The Gonadotropin‐Releasing Hormone Neurosecretory System of the Jerboa (Jaculus orientalis) and its Seasonal Variations

Abstract

The distribution of cells expressing gonadotropin-releasing hormone (GnRH) immunoreactivity was examined in the brain of adult jerboa during two distinct periods of the reproductive cycle. During spring-summer, when the jerboa is sexually active, a high density of cell bodies and fibres immunoreactive (IR) for GnRH was observed at the level of separation of the frontal lobes, in the medial septal nucleus (MS) and in the diagonal band of Broca (DBB), in the preoptic area (POA), in the organum vasculosum laminae terminalis (OVLT), in the retrochiasmatic area and hypothalamus. In autumn, when the jerboa is sexually inactive, GnRH-immunoreactivity was less intense than during spring-summer. In the POA, we noted a 55% decrease in the number of GnRH containing cells with no change in cell numbers in the MS-DBB. Furthermore, a lower density of GnRH immunopositive axon fibres is observed in all the previously mentioned structures and the immunoreaction intensity was very weak particularly within the median eminence and OVLT. Independently of the season, the GnRH immunoreactivity within neurones and fibres was similar in jerboas living in captivity and in jerboas living in their natural biotope. The effects of photoperiod on the density of POA-GnRH and arcuate nucleus beta-endorphin-containing cells were studied in jerboas maintained in long day [(LD) 16-h light, 8-h dark] and short day [(SD) 8-h light, 16-h dark] for 8 weeks. In the POA, the GnRH-IR cell number was not significantly altered by the photoperiod. Similarly, in the mediobasal hypothalamus, the number of beta-endorphin-IR neurones was not affected by such a parameter. Consequently, the GnRH seasonal variations cannot be correlated to changes in the photoperiod alone.

Vasopressin-Containing Neurons of the Hypothalamic Parvocellular Paraventricular Nucleus of the Jerboa: Plasticity Related to Immobilization Stress

“…Cell counts were performed by direct microscopic observation in a blinded fashion. The neuranatomical identification of the hypothalamic structures was based both on the atlas of the rat brain by Paxinos and Watson [34] and data previously described for rats and jerboas [26, 29]. Quantification of VP-immunoreactive cell bodies within the parvocellular PVN of control and stressed jerboas was performed bilaterally on four sections per animal, and an average value was calculated for each animal.…”

“…Parameters such as glycemia and cortisol in hibernating mammals are known to decrease during hibernation in comparison with the active state [14, 15]. Jerboas also display seasonal variations in the hypothalamic expression of several neuropeptides, including VP [27], gonadotropin-releasing hormone [28], neuropeptide Y [29,] and β-endorphin [30], which impinge on their sexual activity. Thus, in the jerboa, hypothalamic neuropeptides most probably play an integrative role in numerous neuroendocrine regulatory mechanisms that determine sexual and feeding behaviors or energy expenditure in order to facilitate the adaptation of the animals to the bioclimatic variations.…”

“…Thus, in the jerboa, hypothalamic neuropeptides most probably play an integrative role in numerous neuroendocrine regulatory mechanisms that determine sexual and feeding behaviors or energy expenditure in order to facilitate the adaptation of the animals to the bioclimatic variations. Furthermore, captive jerboas do not reproduce in the laboratory, even though the gonadotropin-releasing hormone neuronal expression within brains of captive jerboas and jerboas living in the wild is similar [29]. Such blockade of reproduction in laboratory jerboas may be related to the stress of the animal, inhibiting its copulatory behavior.…”

Kisspeptin and RFRP-3 differentially regulate food intake and metabolic neuropeptides in the female desert jerboa

“…The jerboa is a particularly interesting animal model living in a semi-desert milieu characterized by large annual variations in environmental temperature, water and food supply. In autumn/winter, when the natural conditions are unfavorable, jerboas shut down their reproductive activity3233, increase their food intake and body weight and hibernate3435, while in spring/summer when favorable conditions return, the animals display opposite regulations with a reactivation of reproduction and reduction in body weight and food intake32333536.…”

Coordinated seasonal regulation of metabolic and reproductive hypothalamic peptides in the desert jerboa

“…The jerboa is a semi-desert rodent whose reproductive and metabolic activities are well adapted to marked environmental changes. This species is sexually active in spring and early summer (Ghobrial and Hodieb, 1973;El Ouezzani et al, 2000;El Qandil et al, 2004) and hibernates at low ambient temperatures (Andjus et al, 1974;El Ouezzani et al, 2011). It displays seasonal variations in the nocturnal production of melatonin (Lakhdar-Ghazal et al, 1992) and melatonin inhibits testicular activity in male jerboas (El Qandil et al, 2004).…”