DIFFERENTIAL-EFFECTS OF INTRATHECAL THYROTROPIN-RELEASING-HORMONE (TRH) ON PERINEAL REFLEXES IN MALE-RATS

The effects of thytrotopin-releasing hormone (TRH) on the sexual and d efecatory reflexes regulated by pudendal motoneurons were investigated . Intrathecal TRH (10 mu l volume; 0.0, 0.01, 1.0, or 100 mu M concent ration) at lumbosacral spinal segments (L4-S1) in acute preparations p roduced a dose-dependent increase in external anal sphincter (EAS), bu t not bulbospongiosus (BS), electromyographic (EMG) activity. Intraspi nal (L6) injection of 100 mu M TRH (1 mu l/micropipette), significantl y increased EAS EMG activity in acute preparations. Electromyographic activity of the BS muscle was unchanged. All doses of intrathecal TRH (10 mu l volume; 0, 10, 50, 100, or 500 mu M concentration) in awake a nimals significantly reduced the proportion of responders to a penile reflex test. Subsequently, all measures of penile reflexes were signif icantly reduced. Glans tumescence and defecation bouts before or durin g penile reflex testing were unaffected by intrathecal TRH as were ind ices of behavioral and motor hyper-reactivity analogous to that produc ed by serotonin. These data indicate that pudendal motoneurons, in the dorsomedial nucleus, are differentially regulated by neuropeptides pr esent in the lumbosacral spinal cord. Copyright (C) 1996 Elsevier Scie nce Inc.