Evidence that oxytocin is an endogenous stimulator of autonomic sympathetic preganglionics: the pupillary dilatation response to vaginocervical stimulation in the rat

Vaginocervical mechanostimulation (VS) was shown previously to release oxyt ocin within the spinal cord and to induce pupillary dilatation. In the pres ent study, (a) injection of oxytocin directly to the spinal cord (10 or 25 mug intrathecally [i.t.] in 5 mul saline) induced pupillary dilatation when observed 1 min after the end of the injection and (b) injection of an oxyt ocin receptor antagonist ([d(CH2)(5)-Tyr (Me)(2)-Orn(8)]-Vasotncin {OTA}; 5 mug i.t. in 5 mul saline) significantly attenuated the pupillary dilatatio n response to VS, when VS was applied 3 min after the end of the injection. Since activation of autonomic sympathetic preganglionic neurons in the tho racic spinal cord produces pupillary dilatation, we propose that oxytocin i s a central nervous system neurotransmitter that stimulates these neurons d irectly or perhaps indirectly, and thus is a mediator of VS-produced pupill ary dilatation. (C) 2001 Published by Elsevier Science B.V.