Seasonal fluctuations in brain nuclei in the red-sided garter snake and their hormonal control

Abstract

In many vertebrates, breeding seasons are protracted and mating behavior is temporally associated with gonadal growth and increased sex steroid hormone secretion. In the red-sided garter snake (Thamnophis sirtalis parietalis), mating behavior is restricted to the 2-4 weeks immediately following emergence from winter dormancy. During this period mating behavior is sex-specific: chin-rubbing is exhibited only by males and receptivity to chin-rubbing is exhibited only by females. It is remarkable that mating occurs when the gonads are small and circulating concentrations of gonadal hormones are low. As in other vertebrate species, limbic nuclei are involved in the mediation of mating behaviors. To determine if limbic nuclei are sexually dimorphic and, further, whether they fluctuate in size with the seasons, the volume of brain areas was measured in both sexes at different times of the year (spring, fall, hibernation) and after hormone manipulation (gonadectomy and gonadectomy plus hormone treatment). The areas of interest were the preoptic area (POA), ventromedial hypothalamus (VMH), and the nucleus sphericus (NS or amygdala); control areas included the external nucleus of the optic tract (a cell-rich area) and medial forebrain bundle (a fiber-rich area). Comparisons according to season and manipulation revealed only two instances of sexual dimorphism: the POA of females was significantly smaller than that of males during hibernation and the NS of females was significantly smaller than that of males in those animals not subjected to hibernation. This general lack of sexual dimorphisms in the brain despite the sex-specificity of the behavior patterns and their marked seasonality may reflect the dissociated reproductive pattern characteristic of this species.(ABSTRACT TRUNCATED AT 250 WORDS)

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

“…T and/or breeding environmental conditions enhance male sexual behavior and in parallel enhance volume and/or soma size of the POA and AMY in Japanese quail, whiptail lizards and rodents [22,24,25,27,62,71,82,87,90,91]. Interestingly, as in the present study, a seasonal environmental cue (photoperiod) influences the response of a portion of the AMY (the MeApd) to T in Siberian hamsters.…”

Amygdala and Emotional Learning in Vertebrates – A Comparative Perspective

“…Other results in fear context conditioning have showed that lesions of the dorsomedial telencephalic portion in Betta splendens produced a facilitation of habituation to the context (Marino-Neto & Sabbatini, 1983) and variations in levels of aggression (de Bruin, 1980). Taken as a whole, these data indicate that the Dm telencephalon area shares a great similarity with pallial amygdaloid nuclei and homologous structures in reptiles (Crews et al, 1993;Keating et al, 1970;Krohner & Crews, 1987;Tarr, 1977), birds (Cohen, 1975;Dafter, 1975;Ikebuchi et al, 2009;Martínez-García, et al, 2002;Phillips 1968;Phillips & Youngren, 1968;Vowles & Beasley, 1974;Zeier, 1971), and mammals (Ambrogli et al, 1991;Fonberg, 1973;Grossman et al, 1974;Hanwerker et al, 1974;Horvath, 1963;Killcross et al, 1997;Liang & McGaugh, 1983;McIntery & Stein, 1973;Pellegrino, 1968;Roozendaal et al, 1993;Sanchez-Riolobos, 1986;Takashina et al, 1995;van-der-Zee et al, 1997;Werka et al, 1978;Wiersma et al, 1998). These amygdala lesions affect not only the avoidance conditioning, but also the fear conditioning in mammals and birds (Cohen, 1975;Dafter, 1976).…”

“…These data coupled with the effects of Dm lesions on aggressive behavior, breeding, habituation in situations of aggression in a resident/intruder paradigm (de Bruin, 1980;Marino-Neto & Sabbatini, 1983), as well as data from electrical stimulation of Dm in Carassius that show facilitation and inhibition of aggressive and reproductive patterns or startle response and escape (Savage, 1971), support the homology of the fish telencephalic Dmv with the pallial amygdala of mammals. This idea have been proposed on the basis of neuroanatomical and neurohistochemical evidence of similarities between the two structures developing an evolution-based model of brain organization (Braford, 1995;Echteler & Saidel, 1981;Hornby et al, 1987;Ito et al, 1986;Medina & Reiner, 1995;Murakami et al, 1983;Northcutt, 1995;Piñuela & Nortcutt, 1994;Reiner & Northcutt, 1992;Striedter, 1991;Wulliman & Rink, 2002) and that of reptiles (Crews et al, 1993;Keating et al, 1970;Krohner & Crews, 1987;Tarr, 1977), birds (Cohen, 1975;Dafter, 1975;Ikebuchi et al, 2009;Phillips 1968;Phillips & Youngren, 1968;Vowles & Beasley, 1974;Zeier, 1971), and mammals (Ambrogli et al, 1991;Fonberg, 1973;Grossman et al, 1974;Hanwerker et al, 1974;Horvath, 1963;Killcross et al, 1997;Liang & McGaugh, 1983;McIntery & Stein, 1973;Pellegrino, 1968;Roozendaal et al, 1993;…”

“…Reproductive and aggressive behaviors, as well as associated seasonal variations, have been the main object of study in snakes (Thamnophis sirtalis parietalis). These studies show that the sphericus, considered homologous to the amygdala in these reptiles (Bruce & Neary, 1995;Sriedter, 1997), presents sexual dimorphism which is more evident of the males (Crews et al, 1993). Moreover, when the nucleus sphericus is lesioned before the start of the stage of hibernation, there is a facilitation of courtship patterns in the male after the hibernation that correlates with increased blood levels of androgens, indicating a potential facilitating effect of the lesion (Krohner & Crews, 1987).…”

Neurobiology of Seasonal Life-history Transitions

“…I chose two brain regions for this analysis that are both seasonally variable and sexually dimorphic: the medial cortex and NS (Holding et al, 2012;Kabelik et al, 2006;Krohmer et al, 2011;Crews et al, 1993). Because only NPY cells, and not AVT cells, occur in the medial cortex and NS, I distinguished the boundaries of these regions using the same brain atlas used for counting NPY cells Krohmer et al, 2010;Martínez-Marcos et al, 2001), and then outlined the region of interest and measured its area using the calibrated measure feature of ImageJ software (NIH); I repeated this procedure for every tissue section containing the region of interest.…”