Decreased maternal behavior and anxiety in ephrin-A5-/- mice

During development of the nervous system, molecular signals mediating cell-cell interactions play critical roles in the guidance of axonal growth and establishment of synaptic functions. The Eph family of tyrosine kinase receptors and their ephrin ligands has been shown to mediate neuronal interactions in the development of topographic axon projection maps in several brain regions, and the loss of Eph activities result in defects in select axonal pathways. However, effects of deficiencies of the Eph signals on animal behavior have not been well documented. In this study, we showed that inactivation of a ligand of the Eph receptors, ephrin-A5, resulted in defects in maternal behavior and alterations in anxiety. Female ephrin-A5 ^-/- mice show significant defects in nest building and pup retrieval. In addition, lower levels of anxiety were observed in both male and female null mice. These changes were not due to deficiencies in estradiol, progesterone or corticosterone levels. Our observations suggest that ephrin-A5 plays a key role in the development and/or function of neural pathways mediating mouse maternal care and anxiety.

Trimethyltin-induced alterations in behavior are linked to changes in PSA-NCAM expression

The neurotoxic heavy metal trimethyltin (TMT) primarily damages neurons of the hippocampus and limbic areas of the temporal lobe, and causes a dose-dependent decrease in the polysialated form of the neural cell adhesion molecule (PSA-NCAM) in the mouse hippocampus. In the current study, we attempted to associate deficits in spatial learning following TMT exposure at various stages in learning with changes in levels of NCAM-180 and PSA-NCAM in both the hippocampus and frontal cortex. Mice were treated with TMT either before or after training on a spatial learning paradigm and examined for changes in NCAM and PSA-NCAM 12h later. In the first set of experiments, male BALB/c mice were injected with TMT (2.25 mg/kg) or saline i.p. and tested 24-168 h later using hidden and visible versions of the water maze, as well as light avoidance and motor activity. Mice in both treated and control groups which demonstrated a significant improvement in water maze performance also showed an elevation in hippocampal PSA-NCAM at all time points examined. TMT exposure impaired spatial learning and blocked learning-induced elevations in PSA-NCAM expression 24-96 h post-treatment, but these deficits disappeared by 168 h post-treatment. Mice exposed to TMT during reconsolidation of spatial learning (after repeated water maze training) demonstrated a mild and transient difference in escape latency compared to saline exposed mice. TMT administration during this period did not result in the attenuation of PSA-NCAM expression observed when animals were exposed before training. These results confirm a specific role for PSA-NCAM in acquisition and consolidation of spatial memory.

Alterations in alcohol consumption, withdrawal seizures, and monoamine transmission in rats treated with phentermine and 5-hydroxy-L-tryptophan

We have previously shown that coadministration of the dopamine (DA) agonist phentermine plus the serotonergic agonist fenfluramine suppresses alcohol intake and withdrawal seizures in rats. In the present study, phentermine and the serotonin (5-HT) precursor, 5-hydroxy-L-tryptophan (5-HTP), were administered alone, or in combination, to rats fed on a 6% alcohol-containing diet or an isocaloric control diet. Following a 9-h withdrawal period from the alcohol-containing diet, phentermine enhanced the effects of 5-HTP on both reduction of alcohol withdrawal seizures as well as changes in striatal serotonin. Food intake was monitored for 24 h after drug treatment, and neurochemical measures were examined at various time points. Phentermine alone reduced food intake in all diet conditions, but this anorectic effect was followed by hyperphagia in control rats. Phentermine plus 5-HTP reduced the consumption of the alcohol-containing diet, while its effects on consumption of control diets were mixed. In vivo microdialysis in rat nucleus accumbens revealed that phentermine increased extracellular DA, whereas 5-HTP caused marked elevations in extracellular 5-HT. Coadministration of phentermine and 5-HTP evoked simultaneous elevations in extracellular DA and 5-HT that mirrored the effects of each drug alone. Collectively, these findings show that coadministered phentermine plus 5-HTP is effective in reducing alcohol intake and suppressing alcohol withdrawal seizures. These therapeutic actions may be related to elevations in synaptic DA and 5-HT in critical brain regions.

Increased excretion of a lipid peroxidation biomarker in autism

It is thought that autism could result from an interaction between genetic and environmental factors with oxidative stress as a potential mechanism linking the two. One genetic factor may be altered oxidative-reductive capacity. This study tested the hypothesis that children with autism have increased oxidative stress. We evaluated children with autism for the presence of two oxidative stress biomarkers. Urinary excretion of 8-hydroxy-2-deoxyguanosine (8-OHdG) and 8-isoprostane-F2alpha (8-iso-PGF2alpha) were determined in 33 children with autism and 29 healthy controls. 8-iso-PGF2alpha levels were significantly higher in children with autism. The isoprostane levels in autistic subjects were variable with a bimodal distribution. The majority of autistic subjects showed a moderate increase in isoprostane levels while a smaller group of autistic children showed dramatic increases in their isoprostane levels. There was a trend of an increase in 8-OHdG levels in children with autism but it did not reach statistical significance. There was no significant correlation between the levels of the biomarkers and vitamin intake, dietary supplements, medicine, medical disorders, or history of regression. These results suggest that the lipid peroxidation biomarker is increased in this cohort of autistic children, especially in the subgroup of autistic children.

Neurochemical and behavioral deficits consequent to expression of a dominant negative EphA5 receptor

The Eph family tyrosine kinase receptors and their ligands have been linked to axon guidance and topographic mapping of the developing central nervous system. More specifically, the EphA5 receptor has been shown to play a role in development of hippocamposeptal, retinotectal and thalamocortical projections. Recently, a line of transgenic mice was developed which expresses a truncated EphA5 receptor lacking a functional tyrosine kinase domain. In a previous study, axonal tracing revealed that medial hippocampal axons in this strain projected laterally and ventrally away from their normal target area. In the current study, both transgenic and wild-type controls were evaluated in unconditioned (rotorod and locomotor activity) and conditioned (water maze and active avoidance) behavior tasks which tested hippocampal and striatal functioning. Compared to controls, the transgenic strain did not show differences in rotorod motor activity but did show a transient deficit in spatial navigation ability and a consistent impairment in active avoidance. The dominant-negative mutant receptor also resulted in a decrease in striatal dopamine and serotonin concentrations with no change in hippocampal monoamines. Collectively, these data suggest that animals expressing a truncated EphA5 receptor show deficits related to striatal functioning.

Role of monoamine oxidase inhibition and monoamine depletion in fenfluramine-induced neurotoxicity and serotonin release

The role of both monoamine synthesis and monoamine oxidase inhibition in mediating the fenfluramine-induced damage to serotonin neurones was examined; as pretreatment agents, both alpha-methyl-para-tyrosine (AMPT) and parachlorophenylalanine (PCPA) were used to deplete dopamine and serotonin, respectively, while clorgyline and deprenyl were used to inhibit monoamine oxidase types A and B. While both AMPT and deprenyl did not alter fenfluramine induced serotonin or 5-hydroxyindoleacetic acid (5-HIAA) depletion in any area, PCPA did partially reduce the serotonin depletion in the hippocampus and hypothalamus. Although pretreatment with clorgyline did not significantly alter fenfluramine-induced serotonin depletion, it did produce a 65% mortality rate in animals treated with both drugs. Both PCPA and clorgyline significantly increased the depletion of striatal 5-HIAA concentration consequent to fenfluramine; however, these drugs also produced a long-term depletion of striatal 5-HIAA when administered alone, therefore, the changes seen after the coadministration with fenfluramine may be viewed as additive. Finally, acute PCPA pretreatment attenuated the rapid rise in 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (homovanillic acid) induced by fenfluramine, and acute clorgyline reversed the drop in serotonin and rise in 5-HIAA induced by fenfluramine. These results indicate that the rapid increase in dopamine activity induced by fenfluramine is partially dependent on serotonin concentration and release and that the mechanism of fenfluramine-induced toxicity is unlike that of the other substituted amphetamines.

Altered sensitivity of CD81-deficient mice to neurobehavioral effects of cocaine

CD81, also known as target of the antiproliferative antibody, is known to be expressed in astrocytes and involved in cell adhesion and, recently, we demonstrated its induction exclusively in the accumbens following cocaine. In the present study, the sensitivity of CD81-deficient mice to behavioral effects of cocaine was evaluated. It was found that CD81-deficient mice exhibited altered sensitivity to cocaine as assessed in the place preference conditioning paradigm and locomotor activity. This deficit in place preference conditioning was not accompanied by a deficit in acquisition or retention of water maze behavior. In addition, CD81 knockout mice exhibited higher levels of nucleus accumbens dopamine as compared to their controls. These observations are discussed in the context of the role of CD81 in cocaine-mediated behaviors.

Cocaine-induced expression of the tetraspanin CD81 and its relation to hypothalamic function

CD81, a tetraspanin transmembrane protein involved in cell adhesion, was found by differential display to be upregulated in the nucleus accumbens of rat brain following acute cocaine treatment (four injections of 30 mg/kg every 2 h followed by 24 h withdrawal). Cocaine-induced expression of CD81 in adult rat brain was confirmed by quantitative real-time RT-PCR. Its expression in neurons and its function in the brain are unknown. In situ hybridization shows a neuron-specific expression pattern in brain regions functionally related to the regulation of cardiovascular function and fluid homeostasis. CD81 displays codistribution to galanin and, to a lesser extent, to vasopressin. These findings add to data that suggest a connection between the brain reward pathway and the centers regulating endocrine and autonomic functions, in relation to neurochemical, behavioral, and somatic consequences of drug abuse.

Regulation of EphB1 expression by dopamine signaling

The Eph family tyrosine kinase receptors and their ligands have been implicated in axon guidance and neuronal migration during development of the nervous system. In the current study, we aim to characterize the nature of changes in EphB1 receptor expression following increases or decreases in dopamine activity. Neonatal mice (P3) were injected with 6-hydroxydopamine and allowed 13 days to recover. These animals show a profound depletion of dopamine in all areas assayed, with a corresponding dose-dependent decrease in EphB1 expression. Day 3 pups were also injected either chronically (P3-P16) or acutely (P3 only) with cocaine to determine how enhancing dopamine signaling would affect EphB1 signal density. It was found that both treatments significantly increased expression of EphB1 in the cortex, striatum and substantia nigra. Finally, animals were treated prenatally (E15-E17) with cocaine and sacrificed on P7. These animals also showed an increase in EphB1 signal density, but only in the dopaminergic terminal areas in the cortex and striatum. These studies indicate that dopamine activity regulates developmental expression of the tyrosine kinase receptor EphB1.

Avoidance responding following amphetamine-induced dopamine depletion

The effect of an amphetamine-induced depletion of striatal dopamine on active and passive avoidance responding of rats was examined. Sixteen animals received two sets of 4 injections each of 15 mg/kg d-amphetamine, administered at 2 hr intervals with each set delivered one week apart. One week after the last injection, animals were given 50 consecutive active avoidance trials in a shuttle box. Animals treated with amphetamine exhibited a 50%, depletion of striatal dopamine and showed a slower learning curve, as evidenced by significantly fewer avoidances and a slower escape latency during trials 21-30. Both groups demonstrated a 90% avoidance rate by trials 41-50. A separate group of rats was treated as above and trained for several weeks on the active avoidance procedure. Haloperidol (0.01-0.10 mg/kg intraperitoneally) dose-dependently decreased avoidance number and increased avoidance and escape latency in both groups, an effect that was exaggerated in those animals previously treated with amphetamine. Finally, these animals were tested in the same apparatus using a passive avoidance procedure. The amphetamine treatment produced a significantly higher mean number of avoidances in this procedure compared to saline-treated animals during trials 1-20. These results suggest that the impairment in conditioned avoidance following amphetamine treatment is due to a motoric, rather than a cognitive deficit.

Monoaminergic changes associated with audiogenic seizures in ethanol-dependent rats

1. A previous report demonstrated the efficacy of combining dopaminergic and serotonergic agonists in suppressing audiogenic seizures induced in ethanol-dependent rats undergoing withdrawal. Moreover, an increase in dopamine and a reduction in serotonin levels in the striatum were associated with such seizures. 2. The present study was designed to examine neurochemical changes in the striatum associated with repeated episodes of ethanol withdrawal seizures in untreated ethanol-dependent rats as well as in those treated with amphetamine and fenfluramine in combination. 3. Ethanol-dependent rats undergoing audiogenic seizures exhibited an increase in striatal dopamine and a reduction in striatal serotonin as compared to control and ethanol-dependent rats not undergoing seizures. Amphetamine and fenfluramine in combination effectively suppressed the audiogenic seizures by reversing the neurochemical changes in the striatum in ethanol-dependent rats. However, increased dopamine but decreased serotonin levels in the striatum were observed in rats undergoing one episode of ethanol withdrawal, but not in those experiencing multiple episodes of ethanol withdrawal. 4. Thus, alterations in striatal dopamine and serotonin levels were, at best, necessary but not sufficient to predispose audiogenic seizure susceptibility in ethanol-dependent rats.

Methamphetamine-induced striatal dopamine release, behavior changes and neurotoxicity in BALB/c mice

The behaviors associated with the neurotoxic effects of methamphetamine were evaluated in BALB/c mice. Hyperthermia and behavioral observations were measured 60 min after each subcutaneous injection of methamphetamine (4x4 or 8 mg/kg) or saline, each given 2 h apart. The behavioral observations included stereotyped behaviors, incidence of hemorrhage in breast, salivation and self-injurious behavior (SIB). Repeated administration of methamphetamine produced these behavioral changes and hyperthermia, but resulted in hypothermia by the final injection (8 mg/kg). In addition, the methamphetamine treatment induced a long-lasting dopamine depletion of similar magnitude in the 4 and 8 mg/kg-treated animals. In a time course study striatal monoamine levels were measured 60 min after each injection of these doses. The first and second injections of methamphetamine (8 mg/kg) produced a drastic increase in striatal 3-methoxytyramine; this failed to occur after the third or fourth injection of the same dose. In contrast, 4 mg/kg of methamphetamine also produced an increase in 3-methoxytyramine after the second and third injections of the drug and, in this case, these were maintained for the duration of the treatment. Striatal 3, 4-dihydroxyphenylacetic acid levels also drastically decreased following both doses of methamphetamine, suggesting inhibition of monoamine oxidase in striatum. Moreover, a single injection of methamphetamine increased striatal 2,3-dihydroxybenzoic acid formation. These results suggest that the incidence of hyperthermia, SIB and striatal dopamine neurotoxicity are closely linked to striatal dopamine release and inhibition of monoamine oxidase produced by methamphetamine in BALB/c mice.

Evaluation of the effects of alpha-phenyl-N-tert-butyl nitrone pretreatment on the neurobehavioral effects of methamphetamine

A relationship between formation of reactive oxygen species (ROS) and energy depletion has been proposed to play an important role in mediating methamphetamine (METH)-induced neurotoxicity. To evaluate this relationship, we examined the effect of the spin-trap agent, alpha-phenyl-N-tert-butyl nitrone (PBN) on hyperthermia and self-injurious behavior (SIB) and striatal dopamine (DA) depletion produced by METH (4 injections of 4 mg/kg, 2 hr intervals, s.c.) in BALB/c mice. Repeated administration of METH induced hyperthermia, incidence of SIB and striatal DA depletion (84% after 3 days). Pretreatment with PBN (4 injections of 60 or 120 mg/kg, i.p.) reduced METH-induced hyperthermia, but did not significantly attenuate METH-induced SIB or the striatal DA depletion. On the other hand, pretreatment with high doses of PBN (4 injections of 180 or 240 mg/kg, i.p.) protected against METH-induced hyperthermia and SIB, and PBN (180 mg/kg) also completely protected against the acute striatal DA depletion 60 min after the last injection of the drug. However, the long-lasting striatal DA depletion was only attenuated by 52 or 56%, respectively. These results indicate that METH-induced hyperthermia contributes to, but is not solely responsible for METH-induced neurotoxicity, and supports a role for formation of ROS and other mechanisms in the generation of METH-induced striatal dopaminergic neurotoxicity. In addition, the difference in the efficacy of PBN to protect against the acute or long-lasting striatal DA depletion induced by METH may indicate that both ROS formation and other mechanisms are required for METH-induced neurotoxicity to develop.

Acute effects of aspartame on aggression and neurochemistry of rats

The inverse relationship between serotonin and aggression was investigated in rats treated with aspartame, a sweetener thought to interfere with the synthesis of this neurotransmitter. Eleven adult, male Long-Evans rats received either aspartame (200-800 mg/kg, IP) or the vehicle prior to testing in a standard resident-intruder paradigm. Contrary to our hypothesis, aspartame significantly decreased aggression as shown by increased latencies to the first attack and decreased number of bites per session. Corresponding with the effects on aggression, aspartame significantly increased striatal levels of serotonin. It was concluded that high doses of aspartame reduced aggressive attack via a serotonergic mechanism while the lower dose was without effect on either variable.

Effect of gestational and lactational 2,3,7, 8-tetrachlorodibenzo-p-dioxin exposure on the level and catalytic activities of hepatic microsomal CYP1A in prepubertal and adult rats

We determined the inducibility, as well as the persistence of the induction, of hepatic microsomal CYP1A1 and CYP1A2 (by western blot analysis), and their catalytic activities (as measured by resorufin ether O-dealkylation) in prepubertal (25-day-old) and adult (120-day-old) offspring of timed-pregnant Sprague-Dawley rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD treatment was subcutaneous, at a low dose of 0.1 microg/kg, on gestational days 7, 14, and 20, and on lactational days 7 and 14. CYP1A1 protein was induced significantly (23-fold) in prepubertal but not in adult offspring of TCDD-exposed dams, whereas ethoxyresorufin O-deethylase (EROD) activity, which is CYP1A1-preferential, was induced less extensively (5-fold) and slightly (1.7-fold) in the prepubertal and adult offspring, respectively. Benzyloxyresorufin O-debenzylase (BROD) activity, which is CYP2B-preferential but has been reported to be catalyzed by CYP1A1, was also induced 5- and 6-fold in prepubertal and adult offspring, respectively, of TCDD-exposed dams. However, the induced BROD activity was neither inhibited by antibody against CYP1A1 nor accompanied by an elevated level of microsomal CYP2B. CYP1A2 was induced slightly only in prepubertal offspring of TCDD-treated dams. There was suggestive evidence of enhanced lipid peroxidation in hepatic microsomes from prepubertal but not adult offspring of TCDD-treated dams. These data showed that in utero plus lactational TCDD exposure effected transient induction of hepatic microsomal CYP1A1 but sustained induction of BROD activity, which may be catalyzed by enzymes other than CYP1A or CYP2B.

Methamphetamine-induced striatal dopamine neurotoxicity and cyclooxygenase-2 protein expression in BALB/c mice

The expression of cyclooxygenase-2 (COX-2) and striatal dopamine (DA) depletion in BALB/cAnNcrj (BALB/c) mice following a neurotoxic dose of methamphetamine (METH) was investigated. METH-treatment (4 mg/kg x 4, 2 h intervals, s.c.) induced a significant hyperthermia and a persistent depletion of striatal DA levels 72 h after the treatment. COX-2, a marker of the cytotoxic effect of inflammation and oxidative stress and thiobarbituric acid (TBA) were significantly induced in the striatum 72 h after the METH-treatment, but not in the hippocampus. These results suggest that COX-2 may participate in METH-induced neurotoxicity in striatum.

Effects of phentermine and fenfluramine on alcohol consumption and alcohol withdrawal seizures in rats

The drug combination of phentermine plus fenfluramine has been used clinically in both the treatment of obesity and alcoholism. The aim of the current study was to assess the interaction of the two drugs on consumption of both an alcohol-containing and a nonalcoholic diet. Furthermore, the efficacy of the drug combination on suppression of withdrawal seizures was determined. Animals were either maintained on a 6% alcohol-containing diet, free-fed an isocaloric control, or pair-fed the control diet. It was observed that, with regard to body weight growth curves, alcohol provides about 2.5 kcal/g. Both phentermine and fenfluramine caused a decrease in consumption 1 h after administration; however, during the next 23 h, 4 mg/kg phentermine significantly increased consumption of all diets. At doses of 1 and 2 mg/kg, fenfluramine selectively reduced consumption of the alcohol-containing diet as compared to the isocaloric diets. Lower doses of fenfluramine blocked the increases in consumption induced by phentermine. Furthermore, in animals fed the nonalcoholic diet, the drug combination of 2 mg/kg fenfluramine plus 8 mg/kg phentermine produced a 63-82% reduction in consumption, an effect not seen when either drug was administered alone. This greater than additive effect was also seen in the earlier time periods in animals pair-fed the control diet. Neurochemical analysis from these animals revealed that the alcohol-dependent animals displayed a significant reduction of DOPAC and 5-HIAA levels in the striatum, frontal cortex, and hypothalamus after a 9-h withdrawal period, further implicating the serotonergic and dopaminergic systems in mediation of withdrawal symptoms and alcohol craving. Finally, 8 mg/kg phentermine plus 8 mg/kg fenfluramine completely abolished alcohol withdrawal seizures, compared to a 78% rate in saline treated rats. In conclusion, the coadministration of phentermine plus fenfluramine produced a moderate reduction of alcohol consumption and was completely effective at reducing alcohol withdrawal seizures.

Hydroxyl radical formation following methamphetamine administration to rats

Administration of neurotoxic doses of methamphetamine (8 mg/kg, intraperitoneally x 4 times, at 2 hr intervals) caused a significant decrease in dopamine and 3,4-dihydroxyphenylacetic acid and an increase in 3-methoxytyramine levels in the striatum along with a decrease in serotonin and 5-hydroxyindoleacetic acid levels in the striatum and hippocampus. In addition, the methamphetamine treatment caused an increase in rat rectal temperature. Intraventricular injection of salicylate 105 min. after the last injection of methamphetamine produced an increase in 2,3- and 2,5-dihydroxybenzoic acid in the striatum and hippocampus. Moreover, the ratio of 2,3-dihydroxybenzoic acid to salicylate was significantly increased in the striatum, but not in the hippocampus. These results indicate that the hydroxyl radical may play an important role in methamphetamine-induced neurotoxicity in rat striatum and that its formation may be the result of methamphetamine-induced release of dopamine.

Dose-dependent up-regulation of rat pulmonary, renal, and hepatic cytochrome P-450 (CYP) 1A expression by nicotine feeding

In a previous study in which a single 2.5 mg/kg (15.4 micromol/kg) s. c. dose of nicotine effected a transient, lung-specific induction of cytochrome P-450 (CYP) 1A1 in the rat, a dose-response study and assessment of the lung specificity of the induction was limited by toxicity of the acute parenteral nicotine exposure. In the present study, we examined the dose-CYP1A1/2 induction response relationship and the tissue specificity of the induction by orally administered nicotine, which lacks the toxicity of the parenterally administered drug. Nicotine, administered in a nutritionally balanced liquid diet, at a level of 20 (low), 60 (medium), or 200 (high) mg/kg of diet, induced CYP1A1 in the lung and kidney in a dose-dependent manner and in the liver at the high nicotine dose only, whereas CYP1A2 was induced in the liver dose-dependently and in the kidney at the high nicotine dose only. The high nicotine dose up-regulated mRNA level in the three tissues examined, but with the lung being the most responsive to the up-regulation. Induction of the CYP1A1-preferential activity ethoxyresorufin O-deethylase by the low, medium, and high nicotine diets was 1.9-, 4.9-, and 21.6-fold, respectively, in the lung, 1.4-, 1.7-, and 15.9-fold, respectively, in the kidney, and 1.7-, 2.9-, and 5.1-fold, respectively, in the liver. Similarly, albeit to lower extents, the dietary alkaloid induced the CYP1A2-preferential activity methoxyresorufin O-demethylase in all three tissues dose-dependently. Plasma nicotine concentration correlated neither with the dietary nor intake dose of the alkaloid nor with tissue levels of CYP1A, especially with the high-dose diet. Plasma nicotine levels at which CYP1A induction was maximal were comparable to those reported in smokers, suggesting that nicotine may induce CYP1A1 in humans.

Efficacy of providing nicotine in a liquid diet to rats

To determine if rats would consume nicotine at psychoactive levels, a nutritionally balanced diet with 0, 20, 60, or 200 mg of nicotine tartrate per kg of diet was provided. Diet consumption and body weight differences were recorded for 14 days after which, following 16 hr of withdrawal, animals were given access to a two-bottle choice of the previously presented diet and a nicotine-free diet. Spontaneous horizontal motor activity was recorded 8, 16, and 24 hr after withdrawal. By Day 14, all animals showed a significant increase in diet consumption and significant weight gain compared to Day 1. Animals consumed an average of 2.1, 6.8, or 19.5 mg/kg/day of nicotine on the low, medium, and high-nicotine diets, respectively. However, animals receiving the high-nicotine diet consumed less diet and gained less weight than the control, low, and medium nicotine groups. During only the first 4 hr of the two-bottle choice (16-20 hr postwithdrawal), the high-nicotine group consumed significantly higher amounts of nicotine base than the other groups, but also consumed more of the control diet during the first 2 hr. In a replicate experiment, animals receiving the medium-nicotine diet showed an increased consumption of the nicotine diet and increased preference for nicotine following a 14-day exposure compared to the control-fed animals and compared to a baseline preference test. Also, this group showed differences in locomotor activity consistent with other studies using an injection regimen or subcutaneuos pumps to induce dependence. Finally, animals in all three groups exhibited high plasma nicotine and cotinine (a major nicotine metabolite) levels. Because animals in all groups tolerated the diet well, gained weight, selected the nicotine diet in a choice test, and showed withdrawal symptoms, we conclude that the liquid diet proved to be a satisfactory method of inducing nicotine dependence in rats.

Differential effects of monoaminergic agonists on alcohol intake in rats fed a tryptophan-enhanced diet

The goal of the present study was to determine if enhancement of tryptophan levels in a nutritionally balanced liquid diet would affect alcohol intake in a two-bottle choice procedure. Furthermore. the monoaminergic agonists amphetamine, phentermine (dopaminergic- and noradrenergic-releasing drugs), and fenfluramine (a serotonin releaser) were administered to determine if these drugs reduced alcohol intake in animals fed the tryptophan-enhanced diet compared to those fed an alcohol-containing diet without added tryptophan. Amphetamine 0.5 and 2 mg/kg and phentermine 4 mg/kg selectively reduced alcohol intake in animals fed the tryptophan-enhanced diet; higher doses also reduced alcohol intake in animals fed the control alcohol diet. Three hours after drug administration, phentermine 2 and 4 mg/kg produced increases in consumption of the nonalcoholic diet in animals fed the control diet without affecting consumption in animals fed the tryptophan-enhanced diet. Finally, animals in the tryptophan-enhanced group gained less weight than those animals fed an identical diet without the added tryptophan. Neurochemical analysis revealed that the tryptophan-fed groups showed increased 5-HIAA concentrations and serotonin turnover in the striatum. hypothalamus, and frontal cortex compared to animals fed the control diet. The tryptophan-alcohol group also showed almost double the tryptophan levels in the hypothalamus compared to the tryptophan-isocaloric group. These results indicate that, whereas increasing tryptophan levels by itself was not sufficient to alter consumption of an alcohol-containing diet, the administration of monoaminergic agonists significantly interacted with tryptophan in a dose-dependent manner to reduce intake of an alcohol-containing diet without reducing intake of an isocaloric diet.

Neurotoxic effects of amphetamine plus L-DOPA

1. Male Swiss Webster mice were administered a series of amphetamine injections preceded by either saline or L-DOPA. 2. This injection regimen was performed for either one, two or three consecutive weeks and neurotoxic effects of the drugs were determined one week later. 3. Amphetamine treatment for two weeks produced a greater striata-dopaminergic lesion that treatment for only one week. Three weeks of treatment did not exacerbate the lesion, indicating that the damage had reached maximal levels. 4. L-DOPA pretreatment did not significantly alter any of the toxic effects of the amphetamine. Therefore, some dopaminergic neurons may be resistant to the toxic effects of amphetamine.

Specification of distinct dopaminergic neural pathways: roles of the Eph family receptor EphB1 and ligand ephrin-B2

Dopaminergic neurons in the substantia nigra and ventral tegmental area project to the caudate putamen and nucleus accumbens/olfactory tubercle, respectively, constituting mesostriatal and mesolimbic pathways. The molecular signals that confer target specificity of different dopaminergic neurons are not known. We now report that EphB1 and ephrin-B2, a receptor and ligand of the Eph family, are candidate guidance molecules for the development of these distinct pathways. EphB1 and ephrin-B2 are expressed in complementary patterns in the midbrain dopaminergic neurons and their targets, and the ligand specifically inhibits the growth of neurites and induces the cell loss of substantia nigra, but not ventral tegmental, dopaminergic neurons. These studies suggest that the ligand-receptor pair may contribute to the establishment of distinct neural pathways by selectively inhibiting the neurite outgrowth and cell survival of mistargeted neurons. In addition, we show that ephrin-B2 expression is upregulated by cocaine and amphetamine in adult mice, suggesting that ephrin-B2/EphB1 interaction may play a role in drug-induced plasticity in adults as well.

Acute and chronic effects of ginseng total saponin and amphetamine on fixed-interval performance in rats

The effect of ginseng total saponin (GTS) on amphetamine (AMPH)-induced disruption of fixed-interval (FI) responding in rats was examined. GTS (50 mg/kg) significantly improved the temporal responding impaired by 2 mg/kg of AMPH. A higher dose of 100 mg/kg GTS disrupted performance when given alone; this disruption was reversed by a low dose of AMPH (0.5 mg/kg) and tolerance developed to the effects of GTS with its repeated administration. Neurochemical analysis revealed that GTS (50 mg/kg) attenuated the increase in striatal dopamine caused by AMPH leading to the conclusion that brain dopamine may partially mediate the behavioral effects of GTS.

Acute and chronic effects of ginseng total saponin and amphetamine on fixed-interval performance of rats

The effect of ginseng total saponin (GTS) on amphetamine (AMPH)-induced disruption of fixed-interval (Fl) responding in rats was examined. GTS (50 mg/kg) significantly improved the temporal responding impaired by 2 mg/kg of AMPH. A higher dose of 100 mg/kg GTS disrupted performance when given alone; this disruption was reversed by a low dose of AMPH (0.5 mg/kg) and tolerance developed to the effects of GTS with its repeated administration. Neurochemical analysis revealed that GTS (50 mg/kg) attenuated the increase in striatal dopamine caused by AMPH leading to the conclusion that brain dopamine may partially mediate the behavioral effects of GTS.

Methamphetamine-induced changes in activity and water intake during light and dark cycles in rats

1. The authors investigated the ambulatory activity and water intake of rats during each 12 hr light and dark cycle for one week following four s.c. injections of 4 or 8 mg/kg of methamphetamine (METH). 2. Administration of the higher METH dose caused an increase in activity during the dark cycle on days 1 through 6 with the maximal increase on day 3 while the increase in activity during the light cycle was observed only on day 1. 3. Water intake increased the first day after administration of both METH doses, but returned to baseline by day 3. 4. Administration of both METH doses induced hyperthermia and the 8 mg/kg dose produced depletions of striatal dopamine and striatal, hippocampal and hypothalamic serotonin on day 3 but only in hippocampal serotonin by day 7. 5. These results demonstrate that high doses of METH produce a long-lasting increase in activity during the dark cycle and a transient increase in water intake. The behavioral changes which occurred during the dark cycle appear to be related to the depletion of central dopamine and/or serotonin.

Methamphetamine-induced neurotoxicity in BALB/c, DBA/2N and C57BL/6N mice

Repeated administration of methamphetamine (METH; 2 and 4 mg/kg, s.c. four times every 2 h) caused hyperthermia and a dose-dependent depletion of striatal dopamine levels 3 days after the METH-treatment in both BALB/cAnNCrj (BALB) and DBA/2NCrj (DBA) mice, but these responses were lower in C57BL/6NCrj (C57BL) mice. An acute decrease of striatal dopamine levels 30 min after the last injection of METH (4 mg/kg) was observed in both BALB and DBA mice, while an increase in dopamine was observed in C57BL mice. Striatal 3-methoxytyramine levels were drastically increased in both DBA and C57BL mice after this same treatment. Moreover, pretreatment with the superoxide dismutase inhibitor, diethyldithiocarbamate (200 mg/kg, i.p.) exacerbated the METH (4 mg/kg)-induced striatal dopamine-depletion in BALB mice. In addition, pretreatment with an inhibitor of poly(ADP-ribose) polymerase, benzamide (160 mg/kg, s.c.), significantly attenuated the METH (4 mg/kg)-induced striatal dopamine depletion in both BALB and DBA mice. These results suggest that both BALB and DBA mice possess a higher sensitivity to the METH-induced striatal dopaminergic neurotoxicity compared to C57BL mice. In addition, the striatal dopaminergic neurons of BALB mice may be more vulnerable to METH-induced oxidative stress as compared to that in C57BL mice.

Methamphetamine-induced modification of dopamine metabolism in cultured striatal astrocytes

The role of striatal astrocytes in the metabolic processing (by deamination) of methamphetamine-released dopamine is not known. To investigate the relationship between methamphetamine and dopamine metabolism, we measured 6-hydroxydopamine, dopamine and, 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations following methamphetamine treatment of cultured striatal astrocytes prepared from 1-2 day-old rats. Addition of low concentrations of dopamine (5 x 10(-5) to 5 x 10(-4) M) to cultured astrocytes increased DOPAC levels in a dose-dependent fashion while higher concentrations (5 x 10(-3) to 10(-2) M) inhibited its metabolism and induced formation of 6-hydroxydopamine. Under the same experimental conditions, 10(-4) M dopamine in combination with methamphetamine (10(-5) to 10(-3) M) inhibited DOPAC formation and increased dopamine levels in a dose-dependent fashion, but the formation of intracellular 6-hydroxydopamine was not evident. Deprenyl (10(-5) or 10(-4) M), an inhibitor of monoamine oxidase B, and pargyline (10(-5) or 10(-4) M), a non-selective monoamine oxidase inhibitor, completely inhibited DOPAC formation and increased dopamine levels, while clorgyline (10(-5) or 10(-4) M), an inhibitor of monoamine oxidase-A, only partially inhibited DOPAC formation (42 or 45% of control, respectively). These results support the hypothesis that methamphetamine inhibits monoamine oxidase and causes increases in dopamine levels in cultured striatal astrocytes.

Interaction of phentermine plus fenfluramine: neurochemical and neurotoxic effects

Previous studies have reported the use of combined serotonergic and dopaminergic agonists in the treatment of obesity and alcoholism. Along these lines, phentermine plus fenfluramine has been suggested as a possible clinical treatment for alcohol craving. To determine the neurochemical effects of a combined treatment of phentermine plus fenfluramine, animals were injected subcutaneously with saline, phentermine 12 mg/kg, fenfluramine 16 mg/kg, or a combination of phentermine plus fenfluramine. One hour after injection, animals were sacrificed and neurochemical analysis performed. Furthermore, separate groups of animals were given the same injections 8 times, 12 hours apart, to determine the effects on body weight and to detect a possible exacerbation of fenfluramine induced toxicity. The drug combination produced a significant rise in dopamine in the striatum, greater than that seen with either drug alone. Furthermore, the addition of phentermine reduced the fenfluramine induced rise in striatal 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindolacetic acid (5-HIAA). Phentermine plus fenfluramine combination produced a greater weight loss than either drug alone, however, it did not produce a significantly greater drop in striatal serotonin or 5-HIAA levels above that induced by fenfluramine alone. Thus, while previous studies report the potentiated neurotoxicity of phentermine plus fenfluramine over fenfluramine alone, the present study does not indicate that such an effect occurs following an administration regimen analogous to that of patients treated with the drug combination.

L-DOPA exacerbates amphetamine-induced dopamine depletion

Administration of L-DOPA to Parkinson patients has been suggested to exacerbate "functional denervation" of the nigrostriatal system. Therefore, experiments were conducted to determine if L-DOPA combined with the DOPA decarboxylase inhibitor, Ro4-4602 (benserazide hydrochloride) would potentiate amphetamine-induced neurotoxicity. Mice received two injections of saline or benserazide + L-DOPA (25.0 or 100.0 mg/kg) interspersed with four injections of amphetamine (15.0 mg/kg) at 2-h intervals. Significant depletion of striatal dopamine, DOPAC, and HVA was evident 1 wk following amphetamine administered with or without 25.0 mg/kg L-DOPA + benserazide, whereas 100.0 mg/kg L-DOPA + benserazide potentiated amphetamine-induced depletion of striatal dopamine (17 vs 28% of control values). This enhanced toxicity may be consequent to increased dopamine turnover following L-DOPA (360 vs 231%), a situation akin to that observed in compromised dopaminergic nigrostriatal systems of parkinsonian patients. Furthermore, striatal 5-HT was not altered by amphetamine alone, whereas concurrent administration of L-DOPA/ benserazide depleted 5-HT to 82% of control values. No changes were evident in the frontal cortex following amphetamine with or without concurrent L-DOPA/benserazide; however, L-DOPA/benserazide administered alone reduced 5-HT and 5-HT turnover to 58% of control values.

Alcohol utilization and dependence with special reference to protein level in a liquid diet for rats

Experiments were carried out with a nutritionally balanced diet to test the response of rats to levels of ethanol between 0% and 6%, and to different levels and sources of protein and amino acid supplements in relation to alcohol utilization and withdrawal seizures. The high-calorie/high-carbohydrate liquid diet was well tolerated when the alcohol level was less than 30% of total calories, or 4.5% of diet. When alcohol was provided at 6% of diet, or 33% of total calories, growth and withdrawal seizure rates were negatively affected in comparison with the lower ethanol levels, even though ethanol consumption (in g/kg/day) was not different. The 6% alcohol diet was then altered through the addition of more protein calories, from 13% to 20%. This supplementation improved growth rate of the animals and reduced the rate of withdrawal seizures. The improvement from the additional protein was observed with both casein and soy protein, and was not attributable to any one or even several amino acids that might serve as transmitter precursors. A mixture of all essential amino acids representing the difference in amino acids between 13% and 20% casein protein calories was an effective as the equivalent amount of intact protein. The nonessential amino acids equivalent to 7% casein protein calories, when added to the 13% protein calories diet, increased the rate of withdrawal seizures, presumably by exacerbating the protein deficiency in the 13% protein diet. It was concluded that a 1000-1200 kcal/kg diet with 20% kcal from protein and 50% kcal from carbohydrate provides an optimal nutrient balance for efficient utilization of a 6% ethanol liquid diet for rats.

Ginseng total saponin inhibits the dopaminergic depletions induced by methamphetamine

Pretreatment with ginseng total saponin (GTS) reduced the magnitude of the methamphetamine-induced dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillinic acid (HVA) depletions. It is suggested that GTS can, in part, prevent the methamphetamine-induced striatal dopaminergic depletions.

Amphetamine and fenfluramine suppress ethanol intake in ethanol-dependent rats

Alcohol intake or preference for alcohol has been attributed to concomitant dopamine and serotonin dysfunction in rats. Amphetamine and fenfluramine, administered alone, have been shown to reduce food and fluid intake as well as alcohol consumption while acute coadministration of these agents has been shown to suppress audiogenic seizure in rats withdrawn from alcohol. The present study was designed to assess the effectiveness of chronic amphetamine and fenfluramine coadministration on reducing alcohol intake. Chronic coadministration of amphetamine (2 mg/kg) and fenfluramine (8 mg/kg) reduced alcohol consumption during choice trials in both alcohol-dependent and alcohol-nondependent rats while not affecting water intake. The findings indicate that coadministration of amphetamine and fenfluramine, a treatment effective in reducing alcohol withdrawal seizures, also selectively attenuates alcohol consumption.

Diet composition, alcohol utilization, and dependence

Experiments were carried out in which a nutritionally balanced liquid diet previously used in this laboratory was modified as to total calorie content and high or low carbohydrate and fat concentration. Ethanol was added at 4.5% and 6.2% of diet weight and provided either 27% or 34-37% of total calories depending upon the changes in nutrient content. Measurements included 8-day food/calorie and ethanol consumption, plasma ethanol level, liver alcohol dehydrogenase (ADH) activity, and rate of audiogenic-induced withdrawal seizures. The original liquid diet with 4.5% ethanol was consumed in significantly lesser amounts than the alcohol-free diet, and essentially no body weight gain occurred, regardless if the major nonalcohol, nonprotein calorie source was fat or carbohydrate. When the calorie content of the diet was boosted through the addition of extra carbohydrate or fat (at the expense of water), appreciable weight gain was noted; in the case of the higher calorie diet boosted with more carbohydrate (maltodextrin) calories, growth was similar to that observed on the alcohol-free control diet. On this latter diet ethanol calories appeared to be utilized close to their theoretical value of 7 kcal/g. Blood alcohol levels were significantly higher on the lower calorie diets and were lowest on the high-calorie, high-carbohydrate, 4.5% ethanol diet. This diet also allowed for the lowest rate of withdrawal seizures despite an ethanol intake that was as high as on the lower calorie diets. Essentially, no differences were noted among ADH activities for the dietary treatments studied and thus, did not explain the differences observed among blood ethanol levels. When the alcohol concentration in the high-carbohydrate, high-calorie diet was raised to 6.2% from 4.5% to provide 34% of total calories, the rats responded by decreasing their food (and alcohol) intake to the same level as did the animals receiving a much lower calorie diet, but with 37% of caloric alcohol content. This suggests that at a diet alcohol concentration of 34-37%, one or more nutrient metabolites become limiting in the utilization of ethanol, resulting in food intake adjustments that maintain similar amounts of alcohol consumption.

Uridine reduces rotation induced by L-dopa and methamphetamine in 6-OHDA-treated rats

The pyrimidine nucleoside uridine may reduce side effects associated with antipsychotic medication by interacting with dopamine or GABA neurotransmission. Male Sprague-Dawley rats were used to investigate coadministration of uridine with agents that alter food intake (amphetamine, haloperidol, and chlordiazepoxide) and locomotor activity (methamphetamine and L-dopa). Results indicated that chronic uridine [32.0 mg/kg, intraperitoneally (IP)] alone did not alter milk intake or reduction of milk intake induced by amphetamine (dose range 0.5-2.0 mg/kg, IP) or haloperidol (0.125-1.0 mg/kg, IP), nor did it alter the biphasic response induced by chlordiazepoxide (5.0-40.0 mg/kg, IP). However, uridine-treated animals with unilateral striatal lesions exhibited no rotational behavior in the absence of drug challenge, but showed decreased rotation induced by the dopamine agonist, L-dopa (50.0-200.0 mg/kg, IP) compared with controls. In addition, uridine-treated rats exhibited reduced rotation after repeated injections of methamphetamine (4.0 mg/kg, IP) in contrast to increasingly greater rotation observed in control animals. These results are further evidence that chronic uridine may alter drug-induced dopaminergic activity without exerting effects itself.

Simultaneous changes in striatal dopamine, serotonin, and metabolites after withdrawal seizures in rats from dependence on alcohol

Ethanol dependence was achieved in male, Long-Evans rats after 8 days on a balanced liquid diet that supplied 4.5% ethanol. After 1-h access to a solution of 10% ethanol (95%)/5% sucrose, the rats were deprived of food, water, and ethanol for 9 h. Following 30-s key jingling, about 80% of the animals exposed to ethanol experienced tonic-clonic seizures. Neurochemical analyses of striatal tissues revealed a significant (p < 0.05) increase in dopamine (DA) and a significant decrease in serotonin (5-HT) in the ethanol-exposed rats that had seizures compared to control rats. Homovanillic acid concentrations of the ethanol-treated rats with seizures were significantly higher than the levels found in ethanol-treated animals that had experienced no seizures. Daily average ethanol intake of the rats that had seizures vs. those that did not was almost the same at 16 g/kg/day. The findings indicate that rats experiencing ethanol withdrawal-induced seizures manifest opposite alterations in dopaminergic and serotoninergic activity compared to controls. The present results do not reveal if the striatal changes are caused by ethanol rather than by the seizures.

Novel synergistic treatment of ethanol withdrawal seizures in rats with dopamine and serotonin agonists

A recent observation in this laboratory of a simultaneous increase in striatal dopamine and a decrease in serotonin in ethanol-dependent rats during ethanol withdrawal prompted studies with combined dopaminergic + serotoninergic agonists to stop withdrawal seizures. Amphetamine (2 mg/kg) + fenfluramine (8 mg/kg) given jointly, but not separately, prevented ethanol withdrawal seizures as effectively as benzodiazepines (chlordiazepoxide), the current drugs of choice. The combination of amphetamine and fenfluramine, unlike chlordiazepoxide, significantly reduced intake of ethanol during and immediately following ethanol withdrawal.

Effects of pargyline and pyrogallol on the methamphetamine-induced dopamine depletion

The formation of 6-hydroxydopamine (6-OHDA) from dopamine (DA) was investigated in the striatum of male Sprague-Dawley rats following a single administration of methamphetamine hydrochloride (100 mg/kg, sc). Rats were sacrificed 30, 60, and 90 min, and 1 wk after injection, and striatal 6-OHDA, DA, and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured by HPLC with electrochemical detection. Methamphetamine decreased striatal DA and DOPAC levels (to 65 and 50% at 90 min, respectively) in the time-course study and also resulted in a long-lasting dopamine depletion (34%) 1 wk after its administration. However, endogenous 6-OHDA formation proved difficult to detect after administration of the methamphetamine alone. Pretreatment with the monoamine oxidase (MAO) inhibitor pargyline (100 mg/kg, ip) and the catechol-O-methyltransferase (COMT) inhibitor pyrogallol (25 mg/kg, ip) resulted in the HPLC detection of a 6-OHDA-like substance 30 min after methamphetamine administration when the oxidizing potential was set at 0.5 V, but not when it was set at 0.2 V. Moreover, pargyline (25 mg/kg, ip) alone or in combination with pyrogallol exacerbated the long-lasting dopamine depletion induced by methamphetamine (50 mg/kg, sc). These results indicate that simultaneous inhibition of MAO and COMT provides a cellular environment that encourages the autoxidation of dopamine to a 6-OHDA-like substance.

Influence of gonadal hormones on sexual differences in sensitivity to methamphetamine-induced neurotoxicity

The administration of high doses of methamphetamine to mice causes long-lasting depletions of striatal dopamine to a greater extent in males than in females. Likewise, the incidence of Parkinson's disease is higher in males than in females. The present study investigated the roles of estrogen and testosterone in mediating the dopamine depletion induced by methamphetamine. Male and female mice received four cumulative SC doses of methamphetamine (10 mg/kg) at two hour intervals and were sacrificed two weeks later for HPLC analysis of striatal monoamines. Intact male mice were found to have a 76% dopamine depletion, which was significantly greater than the 37% depletion exhibited by the intact female mice. Neither removal of the ovaries nor removal of the testes one month prior to the methamphetamine treatment significantly changed the magnitude of the methamphetamine-induced dopamine depletion. Thus, the reduced sensitivity of female mice to methamphetamine may be independent of physiological gonadal hormones.

Uridine potentiates haloperidol's disruption of conditioned avoidance responding

The pyrimidine nucleoside, uridine, has been proposed as a potential supplement in the treatment of psychosis based on its ability to reduce haloperidol-induced dopamine release. These experiments investigated the effect of uridine (32 mg/kg, i.p.) coadministered with the neuroleptic haloperidol, on rats engaged in one way conditioned avoidance responding. Uridine itself had no effect on animals' performance, while haloperidol (dose range 0.05-0.4 mg/kg, i.p., 90 min before test session) decreased number of avoidances and increased avoidance and escape latencies in a dose-dependent manner. When coadministered with haloperidol, uridine significantly potentiated the disruption of avoidance and avoidance latency induced by haloperidol. This potentiation was still evident after chronic (27 days) uridine treatment. Importantly, coadministration of uridine did not potentiate haloperidol-induced increase of escape latency. The potentiation of haloperidol-induced disruption of conditioned avoidance responding suggests that uridine coadministration might enhance the antipsychotic action of traditional neuroleptics. This would allow for a reduction in the therapeutic dose of the antipsychotic, thereby reducing side effect frequency.

Ethanol consumption following acute treatment with methysergide, fluoxetine, fenfluramine, and their combination

Methysergide (MS), a postsynaptic serotonin antagonist, was administered acutely in three experiments in relation to water or 5% ethanol solution intake of 24-hr, water-deprived male Sprague-Dawley rats. In the first experiment, MS significantly increased the consumption of ethanol at doses of 0.25, 2.0, and 4.0 mg/kg. Water intake was significantly increased by MS at the 2.0 mg/kg dose. In the second experiment, which was different from the first one in that MS was administered during the dark cycle, ethanol solution intake was again significantly increased at all three levels. In the third experiment, fenfluramine (FFL) and fluoxetine (FLU) were administered acutely (at 8 mg/kg) after MS (0.25 mg/kg) followed by measuring water or ethanol solution intake. FFL and FLU significantly decreased intake of both water and ethanol solution, a process that was significantly reversed by MS; to a greater degree for FLU (74%) than for FFL (57%). The successful use of MS in increasing ethanol intake in these studies may be due to the low doses used in comparison with earlier unsuccessful attempts. The procedure of treating 24-hr, water-deprived rats with acute doses of pre- and postsynaptic serotonin agonists and antagonists appears to be a useful model for further elucidation of their interaction in ethanol consummatory behavior.

Propranolol-induced increases in target-biting attack

The effect of a beta-adrenoreceptor blocking agent on defensive aggression in mice was evaluated. Acute doses of d,l-propranolol (0.2, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 mg/kg) were administered to male Rockland-Swiss mice prior to testing in a target-biting paradigm. Baseline conditions established a high target-biting rate low biting rate during a 15-s tone stimulus preceding the next shock. Every dose of propranolol increased target-biting rates above baseline during each interval with one exception: 0.4 mg/kg decreased the biting rate immediately after delivery of the tail shock. The overall increase in aggression observed following dosing with propranolol was not expected from a review of the clinical literature. These results are discussed in reference to propranolol's known effects on the brain serotoninergic systems and the use of an animal model of defensive aggression.

Uridine and stimulant-induced motor activity

Chronic administration of uridine alters dopaminergic activity and related behavior. The present study investigated this effect using amphetamine and cocaine-induced activity and rotation in rats with unilateral dopaminergic lesions. Adult, female Sprague-Dawley rats with free access to food and water received daily intraperitoneal uridine (16 mg/kg) or an equal volume of saline. Activity was assessed for 10 min in a photocell chamber 30 min after intraperitoneal amphetamine or cocaine and 4 hr after the uridine or saline. Additional rats with unilateral dopaminergic lesions were treated comparably and assessed for stimulant-induced rotation. Uridine exerted no effect on body weight, activity, or rotation under baseline conditions. At higher doses, amphetamine and cocaine decreased activity and caused a dose-dependent increase in rotations. In the activity test, uridine-treated rats exhibited a significant increase in sensitivity to amphetamine but not to cocaine. In the rotation test, uridine-treated rats showed increased sensitivity to both stimulants. Finally, neurochemical analysis of a third set of comparably treated rats revealed that uridine blunted the amphetamine-induced increase in striatal dopamine. These observations are interpreted as indicating that chronic uridine modulates the stimulant-induced release of dopamine and, therefore, may be of therapeutic interest.

Effects of monoaminergic agonists on alcohol-induced increases in mouse aggression

Two sets of studies were conducted on alcohol-induced increases in aggression. In the first, the effects of alcohol on target biting and resident-intruder attack were assessed in mice fed a standard diet or one supplemented with 0.5% L-tryptophan. Mice attacked an inanimate target at a high rate following tail shock, an intermediate rate during the intershock interval and a low rate during a tone that preceded the shock. Alcohol increased target biting following shock and during the intershock interval, an effect partially blocked by tryptophan. Resident mice attacked intruders 27.2 +/- 5.3 times per 10-minute session with an average latency of 155 +/- 42 seconds. Alcohol increased the number of attacks and lowered the latency to the first attack. Again, tryptophan partially blocked these effects. Finally, in a second set of mice, the same tryptophan diet was found to potentiate the aggression-reducing effects of fluoxetine and fenfluramine without disrupting motor performance. In the second study, the effects of alcohol administered alone or in combination with tyramine were assessed in the resident-intruder paradigm. Again, it was observed that low doses of alcohol increased the resident attack of intruders. Although this effect was heightened by the co-administration of tyramine, the effect failed to reach statistical significance. These observations are discussed in reference to alcohol-induced increases in offensive and defensive aggression and the possible modulation of this effect by brain monoamines.

Ethanol consumption following acute fenfluramine, fluoxetine, and dietary tryptophan

Male Sprague-Dawley rats fed a commercial diet with or without tryptophan supplementation (0.5% L-TRP) were treated with single IP injections of fenfluramine or fluoxetine. Rats had been water deprived prior to injection and food was removed during the period of fluid availability. They were offered, following drug or saline injection, water, a 5% ethanol solution, or an isocaloric sucrose solution (8.75%) for 1 h. Fenfluramine injection significantly reduced intake of all fluids, but its effect on ethanol was significantly greater than for water or sucrose solutions. Fluoxetine suppressed water and ethanol intake but not that of sucrose; the reduction in ethanol intake was significantly greater than for water. Ingestion of the tryptophan-supplemented diet in the absence of any drug treatment had no effect on fluid intake. However, the tryptophan supplementation significantly enhanced the reduction in ethanol intake induced by fenfluramine and fluoxetine. It appears that both fenfluramine and fluoxetine decrease ethanol intake more so than that of water or sucrose and that this effect is exacerbated by tryptophan supplementation.