Regional and laminar distribution of the dopamine and serotonin innervation in the macaque cerebral cortex: a radioautographic study

Cholecystokinin- and dopamine-containing mesencephalic neurons provide distinct projections to monkey prefrontal cortex

Retrograde transport and immunohistochemical techniques were utilized to determine if cholecystokinin (CCK)-containing neurons of the primate ventral mesencephalon project to prefrontal cortex, and to examine what relation the CCK innervation of prefrontal cortex bears to the dopaminergic projection to this region. Following injections of Fast blue into monkey prefrontal cortex, retrogradely labeled, CCK-positive neurons were observed predominantly in rostromedial portions of the ventral mesencephalon; these CCK-containing projection neurons were not immunoreactive for tyrosine hydroxylase. Furthermore, dual-labeling studies in the prefrontal cortex revealed that CCK and tyrosine hydroxylase were present in separate populations of axons. These results demonstrate that the CCK innervation of monkey prefrontal cortex arises from both intrinsic and extrinsic sources; in contrast to the rat, the extrinsic CCK innervation of monkey prefrontal cortex is distinct from the dopaminergic mesocortical projection.

Postnatal development of somatostatin-containing neurons in the visual cortex of normal and dark-reared rats

The distribution of somatostatin (SRIF)-immunoreactive neurons in the visual cortical areas 17, 18 and 18a of Wistar rats from birth to adulthood was followed in both normal and dark-reared animals. The SRIF neurons show difference in distribution amongst the three cortical areas studied as early as the first postnatal week. Area 17 was distinguished by fewer SRIF cells in the upper layers (I-III), which results in a lower overall density. The SRIF neurons in all areas appeared to increase in numbers up to about 3 weeks and then decline dramatically to adult levels, which were 14-19% of the peak levels. Although this decline was still obvious, it moderated to 25-31% in dark-reared animals. The greatest effect was seen in area 18 where, at 60 days of age, there were twice as many SRIF cells in dark-reared as in normal controls. It is suggested that, under conditions of dark rearing, the overall pattern of development of SRIF neurons, being uninfluenced by extrinsic factors, reveals the cells' genetic potential.

Localization of multiple dopamine receptor subtype mRNAs in human and monkey motor cortex and striatum

Dopamine plays a critical role in motor and cognitive function through actions mediated by specific receptors, multiple subtypes of which have recently been identified. The distribution of mRNAs encoding D1, D2 and D5 receptors in the motor cortex of humans and in the motor cortex and striatum of macaque monkeys was examined using in situ hybridization. In motor cortices from both primate species, hybridization to each receptor probe resulted in numerous labeled cells throughout layers II-VI. In contrast to neocortex, in monkey striatum only the D1 and D2 receptor probes showed significant hybridization. Thus, not only does primate neocortex possess a broader representation of the dopamine receptor subtype mRNAs examined in comparison with striatum, but the unexpected presence and widespread distribution of D2 and D5 receptor mRNAs in cortex suggests that, along with D1 receptors, D2 and D5 receptors play a crucial role in the dopaminergic modulation of cognition and motor behavior, and in dopamine dysfunction associated with neuropsychiatric disorders.

Differential modulation by dopamine of responses evoked by excitatory amino acids in human cortex

The responses of human neocortical neurons to iontophoretic application of excitatory amino acids and their modulation by dopamine (DA) were studied in vitro. Brain slices were obtained from children undergoing surgery for intractable epilepsy. Application of N-methyl-D-aspartate (NMDA) to the slices induced slow depolarizations accompanied by decreased input conductances and sustained action potentials in cortical neurons. Glutamate produced rapid depolarizations and firing with few changes in input conductances. Quisqualate also induced depolarization and firing, but input conductances increased during the rising phase of the membrane depolarization. Iontophoretic application of DA alone produced no change in membrane potential or input conductance. However, when DA was applied in conjunction with the excitatory amino acids, it produced contrasting effects. With either bath application of DA or when iontophoresis of DA preceded application of NMDA, the amplitude of the membrane depolarizations and the number of action potentials were increased, whereas the latency of these responses decreased. In contrast, DA decreased the amplitude of the depolarizations and the number of action potentials evoked by glutamate or quisqualate. The fact that DA affects responses to NMDA and glutamate or quisqualate in opposite directions is of considerable importance to the understanding of cellular mechanisms of neuromodulation and the role of DA in cognitive processing and in epilepsy.

Light and electron microscopic characterization of dopamine-immunoreactive axons in human cerebral cortex

The distribution and synaptic connections of dopamine axons were studied by light and electron microscopy in human cerebral cortex. For this purpose, dopamine immunoreactivity was characterized in apparently normal anteriolateral temporal cortex, which was removed to gain access to the medial temporal lobe during tumor excision or treatment of epilepsy. Nissl sections showed this to be granular neocortex. Dopamine fibers were distributed throughout this cortex, although there were relatively more fibers in layers I-II and in layers V-VIa, compared to layers III-IV and VIb, resulting in a bilaminar pattern of labeling. In all layers, fibers were seen to form numerous varicosities, and to vary in size from thick to very fine. Fibers were relatively straight, sparsely branched and were oriented in various planes within the cortex. However, in layer I, they often ran parallel to the pial surface. In order to analyze the functional interactions of dopamine fibers, individual cortical layers were surveyed for dopamine synapses. These were usually symmetrical (Gray's type II), although 13% of them were asymmetrical. Approximately 60% of dopamine synapses were made with dendritic spines, and 40% with dendritic shafts, and this ratio was similar in all layers. On both spines and shafts, it was common to see dopamine synapses closely apposed to an unlabeled asymmetric input, suggesting a dopamine modulation of excitatory input. Some postsynaptic dendritic shafts had features of pyramidal cells, including formation of spines. Since pyramidal cells are the major type of cortical spiny neuron, they probably represent the main target of dopamine synapses in this cortex. There were also dopamine profiles apposed to membrane densities on unlabeled axon terminals, suggesting another type of synaptic interaction. These findings provide the first documentation of dopamine synapses in the human cortex, and show that they form classical synaptic junctions. The location of these synapses on spines and distal dendrites, and their proximity to asymmetric synapses, suggest a modulatory role on excitatory input to pyramidal cells.

Senile plaques, amyloid beta-protein, and acetylcholinesterase fibres: laminar distributions in Alzheimer's disease striate cortex

The laminar distributions of senile plaques and amyloid beta-protein (A beta P) within the striate cortex of patients with Alzheimer's disease (AD) were studied with enhanced Bielschowsky (roughly equivalent to the Campbell technique) and immunohistochemical methods. The laminar distribution of acetylcholinesterase (AChE) fibres within the striate cortex of both AD patients and control patients was studied with an enzyme histochemical method. Quantification of Bielschowsky-stained plaque numbers along intersect lines drawn parallel to laminar boundaries revealed a significant aggregation of plaques at the interface of layers IVc and V. Lines drawn through layer VI intersected significantly fewer plaques than lines through other laminae. Immunoperoxidase staining for A beta P revealed a similar distribution of senile plaques, and addition, prominent, diffuse deposits of A beta P within layers I and IVc. AChE fibres were markedly depleted in the striate cortex of AD cases. In control cases, AChE fibres were, like A beta P immunoreactivity, concentrated within layer I and IVc. The results indicate that enhanced silver methods may not reveal the complete distribution of A beta P. The codistribution of A beta P-immunoreactive diffuse amyloid deposits and AChE fibres to the same cortical laminae is consistent with the possibility that these deposits may be formed from degenerating cholinergic elements. The formation of a line of senile plaques at the interface of two cortical laminae within the striate cortex, in an anatomically analogous situation to a similar line of plaques within the dentate gyrus, suggests that formation of well-defined plaques may be accelerated by the interaction of specific neuronal systems.

The anatomy of dopamine in monkey and human prefrontal cortex

This chapter reviews recent evidence establishing the comparable organization of dopamine afferents and dopaminergic receptors in the human and monkey prefrontal cortex. Light microscopy using a dopamine-specific antibody reveals that the dopamine innervation in the human prefrontal cortex exhibits a distinct bilaminar distribution with dense bands of fibers in the upper and deeper strata of the cortex, closely resembling the patterning of dopamine fibers in the monkey prefrontal cortex. Also, EM-immunohistochemistry has now revealed identical synaptic complexes both in human and monkey. In both species, dopamine axons from symmetric synapses predominantly on the spines of pyramidal cells. In many cases, the same spine is apposed by an asymmetric, putatively excitatory synapse. Finally, both in human and monkey prefrontal cortex, the dopamine D1-specific ligand, 3H-SCH23390, and the D2-specific ligand, H3-raclopride, label binding sites in laminar positions which match the location of the densest dopamine innervation. These results indicate that the organization of the cortical dopamine system is essentially the same in macaque monkey and human and that the nonhuman primate is a suitable animal model for analysis of dopamine function in prefrontal cortex.

The catecholaminergic innervation of primate prefrontal cortex

This paper reviews recent studies indicating that the marked expansion and differentiation of the prefrontal cortex in primates is associated with an increase in the complexity of both the regional density and laminar distribution of catecholaminergic afferents. The innervation patterns of these systems in monkey prefrontal cortex appear to accurately predict those in human prefrontal cortex, suggesting that studies in non-human primates may be reasonably used to generate hypotheses about the nature of involvement of these systems in disorders such as schizophrenia. In addition, the distinctive developmental pattern of the dopaminergic innervation of primate prefrontal cortex and the possibility of an intrinsic catecholaminergic innervation of primate prefrontal cortex may reveal new avenues of investigation into the roles of prefrontal catecholamines in both normal and pathological states.

L-6-[18F]fluoro-dopa metabolism in monkeys and humans: biochemical parameters for the formulation of tracer kinetic models with positron emission tomography

Characterization of peripheral and cerebral L-3,4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) metabolism in humans and monkeys has shown FDOPA to be an analogue of L-DOPA for the study of the dopaminergic system with positron emission tomography (PET). In human studies with carbidopa pretreatment, L-3,4-dihydroxy-6-[18F]fluoro-3-O-methylphenylalanine (3-OMFD) was the only FDOPA metabolite detected in plasma. FDOPA administration in monkeys resulted in selective accumulation of FDOPA metabolites in central dopaminergic regions, whereas 3-OMFD of peripheral origin was uniformly distributed among putamen, caudate, frontal cortex, and cerebellum. At 60 min, 3-OMFD and 6-[18F]fluorodopamine (FDA) each represented approximately 35% of the total activity, the remainder being FDOPA and FDA metabolites. These data on monkey and human FDOPA metabolism provide the basis for the configuration of an FDOPA tracer kinetic model with PET.

Alterations of dopaminergic and noradrenergic innervations in motor cortex in Parkinson's disease

The motor areas of the cerebral cortex contain dense dopaminergic and noradrenergic innervation in humans. We looked for changes of these innervations in cases with Parkinson's disease (PD). The density of fibers immunolabeled with tyrosine hydroxylase or dopamine-beta-hydroxylase was evaluated in the primary motor, premotor, and prefrontal cortical regions in 6 cases with PD and 7 control cases. Reductions of both noradrenergic and dopaminergic cortical innervations were observed, with similar magnitudes of reduction found in the motor and prefrontal regions of the cortex. Depletion of noradrenergic innervation was diffuse, involving all cortical laminae. Depletion of dopaminergic innervation was laminar specific, with the most significant reductions in layers I and II; reductions in layers V and VI were either less marked (prefrontal cortex) or not detectable (primary motor). The results suggest the existence of two separate mesocortical dopaminergic systems in humans, with the one distributing to upper cortical layers being preferentially involved in PD.

Myelo- and cytoarchitecture of the granular frontal cortex and surrounding regions in the strepsirhine primate Galago and the anthropoid primate Macaca

As the first part of a comparative investigation of primate frontal cortex, we compared the frontal architectonic organization of Galago, a small-brained, strepsirhine (or "prosimian") primate, to that of an anthropoid primate, Macaca, by using myelin- and Nissl-stained material. We were able to distinguish many more areas in both taxa than have been recognized in most previous studies of the primate frontal lobe. In particular, we were able to subdivide many of the areas shown in the commonly cited architectonic map of Walker (J. Comp. Neurol. 73:59-86, 1940). Delineation of areas was greatly facilitated by the use of the Gallyas technique for staining myelin. The areal organization of much of frontal cortex (specifically, the premotor, orbital, and medial regions) appears to be very similar in Galago and Macaca. In these regions, we were able to recognize the same complement of areas in both taxa, with few exceptions. In the granular frontal cortex (GFC), by contrast, we were able to distinguish about twice as many areas in Macaca as in Galago. For most of the GFC areas of Galago, there are architectonically similar areas in Macaca; the areas shared by both taxa correspond mainly to the arcuate and superior areas of Macaca (i.e., the region encompassed by Walker's areas 45, 8A, and 8B). However, there are many additional, more rostral, areas in Macaca for which there are no obvious homologues in Galago. In particular, Galago lacks cortex resembling the distinctive, lightly myelinated cortex of the Macaca principal sulcus (Walker's area 46 and its subdivisions). Our results are difficult to reconcile with the view that frontal lobe organization varies little across taxa. Rather, they suggest that granular frontal cortex underwent considerable change during primate evolution, including the addition of new areas in anthropoids.

Differential laminar distribution of tyrosine hydroxylase-immunoreactive axons in infant and adult monkey prefrontal cortex

Immunohistochemical techniques were used to evaluate the laminar distribution of tyrosine hydroxylase (TH)-immunoreactive axons in area 9 of infant and adult rhesus monkey prefrontal cortex. In neonatal animals, TH-positive axons had a bilaminar location in the superficial and deep cortical layers, whereas in the adults, labeled fibers were more evenly distributed across all layers. These differences reflected the fact that fiber density in the superficial layers was over 35% greater in neonates than in adults, but in the middle cortical layers, fiber density was over 100% greater in adults than in neonates. The most striking changes in fiber distribution appeared to occur during the first few months of life. These findings may reveal differences in the role of dopamine in the regulation of prefrontal cortical function in neonatal and adult monkeys.

Further indication that distinct dopaminergic subsets project to the rat cerebral cortex: lack of colocalization with neurotensin in the superficial dopaminergic fields of the anterior cingulate, motor, retrosplenial and visual cortices

The extent of neurotensin (NT) colocalization in the different dopamine (DA) terminal fields of the rat cerebral cortex has been investigated and compared to previous data obtained in man (Gaspar et al., J. Comp. Neurol., 279 (1989) 249-271). Both innervations were revealed with single- or double-labeling immunocytochemical methods. Tyrosine hydroxylase (TH) was used as a specific marker of DA fibers after lesioning the noradrenergic system either with 6-hydroxydopamine (6-OHDA) at birth or DSP4 in adulthood. Three classes of afferents were observed which had a different regional and laminar distribution. First, a dense meshwork of finely dotted NT-positive varicosities occupied restricted areas of the limbic system: the granular retrosplenial and the deep entorhinal cortices and the subicular complex. These NT projections contained no double-labeled fibers and did not correspond to a mixed NT/TH pathway. Secondly, the mixed NT/DA projections identified previously in the prefrontal cortex (Studler et al., Neuropeptides, 11 (1988) 95-100), extended in fact rostrocaudally in layer VI of the whole cerebral cortex and formed small cluster-like groupings in layers II-III of the medial and lateral entorhinal cortex. In all these areas, the mixed NT/TH projections constituted approximately half of the DA terminals. Finally, the DA projections to the superficial layers of the anterior cingulate, motor, retrosplenial and visual cortices, were not colocalized with NT. The DA innervation of layers I-III of the rat anterior cingulate cortex displays striking similarities with that observed in the cingulate, primary motor, premotor and supplementary motor cortices in man: highest regional and laminar density of DA afferents and lack of colocalization with NT. It might thus represent a valuable model for understanding the pharmacology of the DA system besides the mixed DA/NT pathway which does not seem to have a counterpart in the human cerebral cortex. By contrast, that part of the NT innervation of the limbic system which is not colocalized with DA in rat, appears to represent the major fraction of the cortical NT innervation in man.

Cytoarchitecture of serotonin-synthesizing neurons in the pontine tegmentum of the human brain

We have employed immunohistochemical and morphometric procedures to study serotonin-synthesizing (PH8-immunoreactive) neurons in the pontine reticular formation of the adult human. PH8-immunoreactive neurons were found in three cytoarchitectural regions: the median raphe nucleus (MnR), oral pontine reticular nucleus (PnO), and supralemniscal region (group B9). On the basis of cell size, morphology, and position, it was possible to distinguish distinct subgroups within the MnR (dorsal, midline, and paramedian cell clusters) and within the PnO (dorsal and central cell clusters), whereas within the B9 there were no distinct cell clusters. We have estimated that there are approximately 125,000 PH8-immunoreactive neurons in the human pontine tegmentum; 64,400 in the MnR, 30,700 in PnO and 29,000 in B9. The large numbers of serotonin-synthesizing neurons in the human pontine tegmentum contrasts with their relative paucity in nonprimate species such as rats and cats. Nonhuman primates also have large numbers of pontine serotonergic neurons but the morphology of these neurons and their spatial arrangement is significantly different in humans. These results are discussed with respect to the possible projections and functions of these neurons in humans.

Mechanisms of action of atypical antipsychotic drugs. Implications for novel therapeutic strategies for schizophrenia

The mechanisms which contribute to the actions of atypical antipsychotic drugs, such as clozapine and the putative atypical agents remoxipride and raclopride, are reviewed. Examination of available preclinical and clinical data leads to two hypotheses concerning the mode of action of atypical antipsychotic drugs. The first hypothesis is that antagonism of the dopamine D2 receptor is both necessary and sufficient for the atypical profile, but that interaction with subtypes of the D2 receptor differentiates typical from atypical antipsychotic drugs. The second hypothesis has been previously advanced, and suggests that a relatively high ratio of serotonin 5-HT2:dopamine D2 receptor antagonism may subserve the atypical profile. It seems likely that the atypical antipsychotic drug profile may be achieved in more than one way.

D1 dopamine receptors in prefrontal cortex: involvement in working memory

The prefrontal cortex is involved in the cognitive process of working memory. Local injections of SCH23390 and SCH39166, selective antagonists of the D1 dopamine receptor, into the prefrontal cortex of rhesus monkeys induced errors and increased latency in performance on an oculomotor task that required memory-guided saccades. The deficit was dose-dependent and sensitive to the duration of the delay period. These D1 antagonists had no effect on performance in a control task requiring visually guided saccades, indicating that sensory and motor functions were unaltered. Thus, D1 dopamine receptors play a selective role in the mnemonic, predictive functions of the primate prefrontal cortex.

Quantitative autoradiography of the dopamine uptake complex in rat brain using [3H]GBR 12935: binding characteristics

The dopamine uptake complex was examined in the rat central nervous system using [3H]GBR 12935 and in vitro quantitative autoradiography to determine all binding data. [3H]GBR 12935 labels two unique binding sites, the dopamine uptake complex and a piperazine acceptor site. These two sites differ in their pharmacologic properties, anatomical distributions, densities, and response to lesions. Using appropriate binding conditions, [3H]GBR 12935 can be used to specifically label the dopamine uptake complex. [3H]GBR 12935 labeled a single binding site with characteristics of the dopamine uptake complex when mazindol (25 microM) was used as a blank. The specific binding and autoradiographic appearance of [3H]GBR 12935 to the dopamine uptake complex was improved by including trans-flupentixol (0.75 microM) to displace binding to a previously described piperazine acceptor site, recently determined to be a site on cytochrome P450IID1. Binding was saturable and reversible to the dopamine uptake complex. The equilibrium dissociation constant (1.4 +/- 0.7 nM), maximal number of binding sites (6.0 +/- 1.3 pmol/mg protein), and Hill coefficient (1.1 +/- 0.1) of [3H]GBR 12935 in rat striatum using mazindol to define non-specific binding was not significantly altered by the inclusion of trans-flupentixol (0.75 microM). Using GBR 12909 as a blank produced a greater maximal number of binding sites (8.4 +/- 2.3 pmol/mg protein), but no significant difference in the equilibrium dissociation constant (1.6 +/- 0.3 nM) or Hill coefficient (1.1 +/- 0.1). A series of drugs that bind to the dopamine uptake complex displaced [3H]GBR 12935 in a rank order consistent with other binding and behavioral studies of this complex. The rank order of these drugs was GBR 12909 greater than mazindol greater than nomifensine greater than benztropine greater than desipramine greater than amphetamine greater than dopamine; all these drugs displayed a Hill coefficient near one and were best modeled as a single site. Cocaine and WIN 35,428 (a cocaine congener) were unique in their competition for [3H]GBR 12935 binding, displaying biphasic curves, low Hill coefficients, and were best modeled as two site fits. Lesioning of the dopaminergic median forebrain bundle resulted in a dramatic loss of the dopamine uptake complex in the striatum, nucleus accumbens, olfactory tubercle, and substantia nigra. Other dopaminergic projection areas were decreased to a lesser extent. Striatal ibotenate lesions did not decrease the density of the dopamine uptake complex, despite a large decrease in the dopamine D1 receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of dopaminergic receptors in the primate cerebral cortex: quantitative autoradiographic analysis using [3H]raclopride, [3H]spiperone and [3H]SCH23390

A widespread distribution of dopamine D1 receptors in the neocortex is well recognized. However, the presence of dopamine D2 receptors in this structure has only recently been established [Martres et al. (1985) Eur. J. Pharmac. 118, 211-219; Lidow et al. (1989) Proc. natn. Acad. Sci. U.S.A. 86, 6412-6416]. In the present paper, a highly specific antagonist, [3H]raclopride, was used for autoradiographic determination of the distribution of D2 receptors in 12 cytoarchitectonic areas of the frontal, parietal, and occipital lobes of the rhesus monkey. A low density of D2-specific [3H]raclopride binding (1.5-4.0 fmol/mg tissue) was detected in all layers of all cortical areas studied. Throughout the entire cortex, the highest density of binding was consistently found in layer V. This is a unique distribution not observed so far for any other neurotransmitter receptor subtype in monkey cerebral cortex, including D1 receptor. In addition, a comparison was made of the distribution of [3H]raclopride and [3H]spiperone, which has been commonly used in previous attempts to label cortical D2 receptors. We found marked differences in the distribution of these two radioligands. In the prefrontal cortex, the pattern of [3H]spiperone binding in the presence of ketanserin resembled the combined distribution of 5-HT1C serotoninergic and alpha 2-adrenergic sites as well as D2 receptors. Thus, [3H]raclopride provides a better estimation of the D2 receptor distribution than does [3H]spiperone. The distribution of D2-specific binding of [3H]raclopride was also compared with the D1-specific binding of [3H]SCH23390 in the presence of mianserin to block labeling to 5-HT2 and 5-HT1C sites. The density of D1-specific [3H]SCH23390 binding was 10-20 times higher than that of D2-specific [3H]raclopride binding throughout the cortex. The densities of both [3H]raclopride and [3H]SCH23390 binding sites display a rostral-caudal gradient with the highest concentrations in prefrontal and the lowest concentrations in the occipital cortex. However, the binding sites of these two ligands had different laminar distributions in all areas examined. In contrast to preferential [3H]raclopride binding in layer V, a bilaminar pattern of [3H]SCH23390 labeling was observed in most cytoarchitectonic areas, with the highest concentrations in supragranular layers I, II and IIIa and infragranular layers V and VI. Whereas [3H]raclopride binding was similar in all cytoarchitectonic areas, [3H]SCH23390 exhibited some region-specific variations in the primary visual and motor cortex. The different regional and laminar distributions of D1 and D2 dopaminergic receptors indicates that they may subserve different aspects of dopamine function in the cerebral cortex.

Dopaminergic innervation of the cerebral cortex: unexpected differences between rodents and primates

Until recently, views on the organization and role of the mesotelencephalic dopaminergic (DA) systems were mostly based on studies of rodents, and it was assumed that homology existed across mammalian species. However, recent studies of both human and non-human primates indicate that this might not be so. The mesocortical DA system in primates, which is directly involved in the pathophysiology of severe illnesses such as Parkinson's disease and psychoses, shows substantial differences from that of rodents. These differences include much larger, re-organized terminal fields, a different phenotype for the co-localization of neuropeptides and a very early prenatal development.

Distribution of choline acetyltransferase-immunoreactive axons in monkey frontal cortex

Cholinergic neurons of the nucleus basalis of Meynert project to numerous regions of the cerebral cortex. However, little is known about the regional and laminar distributions of cholinergic axons in monkey frontal cortex. In this study, immunohistochemical techniques were used to identify axons that were immunoreactive for choline acetyltransferase, the enzyme that catalyses the synthesis of acetylcholine, in the frontal cortex of cynomolgus monkeys. Motor cortex contained the greatest density of labeled fibers: the density of labeled fibers was lower in premotor and anterior cingulate cortices and lower still in the association regions of prefrontal cortex. On a laminar basis, choline acetyltransferase-immunoreactive axons were most dense in layer I to superficial layer III. Layer V also contained a distinct band of labeled fibers that was particularly prominent in the agranular regions of frontal cortex. The density of labeled fibers was much lower in the deep portion of layer III to layer IV and in layer VI. These findings demonstrate a specific and regionally distinctive cholinergic innervation of monkey frontal cortex that may reveal the anatomical basis for the influence of acetylcholine on the diverse functions of primate frontal cortex.

Cholecystokinin innervation of monkey prefrontal cortex: an immunohistochemical study

Knowledge of the circuitry of chemically identified systems in primate prefrontal cortex is limited. Although cholecystokinin is very abundant in prefrontal cortex (Geola et al.: Journal of Clinical Endocrinology and Metabolism 53(2):270-275, 1981; Taquet et al.: Neuroscience 27(3):871-883, 1988), the organization of cholecystokinin-containing structures in primate prefrontal cortex has not been investigated. Using immunohistochemical and retrograde transport techniques, we characterized the cholecystokinin innervation of prefrontal cortex in macaque monkeys. The use of two antibodies directed against different portions of the cholecystokinin molecule revealed that distinct forms of the molecule were differentially localized in the same cortical neurons. These small, nonpyramidal cholecystokinin-positive neurons had a variety of somal morphologies and the density of labeled cells did not differ among cytoarchitectonic regions. Labeled neurons had a distinctive laminar distribution with the greatest density of cells present in layers II-superficial III. Labeled fibers also had a distinctive laminar pattern of distribution that differed from that of the immunoreactive neurons. In granular prefrontal cortex, terminal fields were evident in layers II, IV, and VI, with the greatest density in layer VI. Agranular area 24 exhibited a bilaminar pattern of immunoreactivity with a band in layer II and a very dense terminal field in layers V-VI. A high density of cholecystokinin-binding sites has been found in layers III-IV of prefrontal cortex and other association areas in the monkey; this finding has been attributed to possible cholecystokinin-containing afferents from the thalamus (Kritzer et al.: Journal of Comparative Neurology 263:418-435, 1987). The mediodorsal nucleus of the thalamus is known to be a source of afferents which terminate in layer IV of prefrontal cortex. However, combined retrograde transport and immunohistochemical techniques failed to reveal the presence of cholecystokinin-positive neurons in the mediodorsal nucleus of the thalamus that project to prefrontal cortex. These findings, and other observations, suggest that the terminal field in layer IV is formed by descending axons that arise from cholecystokinin-containing neurons in layers II and superficial III. This study demonstrates that the cholecystokinin innervation of prefrontal cortex has a laminar specific organization that is preserved across cytoarchitectonic regions. This distribution of immunoreactive structures suggests a distinctive role of cholecystokinin in cortical circuitry that is common to every region of prefrontal cortex.

Neurotensin innervation of the human cerebral cortex: lack of colocalization with catecholamines

We have localized neurotensin (NT) with immunocytochemical methods in the normal human cerebral cortex. Extensive areas of the frontal cortex, the hippocampal formation, and selected areas of the parietal, temporal and occipital lobes, were examined using post-mortem brain tissue. The peptidergic innervation was characteristically restricted to the limbic belt and to the dorsally contiguous regions. NT-labeled perikarya were found throughout the subiculum, including its dorsal supra-callosal continuation. NT terminal plexuses were particularly abundant in layers I-VI of the anterior cingulate cortex, in layer I of area 32 and of medical areas 9, 8, 6 and in layers II-III of area 29, of the presubiculum and entorhinal cortex. Elsewhere, NT fibers were scarce being more frequent in layer I. This regional and laminar pattern differed significantly from that of tyrosine hydroxylase (TH), which was used to label catecholaminergic axons, and preferentially the dopaminergic ones. Even in zones where TH and NT innervations were abundant, such as the anterior cingulate cortex or area 32, double-labeling procedures disclosed no colocalized fibers. The lack of NT-TH colocalization in human, contrasts with previous findings in the rodent cortex, where a contingent of the DA cortical afferents contains NT. The DA mesocortical neuronal population, labeled by TH antisera, thus seems to change its chemical phenotype, by losing the expression of an associated peptidergic neurotransmitter; this could be related to the predominant extension in the ascent of the phylogenetic scale of the non-colocalized, type of cortical DA innervation which is also found in rodents. The possible origins of the cortical, non-dopaminergic NT innervation in human are discussed: thalamo-cortical, subiculo-cortical or intrinsic. Such cortical NT innervation could be very important in limbic circuitry as a regulatory peptide in affective processes and could be involved in the physiology of pain and memory.

Ultrastructural Double-Labelling Study of Dopamine Terminals and GABA-Containing Neurons in Rat Anteromedial Cerebral Cortex

The aim of this study was to identify, at the ultrastructural level, the neuronal targets of dopamine afferents to the medial prefrontal and the anterior cingulate cortex of the adult rat. Since, in addition to pyramidal neurons, the cortical neuronal population mainly consists of GABAergic nonpyramidal intrinsic neurons, the simultaneous visualization of both dopamine- and GABA-containing neurons should leave the pyramidal neurons as the only unlabelled dopamine postsynaptic target. In this context, we used a double labelling immunocytochemical procedure: a pre-embedding PAP immunostaining to visualize monoclonal conjugated-dopamine (DA) antibody, followed by postembedding immunogold staining with a polyclonal conjugated-GABA antibody. In a single section sampling of 369 DA-immunoreactive (DA-IR) varicosities observed and the GABA-containing elements, 75% of the DA-IR terminals showed no indication of any contact with a GABA neuron. Twenty-five per cent were found in nonsynaptic contiguity with a GABA-immunoreactive neuronal element: axon, dendrite or cell body. When a DA varicosity was in nonsynaptic contiguity with a neuronal perikaryon (5% of cases), this cell was GABA positive. Ten per cent of the DA varicosities were contiguous to a GABA axon, but axoaxonic synapses in either direction were never observed. A symmetrical synapse between a DA varicosity and a GABA-containing dendrite was observed only once. The other 13 DA-IR terminals exhibiting a clear synaptic junction were apposed to nonGABA-containing dendrites, spines and shafts. Triads were observed in which a DA varicosity, forming or not a symmetrical synapse, was apposed to an unlabelled dendrite already receiving a symmetrical junction from another unlabelled axon. These data confirm and extend previous results designating the pyramidal cell dendritic tree as the main synaptic target of DA cortical afferents in rat and primate cerebral cortex. However, a direct effect of dopamine on a subpopulation of intrinsic GABA neurons cannot be excluded.

DARPP-32, a phosphoprotein enriched in dopaminoceptive neurons bearing dopamine D1 receptors: distribution in the cerebral cortex of the newborn and adult rhesus monkey

DARPP-32, a dopamine (DA) and cAMP-regulated phosphoprotein, is associated with dopaminoceptive neurons bearing D-1 receptors in the basal ganglia. The present study addressed the distribution of DARPP-32 in the primate cerebral cortex and its putative association with D-1 receptor laden cells in this structure. DARPP-32-like immunoreactive (LIR) neurons were examined in the cerebral cortex of 3-day-old (P3), 6-week-old (P42), and adult rhesus monkeys. In the younger cases, a large number of DARPP-32 positive neurons, with the morphological characteristics of pyramidal cells, were observed throughout the cortex, in layers V-VI, and to a lesser extent in layer II and uppermost layer III. In the parietal, insular, temporal, and occipital cortices, DARPP-32 positive neurons were arranged in a monolayer in layer Va. They were often clustered in small groups with a bundling of their dendrites. In the primary motor cortex, Betz cells were among the labeled population. In the association and somatosensory areas, the basal dendrites of DARPP-32 positive neurons and the prominent tufting of their apical dendrites in layer I contributed to an essential bilaminar pattern resembling the distribution reported for DA afferents and D-1 receptors in these areas. The prominence and widespread distribution of DARPP-32 positive neurons in layer V may be a specialization of primate cortex since such cells are found only in restricted locations in rodents. The literature on the connections of the cerebral cortex suggests that a large number of the DARPP-32 positive neurons in layer VI and perhaps even in layer Va may be corticothalamic neurons. An important developmental observation was the presence of DARPP-32-LIR neurons in the white matter. They were prominent in the neonates but could not be seen in the adult. Their location as well as their type and shape were reminiscent of interstitial neurons. In the adult monkeys, the distribution of DARPP-32-LIR neurons was more circumscribed: they were numerous in the ventral temporal gyrus and in areas related to the limbic system: caudal orbitofrontal cortex, insula, temporal pole, entorhinal, and anterior cingulate cortex. Weak labeling was detected in layer Va of the superior temporal and parietal cortex, in some prefrontal areas (10, 13, and medial 9), and in the premotor and supplementary motor cortex; in adults, unlike neonates, few DARPP-32-LIR neurons were present in the dorsolateral prefrontal cortex, the primary motor or the primary visual or prestriate cortices.(ABSTRACT TRUNCATED AT 400 WORDS)

Catecholaminergic innervation of the hippocampus in the cynomolgus monkey

We studied the immunocytochemical distribution of catecholaminergic fibers in the hippocampal formation from two cynomolgus monkeys by using phenylethanolamine-N-methyltransferase, dopamine-beta-hydroxylase, and tyrosine-hydroxylase antibodies. There were no phenylethanolamine-N-methyltransferase immunoreactive fibers suggesting the lack of epinephrine containing fibers. In order to compare the distributions of tyrosine-hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers, we counted fibers in four hippocampal regions, the dentate gyrus, CA3, CA1, and the subiculum at three different rostrocaudal levels. The distributions of dopamine-beta-hydroxylase and tyrosine-hydroxylase immunoreactive fibers were overlapping but clearly different, suggesting that the hippocampus receives both noradrenergic and dopaminergic inputs in primates. Dopamine-beta-hydroxylase-immunoreactive fibers were present in moderate density and roughly evenly distributed throughout the hippocampus. Tyrosine-hydroxylase immunoreactive fibers were found in high density in the dentate gyrus, in the stratum lacunosum-moleculare, and in the molecular layer of the subiculum. There were only minor side-side and rostrocaudal differences in the distribution of tyrosine-hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers. The identification of a putative dopaminergic projection to primate hippocampus, which is more dense and widely distributed than in the rodent, parallels similar increases in dopaminergic projections reported for primate cerebral neocortex.

Dopamine synaptic complex with pyramidal neurons in primate cerebral cortex

Dopamine (DA)-containing projections to the cerebral cortex are considered to play an important role in cognitive processes. Using a recently developed monoclonal antiserum directed against DA and an antibody directed against tyrosine hydroxylase in combination with Golgi impregnation and electron microscopy, we have observed that DA and tyrosine hydroxylase afferents establish symmetric membrane specializations with the soma, dendritic shafts, and spines of identified pyramidal cells in the prefrontal, cingulate, and motor cortex of primates. The axospinous contacts invariably formed part of a synaptic complex in which the dendritic spine of a pyramidal neuron was the target of both a DA-positive symmetric and an unlabeled asymmetric bouton. This arrangement allows direct DA modulation of the overall excitability of cortical projection neurons by altering local spine responses to excitatory inputs.

Antibodies directed against tyrosine hydroxylase differentially recognize noradrenergic axons in monkey neocortex

In previous immunohistochemical studies of monkey neocortex, we found that antisera directed against tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) appeared to label distinct populations of neocortical axons, which presumably were dopaminergic and noradrenergic, respectively. In the present study, we further evaluated the apparent selectivity of this rabbit anti-TH antiserum for cortical dopaminergic fibers in monkeys by comparing it with two other anti-TH antibodies, a mouse monoclonal and a sheep polyclonal. In addition, the latter two anti-TH antibodies were used in double-labeling studies with a rabbit anti-DBH antiserum. In both single- and dual-label studies, each anti-TH antibody visualized a similar population of cortical axons, although the number of labeled fibers differed across antibodies. That is, in some cortical regions and layers, both the sheep and mouse anti-TH antibodies labeled more cortical fibers than did the rabbit anti-TH antiserum. Thus, the former two antibodies appeared to identify a subpopulation of TH-containing fibers that the latter antibody did not. Dual-label experiments, involving the rabbit anti-DBH antiserum and either the sheep or mouse anti-TH antibodies, demonstrated numerous neocortical DBH-immunoreactive axons in which TH was not detectable immunohistochemically. The percentage of DBH-immunoreactive fibers that were single-labeled differed across cortical regions and with the anti-TH antibody employed. For example, in primary motor cortex the mouse anti-TH antibody did not label 99.4% of the DBH-positive fibers, whereas in primary visual cortex, 76.4% of the DBH-immunoreactive axons were identified by the sheep anti-TH antibody. The results of these studies indicate that many DBH-immunoreactive, presumably noradrenergic, axons in monkey neocortex are not visualized by anti-TH antibodies, and that the ability of anti-TH antibodies to identify noradrenergic cortical axons in monkeys differs substantially among anti-TH antibodies and across cortical regions. These findings may be consistent with previous reports suggesting that the TH molecule is present in different concentrations or molecular forms in dopaminergic and noradrenergic cortical fibers. Finally, this study demonstrates that the labeling characteristics of a particular anti-TH antibody must be carefully evaluated, particularly in studies of primate neocortex, in order to properly interpret the results of those studies.

Possible existence of a presynaptic positive feedback mechanism enhancing dopamine transmission in the anterior cingulate cortex of the rat

A series of microiontophoretic and VTA stimulation experiments, conducted in intact, GBR-12909-treated, alpha-methylparatyrosine-depleted or 6-hydroxydopamine-denervated rats, provide suggestive evidence for the existence of a presynaptic, positive feedback mechanism triggered by dopamine reuptake and favoring the release of this transmitter in the anterior cingulate cortex.

The monoaminergic innervation of the cerebral cortex is not diffuse and nonspecific

It is generally thought that monoamines play a nonspecific role in modulating cortical activity. However, several lines of evidence now indicate that cortical monoaminergic afferents show remarkable anatomical specificity. In particular, there is unequivocal evidence for regional, laminar and intracortical specificity, and for action of monoamines through conventional synapses.

Comparative distributions of dopamine D-1 and D-2 receptors in the cerebral cortex of rats, cats, and monkeys

The distributions and laminar densities of cerebral cortical dopamine D-1 and D-2 receptors were studied in rats, cats, and monkeys. Distributions were determined by using alternate, adjacent tissue sections processed for D-1 and D-2 receptor subtypes and compared to an adjacent, nearly adjacent, or similar sections stained for Nissl substance. [3H]-SCH 23390 and [3H]-spiroperidol (in the presence of 100 nM mianserin) were used to label the D-1 and D-2 receptors, respectively. The regional distribution and laminar density of dopamine receptors were determined by in vitro quantitative autoradiography and video densitometry of selected isocortical and peri-allocortical regions. Granular (prefrontal, primary somatosensory, and primary visual), agranular (primary motor and anterior cingulate), and limbic (entorhinal and perirhinal) cortices were examined. Where possible, homologous areas among the species were compared. The D-1 receptor was present in all regions and laminae of the cerebral cortex of rats, cats, and monkeys. The regional densities for the D-1 receptor were higher in the cat and monkey than in the rat. The rat D-1 receptor displayed a relatively homogeneous laminar pattern in most regions except that the deeper laminae (V and VI) contained more receptors than the superficial layers. The cats and monkeys, however, had distinctly heterogeneous laminar patterns in all regions of cortex that varied from one region to another and were quite different from that seen in the rat. The cats and monkeys had highest densities of the D-1 receptor in layers I and II and lowest densities in layers III and IV, whereas layers V and VI were intermediate. The density of D-1 receptors was greater than the density of D-2 receptors in all regions and laminae of cerebral cortex of the cat and monkey and greater in most regions and laminae of the rat cerebral cortex. The D-2 receptor was also distributed in all regions of the cerebral cortex of rats, cats, and monkeys. The D-2 receptor was very homogeneous in its regional distribution and laminar pattern compared to the D-1 receptor in all 3 species. The D-2 receptor was denser in the superficial layers (I and II) of the cortex than in the deeper layers in the rats, but more homogeneous in the different laminae of the cat and monkey cerebral cortex. The rat cortical D-2 receptor exceeded the D-1 receptor in restricted laminae of selective regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Schizophrenia: a disease of interhemispheric processes at forebrain and brainstem levels?

The evidence is convincing that each human cerebral hemisphere is capable of human mental activity. This being so, every normal human thought and action demands either a consensus between the two hemispheres, or a dominance of one over the other, in any event integrated into a unity of conscious mentation. How this is achieved remains wholly mysterious, but anatomical and behavioral data suggest that the two hemispheres, and their respective bilateral, anatomical-functional components, maintain a dynamic equilibrium through neural competition. While the forebrain commissures must contribute substantially to this competitive process, it is emphasized in this review that the serotonergic raphé nuclei of pons and mesencephalon are also participants in interhemispheric events. Each side of the raphé projects heavily to both sides of the forebrain, and each is in receipt of bilateral input from the forebrain and the habenulo-interpeduncular system. A multifarious loop thus exists between the two hemispheres, comprised of both forebrain commissural and brainstem paths. There are many reasons for believing that perturbation of this loop, by a variety of pathogenic agents or processes, probably including severe mental stress in susceptible individuals, underlies the extraordinarily diverse symptomatology of schizophrenia. Abnormality of features reflecting interhemispheric processes is common in schizophrenic patients; and the 'first rank' symptoms of delusions or hallucinations are prototypical of what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is focused primarily through, the raphé serotonergic system, that plays such a fundamental role in consciousness, in dreaming, in response to psychotomimetic drugs, and probably in movement, and even the trophic state of the neocortex. This system is also well situated to control the dopaminergic neurons of the ventral tegmental area, thus relating to the prominence of dopaminergic features in schizophrenia; and the lipofuscin loading and intimate relation with blood vessels and ependyma may make neurons of the raphé uniquely vulnerable to deleterious agents.

Light and electron microscopic immunocytochemical analysis of the dopamine innervation of the rat visual cortex

The dopaminergic innervation of the rat primary (area 17) and secondary (areas 18 and 18a) visual cortical areas was examined immunocytochemically using an antiserum directed against dopamine. This innervation was characterized by the differential density of the respective afferents within individual visual areas. Area 18, especially its rostral part, was observed to receive a considerable amount of dopaminergic axons, whereas areas 17 and 18a were sparsely innervated. The innervation of all layers of area 18 seemed to consist to a considerable extent of axonal branches of radial fibres ascending from layer VI to layer I. At the ultrastructural level, dopamine profiles were found to display similar characteristics in all visual areas. Dopamine labelled axon-terminals and axonal varicosities, examined in single and serial ultrathin sections, were seen to form primarily asymmetrical synaptic contacts with dendritic profiles. These observations suggest a 'specific' innervation of cytoarchitectonically distinct cortical regions by dopaminergic axons.

Noradrenergic innervation of monkey prefrontal cortex: a dopamine-beta-hydroxylase immunohistochemical study

Norepinephrine has been implicated in the regulation of a number of cortical functions, yet relatively little is known about the anatomical organization of noradrenergic axons in the expanded and highly differentiated prefrontal cortex of primates. In this study, the distribution of fibers containing dopamine-beta-hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, was characterized immunohistochemically in the prefrontal cortical regions of Old World cynomolgus monkeys (Macaca fascicularis) and New World squirrel monkeys (Saimiri sciureus). In both species, differences in the density of DBH-labeled fibers were detected both across and within many prefrontal cytoarchitectonic regions. In cynomolgus monkeys, area 8B had the greatest density of DBH-immunoreactive fibers; within this region, the medial surface had a greater density of labeled processes than the dorsal surface. Areas 9 and 24 also had a high density of DBH-labeled fibers, areas 11, 12, 13 and 25 were of intermediate density, and portions of areas 10 and 46 had the lowest density of immunoreactive fibers. Regional differences in the density of DBH-immunoreactive fibers were also present in squirrel monkey prefrontal cortex. Despite the regional variations in the density of DBH-immunoreactive fibers, the laminar distribution of these fibers was very similar across cytoarchitectonic areas of cynomolgus prefrontal cortex. Layer I contained a low density of labeled fibers which were primarily tangential in orientation. The predominantly radially oriented fibers in layers II-IV were slightly higher in density. The density of both radially and tangentially oriented immunoreactive fibers increased substantially in layer V. Fiber density decreased in layer VI; a band of tangentially oriented fibers was present in the deep portion of this layer. With a few exceptions, the laminar distribution of DBH-immunoreactive fibers in the prefrontal regions of squirrel monkey cortex was similar to that of cynomolgus monkey. Since other data suggest that anti-DBH selectively labels noradrenergic axons in monkey neocortex, the distinctive innervation patterns exhibited by DBH-immunoreactive fibers reveal the regions and layers that may be the principal sites of action of norepinephrine in exerting its effects on prefrontal cortical function.

Catecholamine innervation of the human cerebral cortex as revealed by comparative immunohistochemistry of tyrosine hydroxylase and dopamine-beta-hydroxylase

The organization of the cortical monoamine systems, dopamine (DA), and noradrenaline (NA), which have been studied extensively in the rat and more recently in the monkey, had not yet been investigated directly in the human brain. We report here the first systematic account of the regional and laminar distributions of the catecholamine fibers in the human cerebral cortex, using immunohistochemistry of the catecholamine biosynthetic enzymes, tyrosine hydroxylase (TH), and dopamine-beta-hydroxylase (DBH) in 13 cytoarchitectonic areas (4, 6, 9, 3b, 5, 40, 17, 18, 23, 24, 29, insula, and hippocampus) sampled postmortem. The noradrenergic (NA) innervation, mapped with DBH-immunoreactivity (DBH-IR), displayed a characteristic density gradient in the neocortex (highest in the primary sensorimotor areas, decreasing rostrally and caudally) that contrasted with the more uniform density in the limbic cortices (24, 23, 29, insula, hippocampus). NA axons were present in all cortical layers and were least numerous in layer I. The DBH-IR fibers were only partly TH-immunostained (10-50%, on double-labeled sections), suggesting a heterogeneity of the cortical NA axons. The putative dopaminergic (DA) fibers were identified by comparing alternate or double-immunolabeled (DBH-TH) sections, as the TH-IR fibers which contain no DBH-IR. A DA-like innervation was present in all cortical areas, with major regional differences in density and laminar distribution, which closely paralleled cytoarchitectural buildups: 1) the DA-like innervation was densest in the agranular areas, primary and secondary motor areas, anterior cingulate, and insula; it distributed throughout layers I-VI; 2) density was lower in the granular cortices, areas 9 (prefrontal cortex), 23, 3b, 5, 40, and 18, displaying a bilaminar pattern in layers I and V-VI. In all areas, DA-like fibers were most abundant in the molecular layer, with a predominant distribution in its deepest part. Convoluted and coily fibers represented a unique morphologic aspect of the CA innervation in the human cortex. These findings are in agreement with findings in nonhuman primates and demonstrate major evolutionary changes in the organization of the cortical aminergic input as compared with rodents. The most striking features are the expansion of the DA innervation to the whole cortex and the peak of highest density in the motor areas. The regional differentiation of NA innervation is also accentuated. Slight differences were found in the laminar distributions of the amines in humans and primates. These data seem quite promising and open new research fields in neurologic and psychiatric diseases.

Evidence for a dopaminergic innervation of cat primary visual cortex

Experiments have been conducted to determine whether dopamine fulfills the criteria to be considered as a neurotransmitter in cat primary visual cortex. N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, a neurotoxin with high selectivity for noradrenergic terminals, was administered into kitten cerebral ventricles. Two weeks later, the concentration of norepinephrine in visual cortex was reduced to 15% of control while dopamine and serotonin were not depleted. Receptor binding assays with [3H]SCH 23390 showed that membranes prepared from cat primary visual cortex contain a binding site that has the properties of a D1 receptor. This site was localized by autoradiography to two bands, one in layer VI and the second in upper layers of visual cortex. A dopamine-stimulated adenylate cyclase activity was demonstrated that was inhibited by SCH 23390 but not by alprenolol. Norepinephrine was shown to stimulate adenylate cyclase activity through both a beta-noradrenergic receptor and a D1 receptor. Binding assays with [3H]spiperone indicated that D2 dopamine receptors are absent from cat visual cortex or present in very low amounts. Taken together these results strongly suggest the existence of a dopamine innervation of cat primary visual cortex. The neurotoxin experiments show that some of the dopamine in cat visual cortex is not in noradrenergic terminals while the receptor assays demonstrate the presence of D1 receptors functionally linked to the synthesis of cyclic 3',5'-adenosine monophosphate. The demonstration of a dopaminergic innervation in cat primary visual cortex is also relevant to the interpretation of data on the involvement of catecholamines in developmental plastic phenomena.