neuroendocrine function and behavior. NO mediates hypothalamic portal blood flow and, thus, affects oxytocin and vasopression secretion; furthermore, NO mediates neuroendocrine function in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes. NO influences several motivated behaviors including sexual, aggressive, and ingestive behaviors. Learning and memory are also influenced by NO. Taken together, NO is emerging as an important chemical mediator of neuroendocrine function and behavior.

Spatiotemporal patterns of secretomotor neuron generation in the parvicellular neuroendocrine system

Spatiotemporal patterns of parvicellular neurosecretory neuron generation (birthdates) were determined in the young adult male rat using a triple fluorescence labeling method. The six classic phenotypes were identified in histological sections with rabbit antisera to neurotransmitters (or related enzymes), nuclear bromodeoxyuridine was detected with a mouse monoclonal antibody, and an axonal projection to the median eminence was determined with the fluorescent retrograde tracer fast blue. The vast majority of triply labeled neurons are generated between embryonic days 12-14, during the time when magnocellular neurosecretory neurons are also generated. This pattern of neurogenesis is distinct from the well-known 'outside-in' pattern of hypothalamic neurogenesis, where the peak of lateral zone birthdates occurs on embryonic days 12 and 13, the peak of medial zone birthdates occurs on embryonic days 14 and 15, and the peak of periventricular zone birthdates occurs on embryonic days 16 and 17. Thus, neuroendocrine motoneurons may constitute 'pioneer neurons' for the various anatomically distinct regions of the periventricular zone. In addition, many intermixed neurons that express the same neurotransmitters as parvicellular neurosecretory neurons but do not send an axon to the median eminence, also appear to be generated between embryonic days 12 and 14. What these results imply about mechanisms underlying neuroendocrine motor zone differentiation is discussed.

Corticotropin-releasing factor in antinociception and inflammation

Corticotropin-releasing factor (CRF) plays a major role at the level of the hypothalamus and pituitary to control the body's response mechanisms to stressful stimuli. The recent discovery of CRF outside the central nervous system suggests that CRF may well play a similar role in peripheral tissues, most likely in a paracrine manner. While its effects in many other peripheral tissues is not known yet, CRF and its receptors are upregulated in inflammatory pain states pointing to a key role under these circumstances. Indeed, locally expressed CRF seems to act on CRF receptors on immune cells which have migrated into the area of the inflamed tissue, and induce the release of opioid peptides synthesized within these immune cells. These opioids subsequently act on peripheral opioid receptors located on peripheral sensory nerves to inhibit the transmission of painful stimuli. CRF may also affect the inflammatory response; however, these data are still controversial. The peripheral paracrine effects of CRF may be similar to those of hypothalamic CRF, i.e., to counterbalance local stressful events, such as inflammation and pain, so that they do not threaten the homeostasis of the body. Interestingly, CRF-like peptides have been identified not only in mammalians, but also in species such as the frog (Stenzel-Poore et al., 1992, Mol. Endocrinol. 6, 1716) and the teleost fish (Okawara et al., 1988, Proc. Natl. Acad. Sci. USA 85, 8439) indicating that this is a peptide that has been conserved over a long period (200 million years) across species (Lederis et al., 1990, Prog. Clin. Biol. Res. 342, 467) and that the release of ACTH-like peptides by peptides of the CRF family may represent an ancestral type of stress response (Ottaviani et al., 1992, Gen. Comp. Endocrinol. 87, 354; Tran et al., 1990, Gen. Comp. Endocrinol. 78, 351).

Serotonin and the regulation of hypothalamic-pituitary-adrenal axis function

That serotonin (5HT) is involved in regulating hypothalamic-pituitary- adrenal axis (HPA) function has long been recognized. A variety of drugs including precursors of 5HT such as 5HTP, drugs which release 5HT such as fenfluramine and drugs which act directly on 5HT receptors such as ipsapirone increase cortisol and ACTH concentrations. There is a general assumption that such stimulation occurs at a hypothalamic level. However, our increasing understanding of the complex interplay between 5HT and the HPA raises questions as to the validity of this simple model. An increasing volume of experimental research indicates that 5HT can act directly on the adrenal gland and possibly on the anterior pituitary as well. These findings have major implications for the interpretation of neuroendocrine studies of 5HT conducted in psychiatric conditions, such as depression.

Melanotropic peptides in the mammalian brain: the melanin-concentrating hormone

Melanin-concentrating hormone (MCH) has been identified in neurons of the mammalian brain. This review summarizes some current information regarding the cell biology of this neuropeptide and the topography of MCH-immunoreactive (-IR) neurons in several species including mouse, rat, hamster, guinea pig, rabbit, dog and monkey; and atlas of MCH-IR neurons in the hypothalamus and subthalamus of the brain of guinea pig is presented. Based upon the location of this MCH cell group, it is hypothesized that they may be functionally involved in circuits of extrapyramidal motor systems from striatal centers to the thalamus and cerebral cortex and to the midbrain and spinal cord.

Estrogens decrease expression of the corticotropin-releasing factor gene in the hypothalamic paraventricular nucleus and of the proopiomelanocortin gene in the anterior pituitary of ovariectomized rats

It is known that estrogens modulate the hypothalamopituitary-adrenal (HPA) axis both under resting conditions and during exposure to stress. Nevertheless, the site of action of estrogens is not still fully elucidated. We sought to determine if estrogens could act on the major hypothalamic ACTH secretagogue: corticotropin-releasing factor (CRF). Mature rats were ovariectomized (OVX) and 2 weeks later implanted with silastic capsules containing 17β-estradiol (E(2)). Animals were sacrificed 7 days later. CRF mRNA in the hypothalamic paraventricular nucleus (PVN) and proopiomelanocortin (POMC) mRNA in the anterior pituitary were measured byin situ hybridization. CRF content in the median eminence was measured by semiquantitative immunocytochemistry. E(2) treatment induced a significant decrease of CRF mRNA levels in the PVN (3.70±0.14vs 4.79±0.15 copies of probe×10(-3)/μm(3) of tissue in OVX rats,P<0.05), an accumulation of immunoreactive CRF in the zona externa of the median eminence (207±36vs 100±15% in OVX rats,P<0.05), and a decrease of POMC mRNA levels in the anterior pituitary (4.6±0.6vs 6.9±0.6 copies of probe ×10(-2)/μm(3) of tissue in OVX rats,P<0.05). These results demonstrate that estrogens have a negative effect on CRF gene expression and secretion and on POMC gene expression. Whether estrogens modulate directly the CRF-synthesizing cells or act through an increase of the glucocorticoid negative feedback remains to be determined.

Lateral septal projections onto tubero-infundibular neurons in the hypothalamus of the guinea pig

Efferent projections of the lateral septal nucleus (LS) to the preoptic area and the hypothalamus were identified in 20 female guinea pigs after iontophoretic injection of the anterograde axonal tracer Fluoro-Ruby. Tubero-infundibular (TI) neurons of the preoptic area and the hypothalamus were retrogradely labeled after intracardiac injection of Granular Blue or Fluoro-Gold. Magnocellular neurons of the supraoptic and paraventricular nuclei were also labeled. The double labeling procedure allowed an estimation of the extent of the direct relationship between LS efferents and TI neurons. Contacts between lateral septal fibers and TI cell bodies were mainly observed at the light-microscopical level in the preoptic area. A group of labeled fibers coursing along the third ventricle established sparse connections with hypothalamic periventricular TI neurons. A few appositions was observed in the infundibular (arcuate) nucleus, suggestive of a monosynaptic regulation of TI neurons by a septo-arcuate tract. Close association with labeled magnocellular neurons was also noted at the edge of the supraoptic and paraventricular nuclei. The sparse but direct connections between LS and TI neurons may be involved in the neuroendocrine functions of the LS.

Reciprocal synaptic relations between CRF-immunoreactive- and TRH-immunoreactive neurons in the paraventricular nucleus of the rat hypothalamus

By double immunoelectron microscopy, we studied synaptic relations between corticotropin-releasing factor (CRF)-immunoreactive (ir) and thyrotropin-releasing hormone (TRH)-ir neurons in the paraventricular nucleus (PVN) of the rat hypothalamus. CRF-ir and TRH-ir neurons made reciprocal synaptic connections in the medial and periventricular parvocellular regions. These results may suggest that both the parvocellular neurons interplay on their hypophysiotropic functions within the PVN.

Ultrastructural localization and afferent sources of corticotropin-releasing factor in the rat rostral ventrolateral medulla: implications for central cardiovascular regulation

We investigated the ultrastructural localization, afferent sources, and arterial pressure effects of corticotropin-releasing factor (CRF) in the nucleus reticularis rostroventrolateralis (RVL), a region of the ventrolateral medulla containing C1 adrenergic neurons and sympatho-excitatory reticulospinal afferents to sympathetic preganglionic neurons. A polyclonal antibody to CRF was localized in acrolein-fixed sections through the rat RVL by the peroxidase-antiperoxidase (PAP) method. Light microscopy showed that 1-7 perikarya/30 micron section and numerous varicose processes contained CRF-like immunoreactivity (CRF-LI). By electron microscopy, CRF-LI was most intensely localized to large (80-100 nm) dense-core vesicles within numerous terminals and a few perikarya and large dendrites. Approximately half of the terminals containing CRF-LI were in direct contact with unlabeled perikarya or dendrites; the remainder were in apposition to either unlabeled terminals or astrocytes. Most synaptic specializations were asymmetric synapses on small, unlabeled dendrites. To examine potential extrinsic sources of CRF-containing terminals in the C1 area of the RVL, PAP immunocytochemical localization of CRF was combined with retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). In all cases examined, a number of dually labeled neurons were found in the paraventricular nucleus (PVN) of the hypothalamus and a few dually labeled neurons were observed in the nuclei of the solitary tract; these labeled neurons were ipsilateral to the unilateral injection of WGA-HRP into the C1 area. Fewer dually labeled perikarya were detected in the lateral hypothalamic area and the lateral parabrachial nuclei, ipsilateral to the WGA-HRP injection. Additional physiological studies showed that bilateral microinjections of CRF into the C1 area of the RVL of urethane-anesthetized rats elicited a dose-related increase in arterial pressure. The results suggest that within the C1 area of the RVL, CRF released from terminals, arising predominantly from the PVN of the hypothalamus and probably from local neurons as well, may excite sympathoexcitatory reticulospinal neurons.

Hypothalamic melanin-concentrating hormone and alpha-neoendorphin-immunoreactive neurons project to the medial part of the rat parabrachial area

Neurons in the middle and posterior parts of the lateral hypothalamus project to the parabrachial area, and in particular to the gustatory relay-station located in the medial part of this area. In the present study we have examined some of the neuropeptide immunoreactivities of the lateral hypothalamus neurons that project to the gustatory region of the parabrachial area. By coupling retrograde transport and immunohistochemistry, we found that 50-60% of medial parabrachial area-projecting cells located in the juxta-capsular region of the posterior lateral hypothalamus are labeled by rat melanin-concentrating hormone antiserum, while 28% of the retrogradely labeled neurons located in the perifornical lateral hypothalamus are visualized with alpha-neoendorphin antiserum. Moreover, a large number of terminals distributed throughout the parabrachial nucleus are immunoreactive to melanin-concentrating hormone or alpha-neoendorphin antisera. These immunoreactivities are not co-localized within the same lateral hypothalamic neurons. The potential role of these peptidergic projections in the reward mechanisms elicited in the medial parabrachial area and in the control of palatability is discussed.

Corticotropin-releasing hormone neurons in the paraventricular nucleus project to the external zone of the median eminence: a study combining retrograde labeling with immunocytochemistry

Corticotropin-releasing hormone (CRH) is the major regulator of the pituitary-adrenal axis. CRH-immunoreactive perikarya are widely distributed in the central nervous system; however, only those which participate directly in the regulation of adrenocorticotropin are connected to the portal circulation in the external zone of the median eminence. The present study describes the identification of these hypophysiotropic neurons using retrograde labeling and CRH immunocytochemistry. Fluoro-Gold was injected peripherally then, 5 days later, the animals were treated with colchicine. Twenty-four hours later the animals were sacrificed, and their brains were immunostained for CRH with the indirect immunofluorescence technique. The results indicate that the vast majority of the Fluoro-Gold-accumulating and CRH-immunopositive perikarya (hypophysiotropic neurons) are located in the medial parvicellular subdivision of the paraventricular nucleus (PVN). However, not each CRH-immunoreactive neuron contains Fluoro-Gold, i.e. a small portion of these neurons project to areas of the brain other than the median eminence. The anterior, lateral and periventricular subdivisions of the PVN also contain hypophysiotropic CRH-immunoreactive perikarya, however, their number is much less than in the medial parvicellular subdivision. Scattered double-labeled cells are also present in the medial preoptic area and the dorsal hypothalamus, just behind the PVN. These results support previous observations that the PVN, particularly the medial parvicellular subdivision, is the predominant source of the hypophysiotropic CRH neurons.

Nitric oxide modulates the release of corticotropin-releasing hormone from the rat hypothalamus in vitro

There is now considerable evidence that nitric oxide (NO) is an important neuroregulatory agent, but there has been very little investigation of the possible role of NO in neuroendocrine mechanisms. We have previously shown that acute rat hypothalamic explants can be used to study the regulation of hypothalamic neuropeptide release, and we have now utilised this experimental approach to investigate the putative involvement of NO in the control of the principal corticotropin-releasing hormone, CRH. We studied the direct effects of the NO precursor L-arginine (L-ARG), as well as the NO donors molsidomine and sodium nitroprusside, on both the basal and stimulated release of CRH; the stimuli used were non-specific depolarisation with potassium chloride (KCl) and the specific cytokine, interleukin-1 beta (IL-1 beta; 100 U/ml). L-ARG was tested in each experimental condition with and without contemporaneous addition of its competitive antagonist NG-monomethyl-L-arginine (L-NMMA). IL-1 beta-induced CRH release was also investigated in the presence of D-arginine (D-ARG), which is not active as a precursor to NO, and ferrous hemoglobin (Hb), a substance which is a potent inactivator of NO. None of the NO precursors (L-ARG, molsidomine, sodium nitroprusside) or antagonists (L-NMMA or Hb) was able to affect basal CRH release. However, L-ARG 10 and 100 microM were found to significantly inhibit the release of CRH induced by 40 mM KCl; CRH fell to 45% of its stimulated level at the higher dose of L-ARG. This effect was attenuated in the presence of L-NMMA at a ten-fold higher dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Enkephalin-immunoreactive neurons in the parvicellular subdivisions of the paraventricular nucleus project to the external zone of the median eminence

The enkephalin-immunoreactive neurons that project to the external zone of the median eminence were identified on thin paraffin and thick vibratome sections using a combination of retrograde labeling with peripherally administered Fluoro-Gold and immunocytochemistry. The vast majority of the enkephalin-immunoreactive neurons that project to the external zone of the median eminence (ME) reside in the paraventricular nucleus (PVN) of the hypothalamus. Within the PVN, the majority of these hypophysiotropic neurons are located in the medial parvicellular subdivision, while a smaller number can be detected in the anterior and the periventricular subdivisions. Although many enkephalin-immunoreactive neurons are present in other hypophysiotropic areas of the hypothalamus, such as the medial preoptic area, the anterior periventricular area, and the arcuate nucleus, only a few of these can be retrogradely labeled from the ME. These results provide morphological evidence for the key role of paraventricular enkephalin-immunoreactive neurons in the regulation of neuroendocrine functions.

Distribution of corticotropin-releasing hormone immunoreactivity in golden hamster brain

The distribution of corticotropin-releasing hormone-immunoreactive (CRH-IR) neurons and fibers was observed in golden hamsters. CRH-IR neurons and fibers were observed within the hypothalamus, thalamus, amygdala, cortex, midbrain, and hindbrain. The largest numbers of CRH-IR neurons were seen within the magno- and parvocellular divisions of the paraventricular nucleus of the hypothalamus and within the septum, bed nucleus of the stria terminalis, preoptic area continuum. The highest density of immunoreactive fibers was observed in the external zone of the median eminence. In addition, many immunoreactive fibers were observed within the bed nucleus of the stria terminalis and the preoptic area. The distribution obtained in hamsters was compared with previously reported distributions from rats, and both were generally similar.

Corticotropin releasing factor and galanin-containing neurons projecting to the median eminence of the rat

To identify corticotropin releasing factor (CRF)- and galanin (GAL)-containing neurons projecting to the median eminence, a retrograde tracing method with True blue was combined with a double-staining method. It was demonstrated that some True blue-labeled CRF neurons in the paraventricular nucleus were also immunoreactive for GAL. These findings support the hypothesis that GAL and CRF are simultaneously involved in regulation of ACTH secretion from the anterior pituitary.

Noradrenergic activation in the paraventricular nucleus during acute and chronic immobilization stress in rats: an in vivo microdialysis study

In vivo microdialysis was used to study the effects of single (2 h) or repeated (2 h for 7 consecutive days) immobilization (IMMO) stress on extracellular fluid concentrations of norepinephrine (NE) and the deaminated metabolites of NE and dopamine, dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC) in the paraventricular nucleus of conscious rats. During IMMO, NE, DHPG, and DOPAC levels increased markedly, with similar peak values and time courses in the repeatedly stressed and previously unstressed groups. NE levels during a 2-h baseline period were lower in the repeatedly stressed group than in the unstressed group (99 +/- 9 pg/ml vs. 167 +/- 13 pg/ml, P less than 0.05), whereas DHPG (1,697 +/- 263 pg/ml vs. 1,424 +/- 194 pg/ml) and DOPAC (5,989 +/- 863 pg/ml vs. 4,428 +/- 1150 pg/ml) levels tended to be higher, so that the NE/DHPG ratio at baseline was significantly lower in the repeatedly stressed group (P less than 0.05). The results indicate that IMMO stress enhances NE release, reuptake, metabolism, and synthesis in the PVN. Repeated exposure to IMMO may decrease the microdialysate NE/DHPG ratio by inhibiting exocytotic release or enhancing neuronal reuptake of NE. In either case, the results suggest that repeated exposure to stress alters the release and disposition of NE in the PVN of conscious animals.

The melanin-concentrating hormone system of the rat brain: an immuno- and hybridization histochemical characterization

In addition to a nonadecapeptide homologous to the teleost melanin-concentrating hormone (MCH), the amino acid sequence predicted from a rat prepro-MCH (ppMCH) cDNA suggested that at least one (neuropeptide EI, or NEI), and possibly a second (NGE), additional neuropeptide may be encoded by this precursor. Cross-reactivity with epitopes of NEI or NGE can account for reported localization of alpha-MSH, rat CRF, and human GRF in rat dorsolateral hypothalamic neurons. We have used antisera raised against rat MCH and NEI in immunohistochemical studies at the light and electron microscopic levels, along with hybridization histochemical localization of ppMCH mRNA, to define the organization of this system. As expected, ppMCH mRNA is prominently expressed in cells in the lateral hypothalamic area and zona incerta. The MCH and NEI peptides were extensively colocalized in neurons in both of these areas. In addition, smaller cell groups in the olfactory tubercle and pontine tegmentum were also positively hybridized for ppMCH mRNA and immunostained for MCH and NEI. Fibers stained for MCH and NEI were similarly, and very broadly, distributed throughout the central nervous system in patterns that generally conformed with known projection fields of the lateral hypothalamic area and zona incerta. A differential distribution was seen in at least one region, the interanterodorsal nucleus of the thalamus, which contained a prominent terminal field stained for MCH but not NEI. At the electron microscopic level, MCH-stained perikarya displayed a prominent staining associated with the Golgi apparatus; this was not encountered in NEI-stained cells. Both peptides were distributed similarly in terminals in the lateral hypothalamic area and median eminence, with staining associated principally with dense-cored vesicles. The results suggest that ppMCH-derived peptides may serve as neurotransmitters or modulators of prominence in a surprisingly expansive projection field of incerto-hypothalamic neurons. The terminal distributions of this system seem most compatible with functional roles in generalized arousal and sensorimotor integration, processes previously implicated as being subject to modulation by the lateral hypothalamic area.

Synaptic associations between oxytocin-containing magnocellular neurons and neurons containing corticotropin-releasing factor in the rat magnocellular paraventricular nucleus

In the paraventricular nucleus (PVN) of the rat hypothalamus, we determined synaptic associations between oxytocin (OXT)-containing magnocellular neurons and parvocellular neurons containing corticotropin-releasing factor (CRF) by using a double immunolabeling technique in 7 animals. In single vibratome sections of the hypothalamus, immunoreactive CRF and OXT were labeled with silver-gold particles and diaminobenzidine (DAB) chromogen, respectively. By light microscopy CRF-containing fibers appeared to be black dots, some of which encircled magnocellular perikarya labeled with brown DAB chromogen in the PVN. By electron microscopy we discriminated OXT neurons having fine DAB-chromogen particles distributed throughout the cytoplasm and on large secretory granules from CRF neurons having dense coarse particles of silver-gold. Occasional CRF axons terminated on perikarya or dendritic processes of OXT neurons, making synaptic contacts. The terminals which were characterized by having clusters of small clear vesicles and a few dense core vesicles showed equal thickenings of pre- and postsynaptic membranes at the synaptic junctions.

Novel antigenic determinant expressed in neurons of the dorsolateral hypothalamus in rat and human

Previous studies have identified a group of cells in the dorsolateral hypothalamus that project to many different areas in the CNS, such as thalamus, diagonal band of Broca, basal ganglia, cerebral cortex, hippocampus, and olfactory bulb. Their role is presently unknown, but the cells have been reported to stain for an intriguing array of putative neurotransmitter-related substances, including alpha-melanocyte-stimulating hormone (alpha MSH), melanin-concentrating hormone (MCH), human growth-hormone-releasing factor 1-37 (hGRF 1-37), corticotropin-releasing factor (CRF), metorphamide, and acetylcholine esterase. A monoclonal antibody produced in the present study, alpha C11, stains both the cell bodies of this system in hypothalamus, with a punctate pattern, and varicose fibers in the various target areas. In double-label immunocytochemical experiments in rat DLH, alpha C11 and MCH staining exactly overlaps. Concentrations of alpha MSH and MCH high enough to completely block staining with the corresponding antisera had no effect on staining with alpha C11. Similarly, CRF, hGRF 1-37, and metorphamide were unable to block alpha C11 staining. The results suggest that the antigenic epitope for alpha C11 is not contained in alpha MSH, MCH, CRF, hGRF, or metorphamide, and thus, that alpha C11 is detecting another antigen uniquely expressed in these neurons. The punctate appearance of staining in the hypothalamus and the concentration of staining in fiber varicosities suggests that the alpha C11 epitope may be involved in synaptic function.

Current status of brain hypophysiotropic factors: morphologic aspects

Nearly 40 putative neurotransmitters and other chemical messengers, mostly peptides, are present in the median eminence that constitutes the final common pathway for signals from the brain to the pituitary. The majority of them are produced in perikarya located in different nuclei of the hypothalamus; however, some of them arise from the brainstem. The neurons contacting capillaries of the median eminence (hypophysiotropic neurons) are intermixed with neurons containing the same transmitter (hypophysiotropic factor(1)), but projecting to other areas of the brain. Depending on their site of release, the hypophysiotropic factors may function as neurohormones acting an the pituitary or neurotransmitters affecting the activity of other neurons in the central nervous system. Based on retrograde tracing studies in combination with immunocytochemistry, the origin of many nerve terminals in the median eminence has been determined.

ACTH and enkephalin axonal input to paraventricular neurons containing c-fos-like immunoreactivity

The presence of c-fos like protein in neuronal nuclei has been observed in several areas of the central nervous system. It is associated with activation of these neurons by specific stimuli, in particular stressful stimuli. The present study investigated the expression of c-fos-like immunoreactivity in the paraventricular nucleus (PVN) of the hypothalamus following stimulation of small diameter, nociceptive afferents in the hindfoot of the rat. The afferent innervation to these c-fos containing PVN neurons was examined in order to identify putative neurotransmitters which might modulate the activity of stress responsive, i.e. c-fos containing neurons in the PVN. Adrenocorticotropic releasing hormone (ACTH), enkephalin (ENK), and corticotropin releasing factor (CRF), peptides whose functions have been related to the regulation of stress behavior, were selected to investigate their potential innervation of c-fos immunolabeled neurons. Analysis of immunocytochemically double-labeled vibratome and semi-thin plastic-embedded sections revealed that ACTH and ENK immunoreactive axonal varicosities were present in close anatomical proximity to a substantial number of parvocellular PVN neurons that contained c-fos in response to noxious stimulation. Few c-fos containing PVN neurons were apposed by CRF axonal varicosities. The resulting data show that a large number of c-fos immunoreactive PVN neurons, though not the majority, is innervated by ACTH and ENK. This suggests that the activity of stress responsive, c-fos expressing neurons can substantially be modulated and regulated by ACTH and ENK and to a lesser degree by CRF.

Hypophysiotrophic TRH-producing neurons identified by combining immunohistochemistry for pro-TRH and retrograde tracing

To determine hypophysiotrophic thyrotropin-releasing hormone (TRH)-producing neurons in the rat hypothalamus, we employed a combination of the immunohistochemistry for TRH prohormone (pro-TRH) and the retrograde tracing of neurons that project to the median eminence (ME) by injecting biotinylated wheat germ agglutinin (WGA) into the ME. In intact rats, immunoreactive pro-TRH-positive neurons occurred in the parvicellular paraventricular nucleus (parvi-PVN), basal part of the anterior and lateral hypothalamus, perifornical area and dorsomedial nucleus, especially accumulating in the parvi-PVN. Twenty-four hours after injection of the WGA into the middle portion of the ME, we found neurons that incorporated the lectin in the anterior periventricular area, the PVN, and the arcuate nucleus. When we examined serial sections consecutively stained with anti-WGA, anti-pro-TRH, and anti-WGA, most of the pro-TRH-labeled neurons in the medial parvi-PVN and a part of the neurons in the anterior periventricular area and in the anterior, lateral, and dorsal parvi-PVN appeared to incorporate WGA. These neurons may correspond with the hypophysiotrophic TRH-synthesizing neurons in the rat hypothalamus.

Existence of mutual synaptic relations between corticotropin-releasing factor-containing and somatostatin-containing neurons in the rat hypothalamus

Light microscopic studies of vibratome sections, which were double-immunostained for corticotropin-releasing factor (CRF) and for somatostatin (SS), suggested the presence of reciprocal synaptic relations between neurons containing immunoreactive (ir) CRF and those containing ir SS in the parvocellular paraventricular nucleus (parvo-PVN) and in the anterior periventricular area (APV) of the rat hypothalamus. In the sections the peptides included in neuronal fibers were labeled black with silver-gold particles, and the peptides included in neuronal cell bodies were labeled brown with diaminobenzidine (DAB). Thereby the brown cell bodies appeared to be surrounded by several black nerve terminals. In electron microscopic studies, the labeling was mostly performed in reverse fashion, because of the convenience for observing the ultrastructural details of the nerve terminals. The neuroplasm of the postsynaptic perikarya and dendrites was labeled with gold-coated silver grains, while the presynaptic axonal terminals were shown with scattered DAB particles. Granular structures in the perikarya or axonal terminals were labeled distinctively. The synaptic morphology appeared to be either symmetric or asymmetric connections. Then we found synaptic connections between presynaptic ir SS containing fiber terminals and postsynaptic ir CRF containing perikarya in the parvo-PVN, and those ir CRF containing fiber terminals and ir SS containing perikarya in the APV. The existence of such a reciprocal association between CRF and SS neurons may suggest that these neuronal systems intervene among different functional systems in the hypothalamus.

Corticotropin-releasing hormone-containing neurons in the hypothalamo-hypophyseal system in rats six weeks after bilateral lesions of the paraventricular nucleus

Corticotropin-releasing factor-like immunoreactive nerve fibers and varicosities are present in the pituitary stalk and median eminence 6 weeks after bilateral lesioning of the hypothalamic paraventricular nucleus. The total immunoreactivity may reach 10% of the control density. The origin of these fibers was investigated 3 days after hypothalamic transections in paraventricular-lesioned (6 weeks postoperatively) rats. Accumulations of corticotropin-releasing factor immunostaining were observed in the proximal portions of the transected axons and in neuronal perikarya. Fibers with retrograde labeling were seen lateral and dorsolateral from the sagittally oriented knife cuts which transected the retrochiasmatic area and cells were found in the supraoptic nucleus and in the perifornical nucleus (dorsal-dorsolateral to the fornix), ipsilateral to the lesion. No corticotropin-releasing factor immunostained cells were seen in other hypothalamic or preoptic nuclei which project to the median eminence or the posterior pituitary. Corticotropin-releasing factor containing cells in the supraoptic and perifornical nuclei may have an importance in stress response in rats with long-term paraventricular lesions.

Immunohistochemical approach to the functional morphology of the hypothalamic-hypophysial system

Immunohistochemical studies at the light and electron microscopic levels have provided much information on functional morphology in the hypothalamic-hypophysial system. The present paper describes the immunohistochemical techniques available at present and their use to determine the localizations of neurons containing hypophysiotrophic substances, the co-storage of plural signals in these neurons, and the synaptic regulation of these neurons in rats.