Elevated monoamine oxidase A activity and protein levels in rodent brain during acute withdrawal after chronic intermittent ethanol vapor exposure.

BACKGROUND: A key component of alcohol dependence (AD), a severe form of alcohol use disorder, is the negative emotional state during withdrawal. Monoamine oxidase A (MAO-A) is an important enzyme that metabolizes monoamines and creates oxidative stress. Elevations in MAO-A level, especially in the prefrontal and anterior cingulate cortex (PFC and ACC), are associated with low mood states, including the dysphoria of early alcohol withdrawal in humans. The aim of the present study was to determine whether chronic alcohol vapor exposure causes an upregulation of MAO-A activity or level in the PFC and ACC of rodents during acute withdrawal. METHODS: Sprague-Dawley rats were exposed to ethanol vapor or control condition for 17 h per day for 8 weeks. MAO-A activity and protein levels were measured immediately after exposure, acute withdrawal (24 h), protracted withdrawal (4 day), and protracted abstinence (3 weeks) (n = 16/group; 8 alcohol exposed, 8 control). RESULTS: Chronic ethanol vapor exposure significantly elevated MAO-A activity and protein levels in the PFC and ACC at 24-h withdrawal (multivariate analysis of variance (MANOVA), activity: F2,13 = 3.82, p = .05, protein: F2,13 = 5.13, p = .02). There were no significant changes in MAO-A level or activity at other timepoints. CONCLUSIONS: The results of this study suggest a causal relationship between acute alcohol withdrawal and elevated MAO-A levels and activity, clarifying the observation of greater MAO-A binding in human alcohol withdrawal. This has important implications for developing methods of targeting MAO-A and/or sequelae of its dysregulation in alcohol dependence.

A vapourized Δ(9)-tetrahydrocannabinol (Δ(9)-THC) delivery system part II: comparison of behavioural effects of pulmonary versus parenteral cannabinoid exposure in rodents.

INTRODUCTION: Studies of the rewarding and addictive properties of cannabinoids using rodents as animal models of human behaviour often fail to replicate findings from human studies. Animal studies typically employ parenteral routes of administration, whereas humans typically smoke cannabis, thus discrepancies may be related to different pharmacokinetics of parenteral and pulmonary routes of administration. Accordingly, a novel delivery system of vapourized Δ(9)-tetrahydrocannabinol (Δ(9)-THC) was developed and assessed for its pharmacokinetic, pharmacodynamic, and behavioural effects in rodents. A commercially available vapourizer was used to assess the effects of pulmonary (vapourized) administration of Δ(9)-THC and directly compared to parenteral (intraperitoneal, IP) administration of Δ(9)-THC. METHODS: Sprague-Dawley rats were exposed to pure Δ(9)-THC vapour (1, 2, 5, 10, and 20mg/pad), using a Volcano® vapourizing device (Storz and Bickel, Germany) or IP-administered Δ(9)-THC (0.1, 0.3, 0.5, 1.0mg/kg), and drug effects on locomotor activity, food and water consumption, and cross-sensitization to morphine (5mg/kg) were measured. RESULTS: Vapourized Δ(9)-THC significantly increased feeding during the first hour following exposure, whereas IP-administered Δ(9)-THC failed to produce a reliable increase in feeding at all doses tested. Acute administration of 10mg of vapourized Δ(9)-THC induced a short-lasting stimulation in locomotor activity compared to control in the first of four hours of testing over 7days of repeated exposure; this chronic exposure to 10mg of vapourized Δ(9)-THC did not induce behavioural sensitization to morphine. DISCUSSION: These results suggest vapourized Δ(9)-THC administration produces behavioural effects qualitatively different from those induced by IP administration in rodents. Furthermore, vapourized Δ(9)-THC delivery in rodents may produce behavioural effects more comparable to those observed in humans. We conclude that some of the conflicting findings in animal and human cannabinoid studies may be related to pharmacokinetic differences associated with route of administration.

A vapourized Δ(9)-tetrahydrocannabinol (Δ(9)-THC) delivery system part I: development and validation of a pulmonary cannabinoid route of exposure for experimental pharmacology studies in rodents.

INTRODUCTION: Most studies evaluating the effects of Δ(9)-tetrahydrocannabinol (Δ(9)-THC) in animal models administer it via a parenteral route (e.g., intraperitoneal (IP) or intravenous injection (IV)), however, the common route of administration for human users is pulmonary (e.g., smoking or vapourizing marijuana). A vapourized Δ(9)-THC delivery system for rodents was developed and used to compare the effects of pulmonary and parenteral Δ(9)-THC administration on blood cannabinoid levels and behaviour. METHODS: Sprague-Dawley rats were exposed to pulmonary Δ(9)-THC (1, 5, and 10mg of inhaled vapour) delivered via a Volcano® vapourizing device (Storz and Bickel, Germany) or to parenteral Δ(9)-THC (0.25, 0.5, 1.0, and 1.5mg/kg injected IP). Quantification of Δ(9)-THC and its psychoactive metabolite, 11-hydroxy-Δ(9)-THC (11-OH-Δ(9)-THC), in blood was determined by liquid chromatography/mass spectrometry (LC/MS). In order to verify the potential for the vapourization procedure to produce a robust conditioned place preference (CPP) or conditioned place avoidance CPA, classical conditioning procedures were systematically varied by altering the exposure time (10 or 20min) and number of exposed rats (1 or 2) while maintaining the same vapourization dose (10mg). RESULTS: Blood collected at 20min intervals showed similar dose-dependent and time-dependent changes in Δ(9)-THC and 11-OH-Δ(9)-THC for both pulmonary and parenteral administration of Δ(9)-THC. However, vapourized Δ(9)-THC induced CPP under certain conditions whereas IP-administered Δ(9)-THC induced CPA. DISCUSSION: These results support and extend the limited evidence (e.g., in humans, Naef et al., 2004; in rodents, Niyuhire et al., 2007) that Δ(9)-THC produces qualitatively different effects on behaviour depending upon the route of administration.

Greater monoamine oxidase a binding in alcohol dependence.

BACKGROUND: Alcohol dependence (AD) is a multiorgan disease in which excessive oxidative stress and apoptosis are implicated. Monoamine oxidase A (MAO-A) is an important enzyme on the outer mitochondrial membrane that participates in the cellular response to oxidative stress and mitochondrial toxicity. It is unknown whether MAO-A levels are abnormal in AD. We hypothesized that MAO-A VT, an index of MAO-A level, is elevated in the prefrontal cortex (PFC) during AD, because markers of greater oxidative stress and apoptosis are reported in the brain in AD and a microarray analysis reported greater MAO-A messenger RNA in the PFC of rodents exposed to alcohol vapor. METHODS: Sixteen participants with alcohol dependence and 16 healthy control subjects underwent [(11)C]-harmine positron emission tomography. All were nonsmoking, medication- and drug-free, and had no other past or present psychiatric or medical illnesses. RESULTS: MAO-A VT was significantly greater in the PFC (37%, independent samples t test, t30 = 3.93, p < .001), and all brain regions analyzed (mean 32%, multivariate analysis of variance, F7,24 = 3.67, p = .008). Greater duration of heavy drinking correlated positively with greater MAO-A VT in the PFC (r = .67, p = .005) and all brain regions analyzed (r = .73 to .57, p = .001-.02). CONCLUSIONS: This finding represents a new pathological marker present in AD that is therapeutically targetable through direct inhibition or by novel treatments toward oxidative/pro-apoptotic processes implicated by MAO-A overexpression.

Toluene inhalation modulates dentate gyrus granule cell output in vivo.

Toluene, a psychoactive volatile solvent found in adhesives and other products, is inhaled for its euphoric and intoxicating effects. Toluene inhalation additionally results in cognitive disturbances including impairments in select types of spatial and non-spatial memory, which converging evidence suggests may involve neurons of the dentate gyrus. In the present study we examined the effects of acute binge-like (~5000 ppm) toluene inhalation on dentate gyrus granule cell output and perforant path synaptic transmission, using extracellular field potential recordings in anesthetized adult rats in vivo. We found that toluene rapidly and reversibly increased or decreased the amplitudes of evoked population spikes from granule cells over a wide range of stimulation intensities. These changes in granule cell output could not be accounted for by changes in perforant path action potential discharge or presynaptic neurotransmitter release. A marked decrease in the power of the theta rhythm measured within the dentate gyrus was additionally noted. Overall our results suggest that inhalation of abuse-relevant concentrations of toluene changes the readout of perforant path inputs by dentate gyrus granule cells, putatively through a postsynaptic mechanism, and may contribute to explanations for specific learning and memory deficits associated with toluene inhalation.

Distribution of c-Fos immunoreactivity in the rat brain following abuse-like toluene vapor inhalation.

Inhalation of vapors from toluene-containing products results in euphoria accompanied by a variety of cognitive impairments and motor dysfunctions. The profound behavioral changes observed during and following toluene inhalation suggest changes in the activity of cells in potentially many brain regions; however, a comprehensive assessment of the neuroanatomical structures activated by toluene vapor has not been completed. Thus in the present study we systematically mapped in over 140 brain structures the distribution of c-Fos immunoreactivity (c-Fos IR), a proxy for neural activation, following exposure to an abuse-like concentration (~5000 ppm) of toluene vapor for 0, 5, 10 or 30 min. Quantitative analyses revealed increases in c-Fos IR in about one-third of the brain structures examined, with most of these structures significantly activated only after prolonged toluene exposure. The majority of brain structures activated by toluene were found in the forebrain and midbrain, with particularly pronounced activation in nuclei implicated in the processing of rewarding, emotional, and olfactory stimuli, and those controlling motor output. These structures included the ventral tegmental area, nucleus accumbens, select regions of the amygdala and hypothalamus, cingulate cortex, olfactory nuclei, piriform cortex, secondary motor cortex and caudate-putamen. In contrast, all subregions of the hippocampus and most thalamic nuclei were not significantly activated by toluene vapor. In the brainstem, effects of toluene vapor were restricted to select nuclei in the pons. The pattern of c-Fos IR evoked by inhalation of toluene vapor appears distinct from other psychoactive substances, consistent with the unique and complex behavioral outcomes associated with acute toluene inhalation.