Facilitation of memory by peripheral administration of substance P.

This report summarizes a recent series of experiments dealing with the effect of peripheral (i.p.) administration of SP on the learning of avoidance and habituation tasks. In summary, the results from these studies show that peripheral post-training SP administration in rats enhances memory in a dose- and time-dependent way. The effect of substance P on retention was observed across tasks with different response requirements and in the absence of explicit punishment. The memory-enhancing effects are long-lasting, until 21 days post-training, and are mediated, at least in part, via interactions with the endogenous opioid system. The mnemotropic effects of peripherally administered SP are sensitive to the functional integrity of the vagus, suggesting that the vagus nerve may be one pathway by which systemic SP influences memory storage processes in the brain. Furthermore, the data indicated that these effects seemed to be encoded by different SP sequences, the N-terminal SP1-7, but not the C-terminal hepta- and hexapeptide sequences being responsible for the memory-promoting effects. Taken together, these studies strongly suggest that SP may be considered to have memory-promoting effects.