Testosterone Regulates Androgen Receptor Immunoreactivity in the Copulatory, but not Courtship, Neuromuscular System in Adult Male Green Anoles

Abstract

Androgens regulate the expression of male reproductive behaviour in diverse vertebrate species, often acting on androgen receptors (AR) to induce structural or functional changes in the nervous system and periphery. Male green anoles possess two sexually dimorphic neuromuscular systems, one controlling throat fan (dewlap) extension, which occurs during courtship, and the other mediating copulatory organ function. Although androgens are required for behavioural activation in both systems, testosterone has differential effects on the neuromuscular morphology. It increases the size of copulatory muscle fibres during the breeding season, but significant effects on dewlap muscle fibre size and motoneurone soma size in either system have not been detected. Corresponding to the lack of testosterone-induced morphological effects in the courtship system, relatively low levels of AR are expressed in the associated motoneurones. The present experiment had two goals, aiming to determine whether: (i) the other courtship and copulatory neuromuscular tissues express AR and (ii) testosterone and/or seasonal environmental changes regulate AR expression. The percentage of AR+ nuclei was evaluated in both the breeding and nonbreeding seasons in gonadally intact adult males (Experiment 1) and in castrated males treated with either testosterone or vehicle (Experiment 2). AR was extensively expressed in the dewlap and copulatory muscles, and in a high percentage of the copulatory motoneurones, but immunoreactivity did not vary across season. Testosterone increased the percentage of AR+ nuclei in the copulatory muscles of both breeding and nonbreeding males but not in the dewlap muscle or copulatory motoneurones. Finally, the target structures for both systems (cartilages and hemipenes) expressed AR in all animals. Therefore, the effects of testosterone on AR immunoreactivity suggest that up-regulation of the receptors may be important for morphological change. However, because all structures investigated in the present experiment expressed AR, the data also indicate that the receptors are involved with other functions.

Courtship and copulation in the adult male green anole: Effects of season, hormone and female contact on reproductive behavior and morphology

“…That is, as in the present study, others have documented that T is important for the display of male sexual behavior in the green anole [53,87]. The present data also replicate T-induced increases in the size of hemipenes, copulatory muscle fibers and renal sex segment cell size, with greater effects under conditions typical of the BS than NBS [41,42,53,61,87]. Fewer statistically significant results were detected in the earlier study on the copulatory system, but the magnitude of the differences was nearly identical to those in the present study.…”

“…ARs are also expressed in ceratohyoid muscles and 45% of AmbX motoneurons, but apparently not in AmbIX/VIImv motoneurons in intact males [42,72]. Unlike the copulatory system, but consistent with the relative lack of plasticity, T does not seem to alter AR expression in dewlap structures [42]. Therefore, T may enhance morphology of peripheral copulatory, but not courtship, structures at least in part via an up-regulation of AR.…”

“…We do have information about neuromuscular structures, however. ARs are located throughout the copulatory system, and exogenous T increases their expression in the hemipenes and RPM, although it does not increase the percent of AR-positive T17-S1 motoneurons [42]. ARs are also expressed in ceratohyoid muscles and 45% of AmbX motoneurons, but apparently not in AmbIX/VIImv motoneurons in intact males [42,72].…”

“…ARs are located throughout the copulatory system, and exogenous T increases their expression in the hemipenes and RPM, although it does not increase the percent of AR-positive T17-S1 motoneurons [42]. ARs are also expressed in ceratohyoid muscles and 45% of AmbX motoneurons, but apparently not in AmbIX/VIImv motoneurons in intact males [42,72]. Unlike the copulatory system, but consistent with the relative lack of plasticity, T does not seem to alter AR expression in dewlap structures [42].…”

“…Following isoflurane anesthesia, males from the BS and NBS were bilaterally gonadectomized while on ice and subcutaneously implanted with a Silastic capsule (7 mm long × 0.7 mm ID × 1.65 mm OD) containing 5 mm of packed testosterone propionate (T) or left blank (Bl) (as in [41,42]). Each male was weighed and measured snout-to-vent (nose tip to cloaca; SVL).…”