Nicotine-induced behavioral sensitization is associated with extracellular dopamine release and expression of c-Fos in the striatum and nucleus accumbens of the rat.

It is well known that repeated injections of nicotine produce progressively larger increases in locomotor activity, an effect referred to as behavioral sensitization. This study was carried out to investigate the neural mechanisms underlying nicotine-induced behavioral sensitization using in vivo microdialysis and Fos-like immunohistochemistry (FLI). Rats were given repeated injections of saline or nicotine (0.4 mg/kg s.c., twice daily for 7 days) followed by one challenge injection on the 4th day after the last daily injection. Systemic challenge with nicotine produced a much larger increase in locomotor activity in nicotine-pretreated rats (659.1+/-94.9 counts/2 h) than in saline-pretreated rats (218.1+/-61 counts/2 h). A direct local challenge of nicotine (1 or 5 mM) via a microdialysis probe in the nucleus accumbens or striatum induced a much greater dose-dependent increase of dopamine (DA) output in nicotine-pretreated rats than in saline-pretreated rats. Furthermore, in parallel with the behavioral and biochemical data, systemic challenge with nicotine produced marked Fos-like immunohistochemistry in the nucleus accumbens and the striatum in the nicotine-pretreated rats. Taken together, this study demonstrates that behavioral sensitization is clearly associated with an increase in DA release and activation of Fos-like immunoreactive cells in the striatum and the nucleus accumbens produced by repeated nicotine treatment. Our results strongly suggest that the striatum and the nucleus accumbens may play a major role in nicotine-induced behavioral sensitization. The present results are discussed in terms of the development and expression of nicotine-induced behavioral sensitization.

Expression and function of striatal nAChRs differ in the flinders sensitive (FSL) and resistant (FRL) rat lines.

Rats of Flinders Sensitive (FSL) and Flinders Resistant lines (FRL) differ in their susceptibility to physiological and associated behavioral responses elicited by nicotine. In the present study, we measured dopamine (DA) content in striatal dialysates to investigate the sensitivity of FSL and FRL rats to nicotine delivered locally through a microdialysis probe placed in the striatum. We also measured the expression density of striatal high-affinity nicotinic acetylcholine receptors (nAChRs), and that of mRNAs encoding for alpha3, alpha4, alpha7 and beta2 nAChR subunits in both lines. The DA content of dialysates was measured before and after a 1-min perfusion of nicotine (6, 10 or 20 nmoles/min) and the resulting DA increase was taken as a measure of the alkaloid's intrinsic activity for nAChRs involved in the release of DA. The nicotine-induced increase of striatal DA release was greater in FSL than in FRL rats for all concentrations of nicotine, suggesting that the intrinsic activity of nicotine was greater in the FSL than in the FRL rats. This was further supported by our finding that the density of high-affinity nAChRs in the striatum of FSL rats was 44% greater than in the FRL rats, whereas affinity (K(D)) was virtually the same in the two lines of rats. Also the expression of mRNAs encoding for alpha(4), alpha(7), and beta(2) subunits in the striatum was greater in FSL than in FRL rats (attomol/microg total RNA, alpha(4):98+/-10 vs. 77+/-7; alpha(7):279+/-16 vs. 184+/-16; beta(2):310+/-19 vs. 201+/-12). We hypothesize that the difference in nicotine-induced DA release in the striatum of FSL and FRL rats depends on the difference in nAChR subunit expression in the striatum between the two lines. The Flinders rats could be used as a model for nicotine self-administration studies to evaluate the susceptibilities of FSL and FRL rats to nicotine dependence.

Striatal application of nicotine, but not of lobeline, attenuates dopamine release in freely moving rats.

We investigated the physiological role of native low- and high-affinity nicotinic acetylcholine receptors (nAChRs) in regulating dopamine (DA) release from striatal DA terminals. To evaluate the functional interactions of the two receptor subtypes, nicotine (which interacts with both high- and low-affinity nAChRs) and lobeline (which selectively interacts with high-affinity nAChRs) were perfused through a microdialysis probe implanted into the striatum of freely moving rats. The DA content of successive dialysates was quantified by HPLC with an electrochemical detector. A short-lasting (1-min) perfusion of nicotine or lobeline dose-dependently increased the DA content of striatal dialysates. A second application of the same dose of nicotine resulted in an attenuated DA increase, compared with the increase elicited by the first application; however, the DA increase elicited by a second application of lobeline was similar to that of the first lobeline application. The nicotine-induced response was not attenuated when it followed a lobeline perfusion; in contrast, if the nicotine perfusion preceded that of lobeline, the lobeline-induced response was attenuated. In the presence of mecamylamine (a noncompetitive nAChR antagonist), the increase in DA content of striatal dialysate samples induced by either nicotine or lobeline was attenuated. However, in the presence of methyllycaconitine (a preferential antagonist for low-affinity alpha7 homomeric nAChRs), the nicotine response was attenuated but that of lobeline was unaffected. These results suggest that the functional inactivation of striatal nAChRs requires the simultaneous activation of both low- and high-affinity nAChRs. Since lobeline is devoid of reinforcing properties, one might infer that the reinforcing properties of nicotine require the simultaneous activation of high- and low-affinity brain nAChRs.

Effect of ginseng total saponin on extracellular dopamine release elicited by local infusion of nicotine into the striatum of freely moving rats.

We investigated the effect of ginseng total saponin (GTS) on nicotine-induced dopamine (DA) release in the striatum of freely moving rats using an in vivo microdialysis technique. In order to further characterize the mechanism by which GTS affects DA release, the effect of GTS on K(+)-induced DA release was also examined. Local infusion of nicotine (1, 5, and 10 mM) into the striatum produced a dose-dependent increase in extracellular DA in dialysate samples (maximal response = 154.0 +/- 10.8%, 308.1 +/- 55.7%, and 499.9 +/- 77.9% over basal levels, respectively). GTS (100 mg/kg i.p.) had no effect on basal levels of extracellular DA. However, GTS inhibited maximal DA release induced by intrastriatal infusion of nicotine (1, 5, and 10 mM) by 35.3%, 36.6%, and 58.5%, respectively. Intra-striatal infusion of high K+ solution (100 mM) produced an increase in extracellular DA in the striatum (maximal response = 796.6 +/- 98.8% over basal levels). However, GTS had no effect on the K(+)-induced increase in extracellular DA. The present study demonstrated that GTS inhibited striatal DA release stimulated by local infusion of nicotine. This may reflect the blocking effect of GTS on the striatum-related behavior induced by nicotine as well as other psychostimulants. The results also suggest that GTS may act on presynaptic nicotinic acetylcholine receptors or receptor-operated Na+ channels in dopaminergic nerve terminals, but not on voltage-sensitive ion channels.

The prolactin response to fenfluramine in schizophrenia is associated with negative symptoms.

We examined the serotonergic system in drug-free inpatients [schizophrenia (n=28) and schizoaffective (n=7)] by administering a challenge dose of oral dl-fenfluramine (fenfluramine) in a controlled angiocatheter study. Seventeen of these patients were also randomized to a placebo condition in addition to receiving fenfluramine. Response to fenfluramine as reflected by changes in serum prolactin and cortisol were examined by repeated measures ANOVA, as well as Area Under the Curves (AUCs). The prolactin response, but not the cortisol response, was significantly correlated with measures of negative symptoms.

Pretreatment plasma homovanillic acid in schizophrenia and schizoaffective disorder: the influence of demographic variables and the inpatient drug-free period.

BACKGROUND: The relationship between plasma homovanillic acid (pHVA) and schizophrenic symptoms has not been conclusively determined. We reexamine pHVA levels in a new sample of patients with emphasis on demographic variables and the drug-free period. METHODS: Plasma HVA levels were studied in 54 schizophrenic and schizoaffective-disordered, drug-free inpatients suffering from a psychotic exacerbation. RESULTS: A significant correlation was observed between pHVA levels and the number of inpatient drug-free days in the total sample, as well as the schizophrenic patient subsample. Further, pHVA was significantly and positively correlated with the duration of illness in the schizophrenic patient subsample. Plasma HVA correlations with behavior, as measured by Brief Psychiatric Rating Scale factors (anxiety/depression and hostility/suspiciousness), emerged only when considering schizophrenic patients drug-free for more than 2 weeks. No correlation was found between pHVA and the age of illness onset or the duration of the delay of treatment of the first psychotic episode. CONCLUSIONS: The effects of antipsychotic withdrawal on levels of pHVA in clinical populations may have to be examined and controlled for in future studies attempting to study the relationship between this metabolite and behavior in acutely ill, drug-free schizophrenic patients.

Imidazenil, a positive allosteric GABAA receptor modulator, inhibits the effects of cocaine on locomotor activity and extracellular dopamine in the nucleus accumbens shell without tolerance liability.

Imidazenil, a benzodiazepine recognition site ligand that acts as partial positive allosteric modulator of gamma-aminobutyric acid (GABA) action at GABAA receptors, inhibits in a dose-dependent manner (0.56-2.5 micromol/kg i.p. to rats) the cocaine-induced increase in dopamine (DA) content in the dialysates of the nucleus accumbens shell and striatum and also inhibits cocaine-induced locomotor activity. Diazepam, a full allosteric modulator of GABA action at GABAA receptors, in a dose of 4.4 micromol/kg i.p. also attenuates the cocaine-induced increase in DA content in the dialysates of nucleus accumbens shell, and striatum and the cocaine-induced locomotor activity. However, imidazenil (2.5 micromol/kg i.p.) fails to reduce spontaneous locomotor activity, whereas diazepam (4.4 micromol/kg i.p.) elicits sedation and ataxia and clearly impairs spontaneous locomotor activity. When added in vitro, both imidazenil and diazepam potentiate the GABA-mediated reduction of the ventral tegmental area DA neuron firing rate. After protracted treatment (14 days/three times a day with an increasing-dose schedule), the inhibitory actions of imidazenil fail to develop tolerance, whereas the actions of diazepam exhibit high tolerance liability. We conclude that imidazenil is devoid of tolerance liability and that, via a GABAA-mediated reduction in the extracellular DA in nucleus accumbens shell, it might reduce the psychomotor activity and reinforcing properties of cocaine.

A two-phase, double-blind randomized study of three haloperidol plasma levels for acute psychosis with reassignment of initial non-responders.

To clarify the plasma level/therapeutic response relationship of haloperidol (HPDL) we used a prospective double-blind design in 95 acutely psychotic patients. After drug washout, patients were randomly assigned to a low, middle or high plasma level range for 2 weeks (phase A), and then 50% of the initial non-responders were randomly reassigned into the putative therapeutic range for an additional 2 weeks (phase B). There were no significant differences in clinical outcome between the three plasma level ranges in phase A. However, in phase B initial non-responders displayed greater improvement in the middle range than in the low or the high ranges. No further benefit was observed when plasma levels were raised to or maintained in the high range.

Prediction of haloperidol steady-state levels in plasma after a single test dose.

Because of large interindividual variabilities in the pharmacokinetics of haloperidol (HPDL), empirically adjusting the dose to achieve steady-state levels in plasma (Css) is a time-consuming process. We report a method to individualize dose to achieve a desired Css from an observed drug level 24 hours after a single 15-mg test dose of HPDL. Drug-free schizophrenic and schizo-affective patients were blindly and randomly assigned to achieve a low (< 5 ng/ml), medium (10-18 ng/ml), or high (> 25 ng/ml) Css range of HPDL. On day 1 of the study, each patient received an oral "test" dose of HPDL (15 mg), and blood was drawn 24 hours later to determine drug levels in plasma (C24h). The first 34 patients (group I) were then maintained empirically on 2, 5 to 8, or 10 to 15 mg twice daily of oral HPDL concentrate for 5 days to achieve a low, medium, or high Css range, respectively. For the next 58 patients (group II), the dose of HPDL to achieve the assigned Css range was computed by using C24h in a prediction formula. Application of the C24h correctly predicted the maintenance dose required to achieve the Css in 73.2% of the cases. Further, there was a highly significant correlation (R2 = 0.877, p < 0.0001) between the predicted dose and the actual dose required to achieve the targeted Css range. On the basis of these results, we have formulated a nomogram to help predict the maintenance dose required to achieve low, medium, or high HPDL targeted ranges at various C24h values.

Cerebrospinal fluid levels of phenylacetic acid in mental illness: behavioral associations and response to neuroleptic treatment.

Cerebrospinal fluid levels of phenylacetic acid (CSF PAA) were obtained from normal controls and from drug-free psychiatric inpatients (schizophrenia, major depression, mania, and schizoaffective disorder). Post-treatment CSF PAA levels were obtained from 16 patients after 4 weeks of neuroleptic treatment. Phenylacetic acid levels were higher in women and were significantly correlated with age. There were no differences in CSF PAA levels between the various diagnostic groups and no difference between the paranoid and the nonparanoid subtypes of schizophrenia. CSF PAA was significantly correlated with several measures of psychopathology, especially the Brief Psychiatric Rating Scale hostility/suspiciousness factor. Neuroleptic treatment did not result in significant PAA changes. These findings are discussed in light of the amphetamine-like role ascribed to phenylethylamine, the precursor of PAA.

Phenylethylamine modulation of affect: therapeutic and diagnostic implications.

A review of the literature indicates that brain phenylethylamine (PEA) may be a neuromodulator of aminergic synapses and that it promotes energy, elevates mood, and favors aggression. Phenylacetic acid, the main metabolite of PEA, is decreased in the biological fluids of depressed subjects and schizophrenic subjects and is increased in schizoaffective subjects. The administration of PEA or of its precursor L-phenylalanine improves mood in depressed patients treated with a selective monoamine oxidase B inhibitor. The authors speculate that studies of PEA metabolism may have diagnostic value and that PEA administration may be therapeutic in selected depressed patients.

Peripheral benzodiazepine receptors are decreased during cocaine withdrawal in humans.

In the present study, homovanillic acid in plasma (pHVA) and benzodiazepine receptors (3H-PK11195 binding) in neutrophil membranes were determined in blood obtained from cocaine-dependent (DSM-III-R) adult male inpatients at baseline-(within 72 hr of last cocaine use) and after 3 weeks of cocaine abstinence, and normal controls. The mean (+/- SEM) pHVA at baseline (10.3 ng/ml +/- 1.1) was similar to normals and did not change after 3 weeks of cocaine abstinence. Similarly, the binding indices of benzodiazepine receptors in cocaine-dependent subjects as a group were not significantly different than in normal controls. In 10 cocaine-dependent subjects, however, where both blood samples were available, the number of 3H-PK11195 binding sites was significantly (p < 0.05) decreased after 3 weeks of cocaine abstinence (mean +/- sem: Bmax = 6371 +/- 657 fmol/mg protein) compared with baseline (Bmax = 7553 +/- 925 fmol/mg protein), although there were no differences in the binding affinity (mean +/- sem: KD = 8.6 +/- 1.2 nmol/L after 3 weeks of abstinence compared with 8.1 +/- 1.0 nmol/L at baseline). These preliminary results suggest that peripheral benzodiazepine receptors may play an important role in the pathophysiology of cocaine withdrawal in cocaine-dependent human subjects.

Clinical pharmacokinetics of antipsychotics.

The antipsychotics are a chemically diverse group of heterocyclic compounds, which ameliorate many symptoms of schizophrenia. Most of the antipsychotics are very lipophilic and cross lipoidal membranes freely. When administered orally, they are well absorbed and undergo substantial pre-systemic elimination (bioavailability: 10-70%), are highly bound to plasma proteins (75-99%) and tissues, and are extensively distributed (VD: 100-1000 L). Primary route of elimination for most of antipsychotics is hepatic metabolism and biotransformation produces active metabolites. There is no linear relationship between the concentration of parent compound and different metabolites, and clinical relevance of pharmacologically active metabolites is not well understood. There are wide interindividual variabilities in pharmacokinetics, which result in large differences in steady-state plasma concentrations on the same dose regimen. The existence of optimal therapeutic ranges for most antipsychotics remains controversial. One of the major problems is the lack of well-designed studies that involve sufficient numbers of patients to clearly establish a therapeutic range for these drugs and is further complicated by the presence of a large number of pharmacologically active metabolites. However, the pronounced interindividual kinetic variabilities, combined with problems of noncompliance and drug interactions, and the delayed onset of clinical response in relation to initiation of treatment with antipsychotics are reasons why drug monitoring in conjunction with clinical status of the patient can be useful. Indications for antipsychotic drug monitoring include lack of response, non-compliance, toxicity, and drug interactions when other drugs are coadministered.

The effects of in vivo cocaine on norepinephrine-stimulated phosphoinositide hydrolysis in rat brain.

We examined the effects of a cocaine challenge on behavioral stimulation and NE-stimulated [3H]inositol-1-phosphate (IP1) formation in rat cerebral cortex after single (high dose) or repeated (low dose) cocaine administration. As previously reported, single high dose (40 mg/kg, IP) and repeated low dose (10 mg/kg, 8 IP injections) administrations of cocaine resulted in behavioral sensitization to a challenge injection of cocaine (10 mg/kg). In saline-pretreated animals, the acute cocaine challenge significantly potentiated the NE-stimulated [3H]IP1 formation as compared with the saline challenge, while in cocaine-pretreated animals, NE-stimulated phosphoinositide (PI) turnover was not significantly altered. These results suggest that although some of the acute effects of cocaine may be mediated by enhanced alpha 1-adrenergic receptor-linked PI hydrolysis, behavioral sensitization does not involve the alpha 1-adrenergic receptor-linked PI signal transduction system.

CSF and plasma MHPG, and CSF MHPG index: pretreatment levels in diagnostic groups and response to somatic treatments.

The authors report a significant positive correlation between levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) in cerebrospinal fluid (CSF) and plasma in drug-free affective disorder patients (major depression, mania, and schizoaffective disorder), but not in schizophrenia. Recent kinetic studies on the relationship between plasma and CSF MHPG discourage the interpretation of independent CSF MHPG levels without correction for the diffusion of MHPG across the blood-brain barrier. The authors therefore examine pretreatment CSF and plasma MHPG levels, and the CSF MHPG index (CSF MHPG corrected for by using simultaneously obtained plasma MHPG according to the method of Kopin et al. [1983]). No significant differences were found in these pretreatment MHPG measures among the four diagnostic groups. Changes in these MHPG indices, and their correlations with behavioral rating scores, are also examined with respect to response to the four major somatic therapies (neuroleptics, lithium, antidepressants, and electroconvulsive therapy).

Homovanillic acid in the cerebrospinal fluid: patterns of response after four weeks of neuroleptic treatment.

Lumbar cerebrospinal fluid (CSF) homovanillic acid (HVA) concentrations were measured before and after 4 weeks of neuroleptic treatment in schizophrenic (n = 15) and schizoaffective (n = 4) patients. Neuroleptic treatment induced a nonsignificant (17%) increase in CSF HVA group mean levels. For the total group, no correlations were found between pretreatment CSF HVA and clinical measures, or between changes in HVA and clinical response. An alternative interpretation was attempted by defining "tolerant" and "nontolerant" subgroups. A "tolerant" response was defined as a reduction in posttreatment HVA values below pretreatment levels, whereas a "nontolerant" response was characterized by posttreatment values above pretreatment levels. When thus defined, nontolerant patients had a significantly inferior clinical response to neuroleptics, in contrast to their tolerant counterparts. Further, although there was no difference in pretreatment CSF HVA values between these two groups, pretreatment clinical profiles did differ significantly. Also, in a retrospective analysis, nontolerant patients were found to have a significantly earlier age of illness onset, a greater number of prior psychiatric hospitalizations, and more time spent in psychiatric hospitals.

Repeated cocaine administration does not affect 5-HT receptor subtypes (5-HT1A, 5-HT2) in several rat brain regions.

In order to examine whether cocaine-induced behavioral sensitization is modulated by changes in serotonin receptor subtypes, we measured the binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) to 5-HT1A receptors and of [3H]-ketanserin to 5-HT2 receptors in various brain regions of cocaine-treated and saline-treated (control) rats. As previously reported, repeated administration of cocaine resulted in behavioral sensitization. Stereotypic scores with the cocaine challenge were significantly (P < 0.05) higher in cocaine-pretreated animals than in the saline-pretreated group. Neither acute nor chronic cocaine administration significantly altered the number (Bmax) or the affinity (KD) of either [3H]8-OH-DPAT or [3H]ketanserin binding sites in any of the brain regions examined. These results suggest that the enhanced functional sensitivity of 5-HT1A or 5-HT2 receptor subtypes seen with cocaine may be associated with alterations in processes distal to receptors rather than changes in the number or the affinity of the receptors.

Cocaine disposition in discrete regions of rat brain.

It has been proposed that various effects of psychoactive drugs on the central nervous system may be related to the capacity of the drug to selectively concentrate in specific regions of the brain. In rat brain, cocaine effects on striatal and nucleus accumbens dopaminergic systems show quantitative differences. However, the disposition of cocaine in various brain regions has not been reported. In the present studies we examined the cocaine concentrations over time in serum and discrete brain regions of the rat after single intraperitoneal (i.p.) injection. At different time points (5, 10, 20, 30, 60, 120, and 240 min) after i.p. injection of cocaine hydrochloride (10 mg kg-1, free base) the rats were decapitated and cocaine in serum and various brain regions was quantitated by a specific gas liquid chromatographic method. There was large inter-individual variability in different rats at each time-point. The disposition pattern of cocaine in rats after i.p. administration was similar to that observed in humans after intranasal administration. Initial absorption rate was rapid and, on average, the peak levels of cocaine were achieved in 10 min. The cocaine levels remained relatively high over the next 50 min indicating continual absorption, and then declined with a rate such that the levels 4 h after cocaine administration were undetectable in most of the animals. The overall changes in cocaine levels in various brain regions paralleled the serum concentrations. The area under the cocaine concentration-time curve (AUC) revealed more than three-fold differences in cocaine accumulation in various brain regions. This unequal disposition of cocaine may be responsible in part for differential biochemical effects in different brain regions.

Behavioral and biochemical effects of methylphenidate in schizophrenic and nonschizophrenic patients.

The authors examined the specific behavioral and biochemical effects of intravenous methylphenidate in a sample of schizophrenic and nonschizophrenic patients. Twenty drug-free patients participated in a double-blind, placebo randomized study of methylphenidate, with multiple samples of plasma homovanillic acid (HVA) and serum growth hormone (GH) obtained during the infusion procedure. Methylphenidate caused a significant increase in positive symptoms that was relatively specific to the schizophrenic patients and was evident even in those with otherwise dormant symptomatology. When behavioral response was correlated with the biochemical responses (i.e., changes in plasma HVA and GH), there was a significant positive relationship between the increase in the BPRS-positive symptoms as well as the hostility/suspiciousness factor, and the increase in GH. These results suggest that the expression of psychotic symptoms may be associated with increased dopaminergic postsynaptic sensitivity, although the nonspecific nature of methylphenidate's actions discourages a stronger interpretation of the results.

Hemodynamic and electrophysiological actions of cocaine. Effects of sodium bicarbonate as an antidote in dogs.

BACKGROUND: Cocaine abuse has been implicated as a cause of death due to sudden cardiac arrest. METHODS AND RESULTS: We examined the hemodynamic and electrophysiological effects of cocaine administered as a series of 5-mg/kg i.v. boluses coupled with a continuous infusion in anesthetized dogs. Sodium bicarbonate (50 meq i.v.) was administered as a potential antidote in 11 of 15 dogs, and intravenous 5% dextrose was given in the remaining four. In a dose-dependent fashion, cocaine significantly decreased blood pressure, coronary blood flow, and cardiac output; increased PR, QRS, QT, and QTc intervals and sinus cycle length; and increased ventricular effective refractory period and dispersion of ventricular refractoriness. No afterdepolarizations were noted in the monophasic action potential recording. Nonsustained monomorphic ventricular tachycardia occurred spontaneously in two dogs, and sustained ventricular tachycardia could be induced by programmed stimulation at the end of the dosing protocol in five of 11 animals. Sodium bicarbonate promptly decreased cocaine-induced QRS prolongation to nearly that measured at baseline but had no effect on the other electrocardiographic or hemodynamic variables. In one dog, sodium bicarbonate administration was associated with reversion of ventricular tachycardia to sinus rhythm. CONCLUSIONS: We conclude that high-dose cocaine possesses negative inotropic and potent type I electrophysiological effects. Sodium bicarbonate selectively reversed cocaine-induced QRS prolongation and may be a useful treatment of ventricular arrhythmias associated with slowed ventricular conduction in the setting of cocaine overdose.