Multiple lines of evidence suggest that schizophrenia (SZ) is a disorder of neurodevelopment caused by the combination of genetic vulnerabilities and environmental risk factors. For example, cannabis use during adolescence is associated with an increased risk for cognitive dysfunction and SZ in genetically vulnerable individuals. The principal psychoactive component in cannabis, delta-9-tetrahydrocannabinol (9-THC), activates cannabinoid 1 receptors (CB1r) that are highly concentrated on the axon terminals of cholecystokinin-expressing basket cells (CB1r/CCK cells) in the primate dorsolateral prefrontal cortex (DLPFC), a region implicated in the cognitive dysfunction of SZ, resulting in the suppression of GABA release from these terminals. In monkeys and humans, DLPFC circuitry continues to mature well into adolescence (~15-42 mos in monkeys and ~13-19 years in humans) in parallel with improvements in cognitive function. In monkey DLPFC, GABAA receptor 1 subunits and CB1r immunoreactivity undergo substantial changes during adolescence, suggesting that key markers for GABA synthesis may also change rapidly in these cells during this period. Our preliminary studies indicate that tissue levels of the two GABA-synthesizing enzymes, glutamic acid decarboxylase 67 and 65 (GAD67 and GAD65), increase in monkey DLPFC throughout postnatal development, with GAD65 mRNA and protein levels substantially and rapidly increasing during adolescence and GAD67 mRNA and protein increasing earlier. Emerging data from our group also suggest that the ratio of GAD65:GAD67 protein is greater in CB1r-positive (CB1r+) terminals than in other classes of GABA terminals in the adult monkey DLPFC. Thus, the developmental courses of GAD65 and GAD67 mRNAs in CB1r/CCK basket cell bodies (Aim 1), and of the cognate proteins in their axon terminals (Aim 2), will be examined to identify potential periods in monkey DLPFC development that by virtue of their rapid change may be especially sensitive to cannabis exposure. Specifically, we predict that a marked increase in GAD65 expression in CB1r/CCK basket cells and terminals during adolescence defines a sensitive period in the maturation of these neurons. This idea will be subjected to a proof-of-concept test by examining these same dependent measures in monkeys exposed for one year to cannabis during adolescence (Aim 3). Such knowledge about the nature and timing of cell-specific developmental trajectories will inform the most appropriate type and timing of early pharmacological interventions in individuals vulnerable for schizophrenia. Thus, this application directly addresses NIMH Strategic Plan Strategy 2.1 by determining how periods of change in development may also be periods of vulnerability for the emergence of risk or symptoms. This proposal also provides the applicant with a crucial opportunity to learn how to conduct hypothesis-driven research and critically analyze results using both novel and well-established molecular neuroscience techniques.
When consumed during adolescence, cannabis, the most widely used illicit drug in America, is associated with a greater risk for developing schizophrenia in vulnerable individuals. The proposed studies will define the developmental trajectories of key components of prefrontal cortical circuitry that are sensitive to cannabis use and are altered in schizophrenia. These studies have important implications for understanding how and when the effects of cannabis may impact sensitive periods of prefrontal cortical development and may contribute to the development of preemptive interventions in individuals vulnerable for schizophrenia.
|Fish, Kenneth N; Hoftman, Gil D; Sheikh, Wasiq et al. (2013) Parvalbumin-containing chandelier and basket cell boutons have distinctive modes of maturation in monkey prefrontal cortex. J Neurosci 33:8352-8|