Glial uptake of monoamines in primary cultures of rat median raphe nucleus and cerebellum. A combined monoamine fluorescence and glial fibrillary acidic protein immunofluorescence study

The Dopaminergic Cells in the Median Raphe Region Regulate Social Behavior in Male Mice

According to previous studies, the median raphe region (MRR) is known to contribute significantly to social behavior. Besides serotonin, there have also been reports of a small population of dopaminergic neurons in this region. Dopamine is linked to reward and locomotion, but very little is known about its role in the MRR. To address that, we first confirmed the presence of dopaminergic cells in the MRR of mice (immunohistochemistry, RT-PCR), and then also in humans (RT-PCR) using healthy donor samples to prove translational relevance. Next, we used chemogenetic technology in mice containing the Cre enzyme under the promoter of the dopamine transporter. With the help of an adeno-associated virus, designer receptors exclusively activated by designer drugs (DREADDs) were expressed in the dopaminergic cells of the MRR to manipulate their activity. Four weeks later, we performed an extensive behavioral characterization 30 min after the injection of the artificial ligand (Clozapine-N-Oxide). Stimulation of the dopaminergic cells in the MRR decreased social interest without influencing aggression and with an increase in social discrimination. Additionally, inhibition of the same cells increased the friendly social behavior during social interaction test. No behavioral changes were detected in anxiety, memory or locomotion. All in all, dopaminergic cells were present in both the mouse and human samples from the MRR, and the manipulation of the dopaminergic neurons in the MRR elicited a specific social response.

Ultrastructural localization of acetylcholinesterase and choline acetyltransferase in oligodendrocytes, glioblasts and vascular endothelial cells in the external cuneate nucleus of the gerbil

This study reports the reactivities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in some of the nonneuronal elements in the external cuneate nucleus (ECN) of gerbils. AChE reaction products were localized in some oligodendrocytes in their cisternae of rough endoplasmic reticulum, nuclear envelope and Golgi saccules. The basal lamina lining the capillary endothelia also displayed AChE reactivity. In ChAT immunocytochemistry, the reaction products were found to be associated with the vascular basal lamina as well as the endothelial plasma membrane facing the lumen. The most remarkable finding was the localization of ChAT immunoreactivity in some oligodendrocytes and occasional glioblasts (small glial precursor cells containing a thin rim of cytoplasm surrounding an irregular nucleus with homogeneous chromatin materials). The ChAT-positive oligodendrocytes consisted of two types, medium-dense and dark cells, either associated with blood vessels or ChAT-stained neuronal elements. It is suggested from these new findings that at least some of the oligodendrocytes and glioblasts in the ECN of gerbils may be involved in the synthesis, storage, release and degradation of acetylcholine.

Direct immunocytochemical localization of 5-hydroxytryptamine receptors in the adult rat spinal cord: a light and electron microscopic study using an anti-idiotypic antiserum

In the present study, we performed the immunodetection of serotonergic (5-HT) receptor subtypes in the spinal cord by using an anti-idiotypic antiserum (TH8) at light and electron microscopic levels. This antibody has been shown to recognize 5-HT1B, 5-HT1C, and 5-HT2 receptor subtypes (Tamir et al.: J Neurochem 57:930-942, 1991). The TH8 immunoreactivity was observed in the dorsal and ventral horns of the gray matter. Light microscopy revealed that small cell bodies located in laminae I-III of the dorsal horn were intensely immunolabeled. A more homogenous and discrete staining was also observed throughout the entire dorsal horn. In the ventral horn, motoneurons were also immunoreactive (IR). Peroxidase deposits were observed as numerous patches covering the motoneuronal surface. Numerous interneurons were moderately and homogeneously immunostained. With the electron microscope, most of the labeled structures were identified as neurons (dendrites and perikarya) in both the dorsal and ventral horns. In the dorsal horn, immunoreactivity was present in dendrites and neuronal perikarya. A large majority of the immunoreactivity found in dendrites was not associated with synaptic differentiations. Indeed, the dendrites, in which peroxidase deposit was seen, were not locally involved in synapses. Very scarce synaptic varicosities were observed in close apposition with IR dendrites. In the ventral horn, TH8 immunoreactivity was present in dendrites, with an accumulation of peroxidase deposit on the active zone of synapses, facing presynaptic membranes. Both the postsynaptic membrane and the submembrane area were IR. In addition, a few astroglial fine processes were immunostained; most of them were observed in the dorsal horn. Scarce IR astroglial profiles were observed in the ventral horn. These observations show that such an antiserum constitutes a useful tool for the ultrastructural analysis of 5-HT receptor distribution. Finally, correlation between the immunocytochemical localization of 5-HT receptor subtypes and the modes of 5-HT transmission in the spinal cord (wiring and volume transmissions) is discussed in the present report.

Astrocytes: targets and mediators of chemical-induced CNS injury

It is now well established that a reciprocal relationship exists between neurons and astrocytes, and that this association is vital for mutual differentiation, development, and functioning of both cell types. It had also become apparent that perturbations in astrocytic function may lead to deleterious consequences in juxtaposed neurons. It is therefore possible that neuronal damage induced by chemicals or neuropathic disease involves dissociation of astrocytic-neuronal interactions. The purpose of this review is to explore astrocytic-neuronal interactions, focusing on potential sites of neurotoxicant actions. In developing this thesis, we briefly examine the functional interactions between astrocytes and neurons, followed by specific examples of astrocyte-mediated neurotoxicity.

Evidence for nonsynaptic serotonergic and noradrenergic innervation of the rat dorsal horn and possible involvement of neuron-glia interactions

We investigated the synaptic incidence of the contacts established by serotonergic and noradrenergic descending fibers in the dorsal horn of the rat spinal cord. Serial electron microscopic sections were performed. Synapses were scarce. The majority of serotonergic and noradrenergic varicosities (more than 60%) are characterized by nonsynaptic contacts. Numerous glial profiles, and particularly astrocytic profiles, were observed in apposition with serotonergic and noradrenergic varicosities. The proportion of astroglia was higher around serotonergic and noradrenergic varicosities devoid of synaptic specialization. The length of the contact between immunoreactive nonsynaptic varicosities and astrocytes was twice as long as that between synaptic varicosities and astrocytes. Thus, the modulation of sensitive messages by serotonin and noradrenaline through pauci-synaptic varicosities in the dorsal horn of the spinal cord could be an example of the concept of "volume transmission" [Fuxe and Agnati (1991) Volume Transmission in the Brain: Novel Mechanisms for Neural Transmission, Advances in Neuroscience, Vol. 1, pp. 1-9.] in the central nervous system. Analysis of the microenvironment of serotonergic and noradrenergic varicosities led us to make the hypothesis that glial cells, particularly astrocytes, could play some role in volume transmission.

Kinetics of dopamine and noradrenaline transport in synaptosomes from cerebellum, striatum and frontal cortex of normal and reeler mice

Recent evidence indicates that the cerebellum has a dopaminergic system. In order to elucidate further the dopaminergic system in the cerebellum, we investigated the transport of dopamine (DA) in synaptosomal preparations of normal and reeler mice. For comparative purposes we also studied DA transport in synaptosomal preparations from striatum and frontal cortex and compared DA transport to noradrenaline (NA) transport. [3H]-DA transport into cerebellar synaptosomes was found to be a Na(+)-dependent, two component system--a high affinity, low capacity and a low affinity, high capacity. In striatum [3H]-DA is transported by a similar high but different low affinity component. Maximal velocities of both transport components in the striatum were higher than the corresponding ones in the cerebellum. In the frontal cortex we also observed two [3H]-DA transport components with affinities significantly lower than those in cerebellum and striatum. [3H]-NA transport into synaptosomes, prepared from the three brain regions studied, showed two transport components with similar Kt and Vmax values, except for the high affinity component in striatum whose affinity is lower. In reeler mice [3H]-DA transport was different from normal only in the cerebellum where the maximal velocity for both transport components was significantly higher (2x). In contrast, no significant difference was observed in the transport of [3H]-NA. The accumulated [3H]-DA from cerebellar slices was found to be releasable by K+ stimulation, in a Ca(++)-dependent manner, and most of the released radioactivity was in the form of [3H]-DA. These results indicate that in the cerebellum there is a low-density dopaminergic system which is distinct from the corresponding noradrenergic system.

Regulation of the Drosophila dopa decarboxylase gene in neuronal and glial cells

A cis-regulatory element selectively required for the Drosophila melanogaster dopa decarboxylase gene (Ddc) in the central nervous system has been identified previously (Scholnick et al. 1986). Here, we show that at least one additional regulatory element is required for normal neuronal expression of Ddc. We find that Ddc is normally expressed in about 125 discrete neurons and in a diffused network comprising a subset of glial cells. The expression of in vitro-altered Ddc genes was studied by immunohistochemistry following germ line reintegration with P-element vectors. Normal neuron-specific Ddc gene expression requires both the initially identified element (element I) which is 60 bp upstream from the RNA start site, and an additional regulatory element located 800-2200 bp upstream. This latter element is required for neuronal expression but is not necessary for glial expression of Ddc. We provide a model to explain how interactions between multiple regulatory elements may serve to specify cell-specific gene expression.

Different developmental schedules of dopaminergic and noradrenergic neurons in dissociation culture of fetal rat midbrain and hindbrain

The development of dopaminergic and noradrenergic neurons in dissociation cultures of mesencephalon and rhombencephalon obtained from 18-day-old rat fetuses was characterized by their capacity to take up and release catecholamines. In both types of cultures, uptake of [3H]dopamine and [3H]noradrenaline was obtained which could be inhibited by reserpine. Autoradiographic studies demonstrated an almost exclusive neuronal localization of the labeled catecholamines. The transmitters could be released by depolarization with K+ in a Ca2+-dependent manner during the entire cultivation period. In contrast, catecholamine uptake by cultures of neocortex was minimal, could not be inhibited by reserpine, and the accumulated radioactivity could not be released upon depolarization. These points provide evidence for an active accumulation of the exogenous transmitters and for the presence of stimulus-secretion coupling in a distinct population of neurons of both brain stem cultures. Striking differences between the two brain stem cultures concerned their sensitivity to desmethylimipramine and benztropine as well as the time course of the development of the uptake capacity. Desmethylimipramine inhibited the uptake of both catecholamines in rhombencephalic, but not in mesencephalic cultures. The reverse was true for benztropine. It is concluded that cultures of rhombencephalon contain predominantly noradrenergic, and those of mesencephalon dopaminergic cells. Comparison of the uptake behaviour suggested that noradrenergic neurons mature considerably later than dopaminergic neurons. The results show that dissociation cultures of mid- and hindbrain, inspite of their heterogeneous composition, can serve as valuable models for the study of development and function of dopaminergic and noradrenergic neurons, respectively.

Striatal dopamine uptake in the rat: in vivo analysis by fast cyclic voltammetry

Electrical stimulation of the median forebrain bundle of the chloral hydrate anaesthetised rat evoked dopamine release in the ipsilateral striatum, which was monitored with fast cyclic voltammetry. On cessation of stimulation, the extracellular concentration of dopamine fell to sub-detectable levels over a period of about 15 s. This fall appeared to be due to a saturable, low affinity uptake system that could be inhibited by nomifensine (20 mg/kg i.p.). These experiments constitute the first characterisation of a dopamine uptake mechanism obtained in the intact animal.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.