Elsevier

Neuropharmacology

Volume 38, Issue 3, 14 March 1999, Pages 433-439
Neuropharmacology

Repeated administration of Δ9-tetrahydrocannabinol produces a differential time related responsiveness on proenkephalin, proopiomelanocortin and corticotropin releasing factor gene expression in the hypothalamus and pituitary gland of the rat

https://doi.org/10.1016/S0028-3908(98)00195-6Get rights and content

Abstract

The purpose of the present study was to explore the time related effects of repeated administration of Δ9-tetrahydrocannabinol on opioid and corticotropin releasing factor gene expression in the hypothalamus and pituitary gland of the rat. By using in situ hybridization histochemistry, the effects of Δ9-tetrahydrocannabinol (THC, 5 mg/kg per day; i.p.) were examined after 1, 3, 7 and 14 days of repeated administration on; (1) proenkephalin gene expression in the paraventricular (PVN) and ventromedial nuclei (VMN) of the hypothalamus, (2) proopiomelanocortin gene expression in the arcuate nucleus (ARC) of the hypothalamus and anterior (AL) and intermediate lobe (IL) of the pituitary gland, and (3) corticotropin releasing factor gene expression in the PVN. The results revealed that, in most of the hypothalamic and pituitary regions examined, repeated cannabinoid administration upregulates opioid and corticotropin releasing factor gene expression. However, the onset, the degree of magnitude of gene expression reached and the time related effects produced by repeated administration with Δ9-tetrahydrocannabinol are dependent upon the brain and pituitary regions examined. Taken together, the results of the present study suggest that cannabinoids produce a time related differential responsiveness in opioid and corticotropin releasing factor gene expression, in areas of the hypothalamus and pituitary that may be related, at least in part, to a molecular integrative response to behavioral, endocrine and neurochemical alterations that occur in cannabinoid drug abuse.

Introduction

Δ9-Tetrahydrocannabinol (THC), the major psychoactive compound of Cannabis sativa preparations (marijuana, hashish) produces a great variety of pharmacological effects that include antinociception, anxiety-like behavior, hypothermia, depression of motor activity, and alterations in the secretion of pituitary hormones (Dewey, 1986). It has been found that in the brain THC acts via a G-protein coupled receptor (CB1) (Matsuda et al., 1990) whose putative endogenous ligands have been identified as arachidonic acid derivatives (Devane et al., 1992). Sn-2 arachidonyl glicerol has been recently described as a second endogenous ligand for cannabinoid receptors, present in the brain in greater amounts than anandamide (Stella et al., 1997). However, a large body of evidence indicates that many of the behavioral and neurochemical effects produced by acute or chronic administration with cannabinoids may involve an interaction between the opioid and the cannabinoid neuronal systems. In recent years, our group and others, have shown that; (1) THC and anandamide modulate the expression of physical signs of opioid dependence (Vela et al., 1995), (2) the antiemetic effect of nabilone, a THC synthetic derivative, is antagonized by the opioid receptor antagonist naloxone (Rang and Dale, 1991), (3) antinociception induced by THC can be blocked by α- or κ-opioid receptor antagonists or selective antibodies against the endogenous κ ligand dynorphin (Reche et al., 1996a, Reche et al., 1996b), and (4) inhibition of opioid degrading enzymes may potentiate THC induced antinociception (Reche et al., 1998). These results suggest that administration of THC may increase the release of endogenous opioids. Indeed, recently, it has been shown that administration of CP-55,940, a selective cannabinoid receptor agonist produces a significant release of dynorphin B in the spinal cord concurrent with the production of antinociception (Pugh et al., 1997). Furthermore, our group has reported that subchronic or chronic administration of THC or cannabinoid receptor agonists increases proopiomelanocortin gene expression in the arcuate nucleus of the hypothalamus (Corchero et al., 1997a), prodynorphin and proenkephalin gene expression in the spinal cord (Corchero et al., 1997b) and proenkephalin gene expression in various forebrain and hypothalamic regions of the rat (Manzanares et al., 1998).

Stress behavior induced by drug abuse has been related to an increase in the secretion of corticotropin or corticosterone in the plasma. Administration with cannabinoid agonists caused a significant increase in the secretion of corticotropin (Dewey, 1986, Weidenfeld et al., 1994, Rubio et al., 1995, Rodriguez de Fonseca et al., 1996) that appears to be mediated via a central mechanism involving an increase in the release of corticotropin releasing factor (Weidenfeld et al., 1994). However, the molecular mechanisms by which cannabinoids regulate the hypothalamic pituitary adrenal axis (HPA) are still unknown.

The present study was undertaken to explore the molecular interaction between the opioid or the corticotropin releasing factor and the cannabinoid system. Time of onset, differential responsiveness and degree of magnitude obtained after repeated administration with THC on opioid and corticotropin releasing factor gene expression were determined in selected regions of the hypothalamus and pituitary gland of male rats. By using in situ hybridization histochemistry, the effects of Δ9-tetrahydrocannabinol (5 mg/kg per day; i.p.) were examined after 1, 3, 7 and 14 days of administration on: (1) proenkephalin gene expression in the paraventricular (PVN) and ventromedial nuclei (VMN) of the hypothalamus, (2) proopiomelanocortin gene expression in the arcuate nucleus (ARC) of the hypothalamus and anterior (AL) and intermediate lobe (IL) of the pituitary gland, and (3) corticotropin releasing factor gene expression in the PVN.

Section snippets

Animals

Adult male Sprague–Dawley rats, weighing 200–225 g, were obtained from Interfauna Iberica Laboratories (San Feliu de Codines, Barcelona, Spain) and maintained under conditions of controlled temperature (23±1°C) and lighting (lights on 08:00–20:00 h), with food and water provided ad libitum. All experiments included in this study were performed following the highest standards of humane animal care, monitoring health care and minimizing pain and suffering, in accordance with the National and

Effects of THC on proenkephalin gene expression in the PVN and VMN of the hypothalamus

The one-way analysis of variance of the results revealed that repeated administration with THC produced a marked increase of proenkephalin mRNA levels in the PVN (F(4,27)=7.39, P<0.0006) and in the VMN (F(4,34)=28.50, P<0.0001). In the PVN, treatment with THC produced a time related increase in proenkephalin mRNA levels reaching a 65% change from vehicle-treated rats on day 14. In contrast, proenkephalin mRNA levels in the VMN increased by day 3(+28%) and day 7 (+38%) and then returned to those

Discussion

The results of the present study demonstrate that exposure to THC markedly increases corticotropin-releasing factor gene expression in the PVN of the hypothalamus. Although some similarities were found in the response of opioid and corticotropin releasing factor genes examined after THC, important regional differences have been detected in the degree of magnitude of each specific gene expression regulation and the onset of this process. Interestingly, as a probe of the system dynamics,

Acknowledgements

This work was supported by the Universidad Complutense of Madrid grant PR294/95-6189, Concerted Action from the European Union grant BMH1-CT-94-1108 and Spanish Ministry of Education grant DGICYT UE95 0017. J. Corchero is a Predoctoral Fellow supported by the ‘Comunidad Autonoma de Madrid’ and J. Manzanares is a Senior Fellow supported by the Spanish Ministry of Education.

References (33)

Cited by (25)

  • Chronic treatment with Δ<sup>9</sup>-tetrahydrocannabinol enhances the locomotor response to amphetamine and heroin. Implications for vulnerability to drug addiction

    2001, Neuropharmacology
    Citation Excerpt :

    It has also been shown that CB1 cannabinoid receptors are involved in the motivational properties of opiates and in physical dependence (Ledent et al., 1999). ( 3) Cannabinoids are potent activators of the hypothalamic–pituitary adrenal axis (HPA) (Jacobs et al., 1979; Dewey, 1986; Elridge et al., 1991; Rodriguez de Foncesca et al., 1995; Corchero et al., 1999; Manzanares et al., 1999b) and we have repeatedly found that enhanced corticosteroid secretion increases the sensitivity to addictive drugs (Piazza et al., 1991a; Deroche et al. 1992, 1993). Cross-sensitization between cannabinoids and other addictive drugs remains to be demonstrated.

View all citing articles on Scopus
View full text