Female behaviour and the interaction of male and female genital traits mediate sperm transfer during mating

Natural selection and post-copulatory sexual selection, including sexual conflict, contribute to genital diversification. Fundamental first steps in understanding how these processes shape the evolution of specific genital traits are to determine their function experimentally and to understand the interactions between female and male genitalia during copulation. Our experimental manipulations of male and female genitalia in red-sided garter snakes (Thamnophis sirtalis parietalis) reveal that copulation duration and copulatory plug deposition, as well as total and oviductal/vaginal sperm counts, are influenced by the interaction between male and female genital traits and female behaviour during copulation. By mating females with anesthetized cloacae to males with spine-ablated hemipenes using a fully factorial design, we identified significant female-male copulatory trait interactions and found that females prevent sperm from entering their oviducts by contracting their vaginal pouch. Furthermore, these muscular contractions limit copulatory plug size, whereas the basal spine of the male hemipene aids in sperm and plug transfer. Our results are consistent with a role of sexual conflict in mating interactions and highlight the evolutionary importance of female resistance to reproductive outcomes.

An airborne sex pheromone in snakes

Most reptile sex pheromones so far described are lipid molecules too large to diffuse through the air; instead, they are detected via direct contact (tongue-flicking) with another animal's body or substrate-deposited trails, using the vomeronasal system. The only non-lipid pheromone reported in snakes involves courtship termination in red-sided gartersnakes (Thamnophis sirtalis parietalis): males that encounter copulatory fluids cease courtship, presumably reflecting the futility of courting an already-mating female. Our field experiments at a communal den in Manitoba show that this pheromone can work via olfaction: courtship is terminated by exposure to airborne scents from mating conspecifics, and does not require direct contact (tongue-flicking). Hence, the sexual behaviour of reptiles can be affected by airborne as well as substrate-bound pheromones.

Temporal dynamics of emergence and dispersal of garter snakes from a communal den in Manitoba

Although garter snakes at communal overwintering dens on the Canadian prairies have attracted considerable behavioural ecology research, previous studies have relied upon sampling of active animals to describe broad patterns of distribution and abundance of snakes within the den population. We conducted a mark–recapture study to directly quantify temporal and spatial variation in the phenotypic traits (sex, size, body condition) of snakes at the den itself, and those dispersing through woodland 50 m away. Captures of 909 snakes on the days they emerged, and 6653 snakes as they dispersed, revealed massive spatiotemporal heterogeneity in phenotypic traits among samples. Day-to-day variation in weather conditions affected numbers and sex ratios of emerging and dispersing snakes; for example, small females dispersed in greater numbers after unusually cold nights, when harassment by courting males was reduced. Most snakes stayed at the den only briefly (<5 days) prior to dispersal, so that sampling at the den itself (the only evidence available from most previous studies) underestimates the number of animals in the population, as well as the proportions of females, of small adult males and of juvenile animals. Overall, the heterogeneous and temporally dynamic distributions of phenotypic traits (such as sex and size) among our samples are predictable on the basis of the central roles of male–male competition and sexual conflict in the mating system of these snakes. Surprisingly, however, many of the snakes that overwinter at this den play no part in den-based breeding aggregations

Pheromone trailing behavior of the brown tree snake, Boiga irregularis

The ability of snakes to follow pheromone trails has significant consequences for survival and reproduction. Of particular importance is the ability of snakes to locate conspecifics during the breeding season via the detection of pheromone trails. In this study, the ability of male brown tree snakes (Boiga irregularis), a tropical, rear-fanged colubrid, to follow pheromone trails produced by reproductively active conspecifics was tested in the laboratory by using a Y maze. Males displayed a trailing response to both female and male pheromone trails over blank controls. As males of this species display ritualized combat behavior, these responses likely represent both direct and indirect mechanisms, respectively, for the location of potential mates in the wild. Males did not, however, discriminate between male and female trails when given a choice on the Y maze.

The influence of sex steroids on the sexual size dimorphism in the red-spotted garter snake, Thamnophis sirtalis concinnus

The red-spotted garter snake exhibits adult size dimorphism in which females are the larger sex. To understand which hormones may influence differential growth in this species, growth curves and hormone profiles of estradiol-17beta (E2) and testosterone (T) were constructed in male and female neonates. Growth was manipulated via implantation of exogenous hormones and hormone antagonists. Female neonates are heavier or longer beginning at either 20 or 24 weeks of age, respectively. Although low circulating levels of E2 and T were present in males and females from birth through 15 weeks of age, these levels were not significantly different between the sexes. Differences in the growth curves of the treated and untreated snakes were significant after 24 weeks of age. Antiestrogen produced male-like growth in females but had no effect on males. Antiandrogen had no effect on either males or females. Exogenous T reduced female growth to that observed in males, and E2 reduced male growth. These results suggest that a basal level of either E2 or T is sufficient in males to retain typical male growth patterns. Similar endogenous levels of E2 appear to have growth-promoting effects in females. Endogenous T does not appear to play a role in female growth.

Behavioral and hormonal responses to corticosterone in the male red-sided garter snake, Thamnophis sirtalis parietalis

Stress and glucocorticoids are generally thought to suppress reproductive function at multiple levels. We tested the hypotheses that exogenous corticosterone would suppress sexual behavior in a dose-dependent manner, as well as drive a decrease in plasma testosterone levels in the male red-sided garter snake, Thamnophis sirtalis parietalis. We examined this by challenging individual males with intraperitoneal injections of exogenous corticosterone, and subsequently exposing them to sexually attractive females or taking a blood sample. Previous work has demonstrated a hormonal but no behavioral response to stress in this species. In this study, increasing concentrations of exogenous corticosterone rapidly suppressed mating behavior in a threshold manner. However, exogenous corticosterone had no effect on plasma levels of testosterone. Thus, these data suggest that the mechanism is in place for corticosterone to suppress mating behavior in this species and that these effects do not occur because of an indirect effect on plasma levels of testosterone but rather are the direct effect of the hormone itself. In addition, the negative relationship observed previously between plasma levels of corticosterone and testosterone in this species was probably not the direct result of corticosterone acting on the hypothalamic-pituitary-gonadal (HPG) axis. Rather, our results seem to indicate that the negative associations between the hypothalamic-pituitary-adrenal axis (HPA) and the HPG axis occur at other levels of these neuroendocrine pathways.

Bumpus in the snake den: effects of sex, size, and body condition on mortality of red-sided garter snakes

Huge breeding aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) at overwintering dens in Manitoba provide a unique opportunity to identify sources of mortality and to clarify factors that influence a snake's vulnerability to these factors. Comparisons of sexes, body sizes, and body condition of more than 1000 dead snakes versus live animals sampled at the same time reveal significant biases. Three primary sources of mortality were identified. Predation by crows, Corvus brachyrhynchos (590 snakes killed), was focussed mostly on small snakes of both sexes. Crows generally removed the snake's liver and left the carcass, but very small snakes were sometimes brought back to the nest. Suffocation beneath massive piles of other snakes within the den (301 dead animals) involved mostly small males and (to a lesser extent) large females; snakes in poor body condition were particularly vulnerable. Many emaciated snakes (n = 142, mostly females) also died without overt injuries, probably due to depleted energy reserves. These biases in vulnerability are readily interpretable from information on behavioral ecology of the snakes. For example, sex biases in mortality reflect differences in postemergence behavior and locomotor capacity, the greater attractiveness of larger females to males, and the high energy costs of reproduction for females.

Environmental and seasonal adaptations of the adrenocortical and gonadal responses to capture stress in two populations of the male garter snake, Thamnophis sirtalis

Stress and reproduction are generally thought to work in opposition to one another. This is often manifested as reciprocal relationships between glucocorticoid stress hormones and sex steroid hormones. However, seasonal differences in how animals respond to stressors have been described in extreme environments. We tested the hypothesis that garter snakes, Thamnophis sirtalis, with limited reproductive opportunities will suppress their hormonal stress response during the breeding season relative to conspecifics with an extended breeding season. The red-sided garter snake, T.s. parietalis, of Manitoba, Canada, has a brief breeding season during which males displayed no change in either plasma levels of testosterone or corticosterone, which were both elevated above basal levels, in response to capture stress. During the summer, capture stress resulted in increased plasma corticosterone and decreased testosterone. During the fall, when mating can also occur, males exhibited a significant decrease in testosterone but no increase in corticosterone in response to capture stress. The red-spotted garter snake, T.s. concinnus, of western Oregon, has an extended breeding season during which males displayed a stress response of increased plasma corticosterone and decreased testosterone levels. The corticosterone response to capture stress was similar during the spring, summer, and fall. In contrast, the testosterone response was suppressed during the summer and fall when gametogenesis was occurring. These data suggest that male garter snakes, in both populations, seasonally adapt their stress response but for different reasons and by potentially different mechanisms. J. Exp. Zool. 289:99-108, 2001.

Conflicts between courtship and thermoregulation: the thermal ecology of amorous male garter snakes (Thamnophis sirtalis parietalis, colubridae)

Thermoregulatory behavior is an important component of daily activities for many reptiles, especially for small heliothermic (sun-basking) species that inhabit cold climates. However, the relative costs and benefits of thermoregulation depend on numerous factors, such that reptiles may sometimes accord a low priority to precise control of body temperatures. We observed and radio tracked garter snakes (Thamnophis sirtalis parietalis) in central Manitoba during the mating season (spring). Previous studies on this species have documented precise behavioral regulation of body temperatures during summer. In contrast, the courting snakes that we studied in springtime spent little time in overt thermoregulatory behavior. Body temperatures were extremely variable (both in outdoor enclosures and in the field) despite abundant opportunities for more precise thermal control. These small elongate reptiles cool so quickly (relative to the time periods needed for effective courtship) that any benefit to higher body temperatures would be transitory at best. Experiments show that hotter males are no better at obtaining matings or at detecting predators. Thus, male garter snakes concentrate on courtship rather than on basking. In the face of conflicting priorities, reptiles may often forgo precise thermoregulation because its benefits are too low, and its costs too high, compared with alternative behaviors.

Relationships between annual cycles of testosterone, corticosterone, and body condition in male red-spotted garter snakes, Thamnophis sirtalis concinnus

Over a 2-yr period, we investigated the annual cycles of plasma testosterone and corticosterone and the relationships between these hormones and body condition in a wild population of male red-spotted garter snakes, Thamnophis sirtalis concinnus. In the 10 mo that were sampled, a peak in testosterone was observed in late summer during gametogenesis and declining through the spring breeding period. Corticosterone and testosterone cycles were positively correlated, in contrast to many vertebrates, suggesting the lack of a direct negative interaction between the two hormones. Body condition, defined as the residual of the regression of mass on snout-vent length, also cycled annually, with individuals being more robust during the summer than during the spring or fall. Individuals with a positive body condition had significantly lower plasma levels of corticosterone than did individuals with a negative body condition, supporting the energetic role of glucocorticoids. There was no relationship between body condition and testosterone. This study suggests that annual cycles of testosterone, corticosterone, and body condition can be associated with one another, and considering all three simultaneously is necessary to understand their control and function.

Behavioural and hormonal responses to capture stress in the male red-sided garter snake, Thamnophis sirtalis parietalis

We measured the behavioural and hormonal responses to capture stress in male red-sided garter snakes. Four hours of capture stress resulted in no suppression of mating behaviour relative to control individuals. In contrast, the same stress resulted in a significant increase in plasma levels of corticosterone and a significant decrease in plasma levels of testosterone. There was a significant negative correlation between plasma levels of corticosterone and testosterone in both control and capture-stress groups, suggesting that the increase in corticosterone directly drives the decrease in testosterone. While there was no relation between body size and initial plasma levels of the two steroids, longer individuals had a significantly greater increase in corticosterone following capture stress than did shorter individuals. Snakes display indeterminate growth, suggesting that older individuals have decreased sensitivity to negative feedback in the hypothalamic-pituitary-adrenal axis and thus hypersecrete glucocorticoids. These results suggest that male red-sided garter snakes have uncoupled their behavioural stress response from their hormonal stress response to maximize reproductive opportunities. Copyright 2000 The Association for the Study of Animal Behaviour.

The transvestite serpent: why do male garter snakes court (some) other males?

In large mating aggregations of red-sided garter snakes, Thamnophis sirtalis parietalis, in Manitoba, male courtship is directed not only to females, but also to other males with female-like skin lipids ('she-males'). We show that 'she-maleness' is an intrinsic property of a male rather than an artefact of lipid transfer from females, and that male-male courtship is very common in the field. She-males were distinctive in terms of appearance (they were heavier than other males and more often covered with mud), behaviour (they were inactive and rarely courted females) and performance (they were slow crawlers, ineffective courters and easily outcompeted by other males in mating trials). 'She-maleness' was not a characteristic of a particular subset of males, as envisaged in previous work; instead, it was a transitory phase that most (perhaps all) male snakes passed through soon after they first emerged from the winter den. Recently emerged males spent their first day or two relatively inactive, while restoring physiological functions (including locomotor performance and courtship ability). Experimental application of female skin lipids on to males dramatically decreased courtship levels of the recipient snakes. Thus, recently emerged males may derive two kinds of benefit from mimicking female skin lipids. First, female mimicry 'switches off' the male's own (energetically expensive) courtship at a time when that courtship would be unproductive. Second, it may disadvantage his rivals by distracting them from females, and increasing their energy expenditure. Copyright 2000 The Association for the Study of Animal Behaviour.

Fatal mycotic dermatitis in captive brown tree snakes (Boiga irregularis)

Cutaneous fungal infections occurred in four captive brown tree snakes (Boiga irregularis). The ventral scales were most commonly affected, and lesions began as areas of erythema and edema with vesicle formation, followed by development of caseous brown plaques. Lesions usually started where ventral scales overlapped and spread rapidly. All snakes died within 14 days after clinical signs were first noted. The deaths of three of the snakes were directly attributable to the cutaneous disease; the other snake died from renal failure and visceral gout, most likely induced by gentamicin therapy. Histologically, lesions consisted of epidermal hyperplasia and hyperkeratosis, with foci of epidermal necrosis, intraepidermal vesicle formation, and subacute inflammation of the underlying dermis. These lesions were associated with bacteria and numerous septate, branched fungal hyphae within the epidermis and overlying serocelluar crusts. Hyphae that penetrated through the superficial surface of the epidermis often formed terminal arthroconidia. The same species of fungus was isolated in pure culture from the skin of three snakes, but fungal cultures were not performed on samples from the fourth snake. The fungus has been identified as the Chrysosporium anamorph of Nannizziopsis vriesii based on its formation of solitary dermatophytelike aleurioconidia and alternate and fission arthroconidia. The source of the fungus in this outbreak was not determined; however, the warm, moist conditions under which the snakes were housed likely predisposed them to opportunistic cutaneous fungal infections.

Gonadotropin antagonist modulates courtship behavior in male red-sided garter snakes, Thamnophis sirtalis parietalis

Behavioral studies were used to investigate the central effects of chicken-I GnRH, chicken-II GnRH, and D-Phe2,6,Pro3-GnRH, a GnRH antagonist, on the courtship behavior of male red-sided garter snakes, Thamnophis sirtalis parietalis. Intracerebroventricular (i.c.v.) injections of chicken-I or chicken-II GnRH had no effect on time spent courting or latency to court when experimental males were exposed to unmated females, or when experimental males were exposed to the female sex attractiveness pheromone. I.c.v. injections of D-Phe2,6,Pro3-GnRH caused a significant decrease in latency to court when experimental males were exposed to unmated females. When males injected with D-Phe2,6,Pro3-GnRH were exposed to the female sex attractiveness pheromone, it caused a significant increase in time spent courting compared to that in saline-injected controls. D-Phe2,6,Pro3-GnRH was not able to initiate courtship behavior during the nonbreeding season, indicating that courtship behavior is dependent on the interaction of multiple components. This study does demonstrate that a hormone or neuropeptide can modulate sexual behavior in garter snakes.

Neuroanatomical distribution of chicken-I gonadotropin-releasing hormone (cGnRH-I) in the brain of the male red-sided garter snake

Immunocytochemistry was used to investigate the neuroanatomical distribution of the chicken-I form of gonadotropin-releasing hormone (cGnRH-I) in reproductively active, male, red-sided garter snakes (Thamnophis sirtalis parietalis). Cell bodies with cGnRH-I immunoreactivity (ir) were found in the terminal nerve ganglion, nucleus of the diagonal band of Broca, medial preoptic area, and the hypothalamus. Fibers containing cGnRH-Iir were distributed in the following brain areas. Within the olfactory bulb, fibers were found in the internal plexiform, mitral and glomerular cell layers, as well as in the terminal nerve; within the forebrain, fibers were observed in the diagonal band of Broca, rostral and lateral septum, lateral pallium, retrobulbar region pars dorsomedialis, nucleus accumbens, medial preoptic area, hippocampal commissure, amygdala, posterior dorsal ventricular ridge, hypothalamus, median eminence, and the thalamus; within the midbrain, fibers were found in the interpeduncular nucleus and the stratum album periventricular of the optic tectum. This study shows that the distribution of cell bodies for cGnRH-Iir in this reptile is consistent with the distribution of immunoreactivity for cGnRH-I in birds and mammalian GnRH in amphibians and mammals. Using antiserum specific to cGnRH-I, the endogenous form of GnRH, this is the first study to show that the terminal nerve in a reptile contains GnRH immunoreactivity.

Plasma triglyceride and beta-hydroxybutyric acid levels in red-sided garter snakes (Thamnophis sirtalis parietalis) at emergence from hibernation

Measurement of plasma levels of triglycerides and beta-hydroxybutyric acid in females and males of the red-sided garter snake (Thamnophis sirtalis parietalis) suggest that the former may provide a useful physiological marker of condition. Levels of triglycerides at emergence from hibernation during a month of natural aphagia were significantly greater in females than in males and she-males, a subset of the male population that mimics females. Higher levels of triglycerides in the females may be attributed to their greater body mass per unit length, which was correlated with the level of triglycerides. Plasma triglyceride levels declined in females within one month of emergence, at the onset of feeding, and were unrelated to mating.

Chemical ecology of the red-sided garter snake, Thamnophis sirtalis parietalis

The red-sided garter snake, Thamnophis sirtalis parietalis is an ideal model for the study of chemical or pheromonal communication in vertebrates. Results of long-term field and laboratory investigations of the chemical ecology of these unusual animals is summarized. These studies include a description of the characterization of the female attractiveness pheromone that serves to induce male courtship behavior. The male sex recognition pheromone system that identifies males as inappropriate individuals to court is also described. She-males, individual males that are courted as if they were females, seem to possess semiochemical components intermediate to both males and females. Finally, investigations of the species-specific nature of these pheromones indicate that chemical differences exist in the methyl ketones of all species examined to date.

Chemical recognition of kingsnakes by crotalines: effects of size on the ophiophage defensive response

When confronted by an ophiophagous (snake-eating) kingsnake, venomous snakes of the subfamily Crotalinae exhibit a suite of defensive responses including head hiding, thrashing, and an unusual response termed 'body bridging'. Other responses observed, such as biting and 'freezing', are more general in nature and can occur in a variety of contexts. Various crotalines of differing sizes were tested for their responses to kingsnakes (Lampropeltis getulus). Responses of individuals were recorded for up to 18 months. The results indicate that, if habituation can be overcome by periodically allowing a kingsnake to confront but not harm the crotaline, the response is dependent on the size of the crotaline, in that smaller specimens (< 0.9 m) respond readily, while larger snakes (> 1.0 m) tend not to respond. The size of the kingsnake apparently does not have an effect on the crotaline response. These data appear to resolve apparent conflicts in the literature regarding whether certain species respond to ophidian ophiophages. In addition, hexane extracts of kingsnake skin were fractionated using an alumina column. The various fractions obtained were tested to determine which elicited the defensive response. Activity was found only in the most non-polar fraction. Preliminary analysis by gas chromatography/mass spectrometry indicated that this fraction contained straight and branched, saturated and polyunsaturated long-chain hydrocarbons.

Uric acid is a major antioxidant in human nasal airway secretions

Airway mucosal surfaces are potentially subjected to a variety of oxidant stresses. Airway submucosal glands secrete a variety of compounds that may protect the airways from injury. Cholinergically induced nasal submucosal gland secretion has recently been found to contain a low molecular weight nasal antioxidant. In this report, the isolation and identification of this nasal secretory antioxidant are described. Concentrated, cholinergically induced human nasal secretions were fractionated through a 10-kDa sieve and subjected to DEAE anion-exchange chromatography. Fractions containing antioxidant activity were subjected to gel filtration with Bio-Gel P-2 gel (resolution range, 200-2000 Da). The resultant antioxidant fractions were then desalted by gel filtration over the same column equilibrated in HPLC-grade water, yielding only a single peak with antioxidant activity. The absorption spectrum of the purified antioxidant revealed peaks at 238 and 292 nm at pH 7. These peaks shifted to 230 and 280 nm in 0.1 M HCl and 226 and 296 nm in 0.1 M NaOH. Sodium borohydride reduction of the antioxidant had no effect on the UV absorption, whereas platinum-catalyzed hydrogenation ablated all absorption peaks. Uric acid had identical absorption peaks and showed the same chromatographic behavior as the nasal antioxidant activity on both gel filtration and DEAE columns. Uricase (which degrades uric acid) metabolized both uric acid and the purified antioxidant. Uric acid was shown to have antioxidant activity at concentrations greater than 1.5 microM. These data indicate that nasal secretions contain uric acid that serves as an antioxidant.

Sex pheromones in snakes

The majority of pheromones identified to date are insect pheromones, which are volatile in nature. Identification of nonvolatile pheromones have been relatively rare, especially in vertebrates. Male and female garter snakes use pheromones to mediate sexual behavior. The female sex attractiveness pheromone of the Canadian red-sided garter snake, Thamnophis sirtalis parietalis, consists of a novel series of nonvolatile saturated and monounsaturated long-chain methyl ketones, whereas the male sex recognition pheromone contains squalene. These compounds were isolated, identified, and partially synthesized, and field tests show them to be biologically active.

Plasma steroid hormone levels of female red-sided garter snakes, Thamnophis sirtalis parietalis: relationship to mating and gestation

Plasma levels of progesterone (P), testosterone (T), estradiol (E2), and corticosterone (B) of female red-sided garter snakes were measured during the period of ovarian development. Differences in hormone levels were analyzed with respect to three factors: whether the female mated in the spring, ovarian condition, and time after emergence from hibernation. The influence of these three factors on steroid hormone levels of two groups of females were then compared. In experiment I, females were obtained in the fall, subjected to an artificial dormancy period, and placed on warm, summer-like conditions in the laboratory. In experiment II, females were collected in the spring and sampled in the field. They were held in the field on fluctuating conditions for several weeks and then returned to the laboratory for sampling during early vitellogenesis. Females in experiment I had a shortened but otherwise normal ovarian and gestational cycle, whereas females in experiment II had an ovarian and gestational cycle typical of females in the field. In spite of these differences, the steroid hormone levels in relation to the ovarian cycle were remarkably similar for the two groups of females. We confirmed that mating in the spring induces a surge in E2; E2 also was elevated in a single sample obtained from animals collected in the fall. This elevation in plasma levels of E2 in the fall occurs at a time when the majority of females have recently deposited sperm in their oviducts. Plasma levels of T, P, and B were not significantly influenced by mating. Unlike previous reports of other viviparous snakes, plasma levels of P were low and mostly nondetectable, even during late gestation. Plasma T was significantly elevated around the time of late vitellogenesis and ovulation, and there was a tendency for E2 levels to be elevated at this time. In the field, plasma B levels were initially high immediately after capture and declined with time. Plasma B was significantly elevated in all females several weeks after emergence, suggesting that levels of B may vary with other annual cycles.

Sex and seasonal differences in the skin lipids of garter snakes

1. This study investigates the skin lipids of male and female red-sided garter snakes both in the breeding season and in the non-breeding season. 2. Skin lipids were analyzed by means of thin-layer chromatography (TLC) and gas chromatography/mass spectrometry (GC/MS). 3. Distinct differences exist in the skin lipids of males and females. 4. Samples obtained during the breeding season were qualitatively different from those acquired during the non-breeding season.

Pinealectomy blocks vernal courtship behavior in red-sided garter snakes

Male red-sided garter snakes (Thamnophis sirtalis parietalis) court only on emergence from winter dormancy. The salient proximate factor responsible for the initiation of courtship behavior appears to be warm ambient temperatures subsequent to sustained exposure to cold temperatures. In the present study, autumn-captured garter snakes were pinealectomized or sham-pinealectomized 1-2 weeks prior to hibernation. After 17 weeks of maintenance in several ambient lighting and temperature conditions, all males were tested for the presence of courtship behavior. No pinealectomized animals exhibited any indications of reproductive behavior, whereas 53% of sham-pinealectomized males actively courted females. Photoperiod did not influence the prevalence of mating behavior. These results suggest that the pineal gland mediates non-photoperiodic seasonal information in the garter snake. This is the first demonstration, in any vertebrate species, that the pineal gland can directly influence reproductive behavior.

Localization of binding sites for calcitonin gene-related peptide in rat brain by in vitro autoradiography

The distribution of binding sites for calcitonin gene-related peptide (CGRP) in rat brain were studied using in vitro autoradiography. In a radioreceptor assay using [125I]human calcitonin gene-related peptide as the radioligand, with cerebellar cortical membranes, rat calcitonin gene-related peptide had a binding affinity constant of 1.16 +/- 0.23 X 10(10) M-1 and a site concentration of 43.4 +/- 3.4 fmol/mg protein. In this system, human calcitonin gene-related peptide had a binding affinity constant of 3.9 +/- 0.7 X 10(9) M-1 whereas salmon calcitonin was very weak with a binding affinity constant of only 6.8 +/- 4.0 X 10(5) M-1. CGRP binding localized by in vitro autoradiography, using [125I]rat calcitonin gene-related peptide, had a characteristic distinct distribution in the rat brain. There were high concentrations of binding found over the accumbens nucleus, the organum vasculosum of the lamina terminalis, ventral caudate putamen, median eminence, the arcuate nucleus, lateral amygdaloid nucleus and lateral mammillary nucleus, the superior and inferior colliculi, pontine nuclei, molecular and Purkinje cell layers of the cerebellar cortex, the nucleus of the solitary tract, the inferior olivary nuclei, hypoglossal complex and the vestibular and cochlear nuclei. The distribution of these binding sites suggests multiple roles for CGRP in the central nervous system including auditory, visual, gustatory and somatosensory processing, and in neuroendocrine control.

Basal and stimulated release of calcitonin gene-related peptide (CGRP) in patients with medullary thyroid carcinoma

Calcitonin gene-related peptide (CGRP) is a recently discovered peptide whose existence was first predicted following sequence analysis of the rat calcitonin gene. In the present study, plasma levels of CGRP were measured in patients with medullary thyroid carcinoma, both basally and following calcium or pentagastrin stimulation. Using a sensitive radioimmunoassay for CGRP, 19 of 21 patients with medullary thyroid carcinoma had elevated plasma levels of immunoreactive CGRP (median value 114 pmol/l) while 23 normal subjects had plasma CGRP levels below the detection limit of the assay (less than 10 pmol/l). Calcium or pentagastrin infusion in medullary thyroid carcinoma patients were potent stimuli to CGRP release, increasing plasma levels two- to five-fold. Chromatographic characterization using high pressure liquid chromatography of the CGRP immunoreactivity in plasma from two patients with medullary carcinoma of the thyroid demonstrated the presence of two molecular forms, neither of which co-eluted with synthetic human CGRP. The role of CGRP in the pathophysiology of medullary thyroid carcinoma is not clear but it may contribute to some of the clinical features associated with the disease. Furthermore, measurement of CGRP in conjunction with calcitonin could help in determining the prognosis of these patients.

Presence of growth hormone-releasing factor-like immunoreactivity in rat duodenum

Growth hormone-releasing factor-like immunoreactivity (GRF-LI) was detected in partially purified extracts of rat hypothalamus and duodenum with a highly specific RIA for rat GRF (rGRF). The concentration of rGRF-LI in the rat hypothalamus was 32.5 fmol/mg dry weight (455 fmol or 3.18 ng/region), while the rat duodenum contained 2.15 fmol/mg dry weight (111 fmol or 0.78 ng/region). Partially purified hypothalamic and duodenal extracts exhibited displacement of the tracer parallel to rGRF. GRF-LI levels in all other brain regions (brainstem, cortex) or gastrointestinal tract tissues (forestomach, antrum, ileum, colon, pancreas) measured were close to the detection level of the RIA. rGRF-LI in hypothalamic and duodenal extracts behaved like synthetic rGRF in both gel filtration and reverse-phase HPLC systems. Coelution of rGRF-LI contained in both these tissue extracts with synthetic rGRF suggests that these molecules are similar, if not identical.

Female mimicry in garter snakes

In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is 'female mimicry', whereby males assume a female-like morphology or mimic female behaviour patterns. In some species males mimic both female morphology and behaviour. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mating aggregations of 5-17 males were observed formed around these individual attractive males, which we have termed 'she-males'. In competitive mating trails, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone.

Neurobiological actions of cysteamine

Somatostatin (SS)-related peptides act within discrete brain regions to inhibit adrenal epinephrine (E) secretion, to prevent hypothermia, and to produce hyperthermia. Depletion of brain concentrations of these SS-related peptides using cysteamine (CSH) or central administration of an SS receptor antagonist increases adrenal E secretion and impairs thermoregulation. These actions of CSH and the SS receptor antagonist are reversed by administration of SS into the central nervous system. These results support the hypothesis that endogenous brain SS-related peptides are involved in the regulation of adrenal E secretion and thermoregulation.

Prostacyclin infusion does not prevent ACTH-induced hypertension in sheep

The present experiments examine the hemodynamic effects of an intravenous infusion of prostacyclin on the development of ACTH-induced hypertension in conscious sheep. Prostacyclin was infused at either 0.01 microgram/kg min-1 for 9 days or 0.25 microgram/kg min-1 for 4 days. At 0.01 microgram/kg min-1 prostacyclin had no effect on blood pressure in normotensive sheep or on the development of ACTH hypertension. Infusion at 0.25 microgram/kg min-1 increased heart rate, cardiac output and plasma renin concentration and decreased stroke volume and peripheral resistance in normotensive sheep. Despite these effects it did not prevent development of ACTH-induced hypertension. It is unlikely on the basis of these results that glucocorticoid-induced inhibition of vasodepressor prostacyclin and resulting increase in pressor responsiveness to circulating agonists is the primary cause of ACTH induced hypertension in sheep.

Blood pressure and metabolic effects of 9 alpha-fluorocorticosterone and 9 alpha-fluorodeoxycorticosterone in sheep

9 alpha-Fluorocortisol has been postulated to have 'hypertensinogenic' as well as 'mineralocorticoid' and 'glucocorticoid' activity. The present study examined the blood pressure and metabolic effect in sheep of the structurally related steroids 9 alpha-fluorodeoxycorticosterone (9 alpha-FDOC) and 9 alpha-fluorocorticosterone (9 alpha-FB). Infusions of these fluorinated steroids at 0.63 and 0.67 mg/day respectively for 5 days produced falls in plasma potassium, but only 9 alpha-FB increased urine volume. 9 alpha-FDOC raised mean arterial pressure by 11 mmHg and 9 alpha-FB raised it by 14 mmHg. Addition of a 9 alpha-fluoro group appears to increase both 'mineralocorticoid' and 'hypertensinogenic' steroid potencies.

Effects of beta-adrenoceptor blockade on prostacyclin mediated renin release in sheep

The effect of prostacyclin (PGI2) infusion on plasma renin concentration (PRC) was examined before and after propranolol treatment in sheep. Increasing doses of prostacyclin (0.05, 0.1 or 0.3 micrograms/kg per min) produced dose dependent increases in PRC. There was a significantly lower PRC response after propranolol at 0.3 micrograms/kg per min only.

The hemodynamic effects of prostacyclin infusions in normotensive and ACTH induced hypertensive conscious sheep

The aim of this study was to determine the effect of ACTH-induced hypertension on the hemodynamic dose-response curves to intravenous infusion of prostacyclin (PGI2) in conscious sheep. PGI2 was infused for 10 minutes at doses of 0.05-0.50 micrograms/kg per min and hemodynamic dose-response curves were performed before, during and after ACTH-induced hypertension. Prior to ACTH administration prostacyclin infusions produced dose dependent decreases in mean arterial pressure (MAP), calculated total peripheral resistance (CTPR) and stroke volume (SV). These changes were accompanied by an increase in cardiac rate (CR) and cardiac output (CO). After five days of ACTH treatment MAP had risen from 72 +/- 1 to 91 +/- 2 mm Hg and infusions of PGI2 produced similar effects on MAP to those seen prior to ACTH. However the effects on CTPR, CO, SV and CR were all potentiated relative to normotensive animals. Three days after ACTH administration had ceased and basal pressure had returned to normotensive levels, the responses of CR, CO and SV to PGI2 infusions were similar to those seen prior to ACTH. However the exaggerated fall in CTPR seen during ACTH treatment was still present and this resulted in a very large decrease in MAP. These studies suggest that in this model of steroid-induced hypertension the resistance vessels are more sensitive to PGI2 and that the blood pressure response to PGI2 is regulated by different mechanisms to those seen prior to ACTH.

A comparison of the haemodynamic effects of dietary sodium restriction and acute sodium depletion in the conscious sheep

The use of a low Na, low K sorghum grain diet supplemented with intraruminal electrolyte infusions has enabled dietary manipulation of sodium status to be studied in the sheep. Dietary sodium restriction reduced urinary sodium excretion within 24 h with maximal retention after 3 days. There were no other substantial metabolic or haemodynamic changes. A more severe form of sodium deficiency produced by parotid salivary drainage resulted after only 2 days in a sodium deficit 3-4 times that seen with 14 days of sodium restriction. Extracellular fluid volume and cardiac output decreased. Blood pressure was unchanged but there was an increase in peripheral resistance and plasma renin concentration.