Immunohistochemical demonstration of the localization of corticotropin releasing factor-containing neurons in the hypothalamus of mammals including primates

Toxicity of Pexacerfont, a Corticotropin-Releasing Factor Type 1 Receptor Antagonist, in Rats and Dogs

Pexacerfont is a corticotropin-releasing factor subtype 1 receptor antagonist that was developed for the treatment of anxiety- and stress-related disorders. This report describes the results of repeat-dose oral toxicity studies in rats (3 and 6 months) and dogs (3 months and 1 year). Pexacerfont was well tolerated in all of these studies at exposures equal to or greater than areas under the curve in humans (clinical dose of 100 mg). Microscopic changes in the liver (hepatocellular hypertrophy), thyroid glands (hypertrophy/hyperplasia and adenomas of follicular cells), and pituitary (hypertrophy/hyperplasia and vacuolation of thyrotrophs) were only observed in rats and were considered adaptive changes in response to hepatic enzyme induction and subsequent alterations in serum thyroid hormone levels. Evidence for hepatic enzyme induction in dogs was limited to increased liver weights and reduced thyroxine (T4) levels. Mammary gland hyperplasia and altered female estrous cycling were only observed in rats, whereas adverse testicular effects (consistent with minimal to moderate degeneration of the germinal epithelium) were only noted following chronic dosing in dogs. The testicular effects were reversible changes with exposure margins of 8× at the no observed adverse effect level. It is not clear whether the changes in mammary gland, estrous cycling, and testes represent secondary hormonal changes due to perturbation of the hypothalamic–pituitary–adrenal axis or are off-target effects. In conclusion, the results of chronic toxicity studies in rats and dogs show that pexacerfont has an acceptable safety profile to support further clinical testing.

Stress axis plasticity during vestibular compensation in the adult cat

The postural, ocular motor, perceptive and neurovegetative syndromes resulting from unilateral vestibular neurectomy (UVN) symptoms could generate a stress and thereby activate the hypothalamo-pituitary-adrenal (HPA) axis. This study was aimed at determining whether UVN causes changes in the activity of the HPA axis, and if so, evaluating the time course of changes associated with UVN syndrome. At the cellular level, corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) immunoreactivity (Ir) were analyzed and quantified in the paraventricular nucleus (PVN) and the vestibular nuclei (VN) complex of cats killed early (1 and 7 days) or late (30 and 90 days) after UVN. Dopamine-beta-hydroxylase (DbetaH), the enzyme synthesizing noradrenaline was examined in the locus coeruleus (LC) in these same cats. At the behavioral level, the time course of recovery of the postural and locomotor functions was quantified at the same postoperative delays in another group of UVN cats. Results showed a significant bilateral increase in the number of both AVP-Ir and CRF-Ir neurons in the PVN and an increase of DbetaH-Ir neurons in the LC at 1, 7 and 30 days after UVN. This increased number of neurons was no longer observed at 90 days. Conversely, a significant bilateral decrease of CRF-Ir neurons was observed in the VN at these same postlesion times, with a similar return to control values at 90 days. Our behavioral observations showed strong posturo-locomotor functional deficits early after UVN (1 and 7 days), which had recovered partially at 30 days and completely by 90 days postlesion. We demonstrate a long-lasting activation of the HPA axis, which likely reflects a chronic stress, experienced by the animals, which corresponds to the time course of full vestibular compensation, and which is no longer present when the animals are completely free of posturo-locomotor symptoms at 90 days.

Corticotropin-releasing factor (CRF) in stress and disease: a review of literature and treatment perspectives with special emphasis on psychiatric disorders

The CRF family of neuropeptides and receptors is involved in a variety of stress responses, in the regulation of appetite, metabolic and inflammatory processes as well as intestinal movements. From a primarily psychiatric perspective, the present paper reviews the literature on its anatomy, physiology and its involvement in psychiatric, neurological and inflammatory diseases. Finally, recent developments in the pharmacological aspects of CRF in these diseases are reviewed.

Vasopressin and the regulation of hypothalamic-pituitary-adrenal axis function: implications for the pathophysiology of depression

The role of arginine vasopressin (AVPNP) in the control of adrenocorticotropic hormone (ACTH) secretion is explored, and in particular, its involvement in various stress response paradigms which may be of relevance in our understanding of the pathophysiology of depression. VP is released from two sites in the hypothalamus; the parvicellular division of the paraventricular nucleus (PVN), where corticotropin releasing hormone (CRH) is also formed, and from the magnocellular neurons of the supraoptic nucleus (SON) and the PVN. The intricate interaction with CRH, the other main ACTH secretagogue, and with glucocorticoids, the inhibitory feedback component of hypothalamic-pituitary-adrenal-axis (HPA) activity, is outlined. That VP plays an important role in the stress response is now beyond doubt. Examination of the impact of psychological stressors on the differential expression of VP and CRH at a hypothalamic and pituitary level has been facilitated by advances in molecular biological techniques. Of importance has been the cloning of the V1b receptor gene, the receptor at which AVP is active in the anterior pituitary. Chronic stress paradigms, associated with HPA hyperresponsiveness, and ACTH release following a novel superimposed stress, have been found with relative consistency to show a shift in the CRH:AVP ratio. This may relate to differing feedback sensitivity of AVP to glucocorticoid feedback restraint and the greater responsivity of AVP over CRH to chronic stimulatory stress input. Evidence for functionally distinct pools of ACTH releasing corticotropes, and the finding that AVP levels more closely correlate with ACTH levels than do CRH levels, suggest a more dynamic role for AVP in activity of the stress axis, and a primarily permissive function for CRH. The renewed interest in the role of VP in HPA axis activity may have important implications for furthering our understanding of psychiatric conditions such as depression, where significant dysregulation of this axis is seen. Elevated baseline cortisol, dexamethasone non-suppression and blunted CRH/ACTH release have been consistently documented. The possible contribution of VP to this hyperactivity, despite its known synergy with CRH, has been largely neglected. In animal models there is clear evidence that chronic psychological stressors increase the ratio of AVP to CRH production. Psychosocial stressors are intrinsically linked with depressive illness. The finding of elevated levels of AVP in postmortem studies of depressives and the lowering of CSF AVP levels by antidepressants, raises the question of the precise role of AVP in the overactivity of the HPA in depression, a finding that is currently attributed to overdrive of its HPA regulatory companion, CRH.

Immunohistochemical localization of corticotropin-releasing factor, [arginine8]-vasopressin and oxytocin neurons in the goat hypothalamus

Distribution patterns of corticotropin-releasing factor (CRF), [arginine8]-vasopressin (AVP) and oxytocin (OXY) neurons were examined immunohistochemically in the female goat hypothalamus. The majority of the CRF immunoreactive (-IR) cells were located in the parvocellular part of the paraventricular nucleus (PVN) with smaller population found in the magnocellular part of the PVN. CRF-IR cells were also found in the suprachiasmatic nucleus, the preoptic area and around the fornix in the caudal part of the hypothalamus. AVP- and OXY-IR cells were similarly distributed in the hypothalamus. The majority of AVP- and OXY-IR cells were observed in the magnocellular part of PVN and the supraoptic nucleus. Smaller numbers of AVP- and OXY-IR cells were found in the parvocellular part of the PVN and lateral hypothalamic area. AVP-IR but not OXY-IR cells were located in the suprachiasmatic nucleus. CRF-IR fibers were concentrated in the external palisade zone of the median eminence (ME) with a few fibers found in the internal palisade zone of the ME, whereas AVP- and OXY-IR fibers were concentrated in the internal palisade zone of the ME with a few fibers found in the external zone. These results support the view that not only CRF but also AVP and OXY are released into the hypophysial portal blood and involved in the control of pituitary endocrine function in ruminant species.

State-dependent cellular activity patterns of the cat paraventricular hypothalamus measured by reflectance imaging

Activity within the cat paraventricular hypothalamus (PVH) during sleep and waking states was measured by quantifying intrinsic tissue reflectivity. A fiber optic probe consisting of a 1.0 mm coherent image conduit, surrounded by plastic fibers which conducted 660 nm source light, was attached to a charge-coupled device camera, and positioned over the PVH in five cats. Electrodes for assessing state variables, including electroencephalographic activity, eye movement, and somatic muscle tone were also placed. After surgical recovery, reflected light intensity was measured continuously at 2.5 Hz during spontaneously varying sleep/waking states. Sequential state transitions from active waking to quiet waking, quiet sleep and active sleep were accompanied by progressively increased levels of PVH activity. Overall activity was highest during active sleep, and decreased markedly upon awakening. Moment-to-moment activity oscillated in the 0-0.1 Hz range, especially during active sleep and active waking; this oscillation diminished during quiet sleep. Distinct sub-regions of enhanced or diminished activity emerged within the imaged area in a state-dependent manner. We conclude that PVH activity changes with behavioral state in a regionally specific manner, and that overall activity increases during quiet sleep, and is even more enhanced in active sleep. PVH activation could be expected to stimulate pituitary release of adrenocorticotropic hormone (ACTH) and affect input to autonomic regulatory sites. Since ACTH and corticotropin releasing factor elicit arousal, and since the PVH projects to other brain areas which modulate state, we speculate that the PVH plays a role in shaping characteristics of sleep/waking states.

Hypothalamic and extrahypothalamic sauvagine-like immunoreactivity in the bullfrog (Rana catesbeiana) central nervous system

In the present study, immunocytochemistry and radioimmunoassay were used to investigate the presence of sauvagine in both hypothalamic and extrahypothalamic areas of the central nervous system (CNS) of the bullfrog (Rana catesbeiana) using a specific antiserum raised against synthetic non-conjugated sauvagine (SVG), a frog (Phyllomedusa sauvagei) skin peptide of the corticotropin-releasing factor (CRF) family. Sauvagine-immunoreactive (SVG-ir) bipolar neurons were found in the nucleus of the fasciculus longitudinalis medialis located in the rostral mesencephalic tegmentum. In the tectal mesencephalon, beaded SVG-ir fibres were present in the optic tectum, and in the torus semicircularis. Abundant SVG-ir varicose fibres were seen in the granulosa layer of the cerebellum, the nucleus isthmi, and the obex of the spinal cord. SVG-ir fibres were also seen by the alar plate of the rombencephalon. In the diencephalon, the antiserum stained parvocellular neurons of the preoptic nucleus (PON) which extended their dendrites into the cerebro-spinal fluid (CSF) of the third ventricle and projected their ependymofugal fibres to the zona externa (ZE) of the median eminence. Immunopositive fibres were also present in the medial forebrain bundle at the chiasmatic field, the posterior thalamus, the pretectal gray, and the ventrocaudal hypothalamus. In the telencephalon (forebrain), SVG-ir fibres were seen in the medial septum, the lateral septum, and the amygdala. The SVG immunoreactivity could not be detected after using the SVG antiserum previously immunoabsorbed with synthetic SVG (0.1 microM), but immunoblock of the antiserum with sucker (Catostomus commersoni) urotensin I (sUI), sole (Hippoglossoides elassodon) urotensin I, sucker CRF, rat/human CRF, or ovine CRF (0.1-10 microM) did not eliminate visualization of the immunoreactivity. In radioimmunoassay, the SVG antiserum did not crossreact with sUI, or the SVG fragments SVG1-16, SVG16-27, and SVG26-34, but it recognized the C-terminal fragment SVG35-40. Crossreaction with mammalian ovine CRF and rat/human CRF was negligible. Both hypothalamic and mesencephalic extracts gave parallel displacement curves to SVG. The results suggest the presence in the bullfrog brain of a SVG-like neuropeptide, i.e., a peptide of the CRF family, that either is SVG or shares high homology with the C-terminus of that peptide. The function of this neuropeptide in amphibians is not known at this time, but based on its anatomical distribution to the ZE it could affect the release of adrenocorticotropin (ACTH) or other substances from the amphibian pars distalis. Involvement of the SVG-like peptide in behavioural (forebrain), visual (thalamus-tegmentum mesencephali-pretectal gray-optic tectum), motor coordination (cerebellum), and autonomic (spinal) functions, as well as an undefined interaction with the CSF in the bullfrog, seems likely.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Autoradiographic characterization of [3H]imipramine and [3H]citalopram binding in rat and human brain: species differences and relationships to serotonin innervation patterns

The neuroanatomical distribution of binding sites for [3H]imipramine and [3H]citalopram was assessed by in vitro autoradiography in select regions of the rat and human forebrain. To determine involvement of serotonin-containing terminals in the binding of [3H]imipramine and [3H]citalopram, binding of these compounds was measured in rats after destroying serotonin-containing neurons with 5,7-dihydroxytryptamine (5,7-DHT). Treatment with this neurotoxin decreased serotonin content by 90% and reduced [3H]citalopram binding to a similar extent. These results demonstrate that [3H]citalopram binding is a reliable marker for serotonin-containing terminals. Binding of [3H]imipramine was reduced by only 15-35% after 5,7-DHT treatment. These latter results suggest that only a small fraction of [3H]imipramine binding to brain sections is associated with serotonergic terminals under standard conditions used in autoradiographic studies with the ligand. Dose-response effects of fluoxetine and desipramine on displacement of [3H]imipramine binding in forebrain regions indicate that the ligand labels predominantly high capacity, low affinity binding sites. To determine the utility of the rat brain as a model for [3H]imipramine and [3H]citalopram binding in the human brain, binding of the ligands was compared in human and rat hypothalamus, amygdala, and hippocampus. The pharmacological characteristics of [3H]imipramine and [3H]citalopram binding were similar in the rat and human brain. However, substantial species differences were observed in topographic patterns of [3H]imipramine binding within the hippocampus and hypothalamus. The distribution of [3H]citalopram binding sites within the amygdala and hypothalamus were also strikingly different in rats compared to humans. This work provides the first demonstration that marked species differences exist in the topography of serotonergic innervation and in the distribution of [3H]imipramine binding sites within the rat and human brain regions examined.

Opioid synapses on vasopressin neurons in the paraventricular and supraoptic nuclei of juvenile monkeys

Opioid peptide- as well as vasopressin-containing neurons synapse on gonadotropin releasing hormone neurons in juvenile macaques. In this study we performed double-label immunostaining for opioid and vasopressin neurons in the paraventricular and supraoptic nuclei in order to assess their interrelationships. Neuroendocrine neurons in the hypothalamus were prelabeled by microinjection of electron-dense retrograde tracer into the median eminence, and were easily identified in frontal Vibratome sections. Sections through the paraventricular and supraoptic nuclei were immunostained for vasopressin with the peroxidase-antiperoxidase technique, and for opioids using the indirect immunogold method. By light microscopy, opioid-immunoreactive inputs appeared to innervate an average of 39% of the vasopressin neurons in the paraventricular nucleus and 33% in the supraoptic nucleus, and were more prevalent anteriorly. Clusters of opioid afferents formed cup-like calices around major processes of many vasopressin neurons, especially in the paraventricular nucleus. Electron microscopy revealed that these groups of opioid axon terminals made frequent symmetrical and fewer asymmetrical synapses on both neuroendocrine and non-neuroendocrine vasopressinergic cell bodies and dendrites. Our study did not reveal vasopressin-opioid synapses in these hypothalamic nuclei, but this does not preclude the possibility of their existence elsewhere. These results indicate that opioid afferents modulate vasopressin neuronal activity in the monkey paraventricular and supraoptic nuclei. Previous results have suggested that corticotropin releasing hormone acts via vasopressinergic neurons to stimulate opioid neuronal activity and to inhibit gonadotropin releasing hormone release. Taken together, the data suggest that stressful stimuli could initiate a series of neuropeptidergic interactions which ultimately alter pulsatile gonadotropin releasing hormone secretion and thus gonadotropin secretion in primates.

Distribution of corticotropin-releasing-factor-like immunoreactivity in brainstem of two monkey species (Saimiri sciureus and Macaca fascicularis): an immunohistochemical study

Immunohistochemical methods were utilized to systematically map the distribution of corticotropin-releasing-factor-like immunoreactivity (CRF-LI) in the diencephalon, mesencephalon, and rhombencephalon of two monkey species (Saimiri sciureus and Macaca fascicularis). A primary antiserum directed against the human form of the peptide was utilized. Immunoreactive neuronal perikarya and processes were evident in numerous areas, and the distributions of these elements were similar for the two species. As previously reported for rats, monkeys, and human, intense immunoreactivity was evident in putative hypophyseal neurons in the parvicellular component of the paraventricular nucleus of the hypothalamus and in fibers extending from this area into the median eminence. The results for other brainstem regions, most of which have been previously examined for CRF-LI only in rats, indicate that many similarities exist between rats and monkeys in the distribution of this peptide in brainstem extrahypophyseal neuronal circuits, although substantial differences are also evident. For example, immunoreactive perikarya previously observed in other hypothalamic nuclei in rats were not evident in monkeys. Conversely, in monkeys, unlike rats, labeled perikarya were evident in several thalamic nuclei, especially in the intralaminar complex. Also, two large groups of immunoreactive neurons which have generally not been observed in rat studies were present in the mesencephalon and rhombencephalon. In the mesencephalon this consisted of a group of neurons just lateral to the mesencephalic tegmentum, extending throughout the rostral-caudal extent of the midbrain. In the rhombencephalon, labeled perikarya were observed throughout the inferior olive. Some of the differences between rats and monkeys in the locations of labeled perikarya may be due to differences in antiserum specificity and/or sensitivity, or they may result from the fact that colchicine pretreatment was not utilized in the present study. The distributions of immunoreactive fibers also exhibited similarities and differences between monkeys and rats. The most striking terminal fields observed in the present study which have not been previously described are a moderate-to-dense field within and adjacent to presumed dopamine-containing neurons in the substantia nigra pars compacta, a dense innervation of certain subdivisions of the interpeduncular nucleus, and a regionally and parasagittally organized distribution of fibers in the Purkinje cell and molecular layers of the cerebellar cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Topographical distribution of CRF immunoreactivity in the pigeon brain

The distribution of corticotropin-releasing factor (CRF) immunoreactivity was demonstrated by immunocytochemistry in intact and colchicine-treated pigeons. Colchicine injections were administered at different times related to the circadian activity of the CRF-adrenocorticotropin (ACTH)-corticosterone axis. Three CRF antisera were used, two directed against synthetic rat CRF and one directed against synthetic ovine CRF. No fundamental differences appeared in the pigeon brain with respect to the specific CRF antiserum used. The most effective colchicine injection times corresponded to hypersecretion in the corticotropic axis. CRF-immunopositive neurons were scattered throughout the pigeon brain. In addition to the paraventricular hypothalamic system, which is involved in adenohypophysial ACTH regulation, several other hypothalamic and extrahypothalamic areas showed CRF neurons. The distribution suggests that CRF may also act as a modulator and a neurotransmitter. Two hypothalamic paraventricular nucleus-median eminence CRF pathways are described here. Moreover, CRF-immunopositive reactions were observed in specific areas of cerebral ventricle walls, suggesting that CRF may be released into the cerebral fluid.

Immunohistochemical identification of corticotropin releasing factor-containing neurons projecting to the stalk-median eminence of the rat

The site of origin of CRF-containing projections to the rat median eminence was studied with immunofluorescence for CRF in combination with the retrograde transport of True blue. After the injection of True blue into the median eminence, retrogradely-labeled CRF producing neurons were identified in the medial division of the paraventricular nucleus and the periventricular nucleus. CRF neurons in the preoptic region had no positive dye. The present findings demonstrate that CRF neurons in the paraventricular and periventricular nuclei project directly to the median eminence.

Organization of ovine corticotropin-releasing factor immunoreactive neurons in the canine hypothalamo-pituitary system

The distribution of corticotropin-releasing factor immunoreactive (CRF-i) cell bodies and varicose fibers in the hypothalamus and the pituitary of the canine brain was studied by indirect immunofluorescence. CRF-i cell bodies were demonstrated mainly in the periventricular zone of the third ventricle, while some CRF-i cell bodies were scattered throughout the ventral part of the caudomedial hypothalamus. CRF-positive fibers were mostly situated in the median eminence. In addition some CRF-positive fibers were detected in the ventromedial aspect of the lateral hypothalamus forming a pathway arising from the CRF-i cell bodies, running via the median eminence through the infundibular stalk and terminating in the pars nervosa of the pituitary. The localization of the cell bodies and their projection points towards a possible (patho)physiological role of this peptide-transmitter system in the release of ACTH and beta-endorphin.

The distribution of neurotransmitter-specific cells and fibers in the anteroventral periventricular nucleus: implications for the control of gonadotropin secretion in the rat

The anteroventral periventricular nucleus (AVPv), which lies in the periventricular zone of the preoptic region, is critical for normal phasic gonadotropin secretion since lesions of this nucleus abolish the progesterone-induced surge of luteinizing hormone secretion from the anterior pituitary, block ovulation, and induce persistent vaginal estrus in female rats. However, very little is known about the neurotransmitter-specific pathways associated with this nucleus. In the present study we evaluated the distribution of biochemically specific cells and fibers within the AVPv and adjacent regions by using an indirect immunohistochemical method with antisera to serotonin (5-HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin-8 (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (ACTH1-24), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). Our findings indicate that both cells and fibers containing these putative neurotransmitters are differentially distributed in and around the AVPv in accordance with the cytoarchitectonic organization of this part of the preoptic region. The AVPv itself appears to receive strong inputs from SP-, VAS-, CCK-, and SS-containing pathways, whereas the highest densities of L-ENK-, NT-, 5-HT-, NPY-, and DBH-immunoreactive fibers were found in the cell-sparse zone just lateral to the AVPv. The suprachiasmatic preoptic nucleus (PSCh), a small group of cells located ventral to the AVPv just dorsal to the optic chiasm, contained high densities of alpha-MSH- and ACTH-immunoreactive fibers, as well as substantial numbers of fibers containing catecholamines or NPY. In contrast, a dense plexus of VAS-stained fibers was distributed fairly evenly throughout the AVPv and PSCh. Numerous L-ENK-immunoreactive cell bodies, and moderate numbers of CCK-, NT-, and CRF-stained cell bodies were found in the AVPv. The PSCh contained many TH-stained cells (presumably dopaminergic), in addition to a moderate number of CCK-containing cell bodies, while a high density of NT- and CRF-stained cells were found in the cell-sparse zone lateral to the AVPv, in addition to several CCK-, SP-, VIP-, and TH-containing cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurotransmitter specificity of cells and fibers in the medial preoptic nucleus: an immunohistochemical study in the rat

The medial preoptic nucleus (MPN) is a sexually dimorphic complex with three major subdivisions. The cell-dense central (MPNc) and medial (MPNm) subdivisions are larger in male rats, while the cell-sparse lateral subdivision (MPNl) occupies a majority of the nucleus in females. In the present study we evaluated the distribution of possible monoaminergic and peptidergic cells and fibers within the MPN, as well as in adjacent regions of the medial preoptic area of the adult male rat. For this, we used an indirect immunohistochemical method with antisera to serotonin (5HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (1-24; ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). The results suggest that cell bodies and/or fibers crossreacting with all of these putative neurotransmitters are differentially distributed within the MPN. Within the MPNm, the densest plexuses of fibers were stained with antisera to SP and NPY, while moderate densities of fibers were stained with anti-DBH, SS, CCK, CGRP, ACTH, and alpha-MSH, and only a few fibers were stained with anti-5HT, TH, NT, VAS, and L-ENK. Moderate numbers of SP- and L-ENK-immunoreactive cell bodies, and a few SS-, NT-, CRF-, and TRH-stained cell bodies were also found within the MPNm. The MPNc contained a dense plexus of CCK-immunoreactive fibers, as well as a few CRF-immunoreactive fibers. Both fiber types were localized almost exclusively to this subdivision, while most of the others studied here appeared to avoid it selectively. This suggests that there are relatively few inputs to the MPNc, and that they tend to avoid other parts of the nucleus, although moderate densities of DBH- and NPY-immunoreactive fibers were found in both the MPNm and MPNc. The MPNc contained several CCK-immunoreactive cell bodies as well as a moderate number of TRH-stained cell bodies. Both cell types were nearly completely localized to the MPNc. The major inputs to the MPNl studied here appear to be stained with antisera to 5HT and L-ENK, although moderate numbers of NT- and CRF- immunoreactive fibers were also found in this part of the nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Corticotropin-releasing factor receptors in the pituitary gland and central nervous system: methods and overview

Studies with the radioiodinated oCRF analog, Nle21, 125I-Tyr32-oCRF have identified, characterized, and localized high affinity binding sites for CRF in anterior and intermediate lobes of rat pituitary, in anterior lobe of human pituitary, and in rat, monkey, and human brain. The pharmacology and distribution of Nle21, 125I-Tyr32-oCRF binding in the pituitary gland correlate well with the biological potency and sites of action of CRF and suggest that these CRF binding sites represent specific receptors that mediate the well-established actions of CRF on the anterior pituitary and on the intermediate lobe of the pituitary. The studies in adrenalectomized rats demonstrating that endogenous CRF is capable of modulating its receptor density provide additional evidence that the radioligand labels the functional CRF receptor. The areas of distribution of Nle21, 125I-Tyr32-oCRF binding sites in the rat CNS correlate well with the immunohistochemical distribution of CRF pathways and the pharmacological sites of action of CRF. These data confirm the established role of CRF in regulating secretion of POMC-derived peptides from the pituitary gland. In addition, the data support a physiological role for endogenous CRF in regulating CNS activity and suggest the importance of this neuropeptide in integrating endocrine and visceral functions and behavior, especially in response to stress. Studies to characterize CRF receptors and CRF-containing pathways in the brain provide a means for better understanding the various functions of this neuropeptide in different areas of the CNS. Finally, the ability to map CRF receptors in postmortem human tissue provides a basis for studying the role of CRF in a variety of endocrine, neurological, and psychiatric disorders.

Ultrastructural alterations of the paraventriculo-infundibular corticotropin releasing factor (CRF)-immunoreactive neuronal system in long term adrenalectomized rats

The corticotropin releasing factor (CRF)-immunoreactive paraventriculo-infundibular neuronal system of long-term adrenalectomized and adrenalectomized-short term dexamethasone treated rats was analyzed at the ultrastructural level using the preembedding peroxidase anti-peroxidase complex (PAP)-immunohistological method. In both groups of animals, parvocellular neurons located in the medial and dorsal subnuclei of the paraventricular nucleus (PVN) showed CRF-like immunoreactivity. The perikarya contained hypertrophied rough endoplasmic reticulum (rER) with dilated cisternae, active Golgi-complexes and numerous neurosecretory granules. The majority of the neurosecretory granules measured 80-120 nm. Dendrites of CRF-immunoreactive neurons contained labeled vesicles, secretory granules, bundles of microtubules, a well-developed smooth endoplasmic reticulum (sER) complex and free ribosomes. Unlabeled terminal boutons of axons were observed to synapse on dendrites and somata of CRF-neurons. In addition, CRF perikarya were found in direct somato-somatic apposition with both CRF-immunopositive and immunonegative parvocellular cells. Retraction of glial processes and the existence of puncta adherentia between the cell membranes characterized these appositions. Varicose CRF axons within the median eminence contained hypertrophied sER, labeled vesicles and neurosecretory granules. The preterminal portions of the CRF-axons were dilated and possessed many labeled 80-120 nm diameter granules. CRF-terminals were greatly enlarged and established direct neurohemal contacts with the external limiting basal lamina of portal vessels without the interposition of tanycytic ependymal foot-processes. These tanycytes were not CRF immunopositive. CRF positive terminals contained clusters of microvesicles, labeled small vesicles and multivesicular bodies, but fewer granular elements than were observed within the the preterminals. Many of the labeled organelles were attached to tubules of sER. Occasionally, CRF-axons were observed within the pericapillary space adjacent to portal vessels. The ultrastructural features of CRF-neurons, obtained from adrenalectomized and adrenalectomized plus short-term dexamethasone treated rats did not differ significantly from each other. The hormone content of the entire CRF-neuron was greater in the steroid treated group. Adrenocorticotrophic hormone (ACTH) synthesizing cells in the pars distalis of adrenalectomized-dexamethasone treated rats also showed increased numbers of immunopositive secretory granules (150-320 nm in diameter).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for local corticotropin releasing factor (CRF)-immunoreactive neuronal circuits in the paraventricular nucleus of the rat hypothalamus. An electron microscopic immunohistochemical analysis

The interrelationships of corticotropin-releasing factor (CRF) immunoreactive neuronal cell bodies and processes have been examined in the paraventricular nucleus (PVN) of adrenalectomized-dexamethasone treated rats. Antisera generated against ovine CRF (oCRF) were used in the peroxidase-anti-peroxidase-complex (PAP)-immunocytochemical method at both the light and electron microscopic levels. In this experimental model, a great number of CRF-immunoreactive neurons were detected in the parvocellular subdivisions of the PVN and a few scattered labelled parvocellular neurons were also observed within the magnocellular subunits. Characteristic features of immunolabeled perikarya included hypertrophied rough endoplasmic reticulum with dilated endoplasmic cisternae, well developed Golgi complexes and increased numbers of neurosecretory granules. These features are interpreted to indicate accelerated hormone synthesis as a result of adrenalectomy. Afferent fibers communicated with dendrites and somata of CRF-immunoreactive neurons via both symmetrical and asymmetrical synapses. Some neurons exhibited somatic appendages and these structures were also observed to receive synaptic terminals. Within both the PVN and its adjacent neuropil, CRF-immunoreactive axons demonstrated varicosites which contained accumulations of densecore vesicles. CRF-containing axons were observed to branch into axon collaterals. These axons or axon collaterals established axo-somatic synapses on CRF-producing neurons in the parvocellular regions of the PVN, while in the magnocellular area of the nucleus they were found in juxtaposition with unlabeled magnocellular neuronal cell bodies or in synaptic contact with their dendrites. The presence of CRF-immunoreactive material in presynaptic structures suggests that the neurohormone may participate in mechanisms of synaptic transfer. These ultrastructural data indicate that the function of the paraventricular CRF-synthesizing neurons is adrenal steroid hormone dependent. They also provide morphological evidence for the existence of a neuronal ultrashort feed-back mechanism within the PVN for the regulation of CRF production and possibly that of other peptide hormones contained within this complex.

Distribution of CRF- and tyrosine hydroxylase-immunoreactive neurons in the brainstem of the domestic fowl (Gallus domesticus)

The distribution of CRF and tyrosine hydroxylase (TH)-immunoreactive neurons was examined in the brainstem of the chicken. Very dense populations of both CRF and TH-immunoreactive (-ir) perikarya are co-extensive in separate neuronal systems throughout a large field of the rostral brainstem, encompassing locus ceruleus, the mesencephalic reticular formation, parabrachial nucleus, and the dorsal and ventral tegmental areas. They are present also in nucleus tractus solitarius, and sparsely in the ventral and lateral areas of the medulla. This co-distribution suggests that the effects of CRF upon central autonomic activity may be mediated via brainstem catecholamine systems. CRF-ir neurons alone are present also in midline nuclei, including n. centralis superior, n.annularis, n.linearis caudalis, and the raphe.

Comparative localization of neurons containing ovine corticotropin releasing factor (CRF)-like and neurophysin-like immunoreactivity in the diencephalon of the pigeon (Columba livia domestica)

Neural elements immunoreactive for ovine corticotropin releasing factor-like immunoreactivity (oCRF-LI) were shown to be present in the diencephalon of the pigeon by using peroxidase-antiperoxidase immunocytochemistry. The external zone of the anterior median eminence contains a rich network of varicose oCRF-LI fibers in close proximity to the pituitary portal capillaries. Perikarya reactive for oCRF-LI were found in several regions known to innervate the median eminence and gave rise to axons which joined the hypothalamo-hypophyseal tract. A close topographical relationship between neurophysin-containing and oCRF-LI-containing neurons was found in anterior periventricular regions. These observations suggest that oCRF-LI material might be involved in the hypothalmic control of anterior pituitary hormone secretion in birds, and that neurophysin- and oCRF-LI-producing nerve cells might be functionally coupled.

Corticotropin-releasing factor (CRF)-like immunoreactivity in the adrenal medulla

Bovine adrenal medulla extract prepared by acid-acetone or acid methanol extraction showed two peaks of CRF-like immunoreactivity on Sephadex G-50 chromatography. One eluted near the void volume and another (low molecular weight CRF-like immunoreactivity) eluted slightly before arginine vasopressin (AVP), while most of the immunoreactivity in bovine hypothalamus coeluted with synthetic ovine CRF. When low molecular weight CRF fractions were chromatographed by reversed phase high performance liquid chromatography, three CRF-like immunoreactive peaks appeared. The first peak appeared near TRH, the second one eluted near AVP and the last one eluted near somatostatin. These three peaks of immunoreactivity showed ACTH releasing bioactivity in rat pituitary cells cultures. Therefore, the adrenal medulla-CRF-like substances might be tissue-CRF which may play a role to stimulate ACTH release in the severe stress conditions.

Localization of corticotropin-releasing factor-containing neurons in the brain of the domestic fowl. An immunohistochemical study

The corticotropin-releasing factor (CRF)-containing neurons were investigated in the brain of the domestic fowl by means of the peroxidase-antiperoxidase technique at the light-microscopic level. The detection of CRF-immunoreactivity was facilitated by silver intensification. CRF-containing perikarya were found in the paraventricular, preoptic and mammillary nuclei of the hypothalamus and in some extrahypothalamic areas (nuclei dorsomedialis and dorsolateralis thalami, nucleus accumbens septi, lobus parolfactorius, periaqueductal gray of the mesencephalon, nucleus oculomotorius ventralis). Immunoreactive nerve fibers and terminals were demonstrated in the external zone of the median eminence and the organum vasculosum of the lamina terminalis. These results indicate that an immunologically demonstrable CRF-neurosecretory system also exists in the avian central nervous system.

Immunohistological detection of degenerating CRF-immunoreactive nerve fibers in the median eminence after lesion of paraventricular nucleus of the rat. A light and electron microscopic study

Corticotropin releasing factor (CRF)-immunoreactive neurons were detected in the paraventricular nuclei (PVN) of the rat brain, using both the traditional and the recently developed silver-gold intensified PAP methods at light and electron microscopic levels. The latter technique was more sensitive, compared to the classical PAP method, and proved to be highly specific at the ultrastructural level. The immunolabeled perikarya showed smooth or rough contoured fusiform or multipolar shape. Bilateral surgical destruction of PVN caused a gradual decrease in the number of CRF-immunopositive fibers of the median eminence. Following the second post-operative week, CRF-immunoreactivity practically disappeared from this area. In the case of unilateral lesion of PVN, the diminution of immunoreactivity was restricted to the ipsilateral side of the median eminence-pituitary stalk region. Applying the silver-gold intensified PAP method to electron microscopy, the detection of immuno-labeled degenerating fibers became possible, among morphologically similar, densely degenerating, but unlabeled, profiles. This study reports that CRF fibers to the capillary system of the median eminence of the rat originate principally from PVN.

CRF-immunoreactive nerve fibers in the circumventricular organs of the monkey, Macaca fuscata

The occurrence of CRF (corticotropin-releasing factor)-immunoreactive nerve fibers in the circumventricular organs of adult male monkeys, Macaca fuscata, was studied on serially sectioned brains, by means of the peroxidase-antiperoxidase technique in combination with a highly specific and sensitive CRF antiserum. CRF-containing nerve fibers were found in high concentrations in the infundibulum and, in addition, in small numbers in the posterior lobe, organum vasculosum laminae terminalis, subfornical organ, and area postrema; they were missing in the pineal body and the subcommissural organ. The CRF-immunoreactive nerve fibers distributed in these organs were located in the proximity of the blood vessels.