Effects of Chronic Cannabis Use on the Neuroendocrine Stress Response

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PROJECT SUMMARY The most commonly cited reason for habitual cannabis use is to cope with stress. Although this may provide acute beneficial effects, the long-term ramifications of chronic cannabis use, particularly under drug-free conditions, remain unknown. We have demonstrated that sober chronic cannabis users display blunted psychological and physiological responses to an acute laboratory stressor relative to non-users. However, this cross-sectional approach precludes the ability to establish causal relationships between cannabis use and the stress response. Preclinical animal models are particularly advantageous in this respect, yet current models of cannabis use have been plagued by methodological concerns that limit the translatability of these data to human populations. To address these limitations, our laboratory has generated important new data using a novel, translationally relevant model of cannabis vapor self-administration that uses response-contingent delivery of vaporized cannabis extracts containing high concentrations of Δ9 tetrahydrocannabinol. This approach is unique in that it uses volitional exposure to natural cannabis extracts (rather than forced delivery of synthetic cannabinoid receptor agonists or isolated cannabis constituents) that are delivered via the pulmonary route of administration that is most common in human users. We will use this approach in the current proposal to determine whether cannabis vapor self-administration causes alterations in basal and stress-induced activation of the hypothalamic- pituitary-adrenal (HPA) stress axis in male and female rats. In Aim 1, we will use immunohistochemistry to quantify activation of the immediate early gene c-fos in different cell types within the paraventricular nucleus (PVN) of the hypothalamus of male and female rats trained to self-administer varying concentrations of cannabis or vehicle vapor. In Aim 2, we will perform radioimmunoassays on plasma harvested from cannabis-exposed and non-exposed rats in stress and no-stress conditions to determine the extent to which chronic volitional cannabis exposure alters basal and stress-induced recruitment of adrenocorticotropic hormone (ACTH) and corticosterone (CORT). Additionally, brains will be extracted to assess corticotropin-releasing hormone (CRH) peptide content in the central nucleus of the amygdala of cannabis-exposed and non-exposed rats under stress or non-stress conditions. We predict that rats trained to self-administer cannabis vapor will exhibit dose- dependent elevations in basal CORT, attenuated stress-induced activation of CRH-positive PVN neurons, increased reliance on passive coping strategies, and dampened recruitment of ACTH, CORT and CRH content relative to vehicle-exposed rats. Results from these studies will provide a foundation for understanding long-term consequences of chronic cannabis use and allow us to identify causal relationships between cannabis use and stress reactivity. Moreover, this work will support the feasibility of future studies that will investigate the mechanisms underlying these effects and identify whether alterations in the stress response are a risk factor for developing problematic cannabis use.