Dexamethasone impairs encoding and expression of aversive conditioning promoted by pentylenetetrazole.

Behavioral and neuroendocrine responses following threatening situations promote the release of corticosterone, which is known to modulate trauma-related learning and memory process. However, it remains unknown whether the aversive learning generated by interoceptive fear conditioning is affected by glucocorticoid modulation. Therefore, the present study aimed to investigate the role of dexamethasone suppression in encoding and expression of pentylenetetrazole-induced olfactory fear conditioning (OFC) and in contextual second-order conditioning promoted by the conditioned odor. Adult male Long-Evans rats were treated with dexamethasone 60 min before the encoding or the expression in both OFC and contextual second-order conditioning. Dexamethasone treatment impaired encoding and expression of the OFC, but failed to impair encoding and expression of the contextual second-order conditioning. Altogether, our results show that although OFC and thereafter contextual second-order conditioning may allow the study of traumatic memories, each order of conditioning seems to present specific features related to their pharmacological modulation. These findings highlight the importance of addressing the role of neuromodulatory systems in first-order and second-order conditioning to gain a better understanding of these phenomena and support future therapies related to traumatic memories.

Enduring effects of muscarinic receptor activation on adult hippocampal neurogenesis, microRNA expression and behaviour.

The cholinergic system is one of the most important neurotransmitter systems in the brain with key roles in autonomic control and the regulation of cognitive and emotional responses. However, the precise mechanism by which the cholinergic system influences behaviour is unclear. Adult hippocampal neurogenesis (AHN) is a potential mediator in this context based on evidence, which has identified this process as putative mechanism of antidepressant action. More recently, post-transcriptional regulation by microRNAs is another candidate mechanism based on its involvement in the regulation of AHN and neurotransmission. Taking into account this background, we evaluated the behavioural effects of a non-convulsant dose of pilocarpine - a non-selective muscarinic receptor (mAChR) agonist - in adult Wistar rats. Furthermore, we quantified the expression of different microRNAs implicated in the regulation of AHN. Our results suggests that pilocarpine treatment increases AHN in the granular cell layer but also induced ectopic neurogenesis. Pilocarpine treatment reduced immobility time in forced swimming test but did not affect fear conditioning response, sucrose preference or novelty supressed feeding behaviour. In addition, treatment with pilocarpine down-regulated the expression of 6 microRNAs implicated in the regulation of neurotrophin signalling and axon guidance pathways. Therefore, we suggest that the low-dose stimulation of the cholinergic system is sufficient to alter AHN of rats through post-transcriptional mechanisms, which might contribute to long-lasting behavioural effects.

Ultra-short heart rate variability recording reliability: The effect of controlled paced breathing.

BACKGROUND: Recent studies have reported that Heart Rate Variability (HRV) indices remain reliable even during recordings shorter than 5 min, suggesting the ultra-short recording method as a valuable tool for autonomic assessment. However, the minimum time-epoch to obtain a reliable record for all HRV domains (time, frequency, and Poincare geometric measures), as well as the effect of respiratory rate on the reliability of these indices remains unknown. METHODS: Twenty volunteers had their HRV recorded in a seated position during spontaneous and controlled respiratory rhythms. HRV intervals with 1, 2, and 3 min were correlated with the gold standard period (6-min duration) and the mean values of all indices were compared in the two respiratory rhythm conditions. RESULTS: rMSSD and SD1 were more reliable for recordings with ultra-short duration at all time intervals (r values from 0.764 to 0.950, p < 0.05) for spontaneous breathing condition, whereas the other indices require longer recording time to obtain reliable values. The controlled breathing rhythm evokes stronger r values for time domain indices (r values from 0.83 to 0.99, p < 0.05 for rMSSD), but impairs the mean values replicability of domains across most time intervals. Although the use of standardized breathing increases the correlations coefficients, all HRV indices showed an increase in mean values (t values from 3.79 to 14.94, p < 0.001) except the RR and HF that presented a decrease (t = 4.14 and 5.96, p < 0.0001). CONCLUSION: Our results indicate that proper ultra-short-term recording method can provide a quick and reliable source of cardiac autonomic nervous system assessment.

The cannabinoid CB2 receptor-specific agonist AM1241 increases pentylenetetrazole-induced seizure severity in Wistar rats.

The potential efficacy of cannabinoid receptor ligands for the treatment of epilepsy remains controversial; cannabis components that act via cannabinoid type 1 (CB1) receptors produce anticonvulsant effects in animal models despite treatment with the CB receptor agonist reliably inducing convulsions in various species. Moreover, the potential role of cannabinoid receptor type 2 (CB2) to modulate seizures remains under-investigated. This study assessed the effects of the selective CB2 receptor agonist, AM1241, on pentylenetetrazole (PTZ)-induced seizures in rats. A stereotactically placed guide cannula was surgically implanted into the right lateral ventricle in adult Wistar rats which, 5-6days later, received an acute intracerebroventricular (i.c.v.) microinfusion of AM1241 (0.01, 1 or 10µg/2µl or vehicle) 5min before intraperitoneal (i.p.) injection of PTZ (70mg/kg). Rats were observed for 30min and the seizure severity behavior measured using a modified Racine's scale. Additional groups of rats were pretreated with a single low dose of the selective CB2 receptor antagonist, AM630 (dose 1mg/kg; i.p.), or vehicle, 30min prior to i.c.v. microinfusion of AM1241 (1µg/2µl). AM1241 administration significantly increased tonic-clonic seizure incidence and severity while also decreasing the onset of generalized seizures (AM1241 1 and 10µg/2µl). Pretreatment with AM630 prevented the proconvulsant effects of AM1241. This study shows, for the first time, that selective activation of CB2 receptors can increase generalized seizure susceptibility and suggests that pathological hyperexcitability phenomena can be differentially regulated by targeting CB1 and CB2 receptors.

The Role of Hippocampal NMDA Receptors in Long-Term Emotional Responses following Muscarinic Receptor Activation.

Extensive evidence indicates the influence of the cholinergic system on emotional processing. Previous findings provided new insights into the underlying mechanisms of long-term anxiety, showing that rats injected with a single systemic dose of pilocarpine--a muscarinic receptor (mAChR) agonist--displayed persistent anxiogenic-like responses when evaluated in different behavioral tests and time-points (24 h up to 3 months later). Herein, we investigated whether the pilocarpine-induced long-term anxiogenesis modulates the HPA axis function and the putative involvement of NMDA receptors (NMDARs) following mAChRs activation. Accordingly, adult male Wistar rats presented anxiogenic-like behavior in the elevated plus-maze (EPM) after 24 h or 1 month of pilocarpine injection (150 mg/kg, i.p.). In these animals, mAChR activation disrupted HPA axis function inducing a long-term increase of corticosterone release associated with a reduced expression of hippocampal GRs, as well as consistently decreased NMDAR subunits expression. Furthermore, in another group of rats injected with memantine--an NMDARs antagonist (4 mg/kg, i.p.)--prior to pilocarpine, we found inhibition of anxiogenic-like behaviors in the EPM but no further alterations in the pilocarpine-induced NMDARs downregulation. Our data provide evidence that behavioral anxiogenesis induced by mAChR activation effectively yields short- and long-term alterations in hippocampal NMDARs expression associated with impairment of hippocampal inhibitory regulation of HPA axis activity. This is a novel mechanism associated with anxiety-like responses in rats, which comprise a putative target to future translational studies.

Anxiogenic-like profile of Wistar adult rats based on the pilocarpine model: an animal model for trait anxiety?

RATIONALE: There is extensive evidence indicating the influence of seizures on emotional responses observed in human and animals, but so far few studies are focusing on the behavioral profile of animals that do not have seizures despite being treated with convulsant agents. OBJECTIVES: We aimed to establish the behavioral profile, biochemical, and electrographic features of rats submitted to the pilocarpine model of temporal lobe epilepsy METHODS: Rats treated with pilocarpine (20 to 350 mg/kg, i.p.) that did not develop status epilepticus or spontaneous recurrent seizures were evaluated 1 month later in the elevated plus maze (EPM), T-maze (ETM), open-field (OF), and step-down avoidance tests. Electroencephalographic (EEG), glutamate uptake, and hippocampal neuronal death assays were also performed RESULTS: Pilocarpine (150 or 350 mg/kg) promoted anxiogenic-like effects in rats evaluated in the EPM, ETM, and OF tests, whereas only the highest dose evoked spike-wave discharges during EEG recordings. Hippocampal theta rhythm was increased by pilocarpine 150 or 350 mg/kg and only the highest dose reduced the L-[(3)H]-glutamate uptake and cell viability on hippocampal slices. CONCLUSIONS: Subconvulsant doses of pilocarpine promote long-lasting alterations on neural circuitry, reflected by an increased theta activity in the hippocampus and an anxiety-like profile of rats evaluated 1 month after the treatment which is independent of seizure occurrence and is not related to changes in glutamate uptake or hippocampal damage. These results prompt us to suggest that a systemic administration of subconvulsant doses of pilocarpine could be useful as a new tool to model trait anxiety in rats.

NMDA preconditioning attenuates cortical and hippocampal seizures induced by intracerebroventricular quinolinic acid infusion.

Searching for new therapeutic strategies through modulation of glutamatergic transmission using effective neuroprotective agents is essential. Glutamatergic excitotoxicity is a common factor to neurodegenerative diseases and acute events such as cerebral ischemia, traumatic brain injury, and epilepsy. This study aimed to evaluate behavioral and electroencephalographic (EEG) responses of mice cerebral cortex and hippocampus to subconvulsant and convulsant application of NMDA and quinolinic acid (QA), respectively. Moreover, it aimed to evaluate if EEG responses may be related to the neuroprotective effects of NMDA. Mice were preconditioned with NMDA (75 mg/kg, i.p.) and EEG recordings were performed for 30 min. One day later, QA was injected (36.8 nmol/site) and EEG recordings were performed during 10 min. EEG analysis demonstrated NMDA preconditioning promotes spike-wave discharges (SWDs), but it does not display behavioral manifestation of seizures. Animals that were protected by NMDA preconditioning against QA-induced behavioral seizures, presented higher number of SWD after NMDA administration, in comparison to animals preconditioned with NMDA that did display behavioral seizures after QA infusion. No differences were observed in latency for the first seizure or duration of seizures. EEG recordings after QA infusion demonstrated there were no differences in the number of SWD, latency for the first seizure or duration of seizures in animals pretreated with saline or in animals preconditioned by NMDA that received QA. A negative correlation was identified between the number of NMDA-induced SWD and QA-induced seizures severity. These results suggest a higher activation during NMDA preconditioning diminishes mice probability to display behavioral seizures after QA infusion.

Behavioral profile and Fos activation of serotonergic and non-serotonergic raphe neurons after central injections of serotonin in the pigeon (Columba livia).

Central injections of serotonin (5-HT) in food-deprived/refed pigeons evoke a sequence of hypophagic, hyperdipsic and sleep-like responses that resemble the postprandial behavioral sequence. Fasting-refeeding procedures affect sleep and drinking behaviors "per se". Here, we describe the behavioral profile and long-term food/water intake following intracerebroventricular (ICV) injections of 5-HT (50, 150, 300 nmol/2 µl) in free-feeding/drinking pigeons. The patterns of Fos activity (Fos+) in serotonergic (immunoreactive to tryptophan hydroxylase, TPH+) neurons after these treatments were also examined. 5-HT ICV injections evoked vehement drinking within 15 min, followed by an intense sleep. These effects did not extend beyond the first hour after treatment. 5-HT failed to affect feeding behavior consistently. The density of double-stained (Fos+/TPH+) cells was examined in 6 brainstem areas of pigeons treated with 5-HT (5-HTW) or vehicle. Another group received 5-HT and remained without access to water during 2h after treatment (5-HTØ). In the pontine raphe, Fos+ density correlated positively to sleep, and increased in both the 5-HTW and 5-HTØ animals. In the n. linearis caudalis, Fos+ and Fos+/TPH+ labeling was negatively correlated to sleep and was reduced in 5-HTØ animals. In the A8 region, Fos+/TPH+ labeling was reduced in 5-HTW and 5-HTØ animals, was positively correlated to food intake and negatively correlated to sleep. These data indicate that hyperdipsic and hypnogenic effects of ICV 5-HT in pigeons may result from the inhibition of a tonic activity of serotonergic neurons, which is possibly relevant to the control of postprandial behaviors, and that these relationships are shared functional traits of the serotonergic circuits in amniotes.