Neurons containing tuberoinfundibular peptide of 39 residues are activated following male sexual behavior.

Tuberoinfundibular peptide of 39 residues (TIP39)-immunoreactive (IR) neurons are present in the medial subdivision of the parvocellular subparafascicular thalamic nucleus (mSPFp) where ejaculation-specific Fos expression is localized. The mSPFp is reciprocally connected to the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST) and the medial nucleus of the amygdala (Me), all of which are critical for the regulation of male sexual behavior. The mSPFp also receives galanin and enkephalin containing projections from a region in the lumbar spinal cord, thought to be a central ejaculation center. Therefore, we hypothesized that TIP39 neurons in the mSPFp may be part of the neuronal circuitry activated by male sexual behavior. To test this hypothesis, we examined induction of Fos in TIP39 containing neurons in the mSPFp following male sexual behavior. Mating-induced Fos expression was evaluated in sexually experienced male rats under four experimental conditions: animals that (1) remained in their home cage without any interaction with females, (2) interacted with stimulus females and displayed intromission without ejaculation, (3) displayed one ejaculation, or (4) displayed 2 ejaculations. We found that Fos was induced in TIP39-IR neurons in the mSPFp in male rats following ejaculation but much less so following intromission without ejaculation. This suggests that TIP39-IR neurons in the mSPFp are part of the afferent circuits that process genital-somatosensory information related to ejaculation, and which contribute to mating and mating-induced changes in reproductive behavior.