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M J Kreek

Publications and source records attributed to M J Kreek.

At least 19 recordsLinked to original sources
PubMed2006

Reliability of salivary cortisol assessments in cocaine dependent individuals.

The aim of this study was to assess the reliability of salivary cortisol as a measure of hypothalmic-pituitary-adrenal (HPA) axis function in cocaine dependent individuals. Saliva and total plasma samples were collected from 49 abusers on 3 testing days in the morning, across eight time points per day. Significant associations between saliva and plasma cortisol were observed across all time points collapsed across 3 days in both men and women. These moderately significant correlations suggest that salivary measurements represent a stable, non-invasive and broad indicator of HPA axis functioning in cocaine dependent individuals.

Adrenocorticotropic Hormone↗
PubMed2006

Cocaine self-administration in mice is inversely related to phosphorylation at Thr34 (protein kinase A site) and Ser130 (kinase CK1 site) of DARPP-32.

The reinforcing effect of cocaine is associated with increases in dopamine in the striatum. The phosphoprotein DARPP-32 (dopamine- and cAMP-regulated phosphoprotein) has been shown to mediate the intracellular events after activation of dopamine receptors. DARPP-32 is phosphorylated at multiple sites by different protein kinases, but little is known about the functional role of these different sites. Cocaine self-administration and striatal levels of dopamine after acute "binge" cocaine administration were measured in separate lines of mice with alanine mutations introduced into DARPP-32 at either Thr34 (protein kinase A site, Thr34A), Thr75, (cyclin-dependent kinase 5 site, Thr75A), Ser97 (kinase CK2 site, Ser97A), or Ser130 (kinase CK1 site, Ser130A). Acquisition of stable cocaine self-administration required significantly more time in Thr34A-/- mice. Both Thr34A- and Ser130A-DARPP-32 mutant mice self-administered more cocaine than their respective wild-type controls. Also, cocaine-induced increases of dopamine in dorsal striatum were attenuated in the Thr34A- and Ser130A-DARPP-32 phosphomutant mice compared with wild-type mice. Notably, levels of P-Thr34- and P-Ser130-DARPP-32 were reduced after self-administration of cocaine in wild-type mice. Thus, phosphorylation states of Thr34- and Ser130-DARPP-32 play important roles in modulating the reinforcing effects of cocaine.

Alanine↗
PubMed2005

Amygdalar vasopressin mRNA increases in acute cocaine withdrawal: evidence for opioid receptor modulation.

In humans, stress is recognized as a major factor contributing to relapse to drug abuse in abstinent individuals; drugs of abuse themselves or withdrawal from such drugs act as stressors. In the animals, evidence suggests that centrally released arginine vasopressin in both amygdala and hypothalamus plays an important role in stress-related anxiogenic behaviors. The stress responsive hypothalamic-pituitary-adrenal axis is under tonic inhibition via endogenous opioids, and cocaine withdrawal stimulates hypothalamic-pituitary-adrenal activity. The present studies were undertaken to determine whether: (1) 14-day (chronic) "binge" pattern cocaine administration (45 mg/kg/day) or its withdrawal for 3 h (acute), 1 day (subacute) or 10 days (chronic) alters arginine vasopressin mRNA levels in amygdala or hypothalamus; (2) the opioid receptor antagonist naloxone (1mg/kg) alters arginine vasopressin mRNA or hypothalamic-pituitary-adrenal hormonal responses in acute cocaine withdrawal; and (3) there are associated changes of mu opioid receptor or proopiomelanocortin mRNA levels. In amygdala, arginine vasopressin mRNA levels were unchanged after chronic "binge" cocaine, but were increased during acute cocaine withdrawal. Naloxone completely blocked this increase. Neither chronic cocaine nor its acute withdrawal altered amygdalar mu opioid receptor mRNA levels. The increase in amygdalar arginine vasopressin mRNA levels was still observed after subacute withdrawal, but not after chronic withdrawal. Although hypothalamic-pituitary-adrenal tolerance developed with chronic "binge" cocaine, there were modestly elevated plasma adrenocorticotropin hormone levels during acute withdrawal. While naloxone produced modest adrenocorticotropin hormone elevations in cocaine-naïve rats, naloxone failed to elicit an adrenocorticotropin hormone response in cocaine-withdrawn rats. In hypothalamus, neither chronic cocaine nor acute withdrawal altered arginine vasopressin, proopiomelanocortin or mu opioid receptor mRNA levels. These results show that: (1) opioid receptors mediate increased amygdalar arginine vasopressin gene expression during acute cocaine withdrawal, and (2) cocaine withdrawal renders the hypothalamic-pituitary-adrenal axis insensitive to naloxone. Our findings suggest a potential role for amygdalar arginine vasopressin in the aversive consequences of early cocaine withdrawal.

Amygdala↗
PubMed2003

Subject-regulated dosing alters morphine self-administration behavior and morphine-stimulated [35S]GTPgammaS binding.

Repeated intake of opioids is associated with dose escalation and alterations in signal transduction at the G-protein-coupled receptor level. The current study utilized two experiments to identify factors in rats that influence consumption rates such as daily intake of self-administered morphine and receptor desensitization. In Experiment 1, rats self-administered either 0.30, 1.00, or 3.00 mg/kg/infusion morphine sulfate (morphine) during 7 daily 4-h sessions. For Experiment 2, rats were assigned to groups that self-administered either 1) self-regulated escalating doses of morphine, 2) a fixed dose of morphine, or 3) saline during 18-h sessions for 7 days to determine if dose control would increase consumption without significantly decreasing response rate. We then assessed morphine-stimulated [(35)S]GTPgammaS binding in the amygdala and thalamus from these three groups in Experiment 2. Results from Experiment 1 demonstrated that 0.30 mg/kg/morphine did not support stable self-administration. For Experiment 2, the self-escalation group self-administered more morphine than the fixed-dose group, yet maintained similar response rates. Additionally, self-escalation rats demonstrated decreased morphine-stimulated [(35)S]GTPgammaS binding in membranes prepared from amygdalar and thalamic nuclei compared to the fixed-dose and control groups. Our results suggest that session length inversely affects consumption rates for fixed doses of morphine. Self-regulated dosing of morphine is also associated with rapid escalation of daily consumption and no significant alterations in consumption rates. These results suggest subject-regulated dosing is a useful approach for modeling dose escalation associated with opioid dependence.

Amygdala↗
PubMed2003

Neuroendocrine alterations in a high-dose, extended-access rat self-administration model of escalating cocaine use.

One approach for studying cocaine addiction has been to permit escalating patterns of self-administration (SA) by rats by prolonging daily drug availability. Rats provided long access (LgA) to high cocaine doses, but not rats provided shorter cocaine access (ShA), progressively escalate their cocaine intake and display characteristics of human addiction. The purpose of the present study was to investigate the effects of 14 days of ShA or LgA, high-dose cocaine SA on plasma corticosterone (CORT), prolactin (PRL), and related mRNAs. Acutely, cocaine SA increased plasma CORT and reduced plasma PRL levels. SA training produced circadian increases in CORT that appeared to occur in anticipation of cocaine availability. With repeated LgA, high-dose SA, the daily CORT area under the curve (AUC) progressively decreased, apparently due to tolerance to cocaine's effects on CORT and a reduction in basal CORT levels. In contrast, the daily CORT AUC in ShA rats increased across testing despite constant rates of SA. When measured 12 days after SA testing, pro-opioimelanocortin and glucocorticoid receptor mRNA levels in the anterior pituitary were lower in LgA rats than in ShA rats. The effects of SA on PRL remained constant across SA testing in LgA rats, but increased in duration in ShA rats. Anterior pituitary dopamine D2 receptor mRNA levels were lower in LgA rats than in ShA rats. These findings indicate that the transition to escalating patterns of SA may be associated with altered levels of hormones and gene expression within neuroendocrine systems. Such changes may underlie the onset of human addictive disease.

Adrenal Glands↗
PubMed2002

Nicotine addiction: insights from recent animal studies.

RATIONALE: Recent preclinical behavioral and neurobiological research has characterized important behavioral features and has identified neurobiological substrates that may underlie nicotine reinforcement and addiction. OBJECTIVE: To examine recent advances on nicotine exposure in preclinical models, from three perspectives: (a) the chronopharmacokinetics of nicotine, (b) behavioral studies on nicotine reinforcement, withdrawal, and reinstatement/relapse, and (c) effects of nicotine on neurobiological substrates after repeated exposure. RESULTS: Preclinical studies can be used to operationally model selected aspects of nicotine reinforcement, withdrawal, and reinstatement or relapse. These may be used to investigate the functional in vivo consequences of acute and long-term changes in neuronal acetylcholine receptor populations that follow nicotine exposure. Behavioral studies focusing on distinct stages of nicotine exposure (e.g., active reinforcement vs. cessation or reinstatement) may also be used in parallel with studies on dopaminergic function, a proposed substrate for the reinforcing effects of nicotine, and of opioid receptor function, a possible site of neuroadaptations secondary to nicotine exposure. CONCLUSIONS: While no single current animal model may capture the experience of human smoking or nicotine addiction, increasingly, separate animal models are capturing the full spectrum of behavioral and neurobiological dimensions of this complex condition.

Animals↗
PubMed2002

The effects of drug abuse on the stress responsive hypothalamic-pituitary-adrenal axis and the dopaminergic and endogenous opioid systems.

OBJECTIVE: Drugs of abuse have a significant impact on the stress responsive hypothalamic-pituitary-adrenal (HPA) axis and an abnormal response to stress may mediate the development or maintenance of addictive diseases. In animals, drugs of abuse, such as cocaine, lead to an activation of the HPA axis. Drugs of abuse also have an impact on the endogenous opioid system (EOS) and the dopaminergic system. Each of these systems has also been implicated in the mediation of aggressive behaviors. This brief report focuses on the effects of drugs of abuse on the stress responsive HPA, EOS and dopaminergic systems, and the role of these systems in mediating aggression and comorbidity of substance abuse and aggressive behaviors. METHOD: Rodents were administered either 'binge' pattern cocaine (15 mg/kg x 3 each day) or the androgenic anabolic steroid nandrolone decanoate and the effects on mRNA levels, receptor binding and circulating levels of stress hormones were analyzed. RESULTS: Both cocaine and nandrolone decanoate significantly impact the HPA axis, the EOS and the dopaminergic systems. CONCLUSION: Drugs of abuse impact substantially the same neural systems that affect aggressive behavior.

Dopamine↗
PubMed2001

Effect of acute binge cocaine on levels of extracellular dopamine in the caudate putamen and nucleus accumbens in male C57BL/6J and 129/J mice.

Levels of dopamine, both basal and after binge-pattern cocaine administration, were measured in the caudate putamen and nucleus accumbens of C57BL/6J and 129/J mice by in vivo microdialysis. Six-week old males were surgically implanted with a CMA guide cannula into the caudate putamen or nucleus accumbens. After 4 days recovery, dialysis probes were lowered into the caudate putamen or the nucleus accumbens and mice were placed in individual microdialysis chambers. The next morning experiments were carried out on freely moving animals. Experimental animals received 1-day binge cocaine administration (15 mg/kgx3, i.p. at hourly intervals) while control animals received saline in the same pattern. Dialysates were collected every 20 min and dopamine content was determined by HPLC with electrochemical detection. Basal levels of dopamine in the dialysate of the caudate putamen were 4.2+/-0.2 nM in C57BL/6J mice and 5.0+/-0.3 nM in 129/J mice. In the nucleus accumbens, basal levels of dopamine were 0.65+/-0.04 nM in the C57BL/6J mice and 0.75+/-0.03 nM in 129/J mice, with no significant differences between strains in either region. Binge cocaine administration significantly increased mean dopamine levels in the caudate putamen in the C57BL/6J mice (with a 3-h mean of 6.80 nM) and in the 129J mice (9.94 nM). In this region, 129/J mice had significantly higher levels of cocaine-induced dopamine than did C57BL/6J mice. In the nucleus accumbens, administration of cocaine also significantly increased dopamine levels in both strains (1.32 nM in C57BL/6J and 1.43 nM in 129/J), but with no difference between strains.

Animals↗
PubMed2001

Novel and previously reported single-nucleotide polymorphisms in the human 5-HT(1B) receptor gene: no association with cocaine or alcohol abuse or dependence.

Evidence from animal self-administration and human genetics studies suggests that the serotonin(1B) (5-HT(1B)) receptor may be involved in modulating responses to cocaine or alcohol. We hypothesize that polymorphisms, including single-nucleotide polymorphisms (SNPs), in the human 5-HT(1B) receptor gene, may be associated with individual differences in vulnerability to cocaine or alcohol abuse or dependence. A total of 210 subjects were studied, including individuals with a primary diagnosis (DSM-IV criteria) of cocaine abuse or dependence, alcohol abuse or dependence, and controls with no history of previous or current illicit drug or alcohol abuse or dependence. Genomic DNA samples were isolated from each individual. For 157 of the subjects, polymerase chain reaction (PCR) was used to amplify the entire coding region of the 5-HT(1B) receptor gene as well as parts of the 5' and 3' untranslated regions. PCR products were sequenced in forward and reverse directions on an automated sequencer. Amplified DNA from an additional 53 subjects was sequenced in the 5' untranslated region to gain additional data on the frequency of one identified SNP. Seven polymorphisms were identified: one novel SNP in the 5' untranslated region (UTR) of the gene (A-161T); one SNP not reported in any published scientific communication (but found to be recorded in GenBank) in the 3' UTR (A1180G); two novel dinucleotide deletions at positions - 184/- 183 and - 182/- 181; and three previously identified SNPs (T-261G, C129T, G861C). Data were stratified by ethnicity and pooled Relative Risk was calculated for combined alcohol abuse and dependence cases and controls, and also for combined cocaine abuse and dependence cases and controls. No significant differences between cases and controls were found.

Alcoholism↗
PubMed2001

kappa-Opioid receptor agonist-induced prolactin release in primates is blocked by dopamine D(2)-like receptor agonists.

Kappa-opioid receptor agonists may have pharmacotherapeutic potential in the management of psychostimulant abuse, due to their ability to modulate dopamine receptor systems involved in drug reinforcement. kappa-Opioid receptor agonists also modulate dopamine receptor function in the hypothalamic tuberoinfundibular system, which has inhibitory control over an anterior pituitary hormone, prolactin. Prolactin levels may thus be a "biomarker" for the ability of kappa-opioid receptor agonists (e.g., (+)-(5 alpha,7 alpha,8 beta)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-yl]-benzeneacetamide (U69,593)) to modulate a dopamine receptor system in vivo in primates. The effectiveness of dopamine D(2)-like receptor agonists (quinpirole and (+/-)-7-hydroxy-dipropylaminotetralin (7-OH-DPAT); 0.0032-0.1 mg/kg) in preventing U69,593-induced prolactin release was studied in intact female rhesus monkeys. Quinpirole and 7-OH-DPAT inhibited U69,593-induced prolactin release (ID(50) values: 0.013 and 0.0072 mg/kg, respectively). However, the dopamine D(1)-receptor agonist (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazapine (SKF 82958; 1 mg/kg) did not inhibit U69,593-induced prolactin release under the same conditions. In contrast, the largest doses of quinpirole or 7-OH-DPAT presently studied (0.1 mg/kg), did not decrease sedation caused by U69,593 (0.01, 0.032 mg/kg), a prominent effect of centrally penetrating kappa-opioid receptor agonists. The sedative effect of U69,593 (0.032 mg/kg) was prevented by naltrexone (0.32 mg/kg), consistent with kappa-opioid receptor mediation of this effect. These studies suggest that prolactin release is a valid biomarker for the ability of kappa-opioid receptor agonists to modulate dopamine D(2)-like receptor function, and may also be used to quantify dopamine D(2)-like receptor agonist potency in primates.

Animals↗
PubMed2001

The frequency of cocaine administration impacts cocaine-induced receptor alterations.

The present study investigated the impact of dosing schedule on cocaine-induced receptor alterations. Rats were injected with 30 mg/kg per day of cocaine given either as a single injection or in two equally divided doses for 14 days. The effects of these two dosing regimens were compared with our previous findings following administration of cocaine three times daily at 1-h intervals. Using receptor autoradiography, twice daily injections of cocaine produced an upregulation of mu opioid receptors in the rostral nucleus accumbens, rostral caudate putamen, and layer I of the rostral cingulate cortex, whereas single daily injections resulted in a significant increase in the nucleus accumbens only. Only small insignificant increases in kappa opioid receptor densities were found following either once or twice daily cocaine injections, whereas three daily injections produced an increase in kappa receptor density in the cingulate cortex, nucleus accumbens, and caudate putamen. Increased dopamine D1 receptor binding was found in the nucleus accumbens and olfactory tubercle following twice daily cocaine injections, but not after single daily injections of the same total daily dose. These results demonstrate that the same total daily dose of cocaine administered in multiple small injections produces a greater effect on receptor regulation than a single larger injection. This suggests that the interval between cocaine injections is an important variable when studying the effects of cocaine on neurochemistry.

Amygdala↗
PubMed2001

Elevation of guinea pig brain preprodynorphin mRNA expression and hypothalamic-pituitary-adrenal axis activity by "binge" pattern cocaine administration.

The endogenous opioid system and the hypothalamic-pituitary-adrenal (HPA) axis have been implicated in many of the neurobiological effects of cocaine. Previous studies in our laboratory showed that "binge" pattern cocaine administration increases preprodynorphin (ppDyn) mRNA levels in the caudate putamen and circulating levels of corticosterone in the rat. The present study extended these findings to guinea pigs, a species known to have a kappa opioid receptor profile similar to that of humans. Male guinea pigs were treated with: (a) "binge" pattern cocaine for 7 days (subchronic) (3 x 15 mg/kg/day, hourly, intraperitoneal); (b) "binge" pattern saline for 5 days followed by "binge" pattern cocaine for 2 days (subacute); or (c) "binge" pattern saline for 7 days. Thirty minutes after the final injection, levels of ppDyn mRNA were quantitated in the nucleus accumbens, caudate putamen, frontal cortex, amygdala, hippocampus, and hypothalamus using a solution hybridization RNase protection assay. Regional distribution of ppDyn mRNA levels in the guinea pig brain was similar to that found in rat, with highest levels in the nucleus accumbens and caudate putamen. In the caudate putamen, ppDyn mRNA was significantly increased following either 2 days (38% increase) or 7 days (32% increase) of "binge" pattern cocaine administration as compared to saline-treated controls. No significant changes in ppDyn mRNA levels were found in any other brain region. Both subacute and subchronic "binge" cocaine administration significantly elevated plasma levels of adrenocorticotropin hormone (ACTH) and cortisol. However, the ACTH and cortisol increases were significantly blunted following 7 days of "binge" cocaine administration as compared to 2 days of drug treatment, reflecting the development of HPA tolerance or adaptation to repeated cocaine administration. Thus, the ppDyn mRNA and HPA responses to cocaine in guinea pigs are similar to those observed in rats.

Animals↗
PubMed2001

Mu-, delta- and kappa-opioid receptor populations are differentially altered in distinct areas of postmortem brains of Alzheimer's disease patients.

The putative role of the opioid system in cognitive and memory functions prompted us to search for possible changes in the cohort of the major opioid receptors, mu, delta and kappa, in Alzheimer's disease. The present study examines alterations in opioid receptor levels by quantitative autoradiography. These experiments were carried out on coronal sections of postmortem brains from Alzheimer's disease patients and from aged-matched, dementia-free individuals. Brain sections were labeled with the tritiated forms of mu-, delta- and kappa-opioid ligands; DAMGO ([D-Ala(2),N-Me-Phe(4),Gly-ol(5)]-enkephalin), DPDPE ([D-Pen2,5]-enkephalin) and bremazocine (in the presence of mu- and delta-ligands), respectively. Nonspecific binding was determined in the presence of naloxone (10 microM). Brain areas analyzed were caudate, putamen, amygdaloid complex, hippocampal formation and various cerebral and cerebellar cortices. Image analyses of autoradiographs show, that in comparison to the same areas in control brain, statistically significant reductions in mu-opioid receptor binding occur in the subiculum and hippocampus of Alzheimer's disease brains. Binding of delta-opioid receptors is also decreased in the amygdaloid complex and ventral putamen of Alzheimer's disease brains. In contrast, large increases of kappa-opioid receptor binding are found in the dorsal and ventral putamen as well as in the cerebellar cortex of Alzheimer's disease brains. Levels of mu- delta- and kappa-opioid receptor binding are unaltered in the caudate, parahippocampal gyrus and occipito-temporal gyrus. These results may suggest an involvement of the endogenous opioid system in some of the multitude of effects that accompany this dementia.

Aged↗
PubMed2001

Quantitative medial temporal lobe brain morphology and hypothalamic-pituitary-adrenal axis function in cocaine dependence: a preliminary report.

Preclinical and clinical studies have shown that cocaine increases plasma adrenocorticotropin hormone (ACTH) and cortisol. Chronic elevation of plasma cortisol exerts direct toxic effects upon hippocampal neurons and exacerbates hippocampal damage resulting from ischemia and seizures. The authors tested for evidence of hippocampal damage in patients with chronic cocaine dependence. Medial temporal lobe and total brain volumes were quantified using magnetic resonance imaging (MRI) in 27 patients with cocaine dependence and 16 healthy subjects. Basal and ovine corticotropin releasing hormone (oCRH) stimulated ACTH and cortisol levels were also examined in a subset of 8 healthy and 9 cocaine dependent subjects after 21 days of abstinence. No evidence for decreased hippocampal or total brain volume in cocaine dependence was observed. Similarly, basal and oCRH stimulated ACTH and cortisol levels in cocaine dependent patients did not differ from those in healthy subjects.

Adrenocorticotropic Hormone↗
PubMed2001

Predictable individual differences in the initiation of cocaine self-administration by rats under extended-access conditions are dose-dependent.

RATIONALE: The characterization of self-administration (SA) under extended access conditions is necessary for the development of addiction models. OBJECTIVE: The purposes of this experiment were to investigate: (1) dose effects on the initiation of cocaine SA under extended access conditions; (2) predictable individual differences in SA under these conditions and their relationships to neuroendocrine function and cocaine dose. METHODS: After they were tested for their locomotor responses to novelty and to cocaine and trained to lever-press under a food-reinforced schedule, male Sprague-Dawley rats were allowed to SA cocaine (0.25, 0.5, 1.0, or 2.0 mg/kg per infusion, IV) by lever-pressing under a FR1 schedule during five consecutive daily 10-h sessions. Plasma corticosterone (CORT) and prolactin (PRL) were measured throughout the experiment. RESULTS: Rats tested at higher cocaine doses more readily acquired and showed increased drug intake and more regular patterns of SA. High responders (HR) to novelty self-administered greater amounts of cocaine, acquired more rapidly and displayed more regular SA compared to LR rats, but only at the lowest cocaine dose tested (i.e., 0.25 mg/kg per infusion). HR rats also exhibited a greater high-dose escalation of SA compared to LR rats. Novelty-induced (but not cocaine-induced) locomotor activity, pre-SA plasma CORT, and pre-SA food-reinforced lever-pressing predicted SA, but only at the lowest cocaine dose tested. No differences in plasma CORT or PRL were observed between LR and HR rats. CONCLUSIONS: The present findings indicate that predictable individual differences in cocaine SA under extended access conditions are relevant only at low doses and are surmountable by increasing the available dose of cocaine.

Animals↗
PubMed2001

Altered HPA axis responsivity to metyrapone testing in methadone maintained former heroin addicts with ongoing cocaine addiction.

Metyrapone testing, a provocation of hypothalamic-pituitary-adrenocortical (HPA) axis function, was performed in 39 in-patient subjects: 10 stable methadone-maintained former heroin addicts without ongoing drug or alcohol abuse or dependence (MM), eight methadone- maintained former heroin addicts without ongoing drug or alcohol abuse or dependence other than ongoing cocaine dependence (C-MM), and 21 normal volunteers (NV). Plasma adrenocorticotrophic hormone (ACTH) levels were determined in samples drawn at 9A.M., just before administration of 2.25 g metyrapone orally and 4 and 8 hours afterward. Following metyrapone, C-MM had levels of ACTH that were significantly higher than both MM (p < .05) and NV (p < .01); whereas, MM and NV had levels that were comparable. Area under the plasma ACTH curves yielded similar results. This study documents hyper-responsivity to removal of glucocorticoid negative feedback associated with cocaine addiction, even in the setting of methadone maintenance for heroin addiction, which here and previously has been shown to be associated with normalization of HPA axis function.

Adolescent↗
PubMed2001

Ablation of pituitary pro-opiomelanocortin (POMC) cells produces alterations in hypothalamic POMC mRNA levels and midbrain mu opioid receptor binding in a conditional transgenic mouse model.

The hypothalamic-pituitary-adrenal (HPA) axis is regulated by stress-related excitatory inputs, and various inhibitory and negative-feedback controls by glucocorticoids and opioids, including pro-opiomelanocortin (POMC)-derived peptides. The role of POMC-derived peptides of pituitary origin in the modulation of brain POMC mRNA expression and opioid receptor binding was investigated using a line of transgenic mice that express a fusion gene composed of the pituitary expression-specific promoter region of the POMC gene driving the herpes simplex viral-1 thymidine kinase (TK). Male adult mice were treated with the antiherpes agent ganciclovir that selectively ablates cells expressing TK. Following treatment, POMC mRNA levels, measured by quantitative solution hybridization/RNase protection assays, were decreased by 48% in the pituitary of the TK+/+ mice, reflecting an expected loss of the pituitary corticotrope POMC cells. This treatment also significantly lowered pituitary beta-endorphin immunoreactivity content and plasma concentrations of corticosterone. In contrast, POMC mRNA levels were increased by 79% in the hypothalamus of the TK+/+ mice with pituitary POMC cell ablation. Binding of [(3)H]DAMGO to mu opioid receptors, as measured by quantitative autoradiography, was significantly reduced in several brain regions including the central grey, median raphe and superficial grey layer of the superior colliculus. These regions are innervated by hypothalamic POMC neurones. No significant differences in binding to either kappa or delta opioid receptors were found in the brain regions studied. These results suggest that POMC-derived peptides of pituitary origin may exert a tonic negative-feedback effect on hypothalamic POMC neurones. In turn, the downregulation of central mu opioid receptors in this model may be mediated through a mechanism related to hypothalamic POMC overexpression.

Amygdala↗