José M. Oliva

Extinction of Cocaine Self-Administration Produces a Differential Time-Related Regulation of Proenkephalin Gene Expression in Rat Brain

The purpose of this study was to examine the time course effects of extinction of cocaine self-administration behavior on proenkephalin (PENK) gene expression in caudate-putamen nucleus (ST), nucleus accumbens (Acc), olfactory tubercle (Tu), piriform cortex (Pir), ventromedial hypothalamic nucleus (VMN), and central amygdala (Ce) as measured by in situ hybridization histochemistry. Seventy-two littermate male Lewis rats were randomly assigned in triads to one of three conditions: (1) contingent intravenous self-administration of 1 mg/kg/injection of cocaine (CONT); (2) noncontingent injections of either 1 mg/kg/injection of cocaine (NONCONT); or (3) saline yoked (SALINE) to the intake of the self-administering subject. The self-administering rats were trained to self-administer cocaine under a FR5 schedule of reinforcement for a minimum of 3 weeks. After stable baseline levels of drug intake had been reached, saline was substituted for drug. Following this first extinction period, cocaine self-administration was reinstated for an additional period of 2 weeks. Immediately after cessation of the last session of cocaine self-administration (day 0) and 1-, 5-, and 10-day after the second extinction period, animal brains in each triad were removed to be processed for in situ hybridization. PENK mRNA levels were significantly higher in the cocaine groups when compared with SALINE group in the ST, Acc, Pir, and Tu regions on days 0, 1, 5, and 10 of the extinction and lower in the Ce region of CONT group when compared to NONCONT and SALINE groups on days 1, 5, and 10 of the extinction period. In the VMN nucleus, PENK mRNA content in CONT group versus NONCONT and SALINE groups was also lower, but there were statistically significant differences only on day 5. These results suggest that changes in PENK gene expression after contingent cocaine administration might be involved in cocaine withdrawal states.

Time course of opioid and cannabinoid gene transcription alterations induced by repeated administration with fluoxetine in the rat brain.

This study examined the time course effects (8, 16 and 31 days) of fluoxetine administration (1 mg/kg, p.o./day) on serotonin transporter (5-HTT), opioid, tyrosine hydroxylase (TH) and cannabinoid CB1 receptor gene expressions in selected regions of the rat brain. Treatment with fluoxetine progressively decreased (35-55%) 5-HTT gene expression in dorsal raphe nucleus at 8, 16 and 31 days. The results revealed that fluoxetine administration decreased (30%) proenkephalin gene expression in nucleus accumbens shell (AcbS) and caudate-putamen (CPu) (31 days) but was without effect in nucleus accumbens core AcbC. A pronounced and time related decrease (25-65%) in prodynorphin gene expression was detected in AcbC, AcbS, CPu, hypothalamic supraoptic and paraventricular nuclei at all time points as well as in proopiomelanocortin gene expression (20-30%) in the arcuate nucleus (ARC) of the hypothalamus. On days 16 and 31, tyrosine hydroxylase gene expression in ventral tegmental area and substantia nigra and cannabinoid CB1 receptor gene expression in the CPu decreased (approximately 45-50% from vehicle). In conclusion, fluoxetine by inhibiting the reuptake of serotonin produced pronounced and time related alterations in genes involved in the regulation of emotional behaviour, suggesting that these neuroplastic changes may be involved, at least in part, in the clinical efficacy of this drug in neuropsychiatric disorders.

Neuroadaptive Changes in NMDAR1 Gene Expression after Extinction of Cocaine Self-Administration

Abstract: The aim of the present work was to study the time course effects in levels of mRNA encoding N‐methyl‐d‐aspartate receptor subunit 1 (NMDAR1) after long‐term cocaine self‐administration (1 mg/kg/ injection) and its extinction using a yoked‐box procedure. NMDAR1 content was measured by quantitative in situ hybridization histochemistry in prefrontal cortex, caudate‐putamen, nucleus accumbens, olfactory tubercle, and piriform cortex immediately after cessation of the last session of cocaine self‐administration (Day 0) and 1, 5, and 10 days after the extinction period. The results show that long‐term cocaine self‐administration and its extinction alter NMDAR1 gene expression in these forebrain regions, and that the changes depend upon the brain region examined and the type of cocaine administration (contingent, noncontingent, and saline). Compared to saline and noncontingent cocaine administration, contingent cocaine produced an up‐regulation in NMDAR1 gene expression on Day 0 in all the brain regions analyzed. NMDAR1 levels of contingent animals decreased progressively in the absence of cocaine, and the decrement persisted 10 days after the extinction of cocaine self‐administration behavior in all the forebrain areas, with the exception of olfactory tubercle. In contrast, noncontingent cocaine administration did not produce any change in NMDAR1 gene expression on Day 0, and extinction resulted in an increase of NMDAR1 mRNA content on Days 1 and 5 and returned to control (saline) values on Day 10. These results suggest that an interaction between environmental stimuli and the pharmacological action of cocaine during drug self‐administration and its extinction may represent an important factor in the regulation of cocaine effects on NMDAR1 gene expression.

Gene Transcription Alterations Associated with Decrease of Ethanol Intake Induced by Naltrexone in the Brain of Wistar Rats

Preclinical and clinical studies suggest that the administration of the opioid antagonist naltrexone decreases the intake of ethanol. However, the neuroplastic adaptations in the brain associated to reduction of ethanol consumption remains to be elucidated. The aim of the study was to identify gene transcription alterations underlying the attenuation of voluntary ethanol intake by administration of naltrexone in rats. Increasing doses of naltrexone (0.7 mg/kg, 4 days and 1.4 mg/kg/day, 4 days) to rats with acquired high preferring ethanol consumption (>3.5 g of ethanol/kg/day) decreased voluntary ethanol intake (50%). Voluntary ethanol consumption altered μ-opioid receptor function in the cingulate cortex, caudate-putamen (CPu), nucleus accumbens core (Acb C) and shell (Acb S), the expression of tyrosine hydroxylase (TH) in the ventral tegmental area and substantia nigra, proenkephalin (PENK) in the piriform cortex, olfactory tubercle, CPu, Acb C and Acb S, ventromedial nucleus (VMN) and paraventricular nucleus (PVN) of the hypothalamus, corticotropin releasing factor (CRF) in PVN, cannabinoid CB1 receptor (CB1-R) in the CPu, hippocampus and VMN, and serotonin transporter (5-HTT) in the dorsal and median raphe nuclei. The reduction of ethanol intake induced by naltrexone was associated with a blockade or significant reduction of the changes produced by ethanol in the expression of these genes in key regions related to drug dependence. These results point to a role for the μ-opioid receptor, TH, PENK, CRF, CB1-R, and 5-HTT genes in specific brain regions in the modulation of neuroadaptative mechanisms associated to the decrease of ethanol intake induced by naltrexone.

Behavioural and gene transcription alterations induced by spontaneous cannabinoid withdrawal in mice.

This study examined behavioural signs that occur during tolerance development to cannabinoid treatment and hormonal and gene expression alterations induced by spontaneous cannabinoid withdrawal in mice. Tolerance to CP‐55,940 treatment developed for hypothermia, ambulatory and exploratory locomotor activity. Cessation of cannabinoid treatment resulted in a behavioural withdrawal syndrome characterized by a pronounced increase in ambulatory activity and rearings. Corticosterone plasma concentrations dramatically increased 24 and 72 h after cessation of cannabinoid treatment. Similarly, an increase (40%) in cannabinoid [35S]GTPγS binding autoradiography was detected on days 1 and 3 of abstinence. Spontaneous cannabinoid withdrawal produced time‐related significant alterations in gene transcription: (i) decreased (20%) tyrosine hydroxylase (TH) mRNA levels in the ventral tegmental area and increased (50%) in substantia nigra; (ii) increased proenkephalin (PENK) gene expression more than 100% in caudate‐putamen, nucleus accumbens, olfactory tubercle and piriform cortex; (iii) increased (20–40%) pro‐opiomelanocortin (POMC) gene expression in the arcuate nucleus of the hypothalamus. These results suggest that spontaneous cannabinoid withdrawal occur after cessation of CP‐55,940 treatment. This ‘syndrome’ includes behavioural, hormonal and gene transcription alterations that seems to be part of the regulation of neuronal plasticity induced by spontaneous cannabinoid withdrawal.

Repeated administration with δ9- tetrahydrocannabinol regulates µ-opioid receptor density in the rat brain

Several studies have demonstrated reciprocal, as well as synergistic interactions between cannabinoid and opioid systems. The aim of this study was to explore the time-related effects of repeated administration of δ9-tetrahydrocannabinol on µ-opioid receptor autoradiography in various brain regions of the rat. To this aim, the effects of δ9-tetrahydrocannabinol (δ9-THC, 5 mg/kg/day; i.p.) were examined after 1, 3, 7 and 14 days of repeated administration on regions containing µ-opioid receptors: (i) forebrain [caudate-putamen, nucleus accumbens (core and shell) and piriform cortex]; (ii) amygdala (medial pars and cortical posteromedial pars), hypothalamus (ventromedial and dorsomedial nuclei, zona incerta), hippocampal regions (CA1, CA2, CA3, dentate girus), hindbrain (substantia nigra and ventral tegmental area); and (iii) thalamus, including 12 thalamic nuclei. In most of these regions, repeated cannabinoid administration increases µ-opioid receptor density; however, the onset, degree of magnitude reached and time-related effects produced by administration with δ9-tetrahydrocannabinol are dependent upon the brain region examined. It appears that the major increase in µ-opioid receptor density occurs 1 and 3 days after δ9-THC administration. In some regions, this increase is maintained and, for most of the brain areas examined, this effect is no longer significant by 14 days of administration, suggesting tolerance to cannabinoid treatment. Taken together, the results of this study suggest that cannabinoids produce a time-related differential responsiveness in µ-opioid receptor density in several brain areas that may be relevant to an understanding of the alterations associated with cannabinoid exposure.

Extinction of cocaine self-administration produces alterations in corticotropin releasing factor gene expression in the paraventricular nucleus of the hypothalamus

The long-term effect of cocaine self-administration on corticotropin releasing factor (CRF) mRNA content in the hypothalamic CRF-containing neurons has not yet been established. The purpose of this study was to examine the time course effects of the extinction of cocaine self-administration behavior on CRF gene expression in the paraventricular nucleus of the hypothalamus (PVN) using in situ hybridization histochemistry (IHHS). Seventy-two littermate male Lewis rats were randomly assigned in triads to one of three conditions: (a) contingent intravenous self-administration of 1 mg/kg/injection of cocaine (CONT), (b) non-contingent injections of either 1 mg/kg/injection of cocaine (NONCONT) or (c) saline yoked (SALINE) to the intake of the self-administering subject. The self-administering rats were trained to self-administer cocaine under a fixed ratio 5 (FR5) schedule of reinforcement for a minimum of 3 weeks. After stable baseline levels of drug intake had been reached, saline was substituted for drug. Following this first extinction period, cocaine self-administration was reinstated for an additional period of 2 weeks. Immediately after cessation of the last session of cocaine self-administration (Day 0) and 1, 5 and 10 days after the second extinction period, animal brains in each triad were removed to be processed for IHHS. CRF mRNA levels in the PVN were significantly lower in the NONCONT cocaine group at Day 0 compared to CONT or SALINE groups. On Day 1, hypothalamic CRF gene expression significantly decreased in the CONT cocaine group with respect to the SALINE group, but there were no differences between the cocaine groups or among the NONCONT cocaine and SALINE groups. After 5 and 10 days of extinction, no differences were found in CRF mRNA content in the PVN between the three conditions of this study. These results suggest that, after the extinction of cocaine self-administration, changes in hypothalamic CRF gene expression are differentially affected depending upon the type of cocaine administration, and that the stages of cocaine withdrawal might not be associated with enduring changes in hypothalamic CRF mRNA levels.

Spontaneous cannabinoid withdrawal produces a differential time-related responsiveness in cannabinoid CB1 receptor gene expression in the mouse brain.

This study aimed to examine the behavioural and neurochemical (cannabinoid CB1 receptor gene expression) changes induced by spontaneous cannabinoid withdrawal in mice. Tolerance was assessed by measuring rectal temperature and motor activity in the open-field test after CP-55, 940 administration. Cannabinoid withdrawal symptoms were determined by measuring motor activity and behavioural signs of abstinence. Cessation of CP-55, 940 treatment in tolerant mice induced a spontaneous time-dependent behavioural withdrawal syndrome consisting of marked increases (140%) in motor activity, number of rearings (170%), decreases in grooming (57%), wet dog shakes (73%) and rubbing behaviours (74%) on day 1, progressively reaching values similar to vehicle-treated mice on day 3. Interestingly, this spontaneous cannabinoid withdrawal resulted in CB1 gene expression upregulation (20–30%) in caudate-putamen, ventromedial hypothalamic nucleus, central amygdaloid nucleus and CA1, whereas in the CA3 field of hippocampus, a significant decrease (15–20%) was detected. Taken together, the results of this study suggest that cessation of CP-55, 940 administration in tolerant mice produces a behavioural cannabinoid withdrawal syndrome and a selective and differential responsiveness in CB1 receptor gene expression in several brain regions of the mice. These findings further suggest a time and regional differential role for cannabinoid receptors in short- and long-term neuroadaptations that occur after exposure to cannabis derivatives.