Galanin and learning

A number of studies indicate that galanin (GAL) is a potent modulator of ba sal acetylcholine release in the rat forebrain e.g. in the cholinergic neur ons of the septo-hippocampal projections. Thus, GAL perfused through the mi crodialysis probe decreased basal acetylcholine release in the ventral hipp ocampus, while it enhanced acetylcholine release in the dorsal hippocampus. This finding indicates that GAL may act via different mechanisms within th e subsystems of the hippocampus. This hypothesis has received support from studies using the Morris swim maze, a learning task dependent on hippocampa l mechanisms. GAL (3 nmol/rat) infused into the ventral hippocampus impaire d spatial learning acquisition, while it tended to facilitate when injected into the dorsal hippocampus. However, the effects of GAL on acetylcholine release and on spatial learning, which are due to activation of GAL-recepto rs, appear to be indirectly mediated possibly via noradrenaline transmissio n. GAL is also a potent inhibitor of mesencephalic 5-HT neurotransmission i n vivo. These findings are discussed in relation to the role of acetylcholi ne and serotonin in cognition. (C) 1999 Elsevier Science B.V. All rights re served.