Vocalization responses after spinal administration of bicuculline or strychnine in rats

Objective. Spinal administration of compounds decreasing inhibition of spinal nociceptive pathways, such as antagonists of GABA or glycine receptors, leads to vocalization. This can be quantified semiautomatically and could be used as a research model. Materials and Methods. Vocalization after intrathecal administration of bicuculline and strychnine was measured in Sprague-Dawley rats. Results. Both bicuculline and strychnine produced short, dose-related vocalization responses that were not significantly different between models of peripheral inflammation and neuropathic pain and normal controls, except for reduced strychnine-induced vocalization during inflammation. The strychnine-induced vocalization responses were also reduced in freely moving rats and increased by light tactile stimulation. Conclusions. Bicuculline-induced vocalization seems to be related to facilitation of nociceptive transmission, and could have limited use as a model of nociception at the spinal level. However, peripheral inflammation or neuropathic pain did not affect it. Strychnine-induced vocalization responses seem to be related to non-noxious somatosensory input.