Japan. J. Pharmacol. 34, 15-21 (1984) 15 Effects of Histaminergic Drugs on Muricide Induced by Thiamine Deficiency Kenji ONODERA and Yasumi OGURA Departmentof Pharmacology,Tohoku University School of Dentistry, Sendai980, Japan Accepted August 8, 1983 Abstract-Male Wistar rats maintained on a thiamine deficient diet showed mouse killing aggression (muricide). On the 30th day of experimental feeding, the incidence of this muricide was about 70%. Intracerebroventricular histamine suppressed the muricide induced by thiamine deficiency in a dose-dependent manner. Histamine H1-receptor blocking agents such as diphenhydramine, promethazine and chlor pheniramine also showed muricidal suppression, but astemizole which lacks central effects did not show muricidal suppression. Mianserin and iprindole showed muricidal suppression, but metiamide i.p. did not. On the 20th day of experimental feeding, the incidence of this muricide was 45.5%. Histamine synthesis inhibitors such as brocresine or a-fluoromethylhistidine could not enhance the muricide on non-killer-rats, but really suppressed the thiamine deficient killer-rats. The results of this paper suggested that muricide induced by thiamine deficiency is not mediated by the central histaminergic system, but pharmacologically characterized by anti depressants, antihistamines and histamine synthesis inhibitors. We have previously found that thiamine histamine receptors might be connected with deficiency caused a muricidal aggression in the targets for antidepressants (9). Mianserin male rats (1 ). We have also reported the and iprindole, which are known as "atypical" characteristics of this muricide and suggested antidepressants, do not inhibit the monoamine central serotonergic neurons are involved in reuptake system, whereas the inhibition of the inhibition of the muricide aggression in noradrenaline or serotonin reuptake was thiamine deficient killer-rats (2, 3). Many believed for many years to be the basis of investigators have shown that serotonin is the clinical action (10, 1 1 ). The antihistaminic predominantly inhibitory on several forms of activity of these antidepressants is well aggression; the number of killer-rats can be documented in vivo (12, 13) and in clinical decreased by agents which are believed to investigations (14). activate the central serotonergic system (4-6). Therefore, we tried to examine the effect Conversely, the number of killer-rats can be of histaminergic drugs including "atypical" increased by brain lesion or drug treatment antidepressants on the muricide induced by which depletes the serotonin content in the thiamine deficiency, which has been reported brain (7, 8). These reports are consistent as a useful experimental model for evaluating with previous results that injection of 5 new antidepressants (3, 15). The final hydroxytryptophan or intracerebroventricular purpose of the current study is to examine (i.c.v.) serotonin suppressed the muricide, pharmacologically whether this muricide is and conversely, parachlorophenylalanine in mediated by the histaminergic system in jection facilitated killing aggression (2, 3). thiamine deficient killer-rats. However, certain mechanisms, except for the serotonergic system, are not yet clear in Materials and Methods thiamine deficient killer-rats. Recently, Animals: Male Wistar rats, weighing 60 Kanof and Greengard suggested that central 80 g at the begining of the experiment, were 16 K. Onodera & Y. Ogura obtained from Funabashi Farm Co. Mice rats still showed muricide aggression. We weighing 18-22 g were sacrificed for the selected rats weighing 180-220 g for surgery. muricide test. The animals were kept at All animals were anesthetized with sodium constant temperature (22±2'C) with a con pentobarbital (30 mg/kg i.p.) and a cannula, stant relative humidity, and the light cycle which was a slightly modified metal hyper was automatically controlled (7:30-19:30 dermic needle (0.5 mm dia.), was implanted hr). The rats were housed individually in mesh into the right ventricle of each rat according cages (17 x 25 x 37 cm) and were provided to the brain atlas of Pellegrino and Cushman with a thiamine deficient diet consisting of a (16). The rats were allowed at least 10 days basic ration, including 67.6% carbohydrate, to recover from the surgical procedure before 18% lipids and supplemented with vitamins the test. Histamine 2HCI (Wako) was dis (except thiamine) and minerals. The complete solved in pyrogen-free Ringer's solution and diet was identical to the thiamine deficient adjusted to pH 6.0-6.5, and it was given diet except that it contained 0.5 mg of i.c.v. to the animals in a volume of 10 el per thiamine hydrochloride per 100 g of diet (1 ). animal with a graduated Hamilton micro Pharmacological test: One hr before drug syringe. The position of the cannula in the adminstration, the thiamine deficient rats were ventricle was verified histologically at the tested for their tendency to kill (during a 3 min end of the experiment by the injection of observation period) a mouse which was thionine blue just prior to sacrificing the introduced into the home cages on a certain animals. Thirty min after i.c.v. histamine, the day of the experimental feedings. When the muricide test was performed for 5 min. rat killed the mouse during this period, the Statistical analysis: Statistical significance rat was labeled as a "killer-rat", and those among the groups was assessed by the which failed to kill were labeled as "non x2-test. The ED50 values were calculated by killer-rats". The drugs used in this experiment the method of Litchfield and Wilcoxon (17). were the antidepressants iprindole HCI (John Wyeth brother Ltd.), mianserin HCI (Nihon Results Organone and Sankyo Co. Ltd.), and ami Effect of intracerebroventricular injection triptyline HCI (Nippon Merck Banyu); the of histamine on the muricide induced by antihistamines diphenhydramine HCI (Kowa), thiamine deficiency: Figure 1 shows that chlorpheniramine maleate (Sankyo), pro muricide induced by thiamine deficiency was methazine HCI (Yoshitomi), astemizole dose-dependently suppressed by i.c.v. hista (Janssen) and metiamide (Smith Kline and mine. Fifty and 100 i g of histamine sig French Lab. Ltd.); the histidine decarboxylase nificantly suppressed this muricide when inhibitors brocresine dihydrogen phosphate compared with the Ringer-treated group (Ledere) and a-fluoromethyl-histidine 2HCI (P<0.01). The ED50 for muricidal sup (Merck Sharp and Dohme). Astemizole and metiamide were suspended in 0.5% tween 80 solution. All other drugs were dissolved in saline solution. The doses were expressed in terms of the salts. All drugs in this pharma cological test were injected intraperitoneally (i.p.). Intracerebroventricular injection of hista mine into killer-rats induced by thiamine deficiency: After 30 days of experimental thiamine deficient feeding, the thiamine deficient killer-rats were given 1 mg/kg Fig. 1. Effect of intracerebroventricular histamine thiamine hydrochloride, i.p. These rats were on muricide induced by thiamine deficiency. still housed in mesh cages, but were provided Statistical difference from the Ringer-treated group the thiamine added complete diet and water (**P<0.01). One hundred ag of histamine showed ad lib. Twenty days after the injections, the a complete suppression of muricide. Histamine and Muricide Aggression 17 pression was approx. 26 i'g (95% con none of the rats showed muricide aggression fidence limits: 14.3-45.5 ig). at the beginning of experimental feedings. Effect of histidine decarboxylase inhibitors Table 1 shows the effect of promethazine on on the killer-rats and non-killer-rats in thiamine deficiency: On the 20th day of experimental feeding, the incidence of muricide aggression was 45.5% in thiamine deficient rats. The thiamine deficient rats were divided into three groups, that is, a fluoromethyl-histidine, brocresine and saline treated groups. Each group consisted of 11 thiamine deficient rats (6 non-killer-rats and 5 killer-rats). a-Fluoromethylhistidine at 100 mg/kg i.p. suppressed this muricide in 2 out of 5 killer-rats at 0.5 and 1 hr after the injections. This suppression was also shown in the brocresine-treated group. The sup pression by a-fluoromethylhistidine was observed in 3 out of 5 rats from 3 to 24 hr, while the effect of brocresine disappeared at 6 hr. Both brocresine and a-fluoromethyl histidine did not convert non-killer-rats into Fig. 2. Effect of histamine synthesis inhibitors on killer-rats at any of the observation periods muricide induced by thiamine deficiency. On the 20th day of experimental thiamine deficient feeding, both (Fig. 2). non-killer-rats and killer-rats were injected with Effect of "atypical" antidepressants and histamine synthesis inhibitors. A -A Brocresine, antihistamines on the muricide induced by 150 mg/kg i.p.: A--A a-fluoromethylhistidine, thiamine deficiency: On the 30th day of 100 mg/kg i.p.: and 0-0 saline-treated group. experimental feedings, the incidence of Statistical difference from the saline-treated group muricide aggression was about 70%, and (*P<0.05). Table 1. Effect of antihistamines on muricide induced by thiamine deficiency ( ) indicates the number of rats. The denominator denotes the total number of rats; the numerator denotes the number in which the muricide was suppressed. Statistical differences from the vehicle treated group (*P<0.05 and **P<0.01) 1 8 K. Onodera & Y. Ogura the muricide induced by thiamine deficiency. dependently suppressed by mianserin, which The histamine H1-receptor blocking agent is known as an "atypical" antidepressant drug. promethazine showed dose-dependent Ten and 20 mg/kg mianserin produced muricidal suppression, 30 min after the significant muricidal suppression when injections. Five and 10 mg/kg promethazine compared with the saline-treated group from showed significant muricidal suppression 0.5 to 3 hr (P<0.01, Table 1 and Fig. 4). occurring in 4 out of 6 rats, and at 25 mg/kg, The ED50 for muricidal suppression by in 5 out of 6 rats (P<0.01 ). Diphenhydramine mianserin at 1 hr was approx. 7.0 mg/kg also produced muricidal suppression dose (95% confidence limits: 3.8-13.0 mg/kg).