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International Journal of Impotence Research (2004) 16, 8690
& 2004 Nature Publishing Group All rights reserved 0955-9930/04 $25.00www.nature.com/ijirCholinergic facilitation of erection and ejaculation
in spinal cord-transected ratsVM Vargas1, D Torres1, F Corona1, M Vergara1, LE Gomez2, R Delgado-Lezama3 and R Cueva-Rolon2*1Departamento de Agrobiologa, Universidad Autonoma de Tlaxcala, Tlaxcala, Mexico; 2Laboratorio de Tlaxcala, Centro
de Investigacion y Estudios Avanzados, Tlaxcala, Mexico; and3Departamento de Fisiologia, CINVESTAV del I.P.N.,
Tlaxcala, MexicoPenile reflexes (PRs) were monitored in chronic spinal cord-transected rats by identifying them
visually, and at the same time they were recorded as the electromyographic activity of
bulbospongiosus muscles. Intraperitoneal injection of the agonist muscarine (10 lg) produced a
facilitation of PRs. A decrease in the latency, an increase in the number of clusters and often an
increase in the duration of cups were found after muscarine. In addition, 66% (six out of nine) of the
animals ejaculated after muscarine. These results suggest that cholinergic receptor stimulation may
be involved in erectile and ejaculatory mechanisms mediated by the spinal cord.International Journal of Impotence Research (2004) 16, 8690. doi:10.1038/sj.ijir.3901169Keywords: erection; ejaculation; spinal cord; acetylcholine receptors; m-receptors; penile reflexesIntroductionThe stimulation of spinal cord acetylcholine receptors has been reported to facilitate ejaculation. For
example, ejaculation is stimulated by cholinesterase
inhibitors in spinal cord-injured men:1,2 intrathecally applied neostigmine stimulates penis erection
and ejaculation in 58% of subjects,1 and ejaculation
is found in 40% of subjects when physostigmine is
given systemically.2 In addition, in freely moving
rats, the stimulation of the spinal M-type cholinergic
receptors facilitates sexual behavior, since a decrease of ejaculatory latency, intromission frequency
and intromission interval is found when the agonist
muscarine is applied intrathecally. On the contrary,
when the muscarinic receptor antagonist homatropine is applied, a decrease in the number of animals
that are able to copulate is found in sexually trained
and vigorous males.3 However, it is unclear how the
activation of the spinal cord muscarinic receptors
facilitates ejaculation; the stimulation of lumbar
reflex centers has been suggested.3,4In addition, it has been found that in spinal cordtransected rats muscarine produces glans penis
erections that often accompany rhythmic discharges
in the bulbospongiosus (BS) muscles. BS discharges
elicited by muscarine had a similar electromyographic (EMG) activity to that found in the urethro
genital reflex (UGR).5 UGR is an experimental model