Male Rough-skinned Newts Research Articles

Opioid κ-receptor agonists suppress sexual behaviors in male rough-skinned newts ( Taricha granulosa)

Four experiments were performed to evaluate a possible opioid involvement in the regulation of sexual behavior (amplectic clasping of a female) in intact adult male rough-skinned newts ( Taricha granulosa) during the breeding season. It was found that an ip injection of bremazocine, a κ-receptor opiate agonist, can markedly reduce sexual activity and that an ip injection of naloxone can reverse this inhibition in a dose-dependent fashion. In contrast, in male newts that were sexually inactive before treatment, injections of naloxone failed to induce sexual behavior, suggesting that opioid mechanisms do not normally exert a tonic inhibition of amphibian sexual behavior. In addition, an injection of ethylketocyclazocine (another κ-receptor agonist), but not morphine (a μ-receptor agonist) suppressed sexual behaviors of male newts. These results indicate that opioid mechanisms that include κ-type opioid receptors may contribute to the regulation of sexual behavior in nonmammalian vertebrates.

Correlation between immunoreactive vasotocin in optic tectum and seasonal changes in reproductive behaviors of male rough-skinned newts

Previous studies have shown that intracranial administration of the amphibian neuropeptide arginine vasotocin (AVT) to male rough-skinned newts ( Taricha granulosa) can stimulate masculine sexual behaviors. The present study was conducted to determine whether concentrations of endogenous AVT in specific brain areas are correlated with seasonal changes in sexual behavior. Immunoreactive (ir) AVT was measured in the dorsal preoptic area and in the optic tectum throughout the course of the reproductive cycle. In the optic tectum, irAVT levels were low throughout the summer, fall, and winter, but rose over fivefold in the spring when sexual behaviors are most prevalent in male newts. In contrast, irAVT levels in the dorsal preoptic area were high in the summer, but declined in the fall and fluctuated widely during the winter and spring. Thus, there are site-specific changes in irAVT concentrations in the brain of male newts during the seasonal reproductive cycle. The finding that irAVT concentrations in the optic tectum are seasonally correlated with newt sexual behaviors provides further evidence that AVT in this brain area may be important in the expression of sexual behavior.

Arginine vasotocin immunoreactivity in hypothalamic and extrahypothalamic areas of an amphibian brain.

The distribution of arginine vasotocin immunoreactivity (irAVT) was investigated in the brain of male rough-skinned newts (Amphibia: Taricha granulosa) using microdissection and radioimmunoassay techniques. The highest levels of irAVT were observed in the neuroendocrine hypothalamo-hypophysial system. However, detectable quantities of irAVT (greater than 0.40 ng/mg protein) also were observed in extrahypothalamic areas such as pallium, amygdala, striatum and thalamic, tectal and brainstem nuclei. No irAVT was detected in the olfactory bulb, rostral telencephalon, or in specific areas of the caudal telencephalon and diencephalon. These results indicate that, in amphibians, AVT is distributed among a wide range of brain areas and that there is regional specificity in irAVT concentrations.

Stress-induced inhibition of reproduction: evidence of suppressed secretion of LH-RH in an amphibian.

Male rough-skinned newts (Taricha granulosa) were used to investigate the hormonal responses associated with stress-induced inhibition of reproduction. When male newts were confined for 1 hr, using a procedure that previously had elicited physiological stress responses, androgen concentrations decreased in the plasma and immunoreactive (ir) LH-RH concentrations increased in the infundibulum and rostral hypothalamus. Likewise, when male newts were injected with 25 micrograms of corticosterone, androgen concentrations decreased and hypothalamic irLH-RH concentrations increased. These data, which are from experiments in February, support the hypothesis that in this amphibian, exposure to acute stress or to exogenous corticosterone can suppress plasma androgen titers by inhibiting the release of LH-RH from the hypothalamus. The effects of the confinement procedure and the injection of corticosterone on the concentrations of irLH-RH and androgens were different for newts in September than for newts in February.

Seasonal changes in luteinizing hormone-releasing hormone concentrations in microdissected brain regions of male rough-skinned newts ( Taricha granulosa)

Luteinizing hormone-releasing hormone (LHRH) concentrations were measured in specific brain areas of male rough-skinned newts collected from a single population throughout the reproductive cycle. Plasma androgen and corticosterone (B) concentrations were also measured. Androgen concentrations were highest during the breeding season (winter) and lowest during the summer. In contrast, plasma B was lowest during the breeding season and highest in the summer. Concentrations of LHRH in the infundibulum (I) and rostral hypothalamus (RH) were positively correlated throughout the reproductive cycle; LHRH was always higher in the I than in the RH. Concentrations of LHRH in the ventral preoptic area (POA) fluctuated independently of concentrations of LHRH in the I and RH. However, LHRH concentrations decreased to undetectable levels in all three brain areas in March and April, which was before the end of the breeding season and before plasma androgen concentrations had decreased. An injection of LHRH into postbreeding males resulted in a significant increase in plasma androgen concentrations, indicating that the pituitary-gonad axis was still functional at the end of the breeding season. These results support the hypothesis that an abrupt decline in LHRH secretion is the initial endocrine event that signals the end of the breeding season in this amphibian.

Stress-induced inhibition of sexual behavior: Corticosterone inhibits courtship behaviors of a male amphibian ( Taricha granulosa)

When male rough-skinned newts ( Taricha granulosa) are exposed to presumptive stressors, the incidence of courtship decreases and plasma corticosterone concentration increases. When sexually active males are injected intraperitoneally with corticosterone (1, 5, 10, 15, 20, or 25 μg), the incidence of courtship decreases rapidly and in proportion to the dose of corticosterone. Intracerebroventricular infusion of synthetic corticotropin-releasing factor (CRF) elevates plasma corticosterone levels and suppresses courtship. When male newts receive an injection of metyrapone, a drug that interferes with corticosterone synthesis, the inhibitory effects of stress or CRF infusion on courtship are reduced. These results support the hypothesis that, in this amphibian, elevated levels of corticosterone associated with exposure to stressful stimuli inhibit sexual behaviors.

Intracranial administration of corticotropin-like peptides increases incidence of amphibian reproductive behavior

Male rough-skinned newts ( Taricha granulosa) exhibit an increase in sexual behavior (amplectic clasping) following intracerebroventricular (ICV) injection of adrenocorticotropin (ACTH 1–39), ACTH 4–10, or melanocyte-stimulating hormone (αMSH). In contrast, intraperitoneal (IP) administration of ACTH 1–39 or corticosterone significantly decreases the incidence of sexual behavior in male newts. These results suggest that a corticotropin-like peptide acts centrally to enhance sexual behavior and that systemic ACTH acts on the interrenal tissue to inhibit sexual behavior by stimulating the release of corticosterone.

Effects of testosterone and methallibure on courtship and plasma androgen concentrations of male newts, Taricha granulosa

The administration of methallibure to male rough-skinned newts, Taricha granulosa, reduced the incidence of male courtship behavior and reduced concentrations of plasma androgens, as measured by radioimmunoassay. Daily injections of testosterone raised the concentration of plasma androgens above that in saline-treated males; however, testosterone treatments failed to moderate the inhibitory effect of methallibure on the expression of male mating behavior. The results indicate that male sexual responsiveness in Taricha is influenced by changes in hormones other than plasma androgens.

Effects of prolactin and methallibure on second metamorphosis and plasma androgens in male newts, Taricha granulosa

1. 1.Male rough-skinned newts, Taricha granulosa, were injected during late spring with ovine prolactin and/or methallibure (ICI 33,828), a known inhibitor of gonadotropin release. 2. 2. Methallibure injections, either alone or with prolactin, reduced androgen concentrations in the plasma, as measured by radioimmunoassay. 3. 3. Exogenous prolactin injections failed to affect plasma androgen titers in intact newts at this season. 4. 4. Saline-injected controls exhibited a diminution in tail fin height and water drive, preference for total submergence in water. 5. 5. The decrease in tail fin height and water drive was inhibited by prolactin treatment and, to a lesser degree, by methallibure treatment, suggesting that methallibure stimulated an increase in endogenous prolactin.