Serotonergic influences on EEG synchronization induced by milk drinking in the cat

Milk drinking elicits electroencephalographic (EEG) synchronization in the parieto-occipital cortex of cats. This EEG change is a reliable correlate of the consummatory phenomena involved in "relaxation" behavior. The effect of varying serotonin brain levels by administering P-chlorophenylalanine (PCPA) or 5-hydroxytryptophan (5HTP) on this response was studied in 25 young cats. Single or repeated injections (4-8 days) of 50, 100 or 150 mg/kg of PCPA resulted in a dose related decrease in the duration of the EEG parieto-occipital synchronization during fixed periods of milk drinking. A single injection of 3, 10 or 30 mg/kg of 5HTP to chronic PCPA treated cats, restored the EEG parieto-occipital synchronization during milk drinking to control values. Moreover, administration of 5HTP to non-treated cats significantly increased the duration of EEG parieto-occipital synchronization during milk drinking. Our results suggest that brain serotonergic neurons are involved in the development of EEG synchronization during milk drinking.