The arcuate nucleus as a circumventricular organ in the mouse.

The present study searched for morphological correlates of the permeability of the ventromedial arcuate nucleus of the mouse to blood-borne proteins. First, we determined that highly permeable microvessels are detected in the ventromedial arcuate nucleus using a rat monoclonal antibody to a mouse-specific endothelial phenotype (clone MECA32) recently recognized as a marker of endothelial fenestral diaphragms and previously shown to label circumventricular organs. Second, in the mild conditions of tissue fixation mandatory for use of MECA32, we observed that after a rapid vascular flush with saline, endogenous immunoglobulins are especially retained in circumventricular organs and ventromedial arcuate nucleus. The ventromedial arcuate nucleus thus shares features in common with classical circumventricular organs.

A second look at the barriers of the medial basal hypothalamus.

The cell bodies of hypothalamic secretory neurons are localized in areas protected by the blood-brain barrier (BBB), whereas their axon terminals are localized in the median eminence, which lacks a BBB. This implies a complex barrier system, allowing neurons of the central nervous system to secrete into the blood stream without making the BBB leaky. In the present study, three experimental protocols were applied to clarify certain relevant aspects of the barriers operating in the medial basal hypothalamus of the rat. We established that the milieu of the arcuate nucleus is exposed to both the ventricular and the subarachnoidal cerebrospinal fluid (CSF). The median eminence milieu, the perivascular space of the portal vessels, and the subarachnoid space appear to be in open communication; also, beta2-tanycytes establish an efficient barrier between the median eminence milieu and the ventricular CSF. Similarly, beta1-tanycytes establish a lateral barrier, separating the intercellular space of the median eminence from that of the arcuate nucleus. We also found that the glucose transporter I (GLUT I), a BBB marker, is localized throughout the whole plasma membrane of beta1-tanycytes, but is missing from beta2-tanycytes. Expression of GLUT I by tanycytes progressively develops during the first postnatal weeks; while the degree of damage of the arcuate nucleus by administration of monosodium glutamate, at different postnatal intervals, parallels that of the GLUT I immunoreactivity of beta1-tanycytes. An explanation is offered for the selective destruction of the arcuate neurons by the parenteral administration of monosodium glutamate to infant rats.

Hypothalamic-pituitary vascularization in pituitary stalk transection syndrome: is the pituitary stalk really transected? The role of gadolinium-DTPA with spin-echo T1 imaging and turbo-FLASH technique.

We examined 14 patients, aged 10-25 years, with idiopathic hypopituitarism. All presented an ectopic posterior pituitary at the median eminence with a hypoplastic anterior pituitary on magnetic resonance imaging (MRI). Eight patients had isolated growth hormone deficit (IGHD) and six had multiple hormone deficits (MPHD). Unenhanced MRI showed the pituitary stalk, which was extremely thin, in only three patients, while T1-weighted images obtained after intravenous injection of gadopentetate dimeglumine (Gd-DTPA) showed a thin pituitary stalk in seven patients (six with IGHD and one with MPHD), demonstrating a preserved vascular component of the stalk. MRI with Gd-DTPA was more sensitive than unenhanced MRI in detecting the pituitary stalk in patients with hypopituitarism with an ectopic posterior pituitary: the stalk was demonstrated in 50 % of the cases (seven patients), versus 21.4 % (three patients) by unenhanced MRI. The dynamic study of the hypothalamo-hypophyseal axis performed with turbo-FLASH sequences after bolus injection of Gd-DTPA showed the residual anterior pituitary to have arterial enhancement times, which suggests that an arterial system compensates for the absent or diminished blood supply from the portal system, independent of stalk detection.

Comparative morphology of the pituitary gland in Australian flying foxes (Megachiroptera: genus Pteropus).

BACKGROUND: Investigations of reproductive endocrinology of flying foxes (genus Pteropus) have been hampered by inadequate information on the normal morphology of the megachiropteran pituitary. METHODS: The novel technique of graphical three-dimensional (3-D) reconstruction, supported by more traditional anatomical techniques, have now been used to examine the shapes of, the interrelations between, the lobes of the pituitary of the little red flying fox, Pteropus scapulatus. Statistical analysis of data from three species tested whether there were changes in pituitary size with annual cycles in function, particularly with key stages of reproduction. RESULTS: In the three species of Australian flying foxes examined, the hypophyseal cleft is closed; the pars intermedia extends over the rostral, ventral, and lateral surfaces of the neural lobe. The pars distalis is broad rostrally and extends over two-thirds of the lateral and ventral pars intermedia. The hypophyseal recess is broad at the median eminence, then narrows and extends through the infundibulum to, but not into, the neural lobe. In adult animals the pituitary weight was 10.0 +/- 0.3 mg (mean +/- s.e.) in P. scapulatus, 14.7 +/- 0.5 mg in Pteropus poliocephalus (greyheaded flying foxes), and 18.7 +/- 1.5 mg in Pteropus alecto (black flying foxes). Pituitary weight was not significantly affected by reproductive stage. CONCLUSIONS: Thus histologically, the adenohypophysis and neurohypophysis are similar to those of other mammals. Comparative differences in pituitary size reflected differences in species body size rather than cyclical reproduction.

An ultrastructural study of gold thioglucose lesion formation in the ventromedial hypothalamus: subnecrotic gold thioglucose dose.

In an ultrastructural study of gold thioglucose (GTG) lesion formation in the mouse ventromedial hypothalamus (VMH), a single intraperitoneal subnecrotic dose of GTG (100 mg/kg) was used to induce a VMH microlesion, visible only by electron microscopy. Definitive neuronal alterations were not evident until eight hours after GTG injection. Large pericapillary processes, probably dendrites, displayed a loss of cytoplasmic density and distention, while the capillary endothelium appeared normal. Some intercellular distention also was apparent. By 24 hours after GTG administration, degenerating neurons were visible. Swollen and disrupted synaptic profiles were seen. However, no vascular damage was evident. These results support the evidence that GTG is a neurotoxin for structures in the mouse VMH.

Ependymal lining of infundibular recess in perinatal rats: relationships with portal capillaries and permeability.

Structure and permeability of the ependymal lining the infundibular recess were studied in perinatal rats with silver impregnation, electron microscopy, radioautography, and tracer techniques. According to our data basal processes of ependymal cells reach the primary portal plexus linking the 3rd ventricle and the hypophysial portal system all through the perinatal period. After birth, some of the processes penetrate into the perivascular space of the primary portal plexus and abut there on the endothelium of capillaries. Ependymal cells of fetuses and neonates are joined by specialized junctions (tight junctions, gap junctions and zonulae adhaerentes). Intraventricularly injected ionic lanthanum crosses the ependymal lining of fetuses both trans- and extra-cellularly everywhere in the infundibular recess. By postnatal day 9 only the rostral portion of the recess remains readily permeable. Caudally, extracellular leakage becomes highly restricted, apparently due to the appearance of circumferential tight junctions. Finally, [3H]dopamine seems to penetrate through the ependymal lining in the same way as ionic lanthanum entering the portal capillaries. These findings suggest that the adenohypophysiotropic neurohormones can penetrate from the cerebrospinal fluid into the portal circulation from the very beginning of the establishment of the hypothalamo-hypophysial functional relationships during ontogenesis.

Formation of a direct arterial blood supply to the anterior pituitary gland following complete or partial interruption of the hypophyseal portal vessels.

If regions of the anterior pituitary gland received systemic blood via a direct arterial blood supply these regions would escape hypothalamic regulation and thus be a sequela in endocrine disorders. Since, in the untreated rat, all of the blood supply to the anterior pituitary gland is via the hypophyseal portal vessels, we hypothesized that partial interruption of the portal vessels could provoke the establishment of a direct arterial blood supply (arteriogenesis). We utilized the injection of polystyrene microspheres (15 or 9 micron diameter) into the left ventricle of the heart to test this hypothesis. Microspheres are trapped in the first capillary plexus they reach since they are too large to traverse the capillaries. No microspheres reached the anterior pituitary gland of control rats, a finding consistent with the fact that the anterior pituitary gland receives all of its blood supply via the hypophyseal portal blood vessels. Microspheres were observed in the primary portal capillary plexus in the infundibulum (median eminence), infundibular stalk (pituitary stalk), and infundibular process (pars nervosa), the first capillary plexus which they reached. A lesion of the medial basal hypothalamus (MBH) which destroyed the long portal vessels did not result in arteriogenesis since few, if any, microspheres were observed in the anterior pituitary gland. We confirmed, using vascular casts, that these lesions resulted in the long-term destruction of the primary portal capillaries in the infundibulum and of the long portal vessels. In MBH-lesioned animals it appears that all of the blood supply of the anterior pituitary gland is via short portal vessels arising from the infundibular stem and process.(ABSTRACT TRUNCATED AT 250 WORDS)

[Functional state of the frontal cortex and ventromedial hypothalamus during physical overexertion and experimental neurosis in the rabbit]. / Funktsional'noe sostoianie frontal'noi kory i ventromedial'nogo gipotalamusa pri fizicheskom perenapriazhenii i éksperimental'nom nevroze u krolikov.

A change of excitability, pO2 and local cortical blood flow under a long-term maximum physical load and in conditions of experimental neurosis, was investigated in rabbits with electrodes implanted in the frontal cortex and ventromedial hypothalamus. It was found that functional activity of these structures under physical orverstrain rises as the blood flow and pO2 increase, and the excitability also increases. In experimental neurosis, a discoordination in functioning of the cortex and hypothalamus is observed. Relative stabilization of the functional state of tested structures, observed during physical overstrain, is absent in conditions of experimental neurosis.

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.

"Gomori-positive" neurosecretion in the rat after deafferentation of the medial basal hypothalamus.

A portion of the "Gomori-positive" peptidergic neurosecretory (NS) cells in the paraventricular and especially in the supraoptic and postoptic nuclei degenerate three weeks after deafferentation of the medial basal hypothalamus. Most of the remaining NS cells show signs of high activity. Regenerating NS fibres form "muffs" around the blood vessels laterally from the lesion; some of them enter the "isolated" area or persist there if a thin layer of the brain tissue is left somewhere untouched under the basal end of the cut. The regenerating NS fibres are also found outside the nervous tissue: within the scar tissue, in the proliferating connective tissue of the brain sheet below the basal end of the cut and in the mantel plexus area. The NS fibres make close contact with blood vessels invading or penetrating the vascular wall. It is suggested that peptide neurohormones discharged from the "Gomori-positive" NS terminals enter the general blood circulation as well as the portal blood at the site of these newly formed axovasal contacts. It is supposed that under these conditions monoaminergic terminals do not discharge monoamines because no stimulation of monoamine-producing NS cells occurs with deafferentation.

The dorsomedial hypothalamic nucleus in autonomic and neuroendocrine homeostasis.

Median eminence and ventromedial hypothalamus have in the past been the principal foci of research in neuroendocrine and neurovisceral control mechanisms. The present report provides an overview of work involving the dorsomedial hypothalamic nucleus (DMV). This structure is located dorsal to the ventromedial hypothalamic nucleus (VMN) to the plane of the dorsal premammillary nucleus. Fibers from the DMN pass with the periventricular system and the dorsal longitudinal fasciculus of Schütz and have been traced to the midbrain tegmentum and reticular formation. Intrahypothalamic connections involve intensive networks between DMN, lateral hypothalamic nucleus (LHN) and VMN. Regarding neurotransmitters, recent studies indicate that the DMN receives noradrenergic innervation along two pathways, a dorsal and a ventral one. Monoamine-containing systems approach the DMN From the lateral hypothalamus and the bulk of these fibers are carried in the medium forebrain bundle from their cells of origin in the brain stem. Studies of the vascular supply indicate that both VMN and DMN receive their blood supply from the internal carotid artery...

Blood supply of the rat hypothalamus. III. Anterior region of the hypothalamus (nucleus suprachiasmatis, nucleus hypothalamicus anterior, nucleus periventricularis).

The arterial and venous blood supply of the anterior hypothalamus was studied by means of double perfusion technique. The angiotopography and cytoarchitecture of the hypothalamus were compared on serial sections by accounting for the three-dimensional coordinates. A detailed description is given of the arteries and veins contributing to the blood supply of the suprachiasmatic, the anterior hypothalamic and the periventricular nuclei. The topography of the arterial and venous trunk on the base surface of the rat diencephalon is described, as well as that of the larger branches which enter from below and pass through the anterior hypothalamus.