Changes in cholinergic enzyme activities in the cuttlefish brain during memory formation

Cephalopods are promising invertebrate models to investigate the neurobiology of learning and memory due to their advanced behavioral abilities. In the present study, acetylcholine synthesis and catabolism were studied in various central nervous system (CNS) regions of cuttlefish subjected to associative learning procedures with different retention delays, with the aim of characterizing the involvement of cholinergic neurotransmission in learning and memory processes in this species. In the first experiment, the acquisition procedure consisted of a single continuous trial. As a response to a short retention delay (60 min), when compared to control or to a very short retention delay (2 min), cholinergic enzymatic activities decreased in structures involved in learning and memory (vertical–subvertical lobes) and in lower motor centers (brachial and pedal lobes). In the second experiment, the same learning paradigm was used but with repeated trials. In this case, a long-term retention (24 h) induced an increase in acetylcholine catabolism in the pedal and optic lobes (lower motor and higher centers, respectively) when compared to control. These results suggest the occurrence of different regulatory mechanisms of cholinergic enzymes as a response to memory formation with a long- or a short-term retention delay.