Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2018-2019)

Central nervous system (CNS) is composed of neurons and astrocytes, which use glutamate as major excitatory and GABA as an inhibitory neurotransmitter. NMDA receptors, major glutamate ionotropic receptors and somatostatin receptors (members of GPCR family) are widely expressed in CNS and linked to many fundamental functions of the brain at the molecular and cellular levels. Several studies have shown an inhibitory role of Somatostatin (SST) via SSTRs on NMDARs mediated neurotoxic effects on CNS suggesting that SST released from neurons and/or astrocytes might play a crucial role in neuronal survival in neurotoxicity. Prior to implementing SSTR subtypes to pathological conditions, it is essential to determine their precise distribution and biological functions. To delineate the morphological, biochemical or biophysical properties of SSTRs and to derive any direct pharmacological relation with NMDAR subtypes in the brain, we will use in-vivo (brain slices) and in-vitro (pure and mixed neuronal and astrocytes culture) models to induce NMDA toxicity. We will address following questions:

Aim 1. Do SSTRs are expressed and developmentally regulated in the CNS? Astrocytes comprise majority of the cell population in the brain, therefore, the understanding of astrocyte-neuron interaction is key to better comprehension of the brain function. SST is synthesized and processed in astrocytes, whether SSTRs are expressed in astrocytes is not known. Accordingly, first, using pure astrocytes culture, the expression of SSTRs at the level of mRNA and protein will be determined. Second, the colocalization of SSTRs with GFAP positive cells (astrocyte) in brain slices and cultured neurons will be determined. Third, using receptor specific agonists, we will identify the SSTRs that might exert an inhibitory role on astrocytes proliferation in pure and mixed astrocyte-neuronal culture.

Aim 2. Do SSTRs regulate signal transduction pathways that promote neuronal death or survival? SSTRs activation is associated with reduction in two key intracellular mediators, cAMP and Ca 2+ , due to receptor linked effect on adenylyl cyclase and K + /Ca 2+ channels. The inhibition of these prominent physiological regulators is associated with several downstream signaling pathways. Here, we propose to determine SSTRs associated with the critical determinants of neuronal fate, including signal transduction pathways, mitochondrial permeability, and Ca 2+ influx in pure and mixed neuronal-astrocytes culture.

Aim 3. Do SSTRs functionally interact with NMDARs in the CNS? Here, we propose to elucidate the functional interaction between SSTR and NMDAR subtypes using biophysical Pb-FRET method in neuronal cultures maintained with or without astrocytes. We will determine whether SSTR(s) functionally interact with NMDARs and interfere with the NMDARs complexes in response to receptor specific agonist or antagonist.