CURRENT THERAPEUTIC RESEARCH VOL. 56, NO. 5, MAY 1995 EFFECTS OF CEREBRAL METABOLIC ENHANCERS ON BRAIN FUNCTION IN RODENTS KOICHIRO TAKAHASHI,l MINORU YAMAMOTO,’ MASANORI SUZUKI,’ YUKIKO OZAWA,’ TAKASHI YAMAGUCHI,l HIROFUMI ANDOH, AND KOUICHI ISHIKAWA2 ‘Department of Pharmacology, Clinical Pharmacology Research Laboratory, Yamunouchi Pharmaceutical Co. Ltd., and ‘Department of Pharmacology, School of Medicine, Nihon University, Tokyo, Japan AFWI’RACT The effects of cerebral metabolic enhancers (indeloxazine, bi- femelane, idebenone, and nicergoline) on reserpine-induced hypother- mia, the immobility period in forced swimming tests, and passive avoidance learning behavior were compared with the effects of ami- triptyline in rodents. Indeloxazine, bifemelane, and amitriptyline antagonized hypothermia in mice given reserpine. Indeloxaxine and amitriptyline decreased the immobility period in mice in the forced swimming test in a dose-dependent manner. The latency of step- through in the passive avoidance test in rats was prolonged by ad- ministration of indeloxazine but shortened by administration of amitriptyline. Neither idebenone nor nicergoline displayed any phar- macologic action in these tests. The results suggest that indeloxaxine possesses an antidepressant activity similar to that of amitriptyline but differs from amitriptyline in its anticholinergic properties and its ability to ameliorate impaired brain function such as that of learning behavior. In addition, indeloxazine exhibited broader effects on brain functions than either bifemelane, idebenone, or nicergoline. INTRODUCTION Cerebral metabolic enhancers (drugs that enhance energy metabolism) including brain glucose and ATP levels such as indeloxazine,1*2 bi- femelane, 3*4idebenone?6 and nicergoline,7>8 are currently used for the treatment of patients with various psychiatric symptoms. These symptoms include reduced spontaneity and emotional disturbance in patients with cerebral vascular disease. Clinical trials of these drugs for the treatment of depression in aged populations are now in progress. However, the antide- pressant actions of these drugs have not been compared under the same experimental conditions. The present study compared the effects of indel- oxaxine, bifemelane, idebenone, and nicergoline with those of amitripty- Address correspondence to: M. Yamamoto, Department of Pharmacology, Clinical Pharmacology Research Laboratory, Yamanouchi Pharmaceutical Co. Ltd., l-l-8, Azusawa, Itabashi-ku, Tokyo 174, Japan. Received forpublication on February 16,1995. Printed in the U.S.A. Reproduction in whole or part is not permitted. 478 oo11-393x196/~3.50 K. TAKAHASH ET AL.. line on reserpine-induced hypothermia, forced swimming, and passive avoidance learning behavior in rodents. Amitriptyline, a typical antide- pressant currently used for the treatment of depressed patients, was cho- sen as the positive control drug to evaluate the antidepressive activity of the other study drugs. MATERIALSANDMETHODS The experiments were carried out using male ICR strain mice (approxi- mately 30 g each) and male Wistar rats (approximately 300 g each). The animals were group-housed in cages under a l&hour light-dark cycle (lights turned on between 7:30 AM and 830 PM) with laboratory chow and water given ad libitum. Test drugs were administered orally to the mice 18 hours after the subcutaneous administration of reserpine (2 mg/kg). Rectal temperature was measured immediately before and at 60, 120, and 180 minutes after drug administration. Drugs Indeloxazine hydrochloride and amitriptyline hydrochloride, synthe- sized at Yamanouchi Pharmaceutical Co., Ltd., Tokyo, Japan, were dis- solved in distilled water and administered orally. Bifemelane hydrochlo- ride, idebenone, and nicergoline, purchased commercially from Eisai, Tokyo, Japan, Takeda, Tokyo, Japan, and Tanabe Co. Ltd., Tokyo, Japan, respectively, were dissolved in 0.3% methylcellulose and administered orally. Distilled water and 0.3% methylcellulose were administered orally as vehicle control. Physostigmine sulfate (Tokyo Kasei Co. Ltd., Tokyo, Ja- pan), used as a positive control drug, was dissolved in saline solution. All drugs and vehicles were administered in a volume of 0.1 mLkg and 1 mL/kg to mice and rats, respectively. Forced Swimming-Induced Immobility in Mice The apparatus consisted of Plexiglass cylinders (24.5 cm x 6 cm x 18 cm; WW-3002, Ohara Co., Tokyo, Japan) with a waterwheel in the center. The waterwheel consisted of a Plexiglass shaft (5 cm long and 8 cm in diameter) on which 24 paddles (0.1 cm wide and 3.6 cm long) were attached at constant intervals. The waterwheel would move when application of a load greater than 5 g was applied to one of the paddles. The number of rotations of the waterwheel through an arc of 120” was counted via a photointerrupter attached to the shaft during the final 4 minutes of a 6-minute test. The tank contained water at a temperature of about 23 “C to a height of 12 cm; half of the paddles were resting in the water. 479 EFFECT OF INDELOWNE ON BRAIN FUNCTION Tests were conducted according to the method of Nomura et al.’ When a mouse was dropped into the water, it attempted to climb onto the wheel to escape from the water but could not do so due to rotation of the water- wheel. However, when the animal’s attempts to escape were finally aban- doned, the waterwheel would stop turning. The number of wheel rotations before the animal abandoned its attempts to escape were counted. Each mouse was placed in the water tank 1 hour after receiving a single oral (PO) administration of the drug. The number of rotations of the wheel was counted every 2 minutes for 6 minutes. The wheel counts during the final 4 minutes of the g-minute test for each mouse receiving the drug were compared with those of a control group of mice which had received distilled water and were exposed to a comparable situation. Passive Avoidance Learning in Rata Training was conducted according to the step-through procedure de- scribed by Jarvik and Kopp. lo The apparatus (Ohara Co.) consisted of two compartments (with clear plastic tops): an illuminated compartment (40 cm x 25 cm x 25 cm) containing a 60-watt lamp 25 cm above the top of the compartment (50 cm above the floor) and a dark compartment (25 cm x 15 cm x 25 cm). The two compartments were separated by a closed guillotine door (10 cm x 7 cm). Before training of passive avoidance learning, each rat underwent a single pretraining trial using the following procedure. The rat was placed in the illuminated compartment and the opaque guillotine door was raised 10 seconds later. After the rat entered the dark compartment, it was al- lowed to remain there for 10 seconds. In order to conduct the training, the rat was placed in the illuminated safe compartment. A door allowed the rat to enter the dark compartment, which contained a grid on the floor. Once the rat’s four paws were on the grid, a foot shock (60 V, 50 Hz) was deliv- ered to the floor grid for 2 seconds. The rat could escape the shock only by stepping back into the illuminated compartment. The rat was then re- turned to its home cage. The test trial was conducted 24 hours after the training session. The rat was again placed in the illuminated compartment of the same appa- ratus used in training, and the response latency before entering into the dark compartment was measured. The results were recorded as the aver- age step-through latency for each experimental group of animals. The rats were given a single po drug dose 60 minutes before the training session, in accordance with the methods of Yamamoto and Shimizu.” The step- through latency was measured both during the acquisition trial and the test trial (24 hours after the acquisition trial). The maximum observation period for monitoring behavior in this test was set at 10 minutes. 480 K. T- ET Al.. Values are expressed as the mean + SE. Results for reserpine- hypothermia, forced swimming-induced immobility, and passive avoid- ance learning behavior were analyzed using Student’s t test and Mann- Whitney U test, respectively. P < 0.05and P < 0.01 were considered significant. RESULTS Reaerpine-Induced Hypothermia in Mice Oral administration of indeloxaxine (1 and 3 mgkg), bifemelane (30 mg/kg po), and amitriptyline (1 and 3 mg/kg) antagonized the reserpine- induced hypothermia in a dose-dependent manner (Table I). In contrast, oral administration of idebenone (10 and 30 mg/kg) and nicergoline (1 to 10 mg/kg) exerted no effect on the reserpine-induced hypothermia. Forced Swimming-Induced Immobility in Mice Both indeloxaxine (50 mg/kg po) and amitriptyline (30 mg/kg po) in- creased the number of rotations by mice in a dose-dependent manner (Ta- Table I. Effects of indeloxazine, bifemelane, idebenone, nicergoline, and amitriptyline on reserpine-induced hypothermia in mice. Each value representa the mean for 6 to 7 mice. Temperature Change (2). Dose Tnatment (mo/lro 0W) 1 hour 2 hours 3houn Control f 0.7 f 0.4 ” 0.7 Control E : x.: 4.5 ” 0.6 Bifemelane 4:3 r 0:3 ;.; I ;.;$ 2:2 : 0’6 1.1 + 0:3 Control Nicergoline ?A I E 2:3 I 013 I!! i:3 f 0.4 1.6 2 0.6 Control 2.9 f 0.5 3.3 !?0.6 Amitriptyline ?: r :.;t 4.4 k 0.6 z.45 ;.;$ 3:9 z 0:7* 5.9 * 0.6$ . +f . * The difference in rectal temperature measured at l-hour intervals after treatment. The rectal temperature immediately before administration of the test drugs ran ed from 28.0 to 28.5 “C. Si nificantly different from the control group: tf < 0.0‘5 , SP c 0.01 (Student’s t test). Ni! = not done. 481 EFFECT OF INDELOXAZINB ON BRAIN FUNCTION ble II). However, bifemelane (10 to 100 mg/kg PO), idebenone (10 to 100 mg/kg PO), and nicergoline (1 to 30 mg/kg po) had little effect on this variable.