The spicules of a male C. elegans contain the sensory-motor neurons SPD and SPV. LeBoeuf et al. found that these SPD and SPV neurons stimulate cholinergic neurons to release acetylcholine (ACh) when the spicule is inserted into the hermaphrodite vulva. This begins the sperm initiation process (that is, sperm are moved from storage in the seminal vesicle to the vas deferens, ready for release). The sensory-motor neurons also stimulate a pair of glutamateric neurons called PCA to release glutamate (Glu), which triggers ejaculation. The release of sperm inhibits the activity of the sensory-motor neurons for several minutes after ejaculation; during this refractory period the male cannot copulate. LeBoeuf et al. also found that glia-like socket cells must also be present if proper ejaculation is to occur. These cells produce dopamine (DA), which controls sperm release and affects the length of the refractory period—more dopamine means a longer wait before ejaculation is possible again.