Elicited PGO waves in rats: Lack of 5-HT1A inhibition in putative pontine generator region

Pontogeniculo-occipital (PGO) waves and an elicited analogue (PGO(E)) may be recorded in the pens of rats. Cholinergic cells in the pedunculopontine tegmental (PPT) and laterodorsal tegmental (LDT) nuclei are implicated in the generation of PGO waves. Serotonin (5-HT) may inhibit the generation of PGO waves, and possibly PGO(E). We examined the role of 5-HT1A receptor mechanisms in the generation of auditory-elicited PGO(E) in rats. Administration of 8-OH-DPAT [8-hydroxy-2-(n-dipropylamino)tetralin] into PPT did not significantly affect PGO(E) amplitude or response frequency. Binding of [H-3]CN-IMI ([H-3]cyanoimipramine) to 5-HT uptake sites located presynaptically was used as a measure of 5-HT innervation. Quantitative autoradiographic analysis of [H-3]CN-IMI binding indicated a moderate to low degree of 5-HT innervation of PPT and a moderately high innervation of LDT compared to the dorsal raphe nucleus (DRN). Binding of [H-3]8-OH-DPAT to 5-HT1A receptors revealed few receptor sites in PPT, and a low to moderate number of receptors in LDT compared to binding in DRN. The results suggest that inhibitory serotonergic modulation of PGO(E) is probably not mediated through a 5-HT1A receptor mechanism in PPT.