SOCIAL-BEHAVIOR IN SHEEP RELATES TO BEHAVIOR AND NEUROTRANSMITTER RESPONSES TO NOCICEPTIVE STIMULI

Sheep in the field display differences in social behaviour. These diff erences allow a division into three social groups with distinct behavi oural occurrences and frequencies. The behavioural and neurotransmissi on responses of each of these groups to aversive stimuli were compared . Behavioural responses were seen to both forelimb electric shocks and thermal heating of the nose in all groups. These responses changed wi th stimulus repetition in a group-dependent manner. Microdialysis prob e studies of neurotransmitter release in the somatosensory cortex indi cated neurotransmitter responses to stimuli in all animals that varied with both animal group and stimulus repetition. Group I animals, aggr essive and socially active, showed increases in gamma amino-4-butyric acid (GABA) with initial stimulus presentation; this increased with st imulus repetition. Behavioural responses to the stimuli decreased with repetition and nonstimulus-related behaviours, during the course of t he experiment, increased. Both of these appeared dependent upon GABA. Group 2 animals, moderately aggressive and socially active, released o pioid-like peptides (OLP) upon initial exposure to stimuli but, with r epetition, switched to using GABA. Group 3 animals, nonaggressive and socially inactive, released OLP with initial and repeat stimuli. In gr oups 2 and 3, both GABA and OLP appear to reduce stimulus-related beha viour, but OLP appeared to also reduce nonstimulus-related behaviour a nd GABA increased these. Changes were independent of animal liveweight . Glutamate was released in response to stimuli in all 3 groups and, w ith repetition, fell in groups 1 and 2 but increased in group 3. An an imal's social behaviour and status may predict its response to a stimu lus.