Nicotine addiction is a major health problem in our society and accounts for millions in health care costs. A fundamental prerequisite for understanding the actions of nicotine is to elucidate the physiological role for nicotinic acetylcholine receptors (nAChRs) in the brain. Recently, it has been shown that nAChRs are expressed in astrocytes. This proposal will examine the role of astrocytic nAChRs on synaptic signaling in the CA3 region of the mouse hippocampus and how these receptors contribute to glia-neuron interactions in the brain. The proposal will address two issues. First, we will characterize nicotinic signaling in astrocytes using acute hippocampal slices from mice expressing GFP linked to the glial fibrillary acidic protein (GFAP). Electrophysiological analyses will be carried out examining nicotinic currents on astrocytes. Calcium imaging will be used to elucidate the details of calcium signaling in these cells, including the contributions from various sources of calcium within astrocytes. nAChR-induced intra- and inter-cellular calcium waves will be examined. We will use transgenic mice that express tau-GFP driven by the cholineacetyl transferase (ChAT) promoter in order to label cholinergic axons. The ability of local stimulation of cholinergic fibers to induce nAChR currents and calcium signals in astrocytes will be examined. These studies will establish the existence of functional nAChRs in astrocytes and their ability to transduce signals in these cells in response to both nicotine and endogenous acetylcholine. The second part of the proposal will address a unique signaling resulting in an action potential- independent form of transmission at the mossy fiber-CA3 synapse in the hippocampus. We will examine the role of astrocytes in mediating or modulating this form of short-term plasticity by its action on the presynaptic mossy fiber terminals. A combination of electrophysiology and calcium imaging will be used in these studies. It is increasingly becoming apparent that addiction is a problem of hedonic homeostasis that involves multiple regions of the brain, not just the mesolimbic dopaminergic system. Understanding the totality of nAChR actions in the brain, in order to arrive at a rational drug design to combat smoking must include the understanding of these receptors on glia as well as neurons. This proposal makes a start in that direction.
Methods that have been developed to combat smoking have been inadequate mainly because of our lack of knowledge on how this drug affects brain functions. It is now being recognized that drugs of abuse like nicotine have far reaching consequences for the brain. They affect not just functions of nerve cells in the brain but also support cells known as glia. These support cells have been shown to play a very active role in determining how the nerve cells function. Here we study the effects of nicotine on astrocytes, a type of glial cells, and determine how nicotine, acting via these cells can affect the functioning of, and signaling by neurons. This study will open a new direction in understanding the consequences of smoking for the brain and aid in the development of better pharmacological interventions to assist people in breaking nicotine addiction.
