Date of Award
Doctor of Philosophy (PhD)
The axial muscles of the rat are active in a wide variety of behaviors; of special interest is their involvement in sexual behavior. In this research their responses to cutaneous inputs and supraspinal influences were studied. The pudendal nerve (PN), which innervates the skin regions contacted by males during sexual behavior, was stimulated electrically and the responses in the dorsal roots, the lateral longissimus muscle (LL) and its muscle nerves (MN's) were recorded. Conduction velocities in the PN were 54 m/s for the largest A- β fibers and averaged 10 m/s for A-δ fibers. Stimulation (stim) of the PN afferents at currents below A-δ threshold potentiated LL motoneuron firing and evoked activity in otherwise silent nerves. The first responses in females occured 8.8 ms after the last shock in a 3 shock stim; in males the onset was 11.4 ms. MN firing peaks occurred at latencies of 14, 24 and 105 ms in both sexes; thel05 ms peak was larger in males. Firing was usually depressed from 37 to 53 ms. Comparable responses were seen with ipsi- or contralateral PN stim; these were facilitated by bilateral stim. In EMG recordings, unit activity was consistent with that seen in the MN's. After total spinal cord transections in the thoracic region, the PN-evoked response in the LL nerves (PNER) consisted of a single activity peak at 22.8 ms: the earliest responses are at least partly segmental. To help identify supraspinal inputs to the PNER various partial transections of the spinal cord were made. When the ventrolateral (VL) columns were spared the PNER was like that in intact animals. If the VL columns were cut the PNER was like that in fully transected rats. Bilateral convergence of PN inputs was seen in the totally transected animals; thus, such convergence occurs segmentally. The lesions which substantially altered the PNER were similar to those which eliminate lordosis in behaving rats. Electrical stim within the medullary reticular formation evoked activity in the LL MN's at latencies of 2.6 to as much as 70 ms from the effective shock in a stim train. Responses were evoked by contra- as well as ipsilateral stim. Combined stim of the brainstem and PN's demonstrated facilitatory effects upon the excitability of LL MN's and evoked responses not seen with stim to either site alone; the response latency was shorter than that to either stim applied alone.
Cohen, Mark Steven, "Cutaneous and Supraspinal Control of the Axial Muscles in the Rat: Implications for Behavior" (1985). Student Theses and Dissertations. 461.