The neurohypophysis

Water deprivation protects photoreceptors against light damage

Photoreceptor cell death after light-damage and during aging in rats is associated with the hormonal status of the animal, as well as other environmental and intrinsic factors. Restricted caloric intake extends the life of rodents and is usually accompanied by a reduction in water consumption. In this study, male and female rats were placed on restricted water intake for either 3 or 7 days to induce dehydration. Following exposure to damaging visible light, the retinas were evaluated for severity of damage and photoreceptor survival, heat shock (stress) protein (HSP) and total protein synthesis, and plasma arginine vasopressin (AVP) levels. Photoreceptor cells of 7-day, dehydrated male and female rats survived light-damage significantly better than those allowed water ad libitum; however, after 3 days of water restriction, only the male rats demonstrated protection from photodamage. Severity of photoreceptor damage could not be correlated with retinal HSP synthesis and content, although the latter was significantly reduced in dehydrated animals. Total retinal protein content and synthesis were unchanged by restricted water intake. AVP increased by 350% during the 7-day period of dehydration. Protection of photoreceptors from light-damage in this study may be correlated with osmotically stimulated changes in the retinas of dehydrated animals.

Selective traumatic infarction of the human anterior hypothalamus. Clinical anatomical correlation

A case of assult with bilateral manual avulsion of the eyes was followed by highly selective infarction of the anterior hypothalamus. The hypothalamic infarction occurred as a result of avulsion of part of the optic chiasm together with the anterior perforating arteries passing through it; Following this assault, symptoms of hypothalamic dysfunction included altered thermoregulation, alternating diabetes insipidus, and inappropriate antidiuretic hormone (ADH) secretion, altered patterns of sleep and arousal, and changing cardiac arrhythmias. The case casts light upon the vascular supply of the human hypothalamus and on the degree of localization existing for various hypothalamic functions.

Osmometry. 2. Osmoregulation

The maintenance of osmolar constancy of the body fluids is dependent upon the recognition of osmolar disequilibrium and its correction by modifying the ingestion and excretion of fluid and solute. Osmolar changes are sensed by the hypothalamus which regulates the secretion of antidiuretic hormone to modify the renal excretion of water. The integrity of the system depends upon the renal ability to vary the solute concentration of urine.

Osmometry. 3. Clinical applications

Measurement of plasma and urine osmolality is quick, easy and accurate. The recognition of the interdependence of urine volume and osmolality on the excretion of the daily obligatory solute load assists in the diagnosis and management of fluid balance and renal excretory problems in the acutely ill. In addition, syndromes of osmotic disequilibrium present a challenge in metabolic care.

Isolated nerve endings (neurosecretosomes) from the posterior pituitary. Partial separation of vasopressin and oxytocin and the isolation of microvesicles

Subcellular fractions of the bovine posterior pituitary, including one composed almost exclusively of pinched-off nerve endings (neurosecretosomes), were characterized electron microscopically, hormonally, and enzymically. 15% of the nerve terminals in the gland were isolated as neurosecretosomes, as estimated from determinations of lactic dehydrogenase, a soluble, cytoplasmic enzyme. Neurosecretosomes were subdivided into three fractions by density-gradient centrifugation. The three subfractions, each shown to be nearly homogeneous populations of neurosecretosomes by means of electron microscopic and enzymic criteria, differed from each other in their vasopressin/oxytocin (VP/OT) ratios. The VP/OT ratio increased from the lightest to the densest fraction, indicating that VP is localized to denser and OT to lighter neurosecretosomes; similar results have been obtained previously for subfractions of neurosecretory granules (NSG). No morphological differences were apparent in neurosecretosomes among the three subfractions. Although complete separation of VP and OT was not achieved, the findings suggest that VP and OT are each stored in a different species of nerve ending and support the hypothesis that a given neurosecretory cell synthesizes, stores, and secretes only one of the peptide hormones. Microvesicles, 40-80 mmicro diameter and contained in typical neurosecretory cell terminals, are believed to be degradation products of membrane ghosts of depleted NSG; electron micrographs indicative of this transformation are presented. A fraction rich in microvesicles, but containing some NSG membranes, was prepared by density-gradient centrifugation of an osmolysate of neurosecretosomes. Smaller, apparently nonneurosecretory nerve endings, lacking NSG but filled with small vesicles, are occasionally seen in sections from whole gland. The vesicles in these atypical posterior pituitary nerve endings may be true neurohumor-containing, "synaptic" vesicles.