General use of animal models for investigation of the physiology of erection

Abstract

Animals have consistently assumed a major place in the scienti®c developments of erection physiology, and in fact the use of animal models can be claimed to have inaugurated this ®eld as a true scienti®c discipline. The roots of the science of sexual medicine do not coincide with its practice, which conceivably pertains to aphrodisiacs and other sexual stimulants touted as therapies since antiquity. Rather, the beginnings of scienti®c study in the ®eld are ®ttingly identi®ed with the pioneering experimental work of Eckhard, who in 1863 showed the importance of the pelvic nerves for erectile function by performing electrical stimulation of these`nervi erigentes' in the anesthetized dog to elicit penile erection. 1 The understanding that penile erection is displayed under neurophysiological control was con®rmed and re®ned towards the late nineteenth century by the work of several important researchers in the ®eld, including Mu È ller, Bernard, Gaskell, and Langley and Anderson, who applied animal models to show the gross anatomic locations and physiological relevance of nerves coursing from spinal levels to the pelvis for regulation of penile erection: the mostly antagonistic parasympathetic and sympathetic autonomic nerves, and the somatic nerves. 2,3 The impressive methods of electrophysiological experimentation in the mammalian pelvis combined with extirpative lesioning of spinal out¯ow tracts employed by many of these early scientists continue to be applied similarly in modern research studies.Other pre-eminent control systems involved in erection physiology, accepted now as basic tenets of the ®eld, are known substantially from animal experimentation. The physiology of genital blood ow as an essential component of the erectile response was discovered early and established in concert with electrophysiological investigation. Research progress in recent decades has built on observations of the role of the vascular system and taken a major focus towards understanding penile vascular smooth muscle properties and penile hemodynamics. The central nervous system control of penile erection has been explored somewhat less intensively thus far, although early neuropharmacological and lesioning methods have suggested that hypothalamic and limbic pathways exert predominant in¯uences in the erectile response. 2,4,5 Scienti®c study in animals has also supported the erection regulatory basis involving circulating male hormones, evidenced by the fact that androgen loss such as that following castration leads to erectile impairment and, oppositely, androgen replacement promotes recovery of erectile function. 6,7 Role of animal models to study penile erectionThe selection of animal models for study in the ®eld of sexual dysfunction research has undergone an evolutionary process much like the ®eld itself. The relatively large size and thus inherent technical feasibility of certain animals such as dogs and monkeys lent these species as the primary models for in vivo investigation of penile erection until recent times. Thei...

Concentration of elastic system fibers in the corpus cavernosum, corpus spongiosum, and tunica albuginea in the rabbit penis

“…15,16,38 Although the animals possess similarities to humans with regard to the erectile function, normal or abnormal, comparative researches provide better comprehension of the similarities and differences about morphological structure and erectile function among the different species and in the human. 40 In this study, we observed a larger amount of elastic fibers in the rabbit penis than in human penis components, that is, CC, CS and TA. The literature points out that rabbits possess the morphological characteristics of a vascular penis, and therefore can be compared with humans.…”

“…1,30 Elastic fibers are the major extracellular matrix components of the human fetal urethra 40 and their Vv in the CS increases in a linear fashion during fetal development (from 5.2% at 15th week to 14.8% at 36th week). In a young male, the elastic fiber Vv is about 19%.…”

Comparison of the involvement of protein kinase C in agonist-induced contractions in mouse aorta and corpus cavernosum

“…Studies have demonstrated that rodents are valid animal models for the investigation of erectile physiology and pharmacology (Burnett, 2001;Giuliano, 2001). Although rats have been widely used for in vivo and in vitro assessments of erectile function, the mouse model has recently become attractive due to the accessibility of genetic manipulations.…”

A novel compound JPM8: in vivo penile activity promotion in rats, effect on the relaxation and cGMP/cAMP accumulation in isolated rabbit corpora cavernosa

“…Among the scientific tools used in animal models for the investigation of penile erection are the varied techniques they afford for stimulation and monitoring of erectile responses in vivo. 11 Erection monitoring methods have included many techniques. 11 Erection monitoring by observation and counting phenomenal erections is a widely used technique due to its simplicity and direct in vivo comparison.…”

“…11 Erection monitoring methods have included many techniques. 11 Erection monitoring by observation and counting phenomenal erections is a widely used technique due to its simplicity and direct in vivo comparison. 12,13 Because of high purchase and maintenance costs of large animals as well as their diminishing availability for medical research, small mammalian species such as lagomorphs and rodents have become the primary models.…”