Retroambiguus projections to the cutaneus trunci motoneurons may form a pathway in the central control of mating

Our laboratory has proposed that the nucleus retroambiguus (NRA) generates the specific motor performance displayed by female cats during mating and t hat it uses direct pathways to the motoneurons of the lower limb muscles in volved in this activity. In the hamster a similar NRA-projection system cou ld generate the typical female mating posture, which is characterized by lo rdosis of the back as well as elevation of the tail. The present study atte mpted to determine whether this elevation of the tail is also part of the N RA-mating control system. The basic assumption was that elevation of the ta il is a function of the cutaneus trunci muscle (CTM), which was verified by bilateral tetanic stimulation of the lateral thoracic nerves innervating t he CTM. It resulted in upward movement of the tail to a position similar to the tail-up position during the lordosis posture. Retrograde tracing resul ts showed that CTM motoneurons are located in the ventral and ventrolateral part of the C-7-C-8 ventral horn, those innervating the tail region ventro lateral to those innervating the axillary region. Anterograde tracing studi es showed that NRA fibers terminate bilaterally in both parts of the CTM mo toneuronal cell groups. Electron microscopical studies revealed that labele d NRA terminals make monosynaptic contacts with retrogradely labeled dendri tes of CTM motoneurons. Almost all of these terminal profiles had asymmetri c synapses and contained spherical vesicles, which suggests an excitatory f unction. The observation that 15% of the labeled NRA terminals make more th an one synaptic contact with a retrogradely labeled CTM motoneuronal dendri te within the same section indicates how powerful the NRA-CTM projection is . The results indicate that during mating the NRA not only could generate t he lordosis posture but also the elevation of the tail.