The Journal of comparative neurology
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Comparative Study
Nucleus paragigantocellularis afferents in male and female rats: organization, gonadal steroid receptor expression, and activation during sexual behavior.
The supraspinal regulation of genital reflexes is poorly understood. The brainstem nucleus paragigantocellularis (nPGi) of rats is a well-established source of tonic inhibition of genital reflexes. However, the organization, gonadal steroid receptor expression, and activity of nPGi afferents during sex have not been fully characterized in male and female rats. ⋯ The majority of regions that contained FG+ cells also contained ER(alpha) or AR, indicating sensitivity to gonadal steroids. The proportions of FG+ cells that co-localized with sex-induced Fos was high in the PVN of both sexes and high in the MPO of males but low in the PAG of both sexes despite the large number of PAG-nPGi output neurons and Fos+ cells in both sexes. The characterization of these afferents will lead to a further understanding of the neural regulation of genital reflexes.
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Comparative Study
Role of endogenous sleep-wake and analgesic systems in anesthesia.
Classical anesthetics of the gamma-aminobutyric acid type A receptor (GABA(A))-enhancing class (e.g., pentobarbital, chloral hydrate, muscimol, and ethanol) produce analgesia and unconsciousness (sedation). Dissociative anesthetics that antagonize the N-methyl-D-aspartate (NMDA) receptor (e.g., ketamine, MK-801, dextromethorphan, and phencyclidine) produce analgesia but do not induce complete loss of consciousness. To understand the mechanisms underlying loss of consciousness and analgesia induced by general anesthetics, we examined the patterns of expression of c-Fos protein in the brain and correlated these with physiological effects of systemically administering GABAergic agents and ketamine at dosages used clinically for anesthesia in rats. ⋯ In contrast, GABAergic agents suppressed Fos in the same arousal-promoting systems but increased the number of Fos-immunoreactive neurons in the VLPO compared with waking control animals. All anesthetics tested induced Fos in the spinally projecting noradrenergic A5-7 groups. 6-hydroxydopamine lesions of the A5-7 groups or ibotenic acid lesions of the ventrolateral periaqueductal gray matter (vlPAG) attenuated antinociceptive responses to noxious thermal stimulation (tail-flick test) by both types of anesthetics. We hypothesize that neural substrates of sleep-wake behavior are engaged by low-dose sedative anesthetics and that the mesopontine descending noradrenergic cell groups contribute to the analgesic effects of both NMDA receptor antagonists and GABA(A) receptor-enhancing anesthetics.