High-affinity uptake of serotonin into immunocytochemically identified astrocytes

Behavioral effects of adult male mice induced by low-level acetamiprid, imidacloprid, and nicotine exposure in early-life

Introduction

Acetamiprid (ACE) and imidacloprid (IMI), the neonicotinoid chemicals, are widely used as pesticides because of their rapid insecticidal activity. Although these neonicotinoids exert very low toxicity in mammals, the effects of early, low-level, chronic exposure on the adult central nervous system are largely unclear. This study investigated the effects of low-level, chronic neonicotinoids exposure in early life on the brain functions of adult mice, using environmentally relevant concentrations.

Methods

We exposed mice to an acceptable daily intake level of neonicotinoids in drinking water during the prenatal and postnatal periods. Additionally, we also exposed mice to nicotine (NIC) as a positive control. We then examined the effects on the central nervous system in adult male offspring.

Results

In the IMI and NIC exposure groups, we detected behavior that displayed impairment in learning and memory. Furthermore, immunohistochemical analysis revealed a decrease in SOX2 (as a neural stem cell marker) and GFAP (as an astrocyte marker) positive cells of the hippocampal dentate gyrus in the IMI and NIC exposure groups compared to the control group.

Discussion

These results suggest that exposure to neonicotinoids at low levels in early life affects neural circuit base formation and post-maturation behavior. Therefore, in the central nervous system of male mice, the effects of low-level, chronic neonicotinoids exposure during the perinatal period were different from the expected effects of neonicotinoids exposure in mature animals.

Necroptotic kinases are involved in the reduction of depression-induced astrocytes and fluoxetine's inhibitory effects on necroptotic kinases

The role of astrocytes in major depressive disorder has received great attention. Increasing evidence indicates that decreased astrocyte numbers in the hippocampus may be associated with depression, but the role of necroptosis in depression is unknown. Here, in a chronic unpredictable mild stress (CUMS) mouse model and a corticosterone (Cort)-induced human astrocyte injury model in vitro, we found that mice treated with chronic unpredictable mild stress for 3-5 weeks presented depressive-like behaviors and reduced body weight gain, accompanied by a reduction in astrocytes and a decrease in astrocytic brain-derived neurotropic factors (BDNF), by activation of necroptotic kinases, including RIPK1 (receptor-interacting protein kinase 1)/p-RIPK1, RIPK3 (receptor-interacting protein kinase 3)/p-RIPK3 and MLKL (mixed lineage kinase domain-like protein)/p-MLKL, and by upregulation of inflammatory cytokines in astrocytes of the mouse hippocampus. In contrast, necroptotic kinase inhibitors suppressed Cort-induced necroptotic kinase activation, reduced astrocytes, astrocytic necroptosis and dysfunction, and decreased Cort-mediated inflammatory cytokines in astrocytes. Treatment with fluoxetine (FLX) for 5 weeks improved chronic unpredictable mild stress-induced mouse depressive-like behaviors; simultaneously, fluoxetine inhibited depression-induced necroptotic kinase activation, reversed the reduction in astrocytes and astrocytic necroptosis and dysfunction, decreased inflammatory cytokines and upregulated brain-derived neurotropic factors and 5-HT1A levels. Furthermore, fluoxetine had no direct inhibitory effect on receptor-interacting protein kinase 1 phosphorylation. The combined administration of fluoxetine and necroptotic kinase inhibitors further reduced corticosterone-induced astrocyte injury. In conclusion, the reduction in astrocytes caused by depressive-like models in vivo and in vitro may be associated with the activation of necroptotic kinases and astrocytic necroptosis, and fluoxetine exerts an antidepressive effect by indirectly inhibiting receptor-interacting protein kinase 1-mediated astrocytic necroptosis.

Neuroprotective and neurotoxic outcomes of androgens and estrogens in an oxidative stress environment

BACKGROUND

The role of sex hormones on cellular function is unclear. Studies show androgens and estrogens are protective in the CNS, whereas other studies found no effects or damaging effects. Furthermore, sex differences have been observed in multiple oxidative stress-associated CNS disorders, such as Alzheimer's disease, depression, and Parkinson's disease. The goal of this study is to examine the relationship between sex hormones (i.e., androgens and estrogens) and oxidative stress on cell viability.

METHODS

N27 and PC12 neuronal and C6 glial phenotypic cell lines were used. N27 cells are female rat derived, whereas PC12 cells and C6 cells are male rat derived. These cells express estrogen receptors and the membrane-associated androgen receptor variant, AR45, but not the full-length androgen receptor. N27, PC12, and C6 cells were exposed to sex hormones either before or after an oxidative stressor to examine neuroprotective and neurotoxic properties, respectively. Estrogen receptor and androgen receptor inhibitors were used to determine the mechanisms mediating hormone-oxidative stress interactions on cell viability. Since the presence of AR45 in the human brain tissue was unknown, we examined the postmortem brain tissue from men and women for AR45 protein expression.

RESULTS

Neither androgens nor estrogens were protective against subsequent oxidative stress insults in glial cells. However, these hormones exhibited neuroprotective properties in neuronal N27 and PC12 cells via the estrogen receptor. Interestingly, a window of opportunity exists for sex hormone neuroprotection, wherein temporary hormone deprivation blocked neuroprotection by sex hormones. However, if sex hormones are applied following an oxidative stressor, they exacerbated oxidative stress-induced cell loss in neuronal and glial cells.

CONCLUSIONS

Sex hormone action on cell viability is dependent on the cellular environment. In healthy neuronal cells, sex hormones are protective against oxidative stress insults via the estrogen receptor, regardless of sex chromosome complement (XX, XY). However, in unhealthy (e.g., high oxidative stress) cells, sex hormones exacerbated oxidative stress-induced cell loss, regardless of cell type or sex chromosome complement. The non-genomic AR45 receptor, which is present in humans, mediated androgen's damaging effects, but it is unknown which receptor mediated estrogen's damaging effects. These differential effects of sex hormones that are dependent on the cellular environment, receptor profile, and cell type may mediate the observed sex differences in oxidative stress-associated CNS disorders.

Biphasic Effect of Buspirone on the H-Reflex in Acute Spinal Decerebrated Mice

Pharmacological treatment facilitating locomotor expression will also have some effects on reflex expression through the modulation of spinal circuitry. Buspirone, a partial serotonin receptor agonist (5-HT_{1 A}), was recently shown to facilitate and even trigger locomotor movements in mice after complete spinal lesion (Tx). Here, we studied its effect on the H-reflex after acute Tx in adult mice. To avoid possible impacts of anesthetics on H-reflex depression, experiments were performed after decerebration in un-anesthetized mice (N = 20). The H-reflex in plantar muscles of the hind paw was recorded after tibial nerve stimulation 2 h after Tx at the 8th thoracic vertebrae and was compared before and every 10 min after buspirone (8 mg/kg, i.p.) for 60 min (N = 8). Frequency-dependent depression (FDD) of the H-reflex was assessed before and 60 min after buspirone. Before buspirone, a stable H-reflex could be elicited in acute spinal mice and FDD of the H-reflex was observed at 5 and 10 Hz relative to 0.2 Hz, FDD was still present 60 min after buspirone. Early after buspirone, the H-reflex was significantly decreased to 69% of pre-treatment, it then increased significantly 30-60 min after treatment, reaching 170% 60 min after injection. This effect was not observed in a control group (saline, N = 5) and was blocked when a 5-HT_{1 A} antagonist (NAD-299) was administered with buspirone (N = 7). Altogether results suggest that the reported pro-locomotor effect of buspirone occurs at a time where there is a 5-HT_{1 A} receptors mediated reflex depression followed by a second phase marked by enhancement of reflex excitability.

Transglutaminase in Receptor and Neurotransmitter-Regulated Functions

Transglutaminases (TGs) and especially TG2 play important roles in neurotransmitter and receptor signaling pathways. Three different mechanisms by which TG2 interacts with neurotransmitter and receptor signaling systems will be discussed in this review. The first way in which TG2 interacts with receptor signaling is via its function as a guanine nucleotide binding protein (G-protein) coupling to G-protein coupled receptors (GPCRs) to activate down-stream signaling pathways. TG2 can exist in a least two conformations, a closed GTP-bound conformation and an open calcium-bound conformation. In the closed GTP-bound conformation, TG2 is capable of functioning as a G-protein for GPCRs. In the open calcium-bound conformation, TG2 catalyzes a transamidation reaction cross-linking proteins or catalyzing the covalent binding of a mono- or polyamine to a protein. The second mechanism is regulation of the transamidation reaction catalyzed by TG2 via receptor stimulation which can increase local calcium concentrations and thereby increase transamidation reactions. The third way in which TG2 plays a role in neurotransmitter and receptor signaling systems is via its use of monoamine neurotransmitters as a substrate. Monoamine neurotransmitters including serotonin can be substrates for transamidation to a protein often a small G-protein (also known as a small GTPase) resulting in activation of the small G-protein. The transamidation of a monoamine neurotransmitter or serotonin has been designated as monoaminylation or more specifically serotonylation, respectively. Other proteins are also targets for monoaminylation such as fibronectin and cytoskeletal proteins. These receptor and neurotransmitter-regulated reactions by TG2 play roles in physiological and key pathophysiological processes.

Alcohol administration during adulthood induces alterations of parvalbumin and glial fibrillary acidic protein immunoreactivity in rat hippocampus and cingulate cortex

Alcohol induces impairment of cognition, learning and memory. Neurotoxic effects of alcohol on the pathology of the hippocampus and the cingulate cortex were investigated in experimental rats. Parvalbumin (PV), a calcium-binding protein, is a crucial component of GABAergic neurons and glial fibrillary acidic protein immunoreactive (GFAP-ir) astrocytes have been used as markers. We investigated the effects of ethanol exposure during adulthood on the PV-ir neurons and GFAP-ir astrocytes in the hippocampus and the cingulate cortex of 3-month-old male Wistar rats. The rats were divided into 2 groups: control (C) and alcohol-exposed groups. The control group received distilled water whereas the alcohol-exposed groups received either a low dose (20%w/v, LD) or high dose (40%w/v, HD) of ethanol for periods of 21 days, 3 or 6 months. The brains of the animals were processed for immunohistochemistry using anti-parvalbumin and anti-GFAP antibodies and the numbers of PV immunoreactive (PV-ir) neurons and GFAP-ir astrocytes were counted/unit area. For each period of administration, the number of PV-ir neurons was significantly reduced for groups exposed to both the low and the high doses of ethanol compared to those of control groups in both the hippocampus and the cingulate cortex (p<0.01). In addition, the number of PV-ir neurons was progressively reduced after prolonged ethanol exposure. In contrast, there was a significantly increased number of GFAP-ir astrocytes observed in the hippocampus and the cingulate cortex in all groups exposed to ethanol and this was a function of both the duration and the dose of ethanol exposure, indicating that PV-ir neurons are as sensitive as the GFAP-ir astrocytes to ethanol exposure. Our data indicate that alcohol exposure induced a reduction of PV-ir neurons and an increase of GFAP-ir astrocytes in the hippocampus and the cingulate cortex and this may be associated with the impairment of cognition, learning and memory after chronic alcohol administration.

Functions of mature mammalian astrocytes: a current view

Before the roles of normal, mature astrocytes in the mammalian CNS can be discussed, we first need to define these cells. A definition proposed here is that such a class is best defined as consisting of the protoplasmic and fibrous astrocytes of the gray and white matter, respectively, the Bergmann glia of the molecular layer of the cerebellum, and the Muller cells of the retina. It is concluded that the established properties and functions of these mature astrocytes are essential support for neuronal activity, in the sense of Claude Bernard's principle of maintaining "la fixité du milieu intérieur." This milieu would be the extracellular space common to astrocytes and neurons. More specialized roles, such as the recently described "light guides" for retinal Muller cells can also be viewed as support and facilitation. The ECS is also, of course, common to all other neural cells, but here, I limit the discussion to perturbations of the ECS caused only by neuronal activities and the resolution of these perturbations by astrocytes, such as control of increases in extracellular K(+), uptake of excitatory amino acids, and alterations in blood vessel diameter and therefore blood flow. It is also proposed how this fits into the current morphological picture for the protoplasmic astrocytes as having small cell bodies with up to 100,000 process endings that occupy separate territories on which the processes of neighboring astrocytes scarcely intrude.

Chronic ethanol-induced glial fibrillary acidic protein (GFAP) immunoreactivity: an immunocytochemical observation in various regions of adult rat brain

In the present study, the effects of chronic ethanol (ETOH) treatment on the glial fibrillary acidic protein (GFAP) immunoreactivity was investigated in adult rat brains. ETOH were administered as increasing concentrations of 2.4%-7.2% (v/v) gradually for 21 days. Immunocytochemistry revealed that chronic-ETOH treatment increased synthesis of GFAP. The increase in the diameter and the number of GFAP (+) cells were statistically significant compared with the control group (p <. 05). An increase of GFAP immunoreactivity was evident in various white matter and gray matter structures. We concluded that functional astrocytic cells responded to chronic ETOH exposure by increasing the synthesis of GFAP.

Through the looking glass: examining neuroanatomical evidence for cellular alterations in major depression

Alterations in brain plasticity are increasingly thought to play important roles in major depressive disorder (MDD) and suicide. To gain a better understanding of the gross structural changes observed in the brains of major depressed and suicide subjects, a number of recent investigations have scrutinized the cellular integrity of brain regions implicated in mood disorders. The purpose of this review is to summarize the current knowledge on the microscopic features of neuronal and glial cell populations in these different brain regions, namely the prefrontal cortex, hippocampus, amygdala, raphe nucleus and locus coeruleus. In general, evidence from this burgeoning field supports the hypothesis of altered cell plasticity in MDD and suicide occurring mainly in key fronto-limbic areas. Interestingly, reported morphometric and cell density alterations are generally region-specific and implicate several neuromodulatory systems, notably GABAergic, serotonergic, noradrenergic and glutamatergic pathways. Cell-specific changes involve reductions in densities of astrocytes and oligodendrocytes, while increases in microglial densities have also been reported. Furthermore, increases in neuronal densities have been found in subcortical regions. The implication of such findings for our understanding of the cellular and molecular underpinnings of MDD and suicide are discussed, and the strengths and weaknesses of morphological approaches used to analyse human postmortem brain tissues are evaluated.

Astroglial plasticity in the hippocampus is affected by chronic psychosocial stress and concomitant fluoxetine treatment

Analysis of post-mortem tissue from patients with affective disorders has revealed a decreased number of glial cells in several brain areas. Here, we examined whether long-term psychosocial stress influences the number and morphology of hippocampal astrocytes in an animal model with high validity for research on the pathophysiology of major depression. Adult male tree shrews were submitted to 5 weeks of psychosocial stress, after which immunocytochemical and quantitative stereological techniques were used to estimate the total number and somal volume of glial fibrillary acidic protein-positive astrocytes in the hippocampal formation. Stress significantly decreased both the number (-25%) and somal volume (-25%) of astroglia, effects that correlated notably with the stress-induced hippocampal volume reduction. Additionally, we examined whether antidepressant treatment with fluoxetine, a selective serotonin reuptake inhibitor, offered protection from these stress-induced effects. Animals were subjected to 7 days of psychosocial stress before the onset of daily oral administration of fluoxetine (15 mg/kg per day), with stress continued throughout the 28-day treatment period. Fluoxetine treatment prevented the stress-induced numerical decrease of astrocytes, but had no counteracting effect on somal volume shrinkage. In nonstressed animals, fluoxetine treatment had no effect on the number of astrocytes, but stress exposure significantly reduced their somal volumes (-20%). These notable changes of astroglial structural plasticity in response to stress and antidepressant treatment support the notion that glial changes may contribute to the pathophysiology of affective disorders as well as to the cellular actions of antidepressants.

Neuronal cytoskeleton and synaptic densities are altered after a chronic treatment with the cannabinoid receptor agonist WIN 55,212-2

Cannabinoid CB1 receptors are the most abundant G-protein-coupled receptors in the brain. Its presynaptic location suggests a role for cannabinoids in modulating the release of neurotransmitters from axon terminals by retrograde signaling. The neuroprotective effects of cannabinoid agonists in animal models of ischemia, seizures, hypoxia, Multiple Sclerosis, Huntington and Parkinson disease have been demonstrated in several reports. The proposed mechanism for the neuroprotection ranges from antioxidant effects, reduction of microglial activation and anti-inflammatory reaction to receptor-mediated reduction of glutamate release. In the present work, we analyzed the morphological changes induced by a chronic treatment with the synthetic cannabinoid receptor agonist, WIN 55,212-2, in four brain regions where the CB1 cannabinoid receptor is present in high density: the CA1 hippocampal area, corpus striatum, cerebellum and frontal cortex. After a twice-daily treatment for 14 days with the cannabinoid receptor agonist (3 mg/kg sc, each dose) to male Wistar rats (150-170 g), the expression of neurofilaments (Nf-160 and Nf-200), microtubule-associated protein-2 (MAP-2), synaptophysin (Syn) and glial fibrillary acidic protein (GFAP) was studied by immunohistochemistry and digital image analysis. Ultrastructural study of the synapses was done using electron microscopy. After the treatment, a significant increase in the expression of neuronal cytoskeletal proteins (Nf-160, Nf-200, MAP-2) was observed, but we did not find changes in the expression of GFAP, the main astroglial cytoskeletal protein. In cerebellum, there was an increase in Syn expression and in the number of synaptic vesicles, while, in the hippocampus, an increase in the Syn expression and in the thickness of the postsynaptic densities was observed. The results obtained from these studies provide evidences on the absence of astroglial reaction and a sprouting phenomena induced by the WIN treatment that might be a key contributor to the long-term neuroprotective effects observed after cannabinoid treatments in different models of central nervous system (CNS) injury reported in the literature.

Postnatal Expression of the Serotonin Transporter in Auditory Brainstem Neurons

To investigate the putative role of serotonin (5-HT) in auditory brainstem development, the expression of the 5-HT transporter (5-HTT) was evaluated in the normal mouse brainstem at 6 different postnatal ages. The brains of C3H/HeJ mice at birth (P0) and P1, P8-P9, P13, P21-P22, P35-P36 and P48-P50 were collected and processed immunohistochemically with an antibody raised against the 5-HTT. 5-HTT immunoreactivity (5-HTT-IR) was first observed in P8 mice and was localized to cell bodies in the ventral cochlear nucleus (VCN) and principal nuclei of the superior olivary complex, including the medial nucleus of the trapezoid body. Labeled neurons were found in similar regions in older mice except at P48-50, where labeled neurons were observed in the VCN only. 5-HTT-IR was especially prominent in VCN neurons at P21 and was observed in all of the brains examined at this age. These results indicate that auditory brainstem neurons of the normal inbred mouse express the 5-HTT postnatally. The presence of 5-HTT-IR in neurons located in the VCN indicates a regional expression of the 5-HTT that is related to the ascending auditory pathway. The timing of 5-HTT expression indicates that 5-HT may modulate developmental processes that rely on cochlear input.

Astrocyte apoptosis: implications for neuroprotection

Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions can critically influence neuronal survival. Recent studies show that astrocyte apoptosis may contribute to pathogenesis of many acute and chronic neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease and Parkinson's disease. We found that incubation of cultured rat astrocytes in a Ca(2+)-containing medium after exposure to a Ca(2+)-free medium causes an increase in intracellular Ca(2+) concentration followed by apoptosis, and that NF-kappa B, reactive oxygen species, and enzymes such as calpain, xanthine oxidase, calcineurin and caspase-3 are involved in reperfusion-induced apoptosis. Furthermore, we demonstrated that heat shock protein, mitogen-activated protein/extracellular signal-regulated kinase, phosphatidylinositol-3 kinase and cyclic GMP phosphodiesterase are target molecules for anti-apoptotic drugs. This review summarizes (1) astrocytic functions in neuroprotection, (2) current evidence of astrocyte apoptosis in both in vitro and in vivo studies including its molecular pathways such as Ca(2+) overload, oxidative stress, NF-kappa B activation, mitochondrial dysfunction, endoplasmic reticulum stress, and protease activation, and (3) several drugs preventing astrocyte apoptosis. As a whole, this article provides new insights into the potential role of astrocytes as targets for neuroprotection. In addition, the advance in the knowledge of molecular mechanisms of astrocyte apoptosis may lead to the development of novel therapeutic strategies for neurodegenerative disorders.

Alternative non-coding exons support serotonin transporter mRNA expression in the brain and gut

A number of studies in recent years have linked polymorphisms within the serotonin transporter (5HTT) gene to affective disorders and anxiety traits. The human 5HTT mRNA is alternatively spliced, and the splice variants are equally expressed in the human placental cell line and dorsal raphe. In this study, using 5' rapid amplification of cDNA ends, we show that the rat 5HTT mRNA is alternatively spliced, leading to three distinct mRNAs differing in the 5' untranslated region. To determine whether the three alternatively spliced mRNA species that contain one of the following untranslated regions (i) exon 1A, 63 bp (ii) exon 1A + 1B, 125 bp or (iii) exon 1C, 101 bp, were expressed in a tissue-specific manner, we used RT-PCR and exon-specific oligonucleotide hybridization. Our results suggest two of the variants (1A + 1B and 1A) may utilize the same promoter; however, they are not equally expressed. While in the adult CNS and adrenal medulla, the shorter mRNA consisting of exon 1A was considerably more abundant, in the stomach and heart, the two variants were equally expressed. The third splice variant exon 1C is only expressed in the gut and to a lesser extent in the heart. The data from this study suggest the splice variant consisting of exon 1C may utilize a distinct promoter compared to the other two.

Up-regulation of 5-HT2B receptor density and receptor-mediated glycogenolysis in mouse astrocytes by long-term fluoxetine administration

The effects were studied of short-term (1 week) versus long-term (2-3 weeks) fluoxetine treatment of primary cultures of mouse astrocytes, differentiated by treatment with dibutyryl cyclic AMP. From previous experiments it is known that acute treatment with fluoxetine stimulates glycogenolysis and increases free cytosolic Ca2+ concentration ([Ca2+]i]) in these cultures, whereas short-term (one week) treatment with 10 microM down-regulates the effects on glycogen and [Ca2+]i, when fluoxetine administration is renewed (or when serotonin is administered). Moreover, antagonist studies have shown that these responses are evoked by activation of a 5-HT2, receptor that is different from the 5-HT2A receptor and therefore at that time tentatively were interpreted as being exerted on 5-HT2C receptors. In the present study the cultures were found by RT-PCR to express mRNA for 5-HT2A and 5-HT2B receptors, but not for the 5-HT2C receptor, identifying the 5-HT2 receptor activated by fluoxetine as the 5-HT2B receptor, the most recently cloned 5-Ht2 receptor and a 5-HT receptor known to be more abundant in human, than in rodent, brain. Both short-term and long-term treatment with fluoxetine increased the specific binding of [3H]mesulergine, a ligand for alL three 5-HT2 receptors. Long-term treatment with fluoxetine caused an agonist-induced up-regulation of the glycogenolytic response to renewed administration of fluoxetine, whereas short-term treatment abolished the fluoxetine-induced hydrolysis of glycogen. Thus, during a treatment period similar to that required for fluoxetine's clinical response to occur, 5-HT2B-mediated effects are initially down-regulated and subsequently up-regulated.

Glial fibrillary acidic protein immunoreactivity in the prefrontal cortex distinguishes younger from older adults in major depressive disorder

BACKGROUND

Recent postmortem studies in major depressive disorder (MDD) provide evidence for a reduction in the packing density and number of glial cells in different regions of the prefrontal cortex; however, the specific types of glia involved in those morphologic changes are unknown.

METHODS

The territory occupied by the astroglial marker glial fibrillary acidic protein (GFAP) was measured as an areal fraction in cortical layers III, IV, and V in sections from the dorsolateral prefrontal cortex (dlPFC) of MDD and control subjects. In addition, the packing density of GFAP-immunoreactive somata was measured by a direct three-dimensional cell counting method.

RESULTS

The mean areal fraction and packing density of GFAP-immunoreactive astrocytes in the dlPFC of MDD subjects were not significantly different from those in control subjects; however, in MDD there was a significant strong positive correlation between age and GFAP immunoreactivity. When the MDD group was divided into younger (30-45 years old) and older (46-86) adults, in the five younger MDD adults, areal fraction and packing density were smaller than the smallest values of the control subjects. In contrast, among older MDD subjects these parameters tended to be greater than in the older control subjects.

CONCLUSIONS

The present results suggest that the GFAP-immunoreactive astroglia is differentially involved in the pathology of MDD in younger compared with older adults.

Short-term ethanol exposure alters calbindin D28k and glial fibrillary acidic protein immunoreactivity in hippocampus of mice

The effects of a short-term ethanol treatment on hippocampus have been studied in mice exhibiting intoxication signs. The alterations of neurons and astrocytes as well as quantitative changes of calbindin D28k-immunoreactivity and glial fibrillary acidic protein-immunoreactivity (GFAP-IR) in selected regions of the dorsal hippocampus were examined using anti-calbindin and anti-GFAP monoclonal anti-body (mAb), respectively. The administration of 6% (v/v) ethanol during first week led to the neuronal death and decrease of the total number of calbindin-IR neurons in the examined brain regions. Moreover, the calbindin positive neurons were shown to have diminished processes following short-term ethanol exposure. These neuronal changes were associated with the increase of the GFAP-IR astrocytes. Hypertrophy of cell bodies and cytoplasmic processes of reactive astrocytes were also seen. In addition, dense, thick and highly-stained GFAP-IR cells with long processes in granular cell layer appeared entering into molecular layer of dentate gyrus. In agreement with the discrepancy percentage of neuronal cell loss and increase of reactive astrocytes detected by calbindin and GFAP-IR using image quantitative analysis, the regional differences in the vulnerability to the neurotoxic effects following short-term ethanol exposure were found: CA3>CA2>CA1>DG. These findings also illustrate the importance of correlation between calbindin and GFAP-IR when determining the morphological alteration of neuron and astroglial following short-term ethanol treatment. The disruption of calbindin and GFAP could affect neuronal-astroglial interaction, resulting in disturbance of behaviors dependent on hippocampus.

Guanethidine evokes vasodilatation in guinea pig mesenteric artery by acting on sensory nerves

In precontracted, endothelium-free guinea pig mesenteric artery rings, in which adrenergic vasoconstrictor responses had been eliminated, guanethidine (1-30 microM) produced a vasodilatation of 69.3+/-4.4%. The vasodilatation was reduced 89% by capsaicin (10 microM) or 55% by tetrodotoxin (10 microM), indicating mediation of this effect by primary sensory nerves. The nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (100 microM, 30 min) but not its stereoisomer reduced the guanethidine vasodilatation by 70%. Blockade of monoamine uptake with ouabain (25 microM, 15 min) or cocaine (5 microM, 5 min) reduced the guanethidine-induced vasodilatation by 85 and 67%, respectively. These results suggest that guanethidine produced vasodilatation by being transported into capsaicin-sensitive primary sensory nerves where it functioned as a substrate for nitric oxide synthase to generate a vasodilatory substance.

Expression of serotonin transporter protein in developing rat brain

Serotonin transporter (5-HTT), a transmembrane protein, has been shown in adult brain to be distributed not only on synaptic terminals but to a great extent on axons as well. Here we report the ontogeny of 5-HTT and its relationship with serotonin (5-HT) neurons using established 5-HTT and 5-HT antibodies. Both 5-HTT- and 5-HT-immunostaining (-im) appear in 5-HT neurons at embryonic day 12 (E12) in rostral raphe nuclei (RRN). Soon after appearing, 5-HTT-im is highly expressed on axons, similar to adult expression. However, in contrast to adult, 5-HTT-im also outlines the soma-dendrites. Rich 5-HTT-im appears along the entire length of projecting axons, extending to the growth tip. In the next 2 days, intensive 5-HTT-im axons from RRN travel a course preferentially in the floor plate and later, the medial forebrain bundle trajectory. A group of new 5-HT-im neurons and 5-HTT-im axons appear at E13 in caudal raphe nuclei. At E16-18, taking the exact trajectory course of 5-HT axons, 5-HTT-im axons reach ganglionic eminence, olfactory bulb, and cortex and disperse into many brain regions in E18-20. No 5-HTT-im cell bodies were seen in nigral, locus ceruleus, or hypothalamus. However, the transient expression of 5-HTT on non-serotonergic system was seen in cortical and striatal neuroepithelia at E12 and sensory thalamic pathways at P0-P10. Prominent 5-HTT-im fibers in thalamocortical bundles project from sensory thalamic nuclei through reticular nucleus, internal capsule bundle and form barrels in somatosensory cortices. No 5-HTT-im was seen in glia-like cells using currently available antibody. These observations indicate that 5-HTT is: (a) associated preferentially with 5-HT neurons in brainstem, (b) temporally co-expressed with 5-HT in 5-HT neurons, (c) expressed on axons prior to synaptical sites at target neurons, which strongly indicates a volumic (extrasynaptic) transmission, (d) expressed in non-5-HT neurons within a specific window, which may affect the development of the systems "borrowing" the 5-HT. The early appearance of 5-HTT may also endow functionality as well as vulnerabilities of 5-HT, sensory thalamic, and cortical neurons to 5-HTT targeting drugs during pregnancy and after birth.

Extrapineal melatonin and exogenous serotonin in seasonal affective disorder

Visible light inhibits the binding of melatonin and serotonin to cultured human peripheral blood mononuclear leukocytes (PBMLs) in winter. The decreased binding switches the metabolism in PBMLs towards serotonin synthesis, resulting in the reduced production of melatonin. The ingestion of L-tryptophan during the day is hypothesized to increase the levels of melatonin, released from the gastrointestinal tract, in patients with winter seasonal affective disorder (SAD). Due to the relative shortage of light, coincident with a predisposed metabolic error, there would be no switch towards serotonin synthesis among winter SAD patients in winter. The rate of serotonin synthesis could thus remain inadequately low to maintain optimal mood in winter SAD patients.

Serotonin transporter messenger RNA in the developing rat brain: early expression in serotonergic neurons and transient expression in non-serotonergic neurons

Serotonin has been shown to affect the development of the mammalian nervous system. The serotonin transporter is a major factor in regulating extracellular serotonin levels. Using in situ hybridization histochemistry the rat serotonin transporter messenger RNA was localized during embryogenesis, the first four weeks postnatally and adulthood. Three general classes of serotonin transporter messenger RNA expression patterns were observed: (i) early detection with continued expression through adult age, (ii) transient expression colocalized with vesicular monoamine transporter 2 messenger RNA but with no detectable tryptophan hydroxylase immunoreactivity, and (iii) transient expression in the apparent absence of both vesicular monoamine transporter 2 messenger RNA and tryptophan hydroxylase immunoreactivity. For example, hybridization for serotonin transporter messenger RNA was strong in serotonin cell body-containing areas beginning early in gestation, and remained intense through adulthood. Immunoreactivity for tryptophan hydroxylase, the rate-limiting enzyme in serotonin synthesis, was completely overlapping with the presence of serotonin transporter messenger RNA in raphe nuclei postnatally. Sensory relay systems including the ventrobasal nucleus (somatosensory), lateral and medial geniculate nuclei (visual and auditory, respectively) as well as trigeminal, cochlear and solitary nuclei were representative of the second class of observations. In general, the limbic system expressed serotonin transporter messenger RNA in the third pattern with various limbic structures differing in the timing of expression. Septum, olfactory areas and the developing hippocampus contained serotonin transporter messenger RNA early in the developing brain. Other regions such as cingulate and frontopolar cortex exhibited hybridization peri- and postnatally, respectively. Several hypothalamic nuclei and pituitary transiently expressed serotonin transporter messenger RNA either postnatally or perinatally, respectively. If the observed patterns correlate with functional protein expression, distinct classes of serotonin transporter messenger RNA expression may reflect different functional roles for the serotonin transporter and serotonin, itself. Since the serotonin transporter is a target for a number of addictive substances including cocaine and amphetamine derivatives as well as antidepressants, transient expression of the serotonin transporter might suggest a window of vulnerability of associated cells to fetal drug exposure. Re-uptake, storage and re-release from non-serotonergic neurons might serve as a feedback mechanism from target neurons to serotonergic neurons. Alternatively, the transient expression of serotonin transporter messenger RNA may reflect critical periods important for tight regulation of extracellular serotonin in several brain regions, and may indicate previously unappreciated roles for serotonin as a developmental cue.

Cellular localization and expression of the serotonin transporter in mouse brain

The high-affinity serotonin (5-HT) transporter (5-HTT) plays an important role in the removal of extracellular serotonin, thereby modulating and terminating the action of this neurotransmitter at various pre- and post-synaptic serotonergic receptors and heteroreceptors. In order to characterize the anatomical distribution of the 5-HTT in mouse brain, in situ hybridization histochemistry using 35S-labeled riboprobes was performed. These results were compared with 5-HTT binding site distribution as evaluated by [125I]RTI-55 autoradiography. High levels of 5-HTT mRNA were detected in all brain stem raphe nuclei, with variations in labeling among the various subnuclei. Those brain areas known to possess serotonergic cell bodies stained intensely for both 5-HTT mRNA and 5-HTT binding sites. In contrast to previous findings in rat brain, the highest densities of 5-HTT sites were found in areas outside the raphe complex, particularly in the substantia nigra, globus pallidus, and superior colliculi.

Antidepressant drugs inhibit a glial 5-hydroxytryptamine transporter in rat brain

We assessed the role of glial cells in the uptake of serotonin (5-hydroxytryptamine, 5-HT). Primary cultures of rat and mouse cortical astrocytes took up and deaminated 5-HT. The antidepressants citalopram, clomipramine, fluoxetine, fluvoxamine, paroxetine and sertraline inhibited this process. The presence of the mRNAs for the 5-HT transporter and monoamine oxidase-A (MOA-A) was established in cultured astrocytes and in adult rat brain areas with (midbrain and brainstem) and without (frontal cortex) serotonergic cell bodies after reverse transcription-polymerase chain reaction and hybridization with probes complementary to the cloned neuronal 5-HT transporter and MAO-A. To examine in vivo the role of astrocytes in the elimination of 5-HT from the extracellular brain space, 5-HT was perfused through dialysis probes implanted in the frontal cortex of conscious rats and its concentration was measured at the probe outlet. Tissue 5-HT recovery was dose-dependently inhibited by the concurrent perfusion of citalopram, fluoxetine and paroxetine, showing that it essentially measured uptake through the high-affinity 5-HT transporter. Rats lesioned with 5,7-dihydroxytryptamine (5,7-DHT; 88% reduction of tissue 5-HT) displayed tissue 5-HT recovery slightly higher than sham-operated rats (55 +/- 2 vs. 46 +/- 3%, P < 0.001), a finding perhaps attributable to the astrogliosis induced by 5,7-DHT denervation. Rats lesioned with 6-hydroxydopamine showed tissue 5-HT uptake similar to controls, suggesting negligible reuptake of 5-HT by catecholaminergic terminals. These results are consistent with the presence of a glial component of 5-HT uptake in the rodent brain, sensitive to antidepressants, which takes place through a 5-HT transporter very similar or identical to that present in neurons.

Extracellular release of serotonin following fluid-percussion brain injury in rats

Serotonin has been implicated in the pathobiology of central nervous system trauma. Using microdialysis techniques, we performed measurements of extracellular serotonin release within the traumatized cerebral cortex of rats subjected to moderate fluid-percussion (F-P) brain injury. Twenty-four hours prior to TBI, a F-P interface was positioned parasagitally over the right cerebral cortex. On the second day, fasted rats were anesthetized with 70% nitrous oxide, 1% halothane and 30% oxygen. Under controlled physiological conditions and normothermic brain temperature (37-37.5 degrees C), rats were injured (n = 6) with a F-P pulse ranging from 1.8 to 2.0 atm. Following trauma, brain temperature was maintained for 4 h at 37 degrees C. Sham trauma animals (n = 7) were treated in an identical manner. Brain trauma induced acute elevations in the extracellular levels of serotonin (p < 0.01, ANOVA) compared to sham-operated controls. For example, serotonin levels increased from 18.85 +/- 7.12 pm/mL (mean +/- SD) in baseline samples to 65.78 +/- 11.36 in the first 10 min after trauma. The levels of serotonin remained significantly higher than control for the first 90-min sampling period. In parallel to the increase in serotonin levels after TBI, a significant 71.1% decrease (i.e., 182.29 +/- 30.08 vs 52.75 +/- 16.92) in extracellular 5-hydroxyindoleacetic acid (5-HIAA) levels was observed during the first 10 min after TBI. These data indicate that TBI is followed by a prompt increase in the extracellular levels of serotonin in cortical regions adjacent to the impact site. These neurochemical findings indicate that serotonin may play a significant role in the pathophysiology of TBI.

Transient uptake and storage of serotonin in developing thalamic neurons

Serotonin (5-HT) has been shown to affect the development and patterning of the mouse barrelfield. We show that the dense transient 5-HT innervation of the somatosensory, visual, and auditory cortices originates in the thalamus rather than in the raphe: 5-HT is detected in thalamocortical fibers and most 5-HT cortical labeling disappears after thalamic lesions. Thalamic neurons do not synthesize 5-HT but take up exogenous 5-HT through 5-HT high affinity uptake sites located on thalamocortical axons and terminals. 3H-5-HT injected into the cortex is retrogradely transported to thalamic neurons. In situ hybridization shows a transient expression of the genes encoding the serotonin transporter and the vesicular monoamine transporter in thalamic sensory neurons. In these glutamatergic neurons, internalized 5-HT might thus be stored and used as a "borrowed transmitter" for extraneuronal signaling or could exert an intraneuronal control on thalamic maturation.

Effects of tianeptine, sertraline and clomipramine on brain serotonin metabolism: a voltammetric approach in the rat

Tianeptine is a substance enhancing the serotonir uptake while sertraline and clomipramine inhibit it. By means of 5-hydroxyin-doleacetic acid (5-HIAA) voltammetric measurements, this study investigated their influence on serotonin metabolism which depends mainly upon the activity of monoamine oxidase type A. After tianeptine injection the 5-HIAA signal increased by about 60%. This effect was maintained when the animals were pre-treated with MDL 72145 (an inhibitor of monoamine oxidase type B) but reduced when clorgyline (an inhibitor of monoamine oxidase type A) was administered after tianeptine. Administration of sertraline or clomipramine reduced the 5-HIAA signal by about 30-50%, whether the animals were pre-treated with MDL 72145 or not. It is to be concluded that tianeptine, sertraline and clomipramine can regulate the 5-HT fraction present in the synaptic cleft, not only by acting at the level of the serotoninergic neurons, but also by favoring or reducing the access of the amine to monoamine oxidase type A which is synthesized within non-serotoninergic neurons and glial cells.

Infusion of glial maturation factor-beta reduces behavioral deficits after caudate nucleus injury in rats

Adult rats with bilateral thermal lesions of the caudate nuclei (CN) show severe learning and memory deficits. The present study was designed to test the effects of an astroglial stimulating growth factor in this behavioral model. Immediately after receiving lesions of the CN, experimental subjects received an injection of one of three doses of glial maturation factor-beta (GMF-beta) directly in the lesion site. All subjects were then tested for twenty days on an active avoidance spatial alternation task. The behavioral recovery of the three groups of experimental animals was compared to that of animals having received the same brain damage and administration of a control substance (lesion controls), and to that of animals receiving a sham operation and no treatment (shams). The beneficial effects of administration were evident in the group of experimental animals receiving the lowest dose of GMF-beta. The performance of animals in this group was indistinguishable from that of the shams, and was significantly better than that of the lesion controls. The results suggest a behavioral role of GMF-beta which, in an in vitro system, is known to be a growth regulator of astroglial cells.

Selective increase in astrocytic elements in the rat dentate gyrus after chronic toluene exposure studied by GFAP immunocytochemistry and electron microscopy

Using glial fibrillary acidic protein (GFAP) immunohistochemistry, and electron microscopy, we examined changes in the features of astrocytes in the dentate gyrus of the hippocampal formation after high-dose chronic toluene inhalation (2000 ppm, 4 h/day) for 1 month. In toluene-treated rats, the numbers of GFAP-immunoreactive (IR) astrocytes were not changed, whereas the area and intensity of GFAP-IR processes were increased markedly in the dentate gyrus. In addition, dense, thick and highly-stained GFAP-IR processes appeared entering into the granular cell layer, compared with those of controls. At the electron microscopic level, numerous astrocytic processes with high electron density intervened between the granular cells. These results suggest that high-dose of chronic toluene exposure induces morphological changes in astrocytes in the dentate gyrus of the hippocampal formation.

Development of an identified serotonergic neuron in the antennal lobe of the moth and effects of reduction in serotonin during construction of olfactory glomeruli

Each olfactory (antennal) lobe of the moth Manduca sexta contains a single serotonin (5-HT) immunoreactive neuron whose processes form tufted arbors in the olfactory glomeruli. To extend our present understanding of the intercellular interactions involved in glomerulus development to the level of an individual, identified antennal lobe neuron, we first studied the morphological development of the 5-HT neuron in the presence and absence of receptor axons. Development of the neuron's glomerular tufts depends, as it does in the case of other multiglomerular neurons, on the presence of receptor axons. Processes of the 5-HT neuron are excluded from the region in which the initial steps of glomerulus construction occur and thus cannot provide a physical scaffolding on which the array of glomeruli is organized. Because the neuron's processes are present in the antennal lobe neuropil throughout postembryonic development, 5-HT could provide signals that influence the pattern of development in the lobe. By surgically producing 5-HT-depleted antennal lobes, we also tested the importance of 5-HT in the construction of olfactory glomeruli. Even in the apparent absence of 5-HT, the glomerular array initiated by the receptor axons was histologically normal, glial cells migrated to form glomerular borders, and receptor axons formed terminal branches in their normal region within each glomerulus. In some cases, 5-HT-immunoreactive processes from abnormal sources entered the lobe and formed the tufted intraglomerular branches typical of most antennal lobe neurons, suggesting that local cues strongly influence the branching patterns of developing antennal lobe neurons.

Radiation-induced changes in the profile of spinal cord serotonin, prostaglandin synthesis, and vascular permeability

PURPOSE

To investigate the profile of biochemical and physiological changes induced in the rat spinal cord by radiation, over a period of 8 months.

METHODS AND MATERIALS

The thoraco-lumbar spinal cords of Fisher rats were irradiated to a dose of 15 Gy. The rats were then followed and killed at various times afterward. Serotonin (5-HT) and its major metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed as well as prostaglandin synthesis. Microvessel permeability was assessed by quantitative evaluation of Evans blue dye extravasation.

RESULTS

None of the rats developed neurologic dysfunction, and histologic examination revealed only occasional gliosis in the ventral white matter at 240 days after irradiation. Serotonin levels were unchanged at 2, 14, and 56 days after radiation but increased at 120 and 240 days in the irradiated cord segments when compared to both the nonirradiated thoracic and cervical segments (p < 0.01) and age-matched controls (p < 0.03). The calculated utilization ratio of serotonin (5-HIAA/5-HT) remained unchanged. Immediately after radiation (at 3 and 24 h) an abrupt but brief increase in the synthesis of prostaglandin-E2 (PGE2), thromboxane (TXB2), and prostacyclin [6 keto-PGF1 alpha (6KPGF)] was noted, which returned to normal at 3 days. This was followed after 7 and 14 days by a significant fall off in synthesis of all three prostaglandins. Thereafter, at 28, 56, 120, and 240 days, escalated production of thromboxane followed, while prostacyclin synthesis remained markedly reduced (-88% of control level at 240 days). Up to 7 days after radiation the calculated TXB2/6KPGF ratio remained balanced, regardless of the observed abrupt early fluctuations in their rate of synthesis. Later, between 7 and 240 days after radiation, a significant imbalance was present which became more pronounced over time. In the first 24 h after radiation, a 104% increase in microvessel permeability was observed which returned to normal by 3 days. Normal permeability was maintained at 14 and 28 days, but at 120 and 240 days a persistent and significant increase of 98% and 73% respectively above control level was noted.

CONCLUSIONS

Radiation induces severe impairment in microvessel function even in the histologically unaffected spinal cord, and alters the secretory phenotype of various cell systems in the central nervous system.

Plasticity of astrocytes

It is becoming apparent that astrocytes carry out a large number of different functions in brain and are able to modify their characteristics throughout life, that is they exhibit a high degree of plasticity in their phenotype. For example, the morphology of astrocytes changes markedly during neuronal migration, maturation, and degeneration. It is conceivable that these cells must constantly adjust their abilities to meet changes in brain environment. Several examples of astrocytic plasticity are presented in this review. First, the ability of astrocytes to recognize neuronal signals can change qualitatively as well as quantitatively; evidence suggests that the expression of glial receptors may be developmentally regulated by both intrinsic and extrinsic signals. Second, the expression of adrenergic receptors by astrocytes in adult brain can change in response to neuronal degeneration. The up-regulation of beta-adrenergic receptors in this case suggests that these receptors play a role in function of reactive astrocytes. Finally, glial morphology can be reciprocally regulated by neurotransmitters such as norepinephrine and glutamate. This reciprocal regulation may be significant since both beta-adrenergic receptors and glutamate transporters are found predominantly in astrocytes in the brain. The change in glial morphology may also affect neuronal activity by changing the volume of the extracellular space.

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.

Neuro-glial neurotrophic interaction in the S-100 beta retarded mutant mouse (Polydactyly Nagoya). II. Co-cultures study

The homozygote of a mouse strain with genetic polydactyly (Polydactyly Nagoya, Pdn) shows several brain abnormalities, and significant decrease of S-100 beta in the brain [17]. An accompanying paper [18] demonstrates that the hippocampus and caudo-dorsal cortex of homozygote (Pdn/Pdn) mouse were markedly reduced in S-100 beta positive astrocytes and serotonergic fibers, and the content of 5-HT and 5-HIAA of hippocampus and cortex of Pdn/Pdn mouse was lower than those of heterozygote (Pdn/+) or wild type (+/+) mice. To further clarify the effects of target tissues from different type brains on the development of serotonergic neurons, raphe neurons from Pdn/Pdn or +/+ newborn mice were co-cultured with hippocampus or cortex of +/+ or Pdn/Pdn newborn mice. The growth of the serotonergic neurons in the mesencephalic raphe tissue dissociated cultures was estimated by measuring the specific uptake of [3H]5-HT. The development of both genotypes (Pdn/Pdn and +/+) of serotonergic neurons was enhanced by co-cultures with target tissues (hippocampus and cortex) of +/+ brain. This effect was not observed in the co-cultures with Pdn/Pdn brain as a source of target tissue. The present results support the idea that the developmental defect of serotonergic fibers in the Pdn mutant mouse is caused by the deficiency of S-100 beta in the astrocyte of this mutant, and suggest that S-100 beta is a serotonergic growth factor. This mutant mouse is a useful in vivo model to study neural-glial neurotrophic interactions.

Uptake inhibitors increase extracellular serotonin concentration measured by brain microdialysis

The physiological role of the serotonin transporter on serotonin neuronal membranes apparently is to inactivate serotonin that has been released into the synaptic cleft. Drugs that inhibit the uptake of serotonin increase the amount of serotonin in the synaptic cleft and enhance serotonergic neurotransmission. As an adaptive response to the increased amount of serotonin in the synaptic cleft, serotonin neurons decrease their firing and release of serotonin to limit the magnitude of the increase in extracellular serotonin concentration. The increase in extracellular serotonin in rat brain caused by inhibitors of the serotonin uptake carrier has been characterized by brain microdialysis coupled to liquid chromatography with electrochemical detection. These drugs cause rapid accumulation of extracellular serotonin in several brain regions, although the increase in frontal cortex may be smaller than in other nerve terminal regions or in the cell body-containing raphe region.

Cellular localization of serotonin transporter mRNA in the rat brain

Expression of serotonin (5-hydroxytryptamine, 5-HT) transporter mRNA in the rat brain was examined by in situ hybridization histochemistry with a synthetic oligonucleotide probe. 5-HT transporter mRNA was expressed in neurons in most of the raphe nuclei. The dorsal and median raphe nuclei contained intensely labeled neurons, while the caudal linear nucleus, raphe magnus nucleus, raphe pontis nucleus, raphe pallidus nucleus and the raphe obscurus nucleus contained weakly or moderately labeled neurons. The localization pattern of the 5-HT transporter mRNA-positive neurons coincides fairly well with that of 5-HT-immunoreactive neurons, indicating that 5-HT transporter is primarily located in serotonergic neurons.

Astrocytic hypertrophy: an important pathological feature of chronic experimental autoimmune encephalitis in aged rats

Experimental autoimmune encephalomyelitis (EAE) was induced in young (2-3 month old), middle-aged (12-13 month old) and geriatric (24-26 month old) Lewis (JC) rats by active immunisation with myelin basic protein (MBP) in complete Freund's adjuvant (CFA). It was found that aged Lewis (JC) rats developed a more chronic form of EAE than younger rats of the same strain, a phenomenon observed in both male and female rats despite males developing more severe disease than females at all ages. Middle-aged recipients also developed more severe disease than young recipients when EAE was induced by the adoptive transfer of lymphocytes from actively immunised young donors, suggesting that disease chronicity in middle-aged animals is a property of the central nervous system (CNS) milieu. Histological studies demonstrated that disease chronicity did not correlate with the number of inflammatory lesions in the CNS, young animals containing substantial numbers of CNS lesions following recovery and lesions being largely absent from middle-aged animals which still exhibited signs of disease. No significant differences were found in the degree of fibrin deposition or demyelination between young and middle-aged or symptomatic and asymptomatic animals. However, astrocytic hypertrophy was found to correlate with manifestation of disease in both young and middle-aged animals and in particular with disease chronicity in middle-aged animals. In parallel studies, no significant differences were found in the levels of the inflammatory mediators tumor necrosis factor (TNF)-alpha, prostaglandin E (PGE)2, reactive nitrogen intermediates (RNI) and corticosterone in young and middle-aged animals. However, markedly elevated corticosterone levels were found in both young and middle-aged animals with the development of clinical signs which returned to baseline levels with the resolution of clinical signs. Elevated levels of RNI were evident in animals immediately prior to and during the early stages of symptomatic EAE. Although these results suggest that nitric oxide may play a role in the pathogenesis of disease, whereas corticosterone may play a role in the immunoregulation of the disease, these factors cannot explain differences in disease chronicity evident in middle-aged animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional neuropathology in schizophrenia: where are we? Where are we going?

This paper presents a neurologic formulation for the clinical features of the schizophrenic syndrome, and tests it against a systematic, region by region review of available postmortem neuroanatomical and neuropharmacological data. Based on this review a model is proposed that postulates a developmental lesion affecting the midline neurotransmitter-specific ascending projection systems. Due to the facilitatory role these systems play in the development of the brain regions to which they project, such a lesion is one parsimonious, and testable, explanation for virtually all the clinical, laboratory, and pathological findings reported to date in schizophrenia research. A case is made for establishing a global antemortem-postmortem collaboration using a Latin square design; the alternative may be that, as has happened in the past, the best efforts of dilligent researchers around the world may lead to little improvement in our understanding of schizophrenia.

Detection of 5-hydroxytryptamine2 receptors by radioligand binding, northern blot analysis, and Ca2+ responses in rat primary astrocyte cultures

Radioligand binding, Northern blot analysis, and changes in [Ca2+]i were used to study serotonin [5-hydroxytryptamine (5HT)] receptor subtypes in primary cultures of astrocytes from neonatal rat cerebral cortex. Radioligand binding studies revealed the presence of 5HT2, but not the 5HT1 or 5HT3 receptor subtypes. Radioligand binding was also used to show the presence of serotonin uptake sites, which had previously been shown to be present by [3H]-5HT uptake, and also alpha 1-adrenergic receptors as has previously been reported by binding studies. Northern blot analysis of cortical astrocyte mRNA demonstrated the presence of transcripts for 5HT2 receptors, but failed to identify mRNA for 5HT1a or 5HT1c receptors. Thus, results from Northern blot analysis correlated with the radioligand binding data which showed only 5HT2 receptors. Equilibrium saturation studies, using 125[I]-LSD to label 5HT2 receptors, yielded a KD of 9 nM and a Bmax of 177 fmol/mg protein. Radioligand binding studies or primary astrocyte cultures prepared from other brain regions also showed the presence of alpha 1-adrenergic, 5HT2 receptor, and 5HT-uptake sites, but no detectable 5HT1a receptors, which were the only 5HT1 receptors studied. Studies demonstrating 5HT-induced, spiperone- and ketanserin-sensitive increases in free [Ca2+]i as measured by FURA-2, showed that the 5HT2 receptors were functional in these cells. These data provide clear evidence for the existence of both 5HT2 receptors and 5HT-uptake sites in the same primary astrocyte cultures from neonatal rat cerebral cortex, with no detectable evidence of 5HT1a or 5HT1c subtypes.

Serotonergic manipulations in experimental neoplastic spinal cord compression

The effects of differing strategies of serotonergic manipulation on vascular permeability, prostaglandin E2 (PGE2) synthesis, and the clinical course are evaluated in an experimental model of neoplastic spinal cord compression in rats. Serotonergic manipulations include in vivo inhibition of serotonin (5-HT) synthesis by p-chlorophenylalanine (p-CPA) and in vivo blockage of serotonin type 2 (5-HT2) receptors either by the selective antagonist ketanserin or by cyproheptadine. In paralyzed rats, the ratio of 5-hydroxyindole-3-acetic acid (5-HIAA) to 5-HT is significantly elevated in the compressed segments, suggesting that 5-HT utilization is increased. Treatment with p-CPA attenuates spinal 5-HT levels by 62.8% +/- 5.1% (mean +/- standard deviation) and reduces the elevated 5-HIAA:5-HT ratio to the normal value. The increased synthesis of PGE2 observed in the compressed cord is unaffected by p-CPA or ketanserin treatment but is markedly attenuated by cyproheptadine. Ketanserin reduces the 10-fold increase in spinal cord permeability observed in paralyzed rats in a clearly dose-related manner. If given at the first sign of neurological dysfunction, ketanserin delays the onset of paraplegia with the 1-mg/kg dose being clearly superior. Cyproheptadine and p-CPA also reduce the increased permeability and protract the course to paraplegia. A comparison of the effect of dexamethasone, indomethacin, cyproheptadine, p-CPA, and ketanserin reveals that they protract the disease course by 48%, 57%, 60%, 64%, and 78%, respectively. These data suggest that 5-HT2 receptors mediate some of the deleterious vascular consequences observed in the compressed spinal cord by a mechanism not coupled with PGE2 synthesis. A potential benefit of serotonergic manipulations for the acute treatment of neoplastic spinal cord compression is suggested.

Monoamine oxidase inhibitors increase preferentially extracellular 5-hydroxytryptamine in the midbrain raphe nuclei. A brain microdialysis study in the awake rat

We have examined the local and systemic effects of clorgyline, tranylcypromine and deprenyl on extracellular serotonin (5-HT) and 5-hydroxyindoleacetic acid in the raphe nuclei and in frontal cortex of awake, freely-moving rats using microdialysis. When administered through the dialysis probe, monoamine oxidase (monoamine: oxygen oxidoreductase (deaminating), E.C. 1.4.3.4., MAO) inhibitors increased 5-HT output in a dose-dependent manner in both brain areas. The effects were more pronounced in the raphe nuclei for the three MAO inhibitors at all doses assayed. When the monoamine oxidase inhibitors were given i.p., dialysate 5-HT increased dramatically, after tranylcypromine (15 mg/kg), in raphe nuclei and frontal cortex (area under the curve (AUC) to 4 h post-treatment: 63-fold and 11-fold, respectively) whereas the effects of clorgyline (10 mg/kg) were much less pronounced (+47% increase in the AUC for raphe nuclei, P < 0.09; +18% increase in the AUC for frontal cortex, n.s.). Deprenyl (2.5 mg/kg, i.p.) induced a moderate (+22%) increase of dialysate 5-HT from the raphe nuclei but did not cause a change in dialysate 5-HT from the frontal cortex (+4%). However, clorgyline, or deprenyl, dramatically increased dialysate 5-HT in animals which had been pre-treated with the above dose of deprenyl, or clorgyline, respectively, showing that the blockade of both forms of MAO results in much larger increases of extracellular 5-HT than does the blockade of either form alone.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effects of serotonin and carbachol on glial and neuronal rubidium uptake in leech CNS

Effects of serotonin (5-HT) and carbachol on Rb uptake (used as a K marker) in leech neuron and glia were studied by electron probe microanalysis (EPMA). Hirudo medicinalis ganglia were perfused 60 s in 4 mM Rb substituted normal leech Ringer's with and without 5-HT (dosage range 5-500 microM) or carbachol (range 10-1000 microM), quench frozen cryosectioned, and subjected to EPMA to determine elemental mass fractions and cell water content. Both 5-HT and carbachol altered leech neuron and glial cell elemental distribution and water content. In glial cells, a dose-dependent increase in Rb uptake was observed following 5-HT (control: 26 +/- 2 microM; 5 microM: 47 +/- 4; 50 microM: 62 +/- 4; 500 microM: 82 +/- 11 mmol/kg dry wt. +/- S.E.M.) and carbachol (10 microM: 35 +/- 3; 100 microM: 52 +/- 3; 1000 microM: 68 +/- 3 mmol/kg dry wt. +/- S.E.M.). In neurons, 5-HT and carbachol had small effects. 5-HT decreased glial and neuronal cell water content. Carbachol decreased neuronal (but not glial) water content by approximately the same amount (mean decrease 9%) regardless of dose. Both 5-HT and carbachol affected glial cell K-accumulating properties, providing evidence that certain neurotransmitters may modulate invertebrate glial cells' K clearance function.

Ischemia-induced extracellular release of serotonin plays a role in CA1 neuronal cell death in rats

BACKGROUND AND PURPOSE

Serotonin, via 5-HT2 receptors, exerts an excitatory effect on CA1 neurons and may play a role in ischemia-induced excitotoxic damage. To evaluate the role of serotonin in ischemia, both neurochemical and histopathological studies were performed.

METHODS

Neurochemical studies included rats that were subjected to 12.5 or 20 minutes of normothermic ischemia by two-vessel occlusion plus hypotension, and extracellular serotonin levels were measured in the hippocampus (12.5 minutes' ischemia, n = 5) or striatum (20 minutes' ischemia, n = 13) by microdialysis. In the histopathological study the effect of 8 mg/kg ritanserin, a 5-HT2 antagonist, administered continuously from 30 minutes prior to ischemia until 1 hour of recirculation was evaluated in five rats subjected to 10 minutes of ischemia. After 3 days, the numbers of normal-appearing neurons in the CA1 subregions were counted.

RESULTS

Ischemia of 12.5 minutes' duration induced a fourfold increase in serotonin in the hippocampus (mean +/- SEM baseline, 1.86 +/- 0.25 pmol/ml perfusate; during ischemia, 8.14 +/- 0.89 pmol/ml; p < 0.05 by analysis of variance). Twenty minutes of ischemia induced a 25-fold increase in serotonin in the dorsolateral striatum (baseline, 0.98 +/- 0.15 pmol/ml; ischemia, 24.4 +/- 5.93 pmol/ml; p < 0.001). The histopathological study demonstrated severe ischemic damage in all CA1 subregions of nontreated animals (medial, 34 +/- 16 normal-appearing neurons, middle, 52.2 +/- 22.9 neurons; lateral, 56.6 +/- 21.8 neurons). Treatment with ritanserin significantly attenuated ischemic damage (medial, 117.6 +/- 6.5 neurons; middle, 131.4 +/- 4.9 neurons; lateral, 130 +/- 7.5 neurons; p < 0.01 different from nontreated).

CONCLUSIONS

Taken together, these results suggest that serotonin plays a detrimental role, mediated by 5-HT2 receptors, in the development of ischemic damage.

Uptake of [3H]serotonin and [3H]glutamate by primary astrocyte cultures. I. Effects of different sera and time in culture

Na(+)-dependent, fluoxetine-sensitive high-affinity uptake of serotonin and Na(+)-dependent uptake of glutamate were studied in primary astrocyte cultures from 1-day-old rat neocortex. This uptake was independent of time in culture from 1 to 6 weeks. High-affinity serotonin uptake was decreased when cells were grown in horse serum as compared to fetal bovine serum and was almost absent when cells were grown in chemically defined medium. In contrast, glutamate uptake was unaffected by the composition of the medium in which the cultures were grown. The serum effect on serotonin uptake was not due to the greater level of serotonin in the fetal bovine serum and was only reversed by a change of serum over a time period of days.

Uptake of [3H]serotonin and [3H]glutamate by primary astrocyte cultures. II. Differences in cultures prepared from different brain regions

Regional astrocyte cultures were derived by dissecting six regions; brain stem, cerebellum, mesencephalon, basal ganglia plus diencephalon, cerebral cortex, and hippocampus, from 3 to 4-day-old neonatal rat brains. Glial fibrillary acidic protein (GFAP) immunocytochemistry was used to confirm the astrocyte composition of the cultures. The percentage of GFAP (+) cells between regions varied from 75% to 100%. Once confluent these cultures were incubated with radiolabeled serotonin or glutamate for uptake and autoradiographic studies. For the different brain regions Na(+)-dependent, [3H] L-glutamate, and fluoxetine-sensitive [3H] 5-HT uptake varied markedly. The relative order of uptake for [3H] 5-HT was MS (mesencephalon) greater than CC (cerebral cortex) greater than BG + DI (basal ganglia + diencephalon) greater than HP (hippocampus) greater than BS (brain stem) greater than CB (cerebellum). For [3H] L-glutamate the order was HP greater than CC greater than BG + DI greater than MS = BS greater than CB. For [3H] 5-HT this essentially corresponds to the reported order of binding in situ of the [3H] 5-HT-specific uptake ligand [3H] citalopram. For [3H] L-glutamate regional variation of the uptake for the different cultures corresponds to the regional uptake reported for different regions of rat brain. Double-label studies with GFAP and radiolabeled neurotransmitters were also used to study uptake into GFAP(+) astrocytes by autoradiography. Flat GFAP cells with or without processes comprised 65-98% of the cultures and represented most of the uptake. The percentage of all GFAP(+) cells that were positive for uptake of ARG varied from 50% to 90% and also showed differences in grain density both intra- and inter-regionally. These differences in transmitter uptake by GFAP(+) astrocytes in primary culture, which are dependent on the region of origin and correspond to regional differences in situ, suggest that such uptake in vitro may reflect uptake by astrocytes in vivo. Implied in this is that uptake by astrocytes represents a significant component of serotonin uptake in vivo.

Postnatal development of dye-coupling among astrocytes in rat visual cortex

Intercellular coupling among astrocytes was studied in rat visual cortex slices from animals aged 1 week to 4 months. Cell coupling via gap junctions was determined by the dye spread of the low molecular weight dye Lucifer Yellow CH injected into electrophysiologically identified cells to adjacent cells. Coupling among glial cells was first detected at postnatal day 11 and was thereafter consistently observed until adulthood. Dye spread was observed up to 300 microns radially from the injected cell covering multiple cortical layers. Following dye injection into a single cell up to several hundred Lucifer Yellow-positive cells could be observed. Quantitative analysis revealed a similar extent of dye spread at different developmental stages including a quite constant number of dye-coupled astrocytes from the end of the second postnatal week to adulthood. Double labelling of Lucifer Yellow-filled cells with an antiserum against the glial fibrillary acidic protein confirmed the astrocytic nature of the injected and coupled cells. Comparison of the density of dye-coupled cells in a given area and the total number of astrocytes as revealed by immunocytochemical staining suggests that dye-coupling includes the entire local astrocytic population. It is concluded that coupling among astrocytes via gap junctions in rat visual cortex occurs shortly after birth and reflects one of the first steps in astroglial maturation.