Proceedings: The effect of apomorphine on oral behaviour in piglets.

The new-born mammal has both nutritive and non-nutritive sucking requirements (Levy, 1934). When non-nutritive sucking is prevented, abnormal oral behaviour which can resemble the effect of apomorphine may be induced. The two types of sucking behaviour can be distinguished using equipment described by Stephens (1975). This consists of a wooden box lined with rubber sheeting. A rubber teat is inserted through a hole in one wall. The teat is connected to two microswitches which record teat movements and milk flow through the teat is also monitored. One-day-old piglets can be trained to feed from the teat in three days at which time they develop a regular pattern of teat activity. This consists of an ingestive phase lasting approximately 15 min during which the piglets drink the milk provided. Then follows a period of sporadic non-nutritive teat activity when the piglets nuzzle at or around the teat without drinking. Low doses of apomorphine (0.1-0.2 mg/kg s.c.) injected during the latter phase greatly prolong and intensify the non-nutritive teat activity. This method is useful for quantifying behavioural effects of apomorphine. The responses of other farm animals to apomorphine and other drugs thought to affect central dopaminergic neuron systems will also be shown and compared with abnormal oral behaviour seen under intensive husbandry conditions.