No abstract

Rationale In depressive disorders, one of the mechanisms proposed for antidepressant drugs is the enhancement of synaptic plasticity in the hippocampus and cerebral cortex. Previously, we showed that the muscarinic acetylcholine receptor (mAChR) agonist oxotremorine (Oxo) increases neuronal plasticity in hippocampal neurons via FGFR1 transactivation. Objectives Here, we aimed to explore (a) whether Oxo exerts anxiolytic effect in the rat model of anxiety-depression-like behavior induced by chronic restraint stress (CRS), and (b) if the anxiolytic effect of Oxo is associated with the modulation of neurotrophic factors, brain-derived neurotrophic factor (BDNF) and fibroblast growth factor-2 (FGF2), and phosphorylated Erk1/2 (p-Erk1/2) levels in the dorsal or ventral hippocampus and in the medial prefrontal cortex. Methods The rats were randomly divided into four groups: control unstressed, CRS group, CRS group treated with 0.2 mg/kg Oxo, and unstressed group treated with Oxo. After 21 days of CRS, the groups were treated for 10 days with Oxo or saline. The anxiolytic role of Oxo was tested by using the following: forced swimming test, novelty suppressed feeding test, elevated plus maze test, and light/ dark box test. The hippocampi and prefrontal cortex were used to evaluate BDNF and FGF2 protein levels and p-Erk1/2 levels. Results Oxo treatment significantly attenuated anxiety induced by CRS. Moreover, Oxo treatment counteracted the CRS-induced reduction of BDNF and FGF2 levels in the ventral hippocampus and medial prefrontal cerebral cortex Conclusions The present study showed that Oxo treatment ameliorates the stress-induced anxiety-like behavior and rescues FGF2 and BDNF levels in two brain regions involved in CRS-induced anxiety, ventral hippocampal formation, and medial prefrontal cortex.

Acute or chronic administration of guanosine (GUO) induces anxiolytic-like effects, for which the adenosine (ADO) system involvement has been postulated yet without a direct experimental evidence. Thus, we aimed to investigate whether adenosine receptors (ARs) are involved in the GUO-mediated anxiolytic-like effect, evaluated by three anxiety-related paradigms in rats. First, we confirmed that acute treatment with GUO exerts an anxiolytic-like effect. Subsequently, we investigated the effects of pretreatment with ADO or A1R (CPA, CCPA) or A2AR (CGS21680) agonists 10 min prior to GUO on a GUO-induced anxiolytic-like effect. All the combined treatments blocked the GUO anxiolytic-like effect, whereas when administered alone, each compound was ineffective as compared to the control group. Interestingly, the pretreatment with nonselective antagonist caffeine or selective A1R (DPCPX) or A2AR (ZM241385) antagonists did not modify the GUO-induced anxiolytic-like effect. Finally, binding assay performed in hippocampal membranes showed that [3H]GUO binding became saturable at 100–300 nM, suggesting the existence of a putative GUO binding site. In competition experiments, ADO showed a potency order similar to GUO in displacing [3H]GUO binding, whereas AR selective agonists, CPA and CGS21680, partially displaced [3H]GUO binding, but the sum of the two effects was able to displace [3H]GUO binding to the same extent of ADO alone. Overall, our results strengthen previous data supporting GUO-mediated anxiolytic-like effects, add new evidence that these effects are blocked by A1R and A2AR agonists and pave, although they do not elucidate the mechanism of GUO and ADO receptor interaction, for a better characterization of GUO binding sites in ARs.