Autonomic adjustments during avoidance and orienting responses induced by electrical stimulation of the central nervous system in toads (Bufo paracnemis).

Electrical stimulation of the central nervous system of conscious toads with permanently implanted electrodes in regions related to orienting and avoidance responses induces cardiovascular (hypertension and tachycardia) and respiratory (increased intrapulmonary pressure) changes together with the somato-motor effects typical of these responses. Sympathetic activation occurs and the main peripheral mediator involved may be adrenergic, since the cardiovascular effects are almost completely blocket by systemic pretreatment with phentolamine and DCI. The cardiovascular changes obtained by central stimulation are qualitatively similar to those recorded for toads whose orienting and avoidance behaviors are obtained by the presentation of visual stimuli (presentation of a prey and of a black card moved over the experimental box). Variations in heart rhythm may occur in both cases in the absence of visible somatic manifestations or of other neurovegetative changes, thus showing the importance of this parameter as an index of sensory reception of biologically significant stimuli. The results are compared to those obtained under similar conditions in other non-mammalian vertebrates.