Striatum Of Monkeys Research Articles

Chronic high dose l -dopa treatment does not alter the levels of dopamine D-1, D-2 or D-3 receptor in the striatum of normal monkeys: an autoradiographic study

To assess the role of dopamine receptors in the genesis of dyskinesia, we have used quantitative autoradiography to determine the effect of chronic L-dopa administration on dopamine D-1 (using [3H]SCH 23390), D-2 (using [3H]spiperone) and D-3 (using [3H]7-OH-DPAT) receptor binding levels in the striatum of dyskinetic or non-dyskinetic monkeys. Total and subregional striatal analysis showed no difference in D-1, D-2 or D-3 receptor binding in the caudate and putamen between monkeys receiving high dose L-dopa treatment with marked dyskinesia and those without dyskinesia compared to untreated animals. It thus appears unlikely that changes in dopamine receptor expression are a primary cause of L-dopa induced dyskinesia. Rather, a functional dissociation of D-2 receptor coupling to co-expressed enkephalin/adenosine-2a receptor activity in the striato-GPe indirect pathway may be more important in the development or expression of L-dopa-induced involuntary movements.

Reward Unpredictability inside and outside of a Task Context as a Determinant of the Responses of Tonically Active Neurons in the Monkey Striatum

Tonically active neurons (TANs) in the monkey striatum are involved in detecting motivationally relevant stimuli. We recently provided evidence that the timing of conditioned stimuli strongly influences the responsiveness of TANs, the source of which is likely to be the monkey's previous experience with particular temporal regularities in sequential task events. To extend these findings, we investigated the relationship of TAN responses to a primary liquid reward, the timing of which is more or less predictable to the monkey either outside of a task or during instrumental task performance. Reward predictability was indexed by the timing characteristics of the mouth movements. The responsiveness of TANs to reward increased with the range and variability of time periods before reward, notably when the liquid was delivered outside of a task. A change in the temporal order of events in a task context produced an increase of response to reward, suggesting an influence of the predicted nature of the event in addition to its time of occurrence. By contrast, we observed no substantial changes in neuronal activity at the expected time of reward when this event failed to occur, suggesting that these neurons do not appear to carry information about an error in reward prediction. These results demonstrate that TANs constitute a neuronal system that is involved in detecting unpredicted reward events, irrespective of the specific behavioral situation in which such events occur. The responses influenced by stimulus prediction may constitute a neuronal basis for the notion that striatal processing is crucial for habit learning.

Loss of metabolites from monkey striatum during PET with FDOPA

The decarboxylation of 6-[(18)F]fluorodopa (FDOPA) and retention of the product [(18)F]fluorodopamine within vesicles of catecholamine fibers results in the labeling of dopamine-rich brain regions during FDOPA/PET studies. However, this metabolic trapping is not irreversible due to the eventual diffusion of [(18)F]fluorodopamine metabolites from brain. Consequently, time-radioactivity recordings of striatum are progressively influenced by metabolite loss. In linear analyses, the net blood-brain clearance of FDOPA (K(D)(i), ml g(-1) min(-1)) can be corrected for this loss by the elimination rate constant k(Lin)(cl) (min(-1)). Similarly, the DOPA decarboxylation rate constant (k(D)(3), min(-1)) calculated by compartmental analysis can also be corrected for metabolite loss by the elimination rate constant k(DA)(9) (min(-1)). To compare the two methods, we calculated the two elimination rate constants using data recorded during 240 min of FDOPA circulation in normal monkeys and in monkeys with unilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesions. Use of the extended models increased the magnitudes of K(D)(i) and k(D)(3) in striatum; in the case of k(D)(3), variance of the estimate was substantially improved upon correction for metabolite loss. The rate constants for metabolite loss were higher in MPTP-lesioned monkey striatum than in normal striatum. The high correlation between individual estimates of k(Lin)(cl) and k(DA)(9) suggests that both rate constants reveal loss of decarboxylated metabolites from brain.

Signal transduction interactions between CB 1 cannabinoid and dopamine receptors in the rat and monkey striatum

Signal transduction interactions between the CB 1 cannabinoid and D 1 and D 2 dopamine receptor systems were studied in rat (Sprague Dawley) and monkey (Macaca fascilaris) striatal membranes. The D 2 agonist quinelorane inhibited forskolin (10 μM)-stimulated adenylyl cyclase in a dose-dependent manner (26% and 20% maximal inhibition; EC 50=2 and 0.5 μM, in rats and monkeys, respectively) and maximal inhibition was completely blocked by the D 2 antagonist sulpiride (10 μM). The CB 1 agonist desacetyllevonantradol inhibited forskolin-stimulated adenylyl cyclase (18% and 36% maximal inhibition; EC 50=160 and 73 nM, in rats and monkeys, respectively) and the CB 1 antagonist SR141716A (10 μM) completely blocked the maximal inhibition. Combined addition of >EC 90 concentrations of quinelorane (10, 30 μM) and desacetyllevonantradol (1 μM) resulted in no greater inhibition than that produced by either drug alone, indicative of signal transduction convergence between the D 2 and CB 1 receptor systems. The D 1 agonist 6-Br-APB (3-allyl-6-bromo-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepin) produced a dose-dependent stimulation of adenylyl cyclase (45% and 26% stimulation; EC 50=24 and 32 nM, in rat and monkey, respectively), and maximal stimulation was completely blocked by the D 1 antagonist SCH23390 (1 μM). D 1 agonist-stimulated activity could be inhibited to basal levels with desacetyllevonantradol (1 μM), indicative of D 1 and CB 1 signal transduction convergence. The data suggest that CB 1 receptors are co-localized with D 1 or D 2 receptors on the same population of striatal membranes and can interact at the level of G-protein/adenylyl cyclase signal transduction. Similar results obtained with both rat and monkey membranes indicate that striatal dopamine and cannabinoid interactions are conserved for these two species.

Progression of Changes in Dopamine Transporter Binding Site Density as a Result of Cocaine Self-Administration in Rhesus Monkeys

The present study examined the time course of alterations in levels of dopamine transporter (DAT) binding sites that accompany cocaine self-administration using quantitative in vitro receptor autoradiography with [(3)H]WIN 35,428. The density of dopamine transporter binding sites in the striatum of rhesus monkeys with 5 d, 3.3 months, or 1.5 years of cocaine self-administration experience was compared with DAT levels in cocaine-naive control monkeys. Animals in the long-term (1.5 years) exposure group self-administered cocaine at 0.03 mg/kg per injection, whereas the initial (5 d) and chronic (3.3 months) treatment groups were each divided into lower dose (0.03 mg/kg per injection) and higher dose (0.3 mg/kg per injection) groups. Initial cocaine exposure led to moderate decreases in [(3)H]WIN 35,428 binding sites, with significant changes in the dorsolateral caudate (-25%) and central putamen (-19%) at the lower dose. Longer exposure, in contrast, resulted in elevated levels of striatal binding sites. The increases were most pronounced in the ventral striatum at the level of the nucleus accumbens shell. At the lower dose of the chronic phase, for example, significant increases of 21-42% were measured at the caudal level of the ventral caudate, ventral putamen, olfactory tubercle, and accumbens core and shell. Systematic variation of cocaine dose and drug exposure time demonstrated the importance of these factors in determining the intensity of increased DAT levels. With self-administration of higher doses especially, increases were more intense and included dorsal portions of the striatum so that every region at the caudal level exhibited a significant increase in DAT binding sites (20-54%). The similarity of these findings to previous studies in human cocaine addicts strongly suggest that the increased density of dopamine transporters observed in studies of human drug abusers are the result of the neurobiological effects of cocaine, ruling out confounds such as polydrug abuse, preexisting differences in DAT levels, or comorbid psychiatric conditions.

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.

A PET study of

Several radiolabelled cocaine analogues have been proposed for brain imaging of the dopamine transporter in research on neuropsychiatric disorders and drug abuse. In a recent positron emission tomography (PET) study we labelled the cocaine analogue ß-CIT-FE with carbon-11 and demonstrated high specific binding in the monkey striatum. In the present study, the selectivity of [11C]ß-CIT-FE binding in the primate brain was examined by pretreatment experiments with reference ligands for the dopamine, serotonin and norepinephrine transporter. In three healthy human subjects the regional binding of [11C]ß-CIT-FE was analysed using equilibrium and kinetic analyses. A Scatchard analysis showed that [11C]ß-CIT-FE bound in a saturable manner yielded a density value of the same order as that reported in vitro. The pharmacological characterization indicated that a high degree of [11C]-CIT-FE binding in the primate striatum represents the dopamine transporter. In human subjects the radioligand provided high brain uptake and reached peak equilibrium within 1 hour after i.v. injection. Different quantitative approaches gave similar values for the binding potential. The results support the view that [11C]ß-CIT-FE is a suitable radioligand for clinical studies of the dopamine transporter. In particular for studies requiring short data acquisition or repeated PET measurements on the same day.

Grafting of encapsulated dopamine-secreting cells in Parkinson's disease: long-term primate study.

The transplantation of encapsulated dopamine-secreting cells into the striatum represents one potential means of treating Parkinson's disease. The present study investigated the ability of encapsulated PC12 cells, which are derived from rat pheochromocytoma, to supply L-dopa and dopamine into the primate brain in the long term and to effect functional improvement in the animals. Following polymer encapsulation, PC12 cells were transplanted into the striatum of hemiparkinsonian monkeys. The secretion of L-dopa and dopamine from the encapsulated cells, the morphology of these cells, the histology of the host striatum surrounding the capsule, and functional changes in the host animals were examined 1, 6, and 12 months after transplantation. Analysis of retrieved capsules revealed that the PC12 cells survived and continued to release L-dopa and dopamine even 12 months after transplantation. The histological response of the host brain surrounding the capsules was minimal and there were no signs of immunological rejection or tumor formation. The physical condition of the host animals was good for 12 months, and hematologic and cerebrospinal fluid analysis revealed that no animals suffered from infection or immunological reaction. These PC12 cell-grafted monkeys showed improvements in hand movements after transplantation, effects that lasted for at least 12 months. These results further support the potential use of this approach for the treatment of Parkinson's disease.

Regional heterogeneity of dopaminergic deficits in vervet monkey striatum and substantia nigra after methamphetamine exposure

Methamphetamine (METH)-induced neurotoxicity within the striatum and substantia nigra of the vervet monkey was characterized by heterogeneous decreases in immunoreactivity (IR) for dopamine system phenotypic markers. Decreases in IR for tyrosine hydroxylase (TH), dopamine transporter (DAT), and the vesicular monoamine transporter (VMAT2) were observed 1 week after METH HCI (2x2 mg/kg; 24 h apart). Regional changes throughout the rostrocaudal extent of the striatum were characterized by a gradient of neurotoxic effect (lateral greater than medial) and the preservation of patches of IR. The decreases in IR in the caudate and putamen were greater than those in the nucleus accumbens. The reduced IR in the METH-exposed striatum allowed for the visualization of dopamine phenotype cell bodies. Within the ventral midbrain, the METH-exposed substantia nigra pars compacta (SNc) also showed a heterogeneous loss of IR (lateral greater than medial). In contrast, the ventral tegmental area (VTA) showed only minor decreases in IR. The magnitude of the decreases in the SNc and VTA subregions corresponded to those observed in their respective striatal projection areas, suggesting that nigrostriatal neuron subpopulations were differentially reactive to METH. The profile of these drug-induced nigrostriatal dopamine system deficits resembles aspects of Parkinson's disease pathology and, as such, may provide a useful model with which to evaluate neuroprotective and neurorestorative strategies.

Age-related decline in striatal volume in monkeys as measured by magnetic resonance imaging

Age-related declines in striatal markers for the dopamine system have been demonstrated in several species. The current study investigated structural changes during aging in the rhesus monkey striatum. Male monkeys were studied using a volumetric spoiled gradient recall (SPGR) magnetic resonance imaging protocol. The caudate nucleus and putamen were segmented by manual tracing using landmarks made in the orthogonal planes. The whole brain volume (defined as volume of gray and white matter plus cerebrospinal fluid in ventricles and sulci) was measured using a semi-automated algorithm. There was no correlation between age and whole brain volume. There were age-related declines in normalized (i.e. brain region/whole brain volume) caudate nucleus and putamen volumes. Monkeys in the young group ( n = 7, 39–45 months old) had larger volumes of both the caudate nucleus and putamen than animals in the middle-age ( n = 5, 120–180 months) or old ( n = 7, 291–360 months) groups. The current results provide normative data to assess potential interventions (e.g. caloric restriction) in the aging process.

Expression of D 3 receptor messenger RNA and binding sites in monkey striatum and substantia nigra after nigrostriatal degeneration: effect of levodopa treatment

D 3 receptors are prominently localized in the primate caudate–putamen, and D 3 receptor agonist properties may offer an advantage in Parkinson’s disease therapy. In the present experiments, we investigated the relationship between D 3 receptor mRNA, D 3 receptor sites and the dopamine transporter in monkey basal ganglia by comparing their distribution in the brain of control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys ( Samirai sciureus). In control monkeys, D 3 receptor mRNA appears to be widely expressed throughout the brain, with a distribution similar to that observed in both man and rodent. D 3 receptors are present in areas which express mRNA but also in some which do not, an observation which suggests they may be both pre- and postsynaptic in the monkey brain. Chronic MPTP administration, which selectively destroys the nigrostriatal system, resulted in a 70 to 99% depletion of the dopamine transporter in the basal ganglia. Autoradiographic analysis showed that after MPTP treatment there was a significant decline in D 3 receptors in the caudate, but not putamen, globus pallidus, substantia nigra or other dopaminergic regions. D 3 receptor mRNA expression was not changed in any region after nigrostriatal lesioning. Two weeks of l-3,4-dihydroxyphenylalanine (levodopa, l-DOPA) treatment, which alleviated Parkinsonism but also induced dyskinesias, reversed the MPTP-induced decline in caudate D 3 receptors. These results show that there is a selective decline in D 3 receptors in the caudate after nigrostriatal degeneration, which is reversed by l-DOPA treatment. Since the majority of dopaminergic nerve terminals were destroyed after MPTP lesioning, the reversal in D 3 receptors after l-DOPA treatment may represent an increase in caudate postsynaptic receptors, which could conceivably contribute to an imbalance in striatal circuitry and the development of dyskinesias.

Impact of Self-Administered Cocaine and Cocaine Cues on Extracellular Dopamine in Mesolimbic and Sensorimotor Striatum in Rhesus Monkeys

Studies were conducted to determine the impact of self-administered cocaine on extracellular striatal dopamine in four rhesus monkeys. The extent to which external cue conditioning contributed to the effects of cocaine and whether there is activation of striatal dopaminergic neurotransmission during drug-seeking behavior was also examined. Microdialysis measurements were made at 2 min intervals in sensorimotor (dorsolateral) and mesolimbic (central and ventromedial) striatum. A fixed-ratio schedule of reinforcement was used, with cocaine availability signaled by a visual cue. Studies examined the effects of cocaine or cocaine cues against a drug-free baseline. Large (fivefold to eightfold) increases in extracellular dopamine after a self-administered infusion of 0.5 mg/kg cocaine were quite rapid and matched the time course of reported subjective effects in human laboratory studies. To determine if conditioning to external cues contributed to the cocaine-induced increases, saline was substituted for cocaine in the infusion, leaving all other visual and auditory stimuli unchanged. No increase in extracellular dopamine in either sensorimotor or mesolimbic striatal subdivisions was observed. Extracellular dopamine during extended periods of drug-seeking behavior triggered by a visual cue was determined in both central and ventromedial striatum. This procedure also did not result in any measurable changes in extracellular dopamine. These studies demonstrate rapid and pronounced pharmacological actions of self-administered cocaine. No apparent conditioned component of those actions was associated with external environmental cues, suggesting that cues that trigger drug-seeking behavior in nonhuman primates do not cause conditioned increases in mesolimbic striatal dopamine.

Effects of GM1 ganglioside treatment on pre- and postsynaptic dopaminergic markers in the striatum of parkinsonian monkeys

GM1 ganglioside administration has previously been shown to increase striatal dopamine levels and to enhance the density of tyrosine hydroxylase-positive fibers in the striatum of monkeys made parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The present study examined the extent to which GM1 administration promotes recovery of dopamine terminals and reverses lesion-induced changes in postsynaptic receptors in the striatum of MPTP-treated monkeys. All MPTP-treated animals developed severe parkinsonism. GM1-treated monkeys exhibited significant functional recovery after 6 weeks of treatment, whereas saline-treated controls remained parkinsonian over the same time period. MPTP exposure resulted in profound decreases in [3H]-mazindol binding to dopamine transporters in the caudate and putamen and increased D1 and D2 receptor binding in several striatal regions. GM1 treatment resulted in significant increases in striatal [3H]-mazindol binding and decreases in D1 binding compared to control animals in many striatal regions. GM1 treatment did not significantly affect D2 binding. These results show that GM1 treatment can partially restore striatal dopaminergic terminals and partially reverse postsynaptic changes in dopamine receptors in a nonhuman primate model of parkinsonism. Synapse 36:120–128, 2000. © 2000 Wiley-Liss, Inc.

Effects of GM1 ganglioside treatment on pre- and postsynaptic dopaminergic markers in the striatum of parkinsonian monkeys.

GM1 ganglioside administration has previously been shown to increase striatal dopamine levels and to enhance the density of tyrosine hydroxylase-positive fibers in the striatum of monkeys made parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The present study examined the extent to which GM1 administration promotes recovery of dopamine terminals and reverses lesion-induced changes in postsynaptic receptors in the striatum of MPTP-treated monkeys. All MPTP-treated animals developed severe parkinsonism. GM1-treated monkeys exhibited significant functional recovery after 6 weeks of treatment, whereas saline-treated controls remained parkinsonian over the same time period. MPTP exposure resulted in profound decreases in [(3)H]-mazindol binding to dopamine transporters in the caudate and putamen and increased D1 and D2 receptor binding in several striatal regions. GM1 treatment resulted in significant increases in striatal [(3)H]-mazindol binding and decreases in D1 binding compared to control animals in many striatal regions. GM1 treatment did not significantly affect D2 binding. These results show that GM1 treatment can partially restore striatal dopaminergic terminals and partially reverse postsynaptic changes in dopamine receptors in a nonhuman primate model of parkinsonism.

Influence of the predicted time of stimuli eliciting movements on responses of tonically active neurons in the monkey striatum.

Changes in activity of tonically active neurons of the primate striatum are determined both by the behavioural significance of stimuli and the context in which stimuli are presented. We investigated how the responses of these neurons are modified by the temporal predictability of stimuli eliciting learned behavioural reactions. Single neurons were recorded from the caudate nucleus and putamen of two macaque monkeys performing a visual reaction time task under conditions in which the timing of the trigger stimulus was made more or less predictable. The monkeys' ability to predict the trigger onset was assessed by measuring arm movement reaction times and saccadic ocular reactions. Of 171 neurons responding to the unsignalled presentation of the trigger stimulus, 32% lost their response when an instruction cue preceded the trigger by a highly practised 1.5 s interval, and the response reappeared when this interval was varied randomly from 1 to 2.5 s or prolonged to 3 or 4. 5 s. Although 43% of the neurons remained responsive irrespective of task condition, the responses were stronger with longer intervals than with the accustomed 1.5 s interval. In addition, a number of neurons responding to the instruction lost their response when the trigger appeared more distant from the instruction. These findings demonstrate that neuronal responses to a movement-triggering signal become more numerous and pronounced when the degree of temporal predictability of that signal was decreased. We conclude that tonic striatal neurons are sensitive to temporal aspects of stimulus prediction.

Striatal interneurons expressing calretinin, parvalbumin or NADPH-diaphorase: a comparative study in the rat, monkey and human

The present study is aimed at evaluating the relative number and comparing the pattern of distribution of interneurons containing calretinin (CR), parvalbumin (PV) or NADPH-d in the striatum of rats, squirrel monkeys and humans. A series of adjacent coronal sections taken at three comparable rostrocaudal levels in the three species were treated to reveal the three neuronal markers and the density of each type of chemospecific interneurons was analyzed with a computerized image analysis system. In primates, the most abundant interneurons were those expressing CR. The ratio of CR+/PV+ neurons was approximately 2–3:1 compared to a ratio of 3–4:1 for CR+/NADPH-d+ neurons. In contrast, the most frequently encountered interneurons in the rat striatum were those expressing PV. In rodents, all three interneurons were more abundant rostrally than caudally, but CR+ neurons displayed a particularly striking rostrocaudal decreasing gradient. In monkeys and humans, the three striatal interneurons were distributed rather uniformly rostrocaudally, but CR+ and PV+ interneurons were significantly more numerous in the caudate nucleus than in the putamen in humans. In monkeys, only PV+ neurons were more abundant in the caudate nucleus than in putamen. Overall, the density of the three striatal interneurons was much higher in monkeys than in rats and humans. These results reveal important species differences in respect to the relative density and pattern of distribution of striatal interneurons. These findings should be taken into account when evaluating the effect of neurodegenerative processes on cell densities in the human striatum or when studying animal models of the such diseases.

Phenotypical characterization of the neurons expressing the D1 and D2 dopamine receptors in the monkey striatum

The striatum is regulated by dopaminergic inputs from the substantia nigra. Several anatomical studies using in situ hybridization have demonstrated that in rodents, dopamine D1 and D2 receptors are segregated into distinct striatal efferent populations: dopamine D1 receptor into γ-aminobutyric acid (GABA)/substance P striatonigral neurons, and dopamine D2 receptor into GABA/enkephalin striatopallidal neurons. The existence of such a segregation has not been investigated in primates. Therefore, to quantify the efferent striatal GABAergic neurons in the adult Cynomolgus monkey, we detected GAD67 mRNA expression while considering that only a minority of the GABAergic population is composed of interneurons. To characterize the peptidergic phenotype of the neurons expressing dopamine D1 or D2 receptors, we examined the mRNA coding for these receptors in the striatum at the cellular level using single- and double in situ hybridization with digoxigenin and 35S ribonucleotide probes. Double in situ hybridization demonstrated a high coexpression of dopamine D1 receptor and substance P mRNAs (91–99%) as well as dopamine D2 receptor and preproenkephalin A mRNAs (96–99%) in medium-sized neurons throughout the nucleus caudatus, putamen, and nucleus accumbens. Only a small subpopulation (2–5%) of the neurons that contained dopamine D1 receptor mRNA also expressed dopamine D2 receptor mRNA in all regions. Large-sized neurons known to be cholinergic expressed D2R mRNA. However, within the nucleus basalis of Meynert, the large cholinergic neurons expressed D2R mRNA, but the neurons producing enkephalin expressed neither D1R nor D2R mRNA. These results demonstrate that the striatal organizational pattern of D1 and D2 receptor segregation in distinct neuronal populations described in rodent also exists in primate. J. Comp. Neurol. 418:22–32, 2000. © 2000 Wiley-Liss, Inc.

Phenotypical characterization of the neurons expressing the D1 and D2 dopamine receptors in the monkey striatum

The striatum is regulated by dopaminergic inputs from the substantia nigra. Several anatomical studies using in situ hybridization have demonstrated that in rodents, dopamine D1 and D2 receptors are segregated into distinct striatal efferent populations: dopamine D1 receptor into gamma-aminobutyric acid (GABA)/substance P striatonigral neurons, and dopamine D2 receptor into GABA/enkephalin striatopallidal neurons. The existence of such a segregation has not been investigated in primates. Therefore, to quantify the efferent striatal GABAergic neurons in the adult Cynomolgus monkey, we detected GAD67 mRNA expression while considering that only a minority of the GABAergic population is composed of interneurons. To characterize the peptidergic phenotype of the neurons expressing dopamine D1 or D2 receptors, we examined the mRNA coding for these receptors in the striatum at the cellular level using single- and double in situ hybridization with digoxigenin and 35S ribonucleotide probes. Double in situ hybridization demonstrated a high coexpression of dopamine D1 receptor and substance P mRNAs (91-99%) as well as dopamine D2 receptor and preproenkephalin A mRNAs (96-99%) in medium-sized neurons throughout the nucleus caudatus, putamen, and nucleus accumbens. Only a small subpopulation (2-5%) of the neurons that contained dopamine D1 receptor mRNA also expressed dopamine D2 receptor mRNA in all regions. Large-sized neurons known to be cholinergic expressed D2R mRNA. However, within the nucleus basalis of Meynert, the large cholinergic neurons expressed D2R mRNA, but the neurons producing enkephalin expressed neither D1R nor D2R mRNA. These results demonstrate that the striatal organizational pattern of D1 and D2 receptor segregation in distinct neuronal populations described in rodent also exists in primate.

Mapping of 5-HT2A receptors and their mRNA in monkey brain: [3H]MDL100,907 autoradiography and in situ hybridization studies.

The anatomic distribution of serotonin 5-HT2A receptors visualized with [3H]MDL100,907 and of their mRNA detected by in situ hybridization were studied in monkey brain. Both autoradiographic patterns of signal showed heterogeneous distributions and were in general in good agreement in the majority of brain regions. In most neocortical areas, [3H]MDL100,907 presented a four-banded pattern with layers I and III-IV more intensely labeled and layers II and V-VI showing weaker labeling. 5-HT2A receptor mRNA was detected in layers III and IV, and in some cases also in layers II and V. In intra- and extra-calcarine areas of striate cortex a five-banded pattern was distinguished, with layers III and IVc-V showing the highest densities of [3H]MDL100,907 labeling. These two areas showed the highest neocortical hybridization signal. An unexpected finding was the presence of low densities of [3H]MDL100,907 labeling and 5-HT2A receptor mRNA in choroid plexus. Comparison of the distribution of [3H]MDL100,907 and [3H]ketanserin binding sites in monkey brain regions with high nonspecific [3H]ketanserin binding (caudate, putamen, substantia nigra, inferior olive) revealed specific binding of [3H]MDL100,907 with very low nonspecific binding. Some differences were noted between the distribution of [3H]MDL100,907-labeled 5-HT2A receptors in monkey brain and the previously reported distribution of these receptors in human brain: absence of striosome labeling in monkey striatum and different patterns of neocortical labeling. The present results provide the first detailed comparison of 5-HT2A receptor and mRNA distribution in primate brain. The observed species differences in 5-HT2A receptor distribution should be considered when extrapolating results among different species.

Prefrontal cortical projections to the striatum in macaque monkeys: evidence for an organization related to prefrontal networks.

The organization of projections from the prefrontal cortex (PFC) to the striatum in relation to previously defined "orbital" and "medial" networks within the PFC were studied in monkeys using anterograde and retrograde tracing techniques. The results indicate that the orbital and medial networks connect to different striatal regions. The ventromedial striatum (the medial caudate nucleus, accumbens nucleus, and ventral putamen) receives input predominantly from the medial PFC (mPFC) and orbital areas 12o, Iai, and 13a, which constitute the "medial" network. More specifically, caudal medial areas 32, 25, and 14r project to the medial edge of the caudate nucleus, accumbens nucleus, and ventromedial putamen, whereas rostral areas 10o, 10m, and 11m are restricted to the medial edge of the caudate. Projections from orbital areas 12o, 13a, and Iai extend more laterally into the lateral accumbens and the ventral putamen. Area 24 gives rise to a divided pattern of projections, including fibers to the ventromedial striatum, apparently from area 24b, and fibers to the dorsolateral striatum, apparently from area 24c. Other areas of orbital cortex (11l, 12m, 12l, 13m, 13l, Ial, and Iam) that constitute the "orbital" network project primarily to the central part of the rostral striatum. This region includes the central and lateral parts of the caudate nucleus, and the ventromedial putamen, on either side of the internal capsule. The results support the subdivision of the orbital and medial PFC into "medial" and "orbital" networks and suggest that the prefrontostriatal projections reflect the functional organization of the PFC rather than topographic location.