Studying Glutamatergic Gliotransmission as a Functional Model to Assess Physio-Pathological Conditions and Receptor Cross-Talk

SUMMARY This thesis is divided into two parts; in the first part, we characterized the effect of acute stress on the astrocytic glutamate release in the prefrontal cortex of rat brain. In the second part, we evaluate the interaction of the Oxytocin receptor (OXTR) with both Adenosine receptor A2A and Dopamine D2 receptors in the brain striatum of male rats. First Part: Stress is known to disturb the physiological homeostasis of the body (McEwen et al., 2000). The number of studies demonstrated that stress leads to damage the prefrontal cortex the brain and results in the modulation in the secretion of various neurotransmitters (Karats Oreos and McEwen, 2011, Sousa and Almeida, 2012). Stress was recognized as a predominant risk factor for many diseases, together with cardiovascular, metabolic, and neuropsychiatric diseases. Among the latter, stress interacts with the variable genetic background of vulnerability in the pathogenesis of mood anxiety disorder (Laura et al., 2010). It may be acute or chronic, can involve neuropsychiatric components such as stress, depression, mood, and anxiety (Laura et al., 207) and produces many behavioral and neurochemical changes, as determined in human (De Kloet et al., 2005, Kim & Diamond 2002). Studies in the literature truly indicated that acute stress have an effect on glutamatergic neurotransmission in the prefrontal cortex, inducing changes in glutamate release, receptor and glutamate clearance and metabolism (Popoli et al., 2012: Licznerski and Duman 3013). The effects of acute footshock stress on glutamate release and transmission were still unknown. In this study, we investigated the release of glutamate from astrocytes. The analyses have been performed in the prefrontal cortex (PFC) at different time intervals straight away after 40 min of stress and 6 and 24 hours after stress start, to monitor the early and delayed effects of acute stress on glutamate release. After the acute stress, animals were subjected to sucrose test to distinguish vulnerable and resilient rats. Second Part: There has been a growing interest in the investigation of the role of astrocytes in neurodegenerative and neuropsychiatric diseases and their complex neuron-astrocytes network function. The receptor–receptor interactions (RRI) can have an important function in the signalling transduction pathways. A previous well established study evaluate the interactions between the G-protein coupled receptors of adenosine A2A receptors (A2A) and dopamine D2 receptors (D2) in several experimental models (Ferré et al., 2008), while it’s barely investigated in astrocytes. Growing evidence shows that adult striatal astrocytes largely express both D2 and A2A receptors (Cervetto et at., 2017). Moreover, the presence of A2A-D2 heteroreceptor complexes has led to a new perspective of molecular mechanisms involved in Parkinson’s disease (PD), providing novel drug targets. Therefore in the present study, we investigate the physical and functional interactions of A2A and D2 with another G protein-coupled receptors i.e. OXTR in astrocytes processes from adult rat striatum. We also evaluate the effect of this interaction on the astrocytic glutamate release in rat striatum.