Platinum nanoparticle-based microreactors protect against the behavioral and neurobiological consequences of chronic stress exposure.

Excitotoxicity is described as the exacerbated activation of glutamate AMPA and NMDA receptors that leads to neuronal damage, and ultimately to cell death. Astrocytes are responsible for the clearance of 80-90% of synaptically released glutamate, preventing excitotoxicity. Chronic stress renders neurons vulnerable to excitotoxicity and has been associated to neuropsychiatric disorders, i.e., anxiety. Microreactors containing platinum nanoparticles (Pt-NP) and glutamate dehydrogenase have shown in vitro activity against excitotoxicity. The purpose of the present study was to investigate the in vivo effects of these microreactors on the behavioral and neurobiological effects of chronic stress exposure. Rats were either unstressed or exposed for 2 weeks to an unpredictable chronic mild stress paradigm (UCMS), administered intra-ventral hippocampus with the microreactors (with or without the blockage of astrocyte functioning), and seven days later tested in the elevated T-maze (ETM; Experiment 1). The ETM allows the measurement of two defensive responses, avoidance and escape, in terms of psychopathology respectively related to generalized anxiety and panic disorder. Locomotor activity in an open field was also measured. Since previous evidence shows that stress inhibits adult neurogenesis, we evaluated the effects of the different treatments on the number of cells expressing the marker of migrating neuroblasts doublecortin (DCX) in the dorsal and ventral hippocampus (Experiment 2). Results showed that UCMS induces anxiogenic effects, increases locomotion, and decreases the number of DCX cells in the dorsal and ventral hippocampus, effects that were counteracted by microreactor administration. This is the first study to demonstrate the in vivo efficacy of Pt-NP against the behavioral and neurobiological effects of chronic stress exposure.

The blockage of ventromedial hypothalamus CRF type 2 receptors impairs escape responses in the elevated T-maze.

In a previous study, the administration of corticotrophin-releasing factor (CRF) into the dorsomedial hypothalamus (DMH), a region that modulates defensive reactions, was shown to facilitate elevated T-maze (ETM) avoidance responses, an anxiogenic-like effect. Intra-DMH administration of the CRF type 1 receptor (CRFR1) antagonist antalarmin induced anxiolytic-like effects and counteracted the anxiogenic effects of CRF. The present study further investigates the role played by CRF receptors of the medial hypothalamus in anxiety. For that, male wistar rats were treated with CRFR1 and CRFR2-modulating drugs in the DMH or VMH, another hypothalamic nucleus implicated with defensive and emotional behavior, and tested in the ETM for inhibitory avoidance and escape measurements. In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. All animals were tested in an open field, immediately after the ETM, for locomotor activity assessment. The results showed that intra-VMH CRF or antalarmin did not alter ETM avoidance or escape performance. Intra-VMH injection of the CRFR2 preferential antagonist antisauvagine-30 or of the selective CRFR2 antagonist astressin 2-B inhibited escape performance, a panicolytic-like effect, without altering avoidance reactions. The CRFR2 agonist urocortin-2 intra-VMH was by itself without effect but blocked the effects of astressin 2-B. None of the drugs administered into the DMH altered ETM measurements. Additionally, none of the compounds altered locomotor activity measurements. These results suggest that VMH CRFR2 modulate a defensive response associated with panic disorder and are of relevance to the better understanding of the neural mechanisms underlying this pathological condition.

Deep brain stimulation of the dorsal raphe inhibits avoidance and escape reactions and activates forebrain regions related to the modulation of anxiety/panic.

One of the main neurochemical systems associated with anxiety/panic is the serotonergic system originating from the dorsal raphe nucleus (DR). Previous evidence suggests that the DR is composed of distinct subpopulations of neurons, both morphologically and functionally distinct. It seems that mainly the dorsal region of the DR (DRD) regulates anxiety-related reactions, while lateral wings DR (lwDR) serotonin (5-HT) neurons inhibit panic-related responses. In this study we used the technique of deep brain stimulation (DBS) to investigate the role played by the DRD and lwDR in defense. Male Wistar rats were submitted to high-frequency stimulation (100µA, 100Hz) in one of the two DR regions for 1h and immediately after tested in the avoidance or escape tasks of the elevated T-maze (ETM). In clinical terms, these responses have been related to generalized anxiety and panic disorder, respectively. After being submitted to the ETM, animals were placed in an open field for locomotor activity assessment. An additional group of rats was submitted to DBS of the DRD or the lwDR and used for quantification of c-Fos immunoreactive (Fos-ir) neurons in brain regions related to the modulation of defense. Results showed that stimulation of the DRD decreased avoidance latencies, an anxiolytic-like effect. DRD stimulation also led to increases in Fos-ir in the medial amygdala, lateral septum and cingulate cortex. DBS applied to the lwDR increased escape latencies, a panicolytic-like effect. This data highlights the importance of raphe topography and the potential benefit of the DBS technique for the treatment of anxiety-related disorders.

Dorsomedial hypothalamus CRF type 1 receptors selectively modulate inhibitory avoidance responses in the elevated T-maze.

Corticotropin-releasing factor (CRF) plays a critical role in the mediation of physiological and behavioral responses to stressors. In the present study, we investigated the role played by the CRF system within the dorsomedial hypothalamus (DMH) in the modulation of anxiety- and panic-related responses. Male Wistar rats were administered into the DMH with CRF (125 and 250 ng/0.2 µl, experiment 1) or with the CRFR1 antagonist antalarmin (25 ng/0.2 µl, experiment 2) and 10 min later tested in the elevated T-maze (ETM) for inhibitory avoidance and escape measurements. In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. To further verify if the anxiogenic effects of CRF were mediated by CRFR1 activation, we also investigated the effects of the combined treatment with CRF (250 ng/0.2 µl) and antalarmin (25 ng/0.2 µl) (experiment 3). All animals were tested in an open field, immediately after the ETM, for locomotor activity assessment. Results showed that 250 ng/0.2µl of CRF facilitated ETM avoidance, an anxiogenic response. Antalarmin significantly decreased avoidance latencies, an anxiolytic effect, and was able to counteract the anxiogenic effects of CRF. None of the compounds administered altered escape responses or locomotor activity measurements. These results suggest that CRF in the DMH exerts anxiogenic effects by activating type 1 receptors, which might be of relevance to the physiopathology of generalized anxiety disorder.