Morphological and functional studies have confirmed that interstitial cells of Cajal (ICCs) are involved in many enteric motor neurotransmission pathways. Recent investigations have demonstrated that human and guinea pig prostate glands possess a distinct cell type with morphological and immunological similarities to ICCs. These prostate ICCs have a close relationship with nerve bundles and smooth muscle cells. Prostate smooth muscle tone is largely induced by stimulation from the sympathetic nervous system, which releases excitatory norepinephrine (NE) to act on the alpha 1-adrenoceptor. We have performed morphological and functional experiments to determine the role of ICCs in sympathetic neurotransmission in the guinea pig prostate based on the hypothesis that prostate ICCs act as mediators of sympathetic neurotransmission. Immunohistochemistry revealed many close points of contact between ICCs and sympathetic nerve bundles and smooth muscle cells. Double-labeled sections revealed that alpha 1-adrenoceptor and the gap junction protein connexin 43 were expressed in prostate ICCs. Surprisingly, prostate ICCs co-expressed tyrosine hydroxylase and dopamine beta-hydroxylase, two markers of sympathetic neurons. Functionally, the application of NE evoked a large single inward current in isolated prostate ICCs in a dose-dependent manner. The inward current evoked by NE was mediated via the activation of alpha 1-adrenoceptors, because it was abolished by the non-specific alpha-adrenoceptor antagonist, phentolamine and the specific alpha 1-adrenoceptor antagonist, prazosin. Thus, ICCs in the guinea pig prostate are target cells for prostate sympathetic nerves and possess the morphological and functional characteristics required to mediate sympathetic signals.