Influence of age-related changes in nitric oxide synthase-expressing neurons in the rat supraoptic nucleus on inhibition of salivary secretion.

Age-related inhibition of salivary secretion has been demonstrated in rats, and the nitric oxide (NO) present in the supraoptic nucleus (SON) and the medial septal area has been reported to play an inhibitory role in the regulation of salivary secretion. In the present study, we investigated the age-related changes occurring in the NO synthase (NOS)-expressing neurons in the SON, which is related to the production of NO, and discussed the interrelation between the age-related changes in the NOS-expressing neurons and the age-related inhibition of salivary secretion. Nissl staining and reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry were performed for young adult and aged rats. Quantitative analysis was also performed using the Nissl-stained and NADPH-d-positive neurons. Although the numbers of the Nissl-stained neurons did not change, significant age-related increases were detected in cell number, cell size and reactive density of the NADPH-d-positive neurons. Therefore, the production of NO in the SON neurons increased with age. We concluded that the age-related increase in the NO in the SON might be a factor that contributes to the age-related inhibition of salivary secretion.

Catecholamine and oxytocin cells respond to hypovolaemia as well as hypotension.

Medullary catecholamine and hypothalamic neurosecretory oxytocin cells are activated by hypotension, but previous studies have provided uncertain outcomes concerning their ability to respond to a purely hypovolaemic stimulus. In the present study, injections of PEG/water and pentolinium were used to elicit non-hypotensive, isosmotic hypovolaemia and isovolaemic, isosmotic hypotension, respectively, in conscious rats. Animals were sacrificed 2 h after treatment. Immunolabelling for Fos, tyrosine hydroxylase and oxytocin established that these two stimuli activate almost identical populations of catecholamine neurons in the ventrolateral and dorsomedial medulla, and very similar populations of oxytocin cells in the supraoptic and paraventricular nuclei of the hypothalamus.

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.