A. De La Calle

Dopamine D5 receptors of rat and human brain

In contrast to dopamine D1 receptors, the anatomical distribution of D5 receptors in the CNS is poorly described. Therefore, we have studied the localization of dopamine D5 receptors in the brain of rat and human using our newly prepared subtype-specific antibody. Western blot analysis of brain tissues and membranes of cDNA transfected cells, and immunoprecipitation of brain dopamine receptors suggest that this antibody is highly selective for native dopamine D5 receptors. The D5 antibody labeled dopaminergic neurons of mesencephalon, and cortical and subcortical structures. In neostriatum, the D5 receptors were localized in the medium spiny neurons and large cholinergic interneurons. The D5 labeling in caudate nucleus was predominantly in spines of the projection neurons that were frequently making asymmetric synapses. Occasionally, the D5 receptors were also found at the symmetric synapses. Within the cerebral cortex and hippocampus, D5 antibody labeling was prominent in the pyramidal cells and their dendrites. Dopamine D5 receptors were also prominent in the cerebellum, where dopamine innervation is known to be very modest. Differences in the localization of D5 receptors between both species were generally indistinguishable except in hippocampus. In rat, the hippocampal D5 receptor was concentrated in the cell body, whereas in human it was also associated with dendrites. These results show that D5 receptors are localized in the substantia nigra-pars compacta, hypothalamus, striatum, cerebral cortex, nucleus accumbens and olfactory tubercle. Furthermore, the presence of D5 receptors in the areas of dopamine pathways suggests that this receptor may participate actively in dopaminergic neurotransmission.

Dynamics of volume transmission in the brain. Focus on catecholamine and opioid peptide communication and the role of uncoupling protein 2

Summary.This review focuses on transmitter-receptor mismatches in the brain, which is one of the hallmarks of the Volume Transmission (VT) concept, and how this phenomenon may be related to local temperature gradients created by brain uncoupling protein 2 (UCP2), which uncouples oxidative phosphorylation from ATP synthesis, hereby generating heat. Recent studies on transmitter-receptor mismatches have revealed dopamine and opioid peptide receptor mismatches in the intercalated islands of the amygdala, which are GABAergic cell clusters regulating amygdaloid output. Such mismatches have also been found in regions belonging to the extended amygdala and the nucleus accumbens shell. Now substantial UCP2 immunoreactivity has been found within the above transmitter-receptor mismatch regions, suggesting that UCP2 may enhance diffusion and convection of DA and opioid peptides in such regions by generation of local temperature gradients, thereby contributing to a dynamic regulation of VT.

Cellular localization and distribution of dopamine D4 receptors in the rat cerebral cortex and their relationship with the cortical dopaminergic and noradrenergic nerve terminal networks

The role of the dopamine D(4) receptor in cognitive processes and its association with several neuropsychiatric disorders have been related to its preferential localization in the cerebral cortex. In the present work we have studied in detail the regional and cellular localization of the dopamine D(4) receptor immunoreactivity (IR) in the rat cerebral cortex and its relationship to the dopaminergic and noradrenergic nerve terminal networks, since both dopamine and noradrenaline have a high affinity for this receptor. High levels of D(4) IR were found in motor, somatosensory, visual, auditory, temporal association, cingulate, retrosplenial and granular insular cortices, whereas agranular insular, piriform, perirhinal and entorhinal cortices showed low levels. D(4) IR was present in both pyramidal and non-pyramidal like neurons, with the receptor being mainly concentrated to layers II/III. Layer I was observed to be exclusively enriched in D(4) IR branches of apical dendrites. Finally, mismatches were observed between D(4) IR and tyrosine hydroxylase and dopamine beta-hydroxylase IR nerve terminal plexuses, indicating that these receptors may be activated at least in part by dopamine and noradrenaline operating as volume transmission signals. The present findings support a major role of the dopamine D(4) receptor in mediating the transmission of cortical dopamine and noradrenaline nerve terminal plexuses.

Uncoupling protein 2/3 immunoreactivity and the ascending dopaminergic and noradrenergic neuronal systems: Relevance for volume transmission

Uncoupling proteins in the inner mitochondrial membrane uncouples oxidative phosphorylation from ATP synthesis. It has been suggested that these proteins are involved in thermogenesis as well as in the regulation of reactive oxygen species production in the mitochondria. The present work was conducted to investigate the localization of the uncoupling protein 2-like immunoreactivity (uncoupling protein 2/3 immunoreactivity) in the main catecholaminergic projection fields in the rat brain as well as in the areas of the dopaminergic and noradrenergic nerve cell groups. In particular, the relationships of tyrosine hydroxylase, dopamine beta-hydroxylase and uncoupling protein 2/3 immunoreactivity were assessed by double immunolabeling and confocal laser microscopy analysis associated with computer-assisted image analysis. Uncoupling protein 2/3 immunoreactivity was observed in discrete dopaminergic terminals in the nucleus accumbens and in the cerebral cortex whereas it was found in scattered noradrenergic terminals in the caudate putamen and Islands of Calleja Magna. One interesting finding was that uncoupling protein 2/3 immunoreactivity together with tyrosine hydroxylase immunoreactivity in the shell of nucleus accumbens was observed surrounding the previously characterized D1 receptor rich nerve cell column system characterized by a relative lack of tyrosine hydroxylase immunoreactivity. Moreover, in animal models of dopaminergic pathway degeneration, plastic changes in uncoupling protein 2/3 terminals have been shown in the cerebral cortex and striatum as seen from the increased size and intensity of uncoupling protein 2/3 immunoreactivity of their varicosities. Taken together, these findings open up the possibility that uncoupling protein 2/3 could play an important role modulating the dopaminergic and noradrenergic neurotransmission within discrete brain regions.

Light microscopy of the medial wall of the cerebral cortex of the lizard Psammodromus algirus

The telencephalic medial wall of the lizard Psammodromus algirus was studied using Golgi and conventional light microscopic techniques. The area is formed by two different cytological fields—medial cortex and dorsomedial cortex. These two cortices possess three layers dorsoventrally: a superficial plexiform layer, a cellular layer, and a deep plexiform layer. The alveus, a deep fiber system, runs adjacent to the ependyma. Four classes of neurons are found in the cellular layer of the medial cortex on the basis of soma shape, dendritic pattern, and position in the layer: horizontal, double pyramidal, and candelabra cells. Solitary cells are present in the superficial and deep plexiform layers of the medial cortex. Those of the superficial plexiform layer are stellate cells. Horizontal and vertical cells are found in the deep plexiform layer. Double pyramidal cells are the most frequently impregnated in the cellular layer of the dorsomedial cortex. In addition, candelabra cells are present at the lateral end of the layer. Two cell types are found in the deep plexiform layer of the dorsomedial cortex: solitary pyramidal cells and, among the fibers of the alveus, horizontal cells. Ependymal tanycytes line the ventricular surface, and protoplasmic astrocytes are found in the plexiform layers of both medial and dorsomedial cortices.

Electron microscopy of the medial cortex in the lizard Psammodromus algirus

The medial cortex of Psammodromus presents a three‐layer organization. Most of the cell bodies are localized in a compact lamina, the cellular layer. Two plexiform layers, superficial and deep, enclose the cellular layer. The most external portion of the superficial plexiform layer is formed by a limiting glial sheet consisting of tanycytic processes that reach the surface of the cortex. Astrocytes are localized close to the glial sheet. There are two types of axon terminals within the superficial plexiform layer: type S with spheric vesicles and type F with pleomorphic vesicles. Large solitary neurons are present at middle levels of the layer. In the cellular layer there are three neuronal types: large neurons with dispersed chromatin, neurons of medium size with chromatin clumps, and electron‐dense neurons. Protoplasmic astrocytes are found superficially in this layer. In the deep plexiform layer numerous neuronal cell bodies are visible, and three types can be distinguished: horizontal fusiform cells, globous neurons with indented nuclei, and electron‐dense neurons. Protoplasmic astrocytes are present throughout this layer. Oligodendrocytes are more frequent in the inner third of the layer, often related to fibers of a thick fascicle running in contact with the ependyma, the alveus. The ependyma is formed by a single row of prismatic cells bordering the lateral ventricle.

A golgi study of the dorsal cortex in the lizard Psammodromus algirus

The dorsal cortex of Psammodromus algirus is three‐layered. From the pia to the ependyma, it consists of a superficial plexiform layer, a cellular layer, and a deep plexiform layer. Five neuronal types have been classified in the dorsal cortex. Pyramidal neurons represent 18.75% of neurons and differ morphologically depending on their position in the pars medialis or lateralis of dorsal cortex. Pyramidal neurons in the pars medialis are smaller and their apical dendritic fields are less extensive than those of pyramidal neurons in the pars lateralis. Bitufted neurons represent 22.5% of dorsal cortical neurons and are only found in the cellular layer of the pars lateralis. Multipolar neurons are distributed in the pars medialis and lateralis, in the cellular layer and the deep plexiform layer; they represent 46.25% of the total impregnated cells. Bipolar neurons are found mainly in the deep plexiform layer and form 11.25% of neurons. Two subtypes may be distinguished: horizontal and vertical bipolar cells. Juxtaependymal neurons represnt 1.25% and are located just above the ependyma. All the neurons in the cellular layer are projection cells.

Monoaminergic innervation patterns in the anterior dorsal ventricular ridge of a lacertid lizard, Psammodromus algirus.

In contrast to the view of a diffuse monoaminergic innervation of the telencephalon, studies on the monoaminergic innervation in certain mammalian isocortical regions have shown a high degree of regional and laminar specificity. The present study was designed to examine the distribution patterns of dopamine, noradrenaline and serotonin in a telencephalic structure, the anterior dorsal ventricular ridge, of the sand lizard Psammodromus algirus (Lacertidae) using specific antibodies against each monoamine. The anterior dorsal ventricular ridge receives an abundant monoaminergic innervation compared to that of cortical telencephalic regions. The distribution of the different monoamines presented zonal and regional patterns throughout the ridge. The cell cluster zone was profusely innervated by catecholamines, whereas no serotoninergic fibers innervated the cell bodies in the cluster zone. On the other hand, the periventricular zone was heavily innervated by serotonin, but catecholaminergic fibers were almost lacking. With regard to regional patterns, dopamine exhibited major differences in the mediolateral axis of the anterior dorsal ventricular ridge: dopaminergic innervation was densest in the lateral region, which in other reptiles is described as a target of visual thalamic projections. Whereas the zonal pattern of the monoaminergic innervation of the anterior dorsal ventricular ridge seems to be a constant feature in the reptiles studied to date, the regional pattern varies among reptilian groups, especially taking into account the density of monoaminergic innervation.

Electron microscopy of the dorsomedial cortex in the lizard Psammodromus algirus

The cellular populations and the plexiform layers of the dorsomedial cortex of Psammodromus algirus are described at the ultrastructural level. Solitary globous cells are located in the outermost layer of the cortex, the superficial plexiform layer. Double pyramidal cells of the cellular layer show uniform ultrastructural characteristics. Displaced double pyramidal cells, vertical fusiform cells, and globous cells are found in the deep plexiform layer. Two types of dendritic spines are described. Large spines may contain membranous sacs and mitchondira and are located at the upper third of the superifical plexiform layer; small spines do not contain organelles and are located throughout the entire cortex. Two types of axon terminals are widely distributed in both plexiform layers: terminals with only clear vesicles and terminals with both dense‐core and clear vesicles. Terminals with large dense‐core vesicles may be related to peptidergic synapses and are more frequent at the upper levels of the superficial plexiform layer. The neuroglia described in the dorsomedial cortex of Psammodromus are protoplasmatic astrocytes and oligodendrocytes.