Cohabitation with receptive females under D2-type agonism in adulthood restores partner preference and brain dimorphism in the SDN-POA following neonatal gonadectomy in male rats.

Perinatal testosterone, or its metabolite estradiol, organize the brain toward a male phenotype. Male rodents with insufficient testosterone during this period fail to display sexual behavior and partner preference for receptive females in adulthood. However, cohabitation with non-reproductive conspecifics under the influence of a D2 agonist facilitates the expression of conditioned partner preference via Pavlovian learning in gonadally intact male rats. In the present experiment, three groups of neonatal PD1 males (N = 12/group) were either gonadectomized (GDX), sham-GDX, or left intact and evaluated for social preferences and sexual behaviors as adults. We then examined whether the effects of GDX could be reversed by conditioning the males via cohabitation with receptive females under the effects of the D2 agonist quinpirole (QNP) or saline, along with the size of some brain regions, such as the sexually dimorphic nucleus of the preoptic area (SDN-POA), suprachiasmatic nucleus (SCN), posterior dorsal medial amygdala (MeApd) and ventromedial hypothalamus (VMH). Results indicated that neonatal GDX resulted in the elimination of male-typical sexual behavior, an increase in same-sex social preference, and a reduction of the area of the SDN-POA. However, GDX-QNP males that underwent exposure to receptive females in adulthood increased their social preference for females and recovered the size in the SDN-POA. Although neonatal GDX impairs sexual behavior and disrupts partner preference and brain dimorphism in adult male rats, Pavlovian conditioning under enhanced D2 agonism ameliorates the effects on social preference and restores brain dimorphism in the SDN-POA without testosterone.

Changes in multiunit activity pattern in cerebellar cortex associated to olfactory cues during sexual learning in male rats.

The cerebellum is a structure of the central nervous system which has been previously studied with different techniques and animal models and even humans, so it is associated with multiple functions such as cognition, memory, emotional processing, balance, control of movement, among others. Its relationship with sensory systems has already been explored, however, the role it plays in olfactory processing in the cerebellum is unclear. Several hypotheses have been proposed from work done in humans and animal models with neuroimaging and immunohistochemical techniques. Everything seems to indicate that the cerebellar function is of vital importance for the olfactory perception, being able to be controlling not only the olfactory aspect, but also the olfactory processing. In this study we analyzed the multiunit activity in the granular layer of the cerebellar vermis during olfactory stimulation: a session being sexually naive and during four sessions of sexual behavior learning. The amplitude was compared between male naive and sexual experts, as well as between olfactory stimuli. The amplitude of the sexually experienced rats showed the highest values compared to naive ones. Odor of receptive female causes the greatest amplitudes, however, in the control group the amplitude increased when they were sexually experts. The motor, sensory and associative learning generated by the acquisition of sexual experience modifies the activation pattern in the cerebellum by presenting neutral odors or associated with a reward.

Olfactory stimulation induces cerebellar vermis activation during sexual learning in male rats.

The cerebellum is a complex structure mainly recognized for its participation in motor activity and balance, and less understood for its role in olfactory processing. Herein, we assessed Fos immunoreactivity (Fos-IR) in the cerebellar vermis following exposure to different odors during sexual training in male rats. Males were allowed to copulate for either one, three or five sessions. One day after the corresponding session they were exposed during 60 min to woodshaving that was either: clean (Control), sprayed with almond scent (Alm) or from cages of sexually receptive females (RF). The vermis of the cerebellum was removed, cut in sagittal sections and analyzed for Fos-IR to infer activation. Our results showed that the cerebellum responded with more Fos-IR in the Alm and RF groups as compared to Control. More copulatory sessions resulted in more odor-induced Fos-IR, especially in the RF group. Accordingly, we discuss possible mechanisms on how the cerebellum mediates processing of both unconditioned and conditioned odors, and how sexual experience accelerates such process.

Characteristics of ejaculated rat semen after lesion of scrotal nerves.

The scrotum, representing the pouch surrounding the testes and their associated structures, plays a significant role in maintaining the gonad at a temperature lower than that of the body. Although thermoregulation of the testes has been ascribed as a main function of the scrotum, here we found that mechanical stimulation of the scrotum is important during mating to facilitate the appropriate expulsion of semen during ejaculation. Previously we showed that the scrotal skin area is innervated by two nerve branches, the proximal (Psb) and distal (Dsb) scrotal branches which supply the proximal or distal half of the scrotum, respectively. The sensory field of each nerve is testosterone-dependent. The decreased androgen levels following castration reduce the sensitive area to mechanical stimuli that can be restored following exogenous administration of the hormone. Here, we tested the effect of scrotal nerve transection on sexual parameters of experienced male rats. Data show that lesion of PSb or DSb alone or combined did not affect the execution of sexual behavior. However, these lesions significantly reduced the proportion of males that expelled semen during ejaculation, with that semen showing a reduced quantity of sperm. Thus, scrotal nerves are important in reproduction not for the appropriate display of sexual behavior, but for the expulsion of a normal quantity of semen and number of sperm during ejaculation. Our suggestion is that scrotal afferents trigger spinal reflexes to activate autonomic efferents supplying the male reproductive tract for the control of seminal emission.

Alterations in the thalamic reticular nucleus of rats neonatally treated with thyroxine

En ratas Wistar normales y tratadas neonatalmente con tiroxina, se obtuvieron cortes seriados del tálamo, teñidos con el método de Golgi-Cox en las edades de 12,20 y 30 días. En la zona de núcleo reticular talámico (TRN), se contó el número de neuronas visibles, el área y la máxima extensión transversal del TRN en un total de 120 secciones. Los hallazgos indicaron que con relación al numero de neuronas en los animales tratados con T4, ocurrió un incremento signifiativo inicial de ellas a los 12 días de edad, seguido de un decremento igualmente significativo a los 20 y 30 días postnatales. Con respecto al área y a la máxima extensión transversal del TRN, sólo se observó una reducción progresiva que alcanzó sus valores más bajos a los 30 días de edad, sin ocurrir el incremento inicial que se ha descrito para el tejido neuronal. Los hallazgos sugieren que el tratamiento neonatal con T4, pudiera interferir con el desarrollo neuronal del TRN y, asimismo, a largo plazo, con las funciones modulatorias sensoriales del TRN