Cholinergic agonist reverses H1-induced memory deficit in mice.

This study investigated the effects of bilateral intraamygdalar microinjections of PNU-282987, a nicotinic cholinergic agonist, on anxiety and the reversal of amnesia induced by chlorpheniramine (CPA), an H1 histaminergic antagonist, in mice subjected to the elevated plusmaze (EPM). Two experiments were performed with seventy-nine adult male Swiss mice. The isolated microinjections of PNU-282987 did not produce effects on emotional memory; however, the combined microinjections of PNU-282987 and CPA were able to reverse the deficit in memory induced by CPA (ANOVA, p<0.05). Taken together, these results suggest that intraamygdalar injections of PNU-282987 did not induce effects on anxiety and emotional memory per se; however, concurrent microinjections of PNU-282987 and CPA-reverse amnesia induced-CPA which is suggestive of an interaction between the histaminergic and cholinergic systems in the modulation of emotion memory acquisition in mice.

Intra-amygdala microinjections of chlorpheniramine impair memory formation or memory retrieval in anxiety- and fear-mediated models.

H1 receptor histaminergic antagonist, chlorpheniramine (CPA) participates in cognitive performance in various animal models. However, little is known regarding the effects of CPA microinjection into the amygdala on emotional behavior. The purpose of this study was to investigate whether CPA microinjection into the amygdala has the same effect on two models, one anxiety- and the other fear-mediated, in various memory stages using the elevated plus maze (EPM) and the inhibitory avoidance task (IAT) tests. Two experiments were performed with seventy-two adult male Swiss mice. Behavioral testing was performed on two consecutive days, and in both experiments, before each trial, the animals received bilateral microinjections of saline (SAL) or CPA (0.16 nmol). The animals were re-exposed to the EPM or IAT 24h after the first trial. Four experimental groups were tested: SAL-SAL, SAL-CPA, CPA-SAL and CPA-CPA. In experiment 1, a decreased open arm exploration (% open arm entries, %OAE and% open arms time, %OAT) for SAL-SAL and SAL-CPA was showed, while these measures did not decrease for the CPA-SAL and CPA-CPA groups in Trial 2. In experiment 2, an increase of retention latency in relation to training 2 for the groups SAL-SAL and CPA-SAL and a significant decrease in latency for the group SAL-CPA was revealed. These results indicate that chlorpheniramine microinjection into the amygdala impairs emotional memory acquisition and/or consolidation in the EPM and retrieval of IAT.

Intoxication with over-the-counter antitussive medication containing dihydrocodeine and chlorpheniramine causes generalized convulsion and mixed acidosis.

We report a 35-year-old man who was referred to our hospital with generalized convulsion and mixed acidosis presumably caused by abuse of SS-BRON tablets, an over-the-counter (OTC) antitussive medication sold in Japan. These tablets contain dihydrocodeine phosphate, methylephedrine, chlorpheniramine, and caffeine. Although it is difficult to discern which component caused these symptoms, it seems that dihydrocodeine phosphate or methylephedrine was involved in the addiction to SS-BRON and chlorpheniramine may have caused the generalized convulsion. It should be recognized that an OTC antitussive, which is quite easy to obtain, can be abused and subsequently induce serious intoxication.

Validation of a high-throughput in vitro alkaline elution/rat hepatocyte assay for DNA damage.

In vitro alkaline elution is a sensitive and specific short term assay which measures DNA strand breakage in a mammalian test system (primary rat hepatocytes). This lab has previously demonstrated the performance of the assay with known genotoxic and non-genotoxic compounds. The methodology employed has relatively low sample throughput and is labor-intensive, requiring a great deal of manual processing of samples in a format that is not amenable to automation. Here, we present an automated version of the assay. This high-throughput alkaline elution assay (HT-AE) was made possible through 3 key developments: (1) DNA quantitation using PicoGreen and OliGreen fluorescent DNA binding dyes; (2) design and implementation of a custom automation system; and (3) reducing the assay to a 96-well plate format. The assay can now be run with 5-50mg of test compound. HT-AE was validated in a similar manner as the original assay, including assessment of non-genotoxic and non-carcinogenic compounds and evaluation of cytotoxicity to avoid confounding effects of toxicity-associated DNA degradation. The validation test results from compounds of known genotoxic potential were used to set appropriate criteria to classify alkaline elution results for genotoxicity.

Preclinical skin sensitization testing of antihistamines: guinea pig and local lymph node assay responses.

Preclinical test methods for allergic contact sensitivity have been widely used for sensitization hazard identification and, with consideration of human exposure conditions, have also been valuable tools for sensitization risk assessment. For many years, the guinea pig has been the test species of choice with a variety of test methods developed to assess the sensitization response. More recently the local lymph node assay (LLNA) in mice has been developed to provide a more objective index of sensitization potential. The standardized methods have proven to be very well suited to most situations in which potential skin sensitization of a chemical needs to be assessed before human exposure. A potential difficulty with all these relatively limited exposure preclinical test methods, however, is in the ability to detect weak contact allergens that prove to be significant clinical allergens due to chronic topical exposure, exposure to compromised skin, and/or highly exaggerated exposure through transdermal delivery. This has been shown with the transdermal drug clonidine and might also be the case for topical antihistamines. The latter are considered significant clinical contact allergens, although predictive preclinical test data are minimal or lacking. A series of guinea pig (modified Buehler) tests with two common antihistamine compounds (triprolidine and diphenhydramine) and LLNA on these and two other compounds (chlorpheniramine and promethazine) was conducted. Positive Buehler test results required use of penetrating vehicle systems and a modified nine-induction patch regimen. Positive LLNA responses were obtained with all four materials (to varying degrees) only if the application site was pre-abraded or a penetrating vehicle (dimethylformamide) was used. These data support the notion that preclinical sensitization test methods can be modified to increase sensitivity. This may be critical for preclinical assessment of topical/transdermal drugs or other materials with chronic or high-concentration exposures in man.

The intravenous self-administration of antihistamines by rhesus monkeys.

Rhesus monkeys were trained to lever press for infusions of cocaine during daily, 1-h experimental sessions. Following stabilization of the cocaine-maintained baselines, various antihistamines were substituted for cocaine to determine whether they would be self-administered. The results indicated that all monkeys tested self-administered tripelennamine and chlorpheniramine. One monkey out of the four self-administered pyrilamine, but only at a single (300 microgram/kg) high dose. Phenyltoloxamine, cimetidine and hydroxyzine were not self-administered. These results further illuminate differences amongst H1 antagonists in their potential for self-administration and, when examined in context with other reports, suggest that stimulant-like properties may help mediate their reinforcing effects when present.

Effect of chloropheniramine maleate on liver and kidney functions as well as blood count of guinea pigs.

The present study aimed at exploring the effect of antihistamine chloropheniramine maleate (H1-blocker) on liver and kidney functions as well as on blood count. 60 mature guinea pigs were used. Histamine or chloropheniramine maleate was given, either alone or together, intramuscularly for 7 successive days. At the end of the experimental period, blood samples were collected for determination of blood counts and of the levels of urea, creatinine, GOT, GPT, and alkaline phosphatase in the sera of different groups. The results showed significant groupwise variations in blood count, liver function as well as kidney function.

Antihistaminics enhance morphine-, but not amphetamine- and scopolamine-induced hyperactivity in mice.

Three histamine H1-receptor antagonists, chlorpheniramine, diphenhydramine and tripelennamine, were tested alone or in combination with morphine, amphetamine and scopolamine on locomotor activity in mice. All three antihistaminics, at some dosage levels, enhanced morphine-induced hyperactivity, but did not change or even reduce locomotor stimulation induced by amphetamine and scopolamine. The results suggest that H1-blocking agents may specifically interact, though not necessarily directly, with opiate mechanisms in producing behavioural effects.

Induction of tumours in rats by feeding nitrosatable amines together with sodium nitrite.

Feed containing 0.2% allantoin or diphenhydramine (as the hydrochloride) or 0.1% chlorpheniramine (as the maleate), with or without 0.2% sodium nitrite, was given ad lib. to groups of 20 or 24 male and 20 or 24 female F344 rats for 106 wk. Groups of 24 male and 24 female F344 rats were given drinking-water that contained N,N-dimethyldodecylamine-N-oxide at a concentration of 0.1%, with or without 0.2% sodium nitrite, for 93 wk. Control rats were given untreated feed or drinking-water and nitrite-treated controls were given sodium nitrite at a concentration of 0.2% in feed or drinking-water. At the end of the treatment period the rats were given untreated feed and water and observed until death. There was little or no life-shortening effect in any treatment group. None of the four amines administered alone induced an increase in the incidence of any tumour in comparison with the untreated control groups. In the male rats given diphenhydramine, chlorpheniramine or N,N-dimethyldodecylamine-N-oxide concurrently with nitrite there was a significant increase in the incidence of liver neoplasms (hepatocellular carcinomas and neoplastic nodules). In the groups given untreated feed or drinking-water there were, respectively, five and three male rats that had liver tumours. In contrast the number of male rats with liver tumours was ten in the group given dimethyldodecylamine-N-oxide plus nitrite, 11 in that given diphenhydramine plus nitrite and 14 (eight with carcinomas) in the group given chlorpheniramine plus nitrite. These results suggest that the ingestion of dimethyldodecylamine-N-oxide, diphenhydramine hydrochloride or chlorpheniramine under conditions when they could be nitrosated with nitrite in the stomach might present an increased carcinogenic risk.