Shuang Y. Ma

Age-Related Declines in Nigral Neuronal Function Correlate With Motor Impairments in Rhesus Monkeys

Although the role of dopamine dysfunction is well established in Parkinsons disease, the effect of nigrostriatal degeneration on motor performance during normal aging is less well understood. In this study, aged rhesus monkeys (25–27 years old) displayed significant impairments relative to young (3–5 years old) cohorts in motor function as assessed on a fine motor task and home cage activity. Additionally, the clinical motor function of aged monkeys was impaired relative to young monkeys as assessed on a clinical rating scale. Unbiased stereologic measurements of the substantia nigra revealed a significant age‐related loss of tyrosine hydroxylase‐immunoreactive (TH‐ir; 50.3%) and dopamine transporter‐immunoreactive (DAT‐ir; 33.2%) nigral neurons. The monkeys performance on the fine motor task and on the clinical rating scale was correlated with TH‐ir neuronal counts. The number of DAT‐ir nigral neurons was correlated with activity and clinical rating scale scores. Our results suggest that age‐related motor impairments in nonhuman primates are associated with spontaneous decreases in TH‐ir and DAT‐ir nigral cells. The correlation of motor deficits with the loss of TH‐ir and DAT‐ir nigral neurons suggests that aged nonhuman primates may provide a useful model for mimicking changes seen in human aging and early Parkinsons disease. J. Comp. Neurol. 401:253–265, 1998.

Loss of nucleus basalis neurons containing trkA immunoreactivity in individuals with mild cognitive impairment and early Alzheimer's disease

Recent studies indicate that there is a marked reduction in trkA–containing nucleus basalis neurons in end–stage Alzheimers disease (AD). We used unbiased stereological counting procedures to determine whether these changes extend to individuals with mild cognitive impairment (MCI) without dementia from a cohort of people enrolled in the Religious Orders Study. Thirty people (average age 84.7 years) came to autopsy. All individuals were cognitively tested within 12 months of death (average MMSE 24.2). Clinically, 9 had no cognitive impairment (NCI), 12 were categorized with MCI, and 9 had probable AD The average number of trkA–immunoreactive neurons in persons with NCI was 196, 632 ± 12,093 (n = 9), for those with MCI it was 106,110 ± 14,565, and for those with AD it was 86,978 ± 12,141. Multiple comparisons showed that both those with MCI and those with AD had significant loss in the number of trkA–containing neurons compared to those with NCI (46% decrease for MCI, 56% for AD). An analysis of variance revealed that the total number of neurons containing trkA immunoreactivity was related to diagnostic classification (P < 0.001), with a significant reduction in AD and MCI compared to NCI but without a significant difference between MCI and AD. Cell density was similarly related to diagnostic classification (P < 0.001). There was a significant correlation with the Boston Naming Test and with a global score measure of cognitive function. The number of trkA–immunoreactive neurons was not correlated with MMSE, age at death, education, apolipoprotein E allele status, gender, or Braak score. These data indicate that alterations in the number of nucleus basalis neurons containing trkA immunoreactivity occurs early and are not accelerated from the transition from MCI to mild AD. J. Comp. Neurol. 427:19–30, 2000.

Loss of basal forebrain P75NTR immunoreactivity in subjects with mild cognitive impairment and Alzheimer's disease

The long‐held belief that degeneration of the cholinergic basal forebrain was central to Alzheimers disease (AD) pathogenesis and occurred early in the disease process has been questioned recently. In this regard, changes in some cholinergic basal forebrain (CBF) markers (e.g. the high affinity trkA receptor) but not others (e.g., cortical choline acetyltransferase [ChAT] activity, the number of ChAT and vesicular acetylcholine transporter‐immunoreactive neurons) suggest specific phenotypic changes, but not frank neuronal degeneration, early in the disease process. The present study examined the expression of the low affinity p75 neurotrophin receptor (p75NTR), an excellent marker of CBF neurons, in postmortem tissue derived from clinically well‐characterized individuals who have been classified as having no cognitive impairment (NCI), mild cognitive impairment (MCI), and mild AD. Relative to NCI individuals, a significant and similar reduction in the number of nucleus basalis p75NTR‐immunoreactive neurons was seen in individuals with MCI (38%) and mild AD (43%). The number of p75NTR‐immunoreactive nucleus basalis neurons was significantly correlated with performance on the Mini‐Mental State Exam, a Global Cognitive Test score, as well as some individual tests of working memory and attention. These data, together with previous reports, support the concept that phenotypic changes, but not frank neuronal degeneration, occur early in cognitive decline. Although there was no difference in p75NTR CBF cell reduction between MCI and AD, it remains to be determined whether these findings lend support to the hypothesis that MCI is a prodromal stage of AD. J. Comp. Neurol. 443:136–153, 2002.

Lentiviral Gene Transfer to the Nonhuman Primate Brain

Lentiviral vectors infect quiescent cells and allow for the delivery of genes to discrete brain regions. The present study assessed whether stable lentiviral gene transduction can be achieved in the monkey nigrostriatal system. Three young adult Rhesus monkeys received injections of a lentiviral vector encoding for the marker gene beta galatosidase (beta Gal). On one side of the brain, each monkey received multiple lentivirus injections into the caudate and putamen. On the opposite side, each animal received a single injection aimed at the substantia nigra. The first two monkeys were sacrificed 1 month postinjection, while the third monkey was sacrificed 3 months postinjection. Robust incorporation of the beta Gal gene was seen in the striatum of all three monkeys. Stereological counts revealed that 930,218; 1,192,359; and 1,501,217 cells in the striatum were beta Gal positive in monkeys 1 (n = 2) and 3 (n = 1) months later, respectively. Only the third monkey had an injection placed directly into the substantia nigra and 187,308 beta Gal-positive cells were identified in this animal. The injections induced only minor perivascular cuffing and there was no apparent inflammatory response resulting from the lentivirus injections. Double label experiments revealed that between 80 and 87% of the beta Gal-positive cells were neurons. These data indicate that robust transduction of striatal and nigral cells can occur in the nonhuman primate brain for up to 3 months. Studies are now ongoing testing the ability of lentivirus encoding for dopaminergic trophic factors to augment the nigrostriatal system in nonhuman primate models of Parkinsons disease.

Galanin transgenic mice display cognitive and neurochemical deficits characteristic of Alzheimer's disease

Galanin is a neuropeptide with multiple inhibitory actions on neurotransmission and memory. In Alzheimers disease (AD), increased galanin-containing fibers hyperinnervate cholinergic neurons within the basal forebrain in association with a decline in cognition. We generated transgenic mice (GAL-tg) that overexpress galanin under the control of the dopamine β-hydroxylase promoter to study the neurochemical and behavioral sequelae of a mouse model of galanin overexpression in AD. Overexpression of galanin was associated with a reduction in the number of identifiable neurons producing acetylcholine in the horizontal limb of the diagonal band. Behavioral phenotyping indicated that GAL-tgs displayed normal general health and sensory and motor abilities; however, GAL-tg mice showed selective performance deficits on the Morris spatial navigational task and the social transmission of food preference olfactory memory test. These results suggest that elevated expression of galanin contributes to the neurochemical and cognitive impairments characteristic of AD.

Dopamine transporter-immunoreactive neurons decrease with age in the human substantia nigra.

Unbiased disector stereologic cell counting was applied to sections from the human substantia nigra that were immunostained by using a monoclonal antibody against the dopamine transporter (DAT). This antibody was found to penetrate the full thickness of the stained section. Quantification of the number of DAT immunostained neurons was performed in human cases stratified into three age groups, young (ages 0–49 years), middle aged (ages 50–69 years), and aged (ages 70–85 years). The number of DAT‐immunoreactive nigral neurons was normalized for each case by constructing a ratio of the number of DAT‐containing neurons to total number of neuromelanin‐containing cells in each subjects sample. Three types of DAT nigral neurons were seen: type 1, intensely stained; type 2, lightly stained; and type 3, DAT‐immunonegative neuromelanin‐containing perikarya. By 50 years of age, the number of type 1 neurons decreased significantly (P < 0.0001), whereas the number of type 2 neurons increased with age (P < 0.0001). Type 3 neurons also increased with age (P < 0.01), although less robustly than type 2 neurons. Type 1 neurons decreased by 11.2% per decade, and the total number of nigral neurons (types 1–3) decreased by 6.7% per decade. Relative to the young group, there were 75% and 88% reductions in type 1 neurons in the middle‐aged and aged groups, respectively. This contrasts with the 35% and 41% reductions in total number of neuromelanin‐containing neurons seen in middle‐aged and aged groups, respectively. The young group had significantly more type 1 neurons and fewer type 2 neurons compared with middle‐aged and aged participants. Post‐hoc analyses indicated that the young group had significantly fewer type 3 neurons compared with middle‐aged and aged participants. These findings demonstrate an age‐related reduction in the number of substantia nigra DAT‐immunoreactive neurons. Therefore, insight into the mechanisms regulating the rate of DAT synthesis may aid in our understanding of the decline of DATs with aging and its functional significance. J. Comp. Neurol. 409:25–37, 1999.

Neuropathology of mice carrying mutant APP(swe) and/or PS1(M146L) transgenes : Alterations in the p75(NTR) cholinergic basal forebrain septohippocampal pathway

Cholinergic basal forebrain (CBF) projection systems are defective in late Alzheimers disease (AD). We examined the brains of 12-month-old singly and doubly transgenic mice overexpressing mutant amyloid precursor protein (APP(swe)) and/or presenilin-1 (PS1(M146L)) to investigate the effects of these AD-related genes on plaque and tangle pathology, astrocytic expression, and the CBF projection system. Two types of beta-amyloid (Abeta)-immunoreactive (ir) plaques were observed: type 1 were darkly stained oval and elongated deposits of Abeta, and type 2 were diffuse plaques containing amyloid fibrils. APP(swe) and PS1(M146L) mouse brains contained some type 1 plaques, while the doubly transgenic (APP(swe)/PS1(M146L)) mice displayed a greater abundance of types 1 and 2 plaques. Sections immunostained for the p75 NGF receptor (p75(NTR)) revealed circular patches scattered throughout the cortex and hippocampus of the APP(swe)/PS1(M146L) mice that contained Abeta, were innervated by p75(NTR)-ir neurites, but displayed virtually no immunopositive neurons. Tau pathology was not seen in any transgenic genotype, although a massive glial response occurred in the APP(swe)/PS1(M146L) mice associated with amyloid plaques. Stereology revealed a significant increase in p75(NTR)-ir medial septal neurons in the APP(swe) and PS1(M146L) singly transgenic mice compared to the APP(swe)/PS1(M146L) mice. No differences in size or optical density of p75(NTR)-ir neurons were observed in these three mutants. p75(NTR)-ir fibers in hippocampus and cortex were more pronounced in the APP(swe) and PS1(M146L) mice, while the APP(swe)/PS1(M146L) mice showed the least p75(NTR)-ir fiber staining. These findings suggest a neurotrophic role for mutant APP and PS1 upon cholinergic hippocampal projection neurons at 12 months of age.

Pramipexole attenuates the dopaminergic cell loss induced by intraventricular 6-hydroxydopamine.

Summary. The D3 preferring dopamine agonist pramipexole has been shown to attenuate the cell loss induced by levodopa in vitro. Pramipexole was herein evaluated in the 6-hydroxydopamine lesion model to determine its in vivo effect. Rats were treated with pramipexole or saline before and after an intracerebroventricular 6-hydroxydopamine injection. In the preliminary study, 6-hydroxydopamine produced a 68% reduction in striatal dopamine and a 62% loss in tyrosine hydroxylase immunoreactive (THir) cell counts in the substantia nigra. Pramipexole treated animals exhibited a 29% and a 27% reduction in striatal dopamine and THir cell counts, respectively. THir cell counts and striatal dopamine were significantly correlated. In the stereological study, 6-hydroxydopamine reduced THir cell counts by 47% in saline treated animals and 26% in pramipexole treated animals. These data demonstrate that pramipexole attenuates the biochemical and THir cell changes normally produced by 6-hydroxydopamine consistent with its neuroprotective actions in vitro.

Reduction in TrkA-immunoreactive neurons is not associated with an overexpression of galaninergic fibers within the nucleus basalis in Down's syndrome

Downs syndrome (DS) individuals develop neuropathological features similar to Alzheimers disease (AD), including degeneration of cholinergic basal forebrain (CBF) neurons. In AD a reduction in CBF/trkA‐containing neurons has been suggested to trigger a hyperexpression of galaninergic fibers within the nucleus basalis subfield of the basal forebrain. The present study examined the interrelationship between reductions in CBF/trkA‐containing neurons and the overexpression of galaninergic fibers within the nucleus basalis in DS. Within the nucleus basalis stereologic evaluation revealed a 46% reduction in the number of trkA‐immunopositive neurons, whereas optical density measurements displayed a nonsignificant 18% reduction in neuronal trkA immunoreactivity in DS as compared with age‐matched controls. Western blot analysis also showed a significant reduction in cortical trkA protein levels in DS. A semiquantitative examination of galaninergic fibers in the nucleus basalis revealed only a modest hypertrophy of galaninergic fibers within the nucleus basalis in DS. The present findings indicate a significant reduction in trkA within the nucleus basalis and cortex with only a moderate hypertrophy of galaninergic fibers in DS. These observations suggest that DS may not be an exact genetic model for investigation of changes in the AD basal forebrain.