Joseph E. Zabik

Effects of toluene inhalation on brain biogenic amines in the rat

The effects of toluene exposure on the biogenic amine concentrations in the central nervous system were investigated in the rat. Toluene was administered via inhalation to groups of rats at concentrations of 0, l00, 300, or 1000 ppm. After an 8-h continuous exposure, animals were sacrificed and whole brain concentrations of dopamine (DA), norepinephrine (NE), and 5-hydroxytryptamine (5-HT) were determined. The data indicated a significant increase in whole brain concentrations of DA following the 100-ppm exposure. A regional analysis of DA, NE, and 5-HT concentrations in rats exposed to 1000 ppm of toluene for 8-h indicated a significant increase in DA concentration in the striatum. A significant increase in NE concentrations was detected in the medulla and midbrain while 5-HT concentrations were significantly increase in the cerebellum, medulla, and striatum. The results indicate that toluene action results in elevated concentrations of behaviorally significant neuro-transmitters.

5-Hydroxytryptophan-induced conditioned taste aversion to ethanol in the rat

This experiment was conducted to determine the efficacy of 5-HTP in producing conditioned taste aversions (CTAs) to ethanol in rats restricted to a one-hour daily access to fluid. Administration of 100 mg/kg of DL-5-HTP immediately following novel exposure to ethanol resulted in an aversion of such magnitude that some rats refused to consume the ethanol solution. Since ethanol was the only fluid available to these rats, they eventually died, presumably of dehydration. By comparison, LiCl administration also produced a CTA to ethanol, but no such persistent rejection was observed. Both 5-HTP and LiCl also produced CTAs when saccharin and tartaric acid solutions were used as novel fluids, but these aversions were short-lived and all rats resumed drinking. The causative factor(s) in the persistent ethanol rejection until death observed in rats treated with 5-HTP remain undetermined but the results have indicated that simple CS-UCS associative learning mechanisms are probably not a primary causative factor.

Stress, Endogenous Opioids and Salt Intake

The effect of stress on NaCl intake was examined in mice given a choice of water and 1.5% NaCl to drink. Immobilization of mice for 15-min and 24-h food deprivation resulted in a 2.5- and 5-fold increases in NaCl intake, respectively, without affecting water intake. Naloxone treatment (0.01, 0.1 and 1.0 mg/kg) produced a dose-dependent decrease in the stress-induced NaCl intake, as did captopril treatment (5, 10 and 50 mg/kg). Intraventricular injection of angiotensin II in mice resulted in an increase in 1.5% NaCl intake, which was blocked by naloxone. Morphine (10 mg/kg) increased the preference of mice for a normally aversive 3.0% NaCl solution, but not for preferred, less concentrated, solutions of NaCl. The results suggest that both endogenous opioids and angiotensin II contribute to stress-induced NaCl intake, and that endogenous opioids may also mediate the increase in NaCl intake, observed with angiotensin II.

Drug interactions with brain biogenic amines and the effects of amphetamine isomers on locomotor activity

Administration of single IP doses of 1.0 or 4.0 mg/kg of d-amphetamine evoked an increase in mouse spontaneous motor activity (SMA); in contrast, 1.0 mg/kg of l-amphetamine had no significant effect, while 4.0 mg/kg caused a decreased SMA. Pretreatment with aMT or pargyline had little effect on the actions of the l-isomer, but reduced the magnitude and duration of the stimulatory effect of d-amphetamine. Pretreatment with p-chlorophenylalanine had little effect on the actions of d-amphetamine but completely abolished the depressant actions of the l-isomer. Reserpine pretreatment markedly reduced basal SMA levels; such pretreatment caused both d- and l-amphetamine to act as stimulants of SMA.

Use of Serotonin-Active Drugs in Alcohol Preference Studies

Interest in finding a cure for alcoholism has sparked enthusiastic research into drugs that might accomplish this goal. Since decreases in brain serotonin had been shown to influence voluntary ethanol ingestion, numerous studies were conducted with the intent of establishing a basis on which a treatment for the alcoholic could be based. Along the path of discovery many inconsistencies have been encountered. After considerable research it became clear that the hope for an effective treatment resided not with impairment of but rather with enhancement of brain serotonergic function. One of the first effective therapeutic approaches has apparently emerged in the case of selective serotonin uptake inhibition. However, even with a wealth of information available, the mechanism by which an elevation of brain serotonergic function diminishes ethanol intake is unclear. The research conducted in this area has resulted not only in a potential therapeutic drug but also insight into the complexity of alcoholism as well. The intent of research reviewed here has been a better understanding of the role that brain serotonergic function may play in the regulation of ethanol ingestion.

Effects of benzodiazepines on taste aversions in a two-bottle choice paradigm

Diazepam (DZ) and chlordiazepoxide (CDP) were tested for their ability to antagonize LiCl-established conditioned taste aversions (CTAs) to saccharin in a two-bottle free-choice paradigm. CTAs to saccharin were established in male Sprague-Dawley rats on a chronic fluid-deprivation schedule by the administration of LiCl (3 mEq/kg, IP) following a forced-choice exposure to a novel saccharin solution (0.1%, w/v). Three days later, rats were provided with a two-bottle choice presentation of saccharin and distilled water. Conditioned rats drank distilled water almost exclusively while unconditioned animals preferred saccharin. Pretreatment with DZ (6, 9, 12 mg/kg, IP) and CDP (12 mg/kg, IP) significantly increased the saccharin intake of conditioned rats indicating an attenuation of the manifestation of the CTA. While these results are consistent with the known disinhibitory effects of benzodiazepines, alternative mechanisms involving polydipsia or interactions with the taste characteristics of saccharin could not be excluded. Both hypertonic saline (16%, w/v NaCl) and Barbital Sodium (100 mg/kg) produced polydipsia without attenuating CTAs suggesting that the two-bottle procedure is capable of distinguishing between polydipsic effects and anti-aversion effects for these drugs.

Central and peripheral components of the inhibitory actions of 5-HTP on ethanol consumption in the rat

When administered under a backward conditioning paradigm, 5-HTP administration resulted in a decrease in ethanol intake followed by a persistently decreased ethanol consumption. A central component to this inhibitory effect was suggested by the inability of xylamidine to significantly reduce the initial inhibitory effect of 5-HTP. The persistent rejection was prevented by xylamidine. Methysergide reduced the initial as well as the persistent effects of 5-HTP. In studies utilizing a forward conditioning paradigm, 5-HTP and lithium were each effective in developing CTAs to ethanol and saccharin. Only the ethanol-5-HTP pairing showed a persistent aversion. A peripheral component to the actions of 5-HTP was suggested by xylamidine blocking the CTAs induced by 5-HTP. Xylamidine also prevented the persistent ethanol avoidance induced by 5-HTP, but was ineffective in antagonizing lithium-induced CTAs. These results suggest central as well as peripheral components associated with the inhibitory effects of 5-HTP on ethanol consumption. Central actions appear to mediate the initial inhibitory effects while peripheral actions appear to be associated with persistent avoidance of ethanol following 5-HTP treatment.

Unreliability of the rat stomach fundus as a predictor of hallucinogenic activity in substituted phenethylamines

A series of three isomeric 2,4,5-substituted monoethoxy dimethoxy phenylisopropylamines were compared for their contractile effect in the rat fundus as potential antagonists to the effect of serotonin in the fundus. The three isomers were also evaluated for their discriminative stimulus properties in rats that had been trained to discriminate injections of saline from LSD tartrate (0.08 mg/kg). The drug discrimination studies revealed that the 2,5-dimethoxy-4-ethoxy substitution was most potent in rats, consistent with the reported clinical activity of this isomer in man. By contrast, of the three isomers examined, this was the weakest in eliciting a contraction in the fundus. None of the compounds antagonized serotonin induced contractions, and it was not possible to determine pA2 values. Questions are raised about the determination of pA2 values for partial agonists and it is concluded that the fundus is not a reliable model for prediction of hallucinogenic activity of phenethylamines.

Method for quantitative operant response measurement during inhalation exposure

A method for pharmacologic and toxicologic investigation of operant responses during inhalation exposure has been developed. The method was tested with rats. Toluene was utilized as a reference chemical. Toluene has been reported to cause significant increases in response rates of animals responding under operant schedules. A fixed interval schedule (F1-120 sec) was used. A significant increase in response rate was observed. Thus, the results indicated that the method was reliable and allowed operant schedule data to be obtained. The significance of this method lies in its versatility to allow an integrative study of operant response, inhalation kinetics, and pharmacologic action. Potential practical applications of the method include studies of the actions of drugs and chemicals administered via inhalation exposure.