Capsaicin increases GFAP and glutamine synthetase immunoreactivity in rat arcuate nucleus and median eminence

Antibodies to glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) were used to determine the effect of s.c. capsaicin (after 75 min) on astroglial cells in the rat arcuate nucleus-median eminence (ARC-ME). Compared to vehicle, capsaicin significantly increased GFAP and GS immunoreactivity in the ARC-ME. Co-localization of GFAP and GS was observed in the ARC-ME complex. Since GS is primarily responsible for glutamate-glutamine metabolism, the increase in total immunostaining for GFAP-and GS- staining suggests a functional adjustment to cope with some of the capsaicin-induced effects. Together with the involvement of nitric oxide synthase in the ARC-ME response to capsaicin, these observations indicate activity-dependent plasticity of the neuronglia network in response to this stressful/noxious stimulus.