Jorge Manzo

Olfactory conditioned partner preference in the female rat.

Paced copulation induces conditioned place preference in female rats. The authors examined whether associating almond-scented males with paced copulation induces conditioned partner preference. The paired group received 4 paced copulations with almond-scented males and 4 nonpaced copulations with unscented males sequentially at 4-day intervals. The unpaired group received the opposite order of association, whereas the randomly paired group received random associations. A 4th group received a single pairing. On the final test, females were placed into an open field with 2 males, 1 scented and 1 unscented. Females in the paired group solicited the scented male more frequently, and most chose the scented male for their 1st ejaculation. Thus, an odor paired with paced copulation elicits conditioned partner preference in female rats.

Electrophysiological evidence for the nomenclature of the pudendal nerve and sacral plexus in the male rat

Surgical microscopy and electrophysiological techniques were used to standardize the nomenclature for the pudendal nerve and sacral plexus according to their somatic axonal composition in the male rat. We conclude that the pudendal nerve is the segment running from the L6-S1 trunk to the sacral plexus, carrying efferent fibers to the coccygeus, internal obturator, ventral and dorsal bulbospongiosus, ischiocavernosus, external anal sphincter, and external urethral sphincter muscles, and afferent fibers from the penis, prepuce, scrotum, and ventral-proximal tail. The sacral plexus is the complex formed by the bridge-like structure connecting the pudendal nerve with the lumbosacral trunk, and two nerve branches emerging from it, one innervating the proximal half of the scrotal skin, and the other innervating the muscles at the base of the penis known as the motor branch. These branches are only considered as a part of the sacral plexus because they integrate axons from both the lumbosacral trunk and pudendal nerve. The gross anatomy of the pudendal nerve and sacral plexus has a main organization that was observed in 70% of cases, whereas the remaining 30% occurred in two variants. This nomenclature is appropriate to describe the pudendal nerve and sacral plexus in studies that involve them being lesioned or electrophysiologically analysed. A main additional finding was that two large afferent branches innervate the scrotum, one the proximal half and the other the distal half. As mentioned above, the proximal branch belongs to the sacral plexus, whereas the distal branch belongs to the pudendal nerve because all its axons travel to the cord via this nerve. Since stimulation or even manipulation of the scrotal branches resulted in the secretion of semen containing spermatozoa, it is suggested that scrotal afferents are involved in some way in the ejaculatory process, a topic that deserves further research.

Regulation of Noncontact Erection in Rats by Gonadal Steroids

Male rats exhibit erections in the presence of inaccessible estrous females, and we investigated which gonadal steroids regulate these noncontact erections (NCEs). Sexually experienced Wistar males (n >/= 8/group) were tested for NCE four times (every 3 days) before castration, after castration, and after receiving subcutaneous implants of 10-mm Silastic capsules that were empty or filled with crystalline testosterone propionate (TP), dihydrotestosterone (DHT), estradiol benzoate (EB), or DHT + EB (10 mm each). Before castration, males responded with NCE in approximately 50% of tests. No males had NCEs after castration, beginning 3 days after surgery. Also, no males responded after treatment with EB or empty capsules. After receiving implants of TP, DHT, or DHT + EB, 50% of males had NCEs, beginning with the first test 3 days after treatment. On every measure of NCE, males treated with DHT or DHT + EB were indistinguishable from each other and from TP-treated males. Among the sexual responses of male rats, NCE appears to be more sensitive than other behaviors to changes in gonadal condition. In its profile of response to gonadal steroids (testosterone+, dihydrotestosterone+, estradiol-), NCE is similar to reflexive erection, for which spinal systems are sufficient, and unlike copulation (T+, DHT-, E+), which depends on discrete areas of the brain. We nonetheless conclude that NCE depends on androgen-sensitive systems in the brain, but androgen-sensitive neurons in the lumbosacral spinal cord may also play a role.

Why should we keep the cerebellum in mind when thinking about addiction

Increasing evidence has involved the cerebellum in functions beyond the sphere of motor control. In the present article, we review evidence that involves the cerebellum in addictive behaviour. We aimed on molecular and cellular targets in the cerebellum where addictive drugs can act and induce mechanisms of neuroplasticity that may contribute to the development of an addictive pattern of behaviour. Also, we analyzed the behavioural consequences of repetitive drug administration that result from activity-dependent changes in the efficacy of cerebellar synapses. Revised research involves the cerebellum in drug-induced long-term memory, drug-induced sensitization and the perseverative behavioural phenotype. Results agree to relevant participation of the cerebellum in the functional systems underlying drug addiction. The molecular and cellular actions of addictive drugs in the cerebellum involve long-term adaptative changes in receptors, neurotransmitters and intracellular signalling transduction pathways that may lead to the re-organization of cerebellar microzones and in turn to functional networks where the cerebellum is an important nodal structure. We propose that drug induced activity-dependent synaptic changes in the cerebellum are crucial to the transition from a pattern of recreational drug taking to the compulsive behavioural phenotype. Functional and structural modifications produced by drugs in the cerebellum may enhance the susceptibility of fronto-cerebellar circuitry to be changed by repeated drug exposure. As a part of this functional reorganization, drug-induced cerebellar hyper-responsiveness appears to be central to reducing the influence of executive control of the prefrontal cortex on behaviour and aiding the transition to an automatic mode of control.

Neurobiology of social attachments

Many types of social attachments can be observed in nature. We discuss the neurobiology of two types (1) intraspecific (with a partner) and (2) parental (with the offspring). Stimuli related to copulation facilitate the first, whereas pregnancy, parturition and lactation facilitate the second. Both types develop as consequence of cohabitation. These events seem to stimulate similar neural pathways that increase (1) social recognition, (2) motivation, reward; and (3) decrease fear/anxiety. Subregions of the amygdala and cortex facilitate social recognition and also disinhibition to decrease rejection responses. The interrelationship between MeA, BNST, LS may mediate the activation of NAcc via the mPOA to increase motivation and reward. Cortical areas such as the ACC discriminate between stimuli. The interaction between OT and D2-type receptors in NAcc shell facilitates intraspecific attachment, but D1-type appears to facilitate parental attachment. This difference may be important for maternal females to direct their attention, motivation and expression of attachment toward the appropriate target.

The effects of enriched environment on BDNF expression in the mouse cerebellum depending on the length of exposure

Environmental enrichment (EE) has been proposed as a factor that improves neuronal connectivity and brain plasticity. The induction of molecular mechanisms that takes place in the cortex, nucleus accumbens and hippocampus resulting from exposure to EE has been attributed partly to the role of neurotrophins as brain-derived neurotrophic factor (BDNF). Recent data directly implicate this neurotrophin in the modulation of plasticity changes in the cerebellum produced by living under environmental enrichment. In the present study, we aimed to assess the effects of different lengths of exposure to EE on cerebellar BDNF expression and western blotting analysis. On the whole, the present data has shown that BDNF increased under EE. However, changes in expression as a result of extending the duration of EE were only seen in Purkinje neurons. In Purkinje neurons, long-term exposure was required in order to fully express this neurotrophin. These data support BDNF as one of the long-term plasticity mechanisms induced by environment, suggesting that cerebellar plasticity can be stimulated as a response to challenges generated by environment. Our findings could have functional implications for various neurodegenerative disorders such as spinocerebellar ataxias, autism, schizophrenia and certain prion encephalopathies, most of them pathologies which have demonstrated to be characterized by alterations in Purkinje neurons and to show a partial recovery by exposure to EE.

Fertility ratio in male rats: Effects after denervation of two pelvic floor muscles

Fertility ratio is defined here as the proportion of females that a male can impregnate after a constant period of in-polygyny living. This ratio was investigated in male rats after denervation of two pelvic floor muscles, the pubococcygeus and iliococcygeus. Denervation was carried out by transecting the somatomotor branch of the pelvic nerve. The lesion did not modify the sexual behavior of males or their overall fertility, but decreased the weight of the ejaculated seminal plug. Consequently, the number of days living in cohabitation to induce pregnancy was increased in lesioned males (approximately 13 days) compared with intact and sham animals (approximately 5 days). These results showed that the fertility ratio was optimal when intact/sham males cohabited with females for two consecutive estrous cycles, but that lesioned males needed up to four cycles to induce most pregnancies. Two hypotheses are raised by our results. The first is that pelvic floor denervation decreases the forceful tension required to expel the semen from the prostatic urethra to the vagina, then an incomplete seminal plug is expelled. The second is that denervation cut afferent fibers that reflexively promote the continence of the semen deposited in the prostatic urethra during seminal emission, allowing some to leak out before ejaculation. The latter hypothesis can also explain the recovery of the fertility ratio in lesioned males. It could be a compensatory mechanism mediated by the pudendal nerve supply to the coccygeus muscle, the other pelvic floor muscle.

Participation of pelvic nerve branches in male rat copulatory behavior

The role of the pelvic nerve branches in the mediation of copulatory behavior was investigated. The somatomotor or the viscerocutaneous branch of the pelvic nerve was bilaterally sectioned in sexually experienced male rats. Somatomotor branch surgery had no detectable effect. Viscerocutaneous branch transection altered copulatory parameters that reflect impairments in penile erection and seminal plug emission. The altered behavioral parameters approached or reached presurgical and sham values 21 days after transection, indicating that the damage to erectile and ejaculatory function was transient. It is suggested that animals with viscerocutaneous branch transection recover copulatory efficiency through a compensatory plastic mechanism, possibly involving the hypogastric nerve.

Changes in pain threshold during the reproductive cycle of the female rat.

Responsiveness to pain was determined in female rats across the whole reproductive cycle using the tail-flick test. When tested immediately after mating, pain thresholds were unaltered, whereas 10 min later animals typically demonstrated hyperalgesia (Experiment 1). They also demonstrated hyperalgesia during most of pregnancy, and had significantly lower pain thresholds than the unmated controls except for the 24 h before parturition, when a sudden increase in tail-flick latencies was recorded (Experiment 2). Pain thresholds were also significantly lower throughout the nursing period but increased significantly when dams were separated from their litters for 6 h, and returned to premating baseline values within 24 h of weaning (Experiment 3). These findings confirm and extend earlier reports that female reproductive state may significantly modify responsiveness to noxious stimuli, and it is suggested that differences between the results of this and previous studies may be at least partly explained by the relatively stress-free test procedure adopted here.

Fos expression at the cerebellum following non-contact arousal and mating behavior in male rats

The cerebellum is considered a center underlying fine movements, cognition, memory and sexual responses. The latter feature led us to correlate sexual arousal and copulation in male rats with neural activity at the cerebellar cortex. Two behavioral paradigms were used in this investigation: the stimulation of males by distant receptive females (non-contact sexual stimulation), and the execution of up to three consecutive ejaculations. The vermis area of the cerebellum was removed following behavioral experiments, cut into sagittal sections, and analyzed with Fos immunohistochemistry to determine neuronal activation. At the mid-vermis region (sections from the midline to 0.1 mm laterally), non-contact stimulation significantly increased the activity of granule neurons. The number of activated cells increased in every lobule, but lobules 1 and 6 to 9 showed the greatest increment. In sexual behavior tests, males reaching one ejaculation had a high number of activated neurons similar to those counted after non-contact stimulation. However, two or three consecutive ejaculations showed a smaller number of Fos-ir cells. In contrast to the mid-vermis region, sections farthest from the midline (0.1 to 0.9 mm laterally) revealed that only lobule 7 expressed activated neurons. These data suggest that a well-delineated group of granule neurons have a sexual biphasic response at the cerebellar vermis, and that Fos in them is under an active degradation mechanism. Thus, they participate as a neural substrate for male rat sexual responses with an activation-deactivation process corresponding with the sensory stimulation and motor performance occurring during copulation.