Psychopharmacology

Steinpreis, R. E.; Moser, Lorna; Parret, Fola; Rutell, Ethan; Panos, John

doi: 10.1007/s002130050652pmid: 9718279

Classic neuroleptic drugs produce a syndrome of vacuous jaw movements in rats, and this syndrome has been offered as an animal model of early onset extrapyramidal side effects. The atypical antipsychotics do not produce elevations in vacuous jaw movements, or do so only at very high doses. The purpose of the present study was to determine the impact of the putative antipsychotic, amperozide, on vacuous jaw movements in rats. Groups of rats received daily injections of haloperidol (0.2, 0.4, or 0.8 mg/kg), clozapine (2.0, 4.0, 8.0 mg/kg), amperozide (2.0, 4.0, 8.0 mg/kg) or vehicle for 4 weeks. Once per week, rats were observed for the presence of vacuous jaw movements. Haloperidol increased vacuous jaw movements with increasing doses. Clozapine only produced elevations in vacuous jaw movements at the highest dose. In contrast, increasing doses of amperozide resulted in decreasing vacuous jaw movements for this portion of the dose-response curve. This is the first report of the effect of amperozide on vacuous jaw movements and results are discussed in terms of a potentially unique behavioral profile with respect to this behavior.

Wood, Robin D.; Tirelli, Ezio; Snyder, Kristyn J.; Heyser, Charles J.; LaRocca, Tara M.; Spear, L. P.

doi: 10.1007/s002130050653pmid: 9718280

While chronic intermittent administration of stimulants often induces behavioral sensitization in adulthood, stimulant sensitization has rarely been reported prior to weaning (around postnatal day (P) 21). Consistent pairing of drug administration with the test context often facilitates sensitization in adults, yet young animals have been typically returned to the home cage immediately post-injection. To determine whether promoting context-dependent sensitization might facilitate expression of sensitization in preweanlings, Sprague-Dawley rats were injected daily from P14 to P20 with 0, 5, 15, or 30 mg/kg cocaine HC1 and placed for 30 min in either the experimental chamber or home cage. On P21 (test day), subjects were challenged with either 15 mg/kg cocaine or saline prior to placement in the experimental chamber. Significant sensitization of cocaine-induced stereotyped head movements was evident in animals given 15 or 30 mg/kg chronically in the experimental chamber, but not when these same doses were given in the home cage. Less consistent evidence for cocaine-induced sensitization was seen when examining locomotion, although trends for sensitization of this behavior were seen in animals chronically injected in either the test chamber or home cage. Thus, preweanlings can exhibit cocaine sensitization, particularly in terms of stereotypy, when tested shortly after the chronic exposure period, with expression of this sensitization being facilitated by pairing the chronic injections with the test context.

Jones, D. N. C.; Kortekaas, R.; Slade, Paula D.; Middlemiss, Derek N.; Hagan, Jim J.

doi: 10.1007/s002130050654pmid: 9718281

The present study determined the behavioural effects of the corticotropin releasing factor (CRF)-related peptides, human/rat CRF (h/rCRF), ovine CRF (oCRF), sauvagine (SAUV), urotensin I (UT) and the recently discovered neuropeptide, rat urocortin (rUCN). All of the peptides dose-dependently increased motor activity in a familiar environment and reduced feeding in hungry rats. There was no apparent relationship between potency/affinity at CRF 2 receptors and effects in these two tests. In a comparison of h/rCRF and rUCN upon discrete spontaneous behaviours, both peptides (3.0 μg ICV) increased activity and grooming, induced a fore-paw tremor and reduced the incidence of motionlessness. However, h/rCRF reduced motionlessness to a greater extent and was a more potent inducer of defaecation, weight loss, oral movements and fore-paw tremor than rUCN. In the elevated X maze, both h/rCRF and rUCN (1.0 μg ICV) had anxiogenic-like effects upon behaviour. In contrast, h/rCRF (1.0 μg ICV), but not rUCN (1.0–10 μg ICV) increased the startle response to an acoustic stimulus. In summary, all the CRF-related peptides increased motor activity and reduced feeding in rats in a similar manner and both rUCN and h/rCRF induced anxiogenesis. However, there were some behavioural differences between rUCN and h/rCRF which require further study. Further pharmacological investigation of the role of CRF receptor subtypes requires the use of subtype selective antagonists.

Taylor, Jane R.; Punch, Laurie J.; Elsworth, John D.

doi: 10.1007/s002130050655pmid: 9718282

Both the locus coeruleus (LC) and the amygdala have been implicated in aspects of opiate dependence and withdrawal. The LC is known to be one of the most sensitive sites for precipitating withdrawal behaviors after local opiate antagonist infusions in morphine-dependent subjects. The amygdala is also known to mediate antagonist-induced withdrawal behaviors and aversive motivational states. The goal of the present study was to evaluate directly the ability of noradrenergic agonists and glutamatergic antagonists to attenuate naloxone-precipitated withdrawal behaviors when infused into the LC or the central nucleus of the amygdala (CeA). The alpha-2-noradrenergic agonists clonidine or ST-91 were infused into the CeA to compare the effects of noradrenergic activation in the CeA to the attenuation of withdrawal previously observed in rats infused with clonidine into the LC, since the LC and CeA are known to contain co-localized opiate and noradrenergic receptors. The effects of microinfusions of the non-NMDA excitatory amino acid antagonist 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX) were also infused into the LC and CeA since opiate withdrawal is associated with increased glutamatergic transmission. Intra-CeA clonidine or ST-91 (2.4 µg/0.5 µl or 1.0 µl) produced significant reductions primarily in the occurrence of irritability. Conversely, intra-CeA or intra-LC infusions of CNQX (2.5 µg/0.5 µl) significantly attenuated naloxone-precipitated withdrawal, an effect similar to the attenuation previously observed after intra-LC clonidine infusions. These data demonstrate the specific behavioral effects of altering glutamatergic and noradrenergic neurotransmission in the LC or CeA during naloxone-precipitated opiate withdrawal. Elucidation of the neuroanatomical circuitry involved in opiate withdrawal should increase our understanding of the neuroadaptations associated with drug dependence and subsequent withdrawal behavior.

Jelic, Petra; Shih, Mei-Fen; Taberner, P. V.

doi: 10.1007/s002130050656pmid: 9718283

Diurnal variation in blood and plasma ethanol levels (BACs) has been observed in animals undergoing chronic ethanol treatment, but the information available is insufficient to determine whether the different patterns seen are due to differences in ethanol administration schedules or to strain of the animal. In this study, we have compared plasma ethanol levels in males of two mouse strains with no innate preference for ethanol, TO and CBA, during two commonly employed chronic ethanol treatment schedules. Ethanol was administered in solution as sole drink (CED) (10% or 20% w/v ethanol) for 4 weeks, or in liquid diet form (ELD), (3.5% w/v ethanol for 2 days, then 7% for 5 days). Mice were housed eight per cage on a 12-h light cycle (0900–2100 hours). Plasma ethanol concentration was monitored over the 24-h period. Activity of liver alcohol dehydrogenase (ADH) was measured between 0900 and 1100 hours. CBA mice showed greater variability in body weights than TO mice, which weighed more throughout the period of study and had significantly higher total energy intakes. TO mice consumed more ELD than CBA mice. Following an initial 2-day period of 3.5% ELD, both strains decreased their diet intake when ethanol content of the diet was increased to 7% w/v, which resulted in weight loss. Mice on the CED schedules decreased their fluid intake with increasing concentration of ethanol in the drinking solution. Highest daily ethanol intakes were observed in mice on ELD (19.1 ± 1.7 and 22.2 ± 0.6 g/kg body weight in CBA and TO mice, respectively). Marked diurnal variation in plasma ethanol levels was observed, which was dependent on the treatment schedule, strain and method of ethanol administration. Highest levels were found in mice on the ELD schedule (104.8 ± 7.7 mM in CBA mice, 113.5 ± 14.5 mM in TO mice), peaking at 1900 and at 0900 hours in CBA and TO mice, respectively. Lower plasma ethanol concentrations were reached in mice on the CED schedules, peaking at midnight (34.6 ± 8.1 mM and 35.4 ± 8.8 mM in CBA and TO mice on 20% CED, respectively, and 3.7 ± 1.2 mM and 6.6 ± 2.1 mM in CBA and TO mice on 10% CED). Naive CBA mice had slightly higher liver ADH activity as compared to their TO counterparts. No effect of 10% CED on liver ADH activity was found in either mouse strain. In conclusion, we have confirmed the importance of monitoring plasma ethanol levels during chronic treatment, as there is marked diurnal variation, dependent on the light/dark cycle. Factors such as strain of the animal and the method of delivery of ethanol are also important, whereas liver ADH plays a minor role. Monitoring the daily ethanol consumption is insufficient to predict the resulting plasma levels of the drug.

Roe, Daniel L.; Bardgett, Mark E.; Csernansky, Cynthia A.; Csernansky, J. G.

doi: 10.1007/s002130050657pmid: 9718284

Antipsychotic drugs increase expression of the immediate early gene, c-fos, in the striatum, nucleus accumbens and prefrontal cortex of rat brain. Since intracerebro-ventricular (ICV) infusion of kainic acid (KA) produces loss of limbic-cortical neurons that project to these brain areas, we postulated that the c-fos responses to antipsychotics in these brain areas would be altered following ICV KA administration. To produce limbic-cortical lesions, rats received ICV infusions of either KA (4.5 nmol) or vehicle. Then, 25–28 days later, rats received 0.13, 0.35, or 1.5 mg/kg haloperidol, 6.3, 17.5, or 30.0 mg/kg clozapine, or saline. In both KA-lesioned and control animals, haloperidol produced greater increases in Fos protein immunoreactivity in the striatum than in limbic-cortical areas, while clozapine produced greater increases in Fos protein immunoreactivity in limbic-cortical areas than in the striatum. In both KA-lesioned and control animals, haloperidol and clozapine administration also produced similar dose-dependent increases in Fos protein immunoreactivity in the striatum and nucleus accumbens. However, the ability of clozapine to increase Fos protein immunoreactivity in the infralimbic prefrontal cortex was significantly enhanced in KA-lesioned rats compared to controls. Since limbic-cortical pathology has been implicated in the negative symptoms of schizophrenia, the enhanced effect of clozapine on limbic-cortical expression of c-fos in KA-lesioned rats may be relevant to understanding clozapine’s unusual therapeutic actions in patients with schizophrenia.

Pierre, Peter J.; Vezina, P.

doi: 10.1007/s002130050658pmid: 9718285

Prior exposure to amphetamine leads to sensitized locomotor responding to subsequent injections and an enhanced predisposition to self-administer low doses of the drug. Because D 1 dopamine (DA) receptors have been shown to play an important role in the development of sensitized locomotor responding to amphetamine, the present experiment assessed their contribution to the development of facilitated amphetamine self-administration produced by prior exposure to the drug. During a pre-exposure phase, rats were administered two injections on each of 10 consecutive days. The first injection (saline, 1 ml/kg, IP, or the D 1 DA receptor antagonist SCH23390, 0.04 mg/kg, SC) preceded the second (saline or amphetamine, 1.5 mg/kg, IP) by 30 min. Starting 10 days after the last injection, animals were given the opportunity to lever press for a low dose of amphetamine (10 μg/kg per infusion) in a two-lever (active versus inactive) continuous reinforcement operant task, in each of seven daily sessions. Consistent with previous reports, prior exposure to amphetamine resulted in an increase in active versus inactive lever pressing. Blocking D 1 DA receptors with SCH23390 prior to each of the amphetamine pre-exposure injections prevented the development of this enhanced self-administration of amphetamine. When animals were grouped according to their locomotor response to a novel environment (assessed prior to the experiment), it was found, again in agreement with previous reports, that enhanced drug self-administration (as indicated by increased active versus inactive lever pressing as well as shorter latencies to emit the first active lever press, shorter inter-response times and more time-out responses on this lever) was observed only in amphetamine pre-exposed rats that had shown a locomotor response to novelty above the median of the subject sample (high responders). Preceding the amphetamine pre-exposure injections with SCH23390 blocked the development of enhanced drug self-administration observed in these animals. These findings, indicating that manipulations known to block the induction of locomotor and dopaminergic sensitization by amphetamine also block the facilitation of drug self-administration, suggest an important and common role for D 1 DA receptor activation in the development of enhanced responding to and for drug.

Grupp, L. A.; Lau, V.; Harding, S.

doi: 10.1007/s002130050659pmid: 9718286

Many adrenergic agonists including isoproterenol, a β 1, 2 -adrenergic agonist, reduce alcohol consumption, but the mechanism of this effect is not known. Adrenergic agonists have a variety of effects, among which are their ability to raise both angiotensin (ANG) II activity and plasma glucose levels. Previous research has shown that ANG II and enhanced glucose levels are accompanied by reductions in alcohol intake. Therefore, the following experiments assessed the roles of each of these factors in the suppression of alcohol intake by isoproterenol. Male Wistar rats were trained to drink a quantity of 6% (w/v) alcohol using the limited access procedure, which offers a daily 40-min access to alcohol and water. In experiment 1, isoproterenol or vehicle was administered SC just prior to alcohol availability, and only the group receiving isoproterenol showed a marked reduction in alcohol intake. Following this, the groups were pretreated IP with either vehicle or ascending doses of the prostaglandin synthetase inhibitor, indomethacin (2, 4 mg/kg), followed by either isoproterenol or vehicle. Control groups received either two vehicle injections or vehicle and indomethacin. Indomethacin alone did not affect alcohol intake at any of the doses tested but did dose-dependently attenuate the reduction in alcohol intake produced by isoproterenol. In experiment 2, isoproterenol was administered just prior to alcohol availability and when the suppression of alcohol intake stabilized, ascending doses of the angiotensin converting enzyme inhibitor, enalapril (1, 20, 40 mg/kg), were given IP 1 h prior to the isoproterenol. Enalapril altered water intake but had no effect on the isoproterenol-induced reduction in alcohol intake. These results show that the inhibition of alcohol drinking by isoproterenol varies more closely with altered glucose levels than with increased ANG II synthesis. They also demonstrate that downstream consequences of a drug may play a role in its effect on alcohol intake.

Dwyer, Suzanne M.; Rosenwasser, A. M.

doi: 10.1007/s002130050660pmid: 9718287

Neonatal exposure to antidepressant monoamine re-uptake inhibitors produces a wide variety of effects on the behavior and physiology of adult rats which are consistent with features of clinical depression. Since depressed patients show characteristic alterations in circadian rhythmicity, our laboratory has examined free-running circadian drinking rhythms in this putative animal depression model. Previously, neonatal desipramine treatment was shown to lengthen free-running period, and increase circadian amplitude, spectral magnitude, and voluntary alcohol intake (10% ethanol v/v) of male rats. The purpose of the present study was to examine the effects of neonatal clomipramine treatment (25 or 30 mg/kg SC, postnatal days 8–21) on circadian drinking rhythms and alcohol intake of both male and female rats. In addition, effects of alcohol exposure on circadian rhythmicity were also examined. Contrary to expectations, free-running period of clomipramine-treated rats did not differ from saline-treated controls in either constant darkness (DD) or constant light (LL), but spectral magnitude was increased in clomipramine-treated males and females, and circadian amplitude was increased in clomipramine-treated females. Neonatal clomipramine also increased voluntary alcohol intake, and both clomipramine- and saline-treated groups displayed significant period-shortening during alcohol exposure. Taken together, these results suggest that alterations in the amplitude and coherence of circadian rhythmicity may be more consistent than alterations in free-running period in animal depression models, as has been suggested previously for depressed patients.

Hatsukami, D.; Lexau, Benjamin; Nelson, David; Pentel, Paul R.; Sofuoglu, Mehmet; Goldman, Anne

doi: 10.1007/s002130050661pmid: 9718288

Previous studies have shown that cotinine, a metabolite of nicotine, antagonizes some of the effects of nicotine. One study showed that cotinine eliminates the beneficial effects of the nicotine patch in reducing cigarette withdrawal symptoms. The purpose of this study was to examine the effects of various doses of cotinine on cigarette self-administration. Subjects were randomly assigned to one of three doses of cotinine fumarate (40, 80 and 160 mg) and placebo, each for a period of 10 days, in a randomized order. Outcome variables included measures of nicotine intake and subjective responses to smoked cigarettes. Results showed no differences in the number of cigarettes smoked, carbon monoxide levels, and weights of cigarette butts across the various doses of cotinine and placebo. However, higher nicotine serum levels were observed in the 160 mg cotinine fumarate condition compared to placebo and to 40 mg cotinine fumarate. No systematic effects of cotinine on subjective responses to cigarettes were observed. Cotinine appears potentially to have a selective modulatory effect on nicotine withdrawal symptoms but not on cigarette smoking.