Regionally selective manifestations of neostriatal aging

Immunohistochemistry of neuronal nitric oxide synthase and protein nitration in the striatum of the aged rat

To ascertain the possible implications of the nitric oxide (NO*) producing system in striatal senescence, and by using immunohistochemistry and image-processing approaches, we describe the presence of the enzyme nitric oxide synthase (NOS), the NADPH-diaphorase (NADPH-d) histochemical marker, and nitrotyrosine-derived complexes (N-Tyr) in the striatum of adult and aged rats. The results showed neuronal NOS immunoreactive (nNOS-IR) aspiny medium-sized neurons and nervous fibres in both age groups, with no variation in the percentage of immunoreactive area but a significant decrease in the intensity and in the number of somata with age, which were not related to the observed increase with age of the striatal bundles of the white matter. In addition, NADPH-d activity was detected in neurons with morphology similar to that of the nNOS-IR cells; a decrease in the percentage of area per field and in the number of cells, but an increase in the intensity of staining for the NADPH-d histochemical marker, were detected with age. The number of neuronal NADPH-d somata was higher than for the nNOS-IR ones in both age groups. Moreover, N-Tyr-IR complexes were observed in cells (neurons and glia) and fibres, with a significant increase in the percentage of the area of immunoreaction, related to the increase of white matter, but a decrease in intensity for the aged group. On the other hand, we did not detect the inducible isoform (iNOS) either in adult or in aged rats. Taken together, these results support the contention that NADPH-d staining is not such an unambiguous marker for nNOS, and that increased protein nitration may participate in striatal aging.

Delay in manifestations of aging by grafting NGF cultured chromaffin cells in adulthood

Dopamine agonists or grafts compensate impaired motor functions in aged rats. However, there is no evidence showing whether grafting in adulthood retard aging manifestations. Motor performance of 13-month-old rats was tested on 2 meter-long wooden beams which had a 15 degree inclination and whose thickness varied from 3, 6, 12, 18, to 24 mm. Rats at 14 months were randomly assigned to 3 groups: sham graft (Group 1); intrastriatal graft of chromaffin cells cultured with NGF (Group 2); intrastriatal graft of chromaffin cells (Group 3). Motor performance was tested at monthly intervals up until rats were 26 months old. Two more groups were included: 26-month-old naive rats (Group 4); and 3- to 5-month-old naive rats (Group 5) both evaluated only once. At 26 months, the basal activity of ventral mesencephalic dopaminergic neurons was recorded. Results showed in Group 2 delay of motor detriments seen in aged rats, maintenance of basal firing rates of nigral cells compared to those of younger rats, and greater survival of substantia nigra cells. It is suggested that NGF cultured chromaffin cells produce a delay of motor detriments in aged rats, as a result of inducing survival and firing rates of nigral cells comparable to those seen in young rats.

Comparison of brain dopamine depletion induced by low-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in young and aged rats

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on dopamine levels in the striatum (ST), substantia nigra (SN), olfactory tubercle (OT), ventral tegmental area (VTA) and nucleus accumbens (NA) were studied in young (1 month) and old (21 months) male Long-Evans rats. Following repeated treatment with MPTP at low dose (3 mg/kg i.p. daily for 8 days) both young and old rats showed a marked depletion of dopamine (DA) concentrations in the ST compared to those of age-matched saline-treated controls. However, a significant reduction in DA levels was observed in the OT and NA of old but not young rats treated with MPTP. In contrast, no changes in 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels in these three regions were seen in either young or old MPTP-treated rats. However, the ratio of DOPAC/DA and HVA/DA in the ST and NA were significantly higher in old MPTP-treated rats than those in old controls. The concentrations of DA, DOPAC and HVA remained unchanged in the SN and VTA of both young and old rats after MPTP treatment. These results indicate that multiple treatment of low-dose MPTP selectively causes more widespread damage to dopaminergic neurons in old rats than in young ones, and further support the view that effects of MPTP on the dopaminergic system in rats may depend on age.

Subcortical dopamine and serotonin turnover during acute and subchronic administration of typical and atypical neuroleptics

The effects of acute (1 day) and subchronic (28 days) treatment with three atypical antipsychotic drugs [clozapine, (+/-)-sulpiride and (-)-3-PPP] on dopamine and serotonin turnover in both the nucleus accumbens (NA) and corpus striatum (CS) of rodents was compared to haloperidol and saline treatment. The equivalent doses of all drugs were determined based upon their ability to compete in vivo for 3H-spiperone binding in the NA and CS. All three atypical drugs, compared to haloperidol, produced preferential elevations of dopamine turnover in the NA. Further, the development of tolerance of this effect was more apparent for the three atypical drugs than for haloperidol. Surprisingly, all three atypical drugs, but not haloperidol, produced changes in serotonin turnover, despite the fact that (+/-)-sulpiride and (-)-3-PPP have no known direct effects on brain serotonin systems. All three atypical drugs produced acute increases in serotonin turnover in both the NA and CS, followed by later diseases.

Preservation of the density of the dopamine uptake complex in aging Fischer 344 rat brain

This study was performed to determine if there are selective regional or global changes in the density or pharmacology of the dopamine uptake complex (DAUC) in aged rodent. Fifteen regions of the Fischer 344 rat (aged 4, 12, and 24 months) central nervous system were analyzed for the density of the DAUC employing [3H]GBR 12935 and in vitro quantitative autoradiography. Additionally, cocaine competitions were performed in the striatum of all of the animals. A 26-fold variation in the DAUC density was found in the regions sampled. However, no significant age-related changes were identified. Intrastriatal analysis of the DAUC density revealed binding heterogeneities; decreasing lateral to medial and decreasing dorsal to ventral gradients. No significant effect of aging on striatal gradients was observed. The proportion of high and low affinity sites for cocaine was unchanged in the three age groups. Taken together, these findings suggest a stability of this dopamine presynaptic marker in aging rat central nervous system.

The relationships between aging, monoamine oxidase, striatal dopamine and the effects of MPTP in C57BL/6 mice: a critical reassessment

Although the effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice have been reported to increase with age, they have not been characterized in the full spectrum of ages. Thus, in spite of a considerable body of scientific literature on the subject, previous reports leave unanswered the question of whether or not the increased susceptibility of fully mature mice is part of the aging process or simply a consequence of maturation. In the present study, the age-related effects of MPTP on striatal dopamine were studied in groups of C57BL/6 mice from young maturity to old age. The major increase in the effects of MPTP occurred between 2 and 10 months of age (equivalent to adolescence and young adulthood in humans). A slight additional increase was observed between 10 and 16 months (young adulthood and middle age) and the dopamine-depleting effects of MPTP significantly declined in truly aged animals (24 months). Of note also is the fact that normal concentrations of striatal dopamine did not decline in the later ages. Additional studies indicated that while neuronal sensitivity to the effects of 1-methyl-4-phenylpyridinium (MPP+; the putative toxic metabolite of MPTP) appears to remain constant, age-related changes in the activity of striatal monoamine oxidase type B (MAO B) paralleled the dopamine-depleting effects of MPTP in the 4 age groups. Indeed, MAO B activity increased between 2 and 16 months and declined slightly, but significantly, between 16 and 24 months. This pattern of age-related changes in MAO B, striatal dopamine and the sensitivity of the nigrostriatal system to toxic insult may provide insights into factors which have been implicated in age-related neurodegeneration and idiopathic Parkinson's disease.

The effect of long-term treatment with deprenyl on basal and L-dopa evoked dopamine release in vitro from the corpus striatum of aged rats

In the present experiment, male rats (15-17 months) were injected with deprenyl (0.25 mg/kg) three times per week for six months. At 21-23 months of age the male rats were sacrificed, the corpus striatum removed and superfused in vitro. Basal and evoked dopamine and DOPAC levels, as obtained with either two infusions of L-dopa (L-dopa/L-dopa) or L-dopa followed by amphetamine (L-dopa/AMPH), were measured from effluent superfusion samples and compared with values obtained from similarly aged animals treated identically with saline and from that obtained with young (2-4 months) animals. Treatment with deprenyl resulted in significantly greater basal dopamine and significantly lower basal DOPAC output compared with basal release levels from saline-treated aged rats and young animals. Responses to L-dopa/L-dopa or L-dopa/AMPH evoked dopamine and DOPAC release did not differ between deprenyl and saline-treated aged rats, however, both groups showed a significantly reduced response profile to these stimulations (L-dopa/L-dopa or L-dopa/AMPH) compared to that of young rats. These results indicate that the selective Type-B monoamine oxidase inhibitor, deprenyl, exerts a basic change in dopamine metabolism within the corpus striatum of aged rats resulting in an increase of endogenous dopamine and a decrease in endogenous DOPAC output.

Sensitization versus tolerance to the dopamine turnover-elevating effects of haloperidol: the effect of regular/intermittent dosing

Recent clinical research suggests that particular patterns of changes in presynaptic dopamine (DA) turnover accompany the therapeutic response to neuroleptics. We sought to determine whether daily versus weekly dosing of haloperidol for 3 weeks produced distinct effects on DA, dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) concentrations in multiple brain areas. Daily dosing favored the development of tolerance to the DA-turnover elevating effects of haloperidol in the striatum and nucleus accumbens. Weekly dosing favored the development of sensitization in the striatum, posterior olfactory tubercle, and ventral tegmental area. These results suggest that dosing schedules may determine, at least in part, the effects of chronic neuroleptic administration on presynaptic DA function.

Effect of aging on concentrations of D2-receptor-containing neurons in the rat striatum

Striatal D2 dopamine receptor concentrations were shown to decrease 30-35% during the lifespan of Wistar rats as assessed both radiochemically and autoradiographically. Binding densities and degree of age-change varied within the striatum; the latter ranging from 17 to 44% in 4 different regions. Overall neuronal loss during aging was 19%, and also varied considerably within the different striatal regions. Thus, it appears that neuronal loss may account for up to roughly half of the striatal D2 receptor loss during aging.