Elenice A. de Moraes Ferrari

THE ANTIDEPRESSIVE EFFECT OF THE PHYSICAL EXERCISE CORRELATES WITH INCREASED LEVELS OF MATURE BDNF, AND proBDNF PROTEOLYTIC CLEAVAGE-RELATED GENES, p11 AND tPA

Clinical studies show an evident antidepressive effect of physical exercise and animal research corroborate such evidence. However, the neurobiological mechanisms underlying the antidepressive effect of exercise are not completely understood. Notwithstanding, it is known that exercise increases brain-derived neurotrophic factor (BDNF) expression in the hippocampus similarly to antidepressant drugs. BDNF is synthesized as a precursor molecule that undergoes a proteolytic cleavage to generate either a mature or a truncated isoform. Precursor and mature BDNF are assumed to elicit opposing biological effects in neuroplasticity. In the present study we investigated the effect of voluntary physical activity on precursor and mature brain-derived neurotrophic factor levels and on proBDNF cleavage related genes, p11 and tissue plasminogen activator (tPA), as well as the antidepressive and cognitive effects of voluntary physical activity. Mice had access to mobile or locked running wheels for 28 days and were submitted to forced-swim, tail suspension and water maze tests. Their hippocampi were dissected and analyzed by Western blot and real time RT-PCR. Voluntary physical activity, but not locked wheel exposure, induced a robust increase in hippocampal mature BDNF protein levels, as well as in p11 and tPA mRNA expression; and also promoted antidepressive effects and improved learning, when compared with sedentary mice. On the other hand, there were no significant differences between any groups in the expression of precursor or truncated isoforms of BDNF. Our data suggest that the antidepressive effect of the physical exercise may depend, at least in part, on changes in BDNF post-translational processing.

Neuronal degeneration and gliosis time-course in the mouse hippocampal formation after pilocarpine-induced status epilepticus.

Temporal lobe epilepsy (TLE) is the most common type of human epilepsy and has been related with extensive loss of hippocampal pyramidal and dentate hilar neurons and gliosis. Many characteristics of TLE are reproduced in the pilocarpine model of epilepsy in mice. This study analyzed the neuronal damage, assessed with Fluoro-Jade (FJB) and cresyl violet, and gliosis, investigated with glial fibrilary acidic protein (GFAP) immunohistochemistry, occurring in the hippocampal formation of mice at 3, 6, 12 and 24h, 1 and 3 weeks after the pilocarpine-induced status-epilepticus (SE) onset. The maximum neuronal damage score and the FJB-positive neurons peak were found in the hilus of dentate gyrus 3 and 12 h after SE onset (P<0.05), respectively. At 1 week after SE onset, the greatest neuronal damage score was detected in the CA1 pyramidal cell layer and the greatest numbers of FJB-positive neurons were found both in the CA1 and CA3 pyramidal cell layers (P<0.05). The molecular, CA3 and CA1 pyramidal cell layers expressed highest presence of GFAP immunoreaction at 1 and 3 weeks after SE onset (P<0.05). Our findings show that, depending on the affected area, neuronal death and gliosis can occur within few hours or weeks after SE onset. Our results corroborate previous studies and characterize short time points of temporal evolution of neuropathological changes after the onset of pilocarpine-induced SE in mice and evidences that additional studies of this temporal evolution may be useful to the comprehension of the cellular mechanisms underlying epileptogenesis.

Effects of comfort food on food intake, anxiety-like behavior and the stress response in rats.

It has been suggested that access to high caloric food attenuates stress response. The present paper investigates whether access to commercial chow enriched with glucose and fat, here referred to as comfort food alters behavioral, metabolic, and hormonal parameters of rats submitted to three daily sessions of foot-shock stress. Food intake, anxiety-like behaviors, and serum levels of insulin, leptin, corticosterone, glucose and triglycerides were determined. The rats submitted to stress decreased the intake of commercial chow, but kept unaltered the intake of comfort food. During the elevated plus maze (EPM) test, stressed rats increased the number of head dipping, entries into the open arms, as well as the time spent there, and decreased the number of stretched-attend posture and risk assessment. These effects of stress were independent of the type of food consumed. Non-stressed rats ingesting comfort food decreased risk assessment as well. Stress and comfort food increased time spent in the center of the open field and delayed the first crossing to a new quadrant. Stress increased the plasma level of glucose and insulin, and reduced triglycerides, although consumption of comfort food increases glucose, triglyceride and leptin levels; no effect on leptin level was associated to stress. The stress induced increase in serum corticosterone was attenuated when rats had access to comfort food. It was concluded that foot-shock stress has an anorexigenic effect that is independent of leptin and prevented upon access to comfort food. Foot-shock stress also has an anxiolytic effect that is potentiated by the ingestion of comfort food and that is evidenced by both EPM and open field tests.

Glutamatergic neurotransmission mediated by NMDA receptors in the inferior colliculus can modulate haloperidol-induced catalepsy.

The inferior colliculus (IC) is primarily involved in the processing of auditory information, but it is distinguished from other auditory nuclei in the brainstem by its connections with structures of the motor system. Functional evidence relating the IC to motor behavior derives from experiments showing that activation of the IC by electrical stimulation or excitatory amino acid microinjection causes freezing, escape-like behavior, and immobility. However, the nature of this immobility is still unclear. The present study examined the influence of excitatory amino acid-mediated mechanisms in the IC on the catalepsy induced by the dopamine receptor blocker haloperidol administered systemically (1 or 0.5 mg/kg) in rats. Haloperidol-induced catalepsy was challenged with prior intracollicular microinjections of glutamate NMDA receptor antagonists, MK-801 (15 or 30 mmol/0.5 microl) and AP7 (10 or 20 nmol/0.5 microl), or of the NMDA receptor agonist N-methyl-d-aspartate (NMDA, 20 or 30 nmol/0.5 microl). The results showed that intracollicular microinjection of MK-801 and AP7 previous to systemic injections of haloperidol significantly attenuated the catalepsy, as indicated by a reduced latency to step down from a horizontal bar. Accordingly, intracollicular microinjection of NMDA increased the latency to step down the bar. These findings suggest that glutamate-mediated mechanisms in the neural circuits at the IC level influence haloperidol-induced catalepsy and participate in the regulation of motor activity.

Effects of voluntary running on spatial memory and mature brain-derived neurotrophic factor expression in mice hippocampus after status epilepticus

Voluntary physical activity improves memory and learning ability in rodents, whereas status epilepticus has been associated with memory impairment. Physical activity and seizures have been associated with enhanced hippocampal expression of BDNF, indicating that this protein may have a dual role in epilepsy. The influence of voluntary physical activity on memory and BDNF expression has been poorly studied in experimental models of epilepsy. In this paper, we have investigated the effect of voluntary physical activity on memory and BDNF expression in mice with pilocarpine-induced epilepsy. Male Swiss mice were assigned to four experimental groups: pilocarpine sedentary (PS), pilocarpine runners (PRs), saline sedentary (SS) and saline runners (SRs). Two days after pilocarpine-induced status epilepticus, the affected mice (PR) and their running controls (SR) were housed with access to a running wheel for 28 days. After that, the spatial memory and the expression of the precursor and mature forms of hippocampal BDNF were assessed. PR mice performed better than PS mice in the water maze test. In addition, PR mice had a higher amount of mature BDNF (14kDa) relative to the total BDNF (14kDa+28kDa+32kDa forms) content when compared with PS mice. These results show that voluntary physical activity improved the spatial memory and increased the hippocampal content of mature BDNF of mice with pilocarpine-induced status epilepticus.

Habituation to Sound During Morning and Night Sessions in Pigeons (Columba livia)

Habituation to acoustic stimulation was analyzed through night and morning sessions in pigeons submitted to a 12:12 h light-dark (LD) cycle. We demonstrate a lack of habituation in nocturnal sessions as compared to typical habituation curves in morning sessions. Temporal organization of the habituation process raises issues concerning the biological meaning of sound in adaptation to the environment and/or the possible interaction of well known endogenous physiological rhythms with learning. A second experiment was performed to establish whether the LD cycle was responsible for the night/day difference observed in the first experiment. In this experiment, the animals were subjected to two days of continuous light (LL) before the learning sessions. No difference in habituation according to time of day was observed in these conditions suggesting a direct effect of the LD cycle in the habituation to sound.

Plasticidade neural: relações com o comportamento e abordagens experimentais

Behavioral adaptiveness to different situations as well as behavioral individuality result from the interrelations between environmental sitmuli and the responses of an organism.These kind of interrelationships also shape the neural circuits as well as characterize the plasticity and the neural individuality of the organism. Studies on neural plasticity may analyze changes in neural circuitry after environmental manipulations or changes in behavior after lesions in the nervous system. Issues on neural plasticity and recovery of function refer both to physiology and behavior as well as to the subjacent mechanisms related to morphology, biochemistry and genetics. They may be approached at the systemic, behavioral, cellular and molecular levels. This work intends to characterize these kinds of studies pointing to their relations with the analyis of behavior and learning.The analysis of how the environmental-organismic interrelationships affect the neural substrates of behavior is pointed as a very stimulating area for investigation.

Enhancement of Latent Inhibition by Chronic Mild Stress in RatsSubmitted to Emotional Response Conditioning

This work evaluated the influence of chronic mild stress on latent inhibition (LI) in rats, using a conditioned emotional response (CER) procedure. Rats were assigned to four groups: a non pre-exposed control group (NPC), a non pre-exposed stressed group (NPS), a preexposed control group (PC), and a pre-exposed stressed group (PS). Stressed animals were submitted to a chronic mild stress (CMS) regimen for three weeks. The off-baseline conditioned emotional response procedure had four phases: licking response training, tone- shock conditioning, retraining, and testing. Conditioning consisted of 2 tone (30 s) and shock (0.5 s) associations. Tone-shock conditioning evidenced by NPS and NPC groups suggests that stress did not interfere with the expression of a conditioned emotional response. Pre-exposure was carried out using 6 tones (30 s) during 2 sessions before conditioning. Prior exposure to the tone resulted in a decrease in learning that was greater in stressed animals. The results indicate an increase in latent inhibition induced by chronic mild stress. Such LI potentiation after CMS may be related to dopamine (DA) neurotransmission reduction in the central nervous system.

Effects of microinjections of apomorphine and haloperidol into the inferior colliculus on the latent inhibition of the conditioned emotional response.

Electrical or chemical stimulation of the inferior colliculus (IC) induces fear-like behaviors. More recently, consistent evidence has shown that electrical stimulation of the central nucleus of the IC supports Pavlovian conditioning and latent inhibition (LI). LI is characterized by retardation in conditioning and also by an impaired ability to ignore irrelevant stimuli, after a non-reinforced pre-exposure to the conditioned stimulus. LI has been proposed as a behavioral model of cognitive abnormalities seen in schizophrenia. The aim of the present study was to determine whether dopaminergic mechanisms in the IC are involved in LI of the conditioned emotional response (CER). To induce LI, a group of rats was pre-exposed (PE) to six tones in two sessions, while rats that were not pre-exposed (NPE) had two sessions without tone presentations. The conditioning consisted of two tone presentations to the animal, followed immediately by a foot shock. PE and NPE rats received IC microinjections of physiological saline, the dopaminergic agonist apomorphine (9.0 microg/0.5 microL/side), or the dopaminergic antagonist haloperidol (0.5 microg/0.5 microL/side) before both pre-exposure and conditioning. During the test, the PE rats that received saline or haloperidol had a lower suppression of the licking response compared to NPE rats that received vehicle or haloperidol, indicating that latent inhibition was induced. There was no significant difference in the suppression ratio in rats that received apomorphine injections into the IC, indicating reduced latent inhibition. These results suggest that dopamine-mediated mechanisms of the IC are involved in the development of LI.

Classical aversive conditioning induces increased expression of mature-BDNF in the hippocampus and amygdala of pigeons.

The expression of brain-derived neurotrophic factor (BDNF), which is found in the pro-BDNF, truncated-BDNF and mature-BDNF isoforms, changes with learning. Mature-BDNF shows a peak of late expression in the hippocampus that is involved in the persistence of aversive memory in rodents. However, the role of BDNF in the hippocampal synaptic mechanisms involved in the classical conditioning aversive memory in birds still needs clarification. This study investigated the late expression of BDNF in the hippocampus and amygdala of pigeons trained with tone-shock conditioning and the effects of intra-hippocampal infusion of anisomycin (Ani) in these changes. Seven days after implantation of intra-hippocampal microcannulae, adult pigeons trained with three tone-shock pairings were assigned to one of three groups: Conditioning and Ani (CondANI), Conditioning and saline vehicle (CondSAL) and Conditioning only (Cond). NAIVE group had no treatment or conditioning. Homogenates of tissues from the hippocampus and amygdala, obtained 12h after training, were used to determine the content of mature-BDNF, truncated-BDNF and pro-BDNF using Western blotting. Higher values for mature-BDNF than for truncated- and pro-BDNF content were seen in the hippocampus of Cond and CondSAL birds, but not in the hippocampus of CondANI or NAIVE birds (p<0.05). The values of mature-BDNF in the amygdala of all the three conditioned groups were higher than those observed for truncated- and pro-BDNF (p<0.05), which indicates that the activation of this protein in the amygdala was not affected by the infusion of Ani in the hippocampus. The data indicate that the tone-shock conditioning induced the activation of molecular pathways of BDNF in the hippocampus and amygdala of the pigeons. The decreases in the content of truncated- and pro-BDNF isoforms found in conditioned pigeons may suggest cleavage mechanisms induced by the training. Our data confirm previous observations of rodent studies and extend these observations to pigeons, revealing that, in spite of the anatomical differences between the hippocampus of rodents and pigeons, there are functional and molecular mechanisms that are conservative between the species.