Sexual activity alters the concentration of amino acids in the cerebrospinal fluid of male rats.

The concentrations of amino acids were measured in cerebrospinal fluid samples obtained from freely moving male rats before sexual activity, immediately after ejaculation and after the end of the postejaculatory refractory period. The concentration of gamma-aminobutyric acid increased by more than 1000% after ejaculation, while the concentrations of Asp and Glu increased by about 200%. Consistent, but small decrements were found in the concentrations of Ser, Arg, Ala and Leu. Thus, the concentration of a major inhibitory neurotransmitter increases markedly in a physiological state when male rats are completely refractory to sexual stimuli.