Blood supply of the rat hypothalamus. V. The medial hypothalamus (nucleus ventromedialis, nucleus dorsomedialis, nucleus perifornicalis)

Using the India ink double-perfusion technique, the blood vessels of the rat's medial hypothalamus were reconstructed from serial sections. The area studied comprised the ventromedial, dorsomedial and perifornical nuclei. The arterial supply of this territory comes from the middle hypothalamic and the anterior, middle and posterior tuberal arteries. The drainage is strictly undirectional: ventralward by the anterior, middle and posterior ventromedial, the posteromedial and posterolateral hypothalamic veins, all ending in the basal vein. The arteries of the ventromedial and dorsomedial nuclei are distinct from those of the arcuate nucleus and median eminence, and their drainage is not connected with the portal vessels. The nuclei studied, even at the levels of their subdivisions, possess own arteries whose territories of supply can well be distinguished with a minimum of overlap. The topography of these arteries is described in detail. The medial hypothalamus has no vascular connections with other regions of the diencephalon including the thalamus.     

Blood supply of the rat hypothalamus. VI. Posterior region of the hypothalamus (nucleus hypothalamicus posterior, nuclei praemammillares, nucleus supramammilaris, mammilary body).

It was shown by the double ink-filling technique that the arteries of the rat premammillary region and mammillary body arise from the a. communicans posterior while these areas are drained by the anterior interpeduncular vein. Disregarding some minor overlaps and anastomoses, the blood supplies of the two territories are independent of each other and from the neighbouring areas of the hypothalamus, diencephalon and mesencephalon. Arteries of the premammillary region arise from the premammillary artery, except for some branches of the posterior tuberal and interpeduncular arteries. The mammillary body is supplied by three mammillary arteries (anterior, posterior and lateral). The premammillary region drains into the anterior and posterior premammillary veins. Venous blood of the mammillary body is collected by the anterior and posterior mammillary veins which end in the anterior interpeduncular vein. The circulation of individual premammillary and mammillary nuclei is described in detail.     

Role of the hypothalamus in regulating liver circulation

In acute experiments on nembutal anesthetized dogs stimulation of anterior hypothalamus elicited changes in the hepatic artery blood flow, which followed those of arterial pressure; the vascular resistance remaining unchanged. The stimulation of medial and posterior hypothalamus led to decrease in flow and increase in the resistance of the hepatic artery. In most cases of hypothalamic stimulation the portal blood flow diminished, portal pressure and vascular resistance increased. The opposite reactions were observed during stimulation of sympathoinhibitory area, paraventricular and lateral hypothalamic nuclei. The conclusion is made that the hypothalamus participates in integrative and differential control of the hepatic circulation.     

The mechanisms of the influence of the anterior and posterior hypothalamus on the electrical activity of the large hemispheres of the forebrain and on autonomic reactions in hens

Studies have been made of the effect of stimulation of the anterior and posterior hypothalamus on the electrical activity of the hemispheres, arterial blood pressure, heart and respiration rates. Mainly desynchronizing mechanisms were revealed in the ascending influences from both the anterior and posterior hypothalamus. Concerning the descending influences, it was found that stimulation of the anterior hypothalamus evokes depressor reactions, whereas stimulation of the posterior hypothalamus results in pressor reactions. Peculiarities of evolutionary development of the ascending and descending mechanisms of the posterior and anterior hypothalamus are discussed.     

Effect of the adrenoreactive structures of the anterior hypothalamus on blood coagulation

In the chronic experiment stimulation of alpha- and beta-adrenoreactive structures of the anterior hypothalamus by adrenolytic substances is carried out before and after the blockade. The results of the experiments show specificity of the influence of alpha- and beta-adrenoreactive structures of the anterior hypothalamus on different phases of the process of blood coagulability.     

Angiology of the brain of the baboon Papio ursinus, the vervet monkey Cercopithecus pygerithrus, and the bushbaby Galago senegalensis

The investigation was undertaken to compare the blood supply and venous drainage of the brain of the baboon P. ursinus, the vervet monkey C. pygerithrus, and the bushbaby G. senegalensis with that of man, because these animals are extensively used as research models. The blood supply of the three primates was found to be similar in each case. Like man they have a complete circulus arteriosus; but they have a single anterior cerebral artery, whereas man has paired anterior cerebral arteries. The arterial supply to the cerebellum in the primates is similar to that in man, the main difference being a "common inferior cerebellar artery" which bifurcates to form the anterior inferior cerebellar and posterior inferior cerebellar arteries. In man, these arteries arise separately from the basilar artery and vertebral arteries, respectively. The dural venous drainage was also found to be similar in these primates but was far more extensive than in man. The primates have additional sinuses--the more important of these being the "basisphenoid sinus" and the petrosquamous sinus. The former drains the basilar sinus and is itself drained via the vertebral venous plexus and internal jugular vein. The latter drains via the petrosquamous foramen into the retromandibular vein. The petrosquamous sinus has a rostral extension which drains through the foramen ovale and two lateral and medial connecting sinuses which drain the cavernous and basilar sinuses, respectively. These sinuses are not found in man.     

Proposed pathways for vocal self-stimulation: Met-enkephalinergic projections linking the mibrain vocal nucleus,auditory-responsive thalamic vocal nucleus,auditory-responsive thalamic regions and neurosecretory hypothalamus

In this study, we have investigated the neuroanatomical pathways that may underlie the influence of a female bird's vocal behavior upon her own reproductive endocrine response. We traced the ascending efferent projections of the midbrain vocal control nucleus, the intercollicularis (ICo), using an anterograde tracer, PHAL, delivered by iontophoretic application. We found labelled terminal fields in the anterior regions of the hypothalamus that contained luteinizing hormone releasing hormone- (LHRH) immunoreactive neurons. We injected into the LHRH-rich anterior medial hypothalamus (AM) the retrograde tracer, fluorogold, to verify the results of PHAL anterograde tracing and exmine whether retrogradely labelled neurons in the ICo can be stained with met-enkephalin antiserum by the immunohistochemical method. Of the retrogradely labelled neurons in the medial division of ICo (mICo), between 5% and 15% were found to be met-enkephalin-immunoreactive positive perikarya. Our data suggest that axonal projections into the anterior medial hypothalamus may arise in part from enkephalin-immunoreactive neurons in the medial ICo. The mICo neurons distributed along the medial border of the midbrain auditory nucleus give rise to projections into the posterior medial hypothalamus (PMH) via synapses within the shell region of thalamic auditory nucleus, ovoidalis (Ov). We conclude that in the ring dove, the medial division of the vocal control nucleus, by virtue of its connection with the auditory thalamus and neurosecretory hypothalamus, is in a position to exert influence on endocrine response partly through enkephalinergic systems. Implications of similar connections in other species are discussed. 1994 John Wiley & Sons, Inc.     

The intestinal blood circulation in the River lamprey, Lampetra fluviatilis

Serial sections, injections with india ink and latex, and observations on fresh material, have been used to determine the pattern of blood circulation within the intestine of larval and adult lampreys. Attention has also been paid to resolving the variable terms previously applied to many of the blood vessels, and to the possible functional significance of the differences found between the two life cycle stages. In the larva, the main arterial supply to the intestine consists of a typhlosolar artery, while the venous return is comprised of a posterior and a left and right anterior intestinal vein that usually unite before entering the liver. Although a typhlosolar artery is also present in the adult, the main venous return of the ammocoete is replaced at metamorphosis by a newly formed typhlosolar vein. Moreover, in the ammocoete a considerable amount of blood is discharged into the haemopoietic sponge-work of the typhlosole and the arterial supply to the intestine is poorly developed. By contrast, the typhlosolar sponge-work is lost in the adult and a more efficient arterial supply is developed within the lamina propria of the various intestinal regions. Furthermore, vascular couples are developed in the adult which facilitate the flow of blood in opposite directions in the intestinal wall. Since, during both life cycle stages, the arterial blood passes into tissue spaces, there is no true capillary network in the intestine and no evidence was found for the presence of a lymphatic system. It is suggested that the changes which take place in the intestinal blood supply and the internal structure of the gut during metamorphosis result in improvements both to the vascular system and to the assimilation efficiency.     

Immunofluorescence of somatostatin-producing sites in the hypothalamus of the tadpole,Alytes obstetricans Laur.

Summary Three sites of somatostatin-synthesizing perikarya, or a related antigen, were determined by immunofluorescence in the hypothalamus of the tadpole, Alytes obstetricans (Amphibia, Anura). Two sites of neurosecretory perikarya were localized in the preoptic nuclei of the anterior hypothalamus; the axons extended either to the anterior diencephalon or to the median eminence and the pituitary. The third site was found in the posterior hypothalamus. These neurosecretory cells showed a strong immunofluorescent reaction; their axons all terminated at the level of the median eminence. Somatostatin cells were only found in intact or hypophysectomized tadpoles given somatotropin (STH). The strong reaction observed in hypophysectomized tadpoles was possibly due to the loss of the terminal portion of the neurosecretory pathway (median eminence and pituitary) by which the agent is transported to the site of discharge.     

Ultrastructure of the neurosecretory cells of the anterior commissural nucleus of the hypothalamus in rats

The ultrastructure of neurosecretory cells of the anterior commissural nucleus of rat hypothalamus is similar to that of the supraoptic nucleus and of the "magnocellular" part of the paraventricular nucleus. The only difference is a less expressed granular endoplasmatic reticulum and a smaller diameter of elementary neurosecretory granules (80-150 nm in diameter). Such elementary granules are characteristic of neurosecretory terminals located in the external zone of the median eminence. It is suggested that neurosecretory cells of the anterior commissural nucleus project to this neurohemal region.     

The antihypertensive effect of ethylcholine aziridinium (AF64A), a cholinergic neurotoxin, in spontaneously hypertensive rats, following administration into the posterior hypothalamus

The aim of this study was to ascertain whether drug-induced cholinergic hypofunction in the posterior hypothalamus would affect the development and the maintenance of hypertension in hypertensive rats. Spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats were treated with AF64A, a neurotoxin which can irreversibly inhibit cholinergic transmission in vivo. AF64A or saline was injected bilaterally into the posterior hypothalamus of rats of two age groups: normotensive one month-old rats whose blood pressure was subsequently measured at the age of three months and hypertensive three month-old rats, whose blood pressure was measured four weeks later. In both age groups there was a significant fall in mean arterial blood pressure in SHR but not WKY rats. In SHR injected at the age of one month, there was a fall of at least 15.9 mm Hg, while in the rats injected at the age of three months there was a fall of 14.3 mm Hg. Heart rate in either strain was not affected. When AF64A was injected into the anterior hypothalamus of one month-old SHR, no antihypertensive effect was observed in these rats at the age of three months. These results show that cholinergic stimulation in the posterior hypothalamus may play a role in both the development and maintenance of hypertension in SHR.     

Posterior hypothalamus action on gastric secretion (author's transl)]

Three groups of cats with surgically created total gastric pouches were employed in this experiment. They were divided as follows: in one group the innervation of the pouch was left intact; in another group the symphathetic innervation of the pouch was removed; and in the third group the pouch was completely denervated. It was seen that an infusion of histamine induced gastric secretion in all three groups. And when the secretion became constant it proved to be less acidic and more abundant in the sympathectomized group and also in the group that had suffered complete denervation. It was observed now that stimulating the posterior hypothalamus of the innervated group produced, in all of the cats, a decrease in the amount of acid secreted per unit of time. Consequently, it was seen that a symphathectomy did not eliminate the gastric effects produced when the posterior hypothalamus was stimulated. Specifically, stimulation of the posterior hypothalamus produced an increase in the amount of secretion rather than a decrease. The increase produced in these animals can be shown not to be due to irradiation of the anterior hypothalamus as the same response is obtained when a symphathectomy is combined with a vagotomy. It is, therefore, believed that it may be concluded that the Posterior hypothalamus does not produce its effect exclusively through its nervous pathways. It is believed its effect may possibly be mediated by an unknown substance liberated upon stimulation which then reaches the stomach by way of its blood supply.     

The arterial and venous blood supply of the septum pellucidum in the rat.

The arterial and venous systems of the rat's septum pellucidum has been studied by means of the perfusion technique. The arteries may be classified into three groups. The branches of each of the three groups originate from the a. hemispherica and enter the septum from the frontal direction. The veins may be divided into an anterior and a posterior group. The anterior veins flow through the v. subcallosa into the sinus cavernosus, the posterior veins into v. cerebri magna. The arterial and venous blood supply of the individual nuclei of the septum are compar independent.     

Anatomical basis for vascular-pedicle transplantation of the hypothalamo-hypophyseal complex

In 240 corpses of mature persons by means of complex morphological methods extraorganic arteries of the hypophysis, anterior hypothalamus have been investigated, as well as topography of the arterial peduncle of the hypothalamo-hypophyseal complex. Blood supply of the hypophysis and of the anterior hypothalamic part is performed from one common vascular pool--the arterial ring of the brain via multiple arterial branches, their amount and diameter varying considerably. Taking into account an important role of anastomotic vessels and numerous arterial plexuses, when the hypothalamo-hypophyseal complex is extirpated for investigation, it is necessary to include into its composition, besides the major arterial peduncle, the optic chiasm, the grey tuber and the system of cavernous sinuses. Owing to this, there is no need to separate the arterial peduncle of the transplant at the moment of obtaining the hypothalamo-hypophyseal complex. The topographic anatomical investigations performed make prerequisites for transplantation of the hypothalamo-hypophyseal complex on the vascular peduncle in clinic.     

Ethanol-related changes in substance P in the hypothalamus and anterior pituitary.

The effect of the administration of a rabbit anti-substance P serum (ASPS) was studied in rats receiving an acute injection of ethanol. ASPS lowered serum prolactin levels and reduced the hyperprolactinemia induced by ethanol. ASPS also decreased LH serum levels in both saline- and ethanol-treated rats. The effect of ethanol on the concentration of substance P-like immunoreactivity (SP-LI) in the mediobasal hypothalamus and the anterior pituitary gland was also investigated. Ethanol reduced SP-LI in the mediobasal hypothalamus but increased it in the anterior pituitary gland. The presence of ethanol (50 mM) did not affect the K(+)-evoked release of SP-LI from either mediobasal hypothalamus or anterior pituitary gland, though it increased the SP-LI concentration remaining in this gland. These results indicate that ethanol increases the content of SP-LI in the anterior pituitary gland and suggest that substance P may be involved in the prolactin release induced by the acute administration of ethanol.     

Estradiol receptors in the pituitary and anterior hypothalamus of the rat: measurement by agar gel electrophoresis.

The reliability of agar gel electrophoresis in the measurement of high-affinity saturable estrogen-binding component in the cytosol of the rat pituitary gland and anterior hypothalamus was assessed. The available binding sites were determined in small samples with good precision and accuracy. Incubation with 100-fold competitor was more satisfactory than heat-treatment for measuring nonspecific binding. There was substantial, but incomplete, dissociation of albumin-estradiol complexes. The total number of estrogen binding sites in the anterior hypothalamus was approximately 15% greater in 28-day-old females than males (p .02). However, differences in the number of binding sites in the pituitary was not significant (p .02). The pituitary was found to contain twice as many binding sites as the anterior hypothalamus in both sexes. The latter finding is consistent with the importance of the direct action of estrogen on the pituitary in mediating pituitary function.     

Thyroid hormone modulation of TRH precursor levels in rat hypothalamus, pituitary, thyroid and blood

In the present study we have examined the in vivo effects of thyroid hormones and TRH on tissue and blood levels of TRH and TRH-Gly (pGlu-His-Pro-Gly), a TRH precursor. Using specific radioimmunoassays (RIAs), we measured TRH immunoreactivity (TRH-IR) and TRH-Gly-IR concentrations in blood, hypothalamus, anterior and posterior pituitary, and thyroid in euthyroid, hypothyroid and thyroxine (T4)-treated 250 g male Sprague-Dawley rats. TRH-Gly-IR and TRH-IR were detected in all of these tissues. Highly significant positive correlations between whole blood TRH-Gly-IR levels and the corresponding serum TSH values (p less than 0.01), whole blood TRH-IR versus serum TSH (p less than 0.01) and whole blood TRH-Gly-IR versus whole blood TRH-IR (p less than 0.01) are consistent with cosecretion of TRH and TRH precursor peptides into the circulation. Euthyroid rats injected with TRH IP (1 microgram/100 g b.wt.) and hypothyroid rats had 4-fold higher whole blood TRH-Gly-IR levels compared to euthyroid controls (p less than 0.0005). Injection of TRH into euthyroid rats significantly increased the TRH-Gly-IR concentration in the hypothalamus, anterior and posterior pituitary and thyroid. The increase in blood TRH-Gly-IR following intravenous TRH may be due, in part, to partial saturation of TRH-degrading enzymes in blood and cell membranes. The ratio of TRH-Gly to TRH was significantly increased in the anterior pituitary by hypothyroidism and TRH injection, suggesting that thyroid hormones and TRH regulate the alpha-amidation of TRH-Gly to form TRH in this tissue. TRH-Gly levels of pooled pituitary and thyroid extracts quantitated by a combination of TRH-Gly RIA and high performance liquid chromatography (HPLC) revealed several-fold increases following incubation at 60 degrees C. Heating at this temperature may block the alpha-amidation activity in extra-hypothalamic tissues but not the "trypsin-like" enzymes which cleave prepro-TRH into TRH-Gly-immunoreactive peptides.     

Effect of a fall of blood pressure on the release of catecholamines in the hypothalamus

The posterior hypothalamus of anaesthetized cats was superfused through a push-pull cannula and the release of endogenous catecholamines was determined in the superfusate which was continuously collected in 15 min periods. Fall in blood pressure elicited by nitroprusside or bleeding led to an increased rate of release of noradrenaline, adrenaline and dopamine in the hypothalamus. Transection of the brain causal to hypothalamus greatly reduced the rate of resting release of the catecholamines and abolished the enhancing effects of bleeding and nitroprusside. Determination of the catecholamines in samples which were collected in 90 s periods suggested a different pattern of release of the three catecholamines. Further shortening of the collection period (10 s) showed that the fall in blood pressure immediately increased the release of dopamine, while the rates of release of noradrenaline and adrenaline were increased gradually. Hypotension did not influence the rates of release of the catecholamines in the anterior hypothalamus. It is concluded that dopamine, adrenaline and noradrenaline systems of the hypothalamus are involved in the regulation of the arterial blood pressure. The different patterns of release might indicate that dopamine exerts a different function from those of noradrenaline and adrenaline in the normalization of the blood pressure after acute hypotension.     

Angiotensinase activity in hypothalamus and pituitary of hypothyroid, euthyroid and hyperthyroid adult male rats.

A local renin-angiotensin system (RAS) that may be involved in their regulatory functions has been identified in hypothalamus and pituitary. Altered thyroid status induces modifications in the secretory function of hypothalamus and pituitary. However, few studies have analyzed the role of the RAS in hypothalamus and, to our knowledge, there is no data on the pituitary RAS during thyroid dysfunction. In the present study, angiotensinase activities (glutamyl, aspartyl and alanyl aminopeptidase: GluAP, AspAP and AlaAP, respectively) were studied in hypothalamus and in the anterior and posterior lobes of pituitary of euthyroid, hypothyroid and hyperthyroid adult male rats. In the anterior pituitary, compared with euthyroid and hyperthyroid rats, hypothyroid animals showed a highly significant increase of GluAP and AspAP activities; the percentage increase in GluAP was markedly higher than the percentage increase in AspAP. This suggests an increased metabolism of angiotensin (Ang) I and Ang II to des-Asp 1-Ang I and Ang III, respectively. We also observed an increase of Ang III-degrading activity (AlaAP) in the hypothalamus of hyperthyroid rats in soluble fraction. Increased Ang I and Ang II metabolism in the anterior pituitary of hypothyroid rats and increased metabolism of Ang III in the hypothalamus of hyperthyroid animals may be related to alterations in the secretory function of hypothalamus and pituitary in these thyroid dysfunctions.     

Expression of corticosterone-binding globulin in the rat hypothalamus.

We observed coexistence of corticosteroid-binding globulin (CBG) with vasopressin (VP) and oxytocin (OT) in magnocellular neurons in rat hypothalamus by combined immunoperoxidase staining and immunofluorescence. A portion of the supraoptic and of the paraventricular neurons showed double immunostaining of CBG with either VP or with OT. CBG staining was intensified by pretreating animals with colchicine to block axonal transport. CBG was also observed in widespread axonal projections throughout the lateral hypothalamus, the median eminence and the posterior pituitary lobe. Single ependymal cells and some of the endocrine cells in the anterior lobe contained specific CBG immunoreactivity. IN SITU hybridization of semithin sections with a synthetic oligonucleotide probe to CBG mRNA provided staining of magnocellular hypothalamic neurons, but not ependymal cells or anterior lobe cells. Western blots of CBG extracted by affinity chromatography from hypothalamus homogenates showed a band at approximately 50 kDa. Our observations indicate the intrinsic expression of CBG in peptidergic hypothalamus neurons in rat. The multiple locations of CBG-expressing neurons indicate multiple functional properties, probably exceeding the role of a mere steroid transporter. CBG is likely to be subject to axonal transport and secretion in a neuropeptide-like fashion, perhaps involved in neuroendocrine regulation, which may include stress responses.