Hypertonic injections, blood changes, and initiation of drinking.
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Biomedical subjects
G I Hatton
Publications and source records attributed to G I Hatton.
Water regulation in the rat: drive intensity and fixed ratio responding.
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Water regulation in the rat: consummatory and excretory responses to short-term osmotic stress.
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Ultrastructural comparisons of neurons of supraoptic and circularis nuclei in normal and dehydrated rats.
A quantitative ultrastructural investigation was undertaken to compare the nucleus circularis (NC) and supraoptic nucleus (SON) of the rat both under normal and water-deprived conditions. NC was found to have dramatically more of its cells and membrane surface involved in direct soma-somatic contact than the SON. Water deprivation, even for one day, brought about a significant increase in both percentage of cells and membrane surface in contact in both nuclei, apparently by the retraction of fine glial processes from between the somata. The normal NC was made up of only one ultrastructurally identifiable cell type. The normal NC had no cells showing expanded endoplasmic reticulum, although these were seen following 5 days (but not 1 day) of water deprivation. The normal SON did have 4.4% of its cells showing expanded endoplasmic reticulum. This percentage significantly increased following water deprivation. The vesicle population per area of cytoplasm was very similar between the two normal nuclei. One day of water deprivation brought about a significant increase in less than 800 A vesicles in NC but not the SON. Five days of water deprivation resulted in a significant decrease in the lysosomal population per unit area in both nuclei. Vesicle changes have been discussed in relation to the volume changes in the cells.
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Nucleus circularis: is it an osmoreceptor in the brain?
The nucleus circularis, in the anterior hypothalamus, is a group of magnocellular elements arranged in a ring around a capillary bed. The cells are predominantly monopolar, tightly packed, and are flattened at the outer border of the ring. The entire nucleus is surrounded or encapsulated by myelinated fibers. Electrical stimulation of this nucleus produced a short-latency, long-lasting and substantial antidiuresis in ethanol anesthetized rats. Water deprivation induced changes in numbers of nucleoli and cell size increases in these cells. The multiplication of nucleoli in this nucleus during water deprivation was more profound than that previously observed in the supraoptic nucleus. Decreases in multiple nucleoli accompanied voluntary rehydration. Seven criteria for status as an osmoreceptor are listed and the nucleus circularis was found to meet 6 of these criteria, the seventh being the demonstration of receptor potentials which has not yet been attempted.
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Paraventricular nucleus: changes in the medial and lateral cell groups during dehydration and rehydration in the rat.
Cell area, percentage of cells with more than one nucleolus, and percentage of cells with the nucleolus apposed to the nuclear membrane (marginated) were compared in the medial and lateral magnocellular portions of the paraventricular nucleus (PVN) during water deprivation and voluntary rehydration. Lateral cells were larger and had a greater percentage of cells with multiple nucleoli in all conditions of deprivation and rehydration. In addition laterals were found to have more cells with marginated nucleoli in these cells with only one nucleoli. Medial and lateral cells showed similar responses to deprivation and rehydration.
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Nucleolar proliferation and cell size changes in rat supraoptic neurons following osmotic and volemic challenges.
Subcutaneous injections of isotonic saline induced nucleolar proliferation in supraoptic neurons in animals sacrificed approximately 5 min postinjection. The magnitude of this proliferation was sustained 4 and 8 hr postinjection. Polyethylene glycol (PG) injections depleted blood volume 4 and 8 hr after the injection, but the percentage of SON cells with multiple nucleoli in these animals was not different from saline-injected controls. The anterior (SOa) portion of the SON in rats given 2% NaCl to drink instead of water for three days contained more cells with multiple nucleoli than controls. This effect was enhanced after five days ingestion, and accompanied by a similar response in the tuberal portion of SON (SOt). Rehydration for ten days after three days of 2% NaCl intake brought the percentage of cells with multiple nucleoli down to control levels. Cell area in SON cells paralleled nucleolar responses during dehydration and rehydration. The results demonstrate the sensitivity of nucleolar proliferation in SON to environmental changes ranging from osmotic to neurogenic stress.
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Spontaneous and osmotically-stimulated activity in slices of rat hypothalamus.
Single unit activity was recorded from 400-500 mu m thick slices of rat hypothalamus, using either NaCl- or horseradish peroxidase-filled glass micropipettes. Spontaneous activity was present in the following hypothalamic loci: anterior hypothalamic-preoptic area, nucleus circularis, nucleus of the diagonal band of Broca, paraventricular accessory nucleus, paraventricular nucleus (all portions), periventricular regions of the anterior hypothalamus, and the suprachiasmatic nucleus. The supraoptic nucleus was the only major cell group studied to exhibit no spontaneous activity. Cells of the paraventricular and circularis nuclei were spontaneously active, displayed firing rates and patterns of activity similar to those recorded in vivo for magnocellular elements of the hypothalamus, and in some cases responded to increases in the osmolality of the bathing medium with altered firing rates and/or patterns of activity. Many cells in these preparations were characterized by phasic, bursting patterns of activity. Slow, irregular and regular, continuous activity was also frequently observed, as is typical in vivo. Median firing rates were in the range of 4-6 spikes/sec, somewhat faster than the rates usually reported for anesthetized in vivo preparations. These rates are more similar to those observed in unanesthetized monkeys or rats with diencephalic islands. Extracellular HRP marking provided a high degree of localization for many of the recorded cells. These results indicate that the hypothalamic slice preparation is useful for studies in which it is desirable to eliminate extrahypothalamic connections and in which it is necessary to exercise a fine degree of control over the extracellular environment of the cells.
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Ultrastructure of neurons in the paraventricular nucleus of normal, dehydrated and rehydrated rats.
Previous reports have shown that the percentage of neuronal somatic membrane in soma-somatic apposition (without intervening glia) increased with brief periods of dehydration (4--24 hr) and decreased with rehydration in the rat supraoptic and circularis nuclei. In the present study, the percentage of somal membrane in soma-somatic appositions was found to increase in the primarily vasopressin-containing lateral portion of the rat paraventricular nucleus with twelve hours of dehydration. Further evidence for altered cellular function in this nucleus was a decrease in the number of smaller dense core vesicles (< 2600A) per unit cytoplasmic area during initial dehydration (4--12 hr). No changes were detected, however, in the number of larger dense core vesicles (> 4000 A) or lysosomes (> 4000 A) per unit cytoplasm. Intranuclear membrane-bound vacuoles were found primarily in hydrated and rehydrated animals. No reliable changes were seen in the dilation of granular endoplasmic reticulum. Cilia were found in the neuropil and were occasionally traced to magnocellular somata. Differences in the patterns of morphological responses among the magnocellular hypothalamic nuclei suggest specializations in their roles, and further support a functional significance of neuronal membrane appositions.
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Brain slice preparation: hypothalamus.
Methods, materials and procedures for producing viable hypothalamic slices are described in detail. Also described are the results of methodological experiments dealing with combatting the problem of evaporative water loss which produces subsequent increases in concentration of the bathing medium. A formula is given by which the amounts of evaporative loss may be calculated and compensated for without direct measurement of the medium osmotic pressure. Finally, ultrastructural data are presented which indicate that paraventricular nucleus neurosecretory cells in the slices undergo a loss of dense core vesicles during the initial 3 hr in vitro, then recover by 5 hr and maintain a relatively constant state for up to 9 hr, the longest time sampled.
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The localization of projection neurons in the rat hypothalamic paraventricular nucleus following vascular and neurohypophysial injections of HRP.
Projection neurons in the rat hypothalamic paraventricular nucleus (pv) were identified using the retrograde transport of horseradish peroxidase (HRP) following injections of this tracer into the neurohypophysis or jugular vein. The objective was to determine if parvocellular pv neurons might be labelled by either injection in addition to the well known magnocellular contingent. Injections confined to the neurohypophysis resulted in the labelling of only magnocellular pv neurons, while intrajugular injections which produced spread of the HRP to the arcuate nucleus-median eminence region resulted in the labelling of both parvocellular and magnocellular pv elements. Thus parvocellular pv neurons may project to the arcuate nucleus and/or the external layer of the median eminance but not to the neurohypophysis.
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