The use of volatile organic solvents as drugs of abuse is an important health problem. These agents, often termed abused inhalants, are voluntarily inhaled or "huffed" for their intoxicating effects. The use of abused inhalants is especially prevalent among children and adolescents since these compounds are legal and are found in a wide variety of household and commercial products including glues, adhesives and paint thinners. Abused inhalants are associated with a variety of adverse effects ranging from reduced academic performance, brain abnormalities and a sudden-death syndrome resulting from solvent-induced cardiac arrhythmia. Although abused inhalants produce ethanol-like signs of intoxication, their sites and mechanisms of action that underlie these effects are largely unknown. Research carried out during the previous funding period of this project used recombinant expression techniques and electrophysiology to study the effects of abused inhalants on ion channels widely expressed by brain neurons. Results from these studies revealed a surprising degree of selectivity for the effects of abused inhalants on both voltage-gated and ligand-gated ion channels that regulate neuronal excitability. In particular, the NR1/2B NMDA receptors and the 1422 nicotinic acetylcholine receptor were among the most sensitive channels identified. In this application, we focus on the role that these channels play in mediating the effects of toluene, the prototype abused inhalant, on the activity of principal neurons within three brain regions known to be important in mediating the effects of drugs of abuse. Whole-cell patch-clamp electrophysiology will be used to study the effects of toluene on dopamine neurons of the ventral tegmental area (VTA), medium spiny neurons of the nucleus accumbens (NAcc) and deep-layer pyramidal neurons of the prefrontal cortex (PFC).
Aim 1 will determine the toluene sensitivity of NMDA EPSCs within the addiction neurocircuitry with a special focus on NR1/2B receptors.
Aim 2 will determine the effect of acute toluene on VTA DA neuron excitability with a special focus on 1422 nAchRs.
Aim 3 will use a novel triple-slice co-culture system to determine the effects of toluene on NR1/2B and 1422 nAchRs that mediate complex firing patterns produced by PFC neurons. Finally, Aim 4 will test the hypothesis that exposure to toluene in vivo induces changes in indicators of plasticity in glutamatergic synapses measured in vitro. Results from these studies will fill an important gap in our knowledge and will define the actions of toluene on key elements of the addiction neurocircuitry.
Abused inhalants are an important class of drugs of abuse that have received relatively little attention with respect to their mechanisms of action. Research to be carried out in this proposal will provide a detailed analysis of the effects of abused inhalants on neurons within brain areas involved in addiction.
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