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[3H]Dopamine accumulation and release from striatal slices in young, mature and senescent rats
436
Brain Research, 224 (1981) 436-440 Elsevier/North-Holland Biomedical Press
[~H]Dopamine accumulation and release from striatal slices in young, mature and senescent rats
JEFFREY M. THOMPSON, JOHN R. WHITAKER and J. A. JOSEPH Laboratories of Neurosciences and Behavioral Sciences, Gerontology Research Center, National Institute on Aging, Baltimore City Hospitals, Baltimore, MD 21224 (U.S.A.)
(Accepted July 30th, 1981) Key words: aging- - dopamine - - neurotransmitter release -- neurotransmitter uptake - - striatum --
brain slice
Examinations of [aH]dopamine ([aH]DA) release following KC1 or amphetamine administration in striatal slices from young (7 month), mature (12 month) and senescent (24 month)Wistar rats showed no age-related changes. Further, the amount of [aH]DA accumulated in the striatal slices showed no changes with age. Thus, previously reported age-related deficits in motor behavior (i.e. rotational) are not produced by changes in striatal DA accumulation or release. Some of the most consistent findings which have emerged with respect to senescence and declining neuronal function have been found within the dopamine (DA) system, especially within the striatum. Several laboratories have reported a loss of striatal D A receptors8,12,1a,15,16, a decline in DA turnover 3,4 and a decrease in the number of striatal neurons I in the aging rodent. To explore the link between these striatal D A changes and behavioral-motor deficits in the aged animal, the rotational modeP 7-~9 has been used. We have previously shown that aged rats in comparison with young rats exhibit deficits in rotational behavior following amphetamine administration 8. Subsequent attempts 10 to reduce these deficits by administering L-DOPA to the old rats 1 h prior to amphetamine administration were not successful, even though rotation was potentiated in the young rat. These findings suggested possible presynaptic deficits in uptake, synthesis or release of DA, as well as deficits in DA receptors. In this report, attempts were made to determine age-related differences in accumulation and release of DA from slices of rat striata from unlesioned young (7 month), mature (12 month) and senescent (24 month) Wistar rats. We found no agerelated deficits in the pre-synaptic events of DA accumulation or release in rat striata. Male Wistar rats 7, 12 and 24 months (mo) of age were obtained from the colony at the Gerontology Research Center, National Institute on Aging. After decapitation, striata were rapidly removed and washed in Earle's salts solution. Each half of a striatum was sliced on a Sorvall Tissue Chopper (200 #m sections). One-half of a striatum was placed in 2 ml Earle's salts plus ascorbic acid (0.5 mg/ml). After
437
(2
f-.
E] 24 MO
c7MO
[] -
5
f
10~
o
~
0
[3
10-~
10-*
10-3
-
A
12 MO
10-z
AMPHETAMINE {M)
Fig. l. [aH]Dopamine release from rat striatal slices in response to amphetamine as a function of age. After 25/~Ci of [aH]DA (spec. act. 22.8 Ci/mmol, New England Nuclear) was added to flasks containing
striatal slices from 7-, 12- and 24-too-old rats, the tissue was incubated at 36.5 °C for 45 min on an orbital shaker (70 rpm). The slices were then washed with Earle's salts and transferred to 13 mm Millipore Swinnex filter holders containing a Whatman GF/C filter. The filter holders were placed in a 37 °C water bath, connected to an 8-channel Gilson Multipulse peristaltic pump and perfused with Earle's salts plus ascorbic acid (0.5 mg/ml) at a rate of 1 ml/min. After a 30 min wash, the perfusate was collected in glass vials every 2 rain using a plexiglass manual fraction collecting system. Using a multichannel 3-way valve, which allowed selection of media from different reservoirs without interrupting the flow of media, the perfusion medium was switched after the third fraction to medium containing KC1 (80 mM) or D-amphetamine (10-6-10 -3 M). The osmolarity of the solutions was adjusted by reducing the NaC1 when necessary. After 10 fractions were collected, the tissue was removed from the filter holders and dissolved in 1 N NaOH. Protein was determined by the Lowry et al. procedurelz. Radioactivity in each fraction and that remaining in the dissolved tissue was determined using Instagel scintillation cocktail and a Beckman LS9100 scintillation counter.
i n c u b a t i o n in [ a H ] D A (spec. act. 22.8 C i / m m o l , N e w E n g l a n d Nuclear), the a m o u n t o f [3H]DA a c c u m u l a t e d in the cells o r released b y KC1 o r a m p h e t a m i n e was determined. Striatal slices f r o m 7-, 12- a n d 2 4 - m o - o l d rats a c c u m u l a t e d [3H]DA a n d released it at a low b a s a l level. W h e n release o f [ a H ] D A f r o m striatal slices in response to 80 m M KC1 was c o m p a r e d a m o n g g r o u p s o f 7-, 12- a n d 24- m o - o l d rats, n o significant differences were f o u n d between the different age g r o u p s (t-test, t < 1, d f ---- 12, P > 0.05). The p e a k release o f [SH]DA f r o m striatal slices was 24.1 ~o (7 mo), 23.2 ~o (12 m o ) a n d 21.9 ~o (24 m o ) o f t o t a l r a d i o a c t i v i t y a n d the net release was 4 7 . 0 ~ (7 mo), 38.9 ~ (12 m o ) a n d 44.3 ~ (24 too) o f total radioactivity. P e a k release refers to the value o f m a x i m u m release. N e t release is the total release in response to the stimulating agent (80 m M KC1 o r a m p h e t a m i n e ) , a n d is calculated b y s u m m i n g the total release due to d r u g m i n u s the b a s a l release. [SH]DA accounts for a p p r o x i m a t e l y 40 ~o o f the 3H efflux after KC1 s t i m u l a t i o n o f rat striatal slices labeled with [ZH]DA (ref. 2). S t i m u l a t i o n o f release b y a m p h e t a m i n e o f [ a H ] D A f r o m striatal slices as a function o f age was studied. In o r d e r to a c c o u n t for possible changes in p o t e n c y o f the d r u g in different ages, d o s e - r e s p o n s e relationships were d e t e r m i n e d at each age (Fig.
438
"~
50 ~ 40
~12 MO 0 24 Me
--
30
7 MO
lO i
&
10
20
i
30
i
~
40
MINUTES Fig. 2. Uptake of [3H]DA in striatal slices from 7-, 12- and 24-mo-old rats. After 5 #Ci of [SH]DA was added to 2 ml of medium, each flask containing one-half of a striatum was placed in a Dubnoffmetabolic shaking water bath (70 rpm) at 36.5 °C and oxygenated. At 2, 5, 15 and 40 rain, triplicate flasks were removed and the slices were rapidly collected on W h a t m a n G F / C filters in a vacuum filtration apparatus. As a blank, flasks were kept on 0 °C and removed at each collection time. The slices were washed twice with 5 ml of Earle's salts. The tissue was dissolved in 1 N N a O H overnight and protein determined by the Lowry et al. procedurelL The a m o u n t of [aH]DA taken into the slices was determined by scintillation spectroscopy.
1) and the results were analyzed by a 3(age) by 4(dose) analysis of variance. No significant differences were seen among ages in the peak release of D A (F (2,21) < 1, P > 0.05). In addition, no changes in the potency of amphetamine occurred during aging, as indicated by the lack of an age × dose interaction (F < 1, P > 0.05). An EDs0 of 2.5 × 10 -3 M was found for all ages. The dose effect of amphetamine was significant (F (7,21) = 11.96, P < 0.001) for all ages. The time course of [3H]DA accumulation was determined in striatal slices from each age (Fig. 2). There were no significant differences as a function of age and time. A subsequent analysis of variance (3 (age) by 4 (time)) carried out on these data showed that the statistical interaction between these variables was not significant (F(6,45) 1.66, P > 0.05). This analysis did show, however, that the overall effects of age were statistically significant, but not in a linear fashion. Rather, the striatal slices from the 7 mo and 24 mo groups showed no differences overall in [aH]DA accumulation (Duncan's test, P < 0.05). Striatal slices from 12 mo animals showed greater DA accumulation than those from the 7 mo animals (Duncan's test, P < 0.05), but no greater accumulation than slices from 24 mo animals. These differences appeared to be due, at least in part, to a decline in [3H]DA accumulation exhibited by the slices from the 7 mo group after 40 min of incubation. There was no consistent evidence that age-related motor-behavioral deficits as measured by the rotational model are produced by changes in striatal DA accumulation or release. Although accumulation at 40 min in 7-mo-old rats was less than in 12mo-old rats, the 7-mo-old values were not significantly different from 24-mo-old rats.
439 Therefore, there is not a clear age-related change in D A accumulation in rats under conditions used for our release experiments. Finch and co-workers 4,~,7 reported decreased uptakes of [aH]tyrosine and [aH]DA only at low concentrations in aged mice (5.5 × 10 -12 M and 1 x 10 -s M, respectively). At higher concentrations similar to those used in this study (1 x 10 -7 M), no age-related differences were seen. Although our study did not determine Vmax or Kra, no age-related differences in accumulation were seen at concentrations similar to those used for our release studies and concentrations greater than the Km for D A uptake determined in mouse striatum6, 7. Stimulated release of [aH]Da by KC1 or amphetamine from striatal slices does not change with age in Wistar rats. Although amphetamine may have several modes of action (stimulation of release, inhibition of uptake or inhibition of monoamine oxidase) which may influence the amount of D A release from neurons, no ageassociated change occurs in the maximum amount of [aH]DA release in response to several amphetamine concentrations. These findings are similar to those of Haycock et al. 5 who reported no decrease in KCl-stimulated, calcium-dependent release of [aH]DA in forebrain synaptosomal preparations from 12-mo-old mice compared to 2mo-old mice. In fact, the 12-mo-old animals showed increases in calcium-dependent release of [SH]DA. At least two events associated with striatal dopaminergic synaptic activity, i.e. uptake and release, appear to be unaffected in the senescent animal. In a previous study 1°, it was shown that striatal D A concentrations were not lower in the aged animal, supporting the results of previous studies 14. In addition, assays of D O P A decarboxylase (EC 4.1.1.26) and tyrosine hydroxylase (EC 1.14.3.a) activities in the striata of young and old animals showed only minimal differences between the two groups 1°. However previous experiments have shown declines in striatal D A receptor number in the aged animal 8,12,18,~5,16 and positive, statistically significant correlations between rotational behavioral strength and [SH]spiroperidol specific binding in the striatumg, 20. The above findings suggest that age-related deficts in dopaminergically mediated m o t o r behaviors may be more closely associated with losses of striatal D A receptors than with alterations in presynaptic events such as release or uptake. We wish to thank Clint Makino and D o n Pelto for their technical assistance and Dr. Richard McGee for his aid in setting up the perfusion system.
1 Bugiani, O., Salvarani, S., Perdelli, F., Mancardi, G. K. and Leonardi, A., Nerve cell loss with aging in the putamen, Europ. Neurol., 17 (1978) 286-291. 2 Bustos, G. and Roth, R. H., Release of monoamines from the striatum and hypothalamus: effect of 7-hydroxybutyrate, Brit. J. Pharmacol., 46 (1972) 101-115. 3 Finch, C. E., Catecholamine metabolism in the brains of aging male mice, Brain Research, 52 (1973) 261-276. 4 Finch, C. E., Jonec, V., Hody, G., Walker, J. P. ,Morton-Smith, W., Alper, A. and Dougher, G. J., Jr., Aging and the passage of L-tyrosine, L-DOPA, and inulin into mouse brain slices in vitro, J. GerontoL, 30 (1975) 33-40.
440 5 Haycock, J. W., White, W. F., McGaugh, J. L. and Cotman, C. W., Enhanced stimulus-secretion coupling from brains of aged mice, Exp. Neurol., 57 (1977) 873-882. 6 Jonec, V. and Finch, C. E., Aging and dopamine uptake by subcellular fractions of the C57BL/6J male mouse brain, Brain Research, 91 (1975) 197-215. 7 Jonec, V. and Finch, C. E., Aging and uptake of catecholamines by striatal and hypothalamic synaptosomes in mice, Fed. Proc., 34 (1975) 277. 8 Joseph, J. A., Berger, R. E. Engel, B. T. and Roth, G. S., Age-related changes in the neostriatum: a behavioral and biochemical analysis, J. Gerontol., 33 (1978) 643-649. 9 Joseph, J. A., Filburn, C. R. and Roth, G. S., Development ofdopamine receptor denervation supersensitivity in the neostriatum of the senescent rat, Life Sci., 29 (1981) 575-584. 10 Joseph, J. A., Filburn, C., Tzankoff, S., Thompson, J. M. and Engel, B. T., Age-related neostriatal alterations in the rat; failure of L-DOPA to alter behavior, Neurobiol. Aging, 1 (1980 119-125. 11 Lowry, O. H., Rosenbrough, N. J., Farr, A. L. and Randall, R. J., Protein measurement with the Folin phenol reagent, J. biol. Chem., 193 (1951) 265-275. 12 Makman, M. H., Ahn, H. S., Thai, L. J., Sharpless, N. S., Dvorkin, B., Horowitz, S. G. and Rosenfeld, M., Aging and monoamine receptors in the brain, Fed. Proc., 38 (1979) 1922-1926. 13 Makman, M. H., Ahn, H. S., Thal, L. J., Sharpless, N. S., Dvorkin, B., Horowitz, S. G. and Rosenfeld, M., Evidence for selective loss of brain dopamine and histamine-stimulated adenylate cyclase activities in rabbits with aging, Brain Research, 192 (1980) 177-t 83. 14 Ponzio, F., Brunello, N. and Algeri, S., Catecholamine synthesis in brains of ageing rats, J. Neurochem., 30 (1978) 1617-1620. 15 Severson, J. A. and Finch, C. E., Reduced dopaminergic binding during aging in the rodent striatum, Brain Research, 192 (1980) 147-162. 16 Thal, L. J., Horowitz, S. G., Dvorkin, B. and Makman, M. H., Evidence for loss of brain [3H]spiroperidol and [3H]ADTN binding sites in rabbit with aging, Brain Research, 192 (1980) 185-194. 17 Ungerstedt, U. and Arbuthnott, G. W., Quantitative recordings of rotational behavior in rats after 6-hydroxydopamine lesions of the nigrostriatal dopamine system, Brain Research, 24 (1970) 485-493. 18 Ungerstedt, U., Postsynaptic supersensitivity after 6-hydroxydopamine induced degeneration of the nigrostriatal dopamine system, Acta physiol, scand., 82, Suppl. 367 (1971) 69-73. 19 Ungerstedt, U., Butcher, L. L., Butcher, S. G., And6n, N. E. and Fuxe, K., Direct chemical stimulation of dopaminergic mechanisms in the nigrostriatum of the rat, Brain Research, 14 (1969) 461-471. 20 Waddington, J. L., Cross, A. J. and Longden, A., Functional distinction between DA-stimulated adenylate cyclase and [SH]spiperone binding sites in rat striatum, Europ. J. Pharmacol., 58 (1979) 341-342.
Brain Research, 224 (1981) 436-440 Elsevier/North-Holland Biomedical Press
[~H]Dopamine accumulation and release from striatal slices in young, mature and senescent rats
JEFFREY M. THOMPSON, JOHN R. WHITAKER and J. A. JOSEPH Laboratories of Neurosciences and Behavioral Sciences, Gerontology Research Center, National Institute on Aging, Baltimore City Hospitals, Baltimore, MD 21224 (U.S.A.)
(Accepted July 30th, 1981) Key words: aging- - dopamine - - neurotransmitter release -- neurotransmitter uptake - - striatum --
brain slice
Examinations of [aH]dopamine ([aH]DA) release following KC1 or amphetamine administration in striatal slices from young (7 month), mature (12 month) and senescent (24 month)Wistar rats showed no age-related changes. Further, the amount of [aH]DA accumulated in the striatal slices showed no changes with age. Thus, previously reported age-related deficits in motor behavior (i.e. rotational) are not produced by changes in striatal DA accumulation or release. Some of the most consistent findings which have emerged with respect to senescence and declining neuronal function have been found within the dopamine (DA) system, especially within the striatum. Several laboratories have reported a loss of striatal D A receptors8,12,1a,15,16, a decline in DA turnover 3,4 and a decrease in the number of striatal neurons I in the aging rodent. To explore the link between these striatal D A changes and behavioral-motor deficits in the aged animal, the rotational modeP 7-~9 has been used. We have previously shown that aged rats in comparison with young rats exhibit deficits in rotational behavior following amphetamine administration 8. Subsequent attempts 10 to reduce these deficits by administering L-DOPA to the old rats 1 h prior to amphetamine administration were not successful, even though rotation was potentiated in the young rat. These findings suggested possible presynaptic deficits in uptake, synthesis or release of DA, as well as deficits in DA receptors. In this report, attempts were made to determine age-related differences in accumulation and release of DA from slices of rat striata from unlesioned young (7 month), mature (12 month) and senescent (24 month) Wistar rats. We found no agerelated deficits in the pre-synaptic events of DA accumulation or release in rat striata. Male Wistar rats 7, 12 and 24 months (mo) of age were obtained from the colony at the Gerontology Research Center, National Institute on Aging. After decapitation, striata were rapidly removed and washed in Earle's salts solution. Each half of a striatum was sliced on a Sorvall Tissue Chopper (200 #m sections). One-half of a striatum was placed in 2 ml Earle's salts plus ascorbic acid (0.5 mg/ml). After
437
(2
f-.
E] 24 MO
c7MO
[] -
5
f
10~
o
~
0
[3
10-~
10-*
10-3
-
A
12 MO
10-z
AMPHETAMINE {M)
Fig. l. [aH]Dopamine release from rat striatal slices in response to amphetamine as a function of age. After 25/~Ci of [aH]DA (spec. act. 22.8 Ci/mmol, New England Nuclear) was added to flasks containing
striatal slices from 7-, 12- and 24-too-old rats, the tissue was incubated at 36.5 °C for 45 min on an orbital shaker (70 rpm). The slices were then washed with Earle's salts and transferred to 13 mm Millipore Swinnex filter holders containing a Whatman GF/C filter. The filter holders were placed in a 37 °C water bath, connected to an 8-channel Gilson Multipulse peristaltic pump and perfused with Earle's salts plus ascorbic acid (0.5 mg/ml) at a rate of 1 ml/min. After a 30 min wash, the perfusate was collected in glass vials every 2 rain using a plexiglass manual fraction collecting system. Using a multichannel 3-way valve, which allowed selection of media from different reservoirs without interrupting the flow of media, the perfusion medium was switched after the third fraction to medium containing KC1 (80 mM) or D-amphetamine (10-6-10 -3 M). The osmolarity of the solutions was adjusted by reducing the NaC1 when necessary. After 10 fractions were collected, the tissue was removed from the filter holders and dissolved in 1 N NaOH. Protein was determined by the Lowry et al. procedurelz. Radioactivity in each fraction and that remaining in the dissolved tissue was determined using Instagel scintillation cocktail and a Beckman LS9100 scintillation counter.
i n c u b a t i o n in [ a H ] D A (spec. act. 22.8 C i / m m o l , N e w E n g l a n d Nuclear), the a m o u n t o f [3H]DA a c c u m u l a t e d in the cells o r released b y KC1 o r a m p h e t a m i n e was determined. Striatal slices f r o m 7-, 12- a n d 2 4 - m o - o l d rats a c c u m u l a t e d [3H]DA a n d released it at a low b a s a l level. W h e n release o f [ a H ] D A f r o m striatal slices in response to 80 m M KC1 was c o m p a r e d a m o n g g r o u p s o f 7-, 12- a n d 24- m o - o l d rats, n o significant differences were f o u n d between the different age g r o u p s (t-test, t < 1, d f ---- 12, P > 0.05). The p e a k release o f [SH]DA f r o m striatal slices was 24.1 ~o (7 mo), 23.2 ~o (12 m o ) a n d 21.9 ~o (24 m o ) o f t o t a l r a d i o a c t i v i t y a n d the net release was 4 7 . 0 ~ (7 mo), 38.9 ~ (12 m o ) a n d 44.3 ~ (24 too) o f total radioactivity. P e a k release refers to the value o f m a x i m u m release. N e t release is the total release in response to the stimulating agent (80 m M KC1 o r a m p h e t a m i n e ) , a n d is calculated b y s u m m i n g the total release due to d r u g m i n u s the b a s a l release. [SH]DA accounts for a p p r o x i m a t e l y 40 ~o o f the 3H efflux after KC1 s t i m u l a t i o n o f rat striatal slices labeled with [ZH]DA (ref. 2). S t i m u l a t i o n o f release b y a m p h e t a m i n e o f [ a H ] D A f r o m striatal slices as a function o f age was studied. In o r d e r to a c c o u n t for possible changes in p o t e n c y o f the d r u g in different ages, d o s e - r e s p o n s e relationships were d e t e r m i n e d at each age (Fig.
438
"~
50 ~ 40
~12 MO 0 24 Me
--
30
7 MO
lO i
&
10
20
i
30
i
~
40
MINUTES Fig. 2. Uptake of [3H]DA in striatal slices from 7-, 12- and 24-mo-old rats. After 5 #Ci of [SH]DA was added to 2 ml of medium, each flask containing one-half of a striatum was placed in a Dubnoffmetabolic shaking water bath (70 rpm) at 36.5 °C and oxygenated. At 2, 5, 15 and 40 rain, triplicate flasks were removed and the slices were rapidly collected on W h a t m a n G F / C filters in a vacuum filtration apparatus. As a blank, flasks were kept on 0 °C and removed at each collection time. The slices were washed twice with 5 ml of Earle's salts. The tissue was dissolved in 1 N N a O H overnight and protein determined by the Lowry et al. procedurelL The a m o u n t of [aH]DA taken into the slices was determined by scintillation spectroscopy.
1) and the results were analyzed by a 3(age) by 4(dose) analysis of variance. No significant differences were seen among ages in the peak release of D A (F (2,21) < 1, P > 0.05). In addition, no changes in the potency of amphetamine occurred during aging, as indicated by the lack of an age × dose interaction (F < 1, P > 0.05). An EDs0 of 2.5 × 10 -3 M was found for all ages. The dose effect of amphetamine was significant (F (7,21) = 11.96, P < 0.001) for all ages. The time course of [3H]DA accumulation was determined in striatal slices from each age (Fig. 2). There were no significant differences as a function of age and time. A subsequent analysis of variance (3 (age) by 4 (time)) carried out on these data showed that the statistical interaction between these variables was not significant (F(6,45) 1.66, P > 0.05). This analysis did show, however, that the overall effects of age were statistically significant, but not in a linear fashion. Rather, the striatal slices from the 7 mo and 24 mo groups showed no differences overall in [aH]DA accumulation (Duncan's test, P < 0.05). Striatal slices from 12 mo animals showed greater DA accumulation than those from the 7 mo animals (Duncan's test, P < 0.05), but no greater accumulation than slices from 24 mo animals. These differences appeared to be due, at least in part, to a decline in [3H]DA accumulation exhibited by the slices from the 7 mo group after 40 min of incubation. There was no consistent evidence that age-related motor-behavioral deficits as measured by the rotational model are produced by changes in striatal DA accumulation or release. Although accumulation at 40 min in 7-mo-old rats was less than in 12mo-old rats, the 7-mo-old values were not significantly different from 24-mo-old rats.
439 Therefore, there is not a clear age-related change in D A accumulation in rats under conditions used for our release experiments. Finch and co-workers 4,~,7 reported decreased uptakes of [aH]tyrosine and [aH]DA only at low concentrations in aged mice (5.5 × 10 -12 M and 1 x 10 -s M, respectively). At higher concentrations similar to those used in this study (1 x 10 -7 M), no age-related differences were seen. Although our study did not determine Vmax or Kra, no age-related differences in accumulation were seen at concentrations similar to those used for our release studies and concentrations greater than the Km for D A uptake determined in mouse striatum6, 7. Stimulated release of [aH]Da by KC1 or amphetamine from striatal slices does not change with age in Wistar rats. Although amphetamine may have several modes of action (stimulation of release, inhibition of uptake or inhibition of monoamine oxidase) which may influence the amount of D A release from neurons, no ageassociated change occurs in the maximum amount of [aH]DA release in response to several amphetamine concentrations. These findings are similar to those of Haycock et al. 5 who reported no decrease in KCl-stimulated, calcium-dependent release of [aH]DA in forebrain synaptosomal preparations from 12-mo-old mice compared to 2mo-old mice. In fact, the 12-mo-old animals showed increases in calcium-dependent release of [SH]DA. At least two events associated with striatal dopaminergic synaptic activity, i.e. uptake and release, appear to be unaffected in the senescent animal. In a previous study 1°, it was shown that striatal D A concentrations were not lower in the aged animal, supporting the results of previous studies 14. In addition, assays of D O P A decarboxylase (EC 4.1.1.26) and tyrosine hydroxylase (EC 1.14.3.a) activities in the striata of young and old animals showed only minimal differences between the two groups 1°. However previous experiments have shown declines in striatal D A receptor number in the aged animal 8,12,18,~5,16 and positive, statistically significant correlations between rotational behavioral strength and [SH]spiroperidol specific binding in the striatumg, 20. The above findings suggest that age-related deficts in dopaminergically mediated m o t o r behaviors may be more closely associated with losses of striatal D A receptors than with alterations in presynaptic events such as release or uptake. We wish to thank Clint Makino and D o n Pelto for their technical assistance and Dr. Richard McGee for his aid in setting up the perfusion system.
1 Bugiani, O., Salvarani, S., Perdelli, F., Mancardi, G. K. and Leonardi, A., Nerve cell loss with aging in the putamen, Europ. Neurol., 17 (1978) 286-291. 2 Bustos, G. and Roth, R. H., Release of monoamines from the striatum and hypothalamus: effect of 7-hydroxybutyrate, Brit. J. Pharmacol., 46 (1972) 101-115. 3 Finch, C. E., Catecholamine metabolism in the brains of aging male mice, Brain Research, 52 (1973) 261-276. 4 Finch, C. E., Jonec, V., Hody, G., Walker, J. P. ,Morton-Smith, W., Alper, A. and Dougher, G. J., Jr., Aging and the passage of L-tyrosine, L-DOPA, and inulin into mouse brain slices in vitro, J. GerontoL, 30 (1975) 33-40.
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