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Substance P markedly ameliorates scopolamine-induced impairment of spontaneous alternation performance in the mouse
BRAIN RESEARCH ELSEVIER
Brain Research 673 (1995) 335-338
Short communication
Substance P markedly ameliorates scopolamine-induced impairment of spontaneous alternation performance in the mouse Makoto Ukai *, Norihiro Shinkai, Kayoko Ohashi, Tsutomu Kameyama Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Meijo UniL,ersity,Nagoya 468, Japan
Accepted 13 December 1994
Abstract
We investigated the effects of intracerebroventricular injection of substance P (SP) on the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance in the mouse. SP (0.001-3 p~g) alone did not influence either spontaneous alternation performance or total arm entries. Scopolamine (1 mg/kg) impaired spontaneous alternation performance accompanied by an increment in total arm entries. In contrast, SP (0.01-1 ~g) significantly improved the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance without influencing the scopolamine (1 mg/kg)-induced increase in total arm entries. The effects of SP (0.1 /~g) on the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance were almost completely reversed by pretreatment with WIN 62577 (1 mg/kg), a tachykinin NK-I receptor antagonist. These results suggest that SP improves the scopolamine-induced impairment of spontaneous alternation performance through the mediation of tachykinin NK-1 receptors. Keywords: Spontaneous alternation performance; Substance P; WIN 62577; NK-1 receptor; Mouse
Substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) belong to a family of neuropeptides called tachykinins defined by their common amino acid sequences of carboxyl C-terminal. The receptors appropriate for SP, N K A and NKB are also termed as NK-1, NK-2 and NK-3, respectively [17]. NK-1 receptors distribute in the hippocampus which plays an important role in m e m o r y modulation [10,20]. In addition, the contents of SP and acetylcholine have been found to decrease in the basal forebrain of Alzheimer's disease patients [3,5,22]. Several studies have indicated that SP influences m e m o r y process. For example, systemic administration of SP improves the dysfunction of water maze performance in old rats [8]. Although SP injected into the nucleus basalis magnocellularis has been found to facilitate inhibitory avoidance response [13], SP injected into the substantia nigra produces marked retrograde amnesia [9]. Thus, the effects of SP on m e m o r y process would depend on sites of the brain injected. However, it is uncertain whether SP affects memory impairment in amnesic animals.
* Corresponding author. Fax: (81) (52) 834-8780. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(94)01460-4
Although the outstanding view today is that general cholinergic disruption influences animal's attention to controlling stimuli and disturbs some aspects of cortical arousal, while having no primary effect on memory, we have considered that the scopolamine-induced impairment of spontaneous alternation performance is associated with dysfunctions of spatial working memory [12,18]. The present study was designed to examine the effects of SP on the scopolamine-induced impairment of spontaneous alternation performance in the mouse. Male mice of the ddY strain (Nihon SLC Co., H a m a m a t s u , Japan), weighing between 30 and 40 g were used. They were housed in a group of eight under standard conditions (22_+ 2°C, 50_+ 10% humidity, l i g h t - d a r k cycle with the light on between 08.00 and 20.00 h) with free access to food and water. The mice were used for the experiments following adaptation to laboratory conditions for at least 1 week and were naive to each of the tests used in the present study. The experiments were conducted between 10.00 and 18.00 h in a sound-attenuated room. SP (Peptide Institute Inc., Minoh, Japan) was dissolved in sterile isotonic saline solution (Otsuka Pharmaceutical Co. Ltd., Tokyo, Japan) and administered into the lateral ventricle (i.c.v.) of the mouse brain
336
M. Ukai et aL / B r a i n Research 673 (1995) 335-338
according to the m e t h o d of Haley and M c C o r m i c k [7] in an injection volume of 5 ~ l / m o u s e over 1 min t h r o u g h injection needle u n d e r brief ether anesthesia as previously described [12]. N o n e of the stereotaxic instruments were employed. T h e site was checked by injecting a 1:10 dilution of India ink in isotonic saline. Histological examinations revealed particles of the ink in the lateral and 3rd ventricles but not in the others. Severe tissue d a m a g e was never seen in the brain. Because the brief etherization during i.c.v, injection should almost completely prevented stress-related events, neither insertion of the needle nor injection of 5 p~l of isotonic saline solution actually had a significant influence on behavior such as s p o n t a n e o u s alternation p e r f o r m a n c e in normal mice as previously described, although there is a possibility that etherization and i.c.v, injection may change corticosterone levels. Scopolamine h y d r o b r o m i d e (Tokyo Chemical Industry Co. Ltd., Tokyo, Japan) was dissolved in 0.9% saline solution, while W I N 62577 (Research Biochemicals Inc., Natick, MO, U S A ) was dissolved in dimethylsulfoxide. T h e y were administered s.c. in an injection volume of 0.1 m l / 1 0 g body weight. T h e control group received an identical volume of injection of the vehicle. Doses were expressed in terms of the free base. Spontaneous alternation p e r f o r m a n c e was assessed in a black-painted Y-maze which was 40 cm long, 12 cm high, 3 cm wide at the b o t t o m and 10 cm wide at the top and positioned at an equal angle. T h e testing p r o c e d u r e was based on that of Sarter et al. [18]. Following vehicle or drugs injections, each mouse was placed at the end of one arm and allowed to move freely t h r o u g h the m a z e for an 8-min test session. T h e sequence of arm entries was r e c o r d e d manually. A n alternation was defined as the entry into all three arms on consecutive choices. The n u m b e r of maximum alternations was then the total n u m b e r of arms entered minus 2, and the percent alternation was calculated as (actual a l t e r n a t i o n s / m a x i m u m alternations) × 100. Mice which exhibited arm entries less than 8 times during the test were eliminated from the study because the data obtained from these mice were not considered to reflect precise alternations. Scopolamine, SP and W I N 62577 were injected 30, 10 and 30 min before the test, respectively. T h e results were expressed as the m e a n _+ S.E.M. and analyzed by a Kruskal-WaIlis n o n - p a r a m e t r i c oneway analysis of variance ( A N O V A ) . F u r t h e r statistical analysis for post hoc comparisons was d o n e with a Bonferroni's n o n - p a r a m e t r i c multiple comparison test (two-tailed). T h e criterion for statistical significance was P < 0.05 in all statistical evaluations. SP (0.001-3/_Lg) alone did not change percent alternation (Kruskal-Wallis analysis: H = 6.54, P > 0.05) or total arm entries (Kruskal-Wallis analysis: H = 8.21, P > 0.05) (data not shown).
80
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Control - Scopolamine (1 m g / k g ) 0 0.001 0.01 0.1 0.3 1 3
Substance P (~g/mouse)
Fig. I. Effects of substance P on the scopolamine-induced decrease in spontaneous alternation and increase in total arm entries in mice. Each value represents the mean±S.E.M. Substance P (i.c.v.) and scopolamine (s.c.) were administered 10 and 30 min before behavioral measurements, respectively. The number of mice used is shown in parentheses. * P < 0.05; * * P < 0.01 vs. control, # P < 0.05 vs. scopolamine alone. Scopolamine (1 m g / k g ) significantly decreased percent alternation (Kruskal-Wallis analysis: H = 29.55, P < 0.01) (Fig. 1), and increased total arm entries as c o m p a r e d with controls (Kruskal-Wallis analysis: H = 18.69, P < 0.05) (Fig. 1). O n the other hand, SP (0.01-1 ~g) significantly inhibited the scopolamine (1 m g / k g ) induced reduction of percent alternation ( P < 0.01) (Fig. 1), although SP (0.001-3 ~ g ) did not influence the scopolamine (1 m g / k g ) - i n d u c e d increase in total arm entries (Fig. 1). The tachykinin NK-1 receptor antagonist W I N 62577 (0.3 and 1 m g / k g ) alone did not influence percent alternation (Kruskal-Wallis analysis: H = 0.20, P > 0.05) or total arm entries in normal mice (Kruskal-Wallis analysis: H = 2.78, P > 0.05) (data not shown). W I N 62577 (1 m g / k g ) almost completely antagonized the effects of SP (0.1 /~g) on the scopolamine (1 m g / k g ) induced reduction of percent alternation (Kruskal-Wallis analysis: H = 17.20, P < 0.05) (Fig. 2) without influencing total arm entries (Kruskal-Wallis analysis: H = 24.33, P > 0.05) (Fig. 2). It has been indicated that SP injected into the nucleus basalis magnocellularis and basal forebrain facilitates inhibitory avoidance response [13,16]. T h e present investigation shows that intracerebroventricular injection of SP did not influence s p o n t a n e o u s alter-
M. Ukai et al. / Brain Research 673 (1995) 335-338 80 c O
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Control --Scopolamine (1 +mg/kg)-+ + Substance P (0.1 ~g/mouse) 0.3 1 WIN 62577(mg/kg) Fig. 2. Effects of substance P combined with WIN 62577 on scopolamine-induced decrease in spontaneous alternation and increase in total arm entries in mice. Each value represents the mean + S.E.M. Substance P (i.c.v.), WIN 62577 (s.c.) and scopolamine (s.c.) were administered 10, 30 and 30 min before behavioral measurements, respectively. The number of mice used is shown in parentheses. • P < 0.05; * * P < 0.01 vs. control, # P < 0.05 vs. scopolamine alone, s p < 0.05 vs. scopolamine plus substance P.
nation performance [11,12,18]. In contrast, SP (0.01-1 /xg) significantly improved the scopolamine-induced impairment of spontaneous alternation performance without influencing total arm entries. Therefore, it seems that spontaneous alternation performance and total arm entries are independent of each other [11]. In addition, the effects of SP on the scopolamine-induced impairment of spontaneous alternation performance were almost completely reversed by pretreatment with WIN 62577, a tachykinin NK-1 receptor antagonist [2,19]. These results suggest that SP improves the scopolamine-induced dysfunction of spontaneous alternation performance through the mediation of NK-1 receptors. On the other hand, although we have considered that spontaneous alternation performance is associated with spatial working memory, some other psychological factors such as attention [14], perseveration [15] and decision-making [21] may primarily play a role. SP has been shown to coexist with acetylcholinesterase in lateral dorsal tegmental neurons projecting to the medial frontal cortex [4]. Moreover, biochemical studies using in vivo microdialysis suggest that SP enhances acetylcholine release in the rat striatum
337
mediated via tachykinin NK-1 receptors [1,6]. It has been demonstrated that SP enhances the cholinergic agonist carbachol-induced increase in stereotyped behavior [4]. Therefore, the improving effects of SP on the scopolamine-induced impairment of spontaneous alternation performance would be due to the activation of cholinergic neurons. Moreover, the dopamine D 2 receptor antagonist sulpiride but not the dopamine D 1 receptor antagonist SCH23390 has been shown to inhibit the scopolamineinduced impairment of spontaneous alternation performance, implying the involvement of dopamine D 2 receptors in the scopolamine-induced disturbance of spontaneous alternation performance [11]. It is thus possible that SP attenuates the scopolamine-induced disturbance of spontaneous alternation performance by way of the inactivation of dopamine D 2 receptor-mediated neurotransmission. In conclusion, this, we believe, is the first demonstration that SP improves the scopolamine-induced impairment of spontaneous alternation performance associated with a primitive working memory capacity through the mediation of tachykinin NK-1 receptors.
[1] Anderson, J.J., Chase, T.N. and Engber, T.M., Substance P increases release of acetylcholine in the dorsal striatum of freely moving rats, Brain Res., 623 (1993) 189-194. [2] Briejer, M.R., Akkermans, L.M.A., Meulemans, A.L., Lefebvre, R.A. and Schuurkes, J.A.J., Substance P-induced contractions of the guinea-pig proximal colon through stimulation of postjunctional tachykinin NK 1 receptors, Eur. J. Pharmacol., 250 (1993) 181-183. [3] Coyle, J.T., Pride, D.L. and DeLong, M.R., Alzheimer's disease: a disorder of cortical cholinergic innervation, Science, 219 (1983) 1184-1190. [4] Crawley, J.N., Olschowka, J.A., Diz, D.I. and Jacobowitz, D.M., Behavioral investigation of the coexistence of substance P, corticotropin releasing factor, and acetylcholinesterase in lateral dorsal tegmental neurons projecting to the medial frontal cortex of the rat, Peptide, 6 (1985) 891-901. [5] Crystal, H.A. and Daves, P., Cortical substance P-like immunoreactivity in cases of the Alzheimer's type, J. Neurochem., 38 (1982) 1781-1784. [6] Guzman, R.G., Kendrick, K.M. and Emson, P.C., Effect of substance P on acetylcholine and dopamine release in the rat striatum: a microdialysis study, Brain Res., 622 (1993) 147-154. [7] Haley, T.J. and McCormick, W.G., Pharmacological effects produced by intracerebral injection of drugs in the conscious mouse, Br. J. Pharmacol., 12 (1957) 12-15. [8] Hasen6hrl, R.U., Huston, J.P. and Schuurman, T., Neuropeptide substance P improves water maze performance in aged rats, Psychopharmacology, 101 (1990) 23-26. [9] Huston, J.P. and Staubli, U., Retrograde amnesia produced by post-trial injection of substance P into substantia nigra, Brain Res., 159 (1978) 468-472. [10] Isaacson, R.L. and Wickelgreen, W.O., Hippocampal ablation and passive avoidance, Science, 133 (1962) 1104-1106. [11] Itoh, J., Ukai, M. and Kameyama, T., Dopaminergic involvement in the improving effects of dynorphin A-(l-13) on scopolamine-induced impairment of alternation performance, Eur. J. PharmacoL, 241 (1993) 99-104.
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M. Ukai et al. /Brain Research 673 (1995) 335-338
[12] Itoh, J., Ukai, M. and Kameyama, T., Dynorphin A-(l-13) potenly improves the impairment of spontaneous alternation performance induced by the /x-selective opioid receptor agonist DAMGO in mice, J. Pharmacol. Exp. Ther., 269 (1994) 15-21. [13] Kafetzopoulos, E., Holzh~iuer, M.-S. and Huston, J.P., Substance P injected into the region of the nucleus basalis magnocellularis facilitates performance of an inhibitory avoidance task, Psychopharmacology, 90 (1986) 281-283. [14] Katz, R.J. and Schmaltz, K., Dopaminergic involvement in attention: A novel animal model, Prog. Neuro-Psychopharmacol., 4 (1981) 585-590. [15] Kokkinidis, L. and Anisman, H., Interaction between cholinergic agents in a spontaneous alternation task, Psychopharmacology, 48 (1976) 261-270. [16] Nagel, J.A. and Huston, J.P., Enhanced inhibitory avoidance learning produced by post-trial injection of substance P into basal forebrain, Behau. Neural Biol., 49 (1988) 374-385. [17] Nakanishi, Y., Mammalian tachykinin receptors, Annu. Rel,. Neurosci., 14 (1991) 123-136. [18] Sarter, M., Bodewitz, G. and Stephens, D., Attenuation of scopolamine-induced impairment of spontaneous alternation
[19]
[20]
[21]
[22]
behaviour by antagonist but not inverse agonist and agonist /3-carbolines, Psychopharmacology, 94 (1988) 491-495. Venepalli, B.R., Aimone, L.D., Appell, K.C., Bell, M.R., Dority, J.A., Goswami, R., Hall, P.L., Kumar, V., Lawrence, K.B., Logan, M.E., Scensny, P.M., Seelye, J.A., Tomczuk, B.E. and Yanni, J.M., Synthesis and substance P receptor binding activity of androstano[3,2-b]pyrimido[1,2-a]benzimidazoles, J. Med. Chem., 35 (1992) 374-378. Walsh, T.J., Tilson, H.A., DeHaven, D.L., Mailman, R.B., Fisher, A. and Hanin, I., AF64A, a cholinergic neurotoxin, selectively depletes acetylcholine in hippocampus and cortex, and produces long-term passive avoidance and radial-arm maze deficits in the rat, Brain Res., 321 (1984) 91-102. Whitaker-Azmitia, P.M., Molino, L.J., Caruso, J. and Shemer, A.V., Serotonergic agents restore appropriate decision-making in neonatal rats displaying dopamine D~ receptor mediated vacillatory behavior, Eur. J. PharmacoL, 180 (1990) 305-309. Whitehouse, P.J., Price, D.L., Struble, R.G., Clerk, A.W., Coyle, J.T. and DeLong, M.R., Alzheimer's disease and senile dementia: loss of neurons in the basal forebrain, Science, 215 (1982) 1237 - 1239.
Brain Research 673 (1995) 335-338
Short communication
Substance P markedly ameliorates scopolamine-induced impairment of spontaneous alternation performance in the mouse Makoto Ukai *, Norihiro Shinkai, Kayoko Ohashi, Tsutomu Kameyama Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Meijo UniL,ersity,Nagoya 468, Japan
Accepted 13 December 1994
Abstract
We investigated the effects of intracerebroventricular injection of substance P (SP) on the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance in the mouse. SP (0.001-3 p~g) alone did not influence either spontaneous alternation performance or total arm entries. Scopolamine (1 mg/kg) impaired spontaneous alternation performance accompanied by an increment in total arm entries. In contrast, SP (0.01-1 ~g) significantly improved the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance without influencing the scopolamine (1 mg/kg)-induced increase in total arm entries. The effects of SP (0.1 /~g) on the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance were almost completely reversed by pretreatment with WIN 62577 (1 mg/kg), a tachykinin NK-I receptor antagonist. These results suggest that SP improves the scopolamine-induced impairment of spontaneous alternation performance through the mediation of tachykinin NK-1 receptors. Keywords: Spontaneous alternation performance; Substance P; WIN 62577; NK-1 receptor; Mouse
Substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) belong to a family of neuropeptides called tachykinins defined by their common amino acid sequences of carboxyl C-terminal. The receptors appropriate for SP, N K A and NKB are also termed as NK-1, NK-2 and NK-3, respectively [17]. NK-1 receptors distribute in the hippocampus which plays an important role in m e m o r y modulation [10,20]. In addition, the contents of SP and acetylcholine have been found to decrease in the basal forebrain of Alzheimer's disease patients [3,5,22]. Several studies have indicated that SP influences m e m o r y process. For example, systemic administration of SP improves the dysfunction of water maze performance in old rats [8]. Although SP injected into the nucleus basalis magnocellularis has been found to facilitate inhibitory avoidance response [13], SP injected into the substantia nigra produces marked retrograde amnesia [9]. Thus, the effects of SP on m e m o r y process would depend on sites of the brain injected. However, it is uncertain whether SP affects memory impairment in amnesic animals.
* Corresponding author. Fax: (81) (52) 834-8780. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(94)01460-4
Although the outstanding view today is that general cholinergic disruption influences animal's attention to controlling stimuli and disturbs some aspects of cortical arousal, while having no primary effect on memory, we have considered that the scopolamine-induced impairment of spontaneous alternation performance is associated with dysfunctions of spatial working memory [12,18]. The present study was designed to examine the effects of SP on the scopolamine-induced impairment of spontaneous alternation performance in the mouse. Male mice of the ddY strain (Nihon SLC Co., H a m a m a t s u , Japan), weighing between 30 and 40 g were used. They were housed in a group of eight under standard conditions (22_+ 2°C, 50_+ 10% humidity, l i g h t - d a r k cycle with the light on between 08.00 and 20.00 h) with free access to food and water. The mice were used for the experiments following adaptation to laboratory conditions for at least 1 week and were naive to each of the tests used in the present study. The experiments were conducted between 10.00 and 18.00 h in a sound-attenuated room. SP (Peptide Institute Inc., Minoh, Japan) was dissolved in sterile isotonic saline solution (Otsuka Pharmaceutical Co. Ltd., Tokyo, Japan) and administered into the lateral ventricle (i.c.v.) of the mouse brain
336
M. Ukai et aL / B r a i n Research 673 (1995) 335-338
according to the m e t h o d of Haley and M c C o r m i c k [7] in an injection volume of 5 ~ l / m o u s e over 1 min t h r o u g h injection needle u n d e r brief ether anesthesia as previously described [12]. N o n e of the stereotaxic instruments were employed. T h e site was checked by injecting a 1:10 dilution of India ink in isotonic saline. Histological examinations revealed particles of the ink in the lateral and 3rd ventricles but not in the others. Severe tissue d a m a g e was never seen in the brain. Because the brief etherization during i.c.v, injection should almost completely prevented stress-related events, neither insertion of the needle nor injection of 5 p~l of isotonic saline solution actually had a significant influence on behavior such as s p o n t a n e o u s alternation p e r f o r m a n c e in normal mice as previously described, although there is a possibility that etherization and i.c.v, injection may change corticosterone levels. Scopolamine h y d r o b r o m i d e (Tokyo Chemical Industry Co. Ltd., Tokyo, Japan) was dissolved in 0.9% saline solution, while W I N 62577 (Research Biochemicals Inc., Natick, MO, U S A ) was dissolved in dimethylsulfoxide. T h e y were administered s.c. in an injection volume of 0.1 m l / 1 0 g body weight. T h e control group received an identical volume of injection of the vehicle. Doses were expressed in terms of the free base. Spontaneous alternation p e r f o r m a n c e was assessed in a black-painted Y-maze which was 40 cm long, 12 cm high, 3 cm wide at the b o t t o m and 10 cm wide at the top and positioned at an equal angle. T h e testing p r o c e d u r e was based on that of Sarter et al. [18]. Following vehicle or drugs injections, each mouse was placed at the end of one arm and allowed to move freely t h r o u g h the m a z e for an 8-min test session. T h e sequence of arm entries was r e c o r d e d manually. A n alternation was defined as the entry into all three arms on consecutive choices. The n u m b e r of maximum alternations was then the total n u m b e r of arms entered minus 2, and the percent alternation was calculated as (actual a l t e r n a t i o n s / m a x i m u m alternations) × 100. Mice which exhibited arm entries less than 8 times during the test were eliminated from the study because the data obtained from these mice were not considered to reflect precise alternations. Scopolamine, SP and W I N 62577 were injected 30, 10 and 30 min before the test, respectively. T h e results were expressed as the m e a n _+ S.E.M. and analyzed by a Kruskal-WaIlis n o n - p a r a m e t r i c oneway analysis of variance ( A N O V A ) . F u r t h e r statistical analysis for post hoc comparisons was d o n e with a Bonferroni's n o n - p a r a m e t r i c multiple comparison test (two-tailed). T h e criterion for statistical significance was P < 0.05 in all statistical evaluations. SP (0.001-3/_Lg) alone did not change percent alternation (Kruskal-Wallis analysis: H = 6.54, P > 0.05) or total arm entries (Kruskal-Wallis analysis: H = 8.21, P > 0.05) (data not shown).
80
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70
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#
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(12}
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40
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(27)
(14)
(14)
(14)
(14)
Control - Scopolamine (1 m g / k g ) 0 0.001 0.01 0.1 0.3 1 3
Substance P (~g/mouse)
Fig. I. Effects of substance P on the scopolamine-induced decrease in spontaneous alternation and increase in total arm entries in mice. Each value represents the mean±S.E.M. Substance P (i.c.v.) and scopolamine (s.c.) were administered 10 and 30 min before behavioral measurements, respectively. The number of mice used is shown in parentheses. * P < 0.05; * * P < 0.01 vs. control, # P < 0.05 vs. scopolamine alone. Scopolamine (1 m g / k g ) significantly decreased percent alternation (Kruskal-Wallis analysis: H = 29.55, P < 0.01) (Fig. 1), and increased total arm entries as c o m p a r e d with controls (Kruskal-Wallis analysis: H = 18.69, P < 0.05) (Fig. 1). O n the other hand, SP (0.01-1 ~g) significantly inhibited the scopolamine (1 m g / k g ) induced reduction of percent alternation ( P < 0.01) (Fig. 1), although SP (0.001-3 ~ g ) did not influence the scopolamine (1 m g / k g ) - i n d u c e d increase in total arm entries (Fig. 1). The tachykinin NK-1 receptor antagonist W I N 62577 (0.3 and 1 m g / k g ) alone did not influence percent alternation (Kruskal-Wallis analysis: H = 0.20, P > 0.05) or total arm entries in normal mice (Kruskal-Wallis analysis: H = 2.78, P > 0.05) (data not shown). W I N 62577 (1 m g / k g ) almost completely antagonized the effects of SP (0.1 /~g) on the scopolamine (1 m g / k g ) induced reduction of percent alternation (Kruskal-Wallis analysis: H = 17.20, P < 0.05) (Fig. 2) without influencing total arm entries (Kruskal-Wallis analysis: H = 24.33, P > 0.05) (Fig. 2). It has been indicated that SP injected into the nucleus basalis magnocellularis and basal forebrain facilitates inhibitory avoidance response [13,16]. T h e present investigation shows that intracerebroventricular injection of SP did not influence s p o n t a n e o u s alter-
M. Ukai et al. / Brain Research 673 (1995) 335-338 80 c O
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(21)
(18)
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Control --Scopolamine (1 +mg/kg)-+ + Substance P (0.1 ~g/mouse) 0.3 1 WIN 62577(mg/kg) Fig. 2. Effects of substance P combined with WIN 62577 on scopolamine-induced decrease in spontaneous alternation and increase in total arm entries in mice. Each value represents the mean + S.E.M. Substance P (i.c.v.), WIN 62577 (s.c.) and scopolamine (s.c.) were administered 10, 30 and 30 min before behavioral measurements, respectively. The number of mice used is shown in parentheses. • P < 0.05; * * P < 0.01 vs. control, # P < 0.05 vs. scopolamine alone, s p < 0.05 vs. scopolamine plus substance P.
nation performance [11,12,18]. In contrast, SP (0.01-1 /xg) significantly improved the scopolamine-induced impairment of spontaneous alternation performance without influencing total arm entries. Therefore, it seems that spontaneous alternation performance and total arm entries are independent of each other [11]. In addition, the effects of SP on the scopolamine-induced impairment of spontaneous alternation performance were almost completely reversed by pretreatment with WIN 62577, a tachykinin NK-1 receptor antagonist [2,19]. These results suggest that SP improves the scopolamine-induced dysfunction of spontaneous alternation performance through the mediation of NK-1 receptors. On the other hand, although we have considered that spontaneous alternation performance is associated with spatial working memory, some other psychological factors such as attention [14], perseveration [15] and decision-making [21] may primarily play a role. SP has been shown to coexist with acetylcholinesterase in lateral dorsal tegmental neurons projecting to the medial frontal cortex [4]. Moreover, biochemical studies using in vivo microdialysis suggest that SP enhances acetylcholine release in the rat striatum
337
mediated via tachykinin NK-1 receptors [1,6]. It has been demonstrated that SP enhances the cholinergic agonist carbachol-induced increase in stereotyped behavior [4]. Therefore, the improving effects of SP on the scopolamine-induced impairment of spontaneous alternation performance would be due to the activation of cholinergic neurons. Moreover, the dopamine D 2 receptor antagonist sulpiride but not the dopamine D 1 receptor antagonist SCH23390 has been shown to inhibit the scopolamineinduced impairment of spontaneous alternation performance, implying the involvement of dopamine D 2 receptors in the scopolamine-induced disturbance of spontaneous alternation performance [11]. It is thus possible that SP attenuates the scopolamine-induced disturbance of spontaneous alternation performance by way of the inactivation of dopamine D 2 receptor-mediated neurotransmission. In conclusion, this, we believe, is the first demonstration that SP improves the scopolamine-induced impairment of spontaneous alternation performance associated with a primitive working memory capacity through the mediation of tachykinin NK-1 receptors.
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