Electrophysiological correlates of stereotyped sniffing in rats injected with apomorphine.

Macroelectrodes were chronically implanted in the olfactory bulb, dorsal hippocampus, neocortex and under the mystacial pad in a group of rats. Recordings were taken during spontaneous behavior, during exploration of novel objects and odorous material, and during handling. Similar observations were made following injection of apomorphine (1.25-5 mg/kg, SC). The lower dose of apomorphine elicited a pattern of sniffing, olfactory bulb activity and vibrissal EMG which resembled closely the patterns observed in undrugged rats sniffing while in tactile contact with a novel object. However, unlike normal rats, the apomorphine-treated rats did not orient toward novel objects or odors. Apomorphine also elicited nearly continuous hippocampal rhythmical slow activity which occurred in correlation with head movements and locomotion. It is suggested that apomorphine elicits a motor pattern which resembles normal contact sniffing but which, unlike normal sniffing, is relatively impervious to control by visual and olfactory stimuli.