Dopaminergic and peptidergic mRNA levels in juvenile rat brain after prenatal cocaine treatment

Gender differences in prodynorphin but not proenkephalin mRNA expression in the striatum of adolescent rats exposed to prenatal cocaine

The objective of this study was to determine if prenatal cocaine affects the levels of prodynorphin and proenkephalin mRNA in male and female adolescent rats. Pregnant dams received cocaine or vehicle from gestational days 8-22 and upon delivery, the pups were fostered. At postnatal days 42-44, pups were killed and brains removed and frozen. Sections of striatum and nucleus accumbens were processed for prodynorphin and proenkephalin mRNA expression. Prenatal cocaine did not affect the expression of proenkephalin mRNA, but males showed higher expression than females. However, prodynorphin mRNA was lower in female rats exposed to cocaine compared to controls. Prenatal cocaine appears to have unique effects on neuropeptides during adolescence.

Antidepressants activate CaMKII in neuron cell body by Thr286 phosphorylation

CaM kinase II, a regulator of synaptic plasticity, is implicated in pathophysiology and pharmacology of psychiatric disorders. Chronic treatment with antidepressants desipramine and reboxetine up-regulated CaM kinase II in neuronal cell bodies of hippocampus. mRNA/protein expression for alphaCaM kinase II was unchanged, whereas Thr phosphorylation was increased in pyramidal/granular cell bodies, suggesting that increased phosphorylation is responsible for kinase activation. Short-term treatment of neuronal cultures with reboxetine reduced kinase activation in a concentration-dependent manner. The short-term inhibitory effect of reboxetine suggests that kinase up-regulation during antidepressant drug treatment is an adaptive response compensating for initial functional down-regulation.

Method for quantitative in situ hybridization histochemistry and image analysis applied for Homer1a gene expression in rat brain

Here we describe the detailed method for quantitative in situ hybridization histochemistry adopted in our previously published short communication on differential gene expression of the postsynaptic density proteins Homer and PSD-95 in rat forebrain after acute treatment with antipsychotic drugs [de Bartolomeis et al., Mol. Brain Res. 98 (2002) 124-129]. Specific 35S radiolabeled oligodeoxyribonucleotides were used to hybridize rat forebrain sections and data analysis was carried out on digitalized images acquired by means of a CCD camera. Special emphasis has been posed on data preprocessing options applied to a dataset obtained using a transparency scanner as an alternative image capturing method.

Selective regulation of presynaptic calcium/calmodulin-dependent protein kinase II by psychotropic drugs

BACKGROUND

Changes in neuroplasticity have been involved in the pathogenesis of psychiatric disorders as well as in psychotropic drug action. Calcium/calmodulin-dependent protein kinase II (CaM kinase II), an enzyme with a pivotal role in synaptic plasticity and cognitive functions, has been implicated in the action of anticonvulsants, benzodiazepines, and antidepressants, but little is known as to its role in the action of different drugs employed for treatment of psychiatric disorders.

METHODS

We studied the function and expression of CaM kinase II following chronic treatment of rats with two antidepressants, fluvoxamine and desipramine, a typical antipsychotic drug, haloperidol, and the typical medication for manic-depressive disorder, lithium.

RESULTS

Antidepressants significantly increased the kinase activity in presynaptic vesicles of frontal/prefrontal cortex. Haloperidol induced no change, whereas lithium significantly decreased the activity. Kinase activation by antidepressants was further demonstrated by increased phosphorylation of exogenously added recombinant synaptotagmin. Immunoreactivity of vesicular kinase (alpha-isoform) was significantly increased by reuptake blockers but not by the two other drugs. Kinetic analysis showed that limiting value of enzymatic velocity (Vmax) of the kinase for substrate was also increased by reuptake blockers and decreased by lithium; however, neither messenger ribonucleic acid nor protein expression level of the kinase was increased in frontal/prefrontal cortex homogenates of antidepressant-treated rats, suggesting the involvement of local synaptic mechanisms.

CONCLUSIONS

These findings show that functional regulation of presynaptic CaM kinase II is selectively affected by different psychotropic drugs, and suggest local synaptic mechanisms for pharmacological regulation of the kinase.

Decreased gene expression of calretinin and ryanodine receptor type 1 in tottering mice

Tottering mice are a spontaneously occurring animal model of human absence epilepsy. They carry a mutation in the P/Q-type calcium channel alpha1A subunit gene which is highly expressed by cerebellar Purkinje cells. In this study, we investigated the role of calretinin and ryanodine receptor type 1 (RyR1) gene expression in the cerebellum of tottering mice. Cerebellar tissue specimens from four experimental groups were processed for in situ hybridization histochemistry (ISHH): (1) wild-type (+/+); (2) heterozygous (tg/+) and two homozygous groups; either (3) without occurrence of an episode of paroxysmal dyskinesia (tg/tg-N); or (4) after an episode of paroxysmal dyskinesia (tg/tg-P) that lasted about 45 min on average. Quantitative analysis showed a statistically significant decrease (p = 0.0001, ANOVA) of calretinin gene expression at the level of the simple lobule of the cerebellum in both homozygous groups compared to the wild-type and heterozygous groups. RyR1 was decreased in the flocculus of the cerebellum in both the tg/tg-N and tg/tg-P groups compared to wild type (p = 0.0174, ANOVA). These results suggest that calretinin gene expression, as well as other genes involved in regulation of calcium homeostasis, such as RyR1, may play a role in the biochemical functional alterations present in tottering mice.

Immediate-early gene expression in concurrent prenatal ethanol- and/or cocaine-exposed rat pups: intrauterine differences in cocaine levels and Fos expression

Concurrent use of cocaine and ethanol is a common mode of abuse. Cocaine and ethanol have distinctive pharmacologies but both have been shown to cause uterine vasoconstriction and fetal hypoxia. We developed a paradigm of chronic ethanol exposure via liquid diet coupled with binge cocaine exposure on the last day of gestation. Lipton et al. demonstrated unequal segregation of cocaine in rat fetuses as a function of proximal-distal location in the uterus, indicating a differential vasoconstriction of the two main arteries supplying the uterus in rats receiving cocaine. By performing C-sections after exposure to cocaine, we were able to measure the cocaine content and immediate-early gene (IEG) induction in the brains of fetuses according to their intrauterine position and assess the potentially vasoconstrictive effect of ethanol. HPLC analysis of fetal brains exposed to cocaine supported the study of Lipton et al.: fetuses from the proximal (lower) end of the uterus had more cocaine than fetuses from the distal (upper) end. Concurrent ethanol decreased the amount of cocaine reaching the fetuses and diminished the proximal-distal gradient. There were increased numbers of Fos-immunoreactive cells in fetuses exposed to both ethanol and cocaine compared to cocaine binge only. Additionally, the gradient of c-fos induction observed as a function of intrauterine position in cocaine-treated rats was in the opposite direction: most distal fetuses generally had the most Fos-immunoreactive cells. These results indicate that IEG induction in fetal brains exposed to cocaine and ethanol may be more related to hypoxic consequences of prenatal drug exposure.

Acute administration of antipsychotics modulates Homer striatal gene expression differentially

Typical and atypical antipsychotics, the mainstay of schizophrenia pharmacotherapy, have been demonstrated to affect differently neuronal gene expression in several preclinical paradigms. Here we report the differential gene expression of the glutamatergic post-synaptic density proteins Homer and PSD-95 in rat forebrain following acute haloperidol or olanzapine treatment. Moreover, considering the extensive interactions between dopaminergic and opioidergic systems we also measured striatal preproenkephalin mRNA. Male Sprague-Dawley rats were treated with haloperidol 1 mg/kg or olanzapine 0.5 mg/kg or vehicle, i.p. and sacrificed 3 h after the injection. Homer gene expression was significantly increased in caudate putamen and nucleus accumbens of rats treated with haloperidol and in the core of accumbens of rats treated with olanzapine. No changes were detected for Homer in prefrontal and parietal cortex in any of the experimental groups. PSD-95 gene expression was not modulated in our paradigm by administration of either typical or atypical antipsychotics. These results (1) suggest a differential modulation of Homer by typical and atypical antipsychotics; (2) confirm that Homer can be induced as an early gene with putative direct effect on neuronal plasticity and (3) demonstrate different response to antipsychotics by different classes of postsynaptic density proteins at glutamatergic synapses.

Attenuation of cocaine-induced genomic and functional responses in prenatal cocaine-exposed rabbits

The effects of in utero cocaine exposure on cocaine-induced genomic and functional responses in postnatal life were examined. Pregnant Dutch Belted rabbits were injected intravenously, twice daily, with cocaine hydrochloride (4 mg/kg) or saline from day 8 through day 29 of pregnancy. Prenatally exposed kits were challenged with cocaine on postnatal day 20. In prenatal saline-exposed kits, cocaine induced time- and dose-dependent c-fos gene expression in both frontal cortex and striatum. Prenatal cocaine exposure reduced cocaine-induced c-fos responses by 35-58% in the frontal cortex and 37-41% in the striatum. Cocaine-induced functional responses that included head bobbing, seizure, and locomotor activity were also attenuated in prenatal cocaine-exposed kits. Cocaine-induced c-fos expression and functional responses were blocked by the D(1) dopamine receptor antagonist, SCH23390, or by the serotonin receptor antagonist, methysergide, but not by the D(2) dopamine receptor antagonist, L-sulpride. The results indicate that in utero cocaine exposure leads to diminished responses to cocaine challenge in the offspring, which may be mediated by prenatal cocaine-induced alterations in one or more components of the D(1) dopamine and/or serotonin receptor signaling systems during early postnatal life.

Gestational exposure to cocaine or pharmacologically related compounds: effects on behavior and striatal dopamine receptors

Gestational cocaine (COC) exposure has been reported to alter behavior and possibly dopamine (DA) receptors. In this paper, we further examined the effects of prenatal COC (40 mg/kg, s.c.) on DA receptor binding and the behavioral response to quinpirole, a DA D2 receptor agonist. In an attempt to elucidate possible mechanisms of such effects, we exposed pregnant dams to specific reuptake blockers; fluoxetine 12.5 mg/kg, a serotonin reuptake blocker; desipramine 10 mg/kg, a norepinephrine reuptake blocker; GBR-12909 10 mg/kg, a DA reuptake blocker; or to a local anesthetic, lidocaine 40 mg/kg. Drugs were administered once daily over gestational days 8-20. Control dams were injected with saline (SAL) or pair-fed to the COC group. Quinpirole challenge was performed in the offspring on post natal day 19. Two pups per litter were injected (s.c.) with 0.03 or 0.09 mg/kg quinpirole-HCl on post-natal day 19. The remaining pups in each litter were sacrificed for analysis of striatal DA receptors. Results showed that only COC exposure altered the behavioral response to the quinpirole challenge by increasing quinpirole-induced stereotypy and motor activity relative to SAL controls. DA receptor analysis showed no alteration in K(D) or B(MAX) for striatal D1 or D2 sites in any group. These results suggest that prenatal COC exposure produces alterations in function of the D2 receptor complex which are not reflected in K(D) or B(MAX) and that these effects are not fully mimicked by exposure to specific monoamine reuptake blockers or a local anesthetic.

Prenatal cocaine exposure increases sensitivity to the attentional effects of the dopamine D1 agonist SKF81297

Sensitivity to the attentional effects of SKF81297, a selective full agonist at dopamine D(1) receptors, was assessed in adult rats exposed to cocaine prenatally (via intravenous injections) and controls. The task assessed the ability of the subjects to monitor an unpredictable light cue of either 300 or 700 msec duration and to maintain performance when presented with olfactory distractors. SKF81297 decreased nose pokes before cue presentation and increased latencies and response biases (the tendency to respond to the same port used on the previous trial), suggesting an effect of SKF81297 on the dopamine (DA) systems responsible for response initiation and selection. The cocaine-exposed (COC) and control animals did not differ in sensitivity to the effects of SKF81297 on these measures. In contrast, the COC animals were significantly more sensitive than were controls to the impairing effect of SKF81297 on omission errors, a measure of sustained attention. This pattern of results provides evidence that prenatal cocaine exposure produces lasting changes in the DA system(s) subserving sustained attention but does not alter the DA system(s) underlying response selection and initiation. These findings also provide support for the role of D(1) receptor activation in attentional functioning.

Repeated prenatal cocaine increases met-enkephalin immunoreactivity in respiratory-related medulla of developing swine

Repeated prenatal exposure to cocaine is associated with attenuated respiratory and arousal responses in infants and piglets. As the normal development of these functions is influenced by medullary opioid systems, the present study explored the possible contribution of the opioid systems to the attenuation induced by cocaine. Methionine-enkephalin (met-enkephalin), an endogenous opioid peptide, was delineated by immunocytochemistry in respiratory- and arousal-related medullary regions of relatively immature (6-7-day-old) and more mature piglets (20-21-day-old). The animals were either unexposed, or exposed prenatally to 2 mg/kg cocaine four times daily administered to the pregnant sows intravenously throughout the last third of gestation. At control, met-enkephalin was found in the neurons, fibers and terminals of the respiratory- and arousal-related medullary regions throughout the age range studied. Prenatal cocaine exposure increased met-enkephalin immunoreactivity in the respiratory-related hypoglossal and solitary tract nuclei of both age groups. These findings support a modulatory role of met-enkephalin in the normal development of respiratory control, and an involvement of this peptide in the attenuation of respiration by repeated prenatal exposure to cocaine.

Prenatal cocaine raises mu-opioid receptor density in piglet cardiorespiratory medulla

Repeated prenatal exposure to cocaine attenuates arousal and cardiorespiratory functions in neonates. This study explored the possible role of brainstem mu- and delta-opioid systems in these effects. Medullary sections were obtained from 6 to 7 (young) and 20 to 21-day-old (older) piglets either unexposed or exposed prenatally to a 2-mg/kg intravenous cocaine hydrochloride dose, injected to the pregnant sow four times a day during the last third of gestation. Mu- and delta-opioid receptor binding was assessed by quantitative autoradiography using, respectively, 125I-DAMGO (Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol) and 125I-DPDPE (Tyr-D-Pen-Gly-pCl-Phe-D-Pen). At control, delta-, but not mu-opioid, receptor density increased with postnatal age. In contrast, cocaine-induced mu-, but not delta-opioid, receptor density increased 1) in the dorsal motor vagal (dmnX) and facial (nF) nuclei, and, at borderline significance level, in the cardiorespiratory-related gigantocellular reticular nucleus (nRG) of the young, and 2) in the spinal trigeminal nucleus and tract (nSp5), and in the cardiorespiratory-related medial solitary tract (nTSm) and lateral reticular (nRL) nuclei of both age groups. These findings support a possible participation of the mu-opioid system in the attenuation of arousal and cardiorespiration after repeated prenatal exposure to cocaine.

Effects of prenatal cocaine exposure on embryonic expression of sonic hedgehog

Cocaine use by pregnant women may adversely affect development and behavior in the exposed infants. Sonic hedgehog (shh) is a secreted protein that induces development of many structures in the embryo, including dopaminergic cells in the ventral midbrain, the limb buds, and eyes. Because prenatal cocaine exposure has been shown to adversely affect the morphogenesis of these and other systems, the present study was undertaken to test the hypothesis that maternal cocaine treatment would alter shh mRNA expression. Cocaine HCl (60 mg/kg i.p.) was administered to pregnant mice on gestational days 6-8, the time that immediately precedes the appearance of shh. Control dams received i.p. saline. Embryos from gestational days 9-11 were examined by in situ hybridization. The temporal and spatial patterns of shh expression were indistinguishable between embryos from cocaine- and saline-treated dams. Examination of forebrain, midbrain, and midbody spinal cord coronal sections failed to reveal any differences in the dorsoventral and mediolateral localization of shh. The distribution of mRNA for patched (ptc), the membrane receptor for shh, was also indistinguishable between both groups. Chick embryos were next used to examine the direct application of cocaine into the developing brain. Shh distribution was similarly unaffected in these chick embryos. These data show that maternal cocaine treatment during early neural tube development does not significantly alter the expression patterns of shh or ptc mRNA. Thus, congenital defects and behavioral abnormalities associated with maternal cocaine use do not appear to result from altered expression of the shh-ptc pathway.

Perinatal cocaine decreases the expression of prodynorphin mRNA in nucleus accumbens shell in the adult rat

Preprodynorphin mRNA expression in the striatal-olfactory tubercle complex was studied in adult rats exposed to cocaine (50 mg/kg) during postnatal days (PnD) 11-20. While multiple regions of the striatum and olfactory tubercle were examined, alterations were only found in the nucleus accumbens. A 50% and 20% reduction in expression within the shell region was observed at 1.2 and 1.7 mm rostral to Bregma respectively. While the core regions at these levels were unaffected, the rostral accumbens showed a trend toward an increase in expression in the cocaine-treated rats. These findings, in combination with other behavioral and neurochemical data collected on similarly treated rats, suggest that perinatal cocaine produces a long-term dampening of function in a specific population of neurons within the mesolimbic system

Cocaine exposure in fetal rhesus monkey: consequences for dopamine D1- and D2-like receptor binding densities

Previously we found that dopamine D1-, D2- and D5-receptor mRNA subtypes are significantly increased in the rostral forebrain of fetal monkeys exposed to cocaine. The purpose of the present study was to determine whether cocaine exposure during gestation also increases dopamine receptor binding densities in the fetal brain. Pregnant monkeys were treated with cocaine (3 mg/kg, i.m., n = 3) or physiological saline (n = 3), 4 times per day from day 22 of pregnancy until day 70. Quantitative receptor autoradiography of dopamine D1-like receptors was performed on day-70 fetal brain sections using [3H]SCH23390. [3H]Spiperone was used to characterize dopamine D2-like receptors. Image analysis of receptor autoradiograms revealed a high-density dopamine D1-like receptor binding in the striatum, nucleus accumbens (ACB) and the substantia nigra (SN), whereas lower binding densities were observed in the frontal cortex and the habenula (Hb). Dopamine D2-like receptor binding was also found in the frontal cortex, striatum and ACB, but was not detected in the Hb or SN. The pattern of dopamine receptor distribution was the same in both control and cocaine-treated animals. However, there was a significant increase in the density of sites for D1-like receptors in the striatum (P < 0.05) and SN (P < 0.01) and for D2-like receptors in the striatum (P < 0.01) of cocaine-treated animals versus saline-treated controls. These findings suggest that D1- and D2-like receptors are present in dopamine target neurons, whereas D2-like autoreceptors can not be detected in day-70 fetal monkey midbrain. The present results provide further support for the hypothesis that gestational cocaine exposure causes reduced synthesis and release of dopamine which leads to dopamine D1- and D2-receptor up-regulation in dopamine target neurons.

Simian virus-40 large-T antigen binds p53 in human mesotheliomas

We found that simian virus 40 (SV40) induces mesotheliomas in hamsters and that 60% of human mesotheliomas contain and express SV40 sequences, results now confirmed by others [ref. 3-5, and presentations by D. Griffiths & R. Weiss, F. Galateau-SallE, and H.I.P. at "Simian virus 40: A possible human polyoma virus," NIH workshop, 27-28 January 1997, Bethesda, MD (transcript available through SAG Corp., Washington, DC 20008)]. Mesothelioma, an aggressive malignancy resistant to therapy, originates from the serosal lining of the pleural, pericardial and peritoneal cavities. The incidence of mesothelioma continues to increase worldwide because of exposure to crocidolite asbestos. However, at least 20% of mesotheliomas in the United States are not associated with asbestos exposure, and only a minority of people exposed to high concentrations of asbestos develop mesothelioma. Thus, other carcinogens may induce mesothelioma in individuals not exposed to asbestos, and/or may render particular individuals more susceptible to the carcinogenic effect of asbestos. We investigated whether the expression of the SV40 large T-antigen (Tag) interferes with the normal expression of the tumor suppressor gene p53 in human mesotheliomas. We found that SV40 Tag retains its ability to bind and to inactivate p53, a cellular protein that when normally expressed plays an important role in suppressing tumor growth and in inducing sensitivity to therapy. Our findings do not establish a cause-and-effect relation, but indicate that the possibility that SV40 contributes to the development of human mesotheliomas should be carefully investigated.

Opioidergic and dopaminergic gene expression in the caudate-putamen and accumbens of the mutant mouse, tottering (tg/tg)

Expression of preproenkephalin, dynorphin and D2 dopamine receptor mRNAs was examined in selected regions of the forebrain of homozygous and heterozygous tottering mice, using in situ hybridization histochemistry. Homozygous tottering mice carry an autosomal recessive mutation causing them to exhibit petit mal-like epilepsy. Preproenkephalin mRNA levels were significantly higher in the lateral caudate and the core of the nucleus accumbens of homozygous tottering mice compared to wild-type controls. No differences were observed in the expression of dynorphin and D2 receptor mRNA distribution in brain regions examined in the mutant mice as compared to wild-type controls.

The neurobiology of social play behavior in rats

Social play behavior is one of the earliest forms of non-mother-directed social behavior appearing in ontogeny in mammalian species. During the last century, there has been a lot of debate on the significance of social play behavior, but behavioral studies have indicated that social play behavior is a separate and relevant category of behavior. The present review provides a comprehensive survey of studies on the neurobiology of social play behavior. Evidence is presented that opioid and dopamine systems play a role in the reward aspect of social play behavior. The role of cholinergic, noradrenergic and opioid systems in attentional processes underlying the generation of social play behavior and the involvement of androgens in the sexual differentiation of social play behavior in rats is summarized. It is concluded that there is not only behavioral, but also neurobiological evidence to suggest that social play behavior represents a separate category of behavior, instead of a precursor for adult social, sexual or aggressive behavior.

Monoamine transporters and the neurobehavioral teratology of cocaine

Prenatal cocaine exposure has been associated with various postnatal behavioral abnormalities in human infants, and also with changes in locomotor activity, learning deficits, and altered responses to drug challenge in nonhuman offspring. Several studies have further demonstrated that cocaine exerts an activating effect on fetal behavior. A variety of mechanisms have been proposed to account for the neurobehavioral teratogenic effects of developmental cocaine treatment, including inhibition of fetal brain neurotransmitter uptake and fetal hypoxemia secondary to constriction of the uteroplacental vascular bed. In support of the hypothesis that cocaine effects may be mediated partly by monoamine uptake inhibition, we and other investigators have recently demonstrated the presence of functional dopamine (DA), serotonin (5-HT), and norepinephrine (NE) transporters in the fetal rat brain. Transporter-related cocaine recognition sites are found in a number of fetal brain areas and could mediate the acute effects of cocaine on these areas as well as developmental changes that are manifested postnatally. For example, DA transporter blockade may underlie the above-mentioned activational effects of cocaine on fetal behavior. Time-dependent changes in DA or 5-HT transporter expression produced by prenatal cocaine exposure could likewise play an important role in some of the behavioral effects observed when offspring are tested postnatally.

Effects of in utero cocaine exposure on the expression of mRNAS encoding the dopamine transporter and the D1, D2 and D5 dopamine receptor subtypes in fetal rhesus monkey

The effects of in utero cocaine exposure on the development of the mRNAs encoding the dopamine transporter (DAT) and the D1, D2 and D5 dopamine receptor subtypes were determined in fetal monkey brains at day 45 and day 60 of gestation. Pregnant monkeys were treated with cocaine 3 mg/kg or saline i.m., four times a day from day 18 of gestation until the pregnancy was terminated at day 45 or day 60. The fetal brains were dissected, and tissue RNA extracted and quantified using ribonuclease protection assay analysis. In day 45 fetal monkeys, dopamine D1 and D2 receptor subtype mRNAs and DAT mRNA were found in low quantities both in control and cocaine-treated subjects. In day 60 fetal monkeys, D1 receptor mRNA levels were highest in the frontal cortex/striatal area, and low to moderate quantities were found in diencephalic and mesencephalic fetal brain regions. Dopamine D2 receptor mRNA levels were highest in the frontal cortex/striatal area, diencephalon and the midbrain, moderate in the brainstem and low in the caudal temporal lobe and surrounding cortical areas. Dopamine D5 receptor mRNA was expressed in low quantities throughout the day 60 fetal monkey brain, whereas DAT mRNA was found in the midbrain only. In utero cocaine exposure caused a significant increase in dopamine D1, D2 and D5 receptor subtype mRNAs in the frontal cortex/striatal area of day 60 fetal monkeys. These results support the hypothesis that dopamine synthesis and release may be reduced in cocaine-treated fetuses, which results in dopamine receptor up-regulation.

Cocaine alters glutamic acid decarboxylase differentially in the nucleus accumbens core and shell

The effects of acute and repeated daily cocaine on the levels of mRNA coding for glutamic acid decarboxylase (GAD), preproenkephalin (PPE), preprotachykinin (PPT), and the dopamine D2 receptor were determined in the striatum, nucleus accumbens core and shell areas (NAcore, NAshell), and medial prefrontal cortex. Rats were given repeated saline or cocaine for 6 days. A cocaine challenge administered 24 h later resulted in an augmented locomotor response in daily cocaine-pretreated rats. Six h after the challenge, rats were sacrificed and Northern blot analysis revealed that acute cocaine increased GAD mRNA levels by 44% in the NAshell, while repeated cocaine prevented the acute cocaine-induced increase. These data suggest that cocaine may differentially regulate GABA release at NA core and shell projection fields.