Dual mechanism of TRKB activation by anandamide through CB1 and TRPV1 receptors

Background. Administration of anandamide (AEA) or 2-arachidonoylglycerol (2AG) induces CB1 coupling and activation of TRKB receptors, regulating the neuronal migration and maturation in the developing cortex. However, at higher concentrations AEA also engages vanilloid receptor TRPV1, usually with opposed consequences on behavior. Methods and Results. Using primary cell cultures from the cortex of rat embryos (E18) we determined the effects of AEA on phosphorylated TRKB (pTRK). We observed that AEA (at 100 and 200 nM) induced a significant increase in pTRK levels. Such effect of AEA at 100 nM was blocked by pretreatment with the CBI antagonist AM251 (200 nM) and, at the higher concentration of 200 nM by the TRPV1 antagonist capsazepine (200 nM), but mildly attenuated by AM251. Interestingly, the effect of AEA or capsaicin (a TRPV1 agonist, also at 200 nM) on pTRK was blocked by TRKB.Fc (a soluble form of TRKB able to bind BDNF) or capsazepine, suggesting a mechanism dependent on BDNF release. Using the marble-burying test (MBT) in mice, we observed that the local administration of ACEA (a CBI agonist) into the prelimbic region of prefrontal cortex (PL-PFC) was sufficient to reduce the burying behavior, while capsaicin or BDNF exerted the opposite effect, increasing the number of buried marbles. In addition, both ACEA and capsaicin effects were blocked by previous administration of k252a (an antagonist of TRK receptors) into PL-PFC. The effect of systemically injected CB1 agonist WIN55,212-2 was blocked by previous administration of k252a. We also observed a partial colocalization of CBI /TRPV1 /TRKB in the PL-PFC, and the localization of TRPV1 in CaMK2+ cells. Conclusion. Taken together, our data indicate that anandamide engages a coordinated activation of TRKB, via CB1 and TRPV1. Thus, acting upon CBI. and TRPV1, AEA could regulate the TRKB-dependent plasticity in both pre- and postsynaptic compartments.Peer reviewe

Elastase-2 Knockout Mice Display Anxiogenic- and Antidepressant-Like Phenotype : Putative Role for BDNF Metabolism in Prefrontal Cortex

Several pieces of evidence indicate that elastase-2 (ELA2; chymotrypsin-like ELA2) is an alternative pathway to the generation of angiotensin II (ANGII). Elastase-2 knockout mice (ELA2KO) exhibit alterations in the arterial blood pressure and heart rate. However, there is no data on the behavioral consequences of ELA2 deletion. In this study, we addressed this question, submitting ELA2KO and wild-type (WT) mice to several models sensitive to anxiety- and depression-like, memory, and repetitive behaviors. Our data indicates a higher incidence of barbering behavior in ELA2KO compared to WT, as well as an anxiogenic phenotype, evaluated in the elevated plus maze (EPM). While a decrease in locomotor activity was observed in ELA2KO in EPM, this feature was not the main source of variation in the other parameters analyzed. The marble-burying test (MBT) indicated increase in repetitive behavior, observed by a higher number of buried marbles. The actimeter test indicated a decrease in total activity and confirmed the increase in repetitive behavior. The spatial memory was tested by repeated exposure to the actimeter in a 24-h interval. Both ELA2KO and WT exhibited decreased activity compared to the first exposure, without any distinction between the genotypes. However, when submitted to the cued fear conditioning, ELA2KO displayed lower levels of freezing behavior in the extinction session when compared to WT, but no difference was observed during the conditioning phase. Increased levels of BDNF were found in the prefrontal cortex but not in the hippocampus of ELA2KO mice compared to WT. Finally, in silico analysis indicates that ELA2 is putatively able to cleave BDNF, and incubation of the purified enzyme with BDNF led to the degradation of the latter. Our data suggested an anxiogenic- and antidepressant-like phenotype of ELA2KO, possibly associated with increased levels of BDNF in the prefrontal cortex.Peer reviewe

Peripheral administration of lactate produces antidepressant-like effects.

In addition to its role as metabolic substrate that can sustain neuronal function and viability, emerging evidence supports a role for l-lactate as an intercellular signaling molecule involved in synaptic plasticity. Clinical and basic research studies have shown that major depression and chronic stress are associated with alterations in structural and functional plasticity. These findings led us to investigate the role of l-lactate as a potential novel antidepressant. Here we show that peripheral administration of l-lactate produces antidepressant-like effects in different animal models of depression that respond to acute and chronic antidepressant treatment. The antidepressant-like effects of l-lactate are associated with increases in hippocampal lactate levels and with changes in the expression of target genes involved in serotonin receptor trafficking, astrocyte functions, neurogenesis, nitric oxide synthesis and cAMP signaling. Further elucidation of the mechanisms underlying the antidepressant effects of l-lactate may help to identify novel therapeutic targets for the treatment of depression

Problems of multi-species organisms: endosymbionts to holobionts

The organism is one of the fundamental concepts of biology and has been at the center of many discussions about biological individuality, yet what exactly it is can be confusing. The definition that we find generally useful is that an organism is a unit in which all the subunits have evolved to be highly cooperative, with very little conflict. We focus on how often organisms evolve from two or more formerly independent organisms. Two canonical transitions of this type—replicators clustered in cells and endosymbiotic organelles within host cells—demonstrate the reality of this kind of evolutionary transition and suggest conditions that can favor it. These conditions include co-transmission of the partners across generations and rules that strongly regulate and limit conflict, such as a fair meiosis. Recently, much attention has been given to associations of animals with microbes involved in their nutrition. These range from tight endosymbiotic associations like those between aphids and Buchnera bacteria, to the complex communities in animal intestines. Here, starting with a reflection about identity through time (which we call “Theseus’s fish”), we consider the distinctions between these kinds of animal–bacteria interactions and describe the criteria by which a few can be considered jointly organismal but most cannot

Antidepressant-like effects of N-acetyl-L-cysteine in rats

Oxidative stress disturbances have been reported in depressed patients and in animals submitted to stress. Recent evidence suggests that antidepressants may have antioxidant properties. However, the therapeutic potential of antioxidants as antidepressant drugs has not been systematically investigated. Therefore, this study tested the hypothesis that N-acetyl-L-cysteine (NAC), a cysteine prodrug with powerful antioxidant activity, would possess anti depressant-like properties in the forced swimming test. Male Wistar rats were subjected to 15 min of forced swimming and immediately afterward, 5, and 23 h later received intraperitoneal injections of NAC (5, 15, 50, 150, and 250 mg/kg), imipramine, 0 5 mg/kg) or vehicle. One hour later they were submitted to the 5 min test swimming session, where immobility time was recorded. Independent groups of animals received the same treatments and their exploratory activity was measured in an open arena for 5 min. NAC (at the doses of 15, 50, and 150 mg/kg) and imipramine induced a significant decrease in immobility time without changing exploratory behavior measured in an open arena. These results suggest that antioxidants such as NAC may have antidepressant effects. Behavioural Pharmacology (C) 19:747-750 2008 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.FAPESPCNPqCAPE

Tolerance to the cataleptic effect that follows repeated nitric oxide synthase inhibition may be related to functional enzymatic recovery

Systemic or intra-striatal acute administration of nitric oxide synthase (NOS) inhibitors causes catalepsy in rodents. This effect disappears after sub-chronic treatment. The aim of the present study was to investigate if this tolerance is related to changes in the expression of NOS or dopamine-2 (D(2)) receptor or to a recovery of NOS activity. Male albino Swiss mice (25-30 g) received single or sub-chronic (once a day for 4 days) i.p. injections of saline or L-nitro-arginine (L-NOARG, 40 mg/kg), a non-selective inhibitor of neuronal nitric oxide synthase (nNOS). Twenty-four hours after the last injection, the animals were killed and their brains were removed for immunohistochemistry assay to detect the presence of nNOS or for `in-situ` hybridisation study using (35)S-labeled oligonucleotide probe complementary to D(2) receptor mRNA. The results were analysed by computerised densitometry. Independent groups of animals received the same treatment, but were submitted to the catalepsy test and had their brain removed to measure nitrite and nitrate (NOx) concentrations in the striatum. Acute administration of L-NOARG caused catalepsy that disappeared after sub-chronic treatment. The levels of NOx were significantly reduced after acute L-NOARG treatment. The decrease in NOx after drug injection suffered a partial tolerance after sub-chronic treatment. The catalepsy time after acute or sub-chronic treatment with L-NOARG was negatively (r = -0.717) correlated with NOx levels. Animals that received repeated L-NOARG injections also showed an increase in the number of nNOS-positive neurons in the striatum. No change in D(2) receptor mRNA expression was found in the dorsal striatum, nucleus accumbens and substantia nigra. Together, these results suggest that tolerance to L-NOARG cataleptic effects do not depend on changes in D(2) receptors. They may depend, however, on plastic changes in nNOS neurons resulting in partial recovery of NO formation in the striatum

Effects of reversible inactivation of the dorsal hippocampus on the behavioral and cardiovascular responses to an aversive conditioned context

In rats, conditioned fear to context causes freezing immobility and cardiovascular changes. The dorsal hippocampus (DH) has a critical role in several memory processes, including conditioning fear to contextual information. To explore a possible involvement of the DH in contextual fear conditioning-evoked cardiovascular (mean arterial pressure and heart rate increases) and behavioral (freezing) responses, DH synaptic transmission was temporarily inhibited by bilateral microinjections of 500 nl of the nonselective synapse blocker, cobalt chloride (COCl2, 1 mmol/l), at different periods of the experimental procedure. During re-exposure to the foot shock chamber in which conditioning had taken place, bilateral DH inhibition 10 min before the conditioning session had no effect on either behavioral or cardiovascular responses. Bilateral DH inhibition immediately after the conditioning session (110 min) decreased both behavioral and cardiovascular responses during the context test. Finally, 48 h after the conditioning session, bilateral DH inhibition 10 min before re-exposure to the foot shock chamber significantly reduced cardiovascular responses but not freezing responses. These results suggest that contextual fear conditioning acquisition does not depend on the DH. This structure, however, is crucial for the consolidation of contextual fear. Moreover, although the DH appears to be less important for the behavioral (freezing) changes induced by re-exposure to the aversive conditioned context, it may play an important role on the cardiovascular responses generated by this model