Effects of Traumatic Brain Injury on Oxycodone Reinstatement and Physical Dependence

Epidemiological data indicate that patients who experience a traumatic brain injury (TBI) have an elevated risk of developing a substance use disorder (SUD), but the underlying neurobiological connections remain unclear. To further understand the relationship between TBI and SUD, we investigated the effects of TBI on the abuse-related effects of oxycodone in preclinical models. Our evaluation utilized a lateral fluid percussion injury of moderate severity in adult male Sprague-Dawley rats. In the first aim, we tested the hypothesis that moderate TBI increases the risk for relapse to an opioid use disorder as measured by reinstatement of lever-pressing behavior following extinction in an intravenous oxycodone self-administration procedure. In the second aim, we tested the hypothesis that moderate TBI increases physiological dependence to oxycodone as measured by decreases in food-reinforced lever-pressing behavior and increases in other withdrawal behaviors in both precipitated withdrawal and spontaneous withdrawal. In tests for self-administration, brain-injured subjects, relative to non-injured subjects, showed no significant differences in the number of oxycodone-reinforced sessions required to meet stable maintenance criteria for lever-pressing behavior. Likewise, brain-injured subjects showed no significant differences in the number of non-reinforced sessions to meet extinction criteria for lever-pressing behavior relative to non-injured subjects. In tests for reinstatement, non-injured subjects reinstated responding under oxycodone-associated cue- and oxycodone prime-induced conditions, however, brain-injured subjects did not reinstate lever-pressing behavior under any conditions. In tests for physical dependence, brain-injured subjects showed no significant differences from non-injured subjects with regards to their mean withdrawal scores or food-reinforced lever-pressing behavior. Overall, these data suggest that brain-injured patients with no significant pre-morbid history of opioid abuse are at a lesser risk of relapse to opioid use disorders. Moreover, the characteristic withdrawal syndrome in opioid-dependent patients may not contribute to continued opioid abuse to a greater degree in brain-injured patients than compared to non-injured patients

Pharmacology of Fentanyl-Related Substances in Mice Reveals Potential Therapeutics With Improved Protective Indices

Fentanyl-related substances constitute a class of compounds that were originally developed in the latter half of the 20th century as combination analgesic-anesthetic agents. Today, many of these compounds have emerged in the recreational drug marketplace as adulterants to heroin, counterfeit prescription pills, and even as standalone products designed to circumvent drug control laws. The objective of this dissertation was to identify the structural determinants of fentanyl analogs that could affect the potency and efficacy for eliciting their therapeutic and toxic effects to identify candidates of potential therapeutic interest. To accomplish this objective, thirty-eight fentanyl-related substances, in addition to the MOR agonist standards fentanyl, morphine, and buprenorphine, were evaluated for their effects in adult male Swiss Webster mice on locomotion, as measured by distance traveled in the open field, nociception, as measured by tail-withdrawal latency in the warm-water tail-withdrawal test, and ventilation, as measured by respiratory rate, tidal volume, and minute volume. The substances included, but were not limited to, N-phenethyl-fluorinated fentanyl analogs, N-phenyl-fluorinated fentanyl analogs, N-phenyl-fluorinated butyrylfentanyl analogs, and N-phenyl-fluorinated valerylfentanyl analogs. The results of the present studies showed that subtle structural changes can have a profound influence on potencies for eliciting their effects between compounds, as well as differential potencies for their effects within compounds. In particular, isobutyrylfentanyl and para-methoxybutyrylfentanyl distinguished themselves for which, under the conditions tested, their protective indices (antinociception vs hypoventilation) were \u3e10x that of both fentanyl and morphine. These findings have both confirmed previous reports and provided new insights into the structural determinants of the in vivo pharmacological effects of fentanyl-related substances that may further efforts to develop analgesics with fewer adverse effects. Overall, fentanyl-related substances, although problematic for their toxic effects, represent a diverse class of compounds that should be explored further for their potential clinical utility

Chronic HIV-1 Tat exposure alters anterior cingulate cortico-basal ganglia-thalamocortical synaptic circuitry, associated behavioral control, and immune regulation in male mice

HIV-1 selectively disrupts neuronal integrity within specific brain regions, reflecting differences in viral tropism and/or the regional differences in the vulnerability of distinct neuronal subpopulations within the CNS. Deficits in prefrontal cortex (PFC)-mediated executive function and the resultant loss of behavioral control are a particularly debilitating consequence of neuroHIV. To explore how HIV-1 disrupts executive function, we investigated the effects of 48 ​h, 2 and/or 8 weeks of HIV-1 Tat exposure on behavioral control, synaptic connectivity, and neuroimmune function in the anterior cingulate cortex (ACC) and associated cortico-basal ganglia (BG)-thalamocortical circuitry in adult, Tat transgenic male mice. HIV-1 Tat exposure increased novelty-exploration in response to novel food, flavor, and environmental stimuli, suggesting that Tat triggers increased novelty-exploration in situations of competing motivation (e.g., drive to feed or explore vs. fear of novel, brightly lit open areas). Furthermore, Tat induced adaptability in response to an environmental stressor and pre-attentive filtering deficits. The behavioral insufficiencies coincided with decreases in the inhibitory pre- and post-synaptic proteins, synaptotagmin 2 and gephyrin, respectively, in the ACC, and alterations in specific pro- and anti-inflammatory cytokines out of 23 assayed. The interaction of Tat exposure and the resultant time-dependent, selective alterations in CCL4, CXCL1, IL-12p40, and IL-17A levels in the PFC predicted significant decreases in adaptability. Tat decreased dendritic spine density and cortical VGLUT1 inputs, while increasing IL-1β, IL-6, CCL5, and CCL11 in the striatum. Alternatively, IL-1α, CCL5, and IL-13 were decreased in the mediodorsal thalamus despite the absence of synaptic changes. Thus, HIV-1 Tat appears to uniquely and systematically disrupt immune regulation and the inhibitory and excitatory synaptic balance throughout the ACC-BG-thalamocortical circuitry resulting in a loss of behavioral control