Elicitation of intraspecific defence reactions in the rat from midbrain periaqueductal grey by microinjection of kainic acid, without neurotoxic effects.

Microinjection of 40 pmol of the neuroexcitotoxin, kainic acid (KA) in the midbrain periaqueductal grey region (PAG) evoked a significant increase in both defensive and immobile behaviours in rats tested in a social situation. The evoked reactions appeared identical to the rat's natural defensive reaction to attack by a conspecific, although they were evoked by the presence, rather than the attack, of another rat. The long duration and natural appearance of the KA-evoked reactions stand in contrast to the short, 'explosive' reactions evoked by injection in the PAG of other excitant amino acids. There was no behavioural evidence of a diminution in the effect of repeated injections of KA in the PAG, nor was there any histological evidence of neurotoxicity.