Application of footshock during the acquisition trial of a one-trial passive avoidance test is associated with a rise in the concentration of
serotonin in the hippocampi of rats 24 hr after termination of the acquisition trial. Rats subjected to amnesic treatment with
carbon dioxide (CO2) immediately after footshock do not show this rise in the hippocampal concentration of
serotonin. The
ACTH-analogues,
ACTH 4-10 and
ACTH 4-10 (7D-Phe), alleviate CO2-induced
amnesia for the passive avoidance response when administered 1 hr before retrieval test 24 hr after acquisition. These
peptides do not have anti-amnesic activity when given before acquistion. Another
ACTH-analogue,
ACTH 11-24 does not affect
amnesia, given before either the acquisition or the retrieval test. The anti-amnesic effect of
ACTH 4-10 AND
ACTH 4-10 (7D-Phe), was correlated with a rise in the hippocampal
serotonin concentration similar to that observed in non-amnesic animals. Pre-acquisition treatment with
ACTH 4-10 or administration of
ACTH 11-24 did not affect hippocampal
serotonin concentrations. Changes in the hippocampal concentrations of
noradrenaline,
dopamine,
tryptophan and
tyrosine were not related to the behavioural activity of any of the
peptides. It is suggested that alterations in hippocampal
serotonin metabolism 24 hr after acquisition of a passive avoidance response are associated with the retrieveability of the passive avoidance response.