Induction of Fos immunoreactivity by acute glucose deprivation in the rat caudal brainstem: relation to NADPH diaphorase localization

Abstract

Neuronal nitric oxide (NO) synthase, a NADPH diaphorase (NADPH-d) enzyme, catalyzes formation of the free radical neurotransmitter, NO, and is distributed within several caudal brainstem structures. The following studies investigated whether these neuron populations express immunoreactivity for the inducible nuclear transcription factor, Fos, in response to acute glucose deprivation. Eight days after bilateral ovariectomy and subcutaneous implantation of silastic capsules containing 30 microg estradiol benzoate/ml, adult female rats were injected i.p. with the glucose antimetabolite, 2-deoxy-D-glucose (2DG; 400 mg/kg), or the vehicle, saline, and killed by transcardial perfusion 2 h later. At 150-microm intervals through the midbrain, pons, and medulla 25-microm sections were taken and processed for dual cytoplasmic NADPH-d enzyme activity and nuclear Fos immunoreactivity (Fos-ir). Although NADPH-d-positive neurons were demonstrated in several neural structures, only those in the dorsal raphe nuclei, central subnucleus of the nucleus of the solitary tract, dorsal vagal motor nucleus, lateral paragigantocellular nucleus, nucleus ambiguus, reticular parvocellular nucleus, and medullary A5 noradrenergic cells were colabeled for nuclear Fos-ir following injection of 2DG. While NADPH-d neurons in the midbrain central gray and the latero- and posterodorsal tegmental, lateral parabrachial, motor trigeminal, and gigantocellular nuclei were not immunolabeled for Fos in the 2DG-treated animals, there was a close neuroanatomical proximity between neurons capable of generating NO and others expressing Fos-ir in these sites. These data reveal that only discrete populations of NADPH-d-containing neurons in the caudal brainstem are transcriptionally activated via the Fos stimulus-transcription cascade in response to glucose substrate imbalance, and suggest that NO and/or other neurotransmitters released by these neurons may function as neurochemical mediators of glucoprivic regulatory effects within this part of the brain.