DAT isn't all that: cocaine reward and reinforcement require Toll-like receptor 4 signaling.

The initial reinforcing properties of drugs of abuse, such as cocaine, are largely attributed to their ability to activate the mesolimbic dopamine system. Resulting increases in extracellular dopamine in the nucleus accumbens (NAc) are traditionally thought to result from cocaine's ability to block dopamine transporters (DATs). Here we demonstrate that cocaine also interacts with the immunosurveillance receptor complex, Toll-like receptor 4 (TLR4), on microglial cells to initiate central innate immune signaling. Disruption of cocaine signaling at TLR4 suppresses cocaine-induced extracellular dopamine in the NAc, as well as cocaine conditioned place preference and cocaine self-administration. These results provide a novel understanding of the neurobiological mechanisms underlying cocaine reward/reinforcement that includes a critical role for central immune signaling, and offer a new target for medication development for cocaine abuse treatment.

Administration of ziprasidone for 10 days increases cocaine toxicity in mice.

Long-term treatment with antipsychotic medications alters the regional density of several of the neurotransmitter receptors that mediate cocaine toxicity. However, the effect of either up- or down-regulation of the neurotransmitter receptors on cocaine toxicity is unknown. In this study, we determined if subacute administration of the atypical antipsychotic ziprasidone altered the toxic effects of cocaine in mice. Ziprasidone (4 mg/kg) or placebo was administered to the first two groups of CF-1 mice for 10 days and, then on day 10, an estimated LD50 dose of cocaine (102 mg/kg) was given to these mice. In a third group, in order to produce a ziprasidone withdrawal state, we administered ziprasidone for 10 days, followed by no treatment for 2 days before cocaine administration. There was no significant difference among the three groups in overall survival: 63% in the treatment group, 60% in the withdrawal group, and 80% in the placebo group. Survival time was significantly shorter for the withdrawal group than for the control group. Our study may have been limited by lower than expected serum ziprasidone concentrations and lower than expected lethality from cocaine. However, our findings suggest that administration of an atypical antipsychotic for 10 days may increase the toxic effects of cocaine.

Chronic and acute regulation of Na+/Cl- -dependent neurotransmitter transporters: drugs, substrates, presynaptic receptors, and signaling systems.

Na+/Cl- -dependent neurotransmitter transporters, which constitute a gene superfamily, are crucial for limiting neurotransmitter activity. Thus, it is critical to understand their regulation. This review focuses primarily on the norepinephrine transporter, the dopamine transporter, the serotonin transporter, and the gamma-aminobutyric acid transporter GAT1. Chronic administration of drugs that alter neurotransmitter release or inhibit transporter activity can produce persistent compensatory changes in brain transporter number and activity. However, regulation has not been universally observed. Transient alterations in norepinephrine transporter, dopamine transporter, serotonin transporter, and GAT1 function and/or number occur in response to more acute manipulations, including membrane potential changes, substrate exposure, ethanol exposure, and presynaptic receptor activation/inhibition. In many cases, acute regulation has been shown to result from a rapid redistribution of the transporter between the cell surface and intracellular sites. Second messenger systems involved in this rapid regulation include protein kinases and phosphatases, of which protein kinase C has been the best characterized. These signaling systems share the common characteristic of altering maximal transport velocity and/or cell surface expression, consistent with regulation of transporter trafficking. Although less well characterized, arachidonic acid, reactive oxygen species, and nitric oxide also alter transporter function. In addition to post-translational modifications, cytoskeleton interactions and transporter oligomerization regulate transporter activity and trafficking. Furthermore, promoter regions involved in transporter transcriptional regulation have begun to be identified. Together, these findings suggest that Na+/Cl- -dependent neurotransmitter transporters are regulated both long-term and in a more dynamic manner, thereby providing several distinct mechanisms for altering synaptic neurotransmitter concentrations and neurotransmission.

Differences in bingeing behavior and cocaine reward following intermittent access to sucrose, glucose or fructose solutions.

Daily intermittent access to sugar solutions results in intense bouts of sugar intake (i.e. bingeing) in rats. Bingeing on sucrose, a disaccharide of glucose and fructose, has been associated with a "primed" mesolimbic dopamine (DA) pathway. Recent studies suggest glucose and fructose engage brain reward and energy-sensing mechanisms in opposing ways and may drive sucrose intake through unique neuronal circuits. Here, we examined in male Sprague-Dawley rats whether or not (1) intermittent access to isocaloric solutions of sucrose, glucose or fructose results in distinctive sugar-bingeing profiles and (2) previous sugar bingeing alters cocaine locomotor activation and/or reward, as determined by conditioned place preference (CPP). To encourage bingeing, rats were given 24-h access to water and 12-h-intermittent access to chow plus an intermittent bottle that contained water (control) or 8% solutions of sucrose, glucose or fructose for 9days, followed by ad libitum chow diet and a 10-day cocaine (15mg/kg; i.p.) CPP paradigm. By day 4 of the sugar-bingeing diet, sugar bingeing in the fructose group surpassed the glucose group, with the sucrose group being intermediate. All three sugar groups had similar chow and water intake throughout the diet. In contrast, controls exhibited chow bingeing by day 5 without altering water intake. Similar magnitudes of cocaine CPP were observed in rats with a history of sucrose, fructose or chow (control) bingeing. Notably, the glucose-bingeing rats did not demonstrate a significant cocaine CPP despite showing similar cocaine-induced locomotor activity as the other diet groups. Overall, these results show that fructose and glucose, the monosaccharide components of sucrose, produce divergent degrees of bingeing and cocaine reward.

Quantitative autoradiographic analysis of 125I-pindolol binding in Fischer 344 rat brain: changes in beta-adrenergic receptor density with aging.

Age-related changes in beta-adrenergic receptor density in Fischer 344 rat brain were examined using in vitro 125I-pindolol (IPIN) binding and quantitative autoradiographic analysis. Localized protein concentrations were determined using a new quantitative histological technique, and these were used to normalize the densities of receptors. Saturation binding studies in brain sections revealed 40-50% decreases in beta-adrenergic receptor density in the thalamus of 23-25-month-old and the cerebellum and brainstem of both 18-19-month-old and 23-25-month-old compared to 4-6-month-old rats. The loss of cerebellar beta-adrenergic receptors may be correlated with reports of deficits in sensitivity to beta-adrenergic-mediated transmission in the cerebellum of aged rats. No changes in specific IPIN binding with age were observed in rat cortex or hippocampus. In all areas examined no age-related differences were observed in receptor affinity. No changes in protein concentration were found in any of the areas examined in the different aged animals. These results demonstrate a region-specific loss of beta-adrenergic receptors with age in the brain of Fischer 344 rats.

Long-term treatment of male F344 rats with deprenyl: assessment of effects on longevity, behavior, and brain function.

L-Deprenyl (selegiline) was chronically administered to male Fischer 344 rats via their drinking water beginning at 54 weeks of age (estimated daily dose: 0.5 mg/kg/day). Beginning at 84 weeks of age, the rats were behaviorally evaluated using a sensorimotor battery, a motor-learning task, and the Morris water maze. At 118 weeks of age, cerebellar noradrenergic function was evaluated in the surviving rats using in vivo electrochemistry. The rats were then sacrificed to measure brain monoamine oxidase activity and perform quantitative autoradiography to evaluate the effect of chronic deprenyl treatment on beta-adrenergic receptors in the cerebellum, alpha 2-adrenergic receptors several brain regions, and D1 and D2 dopamine receptors in the striatum. Deprenyl treatment reduced brain monoamine oxidase B activity by 85%, but had no effect on brain monoamine oxidase A. A clear effect of chronic deprenyl treatment upon longevity was not observed. Several measures of CNS function were altered in the deprenyl-treated animals: 1) spatial learning in the Morris water maze was improved; 2) electrochemical signals recorded following local application of NE were reduced, and the responsiveness to the reuptake blocker nomifensine was enhanced, in the cerebellum; 3) beta-adrenergic receptor binding affinity was increased in the cerebellum; 4) alpha 2-adrenergic receptor density was increased in the inferior colliculus; and 5) striatal D1 dopamine receptor density was reduced but binding affinity was enhanced. In contrast, chronic deprenyl treatment did not cause changes in: 1) sensorimotor function, as evaluated by balance beam, inclined screen, or wire hang tasks; 2) motor learning; 3) alpha 2-adrenergic receptor density in any region examined except for the inferior colliculus, or binding affinity in any region examined; or 4) striatal D2 dopamine receptor number or affinity. Thus, long-term oral administration of deprenyl extended the functional life span of rats with respect to cognitive, but not motor, performance.

Timolol-induced up-regulation of polymorphonuclear leukocyte beta 2-adrenergic receptors in the elderly.

Drug-induced up-regulation of beta-adrenergic receptors is impaired in the brains of aged rats but not in myocardia. To investigate age-related changes in receptor regulation in human beings, young (24 to 35 years of age) and elderly (62 to 78 years of age) healthy volunteers were treated with the beta-adrenergic receptor blocking agent timolol maleate (10 mg b.i.d.) for 8 days. Baseline densities of beta 2-adrenergic receptors on polymorphonuclear leukocyte (PMNL) membranes and heart rates were the same in the two age groups. However, systolic blood pressures were higher in the elderly subjects. Administration of timolol produced similar plasma levels in the two groups. In response to timolol, the density of PMNL beta-adrenergic receptors increased at a similar rate and to the same extent (threefold) in both age groups. Likewise, hemodynamic changes were not related to age. These results suggest that up-regulation of peripheral beta 2-adrenergic receptors in human beings is not impaired with aging.

Terbutaline-induced desensitization of polymorphonuclear leukocyte beta 2-adrenergic receptors in young and elderly subjects.

Potential age-related differences in cardiovascular responsiveness and receptor regulation induced by short-term administration of a selective beta 2-adrenergic receptor agonist were investigated. Young (age range, 23 to 31 years) and elderly (age range, 64 to 73 years) healthy subjects were treated with terbutaline (5 mg, three times daily) for 5 days. Similar plasma terbutaline concentrations were achieved in the two age groups. The elderly group had higher baseline plasma norepinephrine concentrations and mean arterial pressures, neither of which were altered by terbutaline administration. During terbutaline treatment, heart rate increased in both age groups while subjects were supine but consistently increased only in the young group while subjects were standing. In both age groups, the density of beta 2-adrenergic receptors on polymorphonuclear leukocyte membranes was reduced by 50% during terbutaline administration and returned to baseline values at similar rates after drug administration was stopped. Isoproterenol-stimulated cyclic adenosine monophosphate accumulation in polymorphonuclear leukocytes from elderly subjects was regulated similarly. These findings suggest that the ability of terbutaline to increase standing heart rate is selectively impaired in the elderly, whereas the ability of polymorphonuclear leukocyte beta 2-adrenergic receptors to down-regulate and to return to baseline values is not.

Binding characteristics of the dopamine uptake inhibitor [3H]nomifensine to striatal membranes.

Binding of the radiolabeled antidepressant [3H]nomifensine to rat and rabbit striatal membranes has been characterized. The specific binding of [3H]nomifensine to striatal membranes was stable, reversible and saturable. Saturation experiments indicated that [3H]nomifensine labeled a single site with an affinity (Kd) of 80 nM and a total number of binding sites (Bmax) of 6.5 pmoles/mg protein both in rat and rabbit striatal membranes. The affinity constants obtained from kinetic analyses and competition experiments were in fairly good agreement with those obtained in saturation experiments. Compounds known to inhibit [3H]dopamine uptake in vitro, such as nomifensine, 4-hydroxy-nomifensine, mazindol, amfonelic acid and benztropine, were the most potent competitors of nomifensine binding. Additionally, the absolute potencies of various drugs in competing for [3H]nomifensine binding to rat and rabbit striatal membranes correlated closely with their potencies in inhibiting [3H]dopamine uptake into striatal synaptosomes. Specific [3H]nomifensine binding was dependent on the presence of NaCl which is also consistent with its association with the dopamine uptake pump. The number, but not the affinity, of striatal [3H]nomifensine binding sites was reduced significantly following in vivo lesions with 6-hydroxydopamine. The number of [3H]nomifensine binding sites was found to be highest in areas rich in dopamine nerve terminals such as the striatum and olfactory tubercle. These results suggest that [3H]nomifensine binds to a site on dopaminergic nerve terminals associated with the dopamine uptake pump.

Effects of cell isolation procedures and radioligand selection on the characterization of human leukocyte beta-adrenergic receptors.

Radioligand binding techniques are commonly used in the characterization of beta-adrenergic receptors on human peripheral leukocytes. Accurate interpretation of receptor binding parameters necessitates appropriate radioligand selection. In addition, cell isolation techniques should have minimal effect on the binding parameters of receptors. Our observation of curvilinear Scatchard plots with (-)-[125I]iodocyanopindolol (ICYP) resulted in a re-evaluation of this radioligand and the influence of cell isolation techniques on leukocyte beta-adrenergic receptor binding parameters. Membranes from mononuclear (MN) and polymorphonuclear (PMN) cells isolated by a standard procedure (Ficoll-Hypaque) resulted in biphasic Scatchard plots with ICYP in three of four subjects. In contrast, linear Scatchard plots were observed for ICYP binding to membranes from MN and PMN cells isolated from the same four subjects with an alternative procedure utilizing plasma Percoll. Competition and saturation binding assays with ICYP identified a high degree of nonspecific binding. Decreased stereoselectivity with (-)- and (+)-propranolol was observed with membranes from Ficoll-Hypaque cells as compared to plasma Percoll cells. Kinetic analysis with ICYP demonstrated apparent irreversible binding whether displacement was initiated with a beta-adrenergic receptor antagonist or agonist. These problems with ICYP prompted evaluation of an alternative radioligand, (-)-[125I]iodopindolol (IPIN); this radioligand demonstrated rapid and completely reversible binding, improved stereoselectivity, and low nonspecific binding. Using IPIN, Scatchard plots from three additional subjects were linear for both cell isolation procedures. Based on these observations, the preferred method of human leukocyte beta-adrenergic receptor analysis incorporates the plasma Percoll cell isolation technique and the radioligand IPIN.

GABAA receptor function and regional analysis of subunit mRNAs in long-sleep and short-sleep mouse brain.

The greater sensitivity of long-sleep (LS), as compared with short-sleep (SS), mice to ethanol is due in part to differences in GABAA receptor function in specific brain regions. To determine if differences in subunit composition of GABAA receptors contribute to this differential sensitivity, we measured alpha 1 and gamma 2 subunit mRNAs with Northern analysis and in situ hybridization and gamma 2S, gamma 2L and alpha 6 subunit mRNAs with polymerase chain reaction (PCR) amplification. No differences in mRNAs in whole brain were apparent by Northern analysis. In situ hybridization revealed that alpha 1 and gamma 2 subunit mRNAs were co-localized in many brain regions but that they still had distinct patterns of hybridization. However, the few differences observed between LS and SS mice in the levels of hybridization for these subunits did not show a regional distribution consistent with ethanol sensitivity differences. Similar ratios of gamma 2L, and gamma 2S subunit mRNAs were found in LS and SS mouse cerebral cortex and hippocampus, and both mouse lines expressed essentially only gamma 2L subunit mRNA in cerebellum. mRNA for the alpha 6 subunit was detected only in cerebellum and also was qualitatively similar between LS and SS mice. Studies of muscimol-stimulated 36Cl- uptake by cortical membrane vesicles confirmed earlier findings that ethanol does not enhance function of GABAA receptors in SS mice when assayed at 30 degrees C. However, at 34 degrees C ethanol did increase this function in SS mice although the enhancement remained greater in LS mice. These functional results, together with the results showing similar levels of alpha 1, gamma 2S, gamma 2L and alpha 6 subunits in LS and SS mice, suggest that the ethanol-insensitivity of SS mouse GABAA receptors cannot be due solely to lack of subunits required for ethanol action and further suggest that differences in catalytic mechanisms affecting post-translational processing may account for some genetic differences in ethanol sensitivity of GABAA receptors.

On the selection of mice for haloperidol response and non-response.

Mice have been selected over eight generations for response and non-response to haloperidol-induced catalepsy. The selection has been asymmetric, with significantly faster divergence for the haloperidol non-responder (HNR) line as compared to the haloperidol responder (HR) line. After six generations of selection, the ED50 in the HNR line was 4.3 mg/kg and 0.4 mg/kg in the HR line. Spiroperidol, fluphenazine and trifluoperazine showed a 10-fold or greater discrimination between lines. Raclopride, a specific dopamine D2 antagonist, showed a 7-fold discrimination between lines. Chlorpromazine, thiothixene, (+) butaclamol and cis-flupenthixol showed a 3-4-fold discrimination between lines. The specific D1 antagonist, SCH 23390, was the most potent cataleptogenic agent tested (ED50 = 0.1 mg/kg) and did not discriminate between the lines. The HR and HNR lines did not differ in post-synaptic D2 receptor affinity or density as assessed by quantitative receptor autoradiography and membrane binding assays. However, A-9 somatodendritic receptor density was 80% higher in the HNR line as compared to the HR line.

Lack of an effect of age on beta-adrenoceptor-mediated lipolysis in isolated human adipocytes.

We examined the effect of age on the beta-adrenoceptor response in adipocytes that contain both beta 1- and beta 2-adrenoceptors. Twelve healthy young and 12 old subjects on a 150 mEq/24 h sodium diet underwent gluteal fat biopsies. Isolated adipocytes from all the subjects were stimulated with increasing concentrations of isoproterenol for glycerol release. In 13 of the subjects (7 young and 6 old), we also performed beta-adrenoceptor binding studies on adipocyte membranes. In addition in eight subjects (four young and four old), we also utilized a competitive binding assay to calculate the percent of beta-adrenoceptors that were of the beta 1 subtype. Our data showed that old subjects, when treated under identical conditions as the young subjects prior to fat biopsy, did not demonstrate any differences in the beta-adrenoceptor stimulated lipolysis. The Vmax of lipolysis was 10.6 +/- 1.4 nmoles glycerol/mg lipid/2 h in the young group and 9.9 +/- 1.1 in the old group. The concentrations of isoproterenol that resulted in Vmax and 1/2 Vmax were also the same in the two age groups. The addition of 8-cyclopentyl-1,3-dimethylxanthine (CPT), a specific A1-adenosine receptor antagonist, resulted in mild but equivalent enhancement of glycerol release in both age groups. The beta-adrenoceptor numbers and affinities from adipocyte membranes did not demonstrate age-related differences either (Bmax 106 +/- 17 fmol/mg of protein in the young, and 137 +/- 27 in the old; Kd 79.6 +/- 21.3 pM in the young and 81.9 +/- 16.6 in the old). The percent of beta 1-adrenoceptors on the adipocyte membranes was also similar in the two age groups (35.2 +/- 2.6% in the young; 37.1 +/- 4.5% in the old). In conclusion, we could not demonstrate any differences in the beta-adrenoceptor responses from peripheral adipocytes that contain both beta 1- and beta 2-adrenoceptors, in a group of healthy elderly and young subjects who were subjected to identical dietary and orthostatic conditions prior to the biopsy. These data suggest that neither beta 1- nor beta 2-adrenoceptor responses in human adipocytes show significant changes due to aging.

Outflow and overflow of picogram levels of endogenous dopamine and DOPAC from rat striatal slices: improved methodology for studies of stimulus-evoked release and metabolism.

An improved method for the rapid and sensitive determination of endogenous dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in superfusates of single rat striatal slices, using high-performance liquid chromatography (HPLC) coupled with 'coulometric' electrochemical detection (EC), is described. Superfusates are directly injected into an HPLC-EC system following addition of a small aliquot of solubilized ascorbate-oxidase. DA and DOPAC are both separated and quantitated in 3-5 min. Twelve to 15 samples can be analyzed each hour with a nominal detection limit of 1.0 pg per injection for each compound or 10-20 pg/ml of superfusate. The present method was used to study changes in DA and DOPAC outflow and overflow in superfusates of single striatal slices following electrical field stimulation, both in the absence and presence of the catecholamine uptake inhibitor nomifensine. Studies of 1 min superfusate collections clearly showed that electrical field stimulation produced a latent increase in DOPAC as compared to DA. The routine sensitivity and sample throughout of the method allows for studies of both outflow and overflow of DA and DOPAC, as well as studies involving time-dependent overflow of these compounds.

An improved calibration procedure for computer-based quantitative autoradiography utilizing a mathematical model for the non-linear response of camera and film.

A mathematical model which accounts for the non-linear response of both the camera and film in computer-aided quantitative autoradiography is derived. This model and the algorithm to fit the data for radioactive standards by a non-linear least-squares procedure to this model are described. The usefulness of this technique is demonstrated by employing it to analyze a set of 14C-labeled brain paste standards which were exposed to Ultrofilm in such a way that the full response range of the film was used. This technique can be readily implemented on most commercially available image analysis systems and is compatible with most types of video cameras.

Methodology for coupling local application of dopamine and other chemicals with rapid in vivo electrochemical recordings in freely-moving rats.

Methodology is presented for constructing and using an electrode/microcannulae assembly that allows in vivo electrochemical measurements coupled with local application of dopamine (DA) and other chemicals in the unanesthetized freely-moving rat. Rats were implanted with a voltammetric electrode constructed of a carbon fiber sealed in fused silica tubing attached to a pair of stainless steel guide cannulae, into which fused silica injection cannulae were inserted for local application of DA and other chemicals. Precise delivery of nanoliter volumes was accomplished using a syringe drive combined with a fluid swivel to deliver the solutions to the injection cannulae. A newly-designed miniature potentiostat connected to a commutator via a modular telephone jack assembly allowed for high-speed chronoamperometric electrochemical recordings in freely-moving rats. Initial experiments characterized the in vitro electrochemical recording characteristics of the voltammetric electrode. In vivo studies were also carried out to study clearance of locally-applied DA and of potassium-evoked endogenous DA in the striatum and nucleus accumbens of freely-moving rats. In addition, the effects of chloral hydrate anesthesia on DA clearance signals in the nucleus accumbens were investigated. Moreover, the stability and reproducibility of this recording technique for measuring exogenous DA clearance was verified over a period of 5 days. Finally, the concurrent effects of systemic cocaine injection on DA uptake in nucleus accumbens and locomotor activity were examined. These studies support the conclusion that the methodology described herein allows for rapid chronoamperometric electrochemical recordings in freely-moving rats with precise microapplications of DA and other chemicals combined with concurrent measures of animal behavior.

A new densitometric procedure to measure protein levels in tissue slices used in quantitative autoradiography.

A new quantitative staining technique for the assay of protein in tissue sections using the dye Coomassie brilliant blue G 250 is discussed. This densitometric procedure uses commercially available hardware and software employed in the quantitation of receptor autoradiographs. Rather than assuming a homogeneous distribution of protein in the tissue section, regional levels of protein are measured in the same tissue slice used to produce the autoradiograph. Additionally, the process of staining tissue with Coomassie blue for protein is reversible; the tissue can be destained after the measurement of protein is complete and then restained with a standard histological stain such as Cresyl violet. This technique is a more reliable method for normalizing receptor densities by tissue protein levels and allows for a more accurate comparison between QAR and membrane binding techniques.

[35S]TBPS binding sites are decreased in the colliculi of mice with a genetic predisposition to bicuculline-induced seizures.

Several differences have been found in GABAergic function between the long sleep (LS) and short sleep (SS) mice which were genetically selected for different ethanol-induced sleeptimes, and it has been suggested that these differences may explain their differential ethanol sensitivity. However, these lines also differ in seizure susceptibility, a behavior which may also be mediated by GABAergic pathways. Thus, it is difficult to associate differences in GABA neurochemistry with either of these behaviors, particularly when only two selected lines are used. We measured differences in the density and affinity of the [35S]TBPS binding site on the GABAA receptor/Cl- ionophore complex in discrete brain areas; and in order to determine the relationship between receptor binding and behavioral differences, we included mice from 5 of the LS and SS recombinant inbred strains (LS x SS RI) in addition to mice from the LS and SS lines. [35S]TBPS binding in sagittal brain sections was analyzed by quantitative autoradiography, and the amount of binding differed depending on whether bicuculline was added to inhibit endogenous GABA binding. In the presence of bicuculline, the number of [35S]TBPS sites in SS mice was highest in the colliculi (4.5 +/- 0.5 pmol/mg protein), cerebellum (4.8 +/- 0.6 pmol/mg), hippocampus (3.2 +/- 0.7 pmol/mg) and cortex (2.9 +/- 0.3 pmol/mg). The Bmax was two-fold lower in both superior and inferior colliculi (IC) of LS mice. There were no differences between lines in Bmax in any other area and in Kd values in any area (58 +/- 4.0 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine-induced behavioral sensitization and D1 dopamine receptor function in rat nucleus accumbens and striatum.

Based on electrophysiological data showing that repeated cocaine administration produces persistent enhancement of D1 dopamine (DA) receptor-mediated responses in nucleus accumbens (NAc), we investigated whether changes in neurochemical properties of these receptors resulted when rats were injected with cocaine (15 mg/kg) for 6 days followed by a 7-day abstinence period. D1 DA receptor density and affinities for either [3H]SCH 23390 or DA were similar between NAc and striatum and between saline and cocaine treatment groups. DA-stimulated adenylyl cyclase activity was 1.5-fold higher in striatum than in NAc; however, repeated cocaine treatment produced no persistent changes in enzyme activity in either brain area.

The acute effects of 6-hydroxydopamine treatment on noradrenergic function in the rat hippocampus in vitro.

The electrophysiological consequences of in vitro treatment with 6-hydroxydopamine (6-OHDA) were examined in the CA1 region of the rat hippocampal slice. In control slices, norepinephrine (NE) increased the amplitude of the population spike response elicited by synaptic stimulation of hippocampal pyramidal neurons with a threshold of approximately 5 microM. When hippocampal slices were pretreated with 500 microM 6-OHDA for 10 min, perfusion with a subthreshold concentration of NE (0.5 microM) produced responses similar to those observed with a 10-fold higher concentration of NE in untreated slices. Baseline electrophysiological responses were unchanged following the 6-OHDA exposure. The potentiation of the response to NE by in vitro pretreatment with 6-OHDA was accompanied by a greater than 40% decrease in NE content and greater than 90% decrease in [3H]NE accumulation. In vivo treatment with 6-OHDA or N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP4) also potentiated the electrophysiological response to NE in a manner similar to that observed with acute in vitro 6-OHDA pretreatment. This action does not appear to be due to development of beta-adrenergic receptor supersensitivity, because the apparent potency of isoproterenol in increasing the population spike amplitude was unaffected. These data suggest that the increase in the potency of NE in slices pretreated with 6-OHDA is due to the rapid disruption of the high-affinity NE uptake mechanism characteristic of noradrenergic nerve terminals.