Both conditioned taste preference and aversion induced by corticotropin-releasing factor

Postprandial administration in the rat of a wide variety of drugs, peptides and toxins suppresses future consumption of a meal of previously unfamiliar but otherwise attractive saccharin-flavored solution. Since the intensity of this conditioned flavor aversion in the rat is sensitive to plasma stress hormone levels, the present study examined the effects on flavor conditioning of corticotropin-releasing factor, a peptide known to be involved in behavioral and hormonal responses to stress. In two-bottle water vs. saccharin choice tests, CRF (0.5 μg ICV) increased significantly the consumption of saccharin solution following a single saccharin/CRF pairing, while a tenfold larger dose of CRF (5 μg ICV) abolished saccharin intake following two saccharin/CRF pairings. Hence, exogenous CRF is capable of inducing both flavor preference and aversion in a dose- and situation-dependent manner. Further, direct neurotropic actions of CRF probably subserve its aversive effect since dexamethasone pretreatment weakened but did not prevent CRF-induced conditioned taste avoidance. These results suggest that at low doses CRF can produce arousal actions that result in taste preference and at higher doses produces aversive effects that are reflected in taste avoidance.     

Differences in response to the aversive properties of ethanol in rats selectively bred for oral ethanol preference

A conditioned taste aversion (CTA) paradigm was used to determine whether aversion to the pharmacological effects of ethanol, apart from orosensory cues, can contribute to genetic differences in voluntary ethanol consumption. Four doses of ethanol, administered IP, were paired with the consumption of a 0.1% saccharin solution in rats from the alcohol-preferring (P) and alcohol-nonpreferring (NP) lines. Repeated pairing of saccharin and ethanol in a dose of 1.0 g/kg produced stronger and more prolonged aversion to saccharin in NP rats, compared with P rats, at comparable blood ethanol levels. A low dose of ethanol (0.25 g/kg) produced transient conditioned facilitation of saccharin consumption in P rats, but not in NP rats, at comparable blood ethanol levels. The results suggest that rats of the NP line find the postingestional effects of high-dose ethanol more aversive, and low-dose ethanol less reinforcing, than do rats of the P line. Genetic differences in voluntary ethanol consumption may be due, in part, to differences in aversion to the postingestional effects of ethanol.     

Conditioned taste aversions as a behavioral baseline for drug discrimination learning: an assessment with phencyclidine

When PCP was given prior to the pairing of saccharin with LiCl (and the PCP vehicle prior to a nonpoisoned exposure to the same saccharin solution), rats rapidly acquired the discrimination, avoiding saccharin consumption following PCP and consuming saccharin following the vehicle after only three conditioning trials. Conversely, when the PCP vehicle was given prior to the saccharin-LiCl pairing and PCP prior to a nonpoisoned exposure to saccharin, other subjects avoided saccharin consumption following the vehicle injection and readily consumed saccharin after an injection of PCP. During dose substitution sessions, animals displayed greater drug-appropriate responding as the dose of PCP increased. When a range of doses of ketamine was given in place of PCP prior to saccharin access, subjects displayed dose-dependent PCP-appropriate responding. When a range of doses of d-amphetamine was substituted for PCP, subjects displayed vehicle-appropriate responding at all doses. The relative efficacy of the taste aversion procedure as a baseline for drug discrimination learning is discussed.     

The attenuation of a specific cue-to-consequence association by antiemetic agents

Previous research has shown that rats develop a conditioned taste aversion after a single pairing of a distinct taste and subsequent toxicosis. The experiments reported here test the hypothesis that the expression of a taste aversion may reflect classically conditioned nausea mediated by activation of brainstem emetic centers by taste stimuli. Rats were allowed to drink a saccharin solution (1 g/l) and 10 min later were intubated with LiCl (180 mg/kg) to produce nausea. When control rats were posttested for saccharin preference they consumed less than 50% of their pretest intake. Experimental rats were injected with one of four pharmacologically distinct antiemetic drugs 30 min prior to their posttest with saccharin. Each drug significantly attenuated the aversion to saccharin at one dose level. The antiemetic drugs we used were scopolamine HBr, cyclizine, prochlorperazine dimaleate, and trimethobenzamide. These drugs had no effect on the conditioned fear of a noise that signaled foot shock or on a natural aversion to a bitter fluid (quinine monohydrochloride, 100 mg/l). Our data suggest that pharmacological suppression of the neural mechanisms of emesis selectively disrupts conditioned taste aversions, and that moderate dose levels are critical for obtaining this effect.     

Prostaglandin E1 inhibits acute cell dehydration thirst

Intraperitoneally injected PGE₁ (100 μg/Kg) inhibits specifically the drinking induced by both IP and IV 2 M NaCl (6 ml/Kg) and compound 48/80 (100 μg/Kg, IP). Probenecid (150 mg/Kg, IP), which is not a dipsogen, has no effect on the PGE₁ induced inhibition of acute cell dehydration thirst. It is concluded the PGE₁ acts upon the peripheral mast cells, inhibiting their secretion and thus affecting the water intake associated with the activation of these cells either by hypertonicity or specific stimulants of amine release. These results raise the possibility that endogenous prostaglandins might be involved in the modulation of some of the signals which convey to the brain information on the tonicity of the body fluids.     

Antagonism of drug discrimination learning within the conditioned taste aversion procedure.

Animals injected with morphine prior to the presentation of a saccharin-LiCl pairing and the morphine vehicle prior to saccharin alone rapidly acquired the drug discrimination, avoiding saccharin following the administration of morphine and consuming saccharin following its vehicle after only four conditioning trials. Once stimulus control was established, the opiate antagonist naloxone (1 mg/kg) was administered prior to morphine in a test of its ability to antagonize the morphine stimulus. Pretreatment times ranged from 10 to 180 min. Naloxone antagonized the stimulus properties of morphine for all subjects, although there were individual differences in the onset, duration (time course) and degree of antagonism. Together with the rapid acquisition typically reported in this design, the fact that antagonism was demonstrated in the present study suggests that the conditioned taste aversion procedure may be useful in the general assessment of drug discriminations.     

Cycloheximide-induced amnesia for taste aversion memory in rats

Male hooded rats were conditioned in one trial to avoid saccharin by pairing saccharin drinking with an intragastric injection of LiCl. A 24 hr water-saccharin preference test showed that conditioned rats exhibited a very low preference for saccharin whereas rats injected intraventricularly with cycloheximide (CXM, 400 μg) 5, 7, or 9 hr before training exhibited a greatly increased saccharin preference which differed significantly from NaCl injected controls. This 24 hr amnesia was found to be dependent upon the time of administration of CXM, since injection at 1, 3 or 17 hr before training did not confer amnesia. The nature of the task, a control measure and a control experiment indicate that the CXM-induced change in saccharin preference at 24 hr is not due to a CXM-induced aversion, nor a loss in drinking ability nor an inability to retrieve information whilst under the influence of CXM.     

The behavioral effects of pesticides in male mice

Male Swiss mice, 25-30 g, were utilized to define some of the behavioral effects of the herbicides Lasso [alachlor 43%; (A)], Basalin [fluchloralin 45%; (F)], Premerge 3 [dinoseb 51%; (D)], and the fungicide Maneb-80 [maneb 80%; (M)]. These compounds were tested for their effects on locomotor activity and for their ability to establish a conditioned taste aversion following oral or dermal exposure. Individual and grouped (N = 5) activity measures were assessed immediately following the dermal administration of the commercially available pesticide formulations. Grouped activity measures were also assessed following the oral administration of the compounds. Total activity was significantly (p less than 0.05) increased over vehicle controls in both grouped and individual subjects by A, F, and D following dermal administration. Grouped activity measures were also increased by A, F, D, and M following the oral administration of the compounds. Similar subjects were tested in a conditioned taste aversion paradigm using a normally preferred 0.3% saccharin solution. Animals were given 30 min access to the saccharin solution followed immediately by the administration of the pesticide or control solution. Twenty-four hours later, animals were given the choice of 2 solutions, one containing water and the other the 0.3% saccharin solution. The percent saccharin consumed and the total fluid intake were calculated for each group (N = 8/group). A, F, and D produced a significant aversion to (N = 8/group) the saccharin following both oral and dermal administration. Oral administration of M, but not dermal exposure, also resulted in a flavor aversion. Total fluid intake, however, was not altered by any of the treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ethanol preexposure attenuates the interaction of ethanol and cocaine in taste aversion learning

Although the potentiating effects of ethanol and cocaine have been well documented, little has been reported regarding the effects of ethanol or cocaine history on this interaction. In the present study, female Long-Evans rats received five exposures to ethanol (3.5 g/kg ip) or vehicle prior to taste aversion conditioning in which a novel saccharin solution was paired with either ethanol (0.56 g/kg ip), cocaine (25 mg/kg sc) or the combination (or the drugs' vehicle) for a total of five conditioning trials. Nonpreexposed subjects conditioned with the ethanol/cocaine combination displayed aversions, drinking levels significantly less than nonpreexposed subjects conditioned with either drug alone. Further, the aversions produced by the combination were greater than the sum of the aversions produced by ethanol and cocaine, alone. Ethanol-preexposed animals conditioned with the combination displayed an attenuated aversion, drinking significantly greater amounts of saccharin than nonpreexposed conditioned subjects and not differing from controls. Although the basis for the attenuation by ethanol of the aversions induced by the drug combination is not known, the present findings may have implications for the use and abuse of the combination in that alcohol history may reduce the subsequent toxicity of the combination that in turn may affect its acceptability.     

Effect of the acute-phase response on the pharmacokinetics of chlorzoxazone and cytochrome P-450 2E1 in vitro activity in rats.

The acute-phase response is known to produce alterations in hepatic cytochrome P-450 (CYP) expression. Lipopolysaccharide (LPS), a well known inducer of acute-phase response decreases hepatic CYP2E1 in vitro activity in rats. This study was designed to determine if LPS administration produced alterations in the pharmacokinetics of chlorzoxazone (CZN), a marker for CYP2E1 expression. Sprague-Dawley rats were administered a single i.p. injection of LPS (5 mg/kg) or saline control approximately 24 h before a single i.v. bolus dose of CZN (15 mg/kg). Serial blood samples were collected over a 120-min period to quantitate CZN plasma concentrations and protein binding. In addition, livers were removed and processed for evaluating in vitro CYP2E1 protein concentrations and activity. Systemic clearance decreased by 35% in LPS-treated rats, whereas half-life and steady-state volume of distribution increased by 167 and 66%, respectively. The plasma free-fraction of CZN increased 2-fold after LPS treatment. The CZN intrinsic clearance decreased in LPS rats by 71% compared with control values. The CYP2E1 liver microsomal activity decreased between 55 and 75% along with a 41% decrease in CYP2E1 protein concentration. The CZN intrinsic clearance was significantly correlated with both the CZN and p-nitrophenol liver microsomal activity (r = 0.97 and r = 0.91, respectively). This study demonstrated that LPS administration produced expected reductions in the in vivo intrinsic clearance of CZN, and these changes were highly correlated with in vitro activity studies. In addition, LPS produced significant increases in the steady-state volume of distribution of CZN secondary to reductions in its plasma protein binding.     

Selective tolerance of group III and IV somatosympathetic reflexes to the effects of alfentanil

The effect of alfentanil on responses in renal sympathetic nerves evoked by supramaximal electrical stimulation of the radial nerve, has been observed in 6 dogs anaesthesised with -chloralose, paralysed with suxamethonium and ventilated artificially. During an initial infusion of alfentanil the responses of the late group IV (C fibre) and early group III (Aδ) were abolished by mean doses of 68 μg kg⁻¹ (SEM 3.2 μg kg⁻¹) and 797 μg kg⁻¹ (SEM 120 μg kg⁻¹), respectively. Recovery was allowed to occur to approximately 50% of control values (mean time 76 ± 14.3 min). The preparations were then conditioned with 7 incremental doses from 7.5 to 120 μg kg⁻¹ (i.v.) (total dose 308.5 μg kg⁻¹), administered at intervals of 10 min, and subsequently tested with large bolus doses (up to 2000 μg kg⁻¹) of alfentanil. In two preparations, the responses of both group IV and group III became completely tolerant to the effects of alfentanil while in the other four the response of the group IV was still eliminated by the drug and the response of group III showed selective tolerance. The heart rate and arterial pressure were reduced by 45 and 29%, respectively during the initial infusion of alfentanil. Thereafter there were no further significant changes in the circulation until the administration of naloxone (2 mg i.v.), which restored the sympathetic responses, heart rate and arterial pressure to control values.     

Blood alcohol level and caloric intake in the gravid rat as a function of diurnal period, trimester, and vehicle

Blood ethanol levels, caloric intake and weight gain were monitored over the 21-day gestational period in the gravid Sprague-Dawley rat as a function of the administration of ethanol in either a liquid diet (Ensure) or an aqueous saccharin solution. The mean daily percentage of ethanol consumed (38% vs 31%), and g/Kg of ethanol consumed (11.9 vs 9.7 g/Kg) were higher for the liquid diet group than the aqueous solution group. Ethanol consumption varied by the trimester in the Ensure but not in the saccharin solution rats. Proportional maternal weight gain, live litter size, and live litter weight did not vary as a function of the method of ethanol administration. Both groups exhibited significant diurnal periodicity in ethanol consumption, and the greatest caloric intake during the second trimester. The implications of these results for ethanol administration in gravid rats is discussed.     

Simultaneous determination of pyrimethamine, sulfadiazine and N-acetyl-sulfadiazine in plasma for monitoring infants in treatment of congenital toxoplasmosis

A method for the simultaneous determination of pyrimethamine, sulfadiazine and its metabolite N-acetyl-sulfadiazine in small plasma samples from neonates in treatment for congenital toxoplasmosis has been developed. In this method only 25 μl of plasma is used and a simple sample preparation based on protein precipitation and centrifugation provides highly reliable data as the recovery is about 100% and the precision is good. The analysis is performed using high performance liquid chromatography with UV and mass spectrometric (MS) detection. Pyrimethamine was found to give a linear response using MS detection in the range 0.02–5 μg/ml. Sulfadiazine and its metabolite N-acetyl-sulfadiazine were preferably analysed by UV at 269 nm in the concentration ranges 0.2–200 μg/ml for sulfadiazine and 0.2–50 μg/ml for N-acetyl-sulfadiazine.     

Disruption of taste aversion learning by pretreatment with diazepam and morphine.

Laboratory rats were pretreated with either morphine (9 mg/kg IP), diazepam (4 mg/kg 1P) or Ringer's solution 2, 3 1/2, and 2 hr, respectively, prior to ingestion of a novel tasting saccharin solution followed immediately by a single injection of one of these agents. Animals pretreated with Ringer's solution followed by an injection of either morphine or diazepam showed a conditioned taste aversion (CTA) as determined by a significant reduction in the mean saccharin intake on a subsequent test trial. Although the drug pretreatments alone produced no conditioned avoidance behavior, the diazepam pretreatment completely blocked the development of both diazepam and morphine-evoked CTAs while the morphine pretreatment prevented a CTA induced by itself but not by diazepam. The results were discussed in terms of the attenuating effects of the pretreatments on the relative saliency of the subsequent conditioning drug injection.     

Evidence that PGE2 in the dorsal and median raphe nuclei is involved in LPS-induced anorexia in rats

Anorexia is an element of the acute-phase immune response. Its mechanisms remain poorly understood. Activation of inducible cyclooxygenase-2 (COX-2) in blood-brain-barrier endothelial cells and subsequent release of prostaglandins (e.g., prostaglandin E2, PGE2) may be involved. Therefore, we sought to relate the effects of prostaglandins on the anorexia following gram-negative bacterial lipopolysaccharide treatment (LPS) to neural activity in the dorsal and median raphe nuclei (DRN and MnR) in rats. COX-2 antagonist (NS-398, 10 mg/kg; IP) administration prior to LPS (100 μg/kg; IP) prevented anorexia and reduced c-Fos expression the DRN, MnR, nucleus tractus solitarii and several related forebrain areas. These data indicate that COX-2-mediated prostaglandin synthesis is necessary for LPS anorexia and much of the initial LPS-induced neural activation. Injection of NS-398 into the DRN and MnR (1 ng/site) attenuated LPS-induced anorexia to nearly the same extent as IP NS-398, suggesting that prostaglandin signaling in these areas is necessary for LPS anorexia. Because the DRN and MnR are sources of major serotonergic projections to the forebrain, these data suggest that serotonergic neurons originating in the midbrain raphe play an important role in acute-phase response anorexia.     

D-cycloserine enhances short-delay, but not long-delay, conditioned taste aversion learning in rats

NMDA receptors have been implicated in conditioned taste aversion (CTA), a form of associative learning with the unique temporal characteristic of associating taste and toxic stimuli across very long delays. d-cycloserine (DCS), an NMDA receptor agonist, has been shown to enhance short-delay CTA learning. Here we examined the interaction of DCS with varying temporal parameters of CTA. DCS (15 mg/kg) administered prior to the pairing of 0.125% saccharin and LiCl (38 mM, 12 ml/kg) enhanced CTA when there was a short delay between the taste-toxin pairing (10 min), but not when there was a long delay (45 min). DCS activity remained at effective levels over the long delay, because DCS administered 60 min prior to a short-delay pairing enhanced CTA. The interaction of DCS with the delay between taste stimulus onset and LiCl injection was investigated by administering DCS and then 5 min access to saccharin 45 min prior to a short-delay pairing of saccharin and LiCl. DCS failed to enhance CTA in rats pre-exposed to saccharin, even with a short delay between the second saccharin exposure and LiCl injection. These results suggest that DCS enhancement of CTA is dependent on mechanisms underlying gustatory processing during long-delay taste-toxin associations.     

Effects of plant ingestion in rats determined by the conditioned taste aversion procedure

The conditioned taste aversion procedure was used to compare the aversive effects produced by 40 plants (mostly common household varieties) to those of amphetamine, lithium chloride and ethyl alcohol. Test substances (plant homogenates or drug solutions) were given to rats by force-feeding 5 min after the subjects' first exposure to 0·1% saccharin solution, which was available for 15 min from a water bottle. The comparison of the consumption of saccharin solution, two days after test substance administration, to the initial saccharin consumption was taken as a measure of the aversive effects produced by the test substance, e.g. greater suppression of saccharin intake indicating greater aversive properties. Dose dependent suppression of saccharin intake was obtained with most of the substances tested at more than one concentration. Administration of Pokeberry seeds, Japanese Yew, Norfolk Island Pine and Oleander leaves suppressed saccharin intake more than ethyl alcohol. The rest of the plants tested produced less conditioned aversion than ethyl alcohol. Some plants which are frequently called poisonous (Poinsettia, Philodendron and Dieffenbachia) were not particuarly effective in producing conditioned taste aversion. Good correlation existed between suppression of saccharin intake produced by the three drugs tested and their approximate acute lethal doses in rats and humans, suggesting that the conditioned taste aversion procedure may indicate the approximate acute lethality of these substances. Good correlation was also found between the dry weight of the plants and the suppression of saccharin intake.     

Time-dependent exacerbation of amphetamine-induced taste aversions following exposure to footshock

Previous studies have shown that stressors attenuate LiCl-induced conditioned taste aversions (CTA) but not morphine-induced CTA. The current studies examined the effects of footshock on the acquisition and extinction of amphetamine-induced CTA. Experiment 1 demonstrated that exposure to 30 footshocks between saccharin consumption and amphetamine injections did not alter either the acquisition or the extinction of amphetamine-CTA. Experiment 2 demonstrated that exposure to the same shock parameters 2 and 4 days before saccharin-amphetamine pairing increased the magnitude of amphetamine-CTA after one saccharin-amphetamine pairing and delayed the recovery from the CTA. Experiment 2 also demonstrated that footshock increased the initial neophobic response to novel saccharin but did not alter subsequent saccharin consumption among saline-injected animals. These results indicate that stress-induced facilitation of amphetamine CTA are time-dependent and contrast with reports that stressors attenuate LiCl CTA. They also add support to the contention that CTAs induced by self-administered drugs like amphetamine are qualitatively different from CTAs induced by toxic substances like LiCL.     

In vivo and in vitro developmental toxicity in LPS-induced zinc-deficient rabbits

Lipopolysaccharide (LPS) was used to induce maternal hypozincemia in order to test the hypothesis that altered zinc homeostasis is developmentally toxic in the rabbit. Treatment of dams on Gestation Day (GD) 8 with LPS (0.67 μg/kg i.v.) caused total resorption of 78% (7 of 9) of the litters whereas GD 10 treatment increased the percentage of resorbed implantations (18-fold), but resulted in only 14% (1 of 7) totally resorbed litters. Cotreatment with zinc oxide (ZnO) on GD 10 decreased the resorption rate by 44%, indicating that hypozincemia was partially responsible for the resorptions. However, ZnO had no effect on resorption rate in GD 8 LPS-treated dams. No malformations were observed with LPS dosing on either gestation day. To determine whether LPS-induced Zn deficiency had any direct effects on rabbit embryos, normal GD 9 embryos were cultured for 48 h in serum from LPS-treated dams (0.53 ± 0.01 μg/mL Zn) or from controls (1.74 ± 0.07 μg/mL Zn). Embryo growth and development were normal in both groups, indicating a lack of any direct embryo effects of Zn deficiency. Finally, maternal plasma progesterone and the Zn content of conceptus tissues were measured 24 h after LPS injection on GD 10. Despite a marked decrease in maternal serum Zn, no significant changes in embryo, visceral yolk sac, yolk sac cavity-exoceolomic fluid, or placental Zn were found. However, maternal progesterone levels were decreased 33 and 28% in the LPS and LPS + ZnO groups, respectively. Taken together, these results indicate that rabbits may differ from rodent species in their lesser susceptibility to the teratogenic potential of transient maternal Zn deficiency, as well as in their resistance to conceptus Zn changes. Nonetheless, Zn deficiency may be responsible for an increase in resorption rate in the rabbit.     

Behavioral effects of pydrin and ambush in male mice

Male Swiss mice, 20-25 g, were utilized to assess the effects of dermal and oral administration of the pyrethroid insecticide formulations Pydrin (30% fenvalerate) and Ambush (25.6% permethrin). Animals were subjected to a conditioned taste aversion procedure using a normally preferred 0.3% saccharin solution. Subjects were allowed 30 min access to a drinking syringe containing the saccharin solution, followed immediately by the administration of the pyrethroid or control solution. Pydrin (0.3, 3.0, or 30 mg/kg orally; 60, 600, or 1800 mg/kg dermally) and Ambush (0.5, 5.0, or 50 mg/kg orally; 30, or 300 mg/kg dermally) produced significant (p less than 0.05) reductions in the percent saccharin consumed. Total fluid intake, however, was not significantly altered by any of the treatments. The effect of the insecticides on both grouped and individual activity was also assessed in 20-25 g male Swiss mice. Activity measurements were taken over the 4-hr time period immediately following the administration of the pyrethroid or control solution. Pydrin (30 mg/kg orally; 600 and 1800 mg/kg dermally) and Ambush (50 mg/kg orally; 300 mg/kg dermally) significantly (p less than 0.05) increased activity in both grouped and individually tested mice. When subjects were individually tested, significant increases were seen in non-ambulatory, but not in ambulatory activity. The results of this work indicate that administration of the commercially available preparations of Pydrin and Ambush in mice at doses that do not induce the tremor and choreoathetosis-salivation syndromes usually associated with pyrethroid insecticides may result in behavioral changes.