Differential activation of Fos-like immunoreactivity in the arcuate nucleus and amygdala after intracerebroventricular injection of sodium nitroprusside and N omega nitro-L-arginine in conscious and urethane-anesthetized lactating rats

Region-specific alterations of neuronal nitric oxide synthase (nNOS) expression in the amygdala of the aged rats

Although many amygdalar functions are altered by aging, little is known about their mechanisms. As these functions are related with nitric oxide (NO), we examined neuronal nitric oxide synthase (nNOS) expression in the amygdala of the aged rats via immunohistochemical technique. We found that nNOS immunoreactive neurons are decreased in almost all amygdalar areas of the aged rats, while nNOS immunoreactivity of the neuropil is significantly increased in the amygdalar nuclei related with main and accessory olfactory system. These suggest altered levels of NO might provide region-specific mechanisms of many physiological and behavioral deficits of the amygdala developed by aging. However, exact effects of these changes require further elucidation.

Stimulus-dependence of NO-mediated neuronal activation: a Fos expression study in the hippocampus and cortex of lactating rats

We investigated how simultaneous manipulation of suckling and i.c.v. injection of nitric oxide (NO)-related pharmacological agents affect Fos activation in the hippocampus and cortex of lactating rats. Dams received drugs or vehicle injection just prior to reunion with their pups following a 12 h separation and Fos protein activation was examined after 2 h of suckling. In conscious dams, sodium nitroprusside (SNP, an NO donor) significantly activated Fos expression in the hippocampus and cortex compared with vehicle or an NO synthase inhibitor. Urethane anaesthesia abolished Fos expression in the cortex, but not in the hippocampus following simultaneous SNP injection and resumption of suckling. Fos activation in the hippocampus and cortex was significantly attenuated when SNP was injected alone (without dam-pups reunion after separation). Coincident injection of SNP with a NO synthase inhibitor abolished all Fos activation in the hippocampus and cortex. In chronically lactating rats (without any interruption of suckling) SNP injection failed to activate any Fos expression. These observations underscore the importance of stimulus modality in revealing the dynamics of NO-mediated neuronal function within a discrete tissue entity such as the hippocampus or the cortex, which may be relevant to other regions of the brain.