Immunoreactive ACTH/beta-endorphin neurons in the tubero-infundibular hypothalamus of rats

Cyclic adenosine monophosphate differentiated beta-endorphin neurons promote immune function and prevent prostate cancer growth

Pituitary adenylate cyclase-activating peptide (PACAP), a cAMP-activating agent, is highly expressed in the hypothalamus during the period when many neuroendocrine cells become differentiated from the neural stem cells (NSCs). Activation of the cAMP system in rat hypothalamic NSCs differentiated these cells into beta-endorphin (BEP)-producing neurons in culture. When these in vitro differentiated neurons were transplanted into the paraventricular nucleus (PVN) of the hypothalamus of an adult rat, they integrated well with the surrounding cells and produced BEP and its precursor gene product, proopiomelanocortin (POMC). Animals with BEP cell transplants demonstrated remarkable protection against carcinogen induction of prostate cancer. Unlike carcinogen-treated animals with control cell transplants, rats with BEP cell transplants showed rare development of glandular hyperplasia, prostatic intraepithelial neoplasia (PIN), or well differentiated adenocarcinoma with invasion after N-methyl-N-nitrosourea (MNU) and testosterone treatments. Rats with the BEP neuron transplants showed increased natural killer (NK) cell cytolytic function in the spleens and peripheral blood mononuclear cells (PBMCs), elevated levels of antiinflammatory cytokine IFN-gamma, and decreased levels of inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) in plasma. These results identified a critical role for cAMP in the differentiation of BEP neurons and revealed a previously undescribed role of these neurons in combating the growth and progression of neoplastic conditions like prostate cancer, possibly by increasing the innate immune function and reducing the inflammatory milieu.

Differential response of arcuate proopiomelanocortin- and neuropeptide Y-containing neurons to the lesion produced by gold thioglucose administration

The effect of gold thioglucose (GTG) administration on neurons containing feeding-related peptides in the hypothalamic arcuate nucleus was examined in mice. Intraperitoneal GTG injection increased the body weight and produced a hypothalamic lesion that extended from the ventral part of the ventromedial nucleus to the dorsal part of the arcuate nucleus. Neurons containing proopiomelanocortin (POMC) and neuropeptide Y (NPY) present in the dorsal part of the arcuate nucleus were destroyed by GTG. In addition, the peptide-containing fibers that extended from the remaining arcuate neurons were degenerated at the lesion site. The number of POMC-containing fibers in the paraventricular nucleus, dorsomedial nucleus, and lateral hypothalamus was found to have decreased significantly when examined at 2 days and 2 weeks after the GTG treatment. In contrast, the number of NPY-containing fibers in the lateral hypothalamus remained unchanged after the GTG treatment, probably because of the presence of an unaffected NPY-containing fiber pathway passing through the tuberal region and projecting onto the lateral hypothalamus. The number of NPY-immunoreactive fibers in the paraventricular and dorsomedial nuclei showed a moderate but significant decrease at 2 days after the GTG treatment, but it recovered to the normal levels 2 weeks later. The NPY-containing fibers were found to have regenerated across the lesion site 2 weeks later, and this might contribute to the recovery of the NPY-immunoreactive fibers in these regions. The present results first demonstrate that POMC- and NPY-containing neurons in the arcuate nucleus respond differently to the lesion produced by the GTG treatment.

Moderate hypercapnia-induced anesthetic effects and endogenous opioids

The purpose of this report is to explore the mechanisms of hypercapnia-induced antinociception. We carried out three experiments, the first to confirm whether moderate hypercapnia induces anesthetic effects, the second to determine whether naloxone reverses the anesthetic effects, and the third to evaluate whether beta-endorphin is related to the anesthetic effects. In a pre-test, we determined the optimal CO(2) concentration in a chamber which would cause moderate hypercapnia in rats. Eighteen rats were divided into control, hypercapnia, and hypercapnia plus naloxone groups in experiment 1. The naloxone group rats were injected with naloxone (10 mg/kg) intraperitoneally before gas inhalation. After 60 min gas inhalation, 10% formalin was injected into the left rear paw of all rats, and nociceptive behaviors were observed for 1 h. In experiment 2, 11 rats were divided into control and hypercapnia groups. The brain was removed and fixed under pentobarbital anesthesia. Sections were immunostained for c-Fos and beta-endorphin (ACTH) with the ABC method. All neurons double-labeled for c-Fos and beta-endorphin (ACTH) in the arcuate nucleus were counted by blinded investigators. Moderate hypercapnia (PaCO(2) 83+/-7 mmHg) reduced nociceptive behavior in the formalin test and naloxone pre-treatment attenuated this phenomenon. However, beta-endorphin-producing neurons were not activated by CO(2) inhalation. Endogenous opioids are related to moderate, hypercapnia-induced anesthetic effects, but, beta-endorphin-producing neurons in the hypothalamus were not activated by the CO(2) inhalation stress.

Estrogen modulation of two subpopulations of β-endorphin neurons in ovariectomized guinea pigs distinguished by peripherally injected fluorogold

β-endorphin released by neurons in the arcuate nucleus affects the output of several neuroendocrine systems and estrogen levels modulate the production and secretion of β-endorphin. We used intraperitoneal injection of fluorogold to retrogradely label the cell bodies of neurons that project outside the blood-brain-barrier in conjunction with immunohistochemistry for β-endorphin to dual label the subpopulation of β-endorphin neurons that project to the median eminence or other sites of access to the peripheral circulation. We found that some identified β-endorphin neurons in the arcuate nucleus of ovariectomized guinea pigs sequestered fluorogold. Approximately 7% of β-endorphin-containing cells co-localized with fluorogold. The effect of estrogen on the number of identified β-endorphin cells was examined. A single estradiol benzoate injection to ovariectomized guinea pigs 24 h prior to sacrifice dramatically decreased the total number of β-endorphin cells identified in the rostral, medial and the caudal portions of the arcuate nucleus. Also, a significantly smaller percentage of fluorogold-filled cells was found to contain β-endorphin immunoreactivity in the estrogen-treated group. These data suggest that a subpopulation of β-endorphin neurons has access to the peripheral circulation and may alter the output of neurosecretory terminals at the level of the median eminence. Furthermore, estrogen affects this subpopulation and the general population of β-endorphin neurons in the arcuate nucleus in a similar manner.

Effect of acute stress on the expression of hypothalamic messenger ribonucleic acids encoding the endogenous opioid precursors preproenkephalin A and proopiomelanocortin

In addition to the release of adenohypophysial hormones adrenocorticotropin and beta-endorphin, most types of acute stress induce rapid release of prolactin (PRL) from the anterior pituitary lobe. Endogenous opioid peptides are believed to participate in the stress-induced PRL secretion via an action within the central nervous system. In the present study, we have investigated the effect of acute stress on anterior pituitary PRL secretion and the hypothalamic expression of messenger ribonucleic acids (mRNAs) encoding precursors of the endogenous opioids Met-enkephalin and beta-endorphin. Adult male rats were subjected to 1 h of restraint and the stress-induced rise in plasma PRL was measured both during and after termination of the stress paradigm. Using quantitative in situ hybridization histochemistry, it was observed that levels of proenkephalin A mRNA increased significantly within the medial parvocellular subset of the hypothalamic paraventricular nucleus, and within the arcuate nucleus levels of proopiomelanocortin (POMC) mRNA were slightly, but significantly, increased. The employed stress paradigm also induced an elevation of anterior pituitary levels of PRL and POMC mRNAs. The present data suggest that restraint stress activates gene expression of endogenous opioid systems in the hypothalamus and that the employed stress paradigm is of sufficient magnitude to stimulate both mRNA expression and release of PRL in the anterior pituitary lobe.

Tachykinergic afferents to the rat arcuate nucleus. A combined immunohistochemical and retrograde tracing study

The location of the cells giving rise to the tachykinergic innervation of the rat arcuate nucleus was studied by combining immunohistochemistry and retrograde axonal transport of a protein-gold complex (WGA-ApoHRP-gold). Small volumes (20 nl) of this marker were injected into the arcuate nucleus of the rat. Twenty-four to 30 h later, rats were injected with colchicine. After 24-h survival time, the paraformaldehyde-fixed brains were investigated for silver intensification of the gold particles and for tachykinin immunohistochemistry. Doubly immuno-silver-labeled cells were observed mainly in brainstem structures such as raphe nuclei, central gray pontine, and laterodorsal tegmental nucleus. Intranuclear and intrahypothalamic (ventromedial, dorsomedial, premamillary, and supramamillary) cell bodies were also doubly labeled, principally ipsilateral to the injection site. Minor afferent projections arise from the medial preoptic area. This anatomohistochemical study demonstrates that the arcuate nucleus receives intra- and extrahypothalamic tachykinergic inputs and shows that infundibular neurons undergo convergent tachykinergic influences.

Morphology and function of capillary networks in subregions of the rat tuber cinereum

The differentiated cytology, cytochemistry, and functions within subdivisions of the tuber cinereum prompted this morphometric and physiological investigation of capillaries in the medium eminence and arcuate nucleus of albino rats. Morphometric studies established that the external zone of the median eminence had 3-5 times the number and surface area of true and sinusoidal capillaries than the internal or subependymal median eminence zones, or either of two subdivisions examined in the arcuate nucleus. Type-I true capillaries, around which Virchow-Robin spaces comprise 1% of arcuate tissue area, were situated proximally to the median eminence border. This finding is consistent with a premise that confluent pericapillary spaces enable infiltration of arcuate neurons by factors from capillary blood from the median eminence or Virchow-Robin spaces. Physiologically, the rate of penetration across the median eminence capillaries by blood-borne [14C]alpha-amino-isobutyric acid (a neutral amino acid used as a capillary permeability tracer) was 142 times greater than for capillaries in the distal arcuate nucleus within 12 s of tracer administration. A new finding was that the proximal arcuate nucleus had a permeability x surface area product of 69 microliters g-1 min-1, 34 times greater than that in more distal aspects of the tuber where blood-brain barrier properties exist. We also found that the microcirculatory transit time of a plasma space marker, [14C]sucrose, was considerably longer (1.2 s) in the median eminence and proximal arcuate nucleus than in the distal arcuate or ventromedial nucleus (0.4 s). By virtue of its high capillary permeability and extensive blood-tissue surface area, including the wide Virchow-Robin spaces, the median eminence external zone could be a gateway for flooding other tuberal compartments with blood-borne factors. This effect may be compounded by capillary bed specializations in the proximal arcuate nucleus where Type-I true capillaries, Type-III sinusoids, and pericapillary spaces are confluent with those in the median eminence. The results indicate that the proximal arcuate parenchyma could be exposed to circulating neuroactive substances on a moment-to-moment basis.

A small subpopulation of progesterone receptor-containing neurons in the guinea pig arcuate nucleus projects to the median eminence

In female guinea pigs, a combination of retrograde tracing and immunofluorescence for progesterone receptors (PR) was applied to determine if PR-immunoreactive (PR-IR) neurons in the arcuate nucleus (AR) send their axons directly to the median eminence (ME). Axonal projections to the ME were studied by different techniques using fluorescent dyes. From 31 adult animals, ovariectomized and primed by estradiol, small deposits of Lucifer Yellow (LY) were made on the cut surface of the ME, either by direct application of LY crystals or by iontophoresis. These techniques were carried out on excised mediobasal hypothalamus maintained in vitro and allowed visualization of AR perikarya projecting to the ME after dye diffusion in the severed axons. In another group of ten immature animals primed by estradiol, Granular Blue (GB) was injected in the jugular vein. Blood-borne GB was taken up in the ME by intact nerve endings and retrogradely transported to the perikarya of origin. PR-IR neurons and perikarya filled with LY or retrogradely labeled by GB were intermingled with each other throughout the rostrocaudal extent of the AR. Double-labeled cells, displaying PR immunoreactivity and dye labeling, were observed consistently, but their number was small. This result demonstrates that some AR neurons sending axonal projections to the ME are target cells for progesterone. As the majority of PR-IR neurons in the AR do not project to the ME, it is suggested that most PR-IR neurons present in this nucleus form local circuit projections or project to distant areas of the central nervous system.

beta-Endorphin and gonadotropin-releasing hormone synaptic input to gonadotropin-releasing hormone neurosecretory cells in the male rat

Physiological and pharmacological evidence has suggested that both endogenous opiates and gonadotropin-releasing hormone (GnRH) itself can act centrally to exert a tonic inhibition on gonadotropin secretion via an inhibition of the neurosecretion of GnRH. To determine if the effects of these two peptides might be mediated via a direct synaptic input to the GnRH neuron, we undertook a double label ultrastructural study. We were able to localize in the same tissue section beta-endorphin and GnRH. Analysis of serial sections through GnRH perikarya and dendrites in the male rat diagonal band/preoptic area revealed that almost 10% of the synapses impinging on the GnRH neuron contained beta-endorphin; an additional 10% of the terminals contained GnRH. These data provide anatomical evidence in support of both a direct modulation of GnRH release by opiates and of the presence of an ultrashort feedback loop.

Development of hypothalamic neurons in intraventricular grafts: expression of specific transmitter phenotypes

The anlages of the medial-basal hypothalamus (MBH), septopreoptic area (POA), Rathke's pouch, and the parietal cortex (CC) of rats (at 12.5, 14.5 and 16.5 days of gestation) were transplanted singly or in combination into the third ventricle of adult female rats, and the development of neurons in the grafts was investigated immunohistochemically with the use of antisera to tyrosine hydroxylase (TH), somatostatin (SRIH), ACTH, methionine enkephalin-Arg6-Gly7-Leu8 (Enk-8), rat corticotropin-releasing factor (rCRF), rat hypothalamic growth hormone-releasing factor (rhGRF), and luteinizing hormone-releasing hormone (LHRH). TH and all the peptides examined except LHRH were detected in distinct neurons in MBH grafts and in cografts of MBH plus Rathke's pouch from 12.5-day-old embryos. SRIH, rCRF, Enk-8, and TH were found in POA grafts from embryos of the same age. Although immunoreactive LHRH was first detected in neurons in POA grafts from 16.5-day-old embryos, it appeared in cografts of POA and MBH from 12.5-day-old embryos. The immunoreactive fibers developed in the grafts expressed the same characteristic behaviors as in intact brain; the fibers containing hormonal substances formed complexes with the vasculature like in the organum vasculosum laminae terminalis (OVLT) or in the median eminence, while the fibers containing neurotropic signals formed fiber networks surrounding other nerve cell bodies as if they synaptically associate. In CC grafts, the neurons contained TH, SRIH, rCRF, or Enk-8, and their axonal processes formed fiber networks. These findings suggest that all the hypothalamic neurons examined are committed by 12.5 days of gestation to develop maintaining transmitter phenotype and target recognition capacity.

Leumorphin, a novel opioid peptide, promotes lordosis in female rats

The actions of leumorphin, a recently characterized endogenous opioid peptide, oppose of most opioid peptides in facilitating lordosis reflex, a major component of female sexual behavior in the rat. Maximal lordosis appeared promptly after infusion of 1 nmol leumorphin into the ventromedial hypothalamus of ovariectomized estrogen-primed rats. This facilitation lasted for as long as 5 h, unless interrupted by midbrain infusion of an antiserum to prolactin. The result is a discovery of a novel substance of remarkable strength in facilitating lordosis, an effect presumably mediated by midbrain release of prolactin.

ACTH-immunoreactive neurons and their projections in the cat forebrain

The organization of adrenocorticotropin (ACTH)-immunoreactive (IR) cell bodies and fibers in the cat forebrain is described. ACTH-IR cell bodies are found only in and around the arcuate nucleus of the hypothalamus (ARH). They are not detected elsewhere even after pretreatment with colchicine. ACTH-IR fibers are present in discrete areas of the hypothalamus, the septo-limbic areas and in the paraventricular thalamic nucleus. Complete electrolytic lesions of the ARH destroy ACTH-IR cell bodies as well as fibers in all parts of the brain. These results suggest that, in the cat forebrain, the ARH is the only source of ACTH-IR fibers.

Some improvement in tissue preparation and colloidal-gold immunolabeling for electron microscopy

The application of freeze-substitution (FS) and freeze-drying (FD) techniques and the protein A-gold-antibody complex immunocytochemical methods are described. The two tissue-preparation techniques produced excellent ultrastructure and topographical fixation of antigens when compared with conventional tissue-preparation techniques. In the FS preparation, however, occasional extragranular immunolabeling was recognized. This may suggest the leakage of antigens from the secretory granules. The FD procedure was considered the best, since such labeling was almost negligible. The protein A-gold-antibody complexes are easily prepared and label the antigens clearly. If the protein A-coated gold particles are saturated with antibodies, there is no interaction between gold particles. Thus, multiple antigens can be determined even in single secretory granules. In fact, we demonstrated intragranular colocalization of immunoreactive oxytocin, labeled with 50-nm gold particles, and immunoreactive methionine-enkephalin, labeled with 15-nm gold particles, in the axonal terminals of the FD-prepared rat neurohypophysis. This study demonstrates the value of the use of gold-antibody complexes for immunocytochemical labeling on FS- or FD-treated tissues.

Hypothalamic thyrotropin-releasing hormone (TRH)-containing neurons involved in the hypothalamic-hypophysial-thyroid axis. Light microscopic immunohistochemistry

The localization of neurons containing immunoreactive thyrotropin-releasing hormone (TRH) was examined in the hypothalamus of intact, propylthiouracil (PTU)-treated, and colchicine-treated adult rats. In intact animals, immunoreactive TRH neurons were occasionally found in the paraventricular and dorsomedial nuclei, and in the anterior and lateral hypothalamic areas. In PTU-treated animals, the cellular appearance of the hypothalamus with the exception of the paraventricular nucleus was almost similar to that of intact animals. In the paraventricular nucleus, only the cells localized in the periventricular and medial parvocellular subdivisions significantly increased in number and became hypertrophic in comparison with intact animals. The distribution of immunoreactive fibers in the hypothalamus was almost equal among the 3 animal groups with the exception of that in the median eminence, in which the fibers were most densely concentrated in intact animals, and most sparse in PTU-treated rats. The fibers projecting into the median eminence were distinguished into the periventricular and lateral pathways, which are derived from the neurons in the periventricular and medial parvocellular subdivisions of the paraventricular nucleus, respectively. Thus, among immunoreactive TRH neurons in the hypothalamus, only those in the periventricular and medial parvocellular subdivisions of the paraventricular nucleus may be involved in the hypothalamic-hypophysial-thyroid axis.

Light and electron microscopic immunocytochemistry of beta-endorphin/beta-LPH-like immunoreactive neurons in the arcuate nucleus and surrounding areas of the rat hypothalamus

beta-Endorphin/beta-LPH-like immunoreactive neurons in the hypothalamic arcuate nucleus and its surrounding areas were visualized by light and electron microscopic immunocytochemistry. Immunoreactive processes were found in the vicinity of the pia mater, in the lateral part of the external layer of the median eminence and near the lateral wall of the third ventricle. Neuronal perikarya contained immunoreactive dense granules as well as developed cell organellae. They received neuronal inputs from other neurons through axoplasmic and axodendritic synapses. Immunoreactive neuronal processes containing dense granules and mitochondria were found as preterminal elements on non-immunoreactive neuronal soma and dendrites. Immunoreactive processes also make intimate contact with capillaries in the arcuate nucleus near the median eminence.

Topographical distribution of pro-opiomelanocortin-derived peptides (ACTH/beta-END/alpha-MSH) in the rat median eminence

The detailed distribution of adrenocorticotropin (ACTH), beta-endorphin (beta-END) and alpha-melanotropin (alpha-MSH) immunoreactivity was examined in the rat median eminence (ME) and pituitary stalk using light microscopic immunocytochemistry and radioimmunoassay (RIA). Nerve fibers and varicosities immunoreactive for ACTH/beta-END/alpha-MSH had identical distributions in the ME suggesting that they are part of the same arcuate proopiomelanocortin neuronal (POMC) system. The quantitative image analysis of POMC immunoreactive varicosities in the ME indicates no significant differences between the various rostro-caudal segments. In the main (preinfundibular) portion of the ME, a moderate density of immunoreactive elements was located in the lateral part of the internal zone and throughout the postinfundibular ME. Very few scattered varicosities were observed in the neurohemal (external) zone and in the pituitary stalk. By RIA, alpha-MSH is present in a substantially higher concentration than ACTH and beta-END throughout the ME. Knife cuts between the arcuate nucleus and ME indicate that proopiomelanocortin (POMC) fibers enter the ME in its whole rostro-caudal extent. Thus POMC neurons seem to provide innervation of structures in the internal zone but not in the neurohemal/external/zone where the portal capillary system is located. Moreover, the observation that the density of immunoreactive elements is substantially lower in the pituitary stalk than in the ME, suggests that the majority of immunoreactive fibers in the internal zone are not fibers of passage directed towards the neurohypophysis.

Endogenous opioid peptides and the control of the menstrual cycle

This paper reviews recent experimental evidence which supports a role for endogenous opioid peptides in the control of gonadotropin function. In primates, cell bodies containing endogenous opioid peptides have been located within the hypothalamus in areas rich in gonadotropin-releasing hormone (GnRH) and dopamine. The release of beta-endorphin from these hypothalamic neurons is influenced by gonadal steroids, maximal release being observed when both estradiol and progesterone are present. beta-Endorphin has been shown to decrease LH secretion, and naloxone, an opiate antagonist, reverses this action. The LH-releasing activity of naloxone parallels variations in hypothalamic beta-endorphin secretory activity, so that maximal effects are seen during the luteal phase of the cycle. Present evidence indicates that opiates exert their effect on LH via a hypothalamic site. It is concluded that increased opioid inhibition of the GnRH-LH axis is responsible for the decline in LH pulse frequency during the luteal phase. The studies provide evidence for a chemical basis rationalizing relationships between reproductive function and stress, and have further implication on other forms of amenorrhea.

Synaptic regulation of hypothalamic neurons containing ACTH by substance P

Synaptic connections between substance P (SP)- and ACTH-containing neurons in the rat arcuate nucleus were studied by a technique of combined pre- and postembedding immunohistochemical staining. The results showed that immunoreactive (ir) SP fiber terminals form synapses with ir ACTH cell bodies. This strongly suggests that the activity of ACTH neurons is under neuronal regulation by SP neurons.

Hypothalamic substance P-containing neurons. Sex-dependent topographical differences and ultrastructural transformations associated with stages of the estrous cycle

Immunoreactive substance P (ir SP)-containing neurons were examined in rat hypothalamus. In untreated males, few if any ir perikarya were found in the arcuate nucleus, but after intraventricular colchicine administration, many appeared not only in the arcuate nucleus but also in the premammillary region, posterior hypothalamic, ventromedial, dorsomedial, subthalamic and paraventricular nuclei, and zona incerta. This was also the case in females treated with colchicine on the second day of diestrus. In untreated females, perikarya were seen only in the arcuate nucleus, varying in number and ultrastructure during the estrous cycle and being maximal in number in proestrus and estrus. The perikarya possessed well-developed Golgi bodies and lamellar bodies composed of many closely apposed cisternae of endoplasmic reticulum in proestrus, and showed stacks of two or three cisternae of endoplasmic reticulum as well as lysosomes in estrus. In diestrus, the perikarya had only a few granulated vesicles and fragmental cisternae of endoplasmic reticulum. In the perikarya of colchicine-treated males, many granulated vesicles and lysosomal bodies were noted. These findings suggest that, among the widely distributed SP neurons in the hypothalamus, some in the arcuate nucleus are involved in the hypothalamic-hypophysial-gonadal axis.

Morphological evidence for synaptic junctions between substance P-containing neurons in the arcuate nucleus of the rat

The presence of synaptic junctions between substance P-containing neurons (SP neurons) was shown in the hypothalamic arcuate nucleus of rats by pre-embedding electron microscopic immunohistochemistry. The immunoreactive perikarya were synapsed by immunoreactive fiber terminals as well as immunonegative fiber terminals. The functional implication of the synapses between SP neurons is discussed in relation to autoregulatory mechanisms of the neurons.

Distribution of catecholamine neurons in the hypothalamus and preoptic region of mouse

The distribution and morphology of cells containing tyrosine hydroxylase (TH) were mapped by using the immunoperoxidase technique in the hypothalamus and preoptic area in two strains of mouse, CBA/J and BALB/cJ. On the basis of rostral-caudal contiguities between cell aggregates, hypothalamic preoptic neurons were subdivided into three arbitrary groups: (1) dorsal, (2) intermediate, and (3) ventral. New or more prominent collections of TH cells were observed, and in some regions, cells were more complexly organized than originally described. In the dorsal group, a rostral collection of small ovoid cells, previously not described, were located in the anterior preoptic nucleus (APN) of Loo ('31) and extended rostrally and ventrally into the preoptic periventricular gray. The next constituent occupied the paraventricular nucleus (PVN), and was composed of two classes of cells: (1) a small ovoid cell within anterior and medial parvocellular PVN in contiguity rostrally with a similar cell in APN and (2) a larger, angular cell within and adjacent to the lateral PVN in contiguity caudally with cells in the zona incerta (ZI). Further caudally, a larger and more pleomorphic collection of TH neurons was localized in the medial ZI, particularly at midtuberal levels. These cells were not scattered, as previously reported, but were differentiated into two clear-cut densities, a larger medial island and a more elongated lateral island. Cells of ZI, both large and small, extended caudally into the dorsal hypothalamic and subparafascicular nuclei and periventricular gray. In contrast to previous descriptions, no cells were seen in the nucleus reuniens. In the intermediate group, the most rostral constituent occupied the preoptic periventricular gray, extended as far as the lamina terminalis, and merged dorsocaudally with cells in APN. While the variably shaped cells of the hypothalamic periventricular gray (PVG) were still present in the retrochiasmatic region, a striking absence of these cells was noted at midtuberal levels between the dorsomedial and arcuate hypothalamic nuclei. At this level, a new group of small-round TH cells, resembling those of the arcuate nucleus, was identified in the dorsomedial hypothalamic nucleus (DMN). At caudal tuberal levels, similar neurons were found in the posterior hypothalamic nucleus (PH). These neurons overflowed medially into the PVG and caudoventrally into the arcuate nucleus. In the ventral group, the most rostral constituent, composed of both small and ovoid cells in the retrochiasmatic area, appeared to represent the rostral commissural portion of the arcuate nucleus (Arc).(ABSTRACT TRUNCATED AT 400 WORDS)

Axonal projections and peptide content of steroid hormone concentrating neurons

The axonal projections of cell groups containing the most dense collections of steroid hormone concentrating cells have been demonstrated with retrograde neuroanatomical tracing methods. Horseradish peroxidase revealed large numbers of neurons in ventrolateral ventromedial nucleus (VL-VM) which project to dorsal midbrain. Wheat germ agglutinin (immunocytochemical recognition method) revealed large numbers of neurons in medial basal hypothalamus (MBH) and particular subdivisions of paraventricular nucleus (PVN) that project to dorsal caudal medulla or spinal cord. Fluorescent dyes revealed that many preoptic area (POA), anterior hypothalamic (AHA), and bed nucleus of the stria terminalis (BNST) neurons project to ventral tegmental area of Tsai (VTA). Also many neurons in POA and BNST project to amygdala. A method which enabled simultaneous demonstration of the steroid binding capacity and axonal projections of neurons in the same tissue section revealed that 26-36% estradiol (E2) concentrating cells in VL-VM project to dorsal midbrain. E2 concentrating neurons in POA and BNST project to amygdala and E2 concentrating POA neurons project to VTA. These neurons, which send their axons to cell groups located in different brain regions, are probably under the genomic-regulatory influence of E2. Using a method which allows simultaneous demonstration of peptide content and steroid hormone concentrating capacity of cells, many oxytocin-neurophysin and vasopressin-neurophysin containing magnocellular neurons in the caudal PVN were found to concentrate E2. About 4% of the beta-endorphin and about 6% of the dynorphin containing neurons in the MBH concentrate E2. In contrast, virtually none (less than 0.2%) of the LHRH containing hypothalamic neurons concentrate E2.

Substance P-like immunoreactive neurons in the tuberoinfundibular area of rat hypothalamus. Light and electron microscopy

Immunoreactive substance P (ir SP) neurons were examined with special reference to their links with other neurons and blood vessels in the tuberoinfundibular hypothalamic area of normal and colchicine-treated male rats. On intraventricular administration of colchicine, ir SP neuronal cell bodies appeared in both the arcuate nucleus and the ventral portion of the ventromedial nucleus. These ir fibers were seen in the nuclei of untreated animals closely surrounding ir methionine-enkephalin and ACTH cell bodies, suggesting the presence of synaptic junctions. Electron microscopic examination of the arcuate nucleus stained with anti-SP serum showed synapses of ir SP fiber terminals on unlabeled neuronal cell bodies and fibers, some of which might be methionine-enkephalin and ACTH neurons. The ir fiber terminals contained numerous small clear and/or cored vesicles and a few large cored vesicles. Fiber terminals with the same ultrastructural characteristics were seen protruding into the pericapillary space in the external and subependymal layers of the median eminence. The possible role of the SP neurons in the tuberoinfundibular area is discussed.

Corticotropin-releasing factor is a potent inhibitor of sexual receptivity in the female rat

Corticotropin-releasing factor (CRF), the recently characterized and synthesized 41-amino acid polypeptide isolated from ovine hypothalami, has been shown to be a potent stimulator of adenohypophyseal beta-endorphin and corticotropin (ACTH) secretion both in vitro and in vivo. In common with other regulatory peptides, CRF has also been demonstrated to possess extra-hypophysiotropic roles. Indeed, intracerebroventricularly (i.c.v.) administered CRF elicits several endocrine and behavioural responses compatible with the concept that this peptide could be a key signal in coordinating the organism's endocrine and behavioural responses to stressful and other adaptive stimuli. We now provide the first evidence for neurally placed CRF in the control of a specific hormone-dependent behavioural response and unequivocally demonstrate an extremely potent suppressive effect of CRF on sexual behaviour in the female rat when microinfused into the arcuate-ventromedial area of the hypothalamus (ARC-VMH) and the mesencephalic central grey (MCG).

Immunohistochemical localization of avian pancreatic polypeptide-like immunoreactivity in the rat hypothalamus

The distribution of avian pancreatic polypeptide-like (APP) immunoreactivity within the rat hypothalamus was investigated with the indirect immunoperoxidase method. APP immunoreactive perikarya are found in largest numbers in the retrochiasmatic area, the arcuate nucleus, and the supracommissural portion of the interstitial nucleus of the stria terminalis. Small clusters of immunoreactive neurons are also consistently observed in the ventral aspect of the medial preoptic area and lateral hypothalamic area, immediately dorsolateral to the optic chiasm and tracts. These neurons are apparent in all animals but are more intensely strained and occur in larger numbers following colchicine pretreatment. Other immunoreactive neurons are visible only in colchine-treated rats and are scattered throughout the anterior and lateral hypothalamic areas and the supramammillary nucleus. Immunoreactive axons and terminal fields present an extensive and highly characteristic distribution throughout the hypothalamus, which in many instances exhibits differential distribution within specific subfields of hypothalamic nuclei and areas. The heaviest concentrations of APP immunoreactive axons are present in the periventricular nucleus throughout the rostrocaudal extent of the hypothalamus, the ventrolateral portion of the suprachiasmatic nucleus, the retrochiasmatic area, the parvocellular paraventricular nucleus, the ventral supraoptic nucleus, the perifornical nucleus, the ventral dorsomedial nucleus, and the arcuate nucleus. Moderate plexuses of immunoreactive fibers are also present in the medial preoptic area, the anterior and lateral hypothalamic areas, the nucleus circularis, the median eminence, and the ventral premammillary area. Other areas, such as the ventromedial nucleus, contain virtually no immunoreactive axons but are encapsulated by a dense plexus of immunoreactive terminals. The distribution of a major component of APP immunoreactive fibers exhibits a marked similarity to that of previously described norepinephrine-containing hypothalamic afferents. Other groups of APP immunoreactive perikarya and fibers appear to represent components of intrinsic diencephalic systems.

Ontogenesis of hypothalamic immunoreactive ACTH cells in vivo and in vitro: role of Rathke's pouch

The ontogenesis of immunoreactive (ir) ACTH cells and ir alpha-MSH cells in rat hypothalamus was studied in vivo and in vitro. Ir ACTH cells first appeared in the neuroepithelial cell layer lining the floor of the third ventricle on Day 13.5 of gestation, whereas ir alpha-MSH first appeared in the cytoplasm of several ir ACTH cells in the basal part of the arcuate nucleus of the hypothalamus on Day 19.5. When the medial-basal hypothalamus of 12.5-day embryos was cultured alone, a few ir ACTH cells were found after culture for 10 days, but not 3 days, and no ir alpha-MSH cells were observed in the cultures. When the hypothalamus was cultured with Rathke's pouch (intact or without the intermediate lobe anlage), ir ACTH cells appeared within 3 days. In these cultures on Days 6 and 10, long beaded fibers were seen projecting from cells in the neuronal tissue, and some cells showed immunolabeling for alpha-MSH. When the hypothalamus was cocultured with oral epithelium instead of Rathke's pouch, the appearance of neuronal ir ACTH cells was like that in cultures of hypothalamus alone. These in vitro findings suggest that stimulus from the anterior lobe anlage of the pituitary is necessary for normal development of ir ACTH/alpha-MSH cells in the hypothalamus.

Electronmicroscopic study of somatostatin-containing neurons in rat arcuate nucleus with special reference to neuronal regulation

After an intraventricular administration of colchicine, the arcuate nucleus of rat hypothalamus was examined light and electron microscopically by pre-embedding immunohistochemistry for somatostatin. The arcuate nucleus exhibited numerous immunoreactive cell bodies and dense networks of immunoreactive fibers. The fibers appeared to surround immunonegative cell bodies. The immunoreactive cell bodies were multipolar in shape and projected immunoreactive processes to some extent. The immunoreactive cell bodies and fibers received synaptic contacts by immunonegative fiber terminals containing a large number of synaptic clear vesicles. Similarly, immunoreactive somatostatin fibers appeared to terminate upon other immunonegative cell bodies and fibers. The immunoreactive presynaptic terminals contain several labeled granules and numerous synaptic vesicles. In close proximity to these immunolabeled terminals, non-labeled presynaptic terminals were also observed upon the immunonegative cell bodies and fibers. This suggests that in the arcuate nucleus neurons regulated by somatostatin neurons are also under the control of other types of neurons.