Effects of prenatal cocaine exposure upon postnatal development of neostriatal dopaminergic function

Pregnant rats were injected twice daily with 20 mg/kg cocaine (or saline) from gestational day 10 to parturition. Brains from offspring were examined with quantitative receptor autoradiography [D1 receptor (D1R), D2 receptor (D2R) and dopamine transporter (DAT)] and quantitative in situ hybridization [D1R mRNA, D2R mRNA, preproenkephalin (PPE) mRNA] for markers of neostriatal dopaminergic function. Prenatal cocaine exposure did not alter postnatal development of striatal D1R sites, but D1R mRNA levels were reduced by a third at days 14 and 35. D2R sites were increased over control in lateral striatum by day 6, and remained elevated through postnatal day 35. Total D2R mRNA was increased over control in both medial and lateral striatum at 7 and 14 days but was equal to control at 35 days. Prenatal cocaine exposure increased DAT density at postnatal days 1 through 5, but reduced it at days 14 and 35; PPE mRNA expression was reduced at days 7, 14 and 35. Many of these results are similar to those found in experimental animals and humans following cocaine withdrawal. © 1994 Wiley-Liss, Inc.     

Alterations in the dopaminergic receptor system after chronic administration of cocaine

Several studies suggest that one of the most important factors contributing to cocaine dependence is an alteration in the actions of the neurotransmitter dopamine in the central nervous system. In order to understand some of the neuroreceptor consequences of cocaine administration, groups of rats were injected with cocaine (2 daily doses of 15 mg/kg) for 1 to 21 days. Binding of [³H]cocaine, [³H]SCH23390, [³H]raclopride, and [³H]BTCP in striatal and cortical tissue from the treated animals was compared to controls. [³H]Cocaine binding was increased by the drug in the striatum and cortex at days 14 and 21, respectively. The binding of [³H]SCH23390 to D₁ dopamine receptors was significantly increased at day 3 of cocaine exposure. In striatal membranes, [³H]BTCP binding to dopamine uptake sites was significantly increased after day 7, whereas binding in cortical membranes was increased from day 1. [³H]Raclopride binding to D₂ dopamine receptors remained unchanged throughout the study in both cortical and striatal tissues. These results indicate that repeated exposure to cocaine produces an upregulation (possible supersensitivity) in cortical D₁, cocaine, and DA-uptake sites which occurs in a time-dependent manner. These increases are coupled with an upregulation in striatal D₁, cocaine, and DA-uptake sites, without simultaneous changes in D₂ receptors. Thus, cocaine's effects are not uniformly distributed across all brain regions, but rather are focused within areas of the dopamine system. © 1993 Wiley-Liss, Inc.     

Chronic cocaine alters brain mu opioid receptors

The possibility that dopamine may modulate the expression of opioid receptors was investigated by determining the effects of chronic cocaine administration on the density of μ opioid receptors. Quantitative in vitro autoradiography with the highly selective μ opioid ligand [³H]DAMGO was used to measure and localize changes in μ opioid receptors in the brains of rats administered cocaine or saline three times daily for 14 days. Significant increases in [³H]DAMGO binding were measured in areas of the cingulate cortex, nucleus accumbens, caudate putamen, and basolateral amygdaloid nucleus of the cocaine-treated animals. These results demonstrate that μ opioid receptors undergo upregulation in response to chronic cocaine exposure and suggest that dopamine activity can regulate the expression of μ opioid receptors.     

Opioid receptor changes in weaver mouse striatum

The dopaminergic projection from the substantia nigra to the patch and matrix compartments of the caudate-putamen undergoes a spontaneous, early postnatal degeneration in mice which carry the weaver gene. The projection to nucleus accumbens is relatively spared. Dopaminergic afferents have been shown to be important modulators of striatal opioid receptor expression. In the present study, opioid receptor localization in the caudate-putamen and nucleus accumbens of control and weaver mice was examined by quantitative autoradiography. Mu, delta and kappa opioid receptors were differentially distributed in nucleus accumbens and in patch and matrix compartments of the caudate-putamen. In animals which were homozygous for the weaver gene, the density of mu opioid receptors in both patch and matrix compartments was unchanged with respect to control mice. In contrast, the density of delta and kappa opioid receptors was significantly decreased in weaver caudate-putamen and nucleus accumbens. The significance of these results with respect to opioid receptor expression and Parkinson's disease is discussed.     

Localization of the mRNA for the 5-HT2 receptor by in situ hybridization histochemistry. Correlation with the distribution of receptor sites

³²P-labelled oligonucleotides complementary to rat 5-HT₂ receptor mRNA were used as probes to study the distribution of cells in rat brain containing the mRNA coding for this receptor by in situ hybridization histochemistry. 5-HT₂ receptor binding sites were visualized by autoradiography using [¹²⁵I]DOI as ligand. Both distributions were comparable, demonstrating that 5-HT₂ receptors are expressed by cells intrinsic to the neocortex (lamina Va), claustrum, olfactory bulb and several nuclei of the brainstem.     

Mapping of somatostatin receptor localization in rat brain: Forebrain and diencephalon

Using quantitative in vitro receptor autoradiography, minute distributions of 125I-Tyr11-somatostatin (SS)-14 binding sites were investigated in the rat forebrain and diencephalon. In the cerebral cortex, there was a high density of receptors observed in layers V-VI and a low density in layers I-IV. The entorhinal cortex displayed the highest receptor density of the cerebral cortices. The olfactory system had a high SS receptor density. The anterior olfactory nucleus, nucleus of the lateral olfactory tract, medial habenular nucleus and the basolateral amygdaloid nucleus showed moderate densities. In the limbic system, the CA1 and subiculum regions had high receptor densities. More detailed observations revealed high receptor densities in the oriens, radiatum and lacunosum layers and a much lower density in the pyramidal cell layer. The caudate putamen and substantia nigra showed low receptor densities, while the claustrum displayed the highest density of receptors in the rat brain. These data were not consistent with those of previous studies using 125I-SS-28 and 125I-201-995, which had shown that the high receptor density area in the basolateral amygdaloid group was identified as the lateral amygdaloid nucleus, and that the pyramidal cell layer in the hippocampus showed high receptor densities.     

Cocaine-induced sex differences in D1 receptor activation and binding levels after acute cocaine administration

Although it is established that female rats have a more robust behavioral response to acute cocaine administration than male rats, the neurobiological mechanisms underlying these differences remain unclear. The purpose of the present study was to determine whether dopamine (DA) receptor activation influences sex differences in cocaine-induced behaviors. A second study was performed to determine sex differences in D1/D2 receptor levels prior to and post-cocaine administration. Male and female Fischer rats were pre-treated with the D1 antagonist SCH-23390 (0.05, 0.1, and 0.25 mg/kg, i.p.), the D2 antagonist eticlopride (0.03, 0.1 mg/kg, i.p.), or vehicle (saline) 15 min before acute cocaine (20 mg/kg, i.p.) or saline administration. Cocaine-induced ambulatory and rearing activity was greater in female than male rats. Pre-treatment with SCH-23390 affected cocaine-induced ambulatory, rearing, and stereotypic activity in a sex-dependent manner; cocaine-induced ambulatory and stereotypic behavior in female rats was reduced by the lowest dose of SCH-23390. Eticlopride did not alter behavioral responses to cocaine in male or female rats. These results suggest that in both male and female rats, activation of the D1, but not the D2, receptor modulates cocaine's motor effects. There were no sex differences in baseline levels of D1, D2, and DA transporter binding in the caudate putamen (CPu) and the nucleus accumbens (NAc). Cocaine administration reduced D1 binding levels in the CPu only in male rats. Our findings suggest that the regulation of striatal D1 binding levels after acute cocaine administration is a sexually dimorphic process. We also hypothesize that the greater sensitivity to D1 receptor blockade in female rats, as compared to male rats, may contribute to their overall increased hyperactivity in response to acute cocaine. Taken together, the D1 receptor may be an important substrate in the regulation of sex differences to cocaine-induced locomotor activity.     

Lack of long-term monoamine depletions following repeated or continuous exposure to cocaine

Cocaine was administered to rats for prolonged periods either by repeated injections (10 mg/kg twice daily for 10 days and 12.5 mg/kg 8 times daily for 10 days) or by continuous intravenous infusion (100 mg/kg/day for 21 days). None of the regimens produced long-lasting depletions of dopamine (DA), serotonin (5-HT), or major metabolites in striatum, hippocampus, hypothalamus, or somatosensory cortex. These results suggest that prolonged exposure to cocaine does not produce neurotoxicity like that observed with d-amphetamine or d-methylamphetamine.     

Length of continuous cocaine exposure determines the persistence of muscarinic and benzodiazepine receptor alterations

The effects of varied durations of cocaine (1, 3 or 5 days) on muscarinic (MSC) and benzodiazepine (BZD) binding sites in striatum and hippocampus were investigated using homogenate receptor binding. The progressive alterations in these receptor sites from a 5 day cocaine administration were also examined 12 h, 2 days or 21 days after drug exposure. Neither a one nor a three day exposure to cocaine produced any long-term alteration in BZD binding in either structure whereas a 5 day administration produced significant increases in binding. Decreases in MSC receptor binding were apparent in striatum from either a 3 or 5 day cocaine exposure and in hippocampus from a 5 day exposure. The 5 day cocaine exposure produced immediate increases in striatal and hippocampal BZD binding which persisted for 21 days. Conversely, 5 days of cocaine produced a short-term increase in MSC receptor binding im both structures which then became significantly decreased 21 days later. Based on the divergent pattern of changes in BZD and MSC receptor types over time in these structures, it appears that cocaine may induce such changes via separate mechanisms. In addition, it is apparent that changes in the numbers of these receptor sites after cocaine exposure can be quite dynamic, changing rapidly over time.     

Behavioral responses to cocaine and amphetamine administration in mice lacking the dopamine D1 receptor

Cocaine and amphetamine can induce both short-term and long-term behavioral changes in rodents. The major target for these psychostimulants is thought to be the brain dopamine system. To determine whether the dopamine D1 receptor plays a crucial role in the behavioral effects of psychostimulants, we tested both the locomotor and stereotyped behaviors in D1 receptor mutant and wild-type control mice after cocaine and amphetamine treatments. We found that the overall locomotor responses of D1 receptor mutant mice to repeated cocaine administration were significantly reduced compared to those of the wild-type mice and the responses of the D1 receptor mutant mice to cocaine injections were never significantly higher than their responses to saline injections. D1 receptor mutant mice were less sensitive than the wild-type mice to acute amphetamine stimulation over a dose range even though they exhibited apparently similar behavioral responses as those of the wild-type mice after repeated amphetamine administration at the 5 mg/kg dose. Immunostaining experiments indicated that there was no detectable neurotoxicity in the nucleus accumbens in both D1 receptor mutant and wild-type mice after repeated amphetamine administration. The data suggest that the D1 receptor plays an essential role in mediating cocaine-induced behavioral changes in mice. Moreover, the D1 receptor also participates in behavioral responses induced by amphetamine administration.     

Microanatomical localization of dopamine receptor protein immunoreactivity in the rat cerebellar cortex

Dopamine (DA) receptor subtype localization was investigated in rat cerebellar cortex using immunohistochemical techniques with antibodies raised against D1-D5 receptor protein. A faint D1 receptor protein immunoreactivity was developed in molecular and Purkinje neurons layers. D2 receptor protein immunoreactivity was found primarily in cerebellar white matter followed by molecular and granular layers and Purkinje neurons. Antibodies against D2S receptor protein were localized in molecular layer and to a lesser extent, in granular layer. A few Purkinje neurons displayed a faint D2S receptor protein immunoreactivity. D3 receptor protein immunoreactivity was observed primarily in molecular and in Purkinje neurons layers of lobules 9 and 10. A faint D3 receptor protein immunoreactivity was also localized in Purkinje neurons and to a lesser extent, in molecular and granular layers of cerebellar lobules 1-8. D4 receptor protein immunoreactivity was found in cerebellar white matter. A pale immunostaining was also visualized in molecular layer. D5 receptor protein immunoreactivity was localized primarily in molecular and Purkinje neurons layers and to a lesser extent, in granular layer and in white matter. The above results indicate that rat cerebellar cortex expresses the DA receptor subtypes so far identified. Purkinje neurons, which are the only efferent neurons of cerebellum, are richest in DA receptor protein immunoreactivity. This suggests that dopaminergic neurotransmission may modulate efferent inputs from cerebellum. The localization of the majority of D2 and D4 and of a faint D5 protein receptor immunoreactivity in cerebellar white matter suggests that these receptors may be presynaptic and transported axonally.     

Use of positron emission tomography to measure the effects of nalmefene on D1 and D2 dopamine receptors in rat brain

Positron emission tomography (PET) has been used in humans and in non-human primates to image and measure radioligand binding to neuroreceptors. The present study evaluated the feasibility of performing high-resolution PET experiments in a rodent model to measure receptor kinetics. The effects of acute and chronic administration of the opioid antagonist, nalmefene, on the binding activity of [¹¹C]SCH23390 and [¹¹C]N-methylspiperone at D₁ and D₂ dopamine receptors, respectively, was investigated in the rat. The interaction between central opioid and dopaminergic systems has been the focus of much attention due to their interactive role in mediating reinforcement and locomotor activity. In the present study, adult male Sprague–Dawley rats received either a single injection of 10 mg/kg of nalmefene or control vehicle solution 1 h prior to the PET scan or were chronically administered 10 mg/kg/day of nalmefene or vehicle for 7 days by an osmotic minipump. Following acute administration of nalmefene, the binding potential of [¹¹C]SCH23390 in the striatum was significantly increased. No changes in [¹¹C]N-methylspiperone binding were found. Following chronic nalmefene administration, no significant change in either [¹¹C]SCH23390 binding potential or [¹¹C]N-methylspiperone binding was detected. These results suggest that nalmefene administration produces transient changes in the binding potential of D₁-receptors in the striatum that are normalized after 1 week of steady-state administration.     

Effects of chronic treatment with selective agonists on the subtypes of dopamine receptors

The effects of chronic administration of selective dopaminergic agonists on D1 and D2 receptor density, affinity and function were measured in Sprague-Dawley rats. Animals received daily injections (i.p.) of the D1-selective agonist SKF-38393 (10 mg/kg), the D2-selective agonist quinpirole (1 mg/kg), SKF-38393 plus quinpirole, or saline for 14 days. Quantitative autoradiographic analysis revealed that the density of D2 receptors was decreased following chronic treatment with quinpirole alone or in combination with SKF-38393 whereas SKF-38393 by itself had no effect on this receptor. In contrast, the density of D1 receptors was increased following treatment with SKF-38393. Although quinpirole by itself had no effect on D1 receptors, co-administration with SKF-38393 attenuated the up-regulation of D1 receptors produced by SKF-38393 in the caudate-putamen and nucleus accumbens but not in the substantia nigra. The up-regulation of D1 receptors in response to chronic SKF-38393 may be attributed to the partial agonist properties of SKF-38393 which may not provide sufficient D1 receptor stimulation to down-regulate the receptor. Quinpirole-induced hypothermia and SKF-38393-induced hyperthermia were measured before and after chronic agonist treatments to examine the effects of these treatments on thermoregulatory functions mediated by each receptor subtype. Treatment with quinpirole or quinpirole plus SKF-38393 resulted in desensitization of quinpirole-induced hypothermia, whereas treatment with SKF-38393 alone had no effect. All of the chronic treatments produced sensitization of SKF-38393-induced hyperthermia. Since not all treatments result in an increase in the density of D1 receptors, up-regulation of D1 receptors is not the sole mechanism for this sensitization.     

The dopamine D-1 receptor antagonist SCH 23390 injected into the dorsolateral bed nucleus of the stria terminalis decreased cocaine reinforcement in the rat

The effects of bilateral intracranial injections of the D-1 dopamine receptor antagonist SCH 23390 HCl (0, 0.8, 1.6, 3.2, and 6.4 μg total bilateral dose) administered into the dorsolateral bed nucleus of the stria terminalis (dlBNST) immediately prior to a 3 h intravenous cocaine self-administration session were examined. In addition, anatomical control injections of the most effective dose of SCH 23390 HCl (6.4 μg) were made either 1.5 mm dorsal to the dlBNST or into the lateral ventricle. Injections directly into the dlBNST, but not those dorsal to the dlBNST or into the lateral ventricle, significantly increased the rate of cocaine self-administration within the first 20 min of the self-administration session, consistent with a partial attenuation of the reinforcing effects of cocaine under a fixed-ratio schedule of reinforcement (0.25 mg cocaine iv; fixed-ratio 5, timeout 20 s). Injections into all three sites increased cocaine self-administration across the entire 3 h session. These results suggest a role for D-1 dopamine receptors in the dlBNST in the reinforcing properties of self-administered cocaine, and also support the hypothesis that D-1 dopamine receptors in the ‘extended amygdala' may play a significant role in cocaine self-administration.     

Demon voltammetry and analysis software: analysis of cocaine-induced alterations in dopamine signaling using multiple kinetic measures

The fast sampling rates of fast scan cyclic voltammetry make it a favorable method for measuring changes in brain monoamine release and uptake kinetics in slice, anesthetized, and freely moving preparations. The most common analysis technique for evaluating changes in dopamine signaling uses well-established Michaelis-Menten kinetic methods that can accurately model dopamine release and uptake parameters across multiple experimental conditions. Nevertheless, over the years, many researchers have turned to other measures to estimate changes in dopamine release and uptake, yet to our knowledge no systematic comparison amongst these measures has been conducted. To address this lack of uniformity in kinetic analyses, we have created the Demon Voltammetry and Analysis software suite, which is freely available to academic and non-profit institutions. Here we present an explanation of the Demon Voltammetry acquisition and analysis features, and demonstrate its utility for acquiring voltammetric data under in vitro, in vivo anesthetized, and freely moving conditions. Additionally, the software was used to compare the sensitivity of multiple kinetic measures of release and uptake to cocaine-induced changes in electrically evoked dopamine efflux in nucleus accumbens core slices. Specifically, we examined and compared tau, full width at half height, half-life, T₂₀, T₈₀, slope, peak height, calibrated peak dopamine concentration, and area under the curve to the well-characterized Michaelis-Menten parameters, dopamine per pulse, maximal uptake rate, and apparent affinity. Based on observed results we recommend tau for measuring dopamine uptake and calibrated peak dopamine concentration for measuring dopamine release.     

Effects of chronic treatment with selective and nonselective antagonists on the subtypes of dopamine receptors

The effects of chronic blockade of D-1, D-2, or both subtypes of dopamine receptors on the densities and properties of the D-1 and D-2 subtypes of dopamine receptors were measured in rat brain. Animals were treated with 14 daily injections (i.p.) of the D-1-selective antagonist SCH-23390, the D-2-selective antagonist sulpiride, the nonselective antagonist fluphenazine, or vehicle. Serial 32-microns horizontal sections that included the caudate putamen were cut and alternately assigned to assays for D-1 or D-2 receptors. D-1 receptors were labeled with 3H-SKF-83566 or 3H-SCH-23390, and D-2 receptors were labeled with 3H-spiroperidol. Scatchard analysis was performed on the saturation data measured in the head of the caudate putamen to obtain estimates of receptor density. As expected, administration of the D-1-selective ligand SCH-23390 resulted in an increase in the density of D-1 receptors by approximately 47% and had no significant effect on the density of D-2 receptors. Similarly, administration of the D-2-selective ligand sulpiride resulted in an increase in the density of D-2 receptors by 25% and had no significant effect on the density of D-1 receptors. Thus the subtypes of dopamine receptors appear to be independently regulated after selective blockade. In contrast to the effects observed with selective antagonists, the results obtained with fluphenazine were more complex. Administration of the relatively nonselective antagonist fluphenazine resulted in an increase in the density of D-2 receptors by 51% but had no significant effect on the density of D-1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

The expanding effects of cocaine: studies in a nonhuman primate model of cocaine self-administration

Although neuroimaging investigations in human cocaine abusers have provided important insights into the brain changes that accompany drug use, the interpretation of reports in human abusers can be very difficult. Studies in nonhuman primates provide a way to systematically evaluate the structural and functional adaptations engendered by cocaine self-administration without the confounds of human research. Functional activity, measured with metabolic mapping methods, and markers of the dopamine system, assessed autoradiographically, were evaluated over the course of chronic cocaine self-administration (5 days, 3.3 months, and 15–22 months). Within the striatum the topography of these responses shifts dramatically over time. Changes in functional activity and alterations in the dopamine system occupy larger and larger portions of dorsal and ventral striatum with increasing durations of cocaine exposure. The growing impact of cocaine suggests that the elements of the behavioral repertoire outside of the influence of cocaine become smaller and smaller with increasing durations of exposure to drug use resulting in cocaine's dominance over all aspects of the addict's life.     

Somatostatin receptors increase in the olfactory bulb of developing pups after perinatal exposure to cocaine

The effects of chronic prenatal and/or postnatal exposure to cocaine on somatostatin concentration and receptors were studied in the olfactory bulbs of rat pups at birth and at 15 days old. Wistar rats were injected subcutaneously with single daily doses of 40 mg cocaine hydrochloride/kg from days 7 to 19 of gestation, from day 7 of gestation to day 15 postpartum or from parturation to day 15 postpartum. Fetal exposure to cocaine decreased SS concentrations in the olfactory bulb of the newborn pups while prenatal-plus-postnatal exposure increased this parameter. Administration of cocaine only during lactation did not induce any change. Exposure during gestation or during nursing induced an increase in the total number of somatostatin receptors and a decrease in the affinity constant in the olfactory bulb of newborn and 15-day-old pups. These results suggest that the development of somatostatin receptors in the olfactory bulb can be altered by prenatal and/or nursing period exposure to cocaine.