Rhesus Monkey Brain Research Articles

Localization of nAChR subunit mRNAs in the brain of Macaca mulatta.

We present here a systematic mapping of nAChR subunit mRNAs in Macaca mulatta brain. A fragment, from the transmembrane segments MIII to MIV of Macaca neuronal nAChR subunits was cloned, and shown to exhibit high identity (around 95%) to the corresponding human subunits. Then, specific oligodeoxynucleotides were synthesized for in situ hybridization experiments. Both alpha4 and beta2 mRNA signals were widely distributed in the brain, being stronger in the thalamus and in the dopaminergic cells of the mesencephalon. Most brain nuclei displayed both alpha4 and beta2 signals with the exception of some basal ganglia regions and the reticular thalamic nucleus which were devoid of alpha4 signal. alpha6 and beta3 mRNA signals were selectively concentrated in the substantia nigra and the medial habenula. The strongest signals for alpha3 or beta4 mRNAs were found in the epithalamus (medial habenula and pineal gland), whereas there were no specific alpha3 or beta4 signals in mesencephalic dopaminergic nuclei. alpha5 and alpha7 mRNA signals were found in several brain areas, including cerebral cortex, thalamus and substantia nigra, although at a lower level than alpha4 and beta2. The distribution of alpha3, alpha4, alpha5, alpha6, alpha7, beta2, beta3 and beta4 subunit mRNAs in the monkey is substantially similar to that observed in rodent brain. Surprisingly, alpha2 mRNA signal was largely distributed in the Macaca brain, at levels comparable with those of alpha4 and beta2. This observation represents the main difference between rodent and Macaca subunit mRNA distribution and suggests that, besides alpha4beta2*, alpha2beta2* nAChRs constitute a main nAChR isoform in primate brain.

Comparative lateralisation patterns in the language area of human, chimpanzee, and rhesus monkey brains

Lateralised architectural differences in radial cell column structure were detected in the planum temporale of humans but were not found in homologous regions of ape or monkey brains. This study used a new computer imaging method to quantify the architecture of thousands of cortical minicolumns. A study of Lamina III in the left hemisphere of human brains revealed a wider separation between cell columns and more non-neuronal (empty) space within cell columns compared to the right hemisphere. This asymmetry was absent in the chimpanzee brains and weakly reversed in the rhesus monkey brains. The results imply an evolution towards more clearly defined columnar structures in the left hemisphere of human brains compared to those of monkeys.

Comparative lateralisation patterns in the language area of human, chimpanzee, and rhesus monkey brains

Comparative lateralisation patterns in the language area of human, chimpanzee, and rhesus monkey brains

Distribution of Corticosteroid Receptors in the Rhesus Brain: Relative Absence of Glucocorticoid Receptors in the Hippocampal Formation

Chronic stress has been associated with degenerative changes in the rodent and primate hippocampus, presumably mediated in part via neuronal glucocorticoid receptors (GRs). In the rat brain, GRs are widely distributed and are particularly dense in the hippocampus. The distribution of GRs in the primate brain, however, has not been fully characterized. In this study, we used in situ hybridization histochemistry and immunohistochemistry to map the distribution of GR mRNA and GR protein, respectively, in adult rhesus monkeys (Macaca mulatta). In contrast to its well established distribution in the rat brain, GR mRNA was only weakly detected in the dentate gyrus (DG) and Cornu Ammonis (CA) of the macaque hippocampus, whereas it was abundant in the pituitary (PIT), cerebellum (CBL), hypothalamic paraventricular nucleus (PVN), and, to a lesser extent, the neocortex. Immunohistochemical staining indicated a very low density of GR-like immunoreactive cells within the macaque hippocampal formation in contrast to the high density observed within the PVN, prefrontal and entorhinal cortices, and cerebellar cortex. Relative to the low level of GR, mineralocorticoid receptor (MR) mRNA and protein expression were abundant within the DG and CA of the rhesus monkey hippocampal formation. These results indicate that, in the primate, neocortical and hypothalamic areas may be more important targets for GR-mediated effects of glucocorticoids than the hippocampus. Alternatively, it is also possible that glucocorticoid effects are mediated through the MRs present in the hippocampal formation.

Pathologic effects of amyloidβ deposits in the aged rhesus brain

Pathologic effects of amyloidβ deposits in the aged rhesus brain

Noninvasive assessment of aromatic L-amino acid decarboxylase activity in aging rhesus monkey brain in vivo.

The effect of aging on aromatic L-amino acid decarboxylase (AAAD) activity in rhesus monkey striatum was assessed in vivo using PET imaging. Two analogs of L-DOPA, 6-fluoro-m-tyrosine (FMT) and 6-fluoro-L-DOPA (FDOPA), were used to image rhesus monkeys of various ages. Results show that when the animals were grouped between young (3-11 years) and aged (25-37 years), FDOPA uptake in the older animals showed a 21% decline (P < 0.0005), while FMT uptake in young and older animals were not different. On the other hand, when individual uptake values were plotted vs. age, linear regression analysis showed FDOPA uptake similarly declined with age (r = -0.84, P < 0.001) while FMT uptake increased with age (r = 0.66, P < 0.05). Since FMT pharmacokinetics has been shown to be unaffected by metabolic steps occurring after the AAAD step, while FDOPA traces all the steps involved in L-DOPA metabolism, FMT is a suitable tracer to assess AAAD activity while FDOPA traces dopamine turnover. Based on these tracer characteristics, this study found that AAAD activity is maintained or increased in the aging rhesus monkey striatum while the FDOPA uptake decreases with age consistent with age-related declines in neuronal mechanisms whose overall effect is increased striatal dopamine turnover and clearance. Furthermore, comparison of results of this study with previous studies support the notion that the effect of aging in the dopamine system is different from that of MPTP-induced parkinsonism.

Gender differences in brain volume and size of corpus callosum and amygdala of rhesus monkey measured from MRI images

While it has been established that the weight of the female rhesus monkey brain is less than that of the male, the sexual dimorphism of specific brain structures has not been well-documented. To further understand potential sex differences, we measured the whole brain volume and the size of the corpus callosum (mid-sagittal) and amygdala (largest coronal section) in MRI images from juvenile to adult male and female rhesus monkeys between 8 months and 7.2 years of age. The mean volume of the male brain was 89.2±1.9 (S.E.M.) compared to the female brain volume of 70.8±0.72 cm 3. The average area of the corpus callosum increased from 8 months to 4.5 years; 0.56 to 0.93 cm 2 in males and 0.45 to 0.66 cm 2 in females. However, the average area of splenium is significantly greater in females (0.280 cm 2), than males (0.184 cm 2). The average area of the amygdala did not change with age; it was 1.07±0.037 (S.E.M.) in males and 1.08±0.022 cm 2 in females. This data suggests that the whole brain volume and the size of the entire corpus callosum of young adult female rhesus monkeys are approximately 20% smaller than those of young adult males. Interestingly, the area of the splenial portion of the corpus callosum is larger in female monkeys. The size of the amygdala showed no sex difference.

Tau Pathology Generated by Overexpression of Tau

Neurofibrillary changes of abnormally hyperphosphorylated tau are the key lesion in Alzheimer’s disease (AD) and a number of other tauopathies. Recent developments in the field of autosomal dominantly inherited dementias, in particular the frontotemporal dementias and Parkinsonism linked to chromosome 17 (FTDP-17) group, have shown that abnormalities in the tau gene result in neurofibrillary degeneration and cell death. Clinically this disorder presents with behavioral abnormalities, which are followed by dementia and, depending on the affected areas, by motor dysfunction. The location of the lesions does not seem to depend so much on the type of mutation as on the individual’s genetic background and may vary even in the same family with the identical mutation. For instance, in one family with a P 301 S mutation in exon 10 of tau, the father presented with frontotemporal dementia, whereas the son had corticobasal degeneration. 1 FTDP-17 is associated with both exonic and intronic mutations of the tau gene. The microtubule-associated protein (MAP) tau is a family of six proteins derived by alternative mRNA splicing 2,3 from a single gene located on chromosome 17. These molecular isoforms of tau differ in whether they contain three or four tubulin binding domains/repeats of 31 or 32 amino acids each near the C-terminal end and no, one, or two inserts of 29 amino acids each at the N-terminal end of the molecule. There are nine missense mutations on tau exons 9 to 13; all but three are on exon 10. 4-7 Exon 10 codes for the additional insert of the three 4-repeat tau isoforms. The resulting mutated taus possess an altered conformation 8 and a somewhat reduced ability to bind to and assemble microtubules. 9,10 In addition to the exonic mutations, mutations at several sites have been found in the predicted stem loop structure in the 5′ splice site to exon 10. These intronic mutations and certain mutations in exon 10 that are close to the stem loop, and thus able to disrupt it, lead to two- to sixfold higher proportion of tau mRNA containing exon 10 than in control brains. 5 The tau protein resulting from intronic mutations is normal, but the ratio of 4-repeat to 3-repeat isoforms is increased. Presently it is believed that due to the increased proportion of 4-repeat tau in the case of intronic mutations and the compromised biological activity of the tau with missense mutations, excess tau is not bound to the microtubules, which can then be hyperphosphorylated and would lead to neurofibrillary degeneration. In contrast to the FTDP-17 group of diseases, no mutations in the tau gene have been reported in AD at the time of writing this Commentary. In more than 90% of the AD patients the disease occurs sporadically above 60 years of age. In less than 5% of the cases the disease segregates with mutations in the amyloid precursor protein (APP), presenilin-1 (PS-1), or presenilin-2 (PS-2) genes. 11 Frameshift mutations of APP and ubiquitin at the level of transcription have been reported to be associated with sporadic and familial AD and Down’s syndrome. 12 The occurrence of the apolipoprotein E4 allele 13 and, most recently, mutations in the β2 macroglobulin gene 14 have been reported to be risk factors for the development of the late onset, sporadic AD. AD has two prominent neuropathological lesions, the extracellular deposits of the amyloid β peptide (Aβ) as plaques and the intraneuronal paired helical filaments (PHF) of abnormally hyperphosphorylated tau, which accumulate in the neuronal cell body as neurofibrillary tangles, in the neuropil (the so-called neuropil threads), 15 and in the dystrophic neurites surrounding the neuritic plaques. The direct relationship, if any, between the tangles and β-amyloid is not yet understood. At the one extreme, in the normal aged brain there is the significant β-amyloid accumulation and minimal neurofibrillary degeneration, whereas in the early onset familial AD with mutations in the β-APP or presenilin gene, massive β-amyloid deposits, tau hyperphosphorylation, and tangle formation are always seen. The other extreme situation is represented by extensive neurofibrillary degeneration and minimal β-amyloidosis. These include tauopathies like the tangle-predominant form of senile dementia (tangle-only dementia), Guam Parkinsonism dementia complex, dementia with argyrophilic grains, Nieman Pick’s disease type C, subacute sclerosing panencephalitis, Pick’s disease, and the dementia group with mutations in the tau gene. 16 Although at present the exact role of PHF and β-amyloid in the pathogenesis of AD is not established, there is growing evidence from a number of laboratories that the intellectual deterioration in AD patients is associated with neurofibrillary degeneration. 17-20 A third and well characterized phenomenon is synaptic loss and cell death exceeding 50% in certain areas of the brain. 21,22

A polyclonal goat antiserum against the calcium-binding protein calretinin is a versatile tool for various immunochemical techniques

Specific antibodies are useful tools to label particular neurons and at times to delineate neuronal circuits — a task not easily achieved by other techniques. Human recombinant calretinin, a protein belonging to the EF-hand family of Ca 2+-binding proteins, was used to produce an antiserum in goat. The specificity of the antiserum to recognize calretinin was demonstrated in brain extracts from mouse, rat, and chick and in extracts from human tumor cell lines known to express this protein. Immunohistochemically, the antiserum-stained specific neurons in human, rhesus monkey, mouse, and rat brain. The goat anti-calretinin antiserum is an appropriate tool for double- or triple-immunolabeling studies along with previously-established rabbit and mouse antibodies. Thus, it allows for the concomitant staining with antibodies directed against other EF-hand calcium-binding proteins including calbindin-D 28k and parvalbumin. The antiserum can further be used for the quantification of calretinin in different tissues or cell lines in a sandwich ELISA. Additionally, it is well suited for the detection of calretinin in certain cell lines or malignant pleural mesotheliomas. Immunostaining of these samples is comparable to that with the well-characterized calretinin-specific polyclonal rabbit antiserum 7696.

Non-amine dopamine transporter probe [(3)H]tropoxene distributes to dopamine-rich regions of monkey brain.

Drug development in psychopharmacology has adhered to the unwritten precept that compounds targeting monoamine transporters must contain an amine nitrogen in the molecular structure. A series of non-amine-bearing aryloxatropanes that are potent inhibitors of the dopamine transporter (DAT) challenged this precept. In the present study, we investigated the brain distribution of a selective, high-affinity DAT non-amine, [(3)H]tropoxene (2-carbomethoxy-3, 4dichloro-3-aryl-8-oxabicyclo[3.2.1] octene), which binds to the DAT in monkey striatum. The autoradiographic distribution of [(3)H]tropoxene was conducted in tissue sections of rhesus (Macaca mulatta) monkey brain. Highest accumulation of the radioligand was detected in the putamen and caudate nucleus, with significant levels also observed in the nucleus accumbens and substantia nigra. Moderate to low levels of [(3)H]tropoxene binding were noted in the hypothalamus, amygdala, ventral tegmental area, and thalamus. The distribution of [(3)H]tropoxene was restricted to brain regions previously identified as expressing DAT, and the relative densities of [(3)H]tropoxene binding sites in various brain regions corresponded to those observed with other selective monoamine radioligands for the DAT. This is the first report to demonstrate that transporter-selective compounds that bear no amine nitrogen in their structure bind selectively to brain regions rich in the transporter. The results support our conclusion that an amine nitrogen is not necessary for compounds to bind to monoamine transporters and distribute in brain according to the known distribution of transporters. The findings provide further incentives to investigate the pharmacological potential of transport inhibitors lacking an amine nitrogen in the molecular structure.

2-[18F]F-A-85380: a PET radioligand for alpha4beta2 nicotinic acetylcholine receptors.

2-[18F]fluoro-3-(2(S)-azetidinylmethoxy)pyridine (2-[18F]F-A-85380), a ligand for nicotinic acetylcholine receptors (nAChRs) was evaluated in an in vitro binding assay with membranes of rat brain and in vivo by PET in Rhesus monkey brain. The ligand has high affinity for alpha4beta2 nAChRs (K(D)=50 pM), crosses the blood-brain barrier, and distributes in the monkey brain in a pattern consistent with that of alpha4beta2 nAChRs. The specific/non-specific binding ratio increased steadily, reaching a value of 3.3 in the thalamus at 4 h. The specific binding of 2-[18F]F-A-85380 was reversed by cytisine. These results, in combination with the data demonstrating low toxicity of 2-[18F]F-A-85380, indicate that this ligand shows promise for use with PET in human subjects.

In vivo positron emission tomography studies on the novel nicotinic receptor agonist [ 11C]MPA compared with [ 11C]ABT-418 and ( S)(−)[ 11C]nicotine in Rhesus monkeys

The novel 11C-labeled nicotinic agonist ( R, S)-1-[ 11C]methyl-2(3-pyridyl)azetidine ([ 11C]MPA) was evaluated as a positron emission tomography (PET) ligand for in vivo characterization of nicotinic acetylcholine receptors in the brain of Rhesus monkeys in comparison with the nicotinic ligands ( S)-3-methyl-5-(1-[ 11C]methyl-2-pyrrolidinyl)isoxazol ([ 11C]ABT-418) and ( S)(−)[ 11C]nicotine. The nicotinic receptor agonist [ 11C]MPA demonstrated rapid uptake into the brain to a similar extent as ( S)(−) [ 11C]nicotine and [ 11C]ABT-418. When unlabeled ( S)(−)nicotine (0.02 mg/kg) was administered 5 min before the radioactive tracers, the uptake of [ 11C]MPA was decreased by 25% in the thalamus, 19% in the temporal cortex, and 11% in the cerebellum, whereas an increase was found for the uptake of ( S)(−)[ 11C]nicotine and [ 11C]ABT-418. This finding indicates specific binding of [ 11C]MPA to nicotinic receptors in the brain in a simple classical displacement study. [ 11C]MPA seems to be a more promising radiotracer than ( S)(−)[ 11C]nicotine or [ 11C]ABT-418 for PET studies to characterize nicotinic receptors in the brain.

Alzheimer's disease and the amyloid beta protein: What is the role of amyloid?

Alzheimer’s disease (AD) is characterized by the deposition of amyloid in the extracellular compartment of the brain in the form of congophilic amyloid angiopathy (CAA) and amyloid plaques (APs). Intracellular neurofibrillary tangles (NFTs) (Terry, 1963) formed from the abnormally phosphorylated cytoskeletal protein tau are also seen (Lee et al., 1991). The identification of the amyloid b protein (Ab) in CAA and APs (Glenner and Wong, 1984; Masters et al., 1985) led to the cloning of the amyloid protein precursor (APP) (Kang et al., 1987). The discovery of familial AD (FAD) mutations in the APP gene (Chartier-Harlin et al., 1991; Goate et al., 1991; Murrell et al., 1991; Naruse et al., 1991; Tanzi and Hyman, 1991) has supported the view that a defect in APP metabolism or function is directly involved in AD pathogenesis. The demonstration that mutations in the tau gene can lead to non-Alzheimer dementias with neurofibrillary pathology, lacking Ab plaques (reviewed by Spillantini and Goedert, 1998), has reinforced the view that the NFTs are a secondary phenomenon in the pathogenesis of AD. It has long been argued that the deposition of amyloid is an early step in AD pathogenesis (Masters et al., 1985; Hardy and Higgins, 1992; Masters and Beyreuther, 1993). The term amyloid refers to insoluble proteinaceous deposits that are congophilic and exhibit red– green birefringence in the presence of plane polarized light (Kisilevsky, 1994). Implicit in much of the research on the role of APP and Ab has been the assumption that deposits of amyloid are toxic to the brain (Jarrett and Lansbury, 1993) and that these deposits are the underlying cause of AD. The observation that Ab peptides when “aged” (incubated to form amyloid fibrils) become toxic to neurons in culture (Yankner et al., 1989; Frautschy et al., 1991; Kowall et al., 1991; Pike et al., 1991; Howlett et al., 1995) has further supported this view. The amyloid cascade hypothesis of AD, as formalized by Hardy and Higgins (1992), states that Ab “precipitates to form amyloid and, in turn, causes neurofibrillary tangles and cell death.” However, this hypothesis has been challenged (see, e.g., Davis and Chisholm, 1997; Hardy, 1997b). It has been argued that the deposition of amyloid does not correlate with dementia (Terry et al., 1991; Arriagada et al., 1992; Roses, 1994; Samuel et al., 1994; Braak and Braak, 1996), although the failure to observe a correlation may be related to the method by which AP load is measured (Cummings and Cotman, 1995). Whether amyloid deposits have a pathogenic role remains a controversial issue.

Studies of selected phenyltropanes at monoamine transporters

3-Phenyltropane analogues of cocaine are useful neurobiologic tools for examining mechanisms of neurotransmitter transporters and psychostimulant drugs. They are also potential substitute medications for psychostimulant abuse. In this study, 18 3-phenyltropane analogues were characterized in uptake and binding studies at dopamine (DAT), norepinephrine (NET) and serotonin (SERT) transporters from the rat, and in binding at DAT in rat, rhesus monkey, and human brain tissue. In rat brain tissue, potency in inhibiting uptake generally correlated with the potency in inhibiting binding at all three transporters suggesting that none of these compounds have antagonist properties. At the DAT, there was a significant correlation of inhibitory potencies between the rat and monkey, the monkey and human, and the rat and human transporters although some compounds showed some species difference. These findings suggest that with regard to the 3-phenyltropane series, there is generally little pharmacologic difference between DATs from the three species examined, although binding data from rat may not be a perfect predictor of uptake inhibition in human.

Age-associated changes in rhesus CNS composition identified by MRI

Multispectral automated segmentation of MR images of the brains of 10 young (5–8 years), 10 middle-aged (12–17 years), and 11 old (21–27 years) female rhesus monkeys revealed age-associated changes in brain volume and composition. Total brain parenchymal volume (expressed as fraction of intracranial volume—%ICV) decreased at a linear rate of 0.3±0.04% ICV/year. Up to age ∼15 years, this loss was almost entirely due to gray matter loss, with a compensatory increase in cerebrospinal fluid (CSF), and possibly some white matter. Brain tissue composition, expressed as the gray matter/white matter volume ratio confirmed that gray matter loss exceeded white matter loss, but the rate of decline in the gray/white ratio began to slow after ∼15 years. Comparison of these age-associated changes in rhesus brain with those in humans suggest that the brain aging in rhesus is a good model of human brain aging, but occurs ∼3-fold faster.

Functional dissection of CCR5 coreceptor function through the use of CD4-independent simian immunodeficiency virus strains.

With rare exceptions, all simian immunodeficiency virus (SIV) strains can use CCR5 as a coreceptor along with CD4 for viral infection. In addition, many SIV strains are capable of using CCR5 as a primary receptor to infect CD4-negative cells such as rhesus brain capillary endothelial cells. By using coupled fluorescence-activated cell sorter (FACS) and infection assays, we found that even very low levels of CCR5 expression could support CD4-independent virus infection. CD4-independent viruses represent valuable tools for finely dissecting interactions between Env and CCR5 which may otherwise be masked due to the stabilization of these contacts by Env-CD4 binding. Based on the ability of SIV Env to bind to and mediate infection of cells expressing CCR5 chimeras and mutants, we identified the N terminus of CCR5 as a critical domain for direct Env binding and for supporting CD4-independent virus infection. However, the activity of N-terminal domain CCR5 mutants could be rescued by the presence of CD4, indicating that other regions of CCR5 are important for post-binding events that lead to viral entry. Rhesus CCR5 supported CD4-independent infection and direct Env binding more efficiently than did human CCR5 due to a single amino acid difference in the N terminus. Interestingly, uncleaved, oligomeric SIV Env protein bound to both CD4 and CCR5 less efficiently than did monomeric gp120. Finally, several mutations present in chronically infected monkey populations are shown to decrease the ability of CCR5 to serve as a primary viral receptor for the SIV isolates examined.

Localization of vasopressin (V1a) receptor binding and mRNA in the rhesus monkey brain.

Centrally released arginine vasopressin (AVP) has been associated with various behavioural and cognitive effects, such as scent marking, aggression, and memory, which are believed to be mediated by the V1a subtype of the vasopressin receptor. Although the distribution of V1a receptors is conserved in a few brain regions, the pattern of expression of this receptor is, in general, highly species-specific. We have used receptor autoradiography with the linear V1a receptor ligand (125I-Phenylacetyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2) to characterize the pattern of receptor binding in the rhesus monkey brain. Brain sites of V1a receptor synthesis were defined using in-situ hybridization. The regions of highest V1a receptor density included the prefrontal, cingulate, pyriform, and entorhinal cortex, as well as the presubiculum and mamillary bodies. In addition, V1a receptor binding and mRNA were detected in several regions reported to have V1a receptor in most rodents, including the amygdala, bed nucleus of the stria terminalis, lateral septum, hypothalamus and the brainstem. The distribution is consistent with a role for vasopressin in higher cognitive functions, especially memory, in primates.

Comparison between dopamine transporter affinity and self-administration potency of local anesthetics in rhesus monkeys

Local anesthetics bind to dopamine transporters and inhibit dopamine uptake in rodent brain. Additionally, local anesthetics are self-administered in rhesus monkeys. The present study determined binding affinities of cocaine and five local anesthetics at dopamine transporters in rhesus monkey brain, and compared binding affinities to published self-administration potencies in rhesus monkeys. The affinity order at dopamine transporters was cocaine>dimethocaine>tetracaine>procaine≥chloroprocaine>lidocaine. The correlation between dopamine transporter affinities and self-administration potencies was significant. Binding affinities were also determined at sodium (Na 2+) channels in rhesus monkey brain. There was not a significant correlation between Na 2+ channel affinities and self-administration potencies Local anesthetics with high dopamine transporter and low Na 2+ channel affinities were self-administered, whereas those with either high or low affinity at both sites were not consistently self-administered. These data suggest that affinity at dopamine transporters is related to the reinforcing effects of local anesthetics in rhesus monkeys, and Na 2+ channel effects may interfere with the reinforcing effect of these drugs.

The distribution of neurotrophin receptor TrkC-like immunoreactive fibers and varicosities in the rhesus monkey brain

The distribution of immunoreactivity for the neurotrophin receptor tyrosine kinase TrkC was examined in the brain of the adult rhesus monkey. TrkC-like immunoreactivity was widespread and consisted primarily of varicose fibers. The most dense populations of fibers were in the basal forebrain (in the cholinergic cell groups Ch1, Ch2 and Ch4), in the raphé complex throughout its rostrocaudal extent, and in the locus coeruleus. Other fibers were present in the thalamus, hypothalamus, central gray matter of the midbrain, dorsal midline of the brainstem and the cerebral cortex. The only neuronal cell bodies with consistent labeling were located in the lateral hypothalamus. Purkinje cells in the cerebellum showed variable labeling. Specific labeling of varicosities and cell bodies was abolished by omission of the primary antiserum or by preabsorption with the TrkC peptide antigen. We conclude that TrkC-like immunoreactivity can be detected in a wide variety of subcortical locations in the adult rhesus monkey. Labeling was particularly prominent in the vicinity of the major cholinergic, serotonergic and adrenergic nuclei, known from other studies to be vulnerable in the ageing brain. This suggests that the ligand for TrkC, neurotrophin-3, may persist as a survival factor for critical neurons into adulthood.

Topographical distribution of [ 125I]-glial cell line-derived neurotrophic factor in unlesioned and MPTP-lesioned rhesus monkey brain following a bolus intraventricular injection

The present study determined the topographical distribution profile for [ 125I]-glial cell line-derived neurotrophic factor in unlesioned and MPTP-lesioned (unilateral intracarotid injection) rhesus monkeys following an intraventricular injection. Autoradiographic analysis showed that following a bolus intraventricular injection, there was widespread distribution of [ 125I]-glial cell line-derived neurotrophic factor throughout the ventricular system (walls of lateral, third, and fourth ventricles and aqueduct), with some accumulation at the lateral ventricle injection site, possibly associated with the ependymal cell layer. In both unlesioned and MPTP-lesioned monkeys, there was labelling of the cerebral cortex, substantia nigra/ventral tegmental area and sequestration of [ 125I]-glial cell line-derived neurotrophic factor adjacent to the hippocampal formation, globus pallidus, ventral to and in the substantia nigra. However, [ 125I]-glial cell line-derived neurotrophic factor did not appear to diffuse readily or accumulate in the caudate–putamen even though there was some penetration away from the ventricular walls. Throughout the brain, there was also substantial non-parenchymal labelling of [ 125I]-glial cell line-derived neurotrophic factor, possibly associated with extracellular matrix components, meninges and vasculature due to the heparin binding properties of glial cell line-derived neurotrophic factor. In addition to the extensive loss of tyrosine hydroxylase immunoreactivity within the substantia nigra, there was also decreased accumulation of [ 125I]-glial cell line-derived neurotrophic factor and reduced glial cell line-derived neurotrophic factor immunoreactivity ipsilateral to the lesion. Microscopic analysis showed that glial cell line-derived neurotrophic factor immunoreactivity was associated with upper cortical layers including a high density of immunoreactivity at the surface of the cortex (meningeal, pial layer, vasculature) and around the ventricular walls (with some cellular labelling and labelling of vasculature). Moderate staining was observed in nigral cells contralateral to the MPTP-lesion, whereas only minimal levels of that glial cell line-derived neurotrophic factor immunoreactivity were detected ipsilateral to the lesion. This study shows that intraventricularly injected glial cell line-derived neurotrophic factor accumulates not only around the ventricular walls, but also in specific brain regions in which sub-populations of cells are more readily accessible than others. The presence of cells labelled with [ 125I] and immunopositive for glial cell line-derived neurotrophic factor in the substantia nigra indicates that these cells are a target for the trophic factor following intraventricular administration. Thus, the behavioral improvement observed in MPTP-lesioned monkeys following an intraventricular injection of glial cell line-derived neurotrophic factor is likely the result of activation of nigral cells.