In utero Exposure to Anesthetics Alters Neuronal Migration Pattern in Developing Cerebral Cortex and Causes Postnatal Behavioral Deficits in Rats.

During fetal development, cerebral cortical neurons are generated in the proliferative zone along the ventricles and then migrate to their final positions. To examine the impact of in utero exposure to anesthetics on neuronal migration, we injected pregnant rats with bromodeoxyuridine to label fetal neurons generated at embryonic Day (E) 17 and then randomized these rats to 9 different groups receiving 3 different means of anesthesia (oxygen/control, propofol, isoflurane) for 3 exposure durations (20, 50, 120 min). Histological analysis of brains from 54 pups revealed that significant number of neurons in anesthetized animals failed to acquire their correct cortical position and remained dispersed within inappropriate cortical layers and/or adjacent white matter. Behavioral testing of 86 littermates pointed to abnormalities that correspond to the aberrations in the brain areas that are specifically developing during the E17. In the second set of experiments, fetal brains exposed to isoflurane at E16 had diminished expression of the reelin and glutamic acid decarboxylase 67, proteins critical for neuronal migration. Together, these results call for cautious use of anesthetics during the neuronal migration period in pregnancy and more comprehensive investigation of neurodevelopmental consequences for the fetus and possible consequences later in life.

Past, present, and future of Parkinson's disease: A special essay on the 200th Anniversary of the Shaking Palsy.

This article reviews and summarizes 200 years of Parkinson's disease. It comprises a relevant history of Dr. James Parkinson's himself and what he described accurately and what he missed from today's perspective. Parkinson's disease today is understood as a multietiological condition with uncertain etiopathogenesis. Many advances have occurred regarding pathophysiology and symptomatic treatments, but critically important issues are still pending resolution. Among the latter, the need to modify disease progression is undoubtedly a priority. In sum, this multiple-author article, prepared to commemorate the bicentenary of the shaking palsy, provides a historical state-of-the-art account of what has been achieved, the current situation, and how to progress toward resolving Parkinson's disease. © 2017 International Parkinson and Movement Disorder Society.

Post-mortem assessment of the short and long-term effects of the trophic factor neurturin in patients with α-synucleinopathies.

Substantial interest persists for developing neurotrophic factors to treat neurodegenerative diseases. At the same time, significant progress has been made in implementing gene therapy as a means to provide long-term expression of bioactive neurotrophic factors to targeted sites in the brain. Nonetheless, to date, no double-blind clinical trial has achieved positive results on its primary endpoint despite robust benefits achieved in animal models. A major issue with advancing the field is the paucity of information regarding the expression and effects of neurotrophic factors in human neurodegenerative brain, relative to the well-characterized responses in animal models. To help fill this information void, we examined post-mortem brain tissue from four patients with nigrostriatal degeneration who had participated in clinical trials testing gene delivery of neurturin to the putamen of patients. Each had died of unrelated causes ranging from 1.5-to-3-months (2 Parkinson's disease patients), to 4+-years (1 Parkinson's disease and 1 multiple-system atrophy-parkinsonian type patient) following gene therapy. Quantitative and immunohistochemical evaluation of neurturin, alpha-synuclein, tyrosine hydroxylase (TH) and an oligodendroglia marker (Olig 2) were performed in each brain. Comparable volumes-of-expression of neurturin were seen in the putamen in all cases (~15-22%; mean=18.5%). TH-signal in the putamen was extremely sparse in the shorter-term cases. A 6-fold increase was seen in longer-term cases, but was far less than achieved in animal models of nigrostriatal degeneration with similar or even far less NRTN exposure. Less than 1% of substantia nigra (SN) neurons stained for neurturin in the shorter-term cases. A 15-fold increase was seen in the longer-term cases, but neurturin was still only detected in ~5% of nigral cells. These data provide unique insight into the functional status of advanced, chronic nigrostriatal degeneration in human brain and the response of these neurons to neurotrophic factor stimulation. They demonstrate mild but persistent expression of gene-mediated neurturin over 4-years, with an apparent, time-related amplification of its transport and biological effects, albeit quite weak, and provide unique information to help plan and design future trials.

Alpha-synuclein aggregates are phosphatase resistant.

Alpha-synuclein (αsyn) is an intrinsically disordered protein that aggregates in the brain in several neurodegenerative diseases collectively called synucleinopathies. Phosphorylation of αsyn at serine 129 (PSER129) was considered rare in the healthy human brain but is enriched in pathological αsyn aggregates and is used as a specific marker for disease inclusions. However, recent observations challenge this assumption by demonstrating that PSER129 results from neuronal activity and can be readily detected in the non-diseased mammalian brain. Here, we investigated experimental conditions under which two distinct PSER129 pools, namely endogenous-PSER129 and aggregated-PSER129, could be detected and differentiated in the mammalian brain. Results showed that in the wild-type (WT) mouse brain, perfusion fixation conditions greatly influenced the detection of endogenous-PSER129, with endogenous-PSER129 being nearly undetectable after delayed perfusion fixation (30-minute and 1-hour postmortem interval). Exposure to anesthetics (e.g., Ketamine or xylazine) before perfusion did not significantly influence endogenous-PSER129 detection or levels. In situ, non-specific phosphatase calf alkaline phosphatase (CIAP) selectively dephosphorylated endogenous-PSER129 while αsyn preformed fibril (PFF)-seeded aggregates and genuine disease aggregates (Lewy pathology and Papp-Lantos bodies in Parkinson's disease and multiple systems atrophy brain, respectively) were resistant to CIAP-mediated dephosphorylation. The phosphatase resistance of aggregates was abolished by sample denaturation, and CIAP-resistant PSER129 was closely associated with proteinase K (PK)-resistant αsyn (i.e., a marker of aggregation). CIAP pretreatment allowed for highly specific detection of seeded αsyn aggregates in a mouse model that accumulates non-aggregated-PSER129. We conclude that αsyn aggregates are impervious to phosphatases, and CIAP pretreatment increases detection specificity for aggregated-PSER129, particularly in well-preserved biological samples (e.g., perfusion fixed or flash-frozen mammalian tissues) where there is a high probability of interference from endogenous-PSER129. Our findings have important implications for the mechanism of PSER129-accumulation in the synucleinopathy brain and provide a simple experimental method to differentiate endogenous-from aggregated PSER129.

Alpha-synuclein aggregates are phosphatase resistant.

Alpha-synuclein (αsyn) is an intrinsically disordered protein that aggregates in the brain in several neurodegenerative diseases collectively called synucleinopathies. Phosphorylation of αsyn at serine 129 (PSER129) was considered rare in the healthy human brain but is enriched in pathological αsyn aggregates and is used as a specific marker for disease inclusions. However, recent observations challenge this assumption by demonstrating that PSER129 results from neuronal activity and can be readily detected in the non-diseased mammalian brain. Here, we investigated experimental conditions under which two distinct PSER129 pools, namely endogenous-PSER129 and aggregated-PSER129, could be detected and differentiated in the mammalian brain. Results showed that in the wild-type (WT) mouse brain, perfusion fixation conditions greatly influenced the detection of endogenous-PSER129, with endogenous-PSER129 being nearly undetectable after delayed perfusion fixation (30-min and 1-h postmortem interval). Exposure to anesthetics (e.g., Ketamine or xylazine) before perfusion did not significantly influence endogenous-PSER129 detection or levels. In situ, non-specific phosphatase calf alkaline phosphatase (CIAP) selectively dephosphorylated endogenous-PSER129 while αsyn preformed fibril (PFF)-seeded aggregates and genuine disease aggregates (Lewy pathology and Papp-Lantos bodies in Parkinson's disease and multiple systems atrophy brain, respectively) were resistant to CIAP-mediated dephosphorylation. The phosphatase resistance of aggregates was abolished by sample denaturation, and CIAP-resistant PSER129 was closely associated with proteinase K (PK)-resistant αsyn (i.e., a marker of aggregation). CIAP pretreatment allowed for highly specific detection of seeded αsyn aggregates in a mouse model that accumulates non-aggregated-PSER129. We conclude that αsyn aggregates are impervious to phosphatases, and CIAP pretreatment increases detection specificity for aggregated-PSER129, particularly in well-preserved biological samples (e.g., perfusion fixed or flash-frozen mammalian tissues) where there is a high probability of interference from endogenous-PSER129. Our findings have important implications for the mechanism of PSER129-accumulation in the synucleinopathy brain and provide a simple experimental method to differentiate endogenous-from aggregated PSER129.

Health Economic Considerations in the Deployment of an Alzheimer's Prevention Therapy.

INTRODUCTION: As treatments for secondary prevention of Alzheimer's disease (AD) are being studied, concerns about their value for money have appeared. We estimate cost-effectiveness of a hypothetical screening and prevention program. METHODS: We use a Markov model to project cost-effectiveness of a treatment that reduces progression to symptomatic AD by 50% with either chronic treatment until progression to mild cognitive impairment or treatment for one year followed by monitoring with AD blood tests and retreatment with one dose in case of amyloid re-accumulation. Diagnoses would be made with an AD blood test with sensitivity and specificity of 80%, and inconclusive results in 20%. Individuals testing negative would be re-tested in five years and those with inconclusive results in one. RESULTS: The program would generate per-person value of $53,721 from a payer (reduction of direct cost and patient QALY gains) and $69,861 from a societal perspective (adding valuation of reduced caregiver burden). With chronic treatment, it would be cost-effective up to annual drug prices of $7,000 and $10,300, respectively. Time-limited treatment would be cost-effective at annual drug prices of $54,257 and $78,458 from a payer and societal perspective, respectively. Higher specificity of the blood test would decrease cost per person with similar value generation DISCUSSION: A hypothetical prevention treatment for AD could be economically viable from a payer and societal perspective.

Neural transplants in patients with Huntington's disease undergo disease-like neuronal degeneration.

The clinical evaluation of neural transplantation as a potential treatment for Huntington's disease (HD) was initiated in an attempt to replace lost neurons and improve patient outcomes. Two of 3 patients with HD reported here, who underwent neural transplantation containing striatal anlagen in the striatum a decade earlier, have demonstrated marginal and transient clinical benefits. Their brains were evaluated immunohistochemically and with electron microscopy for markers of projection neurons and interneurons, inflammatory cells, abnormal huntingtin protein, and host-derived connectivity. Surviving grafts were identified bilaterally in 2 of the subjects and displayed classic striatal projection neurons and interneurons. Genetic markers of HD were not expressed within the graft. Here we report in patients with HD that (i) graft survival is attenuated long-term; (ii) grafts undergo disease-like neuronal degeneration with a preferential loss of projection neurons in comparison to interneurons; (iii) immunologically unrelated cells degenerate more rapidly than the patient's neurons, particularly the projection neuron subtype; (iv) graft survival is attenuated in the caudate in comparison to the putamen in HD; (v) glutamatergic cortical neurons project to transplanted striatal neurons; and (vi) microglial inflammatory changes in the grafts specifically target the neuronal components of the grafts. These results, when combined, raise uncertainty about this potential therapeutic approach for the treatment of HD. However, these observations provide new opportunities to investigate the underlying mechanisms involved in HD, as well as to explore additional therapeutic paradigms.

Response of aged parkinsonian monkeys to in vivo gene transfer of GDNF.

This study assessed the potential for functional and anatomical recovery of the diseased aged primate nigrostriatal system, in response to trophic factor gene transfer. Aged rhesus monkeys received a single intracarotid infusion of MPTP, followed one week later by MRI-guided stereotaxic intrastriatal and intranigral injections of lentiviral vectors encoding for glial derived neurotrophic factor (lenti-GDNF) or beta-galactosidase (lenti-LacZ). Functional analysis revealed that the lenti-GDNF, but not lenti-LacZ treated monkeys displayed behavioral improvements that were associated with increased fluorodopa uptake in the striatum ipsilateral to lenti-GDNF treatment. GDNF ELISA of striatal brain samples confirmed increased GDNF expression in lenti-GDNF treated aged animals that correlated with functional improvements and preserved nigrostriatal dopaminergic markers. Our results indicate that the aged primate brain challenged by MPTP administration has the potential to respond to trophic factor delivery and that the degree of neuroprotection depends on GDNF levels.

Neurodegeneration prevented by lentiviral vector delivery of GDNF in primate models of Parkinson's disease.

Lentiviral delivery of glial cell line-derived neurotrophic factor (lenti-GDNF) was tested for its trophic effects upon degenerating nigrostriatal neurons in nonhuman primate models of Parkinson's disease (PD). We injected lenti-GDNF into the striatum and substantia nigra of nonlesioned aged rhesus monkeys or young adult rhesus monkeys treated 1 week prior with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Extensive GDNF expression with anterograde and retrograde transport was seen in all animals. In aged monkeys, lenti-GDNF augmented dopaminergic function. In MPTP-treated monkeys, lenti-GDNF reversed functional deficits and completely prevented nigrostriatal degeneration. Additionally, lenti-GDNF injections to intact rhesus monkeys revealed long-term gene expression (8 months). In MPTP-treated monkeys, lenti-GDNF treatment reversed motor deficits in a hand-reach task. These data indicate that GDNF delivery using a lentiviral vector system can prevent nigrostriatal degeneration and induce regeneration in primate models of PD and might be a viable therapeutic strategy for PD patients.

Age-related changes in dopamine transporters and accumulation of 3-nitrotyrosine in rhesus monkey midbrain dopamine neurons: relevance in selective neuronal vulnerability to degeneration.

Aging is the strongest risk factor for developing Parkinson's disease (PD). There is a preferential loss of dopamine (DA) neurons in the ventral tier of the substantia nigra (vtSN) compared to the dorsal tier and ventral tegmental area (VTA) in PD. Examining age-related and region-specific differences in DA neurons represents a means of identifying factors potentially involved in vulnerability or resistance to degeneration. Nitrative stress is among the factors potentially underlying DA neuron degeneration. We studied the relationship between 3-nitrotyrosine (3NT; a marker of nitrative damage) and DA transporters [DA transporter (DAT) and vesicular monoamine transporter-2 (VMAT)] during aging in DA subregions of rhesus monkeys. The percentage of DA neurons containing 3NT increased significantly only in the vtSN with advancing age, and the vtSN had a greater percentage of 3NT-positive neurons when compared to the VTA. The relationship between 3NT and DA transporters was determined by measuring fluorescence intensity of 3NT, DAT and VMAT staining. 3NT intensity increased with advancing age in the vtSN. Increased DAT, VMAT and DAT/VMAT ratios were associated with increased 3NT in individual DA neurons. These results suggest nitrative damage accumulates in midbrain DA neurons with advancing age, an effect exacerbated in the vulnerable vtSN. The capacity of a DA neuron to accumulate more cytosolic DA, as inferred from DA transporter expression, is related to accumulation of nitrative damage. These findings are consistent with a role for aging-related accrual of nitrative damage in the selective vulnerability of vtSN neurons to degeneration in PD.

Fetal nigral transplantation as a therapy for Parkinson's disease.

Fetal nigral grafts have been demonstrated to survive, secrete dopamine, form synaptic connections with host neurons, and reverse behavioral disturbances in experimental models of parkinsonism. These findings suggest that fetal nigral grafting may be a useful therapy for patients with Parkinson's disease (PD). Recent preliminary clinical trials of transplantation in PD have shown increased striatal fluorodopa uptake (measured using positron emission tomography) and clinical benefit in some patients. An autopsy study of one patient who had received fetal nigral transplants demonstrated robust graft survival and striatal reinnervation, with no evidence of host-derived sprouting or immune rejection. The development of a successful clinical transplantation program depends on a careful consideration of the transplantation variables and the related long-term risks and benefits to the patients.

Attenuation of microglial RANTES by NEMO-binding domain peptide inhibits the infiltration of CD8(+) T cells in the nigra of hemiparkinsonian monkey.

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Despite intense investigations, little is known about its pathological mediators. Here, we report the marked upregulation of RANTES (regulated on activation, normal T cell expressed and secreted) and eotaxin, chemokines that are involved in T cell trafficking, in the serum of hemiparkinsonian monkeys. Interestingly, 1-methyl-4-phenylpyridinium (MPP(+)), a Parkinsonian toxin, increased the expression of RANTES and eotaxin in mouse microglial cells. The presence of NF-κB binding sites in promoters of RANTES and eotaxin and down-regulation of these genes by NEMO-binding domain (NBD) peptide, selective inhibitor of induced NF-κB activation, in MPP(+)-stimulated microglial cells suggest that the activation of NF-κB plays an important role in the upregulation of these two chemokines. Consistently, serum enzyme-linked immuno assay (ELISA) and nigral immunohistochemistry further confirmed that these chemokines were strongly upregulated in MPTP-induced hemiparkinsonian monkeys and that treatment with NBD peptides effectively inhibited the level of these chemokines. Furthermore, the microglial upregulation of RANTES in the nigra of hemiparkinsonian monkeys could be involved in the altered adaptive immune response in the brain as we observed greater infiltration of CD8(+) T cells around the perivascular niche and deep brain parenchyma of hemiparkinsonian monkeys as compared to control. The treatment of hemiparkinsonian monkeys with NBD peptides decreased the microglial expression of RANTES and attenuated the infiltration of CD8(+) T cells in nigra. These results indicate the possible involvement of chemokine-dependent adaptive immune response in Parkinsonism.

A confocal microscopic analysis of galaninergic hyperinnervation of cholinergic basal forebrain neurons in Alzheimer's disease.

The galanin (GAL) containing peptide fiber system innervates the basal forebrain and has been shown to hyperinnervate remaining cholinergic neurons in Alzheimer's disease (AD). GAL modulates the release of acetylcholine and, therefore, may depress this neurotransmitter in surviving cholinergic basal forebrain (CBF) neurons in AD. The aim of this study was to identify putative synaptic contacts between GAL immunoreactive processes and CBF neurons and evaluate whether these processes hypertrophy in AD patients. We observed by confocal laser microscopy a hyperinnervation of GAL-containing fibers in both AD and Parkinson's disease patients with concurrent AD (PD/AD). Galaninergic fibers were often seen in direct apposition to remaining CBF neurons and enwrapped cholinergic cell soma and dendrites. Our results demonstrate that GAL-containing fibers are in direct apposition to CBF neurons in normal-aged humans and that this phenotype is enhanced in AD and PD/AD, suggesting that direct synaptic contacts occur between GAL-containing fibers and CBF neurons. Because GAL can modulate acetylcholine release from cholinergic neurons, hyperinnervation of GAL fibers in AD and PD/AD patients may further decrease release of acetylcholine from remaining CBF neurons. We propose that therapies based solely on acetylcholinesterase inhibitors may be insufficient to effectively increase cortical levels of acetylcholine.

Animal models of age- and disease-related cognitive decline: perspectives on the models and therapeutic strategies.

The relative value of animals with memory impairments, due either to experimental lesions or aging processes, is dependent upon the specific hypothesis being tested. The experimental approaches described in the preceding reviews are valuable for basic studies on learning and memory in the mammalian brain. However, because of important differences between available model systems and human disease states, such as Alzheimer's disease, their use at present may be insufficient for understanding and developing treatment strategies for human cognitive dysfunctions. In this commentary, different aspects of animal models of memory dysfunction will be discussed relative to their ability to assess the structural and functional consequences of central nervous system (CNS) repair.

NGF and Alzheimer's disease: unfulfilled promise and untapped potential.

A role for impaired NGF mechanisms as an underlying component in the pathogenesis of Alzheimer's disease has yet to be realized. However, circumspect examination of the available data fails to provide sufficient evidence for rejecting this notion and further systematic evaluation along each step of NGF's mechanism of neurotrophic action is still required. This commentary argues that NGF may be involved in the degeneration observed in the basal forebrain in AD, or at the very least, plays a dynamic role in the disease process.

Tracing neuronal connections in postmortem human hippocampal complex with the carbocyanine dye DiI.

This report describes the ability of the carbocyanine dye DiI to trace hippocampal complex connections in a paraformaldehyde immersion-fixed human postmortem brain. Six months after the placement of DiI crystals into the hilus of the dentate gyrus, the CA1 hippocampal subfield and the lateral entorhinal cortex, 50-microns thick, vibratome cut sections were examined using an epifluorescence microscope with a rhodamine filter. In association with DiI-labeled granule, pyramidal and multipolar type neurons, we observed dendrites containing dendritic spines and axons. DiI-labeled fibers were observed coursing within classically described hippocampal pathways for at least 8 mm distal to the injection site. Photoconversion of diaminobenzidine (DAB)-treated DiI sections produced a stable record of labeled profiles. These findings indicate that DiI is a useful method for investigating intrinsic local circuit connections in normal aldehyde-fixed postmortem human brain and suggests that DiI could be a powerful tool to examine altered neural connectivity in humans with neurological disease.

Nerve growth factor receptor and choline acetyltransferase remain colocalized in the nucleus basalis (Ch4) of Alzheimer's patients.

Previous investigations have demonstrated an almost exclusive "coupling" between the receptor for nerve growth factor and cholinergic neurons within the basal forebrain. The present series of experiments were carried out to address two questions. First, what is the status of nerve growth factor receptor-containing neurons within the basal forebrain of patients with histopathologically confirmed diagnoses of Alzheimer's disease (AD)? More importantly, the second experiment assesses the degree to which the receptor for nerve growth factor and choline acetyltransferase remain colocalized within AD basal forebrain. A "decoupling" of this relationship, in which nerve growth factor receptors are no longer present upon magnocellular cholinergic neurons, would suggest that a loss of trophic support is functionally antecedent to the neuronal shrinkage and neuronal death seen in the basal forebrain in AD. Data obtained from six AD cases and four normal controls demonstrated an extensive reduction in number and shrinkage in size of nerve growth factor receptor containing neurons within the Ch4 region of the basal forebrain. Double label studies using either immunofluorescence or immunoperoxidase techniques demonstrated that the receptor for nerve growth factor and choline acetyltransferase remain colocalized in AD patients. This was true for neurons exhibiting either healthy or dystrophic morphological profiles. These data confirm previous studies, demonstrating that both a loss and shrinkage of cholinergic neurons occurs within the AD basal forebrain. The results of the present immunohistochemical investigation suggest that the degenerative changes associated with these neurons do not result from impaired trophic support related to a loss of NGF receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein E-immunoreactivity in aged rhesus monkey cortex: colocalization with amyloid plaques.

In the present study, we examined the relationship between ApoE and amyloid containing profiles within the cerebral cortex of young, middle aged, and aged Rhesus monkeys. Polymerase chain reaction analysis revealed a pattern consistent with the ApoE e4 phenotype in the rhesus monkey similar to that reported in humans. We found numerous ApoE immunoreactive plaques within the temporal neocortex and amygdala, whereas the hippocampus contained only a few such plaques. Although virtually all ApoE-immunoreactive plaques coexpressed beta-amyloid, most plaques were beta A4 positive/ApoE immunonegative within the aged monkey cortex. Moreover, we observed a close correspondence between ApoE and thioflavin-positive (i.e., amyloid) plaques suggesting that ApoE may play a critical role in the conversion of beta A4 to its beta-pleated form. Because ApoE, beta A4 and amyloid are expressed in plaques within the aged Rhesus macaque cortex, this species may provide an in vivo model for investigations aimed at clarifying the interactions between these proteins in normal and pathologic aging.

NGF receptor (p75)-immunoreactivity in the developing primate basal ganglia.

The distribution of the p75 nerve growth factor receptor (NGFr) was determined within the developing human basal ganglia in specimens between weeks 16 through 40 of gestation, 5 years of age, and adulthood. Although NGFr-immunoreactive neurons were rarely seen in the caudate nucleus, a few such neurons were seen in the putamen between prenatal weeks 16 and 26 of development. At 26 and 40 weeks of gestation, the putamen also displayed NGFr-immunoreactive fibers of putative basal forebrain origin. Some of these fibers coursed through the putamen en route to the cortex while others appeared to remain within the putamen. The external segment of the globus pallidus contained dense collections of NGFr-immunoreactive neurons between 16 and 26 weeks of gestation, whereas the internal segment was devoid of immunoreactive perikarya. A few NGFr-immunoreactive neurons were observed within the globus pallidus at embryonic week 40. The expression of NGFr-immunoreactive neurons within the external segment of the globus pallidus was paralleled by a dense granular NGFr-immunoreactive terminal-like staining pattern within the subthalamic nucleus. This staining pattern was most intense at midgestation (weeks 21-26) and was not observed at 40 weeks of gestation or in adulthood. Interestingly, a similar NGFr-immunoreactive terminal-like pattern was also observed within the monkey subthalamic nucleus at embryonic day 120. These data indicate that NGF receptor mediated mechanisms may underlie developmental processes within the primate basal ganglia. The absence of NGFr-immunoreactive neurons within the caudate nucleus, and the paucity of such neurons in the putamen, suggests that NGF receptors play a limited role in primate neostriatal development. Alternatively, developmental events mediated through NGF receptors may occur prior to embryonic week 16. Furthermore, an NGFr/trophic interaction appears to underlie the development of the pallidal-subthalamic nucleus pathway.