Ibotenic acid lesions of the medial septum retard delay eyeblink conditioning in rabbits (Oryctolagus cuniculus)

S. Berry and R. Thompson (1979) reported that electrolytic lesions of the medial septum significantly retard eyeblink conditioning. However, these electrolytic lesions were nonselective and may have also damaged the subcortical inputs to the hippocampus via the fimbria–fornix. In the present study, the medial septum was selectively lesioned with ibotenic acid in rabbits (Oryctolagus cuniculus), whose performance in a delay eyeblink conditioning paradigm was compared with that of intact controls, sham-operated controls, and intact controls given a systemic injection of scopolamine. Rabbits with selective medial septal lesions and rabbits receiving systemic scopolamine were significantly slower to condition than were intact and sham-lesioned rabbits. This finding demonstrates that the selective removal of the medial septum retards delay eyeblink conditioning in a manner similar to the disruption seen after systemic administration of scopolamine. One interesting feature of work from classical eyeblink conditioning is the finding that, although a hippocampal lesion does not affect delay eyeblink conditioning (Schmaltz & Theios, 1972), a disruption of hippocampal activity greatly retards delay eyeblink conditioning (Berry & Thompson, 1979; Solomon, Solomon, Vander Shaaf, & Perry, 1983). Classical eyeblink conditioning is a simple associative learning paradigm in which a neutral stimulus (the conditioned stimulus [CS], usually a tone or light) is paired with a response-evoking stimulus (the unconditioned stimulus [US], usually a corneal airpuff or periorbital eye shock). Initially, the tone elicits no behavioral response, whereas the airpuff elicits a reflexive eyeblink. By repeatedly pairing the tone and airpuff, the tone alone comes to elicit an eyeblink response (the conditioned response [CR]).