That Stimulate Sexual Behavior

Various clinically used or experimental drugs enhance sexual interest or potency as a side effect in humans. 

Levodopa (L-dopa) is a natural intermediate in the biosynthesis of catecholamines in the brain and peripheral adrenergic nerve terminals. In the biologic sequence of events it is converted to dopamine, which in turn serves as a substrate of the neurotransmitter norepinephrine. Levodopa is used successfully in the treatment of Parkinson s syndrome, a disease characterized by dopamine deficiency. When levodopa is administered to an individual with this syndrome, the symptoms of Parkinson s disease are ameliorated, presumably because the drug is converted to dopamine and thereby counteracts the deficiency. Individuals treated with levodopa, especially older men, have been observed to experience a sexual rejuvenation. This effect has led to the belief that levodopa stimulates sexual powers. Consequently, studies with younger men complaining of decreased erectile ability have shown that levodopa increases libido and the incidence of penile erections. Overall, however, these effects are short lived and do not reflect continued satisfactory sexual function and potency. Thus, levodopa is not a true aphrodisiac. The increased sexual activity experienced by parkinsonian patients treated with levodopa may reflect improved well-being and partial recovery of normal sexual functions that were impaired by Parkinson s disease. 

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Of particular importance for this discussion, however, is that many sexual behaviors may be inadvertently stimulated, inhibited, or even extinguished by the well-meaning physician, who may fail to recognize the behavioral alterations (Gitlin, 1994 Piazza et ah, 1997 Montejo et ah, 2001). Specific psychopharma-cological agents may have a profound impact on pa-... 

An important step toward the correct identification of the sex pheromone of P. americana was the identification of several phytochemicals, such as bomyl acetate and santalol, that stimulated courtship behavior in males (Bowers and Bodenstein, 1971 see p. 196). Some years later, Tahara etal. (1975) and Kitamuta et al. (1976) reported that germacrene-D, extracted from composite plant species, stimulated sexual behavior in males of P. americana and the Japanese cockroach Periplaneta japonica Karny. Persoons etal. (1974, 1976) determined, on the basis... 

Paralleling the findings for crabs, Stebbing et al. (2003) demonstrated that sexually mature female crayfish, Pacifastacus leniusculus, released a pheromone that stimulated mating behavior in males. If water conditioned by mature females was passed through an air-stone into containers holding males, these males commonly seized, mounted, and in a few cases deposited spermatophores onto the air-stones. Such behaviors did not occur if the air-stones carried water conditioned by immature females or control water that had not held crayfish (see also Chap. 13). 

Role of neural directives. Insertion of the spermatophore in the genital chamber has a multiplicity of effects on the female s endocrinology and behavior it stimulates JH production and inhibits pheromone production, calling, and sexual receptivity. Sperm, likewise, inhibits further sexual behaviors, while the ootheca also inhibits JH biosynthesis. The prevalent model is that these actions are conveyed to the CNS through the VNC. But it is not known whether mechanoreceptors transduce this information, how, and what events transpire within the CNS to prevent the expression of sexual behaviors. 

NPY is the most abundant neuropeptide in the brain. Its concentration is many times higher than the other neuropeptides. It is a member of a family of proteins that include pancreatic polypeptide, peptide YY, and seminalplasmin. In addition to its function of stimulating feeding behavior, several other physiologic roles have been assigned to NPY, including involvement in circadian rhythms, sexual function, anxiety responses, and vascular resistance (DiBona, 2002 Halford and Blundell, 2000). 

As explained, we make a distinction between primer pheromones that influence the physiology of the recipient and the releaser hormones that influence its behavior. Primer pheromones are used by social insects to suppress the production of sexual individuals, and by locusts to stimulate the production of migratory winged types when the population density becomes high. The releaser pheromones or analogues are most relevant as insecticides. 

Snakes, as a group, are visually cryptic and auditorially impoverished. Therefore, it is probable that chemical cues are quite important in mate location. The utilization of pheromone trails in the reproductive activity of snakes has been examined to some extent in temperate zone colubrids. In these snakes, sexual behavior occurs primarily in the spring. Males leave the hibernacula first and remain in the vicinity to court the females when they emerge. At this time, female snakes leave trails for the males to follow. The pheromone involved is likely the same lipoprotein (vitellogenin) which the females produce in the liver and secrete through the skin to stimulate male courtship activity (Garstka and Crews, 1981, this volume), although the only evidence for this is that the sexual pheromone trails are also produced by skin secretions and, like a lipoprotein, are non-volatile and persistent (Ford and Low, 1984). 

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