I. Javaid

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.

Circadian differences in behavioral sensitization to cocaine: putative role of arylalkylamine N-acetyltransferase.

Circadian rhythms might be involved in addictive behaviors. The pineal secretory product melatonin decreases cocaine sensitization in rats; mice mutant for the critical melatonin-synthesizing enzyme, arylalkylamine N-acetyltransferase (AANAT), exhibit altered behaviors. We hypothesized that AANAT/melatonin system, which is up-regulated at night, affects cocaine sensitization in mice. Intraperitoneal cocaine treatment (10 and 20 mg/kg) dose-dependently increased locomotor activity of both normal (C3H/HeJ) and AANAT mutant (C57BL/6J) mice; this effect was similar during the day and at night. Injections of cocaine during the day for three days resulted in behavioral sensitization in normal and AANAT mutant mice whereas treatment at night triggered sensitization in AANAT-deficient mice only. AANAT expression and synthesis of N-acetylserotonin/melatonin could play a role in addictive properties of cocaine.

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 methylphenidates actions discourages a stronger interpretation of the results.

Dissociation of hippocampal serotonin release and locomotor activity following pharmacological manipulations of the median raphe nucleus.

In vivo microdialysis was used to investigate the role of serotonin in the locomotor hyperactivity produced by injections of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT), muscimol and baclofen into the median raphe nucleus (MR) of unanesthetized rats. Intra-MR injections of the GABA(A) agonist muscimol (25 ng) resulted in a pronounced increase in locomotor activity which was accompanied by a 42% decrease in hippocampal serotonin release during the first hour following injection. Intra-MR injections of the GABA(B) agonist baclofen (125 ng) induced hyperactivity of a similar magnitude, but failed to affect hippocampal serotonin release. In contrast, the serotonin (5-HT1A) agonist 8-OHDPAT (5 microg) produced only a small effect on locomotor activity but reduced hippocampal serotonin output by 51%. These findings demonstrate that it is possible to dissociate the effects of intra-MR drug injections on locomotor activity and hippocampal 5-HT release and strongly support the view that nonserotonergic neurons in the paramedian tegmentum are importantly involved in the control of behavioral arousal.

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.

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.

Gas-liquid chromatographic determination of total phenylacetic acid in urine

A gas-liquid chromatographic procedure to measure total phenylacetic acid in urine is described. The method is simple, rapid, and reliable. Normal subjects (N = 48) excreted 141.1 +/- 10.1 mg/24 h. Untreated depressed patients (N = 42) excreted 102.77 +/- 15.9 mg/24 h. The difference in the means is significant and supports the role of phenylacetic acid as a biological marker in certain kinds of mental illnesses.

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.

A high-pressure liquid chromatographic method for plasma phenylacetic acid, a putative marker for depressive disorders.

An HPLC procedure for the determination of total phenylacetic acid (PAA) in human plasma is described. After precipitation of plasma proteins with 0.4 N HClO4, the supernatant was hydrolyzed with 1.5 N HCl at 100 degrees C for 5 h, and PAA was extracted with benzene. From the organic layer PAA was back-extracted into 0.5 ml of 0.1 N NaOH. After neutralization with HCl the sample was directly injected onto the HPLC column (C18). An ultraviolet detector at 210 nm was used to monitor PAA. The plasma PAA values for a control population (536.18 +/- 54.99 ng/ml, N = 10) (X +/- SE) obtained by the described method are in agreement with values reported using GC/MS methods. Depressed subjects showed significantly lower values (327.64 +/- 45.44 ng/ml, N = 10), supporting the view that PAA may be a marker for depressive disorders.

Measurement of 3-methoxy-4-hydroxyphenylacetic acid (HVA) in plasma by high-performance liquid chromatography with electrochemical detector (HPLC-EC).

A simple and sensitive high-performance liquid chromatography method with electrochemical detector is described for the determination of free 3-methoxy-4-hydroxyphenylacetic acid (HVA) in human plasma. The method does not involve any extraction, is specific and reproducible, and has the potential to measure serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) simultaneously. The plasma concentration of free HVA in eight normal, healthy adult volunteers was 10.9 +/- 4.6 (mean +/- SD). In a preliminary study, in one schizophrenic patient the plasma HVA increased twofold after neuroleptic treatment.