Functional variations in cerebral cortical activity are accompanied by local changes in blood flow, but the mechanisms underlying this physiological coupling are not well understood. Here we report that dopamine, a neurotransmitter normally associated with neuromodulatory actions, may directly affect local cortical blood flow. Using light and electron-microscopic immunocytochemistry, we show that dopaminergic axons innervate the intraparenchymal microvessels. We also provide evidence in an in vitro slice preparation that dopamine produces vasomotor responses in the cortical vasculature. These anatomical and physiological observations reveal a previously unknown source of regulation of the microvasculature by dopamine. The findings may be relevant to the mechanisms underlying changes in blood flow observed in circulatory and neuropsychiatric disorders.

In the primate neocortex, little is known about the possible associations between functional subclasses of GABA neurons, their morphological properties and calcium-binding protein (CaBP) content. We used whole-cell current clamp recordings, combined with intracellular labeling and fluorescence immunohistochemistry, to determine these relationships for interneurons in layers 2-3 of monkey prefrontal cortex (PFC). Eighty-one interneurons were included in the analysis. Thirty-eight of these cells showed immunoreactivity for one of the three CaBPs tested. Co-localization of more than one CaBP was not observed in any of the interneurons examined. Interneurons with different CaBPs formed distinct populations with specific physiological membrane properties and morphological features. Parvalbumin (PV)-positive cells had the physiological properties characteristic of fast-spiking interneurons (FS) and the morphology of basket or chandelier neurons. Most calretinin (CR)-containing cells had the physiological properties ascribed to non-fast-spiking cells (non-FS) and a vertically oriented axonal morphology, similar to that of double bouquet cells. Calbindin (CB)-positive interneurons also had non-FS properties and included cells with double bouquet morphology or with a characteristic dense web of axonal collaterals in layer 1. Classification of the interneurons based on cluster analysis of multiple electrophysiological properties suggested the existence of at least two distinct groups of interneurons. The first group contained mainly PV-positive FS cells and the second group consisted predominantly of CR- and CB-positive non-FS interneurons. These findings may help to illuminate the functional roles of different groups of interneurons in primate PFC circuitry.

In primates, little is known about intrinsic electrophysiological properties of neocortical neurons and their morphological correlates. To classify inhibitory cells (interneurons) in layers 2–3 of monkey dorsolateral prefrontal cortex we used whole cell voltage recordings and intracellular labeling in slice preparation with subsequent morphological reconstructions. Regular spiking pyramidal cells have been also included in the sample. Neurons were successfully segregated into three physiological clusters: regular-, intermediate-, and fast-spiking cells using cluster analysis as a multivariate exploratory technique. When morphological types of neurons were mapped on the physiological clusters, the cluster of regular spiking cells contained all pyramidal cells, whereas the intermediate- and fast-spiking clusters consisted exclusively of interneurons. The cluster of fast-spiking cells contained all of the chandelier cells and the majority of local, medium, and wide arbor (basket) interneurons. The cluster of intermediate spiking cells predominantly consisted of cells with the morphology of neurogliaform or vertically oriented (double-bouquet) interneurons. Thus a quantitative approach enabled us to demonstrate that intrinsic electrophysiological properties of neurons in the monkey prefrontal cortex define distinct cell types, which also display distinct morphologies.

The monoaminergic innervation of cerebral cortex has long been implicated in its development. Methods now exist to examine catecholamine and serotonin inputs to identified neurons in the cerebral cortex. We have quantified such inputs on pyramidal and nonpyramidal cells in prefrontal cortex of rhesus monkeys ranging in age from 2 weeks to 10 years. Individual layer III neurons were filled with Lucifer yellow and doubleimmunostained with axons containing either tyrosine hydroxylase (TH) or 5-hydroxytryptamine (5-HT). The filled cells were reconstructed, and putative appositions between the axons and dendritic spines and shafts were quantified at high magnification using light microscopy.The density of catecholamine appositions on pyramidal neurons matures slowly, reaching only half the adult level by 6 months of age and thereafter rising gradually to adult levels by 2 years of age. By contrast, the density of serotonin appositions on pyramidal cells reaches the adult level before the second week after birth. The average adult pyramidal neuron in layer III of area 9m receives three times stronger input from catecholaminergic than from serotoninergic axons. The overall density of both inputs to interneurons does not appear to change during postnatal development. Selective changes in the TH innervation of pyramidal cells against a backdrop of constant TH innervation of interneurons suggest that the balance between excitation and inhibition may change developmentally in the prefrontal cortex. By contrast, 5-HT innervation of both types of neurons remains relatively constant over the age range studied.Key words: tyrosine hydroxylase; dopamine; serotonin; 5-hydroxytryptamine; pyramidal neuron; interneuron; rhesus monkey; nonhuman primate; prefrontal cortex Monoaminergic systems of the brain modulate excitatory transmission in cortical circuits that are critical for normal adult function of prefrontal cortex (Williams and Goldman-Rakic, 1995;Vollenweider et al., 1998). The same neurotransmitters have been implicated directly and indirectly in several aspects of neurodevelopment (Mattson, 1988;Levitt et al., 1997), in the pathophysiology of schizophrenia (Lieberman, 1999), and in the psychotomimetic effects of certain hallucinogens (Breier, 1995;Farber et al., 1999;Gouzoulis-Mayfrank et al., 1999). There are timing similarities among the attainment of peak working memory performance (Diamond and Goldman-Rakic, 1989), the typical age of onset of schizophrenia (Lieberman, 1999), and the age at which certain drugs begin to trigger psychosis (Farber et al., 1999). These developmental parallels suggest that a detailed understanding of the postnatal changes in monoaminergic input to cortical neurons may shed light on the changes in circuitry needed for mature working memory performance, as well as on how this circuitry may become disrupted in psychosis.Monoamines have been extensively studied during embryonic development (Lauder and Bloom, 1974;Coyle and Molliver, 1977;Buznikov, 1984;Mattson, 1988;Verney et al., 1993;Levitt, 1...

The heterogeneity of gamma-aminobutyric acid interneurons in the rodent neocortex is well-established, but their classification into distinct subtypes remains a matter of debate. The classification of interneurons in the primate neocortex is further complicated by a less extensive database of the features of these neurons and by reported interspecies differences. Consequently, in this study we characterized 8 different morphological types of interneurons from monkey prefrontal cortex, 4 of which have not been previously classified. These interneuron types differed in their expression of molecular markers and clustered into 3 different electrophysiological classes. The first class consisted of fast-spiking parvalbumin-positive chandelier and linear arbor cells. The second class comprised 5 different morphological types of continuous-adapting calretinin- or calbindin-positive interneurons that had the lowest level of firing threshold. However, 2 of these morphological types had short spike duration, which is not typical for rodent adapting cells. Neurogliaform cells (NGFCs), which coexpressed calbindin and neuropeptide Y, formed the third class, characterized by strong initial adaptation. They did not exhibit the delayed spikes seen in rodent NGFCs. These results indicate that primate interneurons have some specific properties; consequently, direct translation of classification schemes developed from studies in rodents to primates might be inappropriate.