Rebeca Toledo

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.

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.

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.

Prostate response to prolactin in sexually active male rats.

BackgroundThe prostate is a key gland in the sexual physiology of male mammals. Its sensitivity to steroid hormones is widely known, but its response to prolactin is still poorly known. Previous studies have shown a correlation between sexual behaviour, prolactin release and prostate physiology. Thus, here we used the sexual behaviour of male rats as a model for studying this correlation. Hence, we developed experimental paradigms to determine the influence of prolactin on sexual behaviour and prostate organization of male rats.MethodsIn addition to sexual behaviour recordings, we developed the ELISA procedure to quantify the serum level of prolactin, and the hematoxilin-eosin technique for analysis of the histological organization of the prostate. Also, different experimental manipulations were carried out; they included pituitary grafts, and haloperidol and ovine prolactin treatments. Data were analyzed with a One way ANOVA followed by post hoc Dunnet test if required.ResultsData showed that male prolactin has a basal level with two peaks at the light-dark-light transitions. Consecutive ejaculations increased serum prolactin after the first ejaculation, which reached the highest level after the second, and started to decrease after the third ejaculation. These normal levels of prolactin did not induce any change at the prostate tissue. However, treatments for constant elevations of serum prolactin decreased sexual potency and increased the weight of the gland, the alveoli area and the epithelial cell height. Treatments for transient elevation of serum prolactin did not affect the sexual behaviour of males, but triggered these significant effects mainly at the ventral prostate.ConclusionThe prostate is a sexual gland that responds to prolactin. Mating-induced prolactin release is required during sexual encounters to activate the epithelial cells in the gland. Here we saw a precise mechanism controlling the release of prolactin during ejaculations that avoid the detrimental effects produced by constant levels. However, we showed that minor elevations of prolactin which do not affect the sexual behaviour of males, produced significant changes at the prostate epithelium that could account for triggering the development of hyperplasia or cancer. Thus, it is suggested that minute elevations of serum prolactin in healthy subjects are at the etiology of prostate abnormal growth.

A study of the prostate, androgens and sexual activity of male rats

BackgroundThe prostate is a sexual gland that produces important substances for the potency of sperm to fertilize eggs within the female reproductive tract, and is under complex endocrine control. Taking advantage of the peculiar behavioral pattern of copulating male rats, we developed experimental paradigms to determine the influence of sexual behavior on the level of serum testosterone, prostate androgen receptors, and mRNA for androgen receptors in male rats displaying up to four consecutive ejaculations.MethodsThe effect of four consecutive ejaculations was investigated by determining levels of (i) testosterone in serum by solid phase RIA, (ii) androgen receptors at the ventral prostate with Western Blots, and (iii) androgen receptors-mRNA with RT-PCR. Data were analyzed with a one-way ANOVA followed by a post hoc application of Dunnetts test if required.ResultsThe constant execution of sexual behavior did not produce any change in the weight of the ventral prostate. Serum testosterone increased after the second ejaculation, and remained elevated even after four ejaculations. The androgen receptor at the ventral prostate was higher after the first to third ejaculations, but returned suddenly to baseline levels after the fourth ejaculation. The level of mRNA increased after the first ejaculation, continued to increase after the second, and reached the highest peak after the third ejaculation; however, it returned suddenly to baseline levels after the fourth ejaculation.ConclusionFour consecutive ejaculations by sexually experienced male rats had important effects on the physiological responses of the ventral prostate. Fast responses were induced as a result of sexual behavior that involved an increase and decrease in androgen receptors after one and four ejaculations, respectively. However, a progressive response was observed in the elevation of mRNA for androgen receptors, which also showed a fast decrease after four ejaculations. All of these changes with the prostate gland occurred in the presence of a sustained elevation of testosterone in the serum that started after two ejaculations. A consideration of these fast-induced changes suggests that the nerve supply plays a key role in prostate physiology during the sexual behavior of male rats.

Inhibition of endoplasmic reticulum Ca2+ ATPase in preBötzinger complex of neonatal rat does not affect respiratory rhythm generation

PreBötzinger complex (preBötC) neurons in the brainstem underlie respiratory rhythm generation in vitro. As a result of network interactions, preBötC neurons burst synchronously to produce rhythmic premotor inspiratory activity. Each inspiratory neuron has a characteristic 10-20 mV, 0.3-0.8 s synchronous depolarization known as the inspiratory drive potential or inspiratory envelope, topped by action potentials (APs). Mechanisms involving Ca(2+) fluxes have been proposed to underlie the initiation of the inspiratory drive potential. An important source of intracellular Ca(2+) is the endoplasmic reticulum (ER) in which active Ca(2+) sequestration is mediated by a class of transporters termed sarco/endoplasmic reticulum Ca(2+) ATPases (SERCAs). We aim to test the hypothesis that disruption of Ca(2+) sequestration into the ER affects respiratory rhythm generation. We examined the effect of inhibiting SERCA on respiratory rhythm generation in an in vitro slice preparation. Bath application of the potent SERCA inhibitors thapsigargin or cyclopiazonic acid (CPA) for up to 90 min did not significantly affect the period or amplitude of respiratory-related motor output or integral and duration of inspiratory drive in preBötC neurons. We promoted the depletion of intracellular Ca(2+) stores by a transient bath application of 30 mM K(+) (high K(+)) in the continuous presence of thapsigargin or CPA. After washing out the high K(+), respiratory rhythm period and amplitude returned to baseline values. These results show that after inhibition of SERCA and depletion of intracellular Ca(2+) stores, respiratory rhythm remains substantially the same, suggesting that this source of Ca(2+) does not significantly contribute to rhythm generation in the preBötC in vitro.

Multiunit Recording of the Cerebellar Cortex, Inferior Olive, and Fastigial Nucleus During Copulation in Naive and Sexually Experienced Male Rats

The sexual behavior of male rats constitutes a natural model to study learning of motor skills at the level of the central nervous system. We previously showed that sexual behavior increases Fos expression in granule cells at lobules 6 to 9 of the vermis cerebellum. Herein, we obtained multiunit recordings of lobules 6a and 7 during the training period of naive subjects, and during consecutive ejaculations of expert males. Recordings from both lobules and the inferior olive showed that the maximum amplitude of mount, intromission, and ejaculation signals were similar, but sexual behavior during training tests produced a decrease in the amplitude for mount and intromission signals. The fastigial nucleus showed an inverse mirror-like response. Thus, the cerebellum is involved in the neural basis of sexual behavior and the learning of appropriate behavioral displays during copulation, with a wiring that involves the cerebellar cortex, inferior olive, and fastigial nucleus.

Androgen receptors in Purkinje neurons are modulated by systemic testosterone and sexual training in a region-specific manner in the male rat

The androgen receptor (AR) is a widely distributed molecule indicating the spread actions of its ligand steroid, and plays an important role underlying male sexual behavior. Nevertheless, the influence of steroid hormones and their receptors on cerebellar neurons, as foundation of sexual behavior, is largely unknown. We sought to determine the influence of peripheral hormones on the AR expression in Purkinje neurons across cerebellar lobules in the vermis of male rats. First, we found a basal AR expression in Purkinje neurons that was higher in the superficial region than the deep region only in cerebellar lobules 2, 4, 5, 7, 8 and 9. Moreover, only the cerebellar lobule 10 showed a significant difference between the coordinates 0.1, 0.3 and 0.9. Second, males with four sessions of sexual training showed a decreased AR density in cerebellar lobules 7, 8, 9 and 10, but not in lobules 2, 4 or 5 when compared to males with one session of sexual training. However, sexual training did not affect AR expression in Purkinje neurons according to their location in any of the cerebellar lobules studied. Third, castration decreased the AR density in the cerebellar lobules 1, 2, 5 and 9 in the superficial region, while in the deep region all cerebellar lobules, except lobule 6, showed a lower AR density after castration. Finally, testosterone replacement restored AR density to control levels in all cerebellar lobules in the superficial region that were affected by castration. Contrary, in the deep region hormonal replacement failed to restore the AR density to control level in the majority of the cerebellar lobules that were affected by castration. Altogether, our findings indicate that Purkinje neurons in the vermis are influenced by systemic testosterone in a region-dependent manner highlighting a link between the cerebellum and gonads in the male rat. The AR function in Purkinje neurons may be related to cerebellar plasticity since both estrogen and progesterone receptors, members of the nuclear receptor family, regulate plasticity processes in Purkinje neurons. We concluded the cerebellum is an important component of the neural circuit for male sexual behavior.

Histological modifications of the rat prostate following transection of somatic and autonomic nerves

It is known that hormones influence significantly the prostate tissue. However, we reported that mating induces an increase in androgen receptors, revealing a neural influence on the gland. These data suggested that somatic afferents (scrotal and genitofemoral nerves) and autonomic efferents (pelvic and hypogastric nerves) could regulate the structure of the prostate. Here we assessed the role of these nerves in maintaining the histology of the gland. Hence, afferent or efferent nerves of male rats were transected. Then, the ventral and dorsolateral regions of the prostate were processed for histology. Results showed that afferent transection affects prostate histology. The alveoli area decreased and increased in the ventral and dorsolateral prostate, respectively. The epithelial cell height increased in both regions. Efferent denervation produced dramatic changes in the prostate gland. The tissue lost its configuration, and the epithelium became scattered and almost vanished. Thus, afferent nerves are responsible for spinal processes pertaining to the trophic control of the prostate, activating its autonomic innervation. Hence, our data imply that innervation seems to be synergic with hormones for the healthy maintenance of the prostate. Thus, it is suggested that some prostate pathologies could be due to the failure of the autonomic neural pathways regulating the gland.

Circadian and photic-induced expression of Fos protein in the suprachiasmatic nucleus of the rabbit

Even though the rabbit has been widely used for circadian studies, very little information is available in this species about the morphology and physiology of the suprachiasmatic nucleus (SCN). The aim of the present study was to characterize expression of the Fos protein by immunocytochemistry in the rabbits SCN under two conditions: light – dark (L/D, 12:12 h, lights on at 7:00 a.m.) every four hours, starting at ZT01 (08:00 h geographical time) and constant darkness (D/D), starting at CT03. We also analyzed the induction of Fos in the SCN in response to a light pulse (850 lux/30 min) at CT03, CT11, CT15 and CT19 in D/D conditions. In L/D there was a clear Fos induction by light at ZT01 and ZT05 (p < 0.01) in comparison to the other time points. In D/D we found an endogenous rhythm of Fos that peaked at CT07 (p < 0.01). Light pulses induced a strong Fos immunoreactivity only during the subjective night at CT15 and CT19, in the ventrolateral region of the SCN (p < 0.05), in contrast to the maximum expression of Fos during L/D and D/D, where only a sparse distribution in the nucleus was found. In conclusion, we found a daily and a circadian rhythm of Fos and a photic induction at times that produce phase-shifts in other species.