Area in the rat brain producing rhythmical slow activity after chemical stimulation

Serotonin, carbamylcholine, norephinephrine, and various control substances were implanted stereotaxically into various areas of the rat brain, and the effects of the compounds in altering the hippocampal rhythmical slow activity (RSA) were noted. Both carbamylcholine and serotonin implanted into the tip of the diagonal bands of Broca were observed to produce a regular rhythm of 7 Hz in both dorsal and ventral hippocampal recording sites. Carbamylcholine implanted into the medial parolfactory area consistently elicited RSA only in the ventral hippocampus recording area, while carbamylcholine implanted into the lower limb of the diagonal bands elicited the rhythm only in dorsal hippocampal recording sites. In rats in which the rhythm was elicited by serotonin, no effect was seen upon further implantation of carbamylcholine, whereas the converse was not true. These results are interpreted as suggesting a serotonergic influence upon hippocampal RSA separate from the usual cholinergic system which seemed to be inhibitory in nature.