A pivotal role of lumbar spinothalamic cells in regulation of ejaculation via intraspinal connections

different aspects, with ejaculation being the most rewarding. Ejaculation is a complex reflex controlled by a central pattern generator in the lumbosacral spinal cord, named the spinal ejaculation generator.1 This generator receives sensory inputs during mating via the dorsal penile nerve and triggers emission and expulsion of seminal fluids via projections to autonomic and motor neurons in the lumbosacral spinal cord. For a long time it was hypothesized that the integration of sensory inputs and autonomic/motor outflow is mediated by a key group of interneurons located in the lumbar spinal cord. Indeed, 10 years ago, our laboratory identified this key population of interneurons as a group of spinothalamic cells located in lumbar levels L3-4 surrounding the central canal in laminae VII and X.2 Based on their location and axonal projections, this cell group is referred to as lumbar spinothalamic (LSt) cells. These neurons express several neuropeptides, including galanin, and exclusively express neurokinin-1 (NK-1) receptors (Figure 1A), thus allowing us to test questions concerning the functional role of LSt cells using saporin conjugated to SSP (Cat. #IT-11), the substance P analog [Sar9, Met(O2)11], from Advanced Targeting Systems. In our previous paper we demonstrated that cell-specific lesions of the LSt cells, completely eliminated ejaculatory behavior, demonstrating the pivotal role of this neural population for ejaculation as the key component of the spinal ejaculation generator.2 Moreover, we showed that LST cells have projections to the autonomic preganglionic and motor centers controlling ejaculation and are activated by sensory inputs from the dorsal penile nerve;3,4 stimulation of this nerve triggers ejaculation in mammals (Figure 2).5 However, several questions remained to be addressed. The spinal ejaculation generator, and thus the ejaculatory reflex, is influenced by inhibitory and