Inhibition period of self-stimulation and the involvement of the serotonergic nervous system in long-term intracranial self-stimulation in rats

Abstract

Inhibition periods (less than 10 times/min) for dozens of minutes were often observed in a long-term (24 hours) intracranial self-stimulation (ICSS; 50-60 times/min) in rats; electrical stimulations were applied to the hemi-lateral medial forebrain bundle of rats when the rats pressed a lever. The inhibition was not induced by thermal effect on neural function or by muscular fatigue, since the animals in the inhibition period started ICSS again when more intensive stimulations to the ipsi-lateral medial forebrain bundle or stimulations to the contra-lateral medial forebrain bundle were applied to the animals. In such a long-term ICSS, the inhibition period was significantly decreased in the animals pharmacologically treated with 5,7-dihydroxy-tryptamine just after their birth for inducing degeneration of serotonergic neurons in the dorsal raphe nucleus, although the treatment did not affect ICSS in short duration. These observations indicate that the serotonergic nervous system facilitates or modulates the inhibition of the long-term ICSS and would be involved in weariness or fatigue sensation. [Jpn J Physiol 54 Suppl:S209 (2004)]