Aspects of animal experiments for evaluation of cognitive enhancers: in particular, the behavioral characteristics of Mongolian gerbils

1. The step-through passive avoidance response and discrete lever-press avoidance response of Mongolian gerbils were evaluated to point out the basic problems in the learning and memory tests in this species. 2. Mongolian gerbils exhibited extremely poor acquisition and maintenance of the passive avoidance response. 3. In contrast to the result under the passive avoidance situation, Mongolian gerbils demonstrated an excellent performance under the discrete lever-press avoidance situation. 4. A 5-min brain ischemia elicited a severe morphological damage of the pyramidal cells in hippocampal CA1 region. 5. A small part of such ischemic animals showed a deficit of acquisition of the discrete lever-press avoidance. 6. These results suggest that there is merit and demerit of the acquisition dependent on the type of tasks, and that the brain function of Mongolian gerbils may be maintained even after the ischemic operation.

Behavioral evaluation of psycho-pharmacological and psychotoxic actions of methylxanthines by ambulatory activity and discrete avoidance in mice

The behavioral effects of methylxanthines, caffeine, theophylline and theobromine, were compared by means of ambulatory activity and discrete lever-press avoidance response in mice. The single oral administration of 10-100 mg/kg of caffeine, 30-300 mg/kg of theophylline, and 10 mg/kg of theobromine significantly increased the mouse's ambulatory activity. However, 1000 mg/kg of theobromine decreased the activity. The ambulation-increasing effect of methamphetamine (2 mg/kg s.c.) was enhanced by coadministration with caffeine (3-100 mg/kg), theophylline (10-300 mg/kg), and theobromine (10-100 mg/kg). On the other hand, comparatively higher doses of caffeine (up to 30 mg/kg) slightly but significantly decreased the avoidance rate without eliciting any significant change in the response rate. Theobromine significantly decreased the response rate at higher than 300 mg/kg, and the avoidance rate at higher than 100 mg/kg. Furthermore, 1000 mg/kg of theobromine was much toxic for mice, i.e., half mice died within a few hr after the end of the 1-hr avoidance session. Theophylline did not produce any significant change in the avoidance response at the dose range of 3-300 mg/kg. These results may indicate the relative order of the centrally stimulant and/or behavioral toxic actions of methylxanthines in human.

[Behavioral study on reduction of psychotic and behavioral disorders induced by antitussive and expectorant]

Previously, we reported that psychotic and behavioral disorders induced by repeated abuse of a commercial preparation of antitussive and expectorant (BRON-W Solution, SS Pharmaceut.) was mainly due to caffeine (CAF). In order to reduce such problem, we assessed effects of a preparation containing theophylline (THEO) as the substitution of CAF, and dihydrocodeine (2HCOD), methylephedrine (MEPH) and chlorpheniramine (CPA) on ambulatory activity and discrete lever-press avoidance response in mice. It is well known that THEO is less potent in the central action than CAF, but its relaxant action on smooth muscle is about 2 times as potent as that of CAF. Therefore, the dose of THEO administered was half of that of CAF. A significant increase in the ambulatory activity was produced by the administration of CAF and/or mixed preparations, in which CAF was contained with 2HCOD, MEPH and CPA at the same doses with those in BRON 10 ml/kg. The ambulation-increasing effects of THEO and THEO-containing preparations were less potent than those of CAP and CAF-containing preparations. Furthermore, repeated 5 times administration of CAF-containing 4-drug preparation (CAF + 2HCOD+MEPH+CPA) elicited a progressive enhancement of the ambulation-increasing effect. Whereas, almost the same effect was reproduced throughout the 5 times administration of THEO-containing 4-drug preparation (THEO + 2HCOD+MEPH+CPA). The discrete lever-press avoidance response was disrupted (i.e., decrease in the avoidance rate) by CAF-containing preparations. However, THEO-containing preparations did not induce such disruption of the avoidance response, but rather improved the avoidance response (i.e., increase in the avoidance rate).(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral effects of cocoa and its main active compound theobromine: evaluation by ambulatory activity and discrete avoidance in mice

Effects of cocoa and its main CNS active constituent methylxanthine theobromine as well as caffeine were evaluated by ambulatory activity, and discrete lever-press and shuttle avoidance in mice. Cocoa (1 g/kg p.o.) and theobromine (10 mg/kg p.o.) significantly increased ambulatory activity. However, the other doses of cocoa and theobromine had no effect on the ambulatory activity. Caffeine increased ambulatory activity with the maximum action at 30 mg/kg p.o. Furthermore, cocoa (0.1, 0.3 and 1 g/kg), theobromine (3, 10, 30 and 100 mg/kg) and caffeine (3, 10, 30 and 100 mg/kg) enhanced the ambulation-increasing effect of methamphetamine (2 mg/kg s.c.). The ambulation-increasing effect of cocaine (20 mg/kg s.c.) was also enhanced by cocoa (1 g/kg), theobromine (10, 30 and 100 mg/kg) and caffeine (10, 30 and 100 mg/kg). On the other hand, comparatively higher doses of theobromine and caffeine disrupted the well established avoidance response. Thus, the avoidance rate was significantly decreased by theobromine (100 mg/kg and more) and caffeine (30 mg/kg and more) under the lever-press situation, and by theobromine (100 mg/kg and more) and caffeine (100 mg/kg) under the shuttle situation. These dose effect relationships revealed that cocoa contains about 1% theobromine. The present results indicate that we may receive the CNS action of theobromine through consumption of theobromine-containing foodstuffs or beverages in our every day life.

Sensitization to ambulation-increasing effects of cocaine after repeated administration in mice--roles of dose and interval of administration as well as experimental environments

Effects of 5 subcutaneous injections of cocaine (COC) at 10, 20 or 40 mg/kg at intervals of 1 to 7 days were investigated by placing mice individually into tilting activity cages (20cm in diameter and 18 cm height). A progressive enhancement of the ambulation-increasing effect was noted for 3 to 4 hrs after each administration, showing marked sensitization (reverse tolerance). The enhancement of the effect progressed rapidly and the maximum sensitization was observed after the 3rd to 4th administration of 10 to 20 mg/kg at intervals of 3 to 7 days. The peak effect of the enhancement was of short duration. Sensitization lasted for at least one month. However, 40 mg/kg of COC produced stereotyped behaviors concurrent with preconvulsive signs which were also enhanced by serial administration. In contrast, pretreatment with COC in a narrow environment (glass jar, 5.5 cm in diameter and 15 cm height) did not cause the enhancement to the ambulation-increasing effect of the drug. Cross-sensitization was observed from COC to methamphetamine.

[Changes in rhythmicity of ambulatory and drinking activities produced by presentation of short time lightings during dark period in rats]

It is well known that the lighting conditions affect many physiological phenomenon of laboratory animals. However, lighting conditions are frequently disturbed by investigators themselves. In this study, behavioral (ambulation and drinking) rhythmicities of rats were investigated after irregular lighting; i. e. presentation of short time lighting at 21:00, 24:00 and 3:00 for 12 min during dark period (18:00-6:00). Vaginal smear was taken and sexual cycle was observed everyday. Ambulatory and drinking activities were measured by Gundai type Ambulo-drinkometer. The irregular lighting produced the following changes in the rhythmicities: 1) increase in the ambulatory activity during 15:00-18:00 immediately before dark period 2) decrease in ambulatory activity before ovulation 3) disappearance of inhibitory phenomenon of drinking activity which was usually observed before ovulation 4) increase in the drinking activity during 6:00-9:00 immediately after dark period 5) the changes in rhythmicities of the behavioral activities lasted for more than 1 month after replacement to the regular lighting condition.

Changes in rhythmicities of ambulatory and drinking activities after hypophysectomy in rats

Effects of hypophysectomy on circadian rhythms of ambulatory and drinking activities in adult male rats were automatically recorded and investigated with a Gundai-type ambulodrinkometer. The rats were maintained under LL conditions following an LD condition. When free-running rhythms had stabilized, the rats were hypophysectomized. The rhythmicities of both activities became indistinct over the 2-4 weeks following surgery, and then gradually recovered. At this time phase shifts (phase advance) were observed in the hypophysectomized rats, while these changes were not observed in sham-operated rats. All rats entrained to lighting when kept under LD conditions again. These results suggest that the pituitary does not play an essential role in maintaining circadian rhythms, but does function as an important subordinal oscillator.

Effects of repeated MK-801 on ambulation in mice and in sensitization following methamphetamine

The noncompetitive NMDA receptor antagonist MK-801, (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]-cyclohepten-5,10-imine , increased ambulatory activity in the mouse at doses over 0.1 mg/kg (IP). The effect was enhanced when 0.3 mg/kg MK-801 was repeatedly administered at intervals of 3-4 days. In contrast, a reduction of the effect was induced with repeated doses of 0.1 and 1 mg/kg. The mice that had repeatedly experienced 1 mg/kg MK-801 exhibited a decrease in the sensitivity to methamphetamine (2 mg/kg SC). In addition, the repeated co-administration of 1 mg/kg MK-801 with methamphetamine induced a decrease in the sensitivity to methamphetamine. No modification of methamphetamine sensitivity was elicited by 0.1 and 0.3 mg/kg MK-801 in both the single and co-administration schedules. On the other hand, established sensitization to methamphetamine was hardly affected by repeated treatment with 0.1-1 mg/kg MK-801. These results indicate that the mechanism of the inhibitory action of MK-801 on the development of methamphetamine sensitization is different from that of dopamine D2 antagonists, which may act to decrease the effective unit dose of methamphetamine and reduce ambulation-increasing effect of methamphetamine.

Characteristics of the ambulation-increasing effect of the noncompetitive NMDA antagonist MK-801 in mice: assessment by the coadministration with central-acting drugs

Characteristics of the ambulation-increasing effect of MK-801, a non-competitive NMDA antagonist, were assessed through the coadministration of MK-801 with various central-acting drugs in mice. The MK-801 (0.3 mg/kg, i.p.)-induced ambulation-increment with a slight ataxia was maximum at around 50 min, and ambulation returned to the control level at about 3 hr after the administration. At 1 mg/kg, the mouse's activity transiently increased, followed by a decrease due to a marked ataxia, which was due to neither stereotypy nor convulsion, for 20-50 min, and then increased again; the ambulation-increment continued even at 4 hr after the administration. Coadministration of MK-801 (0.3 mg/kg, i.p.) with either methamphetamine (2 mg/kg, s.c.), cocaine (20 mg/kg, s.c.), GBR-12909 (10 mg/kg, i.p.), scopolamine (0.5 mg/kg, s.c.), caffeine (10 mg/kg, s.c.) or morphine (10 mg/kg, s.c.) produced a significant enhancement of the effect. However, 0.1 mg/kg of MK-801 had no effect on the interaction with these drugs. On the other hand, the ambulation-increasing effect of MK-801 (0.3 mg/kg) was significantly reduced by haloperidol (0.3 and 0.1 mg/kg, s.c.), ceruletide (0.01 and 0.1 mg/kg, i.p.), reserpine (0.05 and 2 mg/kg, s.c., pretreatment 4 hr before) and nimodipine (1 and 3 mg/kg, i.p.), but it was scarcely modified by alpha-methyl-p-tyrosine (100 and 200 mg/kg, i.p., pretreatment 24 hr and 4 hr before), imipramine (20 mg/kg, i.p.), 6R-L-erythro-5,6,7,8-tetrahydro-biopterin (100 mg/kg, i.p.), pilocarpine (1 and 4 mg/kg, s.c.), N6-(L-2-phenylisopropyl)-adenosine (0.03 and 0.1 mg/kg, s.c.) and naloxone (1 and 5 mg/kg, s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of sensitization to ambulation-increasing effects of cocaine and methamphetamine after repeated administration in mice

The effects of repeated (5 times) subcutaneous administration of cocaine (10, 20 or 40 mg kg-1) and methamphetamine (1, 2 or 4 mg kg-1) at 3-4 day intervals have been compared in mice placed individually into tilting activity cages. A progressive enhancement of the ambulation-increasing effect was noted for 3-4 h after each administration, indicating that sensitization occurred. This occurrence and the existence of an optimal dose producing sensitization were similar for both drugs. However, enhancement of the effect after cocaine progressed rapidly and maximum sensitization was observed earlier than after methamphetamine administration. Moreover, the higher doses of cocaine (40 mg kg-1) caused stereotypies concurrent with preconvulsive signs of short duration that were enhanced by serial administration. In contrast, methamphetamine caused a more progressive enhancement, but stereotypies with no preconvulsive signs were produced by the higher dose (4 mg kg-1). The respectively, effective doses for the development of enhancement suggested that cocaine was less potent than methamphetamine in producing sensitization. Cross-sensitization occurred between both drugs. Thus, sensitization to cocaine was distinct from that to methamphetamine due to differences in its rapidity, intensity, and the presence or absence of preconvulsive changes.

Modifications of ambulation-increasing effect of morphine and buprenorphine following repeated administration in mice

Interaction of behavioral effects of morphine (10 and 20 mg/kg s. c.) and buprenorphine (0.3 and 1 mg/kg s. c.) were investigated by means of ambulatory activity following repeated administration of either drug in mice. The repeated administration of buprenorphine (1 mg/kg, but not 0.3 mg/kg) total of 5 times at intervals of 3-4 days induced a gradual decrease in the sensitivity to its ambulation-increasing effect. The buprenorphine-experienced mice showed an increase in the sensitivity to the ambulation-increasing effect of morphine (20 mg/kg) in parallel with the doses of buprenorphine. On the other hand, the ambulation-increasing effect of morphine (10 and 20 mg/kg) progressively enhanced during the repeated administration schedule. The morphine-experienced mice demonstrated a decrease in the sensitivity to buprenorphine (1 mg/kg). The present results may reflect differential characteristics between morphine and buprenorphine in their ambulation-increasing effects in mice.

Differential antagonism of the stimulant effects of MK-801 and methamphetamine by ceruletide: evaluation by discrete shuttle avoidance response in mice

A noncompetitive NMDA antagonist MK-801 (0.03-0.3 mg/kg, i.p.) increased the response rate of mice trained under the discrete shuttle avoidance situation to a degree similar to the increase by methamphetamine (0.1-1 mg/kg, i.p.). The cholecystokinin-like decapeptide ceruletide significantly reduced the response-increasing effect of MK-801 (0.1 mg/kg) at 0.001 micrograms/kg; however, only 10 micrograms/kg of ceruletide, which per se inhibited the response, attenuated that of methamphetamine (0.3 mg/kg). The coadministration of MK-801 (0.1 mg/kg) and methamphetamine (0.3 mg/kg) produced no potentiation of the effect, and almost the same effect was maintained even after the additional administration of ceruletide (0.1 microgram/kg).

[Radical surgery with pubectomy for primary male posterior urethral cancer--a case report]

A 38-year-old male patient with the past history of polioencephalopathy was admitted with urinary retention and high grade fever. Although he was able to walk he had the intelligence of a 3-year-old child and his spine, thorax, fingers were deformed remarkably. Immediately after the admission, cystostomy was carried out and 600 ml of stinky and cloudy urine was noted. Although intensive antibiotic therapy was performed, high grade fever with leucocytosis (greater than 15,000/mm2) persisted for more than 10 days. Retrograde urethrogram showed stricture in the anterior urethra as well as irregular filling defect in the bulbomembranous urethra. After urethral dilation using urethral dilators, 18Fr nephrostomy balloon catheter was indwelled and the patient was discharged. However, the urethral irregular filling defect was unchanged and cytological examination of urine and urethral secretions revealed class V. After the readmission, endoscopic examination revealed papillary tumor lesions occupying the whole posterior urethra were found. With the diagnosis of invasive posterior urethral cancer, anterior exenteration by en bloc pubectomy, pelvic lymphadenectomy and ileal conduit urinary diversion were carried out. On the surgical specimen, the tumor occupied the bulbomembranous and prostatic urethra. Histopathological diagnosis was TCC G3 greater than SCC, stage B. Since the tumor invaded the serosa of the membranous urethra, we thought it could not be removed completely without the pubctomy.

[Behavioral effects of febarbamate (MS-543): evaluation by ambulatory activity, active avoidance and passive avoidance in mice]

Febarbamate (MS-543: 100 and 10000 mg/kg, p.o.) neither produced significant change in the mouse's ambulatory activity after the single administration nor modified the ambulation-increasing effects of the following drugs: methamphetamine (2 mg/kg, s.c.), apomorphine (0.5 mg/kg, s.c.) and scopolamine (0.5 mg/kg, s.c.). MS-543 (100 and 1000 mg/kg, p.o.) scarcely affected the established active avoidance response in mice under a discrete shuttle avoidance situation. However, MS-543 (1000 mg/kg, p.o.) tended to enhance the decrease in response and/or avoidance rates induced by chlorpromazine (2 mg/kg, s.c.) and physostigmine (0.2 mg/kg, s.c.). Finally, the disruption of the step-through passive avoidance response induced by pre-training administration of scopolamine (0.5 mg/kg, s.c.) in a one trial task was reduced when MS-543 was administered before the scopolamine administration. However, the post-training administration of MS-543 was without effect on the scopolamine-induced disruption of the avoidance. Furthermore, no significant effect of MS-543 was observed in the multi-trial passive avoidance task. The present results suggest that MS-543 activates cholinergic function and possesses a slight sedative action.

Differential sensitization to ambulation-increasing effect of methamphetamine after repeated administration to mice in activity cages of different sizes

We have demonstrated that repeated administration of methamphetamine (MAP) 1-2 mg/kg, s.c. in a tilting-type round activity cage with a diameter of 20 cm (20 cm-cage) at 1-7 day intervals produces progressive enhancement of the ambulation-increasing effect (AIE), showing sensitization (reverse tolerance) in mice. However, almost no sensitization was observed when mice had been pretreated with the same doses of MAP but confined in a narrow environment repeatedly. In this experiment, changes in the sensitization were investigated in mice after repeated pretreatments with MAP at 2 mg/kg at 3-4 day interval for 4 times in activity cages of 5 different sizes (5, 10, 15, 30 and 40 cm in diameter) in comparison with that of in the 20 cm-cage. AIE obtained after MAP in the 5- and 10-cm cages was not enhanced, whereas AIE was significantly enhanced in the cages of more than 15 cm in diameter. There was no significant difference in the enhanced AIE among the 4 groups that received the same pretreatment repeatedly in the cages of 15, 20, 30 and 40 cm in diameter. The present results suggest that in accordance with the all-or-none law, development of the sensitization is affected by the size of the activity cage in which the animals have repeatedly experienced the acute drug effect.

Enhancement of the ambulation-increasing effect of opioid analgesics by ethanol in mice

The interaction between opioid analgesics (morphine and buprenorphine) and central depressants (ethanol, pentobarbital and diazepam) was investigated by means of ambulatory activity in mice. The ambulation-increasing effect of both morphine (10 mg/kg, s.c.) and buprenorphine (1 mg/kg, s.c.) was enhanced by the combined administration of ethanol (0.8-3.2 g/kg, p.o.) in a dose-dependent manner. Naloxone (0.1 mg/kg, s.c.) was effective for reducing the enhanced ambulatory activity. The pretreatment with Ca-cyanamide (5 mg/kg, p.o., 30 min before) reduced the enhancement of the ambulation-increasing effect induced by the combined administration of opioid analgesics with ethanol, although it scarcely modified that of morphine and buprenorphine alone. On the other hand, neither pentobarbital (1-30 mg/kg, s.c.) nor diazepam (0.25-2 mg/kg, s.c.) modified markedly the ambulation-increasing effect of morphine and buprenorphine. The present results suggest that ethanol specifically interacted with opioid analgesics when the mouse's ambulatory activity was used as the indicator.

[Modification of stereotypy-producing and ambulation-increasing effects following repeated administration of methamphetamine in rats]

Effects of repeated administration of methamphetamine (MAP: 1.25, 2.5 and 5 mg/kg, sc) at an interval of 4 days for 10 times on stereotyped behaviors as well as ambulatory activity in adult male rats of Wistar strain were investigated. In the first administration of MAP 1.25 mg/kg, marked ambulation-increasing effect was observed mixing with simple stereotyped behaviors such as sniffing and head-bobbing. The stereotypy-producing effect of MAP was apparently observed in a dose-dependent manner, and complicated stereotyped behaviors such as head-weaving and licking simultaneously with sniffing and head-bobbing were frequently demonstrated when 5 mg/kg of MAP was first administered. Furthermore, the ambulation-increasing effect after the drug showed biphasic pattern, i.e. pre-stereotypic and post-stereotypic increases in ambulatory activity, because the activity was interfered by the stereotyped behaviors. When MAP was administered repeatedly, the sniffing- and head-bobbing-producing effects were selectively enhanced at any dose, showing sensitization phenomenon (reverse tolerance), and the pre-stereotypic increase in ambulatory activity was inhibited, while the post-stereotypic increase was progressively enhanced. Although the sensitized stereotypy-producing effect was observed more markedly in the 10th administration of MAP 2.5 mg/kg than that in the first administration of MAP 5 mg/kg, the complicated stereotyped behaviors were hardly seen. It is suggested that the sensitization effects are not always identical qualitatively with the effects observed after increase in MAP-dose.

Effects of repeated administration of buprenorphine on ambulatory activity in mice

Effects of repeated administration of buprenorphine, given 5 times at intervals of 3-4 days, were investigated by ambulatory activity in mice. Buprenorphine (0.3 and 1 mg/kg sc) significantly increased the activity, and tolerance to the effect tended to be produced during the repeated administration schedule. The mice that experienced the repeated administration of buprenorphine exhibited an increased sensitivity to the ambulation-increasing effect of methamphetamine (2 mg/kg) in parallel with the doses of buprenorphine. However, no significant modification of the sensitivity to buprenorphine was produced in the mice that had experienced the repeated methamphetamine administration. Furthermore, the established reverse tolerance to methamphetamine was not significantly modified by the repeated treatment with buprenorphine (0.1, 0.3 and 1 mg/kg).

[Course and morphology studies in penile cancer]

A 75-year-old male patient showed an extensive erosion mainly restricted to the penile site, which was found when he received appendectomy. The penile lesion had persisted for about ten years, during which period the erosion extended gradually while he missed to consult a physician. The lesion was a florid and wetting erosion, with a definite boundary, which covered the entire circumference of the penile foreskin and also extended to the suprapubic area, scrotum and external urethral orifice. Although the diagnosis could not be made by biopsy, extra mammary Paget's disease was strongly suspected. Bilateral modified inguinal lymphadenectomy and systemic evaluation were first performed to confirm that there was no metastasis or complexed disease in other organs. Then extensive wide resection of the skin lesion and reconstruction using a split-thickness skin graft were performed. Histopathological examination of the surgical specimen revealed poorly differentiated squamous cell carcinoma, although most part showed only inflammatory erosion. Clinical course and the histopathological findings including specific staining patterns led to the diagnosis of poorly differentiated squamous cell carcinoma originated from erythroplasia. During post-operative 18 months until now, no local recurrence or distant metastasis has been observed.

[Changes in rhythmicity of ambulatory and drinking activities in immature female rats]

Adult female rats showed increase in ambulatory activity and marked decrease in drinking behavior at early dark period (18:00-24:00) of proestrus stage before ovulation. In this study, we observed the changes in patterns of ambulatory and drinking activities of immature rats associated with estrous cycle during growing period. Immature female rats of the Wistar-Imamichi strain were used, and both behavioral activities were measured continuously, using Gundai type Ambulodrinkometer. From these observations, it was found that the typical patterns of ambulatory and drinking activities which were observed in adult female rats appeared at the sixth (51-60 days old) and the third (39-49 days old) estrous cycle, respectively.

[Characteristics of antagonism between ceruletide and various central-acting drugs: investigation by means of ambulatory activity in mice]

Behavioral characteristics of ceruletide, a cholecystokinin-like decapeptide, were investigated by means of ambulatory activity in mice. Ceruletide at 100 and 300 micrograms/kg, i.p. slightly but significantly decreased the mouse's activity for 20 min. Therefore, 100 micrograms/kg of ceruletide was used in the experiment of combined administration with the central-acting drugs. Ceruletide reduced the increased activity which was produced by methamphetamine (2 mg/kg, s.c.), ephedrine (80 mg/kg, i.p.), methylphenidate (4 mg/kg, s.c.), cocaine (20 mg/kg, s.c.), mazindol (2.5 mg/kg, s.c.), apomorphine (0.5 mg/kg, s.c.), bromocriptine (8 mg/kg, i.p.), scopolamine (0.5 mg/kg, s.c.), caffeine (10 mg/kg, s.c.) and morphine (20 mg/kg, s.c.) with different potencies and durations. The mice that had experienced ceruletide at 3 micrograms/kg for 5 times at intervals of 3-4 days demonstrated a significant increase in the sensitivity to methamphetamine, although the same treatment with 10-300 micrograms/kg of ceruletide was without effect. On the other hand, when 3-300 micrograms/kg of ceruletide was combined with 2 mg/kg of methamphetamine, the development of reverse tolerance to the ambulation-increasing effect of methamphetamine was inhibited dependently on the doses of ceruletide. However, the reverse tolerance to methamphetamine once established was scarcely modified by ceruletide when it was administered afterwards.

Effects of ceruletide, administered singly and in combination with central-acting drugs, on discrete shuttle avoidance response in mice

The single administration of ceruletide at 10-300 micrograms/kg, i.p., slightly but significantly decreased the response rate (frequency of shuttles) under a discrete avoidance task in mice. Over 10 micrograms/kg of ceruletide attenuated the increase in the response rate induced by methamphetamine (0.5 mg/kg, s.c.). However, ceruletide, at 1-300 micrograms/kg, did not significantly enhance the response- and/or avoidance-decreasing effects of chlorpromazine (1 mg/kg, s.c.), haloperidol (0.1 mg/kg, s.c.), pilocarpine (4 mg/kg, s.c.) and N6-(L-2-phenylisopropyl)-adenosine (0.1 mg/kg, s.c.), but rather tended to reduce the avoidance-decreasing effect of chlorpromazine and pilocarpine at 1-100 micrograms/kg.

Behavioral study on mergocriptine (CBM36-733) by ambulatory activity in mice: repeated administration and interaction with methamphetamine

Effects of repeated administration of mergocriptine (CBM36-733: CBM), a long-acting ergot derivative with an agonistic action on both dopamine D1 and D2 receptors, as well as interaction between CBM and methamphetamine (MAP: 2 mg/kg, s.c.), were investigated by ambulatory activity in mice. CBM at 4 mg/kg significantly suppressed the ambulatory activity, but significantly increased it at 16 mg/kg in the drug-naive mice. However, 4 and 8 mg/kg of CBM were effective for increasing the ambulatory activity when these doses were repeatedly administered for 9 times at intervals of 7 days. The same treatment with 16 mg/kg of CBM produced a reverse tolerance to the ambulation-increasing effect. The mice that had received CBM at 1 and 2 mg/kg, but not 4-16 mg/kg, demonstrated a significantly lower sensitivity to MAP than the saline-experienced mice. On the other hand, the repeated MAP administration induced not only a reverse tolerance to itself, but also a cross reverse tolerance to 8 and 16 mg/kg of CBM. Furthermore, the established reverse tolerance to MAP was scarcely attenuated by the repeated treatment with any doses of CBM, but rather enhanced by 8 and 16 mg/kg of CBM. The present results indicate that, although the dose-effect relations are partially different, the behavioral characteristics of CBM were almost identical with those of bromocriptine, another long-acting ergot derivative having antagonistic and agonistic actions on dopamine D1 and D2 receptors, respectively.

The anticonflict effect of MK-801, an NMDA antagonist: investigation by punishment procedure in mice

The NMDA antagonist MK-801 at 0.3 mg/kg, i.p. increased the punished response under a MULT VI 1.5/FR 5-punishment schedule of food reinforcement in mice. Furthermore, although neither MK-801 (0.1 mg/kg, i.p.) nor diazepam (0.25 mg/kg, s.c.) was without effect when separately administered, a significant increase in the punished response appeared after the combined administration of these two drugs. The present results suggest that MK-801 not only shows an anticonflict effect, but also enhances the anticonflict effect of benzodiazepine anxiolytics in mice.