3H]vesamicol binding in brain: autoradiographic distribution, pharmacology, and effects of cholinergic lesions

An autoradiographic analysis of high-affinity binding sites for the vesicular acetylcholine transport blocker [3H]vesamicol (2-(4-phenylpiperidino) cyclohexanol; AH 5183) was conducted in rat brain. [3H]Vesamicol binding was displaced 52-99% by DPPN [( 2,3,4,8]-decahydro-3-(4-phenyl-1-piperidinyl)-2-napthalenol) (IC50 = 14 nM) and by ketanserin (500 nM), haloperidol (43 nM), and vesamicol analogs, but not by drugs selective for adenosine, adrenergic, amino acid, calcium channel, monoaminergic, opioid, PCP, sigma, or several other receptor classes. [3H]Vesamicol binding was most concentrated in the interpeduncular nucleus and fifth and seventh cranial nerve nuclei. Moderate binding was found in the lateral caudate-putamen, medial nucleus accumbens, olfactory tubercle, vertical and horizontal diagonal bands of Broca, and basolateral amygdala. The distribution of [3H]vesamicol binding was similar to distributions of acetylcholine (r = 0.88), acetylcholine esterase (r = 0.97), choline acetyltransferase (ChAT) (r = 0.97), and [3H]hemicholinium-3 binding sites (r = 0.95-0.99). Lower correlations were obtained between [3H]vesamicol and muscarinic receptor densities (r = 0.50-0.70). Few exceptions to the match between binding and cholinergic neuronal markers were found, e.g., the molecular layer of the cerebellum and the thalamus. Lesions of cholinergic neuronal projections to the neocortex or hippocampus reduced [3H]vesamicol binding in each of these regions, but to a lesser extent than reductions in ChAT. [3H]Vesamicol binding sites appear to be anatomically associated with brain cholinergic neurons, a locus that is consistent with the control by this site of vesicular acetylcholine uptake.     

Hemicholinium-3 binding sites in rat brain: a quantitative autoradiographic study

Quantitative in vitro autoradiography was used to study the distribution of [3H]hemicholinium-3 ([3H]HC-3) binding sites in the rat brain. Regional concentrations of HC-3 binding sites were corrected for regional tissue quenching of tritium in a number of brain structures. Specific binding of 10 nM [3H]HC-3 was highest in the interpeduncular nucleus, followed by the caudate-putamen, olfactory tubercle, amygdala, and the medial and lateral habenulae. There was a high positive correlation between regional HC-3 binding and choline acetyltransferase activity in rat brain; however, a novel pattern of the distribution of cholinergic terminals in the subnuclei of the interpeduncular nucleus was discovered. The apparent Kd in the 1-5 nM range and the pharmacological specificity of the HC-3 binding site agreed with data for choline uptake and for the HC-3 binding site as determined in membrane preparations. HC-3 autoradiography appears to be a useful anatomical marker for cholinergic terminals.     

High-affinity choline uptake carrier in Alzheimer''s disease: implications for the cholinergic hypothesis of dementia

We examined the density and the state of affinity of [3H]hemicholinium-3 ([3H]HC-3) binding sites, a marker of the presynaptic high-affinity choline uptake (HACU) carrier, in 4 representative regions of 13 postmortem Alzheimer's disease (AD) brains, as well as in 12 matched control brains. Significant reductions in the densities of [3H]HC-3 binding sites were found both in frontal cortex (-44.7%) and hippocampus (-36.5%) of AD brains in comparison to controls. On the other hand the densities of [3H]HC-3 binding sites in AD brains in caudate-putamen and cerebellar cortex showed no significant differences when compared to controls. No significant change in the state of affinity of these sites could be observed in the saturation assays carried out in hippocampus and frontal cortex. Our findings concur with the reported data by using other presynaptic cholinergic markers in AD and confirm that some degree of cholinergic degeneration, highly specific for the basal forebrain neurons, occurs in AD. However, these results, obtained in a group of AD brains belonging to severely demented patients, do not show a dramatic loss of the HACU in many AD brains. Although this fact could be due to the existence of a compensatory mechanism, our results probably suggest that dementia in AD cannot be explained only by the loss of neocortical cholinergic presynaptic terminals arising from the basal forebrain and also may clarify as to why the acetylcholine precursors or the muscarinic agonists are not effective in AD dementia.     

MKC-231, a choline uptake enhancer: (3) mode of action of MKC-231 in the enhancement of high-affinity choline uptake

MKC-231, a putative cholinergic activity, is reported to improve learning and memory impaired in AF64A-treated animals. MKC-231 enhances high-affinity choline uptake (HACU) known as the rate-limiting step of acetylcholine (ACh) synthesis. We investigated the mode of action (MOA) of HACU enhancement by MKC-231. Intracerebroventricular (i.c.v.) injections of AF64A (3 nmol/brain) resulted in significant HACU reduction in hippocampal synaptosomes. Treatment with MKC-231 increased Vmax of HACU and Bmax of [3H]-HC-3 binding 1.6 and 1.7-fold, respectively. In studies of [3H]-MKC-231 binding and Biacore analysis, MKC-231 showed noticeable affinity for cloned high-affinity choline transporters (CHT1). The present study suggests that MKC-231 directly affects trafficking of CHT1 and increases the numbers of transporter, working for HACU, at the synaptic membrane.     

Quantitative distribution of muscarinic receptors and choline acetyltransferase in rat medulla: examination of transmitter-receptor mismatch

Recent reports have identified discrepancies between the anatomical distribution of transmitters and their receptors, a phenomenon known as transmitter-receptor mismatch. However, quantitative determinations of transmitter activity and receptor density in individual brain regions have not been conducted in parallel. We therefore sought to determine quantitatively the relationship between muscarinic acetylcholine receptor density and the density of cholinergic innervation as reflected by activity of the biosynthetic enzyme for acetylcholine, choline acetyltransferase (ChAT). To assure sampling of equivalent regions using the two methods, an 'electronic micropunch' technique was developed to allow measurement of [3H]quinuclidinyl benzilate ([3H]QNB) binding within the corresponding cylinders of tissue obtained by the micropunch cannula. Nineteen regions of the rat medulla (1 mm diameter, 1 mm height) were studied. The micropunch region containing the gracile nucleus, the area postrema and the choroid plexus of the fourth ventricle contained the highest ChAT activity, but exhibited little [3H]QNB binding to muscarinic receptors. However, among the remaining 18 regions a strong correlation was obtained between uncorrected muscarinic receptor density and ChAT activity within each micropunched region (r = 0.89, n = 18). Correction for autoradiographic efficiency weakened the overall relationship between receptor density and ChAT activity (r = 0.58, n = 18). This was due to a relatively high density of receptors associated with fiber tract regions containing low ChAT activity. The presence of receptors within white matter is ordinarily obscured by high tritium quenching. This is consistent with the hypothesis that a portion of muscarinic receptors are located extrasynaptically and may be present within axons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantitative light microscopic autoradiography of [3H]hemicholinium-3 binding sites in the rat central nervous system: a novel biochemical marker for mapping the distribution of cholinergic nerve terminals

The distribution of specific [3H]hemicholinium-3 ( [3H]HC-3) binding sites sites throughout the rat forebrain was studied by means of quantitative light microscopic autoradiography. Tissue sections were labeled with 2.5 nM [3H]HC-3, apposed to tritium-sensitive film for 2 months and analyzed by computer-assisted densitometry. Regions of intense [3H]HC-3 labeling include the caudate-putamen, nucleus accumbens, olfactory tubercle, amygdala, habenula and the granule cell layer of the dentate gyrus. Little or no specific binding was detected in the corpus callosum, a white matter region. This distribution of specific [3H]HC-3 binding sites is compatible with a selective labeling of central cholinergic nerve terminals.     

Biochemical evidence for cholinergic innervation of intracerebral blood vessels

Muscarinic cholinergic receptor sites were detected with [3H]quinuclidinylbenzilate (QNB) binding techniques in two fractions of bovine intracerebral vessels; one of the fractions contained primarily small arteries and veins with some attached capillaries, and the other one was highly enriched in capillaries. The amounts of binding were similar in equivalent vascular fractions isolated from cerebral cortex, caudate nucleus and cerebellar cortex in spite of large differences among the 3 regions in [3H]QNB binding to brain tissue. The different distribution of muscarinic receptors in brain tissue and blood vessels argues against the possibility that the receptors represent a contamination of the vascular fractions by brain parenchyma. Cerebral endothelial cells, which were isolated by treating capillaries with collagenase, bound [3H]QNB to the same extent as did cerebral capillaries. This is consistent with an endothelial localization of capillary muscarinic receptors. Choline acetyltransferase (ChAT) activity, a marker for cholinergic neurons, also was present in the vascular preparations. Within each brain region, ChAT activities in capillaries and larger vessels were similar, but significant regional differences were found for vascular ChAT activity, with the highest values in the caudate. Isolated endothelial cells contained significantly lower levels of ChAT activity than intact capillaries, suggesting a periendothelial location of the enzyme, as would also be the case for attached nerve terminals. The presence of [3H]QNB binding sites and ChAT activity in intracerebral blood vessels is consistent with an innervation of the cerebral vasculature by a cholinergic system that may regulate cerebral blood flow and capillary permeability.     

Decreased [H]hemicholinium binding to high-affinity choline uptake sites in aged rat brain

The binding of [³H]hemicholinium ([³H]HCh-3) to sodium-dependent high-affinity choline uptake sites provides a useful neuroanatomical and functional marker of the cholinergic system. We examined the autoradiographic distribution of [³H]HCh-3 binding sites in the forebrain of young (4–6 months) and old (32 months) rats. There was a widespread reduction of [³H]HCh-3 binding site density in the aged rat brain. This loss presented regional differences with maximal reduction in the medial and posterior striatum (55%) and in the dentate gyrus (47%), in limbic areas such as basolateral amygdala, tubercle olfactorium and piriform cortex the autoradiographic signal was about 25–30% lower. In aged hippocampus and cerebral cortex the density of [³H]HCh-3 binding sites was about 40% lower, the difference between young and senescent animals being less evident in the medial septum and basal nucleus. No significant alterations were observed in interpeduncular nucleus from old rats. These data are in agreement with the functional results obtained by measuring other cholinergic parameters in the aged rat and confirm the vulnerability of cholinergic system during aging     

Synthesis, release and receptor binding of acetylcholine in the C1 area of the rostral ventrolateral medulla: contributions in regulating arterial pressure

This study sought to determine whether release of acetylcholine (ACh) within the C1 area of nucleus reticularis rostroventrolateralis (RVL) contributes to the tonic maintenance of arterial pressure (AP) in the rat. The activity of choline acetyltransferase (ChAT), the biosynthetic enzyme for ACh, varied 5.5-fold in micropunches of the 6 medullary regions examined. ChAT activity in the C1 area (179 +/- 35 nmol [14C]ACh formed/mg protein/60 min; n = 4) was intermediate between that of the hypoglossal nucleus (249 +/- 38; highest) and the pyramids (45 +/- 11; lowest) and equivalent to that found in the parietal cortex (147 +/- 15). Release of [3H]ACh from C1 area micropunches was increased by raising extracellular K+ concentrations (5-55 mM) and was entirely Ca2(+)-dependent. Muscarinic receptor binding density was assessed using [3H]quinuclidinyl benzylate ([3H]QNB) as ligand and a recently developed 'electronic micropunch' technique which allows measurement of quench-corrected [3H]QNB binding within corresponding cylinders of tissue obtained by the mechanical micropunch cannula. [3H]QNB binding density varied 2.6-fold: lateral reticular nucleus pars lateralis greater than C1 area greater than nucleus ambiguus = hypoglossal nucleus = pyramid = oral spinal trigeminal nucleus. In urethane-anesthetized rats, inhibition of ACh synthesis by hemicholinium-3 (HC-3, 3 nmol/50 nl), or blockade of muscarinic receptors by scopolamine (SCOP, 3 nmol/50 nl), reduced resting mean AP by 18-24 mm Hg following bilateral microinjection into the C1 area. These concentrations of HC-3 and SCOP were sufficient to attenuate by 70-80% the increase in local cholinergic neurotransmission elicited by the cholinesterase inhibitor physostigmine given systemically. High concentrations of SCOP (30-150 nmol/50 nl) lowered AP by 46-60 mm Hg. Similarly, bilateral microinjections of GABA (10 nmol/50 nl) into the C1 area markedly reduced mean AP by 51 +/- 6 mm Hg to levels normally found after transection of the spinal cord. Thus, a substantial portion of tonic sympathetic activity may be driven by activation of muscarinic receptors in the C1 area. In the spontaneously hypertensive rat (SHR), a genetic model of hypertension, neither spontaneous nor K(+)-evoked release of [3H]ACh from the C1 area differed from that of normotensive Wistar-Kyoto rats (WKY).(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantitative light microscopic autoradiography of [H]hemicholinium-3 binding sites in the rat central nervous system: a novel biochemical marker for mapping the distribution of cholinergic nerve terminals

The distribution of specific [³H]hemicholinium-3 ([³H]HC-3) binding sites throughout the rat forebrain was studied by means of quantitative light microscopic autoradiography. Tissue sections were labeled with 2.5 nM[³H]HC-3, apposed to tritium-sensitive film for 2 months and analyzed by computer-assisted densitometry. Regions of intense [³H]HC-3 labeling include the caudate-putamen, nucleus accumbens, olfactory tubercle, amygdala, habenula and the granule cell layer of the dentate gyrus. Little or no specific binding was detected in the corpus callosum, a white matter region. This distribution of specific [³H]HC-3 binding sites is compatible with a selective labeling of central cholinergic nerve terminals.     

Hemicholinium-3 binding sites in subnuclei of the rat interpeduncular nucleus: Quantitative in vitro autoradiography

The interpeduncular nucleus (IPN) receives dense cholinergic input from the medial habenulae (MH) via the fasciculus retroflexus (FR). This projection is known to terminate in the rostral, central and intermediate subnuclei. Correspondingly, the concentration of hemicholinium-3 (HC-3) binding sites in these subnuclei was equal to or greater than that reported in any other brain areas. Moderate values in the distal FR and in the lateral subnuclei indicate that choline uptake sites are located on nonterminal portions of MH afferent axons as well. Possible relationships of HC-3 binding to the unusual metabolic properties of FR and IPN, and to the distribution of choline acetyltransferase-containing axons and terminals in FR and IPN are suggested.     

Small pial vessels, but not choroid plexus, exhibit specific biochemical correlates of functional cholinergic innervation

In an attempt to provide the biochemical foundations for a putative cholinergic innervation of small pial vessels and choroid plexus, we have assessed their ability to specifically accumulate choline, synthesize and release acetylcholine (ACh) in response to depolarization. Our results show that both small pial vessels and choroid plexus avidly accumulate choline via a sodium-dependent mechanism which could be inhibited by hemicholinium-3 (IC50 in pial vessels = 47.8 microM). Light microscopic examination of radioautographs from vessels incubated with [3H]choline revealed two distinct sites of accumulation in the vessel wall. One site probably corresponded to nerve terminals and the other was closely associated with the endothelial cells. In small pial vessels, a major proportion (60%-70%) of the choline acetyltransferase (ChAT) activity could be inhibited by 4-naphthylvinylpyridine (4-NVP), a potent inhibitor of neuronal ChAT; and, following either K+ or veratridine depolarization, a Ca2(+)-dependent release of authentic [3H]ACh could be measured. In contrast, the choroid plexus exhibited a rather low ChAT activity which was not inhibited by 4-NVP and no release of ACh could be detected in this tissue following depolarization. Altogether, the results of the present study show that (1) small pial vessels exhibit all the most selective biochemical markers that are characteristic of cholinergic nerves; (2) [3H]choline in pial vessels can be accumulated in non-neuronal elements which probably correspond to the endothelial cells; and (3) the choroid plexus failed to exhibit convincing biochemical markers that would attest in favor of a functional cholinergic innervation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modeling adolescent nicotine exposure: effects on cholinergic systems in rat brain regions

Smoking among teenagers is increasing and the initiation of tobacco use during adolescence is associated with subsequently higher cigarette consumption and lower rates of quitting. Few animal studies have addressed whether adolescent nicotine exposure exerts unique or lasting effects on brain structure or function. Initial investigations with a rat model of adolescent nicotine exposure have demonstrated that the vulnerable developmental period for nicotine-induced brain cell damage extends into adolescence. In the current study, we examined the effect of nicotine on cholinergic systems in male and female adolescent rats with an infusion paradigm designed to match the plasma levels found in human smokers or in users of the transdermal nicotine patch. Choline acetyltransferase activity (ChAT) and [3H]hemicholinium-3 binding (HC-3) were monitored; ChAT is a static marker that closely reflects the density of cholinergic innervation, whereas HC-3 binding, which labels the presynaptic high-affinity choline transporter, is responsive additionally to nerve impulse activity. Measurements were carried out in the midbrain, the region most closely involved in reward and addiction pathways, as well as in the cerebral cortex and hippocampus. During nicotine treatment and for 1 month after the termination of treatment, ChAT activity was reduced significantly in the midbrain but not in the other regions. HC-3 binding showed a substantial increase during the course of nicotine treatment and again, the effect was limited to the midbrain. Midbrain values returned to normal immediately after the cessation of nicotine exposure and then showed a subsequent, transient suppression of activity. Although the cerebral cortex showed little or no change in HC-3 binding during or after nicotine administration, activity was reduced persistently in the hippocampus. The regionally-selective effects of adolescent nicotine treatment on cholinergic systems support the concept that adolescence is a vulnerable developmental period for ultimate effects on behavior.     

Persistent cholinergic presynaptic deficits after neonatal chlorpyrifos exposure

The commonly-used organophosphate insecticide, chlorpyrifos (CPF), impairs brain cell development, axonogenesis and synaptogenesis. In the current study, we administered CPF to neonatal rats on postnatal (PN) days 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), treatments that were devoid of overt toxicity. We then examined two cholinergic synaptic markers, choline acetyltransferase activity (ChAT) and [3H]hemicholinium-3 binding (HC-3) in the hippocampus, midbrain, striatum, brainstem and cerebral cortex in the juvenile (PN30) and young adult (PN60). Across all brain regions, CPF exposure evoked significant reductions in both markers, with larger effects on HC-3 binding, which is responsive to neuronal impulse activity, than on ChAT, a constitutive marker. Superimposed on the deficits, there were gender-selective effects and distinct regional disparities in the critical exposure period for vulnerability. In the hippocampus, either the early or late treatment regimen evoked decreases in ChAT but the early regimen elicited a much larger decrease in HC-3; effects persisted into adulthood. In the midbrain, CPF administration on PN1-4 elicited deficits similar to those seen in the hippocampus; however, exposure on PN11-14 elicited changes preferentially in females. Gender selectivity was also apparent in the striatum, in this case reflecting deficits in females after CPF treatment on PN1-4. In contrast, the effects of CPF on the brainstem were relatively more robust in males; effects in the cerebral cortex were less notable than in other regions. These results indicate that neonatal CPF exposure produces widespread deficiencies in cholinergic synaptic function that persist into adulthood. The effects are likely to contribute to gender-selective alterations in behavioral performance that persist or emerge long after the termination of exposure and well after the restoration of cholinesterase activity.     

Development of high-affinity choline transport sites in rat forebrain: a quantitative autoradiography study with [3H]hemicholinium-3.

The development of cholinergic terminals in rat brain has been quantitatively analyzed by [3H]hemicholinium-3 autoradiography. [3H]Hemicholinium-3 binds to high affinity choline transport sites, a specific marker for cholinergic neurons. In neonatal animals, kinetic and pharmacologic binding characteristics and regional distribution of [3H]hemicholinium-3 sites are consistent with specific cholinergic localization, as in the adult. The distribution of cholinergic terminals is described in the adult rat brain and during development, including heterogeneity of binding within several regions such as the striatum, nucleus accumbens, olfactory tubercle, cortex, and hippocampus. Early development and maturation vary greatly between brain regions. At embryonic day E18 and day 0, specific binding density is high only in the medial habenula. Development occurs primarily during the postnatal period in most brain regions examined. Many brain regions exhibit a lull in development between days 5 and 10, although the rate of development is highly region specific. Specific binding increases 2-12-fold between day 5 and adult animals, with adult density being achieved anywhere from day 15 to after day 21. The ontogeny of [3H]hemicholinium-3 binding sites generally occurs in a rostral to caudal direction. In the striatal body the characteristic lateral to medial gradient of binding site density is apparent by day 5, and development is more rapid in the lateral striatum. Patches of dense [3H]hemicholinium-3 binding coincident with acetylcholinesterase are observed on day 5 in the caudal striatum. The various patterns of cholinergic terminal development suggest that factors regulating cholinergic development are regional and complex.     

Direct autoradiographic determination of M1 and M2 muscarinic acetylcholine receptor distribution in the rat brain: Relation to cholinergic nuclei and projections

The autoradiographic distributions of receptors with high affinity for [3H]oxotremorine-M (the M2 receptor) and [3H]pirenzepine (the M1 receptor) were studied in the rat brain. M1 receptors were seen in highest density only in telencephalic structures: cerebral cortex (layers I-II), hippocampus, dentate gyrus, medial and basolateral amygdala, nucleus accumbens and caudate/putamen. M2 receptors were detected throughout the brain, with highest levels observed in cerebral cortical layers III and V, forebrain cholinergic nuclei, caudate/putamen, various thalamic areas, inferior and superior colliculus, interpeduncular and pontine nuclei, brainstem cholinergic nuclei and cervical spinal cord regions. M2 receptors were found to be good markers for cholinergic cell groups and the majority of cholinergic projection areas, whereas M1 receptors were only found in a large sub-group of telencephalic cholinergic projection areas, and the pattern of distribution of receptors in these areas differed from that of M2 receptors. Scatchard analysis of [3H]oxotremorine-M binding to inferior collicular slices revealed one site with a dissociation constant (Kd) of 1.9 nM and a receptor density (Bmax) of 1.4 pmol/mg protein. Our data support the hypothesis that M1 and M2 receptors are physically distinct sub-types of the muscarinic acetylcholine receptor.     

Parameters of cholinergic neurotransmission in the thalamus in Parkinson's disease and Alzheimer's disease

Loss of cholinergic cells in the basal forebrain is associated with commensurate reductions in cortical acetylcholine-related enzyme activities in both Alzheimer's disease (AD) and Parkinson's disease (PD). Nerve cell loss from the cholinergic pontine tegmental nuclei also occurs. As the latter nuclei project to the diencephalon, we used frozen tissue from 5 controls, 5 PD and 5 AD cases to study the distribution of ChAT, AChE and [3H]nicotine binding in the thalamus and subthalamic nucleus. The anterior nuclear group and the mediodorsal nucleus showed high activities of ChAT and AChE together with relatively high levels of [3H]nicotine binding. The centromedian nucleus and subthalamic nucleus contained equally high levels of ChAT but negligible levels of [3H]nicotine binding. There were no significant changes in the levels of ChAT, AChE and nicotine binding in the PD and AD groups indicating that involvement of the pedunculopontine tegmental nucleus is likely to be a secondary retrograde phenomenon rather than part of a systematic cholinergic fibre degeneration.     

In vitro measurements of cholinergic activity in brain regions of hibernating ground squirrels

High affinity choline uptake (HACU) and choline acetyltransferase (ChAT) activity were measured in synaptosomal P2 fractions from four brain regions in a mammalian hibernator, the golden-mantled ground squirrel. The 14CO2 evolution from [6-14C]glucose was also measured. Comparisons were made across the euthermic (not hibernating) and hibernation state in synaptosomes from cortex (CTX), preoptic area and hypothalamus (POA/HYP), olfactory apparatus (OA), and hippocampus (HPC). HACU was significantly increased in the CTX, from hibernating ground squirrels compared to euthermic animals. ChAT activity was significantly increased in the CTX and OA from hibernating animals. No change in either cholinergic marker was evident for the POA/HYP and HPC. The evolution of 14CO2 from [6-14C]glucose was generally, though not significantly, higher for synaptosomes from euthermic animals compared to hibernating animals. The results are discussed with reference to the involvement of cholinergic mechanisms in the control of hibernation.     

Compartment-specific changes in the density of choline and dopamine uptake sites and muscarinic and dopaminergic receptors during the development of the baboon striatum: a quantitative receptor autoradiographic study

In the fetal and young primate neostriatum, cholinergic and dopaminergic markers show patches of high density surrounded by a lower-density matrix. In the adult, the same markers display the opposite pattern, a lower density in striosomes, surrounded by a higher-density matrix. In order to understand the developmental sequences leading to the adult compartmental organization of the primate neostriatum, a quantitative technique was used to study the ontogeny of pre- and postsynaptic components of cholinergic and dopaminergic neurons in baboon caudate nucleus and putamen. The development of specific uptake mechanisms for choline and dopamine and receptors was studied by means of quantitative autoradiography of the specific binding of [3H]-hemicholinium-3 [( 3H]-HC3) and [3H]-mazindol [( 3H]-MAZ) to the choline and dopamine uptake systems, respectively. [3H]-pirenzepine [( 3H]-PIR) was used to label M1 muscarinic receptors and [3H]-spiroperidol [( 3H]-SPI) was used to label striatal dopamine D2 receptors. Serial sections were used for each ligand to determine the precise anatomical relationships between the binding patterns of the different markers. Our aim was to determine whether the adult striosomal distribution of the binding sites studied was due to 1) a selective decrease in patch/striosomal binding density or 2) a selective increase in matrix binding density. Our studies show that a postnatal decrease in the density of [3H]-HC3 sites in the patch/striosomes and an increase in the matrix density of [3H]-MAZ sites are the primary, but not the sole, changes in the compartmental distribution of these sites leading to the adult striosomal organization of the striatal cholinergic and dopaminergic innervation. D2 receptors follow the general developmental pattern of [3H]-MAZ and [3H]-HC3, changing their density of distribution in both compartments during the developmental period examined. In addition, M1 muscarinic receptors already display their adult pattern in the newborn baboon striatum, and therefore represent one of the first neurochemical makers to adopt its mature organization.