Deprenyl treatment attenuates long-term pre- and post-synaptic changes evoked by chronic methamphetamine

Deprenyl, used clinically in Parkinson's disease, has multiple pharmacological effects which make it a good candidate to treat neurotoxicity. Thus, we investigated deprenyl's ability to attenuate methamphetamine-induced dopamine neurotoxicity. We also examined deprenyl's effect in changing markers associated with psychostimulant sensitization. A potential therapeutic effect on either pathological domain would be a boon in developing novel treatments for methamphetamine abuse. Adult male Sprague-Dawley rats were split into 6 groups. Three groups received a 7-day saline minipump with saline, 0.05 or 0.25 mg/kg SC deprenyl injections given for 10 days before, during and 5 days after the 7-day saline minipump implant. Similarly, 3 groups received methamphetamine pumps (25 mg/kg/day) with escalating daily injections of methamphetamine (0-6 mg/kg) in addition to the minipump treatment. These rats also received saline, 0.05 or 0.25 mg/kg deprenyl injections given before, during and the 7-day minipump treatment. Rats were killed on day 28 of withdrawal and brain samples taken. HPLC analysis for dopamine and 3,4-Dihydroxy-Phenylacetic Acid (DOPAC) revealed a loss of dopamine in the caudate and accumbens which was partially reversed by high dose deprenyl. Tyrosine hydroxylase immunostaining in the midbrain was unaffected by methamphetamine, suggesting that dopamine neurotoxicity was localized to the caudate. Western blot analysis of the caudate after methamphetamine revealed little change in Alpha-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionic Acid (AMPA) GluR1 or N-Methyl-d-Aspartate (NMDA) NR2B subunits, or their phosphorylation state. However, methamphetamine increased levels of GluR1 and its phosphorylation state in the prefrontal cortex (PFC), and these increases were attenuated by deprenyl. Methamphetamine also increased levels of PFC NR2B subunit, but these increases were not attenuated by deprenyl. We suggest that deprenyl may be effective in reducing the neurotoxic effects of methamphetamine and may also attenuate changes in prefrontal AMPA receptor function, presumably more associated with addiction rather than neurotoxicity.

Reversal of cocaine sensitization-induced behavioral sensitization normalizes GAD67 and GABAA receptor alpha2 subunit expression, and PKC zeta activity

We have recently shown in rats that cocaine-induced behavioral sensitization can be reversed by a 5-day treatment with ondansetron given 3.5 h after daily pergolide injections. In this study we further investigated the molecular/neurochemical alterations underlying cocaine sensitization and pergolide/ondansetron-mediated reversal. Results revealed that glutamic acid decarboxylase (GAD(65)/GAD(67)) is higher abundant in the nucleus accumbens (NAc) than that in the caudate and medial prefrontal cortex (mPFC), while GABA(A) receptor alpha2 subunit level in the NAc shell is less abundant than that in the NAc core, mPFC and caudate. Cocaine sensitization led to (1) a decrease in GAD(67) expression, an increase in total protein kinase C (PKC) zeta subtype and phosphorylated PKC zeta/lambda levels in the NAc core; (2) a decrease in GAD(67) and GABA(A) receptor alpha2 subunit expression, and an increase in phosphorylated PKC zeta/lambda levels in the NAc shell; (3) an increase in GAD(67) expression in the caudate. Importantly, pergolide/ondansetron treatment reversed these alterations. These results suggest that reversal of cocaine-induced behavioral sensitization is associated with reversal of region-specific changes in GABA function and PKC activity in the striatum.

Reduction in methamphetamine induced sensitization and reinstatement after combined pergolide plus ondansetron treatment during withdrawal

We have previously found the 5-HT3 receptor antagonist ondansetron to be useful in reducing cocaine self-administration and cocaine induced sensitization in rats when given during cocaine withdrawal. More recently we have found the combination of the dopamine agonist pergolide plus ondansetron, 3.5 h later, to reverse cocaine sensitization and associated changes in NMDA and AMPA receptors. Here we tested this drug combination in 1) a methamphetamine sensitization model and 2) a reinstatement model after intravenous methamphetamine self-administration using a nose-poke task. We found pergolide plus ondansetron given from days 3-7 of methamphetamine withdrawal to reverse methamphetamine induced sensitization and attenuate reinstatement. We hypothesize that pergolide may evoke a methamphetamine associated memory and that ondansetron can disrupt its reconsolidation. These data suggest that pergolide plus ondansetron treatment may be useful as a therapy to reduce relapse in methamphetamine abusers.

Reversal of cocaine-induced behavioral sensitization and associated phosphorylation of the NR2B and GluR1 subunits of the NMDA and AMPA receptors

Cocaine abusers remain vulnerable to drug craving and relapse for many years after abstinence is achieved. We have recently shown that ondansetron (a 5-HT3 receptor antagonist) given 3.5 h after each daily cocaine injection reverses previously established behavioral sensitization. The purpose of the present investigation was two-fold. First, as cocaine cannot be used as therapy, we examined whether pergolide (a D1/D2 receptor agonist with reduced abuse potential) and ondansetron could reverse behavioral sensitization. Second, we investigated whether these behavioral changes were associated with parallel alterations in expression levels and/or phosphorylation changes in the NR2B and GluR1 subunits of the respective NMDA and AMPA receptors. Rats were injected for 5 consecutive days with cocaine or saline followed by 9 days of withdrawal. Starting on withdrawal day 10, animals were given vehicle, pergolide/saline, or pergolide/ondansetron for 5 consecutive days. Following a second 9-day period of withdrawal, all animals were challenged with cocaine for assessment of behavioral sensitization and tissues were collected on the following day for Western blot. Sensitization was associated with increased NR2B expression in the accumbens (NAc) shell and decreased Tyr1472 phosphorylation in the NAc core, as well as increased Ser845 phosphorylation of the GluR1 subunit in prefrontal cortex, NAc core, and shell. Pergolide/ondansetron treatment, but not pergolide alone, consistently reversed both the behavioral sensitization and the associated changes in the NMDA and AMPA receptor subunits. To the extent that sensitization plays a role in chronic cocaine abuse, a combination of these clinically available drugs may be useful in treatment of the disorder.

Methamphetamine induces long-term changes in GABAA receptor alpha2 subunit and GAD67 expression

The present study investigated whether GABA(A) receptor alpha2 subunit and GAD(67) are involved in chronic high dose methamphetamine (METH)-induced sensitization and neurotoxicity. The METH sensitization was established in rats by 7-day pump infusion plus daily injection (25mg/kg/day) and a subsequent 28-day withdrawal period. Behavioral sensitization was assessed by behavioral ratings after challenge with METH (0.5mg/kg). The neurotoxicity was evaluated by the expression of glial fibrillary acidic protein (GFAP). Western blot assay showed that METH sensitization decreases GABA(A) alpha2 subunit and GAD(67) protein levels in the nucleus accumbens (NAc) core and shell, and conversely, these proteins were increased in the caudate. An upregulation of GFAP expression was observed in the caudate, but not in the NAc core and shell. These data suggest that inhibition of GABA transmission in the NAc is related to METH behavioral sensitization, whereas activation of GABA transmission in the caudate is associated with METH-induced neurotoxicity.

PI3 kinase is involved in cocaine behavioral sensitization and its reversal with brain area specificity

Phosphatidylinositol 3-kinase (PI3K) is an important signaling molecule involved in cell differentiation, proliferation, survival, and phagocytosis, and may participate in various brain functions. To determine whether it is also involved in cocaine sensitization, we measured the p85alpha/p110 PI3K activity in the nuclear accumbens (NAc) shell, NAc core, and prefrontal cortex (PFC) following establishment of cocaine sensitization and its subsequent reversal. Naïve rats were rank-ordered and split into either daily cocaine or saline pretreatment group based on their locomotor responses to an acute cocaine injection (7.5 mg/kg, i.p.). These two groups were then injected with cocaine (40 mg/kg, s.c.) or saline for 4 consecutive days followed by 9-day withdrawal. Cocaine sensitization was subsequently reversed by 5 daily injections of the D1/D2 agonist pergolide (0.1 mg/kg, s.c.) in combination with the 5-HT3 antagonist ondansetron (0.2 mg/kg, s.c., 3.5h after pergolide injection). After another 9-day withdrawal, behavioral cocaine sensitization and its reversal were confirmed with an acute cocaine challenge (7.5 mg/kg, i.p.), and animals were sacrificed the next day for measurement of p85alpha/p110 PI3K activity. Cocaine-sensitized animals exhibited increased PI3K activity in the NAc shell, and this increase was reversed by combined pergolide/ondansetron treatment, which also reversed behavioral sensitization. In the NAc core and PFC, cocaine sensitization decreased and increased the PI3K activity, respectively. These changes, in contrast to that in the NAc shell, were not normalized following the reversal of cocaine-sensitization. Interestingly, daily injections of pergolide alone in saline-pretreated animals induced PI3K changes that were similar to the cocaine sensitization-associated changes in the NAc core and PFC but not the NAc shell; furthermore, these changes in saline-pretreated animals were prevented by ondansetron given 3.5h after pergolide. The present study suggests that selective enhancement of the PI3K activity in the NAc shell may be one of key alterations underlying the long-term cocaine sensitization. To the extent cocaine sensitization is an important factor in human cocaine abuse, pharmacological interventions targeted toward the NAc shell PI3K alteration may be useful in cocaine abuse treatment.

Acute and chronic continuous methamphetamine have different long-term behavioral and neurochemical consequences

We compared two different methamphetamine dosing regimens and found distinct long-term behavioral and neurochemical changes. Adult rats were treated with 1-day methamphetamine injection (3x5 mg/kg s.c., 3 h apart) or 7-day methamphetamine minipump (20 mg/kg/day s.c.). The minipump regimen models the sustained methamphetamine plasma levels in some human bingers whereas the 1-day regimen models a naive user overdose. On withdrawal days 7 and 28, rats were acutely challenged with cocaine to test for behavioral sensitization and subsequently sacrificed for caudate and accumbens dopamine tissue content. Other rats were analyzed on withdrawal days 3, 7 or 28 using voltammetry in caudate slices. On withdrawal days 7 and 28, the methamphetamine injection but not the minipump rats showed behavioral cross-sensitization to cocaine. There was no change in baseline dopamine release, reuptake or sensitivity to quinpirole in any treatment group on either withdrawal day. However, consistent with the behavioral sensitization, cocaine had a greater effect in potentiating dopamine release and in blocking dopamine reuptake in methamphetamine injection versus saline irrespective of withdrawal day. The minipump group showed tolerance to the dopamine releasing effect of cocaine on withdrawal day 28 and had lower dopamine tissue content in the caudate versus the methamphetamine injection group. Dopamine turnover as measured by the DOPAC/dopamine ratio tended to be higher in the minipump-treated rats. These data suggest that the behavioral cross-sensitization seen in the methamphetamine injection rats could be in part due to the increased potency of cocaine in blocking dopamine reuptake and in increasing dopamine release. The decreased potency of cocaine in the caudate slices from the minipump-treated group may be related to decreased dopamine tissue content.

Ondansetron, given during the acute cocaine withdrawal, attenuates oral cocaine self-administration

We have previously shown that ondansetron, given 3.5 h after intravenous cocaine self-administration, can attenuate self-administration the following day. Here we tested ondansetron given either before or after a 14-h oral cocaine session in rats. Ondansetron (0.2 mg/kg sc) given 30 min before the cocaine session had no effect. However, when given 3.5 h after, ondansetron attenuated cocaine intake the following day while having no effect on water intake. Taken with our previous data in intravenous cocaine self-administration, we suggest that the acute cocaine withdrawal period may be an important treatment window and that ondansetron may be an effective cocaine abuse therapy.

The NK1 receptor antagonist WIN51708 reduces sensitization after chronic cocaine

We tested the tachykinin NK(1) receptor antagonist WIN51708 (17betahydroxy17alphaethynyl5alphaandrostanol[3,2b]pyrimido[1,2-a]benzimidazole) in a behavioral sensitization model. Rats were given 7 days of cocaine then 7 days of withdrawal to induce sensitization. Thereafter, another 7 days of cocaine with WIN51708 (2 mg/kg i.p.) given 3.5 h after each cocaine injection was given. WIN51708 reversed sensitization but had no effect on controls. NK(1) receptor antagonists may have use in stimulant abuse and schizophrenia treatment.

5-HT2 receptor antagonists given in the acute withdrawal from daily cocaine injections can reverse established sensitization

Male Sprague-Dawley rats were given two separate sensitizing regimens of cocaine (7 days on, 7 days off, 7 days on at 40 mg/kg/day, s.c.) or saline injections. Half of the animals also received a drug with 5-hydroxytryptamine-2 (5-HT2) receptor antagonist properties (clozapine, 3 mg/kg; mianserin 6 mg/kg; ketanserin 1 mg/kg, all s.c.) or saline during the second cocaine dosing regimen in the acute withdrawal period, 3.5 h after each cocaine injection. On day 10 of withdrawal animals were challenged with cocaine (7.5 mg/kg, i.p.) and assessed by a behavioral rating scale and locomotor activity monitoring. The 5-HT2 receptor antagonists, but not saline, reversed behavioral sensitization and had little effect on behavior in the control animals. 5-HT2 receptor antagonists, therefore, may be a useful treatment for cocaine addicts that have undergone previous sensitization periods. The pharmacological profile of these antagonists suggests that the 5-HT2A receptor subtype may mediate this effect.

Ondansetron given in the acute withdrawal from a repeated cocaine sensitization dosing regimen reverses the expression of sensitization and inhibits self-administration

Male Sprague-Dawley rats were given two separate sensitizing regimens of cocaine (7 days on, 7 days off, 7 days on; 40 mg/kg/day s.c.) along with saline controls. Furthermore, animals also received the 5-HT(3) antagonist ondansetron (0.2 mg/kg s.c.) either during the second dosing regimen (3.5 h after each cocaine/saline injection) or during the first five days of the second withdrawal period. Animals were then challenged, on day 10 of withdrawal, with cocaine (7.5 mg/kg i.p.) and assessed by a behavioral rating scale and locomotor activity monitoring. The cocaine regimen induced behavioral and locomotor sensitization on day 10 of withdrawal, further, ondansetron inhibited sensitization regardless of whether given after each second cocaine regimen dose or during the second withdrawal period, although treatment 3.5 h after each cocaine injection appeared more effective. Ondansetron did not inhibit behavior in control animals. In a second experiment animals were trained to self-administer cocaine via an indwelling jugular catheter. After stable fixed-ratio responding (FR1 then FR2) they were given a progressive ratio (PR) schedule until PR each day was stable. During the first five days of withdrawal they were given either ondansetron (0.2 mg/kg s.c.) or saline injections. On day 10 of withdrawal the cocaine PR schedule was reinstated. The ondansetron treated rats showed only a non-significant decrease in break point. After day 2 of the PR session rats were again injected with either ondansetron (0.2 mg/kg s.c.) or saline, 3.5 h after each PR session for five days. Ondansetron inhibited cocaine self-administration on each of the following days. Ondansetron may be a useful treatment for cocaine addicts who have undergone previous sensitization periods.

Effect of daily dosing duration of direct and indirect dopamine receptor agonists: cocaine cross-tolerance following chronic regimens

One therapeutic paradigm for cocaine abuse is a 24-h 'agonist' treatment which reduces reinforcing effects in a manner similar to the methadone maintenance model for heroin. However, 24-h dosing of dopamine (DA) agonists may induce side effects of insomnia and psychosis, as well as anergia and anhedonia which may actually potentiate abuse. Thus, it is important to determine the daily dose duration of potential treatments such as direct (e.g. pramipexole) and indirect (e.g. GBR 12909) DA agonists, that may induce cross-tolerance with cocaine. We gave a cocaine challenge (15 mg/kg i.p.) on withdrawal day 7 and recorded ambulations and a behavioral rating. We found that 20- and 24-, but not 16-h, daily dosing with cocaine (40 mg/kg), for 14 days, induced tolerance. Pramipexole (4 mg/kg), administered for 24 but not 12 h per day, for 14 days, induced cocaine cross-tolerance while GBR 12909 (18 mg/kg), administered i.p. over 24 or 16 h a day, for 7 days, did not. Thus daily dosing duration is an important variable in consideration of stimulant abuse treatment.

Direct, real-time assessment of dopamine release autoinhibition in the rat caudate-putamen

Inhibition of endogenous dopamine release by photo-released dopamine (i.e., autoinhibition) was characterized in the rat caudate-putamen using combined caged-dopamine photolysis and fast-scan cyclic voltammetry. Coronal brain slices (400 microm thick) were perfused with caged-dopamine (150-200 microM in artificial cerebrospinal fluid). Ultraviolet illumination of increasing duration (25-250 ms, approximately 100 microm beam diameter) was focused at the tip of the recording electrode to uncage increasing amounts of exogenous dopamine at the recording sites (0.5-5 microM); a single biphasic electrical stimulus was delivered 0.1-10 s later to induce endogenous dopamine release. The concentrations of both endogenous and exogenous dopamine were determined using voltammetry, thus enabling determination of concentration-dependent inhibition of the endogenous release by the latter. While unaffected by control ultraviolet illumination, endogenous dopamine release was rapidly inhibited by photo-released dopamine in a concentration-dependent manner. Photo-application of 3-5 microM exogenous dopamine inhibited the endogenous release by 90-100% (electrical stimulus applied 1 s after photolysis initiation), an effect prevented by 2 microM sulpiride. The autoinhibition was dependent on the time between photolysis onset and electrical stimulation. Terminal dopamine autoreceptor stimulation led to robust inhibition of endogenous dopamine release with a latency of approximately 200 ms and effective duration of less than 5 s. The percent autoinhibition was a skewed, U-shaped function of photolysis/electrical stimulation intervals with the peak inhibition at 1 s. This study directly demonstrates that autoreceptor-mediated inhibition of terminal dopamine release in caudate-putamen is designed to provide a rapid, robust, yet short-lasting modulation of terminal dopamine release.

Behavioral sensitization is greater after repeated versus single chronic cocaine dosing regimens

Cocaine dosing regimens in animals are used to model behavioral and neurochemical changes in human cocaine abusers. Typically, rats are dosed for 5-14 days and assessed at some point during withdrawal. However, human cocaine bingers undergo multiple periods of several days of abuse. Here, we model the human binge pattern by giving rats two separate cocaine dosing regimens which results in greater behavioral sensitization than a single cocaine dosing regimen. This model also allows for the testing of drugs in reversal of a previously established sensitization. Multiple cocaine regimens may thus provide a better model for the human condition.

Differential time-course profiles of dopamine release and uptake changes induced by three dopamine uptake inhibitors

Using real-time voltammetry, we compared the effects of cocaine (1.0, 3.0, or 10 microM), WIN 35428 (0.1, 0.5, or 2.0 microM), and nomifensine (0.2, 1.0, or 5.0 microM) on electrically evoked dopamine release and uptake in the rat accumbens slice. The time course for onset and offset of the drug effects were determined by perfusing single drug concentration for 30 min, followed by a 60-min washout. Cocaine elicited a rapid, concentration-independent increase in dopamine release and a more gradual, concentration-dependent inhibition of uptake. During washout, uptake inhibition rapidly abated to near baseline values. During the same period, the potentiation of dopamine release exhibited a slower offset for all concentrations and, for 10 microM cocaine, was even greater than that observed during drug perfusion ("rebound" increase). The release rebound was not observed during continuous 90-min perfusion, verifying that cocaine washout per se was a sufficient condition. Selective D1 or D2 antagonists (0.5 microM SCH 39166 or 2 microM sulpiride, respectively) were without effect on cocaine-induced release alterations. WIN 35428 and nomifensine induced similar changes in dopamine kinetics during perfusion. However, in contrast to cocaine, no consistent release rebound was observed during their washout. For 2 microM WIN 38425, washout and continuous perfusion groups exhibited similar changes in dopamine release and uptake. The time-course mismatch between uptake inhibition and DA release potentiation as well as release rebound during washout suggests that altered dopamine release might play a role in behavioral effects of cocaine.

Methamphetamine neurotoxicity: necrotic and apoptotic mechanisms and relevance to human abuse and treatment

Research into methamphetamine-induced neurotoxicity has experienced a resurgence in recent years. This is due to (1) greater understanding of the mechanisms underlying methamphetamine neurotoxicity, (2) its usefulness as a model for Parkinson's disease and (3) an increased abuse of the substance, especially in the American Mid-West and Japan. It is suggested that the commonly used experimental one-day methamphetamine dosing regimen better models the acute overdose pathologies seen in humans, whereas chronic models are needed to accurately model human long-term abuse. Further, we suggest that these two dosing regimens will result in quite different neurochemical, neuropathological and behavioral outcomes. The relative importance of the dopamine transporter and vesicular monoamine transporter knockout is discussed and insights into oxidative mechanisms are described from observations of nNOS knockout and SOD overexpression. This review not only describes the neuropathologies associated with methamphetamine in rodents, non-human primates and human abusers, but also focuses on the more recent literature associated with reactive oxygen and nitrogen species and their contribution to neuronal death via necrosis and/or apoptosis. The effect of methamphetamine on the mitochondrial membrane potential and electron transport chain and subsequent apoptotic cascades are also emphasized. Finally, we describe potential treatments for methamphetamine abusers with reference to the time after withdrawal. We suggest that potential treatments can be divided into three categories; (1) the prevention of neurotoxicity if recidivism occurs, (2) amelioration of apoptotic cascades that may occur even in the withdrawal period and (3) treatment of the atypical depression associated with withdrawal.

Hippocampal abnormalities in depression

A quantitative magnetic resonance imaging study of regional brain T1 spin-lattice relaxation times in 29 normal volunteers and in 20 patients with major depression revealed significantly shortened T1 relaxation times for the hippocampus in depressed patients. These differences were particularly prominent in elderly depressed patients. T1 relaxation times are reflective of the content and macromolecular environment of tissue water protons; shorter hippocampal T1 values may reflect differences in the content or organizational properties of hippocampal water protons. These findings are consistent with several lines of evidence that have implicated a role for the hippocampus in the regulation of mood and in the pathophysiology of the stress response, and they suggest that major depression may be associated with biophysical tissue changes in the aging hippocampus.

Profile of acute tolerance to three sedative anxiolytics

Acute tolerance, defined as a decreasing drug effect relative to drug-plasma levels (DPL) over a period of minutes to a few hours, is pronounced following single doses of diazepam or pentobarbital. Both of these lipid-soluble drugs produce an early peak behavioral impairment and subsequent rapid recovery component that is followed by a much slower blood-drug rise time. These pronounced early peak effects were not shared by alcohol, and contribute significantly to the lack of correlation between impairment and DPL.

Subcortical hyperintensities on brain magnetic resonance imaging: a comparison of normal and bipolar subjects

Bipolar disorder has been reported to occur frequently in a number of subcortical diseases. This suggests that subcortical structures may be involved in the etiology of bipolar disorder in some patients. With the advent of brain magnetic resonance imaging (MRI), in vivo visualization of the subcortical white and gray matter is now possible, allowing the examination of these structures. The authors report a higher occurrence of deep white matter lesions in bipolar patients (44%) compared with age-matched controls (6%). The neuroanatomic and clinical correlates of these lesions will be discussed, along with their potential pathophysiologic significance.

Benzodiazepine pharmacodynamics: evidence for biophase rate limiting mechanisms

Pharmacokinetics do not adequately reflect recovery from cognitive neuromotor impairment induced by most benzodiazepines. This paper examines across time the nature of the relationship of effect to serum concentration of three benzodiazepines. Using the same protocol lorazepam, alprazolam, diazepam and placebo were administered to eight healthy males at doses of 0.057, 0.029, 0.286 and 0.000 mg/kg, body weight, respectively for the first study and at 0.028, 0.014, 0.143 and 0.000 mg/kg, respectively, for the second study. After each dose administration multiple measurements were made over a period of 5.5-11.5 h using two different psychomotor performance tests. Serum drug concentrations were also measured. The profiles for diazepam and alprazolam effects demonstrate a stepwise decrement in the slopes of the concentration versus response curves across time, illustrating the rapid development of acute tolerance. In contrast, lorazepam induced a remarkably constant relationship between concentration and effect across testing intervals.

Aging of the human corpus callosum: magnetic resonance imaging in normal volunteers

A brain magnetic resonance imaging (MRI) study of the corpus callosum in 36 normal volunteers, ages 26-79 years, revealed that age was positively correlated with the T1 spin-lattice relaxation time of the corpus callosum and was negatively correlated with the corpus callosum cross-sectional area. T1 relaxation times are sensitive to the content and macromolecular environment of tissue water, and variations in callosal T1 may reflect differences in the content or relaxation properties of callosal water. Such changes also potentially could occur secondary to alterations in the composition of callosal myelin. This study confirms and extends prior morphological studies that have reported age-related dimensional changes in the corpus callosum and, in addition, provides evidence of age-related biophysical tissue differences in the human corpus callosum.

Use of simple tasks to test for impairment of complex skills by a sedative

Examination of the effect of three doses of pentobarbital on the comparative performance of a complex psychomotor task with two simple neuromotor tasks, i. e., standing steady and pendulum eye tracking, revealed a high correlation. These simple tasks could be used as measures of intoxication since they do not require extensive training. Examination of the complex task impairment blood level ratio revealed that impairment relative to blood level was much greater in the absorption phase. This changing ratio underscores the point that blood levels alone are not an adequate estimate of intoxication.

Age-related increase in CNS sensitivity to benzodiazepines as assessed by task difficulty

The differential sensitivity of young and elderly healthy adults to the impairment effects of benzodiazepines was assessed by tasks with several levels of difficulty. Using a double-blind procedure, single doses of placebo, alprazolam (0.75 and 1.5 mg) and triazolam (0.25 and 0.5 mg) were ingested orally by 10 young men, 9 young women, 7 elderly men, and 10 elderly women. Order of drug administration was determined by a random Latin square design. Different versions of the subcritical tracking and digit symbol substitution tasks were characterized by three difficulty levels. Assessments of task performance were conducted at varying intervals for 7 h after drug administration. Both drugs induced a rapid initial onset of impairment in the two age groups. Evidence of increased drug sensitivity in the elderly was provided by the more prolonged duration of the pharmacologic effect in the older than young subjects, especially for the harder versions of the SCT and DSS tasks. In summary, the data provide support for the hypothesis of an age-related decline in the adaptive capacity to inhibit adverse drug effects.

The effect of reserpine on concurrent repeated administration of d-amphetamine

The augmentation of the rat stereotypy response with repeated amphetamine doses, put forward as a model of human amphetamine psychosis, was examined during concurrent reserpinization. The effects of reserpinization, amphetamine treatment, and amphetamine dose on four dependent variables representing the time course of stereotypy ratings after a post-treatment amphetamine dose, were tested by three-way MANOVA. An earlier onset of stereotypy , as occurred in nonreserpinized rats, was not detected in reserpinized rats, but an earlier offset of stereotypy with repeated amphetamine occurred in these rats when high amphetamine doses were used.

Neuroanatomical substrates of depression in the elderly

The etiology of depression in the elderly is poorly understood. In this study, magnetic resonance imaging was used to evaluate the role of subcortical structures in the pathophysiology of depression in the elderly. Elderly depressed patients were found to have smaller caudate nuclei, smaller putaminal complexes and in increased frequency of subcortical hyperintensities compared with normal, healthy controls. These findings were more pronounced in patients with late-onset depression. Based on these findings, the authors discuss the role of the basal ganglia in the pathophysiology of depression in the elderly.

Dopamine efflux during withdrawal from continuous or intermittent cocaine

Daily, intermittent, subcutaneous cocaine injections produce sensitization, while the continuous administration of cocaine produces tolerance to the behavioral effects of subsequent cocaine injections. The present experiments examined whether these behavioral differences are related to differences in the ability of cocaine to increase extracellular dopamine. Increases in perfusate DA, in response to different concentrations of cocaine, were measured in caudate-putamen slices obtained from rats withdrawn for 7 days from a 14-day treatment of either continuous or daily subcutaneous cocaine injections. Compared to saline controls, cocaine-induced DA efflux was increased in subjects receiving daily injections and markedly decreased in subjects receiving continuous cocaine. Thus, different temporal patterns of cocaine administration produce dramatically different alterations in DA neurotransmission. Such changes in dopamine release may be related to the withdrawal symptoms experienced by human cocaine abusers.

Comparative pharmacokinetics and pharmacodynamics of lorazepam, alprazolam and diazepam

The contribution of differential absorption-distribution pharmacokinetics to drug activity can be partially determined by comparing simultaneous estimates of drug serum level with pharmacodynamic effects. In the present paper we have contrasted the effects of clinically equipotent doses of lorazepam, alprazolam, and diazepam on the performance of tracking and digit symbol substitution tasks. Eight young males were tested for 12 h after ingesting the drug. The three benzodiazepines and placebo were administered to each subject according to a balanced double-blind Latin square design. A model is presented that describes the relationship between drug concentration and the degree of impairment across time after the final peak effect. Exponential rate constants were determined for each drug using a Marquardt nonlinear fit of the pooled data. Basically, the constants relate offset serum drug values to the impairment curves at a time when serum-brain equilibrium is assumed to have occurred. The values indicate markedly rapid acute tolerance for alprazolam and diazepam but relatively little acute tolerance for lorazepam. Whether these constants reflect adaptation or differential association-dissociation receptor rate constants cannot be determined, but they do highlight the need to consider receptor kinetics as an important factor in benzodiazepine pharmacodynamics.

Comparison of the effects of quazepam and triazolam on cognitive-neuromotor performance

The pharmacological activity of quazepam, a BZ1 specific benzodiazepine, was compared to the effects of triazolam, a BZ1, BZ2 nonspecific benzodiazepine. Using a double-blind procedure, single oral doses of quazepam (15 or 30 mg), triazolam (0.5 or 1.0 mg) and placebo were administered to 21 healthy young men according to a random Latin square design balanced for order of drug administration. The drug effects on the performance of motor coordination and cognitive tasks were monitored for 7 h following drug ingestion. The results did not indicate any differential effects on cognitive-neuromotor performance for the BZ1 specific quazepam and 2-oxoquazepam compared with the BZ1, BZ2 nonspecific N-desalkylflurazepam metabolite. The impairment magnitude for 30 mg quazepam was closer to that of 0.5 mg triazolam. The onset of the initial drug effect was considerably slower for quazepam than for triazolam. The time course of the impairment profiles for the tasks was compared to pharmacokinetic data from previous studies and suggested that published pharmacokinetic rate constants explain only a limited portion of the impairment time course. In particular, the performance scores were already showing recovery from peak impairment 2 h post-drug ingestion, although quazepam's potent N-desalkylflurazepam metabolite has been found to maintain a maximum plateau level from 2 to 24 h.

The dopamine D2/D3 antagonist DS121 potentiates the effect of cocaine on locomotion and reduces tolerance in cocaine tolerant rats

To explore the significance of dopamine (DA) autoreceptors in cocaine tolerance and cocaine induced locomotor activity rats were treated with saline and cocaine (40 mg/kg per day via osmotic minipump; normal and cocaine tolerant rats, respectively). Injections of DS121 (0-7 mg/kg, i.p.; S(-)-3-(3-(cyanophenyl)-N-n-propylpiperidine), a DA D2/3 and autoreceptor preferring antagonist, either alone (i.e. DS121 + saline injection) or in combination with cocaine (7.5 mg/kg, i.p.) were also given. DS121 (+ saline) increased locomotor activity in both saline and cocaine pump (CP) treated animals. DS121 also potentiated the effect of cocaine on locomotor activity; this effect was greatest in CP (tolerant) animals. It is concluded that DS121 can increase locomotor activity and that this effect is greatest when the DA tone is high, that is when cocaine is present, suggestive of a presynaptic mechanism. Furthermore, because DS121 potentiation of cocaine induced locomotor activity is greatest in tolerant animals it is concluded that supersensitive DA autoreceptors underlie this effect. These data further support our previous data, which show that DA autoreceptors are sensitized after continuous cocaine (minipump) treatment.

Effect of cocaine, nomifensine, GBR 12909 and WIN 35428 on carbon fiber microelectrode sensitivity for voltammetric recording of dopamine

Electrochemical measurements using voltammetry or amperometry at carbon-fiber microelectrodes have been used in vitro and in vivo to examine regulatory mechanisms for the central dopamine system. In many of these experiments, dopamine efflux concentrations under control conditions are determined followed by their alterations in response to a drug treatment. The present study demonstrates that some drugs can affect dopamine measurements, not only by their expected pharmacological action but also by directly altering the microelectrode responsivity. The commonly used reuptake inhibitors GBR 12909 (10 microM) and nomifensine (5 microM) drastically reduce electrode sensitivity and, in the case of nomifensine, increase the time to reach a plateau in response to dopamine boluses (i.e. reduced 'frequency response'). Cocaine (10 microM) and WIN 35428 (2 microM) have negligible effect on these indices. This decrease in sensitivity was found in both nafion and non-nafion coated electrodes. Further, the reduction in sensitivity seen in non-nafion coated electrodes was not prevented by increasing the reversal potential (from +1.0 to +1.3 V) and voltage scan rate (from 350 to 450 V/s). These data suggest that care must be taken when interpreting data from voltammetric or amporometric experiments using carbon electrodes where GBR 12909 or nomifensine are used, especially at high concentrations. Furthermore, wherever possible, direct effects of a drug on electrode sensitivity and frequency response should be determined.

Long-term blockade of the expression of cocaine sensitization by ondansetron, a 5-HT(3) receptor antagonist

Intermittent cocaine administration induces sensitization (reverse tolerance) to its behavioral effects. The mechanism(s) mediating sensitization is not clear, however, previous research has implicated 5-HT(3) receptors in the expression of sensitization. The present experiment evaluated the ability of the 5-HT(3) receptor antagonist, ondansetron, administered during withdrawal from chronic intermittent cocaine administration, to block the expression of sensitization. Rats were pretreated for 14 days by daily subcutaneous injections of either 40 mg/kg cocaine or 0.9% saline. During the first 5 days of withdrawal from this pretreatment regimen, all rats received a daily subcutaneous injection of 0-1.0 mg/kg ondansetron. On days 7, 14 or 28 of withdrawal from the cocaine pretreatment, the rats received a 15.0-mg/kg cocaine challenge. Ambulatory behavior was automatically recorded for 60 min. Ondansetron had no significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron blocked the expression of sensitization at all withdrawal times. We thus report that it is possible to permanently block the expression of sensitization once it has developed by administering a 5-HT(3) receptor antagonist.

Altered sensitivity of dopamine autoreceptors in rat accumbens 1 and 7 days after intermittent or continuous cocaine withdrawal

Using slice preparations, we investigated the effects of chronic cocaine treatment on dopamine autoreceptor sensitivity in the nucleus accumbens core. Cocaine (40 mg/kg/day) was given for 14 days, either by continuous subcutaneous infusion (osmotic minipumps) or single daily injections. One or 7 days after cocaine withdrawal, we used fast scan cyclic voltammetry (10 Hz sampling rate) to measure inhibition of electrically evoked dopamine release by quinpirole (3-300 nM). Continuous cocaine infusion increased quinpirole sensitivity on day 1 of withdrawal, particularly at low concentrations of quinpirole, but this effect was no longer evident by day 7. Intermittent cocaine injections had no effect on day 1 of withdrawal but by day 7 there was a quinpirole subsensitivity. On either withdrawal day, the baseline peak dopamine release or uptake half-life exhibited no treatment group differences. It is suggested that these cocaine dosing regimes cause differential and dynamic changes in dopamine autoreceptor sensitivity during the early withdrawal phase.

The effects of continuous cocaine dose on the induction of behavioral tolerance and dopamine autoreceptor function

The current experiment evaluated the dose-dependent nature of the induction of behavioral tolerance, and changes in dopamine autoreceptor function, by continuously administering different doses of cocaine. For all experiments, rats were exposed to a 14-day pretreatment regimen involving the continuous administration of either 0, 5, 10, 20, or 40 mg/kg/day cocaine. All subjects were then withdrawn from the pretreatment regimen for 7 days. The subjects were placed in activity monitors, and ambulation measured. In experiment 1, the subjects were challenged with 0.0, 7.5, or 15.0 mg/kg i.p. cocaine on day 7 of withdrawal from the continuous cocaine administration regimen. The results indicated that all continuous cocaine doses induced significant tolerance to the 15.0 mg/kg cocaine challenge, relative to the control group. Furthermore, the 5.0 mg/kg/day group exhibited significantly less tolerance than the 40.0 mg/kg/day group. In experiment 2, the subjects were challenged with 0.0, 0.063, or 0.125 mg/kg quinpirole. The results indicated that the 0.063-mg/kg quinpirole challenge inhibited activity, while the 0.125 mg/kg quinpirole challenge enhanced behavior. The results further suggested that the inhibition of behavior was greater in the cocaine-pretreated subjects than in the saline control group. In experiment 3, the subjects were challenged with the same doses of quinpirole in combination with 15 mg/kg i.p. cocaine. The low quinpirole challenge dose inhibited cocaine-induced hyperactivity, while the higher challenge dose enhanced cocaine-induced hyperactivity. The results suggest that the induction of tolerance by continuous cocaine administration is dose-dependent. Continuous cocaine administration did induce dopamine autoreceptor supersensitivity. However, different continuous cocaine doses did not induce differential degrees of dopamine autoreceptor supersensitivity.

Altered activity of midbrain dopamine neurons following 7-day withdrawal from chronic cocaine abuse is normalized by D2 receptor stimulation during the early withdrawal phase

Using in vivo single-unit recording in rats, we compared the effects of continuous cocaine infusion via minipump or single daily injections (both 40 mg/kg/d x 14 days, S.C.) on the activity of putative dopamine (DA) neurons in the substantia nigra pars compacta (SNC) and ventral tegmental area (VTA). On days 1-5 after cocaine withdrawal, animals were further treated with single daily injections of DA agonists. On withdrawal day 7 continuous cocaine caused a reduction in spontaneously active neurons in the SNC and reduced bursting in the VTA. In contrast, intermittent cocaine resulted in an increase in the number of active neurons in the VTA. These changes were all reversed by apomorphine or quinpirole given during the first 5 withdrawal days. The D1 antagonist SCH 39166 did not antagonize the effects of apomorphine in either region. The role of D2 receptors in modulating baseline DA activity during intermediate cocaine withdrawal is discussed.

Withdrawal from continuous cocaine administration: time dependent changes in accumbens 5-HT3 receptor function and behavioral tolerance

We have previously reported that continuous cocaine administration functionally down regulates 5-HT3 receptors in the nucleus accumbens. The current experiments evaluated the duration of behavioral tolerance to cocaine and whether the duration of behavioral tolerance and 5-HT3 receptor down-regulation co-varied. Rats were withdrawn from a pretreatment regimen (40 mg/kg/per day cocaine or 0.9% saline for 14 days) for 1, 7 or 14 days. The rats were either sacrificed, and slices from the nucleus accumbens obtained, or were exposed to behavioral rating procedures. The results indicated that continuous cocaine administration significantly attenuated the ability of mCPBG to facilitate K+ -stimulated DA release on days 1 and 7, but not day 14, of withdrawal. Furthermore, continuous cocaine administration induced behavioral tolerance to a cocaine challenge on days 1 and 7, but not day 14, of withdrawal. These results suggest that continuous cocaine administration functionally down-regulates 5-HT3 receptors in the nucleus accumbens, and this functional down-regulation co-varies with the behavioral tolerance induced by continuous cocaine administration. Hence, a functional down-regulation of accumbens 5-HT3 receptors may represent a partial mechanism for the tolerance following continuous cocaine administration.

Blockade of accumbens 5-HT3 receptor down-regulation by ondansetron administered during continuous cocaine administration

The present experiment examined whether ondansetron, co-administered with continuous cocaine, would block the down regulation of accumbens 5-HT3 receptors. Rats were exposed to a 14-day pretreatment regimen that involved the continuous infusion of 40 mg kg(-1) day(-1) cocaine or 0.9% saline via a subcutaneously implanted osmotic minipump. In addition to the continuous cocaine or saline administration, all subjects received daily subcutaneous (s.c.) injections of either vehicle or 0.1 mg kg(-1) ondansetron for the entire 14-day pretreatment regimen. The rats were then withdrawn from this pretreatment regimen for seven days, and slices from the nucleus accumbens obtained. The slices were perfused with 25 mM K+ in the absence and presence of 0, 12.5, 25, or 50 microM m-Chlorophenyl-biguanide HCl (mCPBG). The efflux samples were assayed for dopamine content by high pressure liquid chromatography (HPLC) with electrochemical detection. Continuous cocaine administration significantly attenuated the ability of mCPBG to facilitate K+-induce dopamine overflow compared to saline control rats. In addition, the rats that received ondansetron and cocaine during the 14-day pretreatment period, the ability of mCPBG to enhance K+ stimulated dopamine release was not significantly different from the saline control subjects. For all groups except the cocaine alone group, the effects of mCPBG on K+ stimulated dopamine release were Ca2+ dependent, suggesting that these effects are receptor mediated. These results suggest that continuous cocaine administration functionally down-regulates 5-HT3 receptors in the nucleus accumbens, and that this down-regulation can be blocked by chronic ondansetron administration. Hence, a functional down regulation of accumbens 5-HT3 receptors represents a significant contribution to the tolerance induced by continuous cocaine administration.

Acute deleterious effects of cocaine on cardiac conduction, hemodynamics, and ventricular fibrillation threshold: effects of interaction with a selective dopamine D1 antagonist SCH 39166

Cocaine has demonstrated cardiotoxicity that has led to sudden death by unknown mechanisms. SCH 39166, a selective dopaminergic D1-receptor antagonist, suppresses the compulsive drug-intake actions of cocaine in primates. This study examined the cumulative toxic effects of cocaine after the long-term administration of SCH 39166. After pretreatment with oral placebo/SCH 39166 for 5 days, an i.v. infusion of 0.25 mg/kg/min of cocaine HCl was delivered to 14 anesthetized dogs, and cardiac conduction, arterial blood pressure, ventricular refractoriness, and arrhythmogenesis were examined. The cocaine infusion was stopped when QRS width increased by 20% from baseline (QRS20). In Coc + Placebo regimen, the QRS and His-Ventricular (HV) intervals showed a dose-dependent lengthening. Initially, the mean blood pressure (MBP) increased followed by a precipitate decrease at a mean dose of 2.03 +/- 0.5 mg/kg of cocaine. At QRS20, the ventricular effective refractory period (ERP) increased significantly, whereas the ventricular fibrillation threshold (VFT) showed a significant reduction from the baseline. In Coc + SCH, the QRS, HV intervals, and ERP increased similarly, but the decrease in MBP was attenuated, and the VFT was increased. A relatively small infusion of cocaine causes a hemodynamic compromise. The His-ventricular conduction delay and lengthened ERP suggest a predominant direct local anesthetic effect. Cocaine additionally decreased the VFT, suggesting an increased susceptibility to VF. SCH 39166 did not potentiate the cardiotoxic effects of cocaine. It displayed a protective trend by suppressing the arrhythmogenic effects and the hemodynamic compromise caused by cocaine.

Altered cocaine potency in the nucleus accumbens following 7-day withdrawal from intermittent but not continuous treatment: voltammetric assessment of dopamine uptake in the rat

Using in vitro fast scan cyclic voltammetry, we measured cocaine potency for inhibiting dopamine uptake/clearance in accumbens slices 7 days after withdrawal from chronic cocaine pretreatments. Rats were pretreated with 40 mg/kg per day for 14 days, either via continuous osmotic minipumps or by once-daily injections. The cocaine potency was subsequently assessed for endogenous and exogenous dopamine applied via single-pulse electrical stimulation and caged-dopamine photolysis, respectively. Under baseline conditions, no differences in either endogenous or exogenous dopamine kinetics were observed in the two cocaine pretreatment groups. In contrast, the potency of bath-applied cocaine for inhibiting endogenous dopamine uptake was enhanced in the intermittent injection group with no change in the continuous infusion group. The selective increase in the cocaine potency following injections was also demonstrable for clearance of photo-applied DA. The enhanced cocaine potency in the accumbens slices following 7 days of withdrawal is consistent with the residual sensitization to cocaine-induced locomotion following daily cocaine injections. Behavioral tolerance following continuous infusion, on the other hand, may be mediated via a mechanism distinct from altered dopamine uptake.

Alterations in baseline activity and quinpirole sensitivity in putative dopamine neurons in the substantia nigra and ventral tegmental area after withdrawal from cocaine pretreatment

Using in vivo single-unit recording, we compared in rats the-effects of continuous infusion and once-a-day injections of cocaine on the activity of single putative dopamine neurons in the substantia nigra and ventral tegmental area. After a 7-day withdrawal, we determined: (1) the number of spontaneously active neurons and their bursting patterns and (2) sensitivity of these neurons to intravenous quinpirole. In the substantia nigra, continuous cocaine infusion reduced the number of neurons without affecting the bursting patterns; daily injections were without effects. In the ventral tegmental area, continuous infusion reduced the bursting activity without affecting the number of neurons, whereas injections increased number of neurons without changes in the bursting pattern. Acute sulpiride normalized all the changes in both cell body areas. The quinpirole sensitivity was selectively increased in the nigral neurons following withdrawal from continuous infusion. Possible role of D2/autoreceptor mechanisms in these changes is discussed.

Blockade of the expression of sensitization and tolerance by ondansetron, a 5-HT3 receptor antagonist, administered during withdrawal from intermittent and continuous cocaine

The present experiment evaluated the ability of the 5-HT3 antagonist, ondansetron, administered during withdrawal from chronic cocaine administration, to block the expression of sensitization and tolerance induced by the intermittent or continuous administration of cocaine, respectively. Rats were pretreated with 40 mg/kg/per day cocaine for 14 days by either s.c. injections or osmotic minipumps, or 0.9% saline, administered via osmotic minipump. During the first 5 days of withdrawal from this pretreatment regimen, all rats received a daily s.c. injection of 0-1.0 mg/kg ondansetron. On day seven of withdrawal from the cocaine pretreatment (2 days after the final ondansetron injection) all subjects received a 15.0 mg/kg i.p. cocaine challenge. Their behavior was then rated according to the Ellinwood and Balster (1974) scale for 60 min. The results indicated that daily injections of ondansetron, on days 1-5 of withdrawal from the pretreatment regimen, had no significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron, on days 1-5 of withdrawal from intermittent cocaine administration, significantly blocked the expression of sensitization. In the continuous cocaine group, ondansetron injections, on days 1-5 of withdrawal from continuous cocaine administration, also blocked the expression of behavioral tolerance. The results therefore indicate that changes in 5-HT3 receptor function are associated with the expression of tolerance and sensitization, respectively.

Psychomotor effects of the anxiolytic abecarnil: a comparison with lorazepam

Abecarnil is a metabolically stable beta-carboline that binds with high affinity and selectivity to central benzodiazepine receptors. The effects on cognitive and psychomotor skills of abecarnil (ZK 112-119), 2.5 mg and 5.0 mg, were compared with lorazepam 2.0 mg and placebo. Twenty-four healthy, young males participated in a double-blind, four-way Latin square design and performed batteries of behavioral tests at predrug and at 20, 40, 60, 80, 100, 120, 180, 240, 360 and 480 min after drug administration. Abecarnil 5.0 mg and lorazepam 2.0 mg displayed similar impairment profiles in tests of cognitive functions including memory encoding. Abecarnil 2.5 mg was substantially less impairing than lorazepam. Impairment levels of the abecarnil and lorazepam treatments peaked at 2-3 h after oral administration. The two abecarnil doses showed dose-dependent effects on the cognitive and psychomotor tasks. All three drug treatments were well tolerated by the subjects, with no one terminating early due to adverse events. The incidence of reported adverse events for abecarnil was dose-dependent. The most frequent, statistically significant adverse effects were drowsiness, lack of concentration and visual disturbance for abecarnil 5.0 mg; and lack of concentration and dizziness for lorazepam 2.0 mg. There were no significant differences in adverse incidence rates between abecarnil 2.5 mg and placebo.

Blockade of cocaine sensitization and tolerance by the co-administration of ondansetron, a 5-HT3 receptor antagonist, and cocaine

The present experiment evaluated the ability of the 5-HT3 antagonist, ondansetron, administered during chronic cocaine administration, to block the development of sensitization and tolerance induced by the intermittent or continuous administration of cocaine, respectively. Rats were pretreated with 40 mg/kg per day cocaine for 14 days by either SC injections or osmotic minipumps, or 0.9% saline, administered by SC injection. During this chronic (cocaine) treatment, all rats received a daily SC injection of 0-1.0 mg/kg ondansetron. The rats were then withdrawn from the pretreatment regimen for 7 days. On day 7 of withdrawal from the cocaine pretreatment all subjects received a 15.0 mg/kg IP cocaine challenge, and their behavior was then rated according to the modified Ellinwood and Balster scale for 60 min. The results indicated that daily injections of ondansetron had no consistent or significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron with cocaine significantly blocked the development of sensitization with an inverted U-shape dose-response curve. In the continuous cocaine group ondansetron injections also attenuated the development of behavioral tolerance. The results therefore indicate that 5-HT3 receptor stimulation during continuous and intermittent cocaine administration is an important link in the development of behavioral tolerance and sensitization.

Cocaine and amphetamine elicit differential effects in rats with a unilateral injection of dopamine transporter antisense oligodeoxynucleotides

We have developed an antisense oligodeoxynucleotide to the dopamine transporter and used it to discriminate the behavioral properties of amphetamine and cocaine. In SK-N-MC cells permanently transfected with the dopamine transporter complementary DNA, treatment with 5 mM antisense oligodeoxynucleotide reduced dopamine uptake by 25% when compared to sense control. Unilateral intranigral administration of dopamine transporter antisense (50 microM) twice daily in freely moving rats for 2.5 days was sufficient to reduce dopamine transporter messenger RNA by 70% as measured by in situ hybridization, but not protein levels as measured by [3H]mazindol binding. However, intranigral treatment via implanted osmotic minipump over a period of seven days produced reductions in both dopamine transporter messenger RNA and protein levels (32%) at a dose of 500 pmol/day. These results indicate a longer half-life for the dopamine transporter than expected. Potassium chloride depolarization of ipsilateral striatal slices showed a greater than 200% increase in dopamine overflow on the antisense-treated side compared to the control side. Since imbalance of dopamine tone is known to induce rotational activity, we tested this behavioral paradigm in rats treated with various oligodeoxynucleotides at different doses and time-points. We have found that antisense-treated animals did not rotate spontaneously under any experimental conditions. Using various psychostimulants that target the dopamine transporter and increase dopamine levels, we found that the antisense-treated animals consistently rotated contralaterally in response to amphetamine (2 mg/kg), but not to cocaine (10 mg/kg) or nomifensine (10 mg/kg). These results bring in vivo evidence for a different mode of action of amphetamine and cocaine on the dopamine transporter and lend direct support to the view that amphetamine acts as a dopamine releaser, whereas cocaine acts by blocking dopamine transport.

Differential effects of SCH 23390 on the apomorphine subsensitivity in the substantia nigra and ventral tegmental area 1 day following withdrawal from continuous or intermittent cocaine pretreatment

Using extracellular single-unit recordings in rats, the effects of chronic intermittent injections and continuous infusion of cocaine on single dopamine neurons were directly compared in the substantia nigra and ventral tegmental area. After 1-day withdrawal we determined: (1) the neuronal sensitivity to the mixed D1/D2 agonist apomorphine and (2) its modulation by the D1 antagonist SCH 23390. The nigral dopamine neurons exhibited subsensitivity to the impulse-inhibiting effects of apomorphine following both intermittent and continuous regimens. SCH 23390 selectively reversed the apomorphine subsensitivity in the intermittent group, while having minimal effects in the other group. Dopamine neurons in the ventral tegmental area, on the other hand, were sub- and normosensitive to apomorphine following intermittent and continuous dosing regimens, respectively. In contrast to the substantia nigra, SCH 23390 failed to alter the apomorphine sensitivity in either of the pretreatment groups. Possible mechanisms underlying these distinctive changes in the substantia nigra and ventral tegmental area following intermittent and continuous cocaine pretreatment regimens are discussed.