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Monoamine levels and monoamine oxidase activity in different regions of rat brain as a function of age
Mechanisms of Ageing and Development, 23 (1983) 151-160 Elsevier ScientificPublishers Ireland Ltd.
151
MONOAMINE LEVELS AND MONOAMINE OXIDASE ACTIVITY IN DIFFERENT REGIONS OF RAT BRAIN AS A FUNCTION OF AGE
D. B H A S K A R A N * and E. R A D H A * * I
Department of Zoology, Bangalore University, Bangalore-560 056 (India)
(Received November 23rd, 1982) (Revision received February 12th, 1983) SUMMARY The levels of norepinephrine, dopamine, 5-hydroxytryptamine and the activity of monoamine oxidase were estimated in cerebral cortex, cerebellum, medulla oblongata, hypothalamus, striatum and midbrain of 21-day-old, 3-, 6-, 12- and 24-monthold male albino rats of Wistar strain. No significant change with age was found in the levels of all the three amines in cerebral cortex and cerebellum, while medulla oblongata showed a significant decrease of all the amines by 24 months of age. Hypothalamic norepinephrine, dopamine and striatal dopamine showed a highly significant decrease by 24 months of age, whereas 5-hyd~oxytryptamine in hypothalamus, norepinephrine and 5-hydroxytryptamine in striatum and dopamine in midbrain did not show any appreciable change with age. Monoamine oxidase activity in all the regions except cerebellum showed a significant increase by 24 months of age compared to 3- and 6-month-old rats. Key words: Monoamines; Brain; Neurotransmitters; Monoamine oxidase; Aging; Age-related
INTRODUCTION There are several reports to correlate t h e age-related changes in many physiological functions with the neurotransmitters, especially norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), acetylcholine and gamma-aminobutyric acid. The literature in these areas has been reviewed [1--6] and has shown large variations in the data obtained.
*Present address: Department of Nephrology, School of M~dicine, University of Southern California, Los Angeles, California 90033, U.S.A. **Address all correspondence to E. Radha, Department of Pharmacologyand Nutrition, University of Southern California, 2025 Zonal Avenue, Los Angeles, California 90033, U.S.A. 0047-6374/83/$3.00 Printed and Published in Ireland
© 1983 Elsevier ScientificPublishers Ireland Ltd.
152 This is the first report of NE, D A , 5-HT levels and the activity of the m a j o r degrading enzyme m o n o a m i n e oxidase ( m o n o a m i n e : o x y g e n oxidoreductase, E C 1.4.3.4, M A O ) in six different regions and five different age groups of rats. O u r results on these p a r a m e t e r s as a function of time (circadian) are reported elsewhere. MATERIALS AND METHODS A colony of albino rats of Wistar strain (maximum lifespan of about 3 years) was maintained at 2 8 - 2 ° C , on a 12:12 h light-dark cycle (lights on at 6.00 a.m.) with food (commercial rat feed, Hindustan L e v e r Ltd., B o m b a y ) and water ad libitum. Male rats of age 21 days (31--40 g), 3 months (110-128g), 6 months (173-192g), 12 months (237-258 g) and 24 months (282-311 g) were used in this study. Rats which manifested pathological symptoms were discarded. The animals were decapitated at the same time of the day for all the experiments, in order to avoid the possible circadian variations, and the brains were r e m o v e d quickly and chilled. All dissections were p e r f o r m e d in tl~e cold. Different regions like cerebral cortex, cerebellum, medulla oblongata, hypothalamus, striatum and midbrain were isolated as described by Glowinski and lversen [7]. The different regions were washed in ice-cold saline, blotted, transferred to precooled beakers and weighed. The methods used for the estimation of NE, D A and 5 - H T were those of Shellenberger and G o r d o n [8] using a Perkin-Elmer spectrophotofluorometer. Final recovery estimated in each experiment by internal standards averaged about 90%. Extracts from each region were analyzed for NE, D A and 5 - H T contents in duplicates. M A O activity was estimated as described by Weissbach et al. [9] using kynuramine dihydrobromide as substrate. Protein content was estimated according to the m e t h o d of Lowry et al. [10]. Results are expressed as the m e a n +_standard deviation, and the values of one age group to the next older age group was c o m p a r e d using Student's t-test. RESULTS Figure 1 shows NE, D A , 5 - H T levels and M A O activity in the cerebral cortex. T h e r e is a sharp increase (p < 0.05) in M A O activity (after 12 months of age) but there was no significant change in the amine levels of 3-, 6-, 12- and 24-month-old rats. It is interesting to note that the cerebellum had almost no D A in any of the age groups studied (Fig. 2). The levels of N E and 5-HT are relatively lower in the cerebellum of all the age groups when c o m p a r e d to the other regions; also there was no change in the levels of these amines or in M A O activity with age. In m e d u l l a oblongata, all the amines showed a significant decrease by 24 months of age c o m p a r e d to 12 months (NE and D A p < 0.01, and 5 - H T p < 0.02). This can be correlated with the increase in M A O activity (Fig. 3).
153
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AGE IN MONTHS Fig. 1. T h e level of norepinephrine, dopamine, ~erotonin and m o n o a m i n e oxidase activity in the cerebral cortex of rats of different age groups. Values are represented as mean-+ S.D. of 4 observations.
NE and D A levels in hypothalamus (Fig. 4) significantly decreased with age (p < 0.001), whereas 5-HT remained more or l~ss stable up to 24 months (N.S.). M A O activity showed a linear increase with age. Striatum showed the highest level of D A (Fig. 5) which declined significantly by 24 months of age (p < 0.001). NE and 5-HT showed less change with age (N.S.) while M A O activity increased with age. In the midbrain a decline in the amine levels was found by 24 months of age (Fig. 6). NE and 5-HT showed a significant decline (/7 <0.01), whereas D A
154
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The level of norepinephrine, serotonin and m o n o a m i n e oxidase activity in the cerebellum of rats of different age groups. Values are represented as m e a n _+S.D. of 4 observations.
showed no significant change with age, and M A O activity showed an increasing trend.
DISCUSSION The cortex regions due to various
present results, which have shown a total absence of D A in the cerebral and cerebellum and very little in the medulla compared to the other of 21-day-old rat, are an interesting observation. This could probably be the proliferation of D A containing neurons at different speeds and at times during ontogeny [11]. N E and 5-HT levels were found to be low in
155
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AGE IN MONTHS Fig. 3. The level of norepinephrine, dopamine, serotonin and monoamine oxidase activity in the medulla oblongata of rats of different age groups. Values are represented as mean-+ S.D. of 4 observations. all the regions compared to other age groups. The hypothalarnic NE level of 2-month-old rat was remarkably lower, which was attributed to the incomplete development of the functional capacity [12]. Similarly, the poorly developed patterns of behavior of newborn rats were related to the low levels of brain NE and 5-HT [13]. Time-dependent maturation of 5-HT in different regions of the mouse brain has been reported [14]. Low MAO activity was found in different regions of 21-day-old rat brain, so also in the whole brain of 15-day-old rats, whereas in 30-day-old animals there was noticeable MAO activity [15].
156
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AC~ IN MONTHS • Fig. 4. The level of norepinephrine, dopamine, serotonin and monoamine oxidase activity in the hypothalamus of rats of different age groups. Values are represented as mean _+S.D. of 4 observations. T h e a m i n e levels in t h e c e r e b r a l c o r t e x of rat b r a i n as a f u n c t i o n of age d i d n o t s h o w m u c h c h a n g e , w h e r e a s M A O activity s h o w e d a small b u t statistically significant i n c r e a s e a f t e r 12 m o n t h s of age. H o w e v e r , an i n c r e a s e in c e r e b r a l 5 - H T level a n d n o c h a n g e in N E a n d D A w e r e f o u n d with age in t h e rat b r a i n [16]. A n i n c r e a s e in M A O activity with age in t h e c o r t e x of r h e s u s m o n k e y was r e p o r t e d [17]. C e r e b e l l u m of t h e r a t b r a i n s h o w e d a p a t t e r n s i m i l a r to c e r e b r a l c o r t e x , b u t n o D A c o u l d b e d e t e c t e d in any of t h e a g e g r o u p s s t u d i e d , which m a y b e d u e to t h e m e t h o d which is less sensitive in d e t e c t i n g v e r y low levels of D A . M e d u l l a r y a m i n e s s h o w e d a significant d e c r e a s e b y 24 m o n t h s , w h e r e a s M A O activity
157
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AGE IN MONTHS Fig. 5. The level of norepinephrine, dopamine, serotonin and monoamine oxidase activity in the striatum of rats of different age groups. Values are represented as mean _+ S.D. o f 4 observations.
showed an increasing trend. There are similar reports on NE, 5-HT and MAO activity in human hindbrain [18-20], whereas 5-HT was shown to have a positive correlation with age in human medulla [21]. Hypothalamic NE and D A levels showed a highly significant decrease with age, whereas the 5-HT content did not vary. MAO activity showed a linear increase with age. This supports the findings of Sun, Miller e t al. and Timiras e t al. [22-24]. Striatal DA level showed a significant decline by 24 months of age, whereas NE and 5-HT showed less change with age. In midbrain both NE and 5-HT showed a significant change by 24 months of age. MAO activity of these two regions also showed an increase. A
158
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AGE. IN MONTHS Fig. 6. T h e level of norepinephrine, dopamine, serotonin and m o n o a m i n e oxidase activity in the midbrain of rats o£ ditierent age groups. Values are repres e nt e d as me a n + S.D. of 4 observations.
significant decline in the D A content of caudate nucleus, putamen, hippocampus and mesencephalon of human brain with age [25, 26] and a clear loss of 5-HT content in the nuclei of aged rat brain have been reported [27]. Decrease in the amine levels and the ultimate increase in their metabolites could be correlated to the significant increase in M A O activity with age. Most of the reports have confirmed an increase in M A O activity with age in different brain regions [17, 19, 28, 29]. It was suggested that aging process may significantly affect monoamine mechanisms and be a predisposing factor in the development of clinical diseases of central nervous system disorders [20]. The conversion of monoamines from their p r e c u r s o r s - t y r o s i n e to N E in the brainstem and
159
h y p o t h a l a m u s a n d to D A in the s t r i a t u m a n d h y p o t h a l a m u s - w a s significantly r e d u c e d in o l d e r rats [30]. A g e - r e l a t e d loss of striatal d o p a m i n e r g i c t e r m i n a l s m a y also b e p r e d i c t e d in a d d i t i o n to the p u t a t i v e p o s t s y n a p t i c c h a n g e s [31]. T h e decline in the capacity with age to synthesize n e u r o t r a n s m i t t e r s u b s t a n c e s m a y b e associated with a b n o r m a l i t i e s in circulating m e t a b o l i t e s , particularly d u r i n g the later periods of life, with cell death, disease a n d o t h e r c o n d i t i o n s m a y f u r t h e r alter n e u r o t r a n s m i t t e r activity in the b r a i n [2]. T h e p r e s e n t results s u p p o r t the c o n c e p t that m o n o a m i n e s are i m p o r t a n t for the b r a i n in its role as a " r e g u l a t o r " or " p a c e m a k e r " of the aging process. REFERENCES 1 E.G. McGeer and P.L. McGeer, Neurotransmitter metabolism in the aging brain. In R.D. Terry and S. Gershon (eds.), Aging, Vol. 3, Raven Press, New York, 1976, pp. 389--403. 2 T. Samorajski, Central neurotransmitter substances and aging: A review. J. Am. Geriatr. Soc., 25 (1977) 337-348. 3 S.N. Pradhan, Central neurotransmitters and aging: Mini review. Life Sci., 26 (1980) 1643-1656. 4 T.R. Bartus, R.L. Dean, B. Beer and A.S. Lippa, The cholinergic hypothesis of geriatric memory dysfunction. Science, 217 (1982) 408--417. 5 C.G. Gottfries, Brain, monoamines, and aging. In R.D. Terry, C.L. Bolis and G. Tottano (eds.), Neural Aging and its Implications in Human Neurological Pathology [Aging, Vol. 18], Raven Press, New York, 1982, pp. 161-168. 6 T.P. Bridge, S. Potkin, C.D. Wise, B.H. Phelps and R.J. Wyatt, Monoamine oxidase and aging. In A. Raskin, D.S. Robinson and J. Levine (eds.), Age and the Pharmacology of Psychoactive Drugs, Elsevier, New York, 1981, pp. 79-89. 7 J. Glowinski and L.L. Iversen, Regional"studies of catecholamines in the rat brain-I. Dissection of rat brains. J. Neurochem., 13 (1966) 655--669. 8 M.K. Shellenberger and J.H. Gordon, A rapid, simplified procedure for simultaneous assay of norepinephrine, dopamine and 5-hydroxytryptamine from discrete brain areas. Anal. Biochem., 39 (1971) 356--372. 9 H. Weissbach, T.E. Smith, J.W. Daly, B. Witkop and S. Udenfriend, Spectrophotometric assay of monoamine oxidase. J. Biol. Chem., 235 (1960) 1160-1163. 10 O.H. Lowry, N.J. Rosebrough, A.L. Farr and R.J. Randall, Protein measurement with the Folin phenol reagent. J. Biol. Chem., 193 (1951) 265-275. 11 L.A. Loizou, The development of monoamine-containing neurons in the brain of the albino rat. J. Anat., 104 (1969) 588. 12 E. Nicolescu and A. Ciplea, Comparative modifications of the hypothalamus and adrenal catecholamine level in young and adult male rats after standardized physical effort. Rev. Roum. Physiol., 10 (1973) 245-250. 13 N. Karki, R. Kunitzman and B.B. Brodie, Storage, synthesis and metabolism of monoamines in the developing brain. J. Neurochem., 9 (1962) 53--58. 14 P.C. Baker and K.M. Hoff, Maturation of 5-hydroxytryptamine levels in various brain regions of the mouse from 1 day post partum to adulthood. J. Neurochem., 19 (1972) 2011-2015. 15 N. Robinson, Histochemistry of monoamine oxidase in the developing rat brain, J. Neurochem., 14 (1967) 1083-1089. 16 V.N. Anisimov, V.K. Pozdeev, A. Yu. Dmitrievskaya, G.M. Gracheva, A.P. II'in and V.M. Dil'man, Age-related changes of the biogenic amine levels in the rat brain. Fiziol. Zh. SSSR ira. LM. Sechenova, 63 (1977)353-358. 17 T. Samorajski and C. Rolsten, Age and regional differences in the chemical composition of brains of mice, monkeys and humans. Progr. Brain Res., 40 (1973) 253-265.
160 18 A. Nies, D.S. Robinson, J.M. Davis and C.L. Ravaris, Changes in monoamine oxidase with aging. In C. Eisdorfer and W.E. Fann (eds.), Psychopharmacology and Aging, Plenum Press, New York, 1973, pp. 41-54, 19 D.S. Robinson, J.M. Davis, A. Nies, R.W. Colburn, J.N. Davis, H.R. Bourne, W.E. Bunney, D.M. Shaw and A.J. Coppen, Ageing, monoamines and monoamine oxidase levels. Lancet, i (1972) 290-291. 20 D.S. Robinson, Changes in monoamine oxidase and monoamines with human development and aging. Fed. Proc. 34 (1975) 103-107. 21 A. Carlsson, R. Adolfsson, S.-M. Aquilonius, C.-G. Gotffries, L. Oreland, L, Svennerholm and B. Winblad, Biogenic amines in human brain in normal aging, senile dementia and chronic alcoholism. Adv, Biochem. Psychopharmacol., 23 (1980) 295-304. 22 A.Y. Sun, Aging and in vivo norepinephrine-uptake in mammalian brain. Exp. Aging Res., 2 (1976) 207-219. 23 A.E, Miller, C.J. Sharp and G.D. Riegle, Aging ettects on hypothalamic dopamine and norepinephrine content in the male rat. Exp. Aging Res., 2 (1976) 475-480. 24 P.S. Timiras, D.B. Hudson and C. Miller, Developing and aging brain serotonergic systems. In E. Giacobini et al. (eds.), The Aging Brain: Cellular and Molecular Mechanisms of Aging in the Nervous System, Raven Press, New York, 1982, pp. 173-184. 25 A. Bertler, Occurrence and localization of catecholamines in the human brain. Acta Physiol. Scand., 51 (1961) 97-107. 26 R. Adolfsson, C.G. Gottfries and B.E. Roos, Post-mortem distribution of dopamine and homovanillic acid in human brain, variations related to age and a review of the literature. J. Neural Transm., 45 (1979) 81-105. 27 J.L. Meek, B. Leif, L. Darwin, Cheney, Z. Gabriella and C. Erminio, Aging-induced changes in acety!.choline and serotonin content of discrete brain nuclei. J. Gerontol., 32 (1977) 129-131. 28 S.S. Grote, S.G. Moses, E. Robins, R.W. Hudgens and A.B. Croninger, A study of selected catecholamine metabolizing enzymes: A comparison of depressive suicides and alcoholic suicides with controls. Z Neurochem'., 23 (1974) 791--802. 29 L.J. Cote and L.T. Kremzner, Changes in neurotransmitter systems with increasing age in human brain. Trans. Am. Soc. Neurochem., 5 (1974) 83. 30 F. Ponzio, N. Brunello and S. Algeri, Catecholamine synthesis in brain of aging rat. J. Neurochem., 30 (1978) 1617-1620. 31 J.A. Severson and C.E. Finch, Reduced dopaminergic binding during aging in the rodent striatum. Brain Res., 192 (1980) 147-162.
151
MONOAMINE LEVELS AND MONOAMINE OXIDASE ACTIVITY IN DIFFERENT REGIONS OF RAT BRAIN AS A FUNCTION OF AGE
D. B H A S K A R A N * and E. R A D H A * * I
Department of Zoology, Bangalore University, Bangalore-560 056 (India)
(Received November 23rd, 1982) (Revision received February 12th, 1983) SUMMARY The levels of norepinephrine, dopamine, 5-hydroxytryptamine and the activity of monoamine oxidase were estimated in cerebral cortex, cerebellum, medulla oblongata, hypothalamus, striatum and midbrain of 21-day-old, 3-, 6-, 12- and 24-monthold male albino rats of Wistar strain. No significant change with age was found in the levels of all the three amines in cerebral cortex and cerebellum, while medulla oblongata showed a significant decrease of all the amines by 24 months of age. Hypothalamic norepinephrine, dopamine and striatal dopamine showed a highly significant decrease by 24 months of age, whereas 5-hyd~oxytryptamine in hypothalamus, norepinephrine and 5-hydroxytryptamine in striatum and dopamine in midbrain did not show any appreciable change with age. Monoamine oxidase activity in all the regions except cerebellum showed a significant increase by 24 months of age compared to 3- and 6-month-old rats. Key words: Monoamines; Brain; Neurotransmitters; Monoamine oxidase; Aging; Age-related
INTRODUCTION There are several reports to correlate t h e age-related changes in many physiological functions with the neurotransmitters, especially norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), acetylcholine and gamma-aminobutyric acid. The literature in these areas has been reviewed [1--6] and has shown large variations in the data obtained.
*Present address: Department of Nephrology, School of M~dicine, University of Southern California, Los Angeles, California 90033, U.S.A. **Address all correspondence to E. Radha, Department of Pharmacologyand Nutrition, University of Southern California, 2025 Zonal Avenue, Los Angeles, California 90033, U.S.A. 0047-6374/83/$3.00 Printed and Published in Ireland
© 1983 Elsevier ScientificPublishers Ireland Ltd.
152 This is the first report of NE, D A , 5-HT levels and the activity of the m a j o r degrading enzyme m o n o a m i n e oxidase ( m o n o a m i n e : o x y g e n oxidoreductase, E C 1.4.3.4, M A O ) in six different regions and five different age groups of rats. O u r results on these p a r a m e t e r s as a function of time (circadian) are reported elsewhere. MATERIALS AND METHODS A colony of albino rats of Wistar strain (maximum lifespan of about 3 years) was maintained at 2 8 - 2 ° C , on a 12:12 h light-dark cycle (lights on at 6.00 a.m.) with food (commercial rat feed, Hindustan L e v e r Ltd., B o m b a y ) and water ad libitum. Male rats of age 21 days (31--40 g), 3 months (110-128g), 6 months (173-192g), 12 months (237-258 g) and 24 months (282-311 g) were used in this study. Rats which manifested pathological symptoms were discarded. The animals were decapitated at the same time of the day for all the experiments, in order to avoid the possible circadian variations, and the brains were r e m o v e d quickly and chilled. All dissections were p e r f o r m e d in tl~e cold. Different regions like cerebral cortex, cerebellum, medulla oblongata, hypothalamus, striatum and midbrain were isolated as described by Glowinski and lversen [7]. The different regions were washed in ice-cold saline, blotted, transferred to precooled beakers and weighed. The methods used for the estimation of NE, D A and 5 - H T were those of Shellenberger and G o r d o n [8] using a Perkin-Elmer spectrophotofluorometer. Final recovery estimated in each experiment by internal standards averaged about 90%. Extracts from each region were analyzed for NE, D A and 5 - H T contents in duplicates. M A O activity was estimated as described by Weissbach et al. [9] using kynuramine dihydrobromide as substrate. Protein content was estimated according to the m e t h o d of Lowry et al. [10]. Results are expressed as the m e a n +_standard deviation, and the values of one age group to the next older age group was c o m p a r e d using Student's t-test. RESULTS Figure 1 shows NE, D A , 5 - H T levels and M A O activity in the cerebral cortex. T h e r e is a sharp increase (p < 0.05) in M A O activity (after 12 months of age) but there was no significant change in the amine levels of 3-, 6-, 12- and 24-month-old rats. It is interesting to note that the cerebellum had almost no D A in any of the age groups studied (Fig. 2). The levels of N E and 5-HT are relatively lower in the cerebellum of all the age groups when c o m p a r e d to the other regions; also there was no change in the levels of these amines or in M A O activity with age. In m e d u l l a oblongata, all the amines showed a significant decrease by 24 months of age c o m p a r e d to 12 months (NE and D A p < 0.01, and 5 - H T p < 0.02). This can be correlated with the increase in M A O activity (Fig. 3).
153
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•
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Oopamine (DA) •
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AGE IN MONTHS Fig. 1. T h e level of norepinephrine, dopamine, ~erotonin and m o n o a m i n e oxidase activity in the cerebral cortex of rats of different age groups. Values are represented as mean-+ S.D. of 4 observations.
NE and D A levels in hypothalamus (Fig. 4) significantly decreased with age (p < 0.001), whereas 5-HT remained more or l~ss stable up to 24 months (N.S.). M A O activity showed a linear increase with age. Striatum showed the highest level of D A (Fig. 5) which declined significantly by 24 months of age (p < 0.001). NE and 5-HT showed less change with age (N.S.) while M A O activity increased with age. In the midbrain a decline in the amine levels was found by 24 months of age (Fig. 6). NE and 5-HT showed a significant decline (/7 <0.01), whereas D A
154
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Fig. 2.
The level of norepinephrine, serotonin and m o n o a m i n e oxidase activity in the cerebellum of rats of different age groups. Values are represented as m e a n _+S.D. of 4 observations.
showed no significant change with age, and M A O activity showed an increasing trend.
DISCUSSION The cortex regions due to various
present results, which have shown a total absence of D A in the cerebral and cerebellum and very little in the medulla compared to the other of 21-day-old rat, are an interesting observation. This could probably be the proliferation of D A containing neurons at different speeds and at times during ontogeny [11]. N E and 5-HT levels were found to be low in
155
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AGE IN MONTHS Fig. 3. The level of norepinephrine, dopamine, serotonin and monoamine oxidase activity in the medulla oblongata of rats of different age groups. Values are represented as mean-+ S.D. of 4 observations. all the regions compared to other age groups. The hypothalarnic NE level of 2-month-old rat was remarkably lower, which was attributed to the incomplete development of the functional capacity [12]. Similarly, the poorly developed patterns of behavior of newborn rats were related to the low levels of brain NE and 5-HT [13]. Time-dependent maturation of 5-HT in different regions of the mouse brain has been reported [14]. Low MAO activity was found in different regions of 21-day-old rat brain, so also in the whole brain of 15-day-old rats, whereas in 30-day-old animals there was noticeable MAO activity [15].
156
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AC~ IN MONTHS • Fig. 4. The level of norepinephrine, dopamine, serotonin and monoamine oxidase activity in the hypothalamus of rats of different age groups. Values are represented as mean _+S.D. of 4 observations. T h e a m i n e levels in t h e c e r e b r a l c o r t e x of rat b r a i n as a f u n c t i o n of age d i d n o t s h o w m u c h c h a n g e , w h e r e a s M A O activity s h o w e d a small b u t statistically significant i n c r e a s e a f t e r 12 m o n t h s of age. H o w e v e r , an i n c r e a s e in c e r e b r a l 5 - H T level a n d n o c h a n g e in N E a n d D A w e r e f o u n d with age in t h e rat b r a i n [16]. A n i n c r e a s e in M A O activity with age in t h e c o r t e x of r h e s u s m o n k e y was r e p o r t e d [17]. C e r e b e l l u m of t h e r a t b r a i n s h o w e d a p a t t e r n s i m i l a r to c e r e b r a l c o r t e x , b u t n o D A c o u l d b e d e t e c t e d in any of t h e a g e g r o u p s s t u d i e d , which m a y b e d u e to t h e m e t h o d which is less sensitive in d e t e c t i n g v e r y low levels of D A . M e d u l l a r y a m i n e s s h o w e d a significant d e c r e a s e b y 24 m o n t h s , w h e r e a s M A O activity
157
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AGE IN MONTHS Fig. 5. The level of norepinephrine, dopamine, serotonin and monoamine oxidase activity in the striatum of rats of different age groups. Values are represented as mean _+ S.D. o f 4 observations.
showed an increasing trend. There are similar reports on NE, 5-HT and MAO activity in human hindbrain [18-20], whereas 5-HT was shown to have a positive correlation with age in human medulla [21]. Hypothalamic NE and D A levels showed a highly significant decrease with age, whereas the 5-HT content did not vary. MAO activity showed a linear increase with age. This supports the findings of Sun, Miller e t al. and Timiras e t al. [22-24]. Striatal DA level showed a significant decline by 24 months of age, whereas NE and 5-HT showed less change with age. In midbrain both NE and 5-HT showed a significant change by 24 months of age. MAO activity of these two regions also showed an increase. A
158
]'II/IIDBRAIN 0-- . . . . . . ~ P -
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."
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/
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AGE. IN MONTHS Fig. 6. T h e level of norepinephrine, dopamine, serotonin and m o n o a m i n e oxidase activity in the midbrain of rats o£ ditierent age groups. Values are repres e nt e d as me a n + S.D. of 4 observations.
significant decline in the D A content of caudate nucleus, putamen, hippocampus and mesencephalon of human brain with age [25, 26] and a clear loss of 5-HT content in the nuclei of aged rat brain have been reported [27]. Decrease in the amine levels and the ultimate increase in their metabolites could be correlated to the significant increase in M A O activity with age. Most of the reports have confirmed an increase in M A O activity with age in different brain regions [17, 19, 28, 29]. It was suggested that aging process may significantly affect monoamine mechanisms and be a predisposing factor in the development of clinical diseases of central nervous system disorders [20]. The conversion of monoamines from their p r e c u r s o r s - t y r o s i n e to N E in the brainstem and
159
h y p o t h a l a m u s a n d to D A in the s t r i a t u m a n d h y p o t h a l a m u s - w a s significantly r e d u c e d in o l d e r rats [30]. A g e - r e l a t e d loss of striatal d o p a m i n e r g i c t e r m i n a l s m a y also b e p r e d i c t e d in a d d i t i o n to the p u t a t i v e p o s t s y n a p t i c c h a n g e s [31]. T h e decline in the capacity with age to synthesize n e u r o t r a n s m i t t e r s u b s t a n c e s m a y b e associated with a b n o r m a l i t i e s in circulating m e t a b o l i t e s , particularly d u r i n g the later periods of life, with cell death, disease a n d o t h e r c o n d i t i o n s m a y f u r t h e r alter n e u r o t r a n s m i t t e r activity in the b r a i n [2]. T h e p r e s e n t results s u p p o r t the c o n c e p t that m o n o a m i n e s are i m p o r t a n t for the b r a i n in its role as a " r e g u l a t o r " or " p a c e m a k e r " of the aging process. REFERENCES 1 E.G. McGeer and P.L. McGeer, Neurotransmitter metabolism in the aging brain. In R.D. Terry and S. Gershon (eds.), Aging, Vol. 3, Raven Press, New York, 1976, pp. 389--403. 2 T. Samorajski, Central neurotransmitter substances and aging: A review. J. Am. Geriatr. Soc., 25 (1977) 337-348. 3 S.N. Pradhan, Central neurotransmitters and aging: Mini review. Life Sci., 26 (1980) 1643-1656. 4 T.R. Bartus, R.L. Dean, B. Beer and A.S. Lippa, The cholinergic hypothesis of geriatric memory dysfunction. Science, 217 (1982) 408--417. 5 C.G. Gottfries, Brain, monoamines, and aging. In R.D. Terry, C.L. Bolis and G. Tottano (eds.), Neural Aging and its Implications in Human Neurological Pathology [Aging, Vol. 18], Raven Press, New York, 1982, pp. 161-168. 6 T.P. Bridge, S. Potkin, C.D. Wise, B.H. Phelps and R.J. Wyatt, Monoamine oxidase and aging. In A. Raskin, D.S. Robinson and J. Levine (eds.), Age and the Pharmacology of Psychoactive Drugs, Elsevier, New York, 1981, pp. 79-89. 7 J. Glowinski and L.L. Iversen, Regional"studies of catecholamines in the rat brain-I. Dissection of rat brains. J. Neurochem., 13 (1966) 655--669. 8 M.K. Shellenberger and J.H. Gordon, A rapid, simplified procedure for simultaneous assay of norepinephrine, dopamine and 5-hydroxytryptamine from discrete brain areas. Anal. Biochem., 39 (1971) 356--372. 9 H. Weissbach, T.E. Smith, J.W. Daly, B. Witkop and S. Udenfriend, Spectrophotometric assay of monoamine oxidase. J. Biol. Chem., 235 (1960) 1160-1163. 10 O.H. Lowry, N.J. Rosebrough, A.L. Farr and R.J. Randall, Protein measurement with the Folin phenol reagent. J. Biol. Chem., 193 (1951) 265-275. 11 L.A. Loizou, The development of monoamine-containing neurons in the brain of the albino rat. J. Anat., 104 (1969) 588. 12 E. Nicolescu and A. Ciplea, Comparative modifications of the hypothalamus and adrenal catecholamine level in young and adult male rats after standardized physical effort. Rev. Roum. Physiol., 10 (1973) 245-250. 13 N. Karki, R. Kunitzman and B.B. Brodie, Storage, synthesis and metabolism of monoamines in the developing brain. J. Neurochem., 9 (1962) 53--58. 14 P.C. Baker and K.M. Hoff, Maturation of 5-hydroxytryptamine levels in various brain regions of the mouse from 1 day post partum to adulthood. J. Neurochem., 19 (1972) 2011-2015. 15 N. Robinson, Histochemistry of monoamine oxidase in the developing rat brain, J. Neurochem., 14 (1967) 1083-1089. 16 V.N. Anisimov, V.K. Pozdeev, A. Yu. Dmitrievskaya, G.M. Gracheva, A.P. II'in and V.M. Dil'man, Age-related changes of the biogenic amine levels in the rat brain. Fiziol. Zh. SSSR ira. LM. Sechenova, 63 (1977)353-358. 17 T. Samorajski and C. Rolsten, Age and regional differences in the chemical composition of brains of mice, monkeys and humans. Progr. Brain Res., 40 (1973) 253-265.
160 18 A. Nies, D.S. Robinson, J.M. Davis and C.L. Ravaris, Changes in monoamine oxidase with aging. In C. Eisdorfer and W.E. Fann (eds.), Psychopharmacology and Aging, Plenum Press, New York, 1973, pp. 41-54, 19 D.S. Robinson, J.M. Davis, A. Nies, R.W. Colburn, J.N. Davis, H.R. Bourne, W.E. Bunney, D.M. Shaw and A.J. Coppen, Ageing, monoamines and monoamine oxidase levels. Lancet, i (1972) 290-291. 20 D.S. Robinson, Changes in monoamine oxidase and monoamines with human development and aging. Fed. Proc. 34 (1975) 103-107. 21 A. Carlsson, R. Adolfsson, S.-M. Aquilonius, C.-G. Gotffries, L. Oreland, L, Svennerholm and B. Winblad, Biogenic amines in human brain in normal aging, senile dementia and chronic alcoholism. Adv, Biochem. Psychopharmacol., 23 (1980) 295-304. 22 A.Y. Sun, Aging and in vivo norepinephrine-uptake in mammalian brain. Exp. Aging Res., 2 (1976) 207-219. 23 A.E, Miller, C.J. Sharp and G.D. Riegle, Aging ettects on hypothalamic dopamine and norepinephrine content in the male rat. Exp. Aging Res., 2 (1976) 475-480. 24 P.S. Timiras, D.B. Hudson and C. Miller, Developing and aging brain serotonergic systems. In E. Giacobini et al. (eds.), The Aging Brain: Cellular and Molecular Mechanisms of Aging in the Nervous System, Raven Press, New York, 1982, pp. 173-184. 25 A. Bertler, Occurrence and localization of catecholamines in the human brain. Acta Physiol. Scand., 51 (1961) 97-107. 26 R. Adolfsson, C.G. Gottfries and B.E. Roos, Post-mortem distribution of dopamine and homovanillic acid in human brain, variations related to age and a review of the literature. J. Neural Transm., 45 (1979) 81-105. 27 J.L. Meek, B. Leif, L. Darwin, Cheney, Z. Gabriella and C. Erminio, Aging-induced changes in acety!.choline and serotonin content of discrete brain nuclei. J. Gerontol., 32 (1977) 129-131. 28 S.S. Grote, S.G. Moses, E. Robins, R.W. Hudgens and A.B. Croninger, A study of selected catecholamine metabolizing enzymes: A comparison of depressive suicides and alcoholic suicides with controls. Z Neurochem'., 23 (1974) 791--802. 29 L.J. Cote and L.T. Kremzner, Changes in neurotransmitter systems with increasing age in human brain. Trans. Am. Soc. Neurochem., 5 (1974) 83. 30 F. Ponzio, N. Brunello and S. Algeri, Catecholamine synthesis in brain of aging rat. J. Neurochem., 30 (1978) 1617-1620. 31 J.A. Severson and C.E. Finch, Reduced dopaminergic binding during aging in the rodent striatum. Brain Res., 192 (1980) 147-162.