Biomedical subjects

J L Barker

Publications and source records attributed to J L Barker.

At least 37 records · Page 2Linked to original sources

PubMed2000

Striatal matrix neurons of the rat differentiate in culture from dissociated fetal progenitor cells isolated by buoyant density centrifugation.

The adult striatum is composed of interlacing compartments known as patches (striosomes) and matrix, which differ with respect to a host of architectonic, biochemical and developmental parameters. We have exploited the 2-phase development of the striatum, employing buoyant-density fractionation to separate proliferating/undifferentiated neural precursors from the differentiated neurons of the E19 striatum. Primary cell cultures were established for the collected fractions, and immunohistochemistry for maturational and compartment-specific markers performed. The results indicate that the least buoyant, striatal precursors concentrate principally in the low buoyancy fraction of the gradient, and in culture express known matrix phenotype markers in an appropriate time frame.

Animals↗

PubMed2000

Testosterone and estrogen affect neuronal differentiation but not proliferation in early embryonic cortex of the rat: the possible roles of androgen and estrogen receptors.

We examined the effect of testosterone (T) and 17 beta-estradiol (E) on differentiation and proliferation of cultured neurons from the cortex of 14-day-rat embryos (E14) using immunocytochemistry. We found that the cultures receiving E had significantly more neurons with longer neurites than the control cultures, while both fewer and less differentiated neurons were seen after 24 h of incubation with T. However, neither T nor E changed the number of cells positive for BrdU, a proliferation marker. We also found that the androgen receptor (AR) was markedly expressed in the neurons, whereas the expression of estrogen (ER(alpha)) receptor was barely detectable. These results suggest that E and T differ in effect on differentiation, while neither affect proliferation in early developmental cortex. Furthermore, since the AR is expressed in the cortical neurons by E14, the inhibitory effect of T on differentiation may be receptor-mediated, while the stimulatory effects of estrogen in the cortex do not appear to involve nuclear ER(alpha) at this developmental stage.

Androgens↗

PubMed2000

TNF-alpha induced over-expression of GFAP is associated with MAPKs.

Increased levels of tumor necrosis factor-alpha (TNF-alpha), a pluripotent cytokine that is reportedly mitogenic to astrocytes, are associated with the expression of glial fibrillary acidic protein (GFAP), the most specific marker for astrocytes, in many neuropathological conditions, including brain injury, CNS infection, Creutzfeldt-Jakob disease and Alzheimer's disease. Here, we show that treatment of cultured astrocytes with TNF-alpha resulted in dramatic over-expression of GFAP, associated with a substantial activation of the mitogen activated protein kinase (MAPK) Erk2 (extracellular signal-regulated protein kinase). We also demonstrate that TNF-alpha-induced over-expression of GFAP was significantly attenuated by the MAPK inhibitor PD98059. We conclude that TNF-alpha may upregulate GFAP through the MAPK signaling pathway. Because increased GFAP is a hallmark of reactive gliosis, understanding the mechanisms that regulate GFAP expression may facilitate development of strategies to minimize the gliosis associated with many brain diseases.

Animals↗

PubMed2000

Surface-accessible GABA supports tonic and quantal synaptic transmission.

Exocytosis is commonly viewed as the only secretory process able to account for quantal forms of fast synaptic transmission. However, the demonstrated variability and composite properties of miniature postsynaptic signals are not easily explained by all-or-none exocytotic discharge of transmitter in solution from inside vesicles. Recent studies of endocrine secretion have shown that hormone release does not coincide with exocytosis due to its trapping in the core matrix of the granule. Thus, we tested whether the synaptic transmitter GABA could also be held in a matrix before being released. Using confocal microscopy and flow cytometry of embryonic rat hippocampal neurons, we found a GABA immunoreaction at the surface of live cell bodies and growth cones that coincided spatially and quantitatively with the binding of tetanus toxin fragment C (TTFC). TTFC binds predominantly at membrane sites containing the trisialoglycosphingolipid GT1b. Using flow cytometry, GT1b-containing liposomes preincubated in 100 nM GABA exhibited the same relationship between GABA and TTFC surface binding as found on neurons and growth cones. Embryonic neurons differentiated in culture expressed initially a tonic, and after 3-5 days, transient, postsynaptic signals mediated by GABA acting at GABA(A) receptor/Cl(-) channels. A stream of saline applied to the neuronal surface rapidly and reversibly suppressed both tonic and transient signals. A brief application of the GABAmimetic isoguvacine immediately transformed both tonic and transient GABAergic signals into tonic and transient isoguvacinergic signals. These results and those in the literature are consistent with an immediately releasable compartment of transmitter accessible from the presynaptic surface.

Adsorption↗

PubMed2000

Dual video microscopic imaging of membrane potential and cytosolic calcium of immunoidentified embryonic rat cortical cells.

Membrane potential (MP) and cytosolic Ca2+ (Ca2+(c)) constitute important components involved in the physiological regulation of a myriad of cell functions in eukaryotic organisms. In particular, during development of the central nervous system, both properties are thought to be important in the regulation of cell cycle, cell migration, cell differentiation, cell-cell communication, and naturally occurring cell death. However, obtaining insight into the precise relationship between these two parameters of cell function is relatively limited either by technical difficulties inherent in using electrical recordings of membrane properties in conjunction with optical imaging of single cells or by employing optical imaging of either one or another property alone. Here, we describe in detail a novel strategy to record changes in both MP and Ca2+(c) from many intact single cells in a noninvasive manner using digital video microscopy. This method involves double-loading the cells with voltage- and calcium-sensitive fluorescent indicator dyes, green oxonol, and fura-2, which can be sequentially excited with a mercury arc lamp filtered at appropriate wavelengths and their resulting emissions can be captured with an intensified charged-coupled device camera at 1-s intervals. As an example of the utility of dual-recording strategy, we present data on a distinct functional expression of excitable membrane and cytoplasmic calcium properties in proliferating and differentiating embryonic rat cerebral cortical cells.

Animals↗

PubMed2000

Acetylcholine stimulates cortical precursor cell proliferation in vitro via muscarinic receptor activation and MAP kinase phosphorylation.

Increasing evidence has shown that some neurotransmitters act as growth-regulatory signals during brain development. Here we report a role for the classical neurotransmitter acetylcholine (ACh) to stimulate proliferation of neural stem cells and stem cell-derived progenitor cells during neural cell lineage progression in vitro. Neuroepithelial cells in the ventricular zone of the embryonic rat cortex were found to express the m2 subtype of the muscarinic receptor. Neural precursor cells dissociated from the embryonic rat cortical neuroepithelium were expanded in culture with basic fibroblast growth factor (bFGF). reverse transcriptase-polymerase chain reaction (RT-PCR) revealed the presence of m2, m3 and m4 muscarinic receptor subtype transcripts, while immunocytochemistry demonstrated m2 protein. ACh and carbachol induced an increase in cytosolic Ca2+ and membrane currents in proliferating (BrdU+) cells, both of which were abolished by atropine. Exposure of bFGF-deprived precursor cells to muscarinic agonists not only increased both cell number and DNA synthesis, but also enhanced differentiation of neurons. These effects were blocked by atropine, indicating the involvement of muscarinic ACh receptors. The growth-stimulating effects were also antagonized by a panel of inhibitors of second messengers, including 1,2-bis-(O-aminophenoxy)-ethane-N,N,N', N'-tetraacetic acid (BAPTA-AM) to chelate cytosolic Ca2+, EGTA to complex extracellular Ca2+, pertussis toxin, which uncouples certain G-proteins, the protein kinase C inhibitor H7 and the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Muscarinic agonists activated MAPK, which was significantly inhibited by atropine and the same panel of inhibitors. Thus, muscarinic receptors expressed by neural precursors transduce a growth-regulatory signal during neurogenesis via pathways involving pertussis toxin-sensitive G-proteins, Ca2+ signalling, protein kinase C activation, MAPK phosphorylation and DNA synthesis.

Acetylcholine↗

PubMed2000

Developmental changes in cell calcium homeostasis during neurogenesis of the embryonic rat cerebral cortex.

We quantified cytoplasmic Ca(2+) (Ca(2+)(c)) levels in cells dissociated from the embryonic (E) rat cortex during neurogenesis. Dual-recordings by flow cytometry using calcium and voltage-sensitive dyes revealed that, at the beginning of cortical development (E11-12), precursor cells exhibited either low (<100 nM), moderate (approximately 250 nM) or high (>1 microM) resting Ca(2+)(c) levels and well-polarized (-70 mV) or less-polarized (-40 mV) resting membrane potentials which reflected postmitotic or proliferative stages of the cell cycle. Ca(2+)(c) levels of all cells included a Ca(2+)(o) entry component, which was also Mn(2+)-permeant in actively proliferating precursors. Postmitotic, but not premitotic, precursors exhibited thapsigargin-sensitive intracellular Ca(2+) (Ca(2+)(i)) stores, which had similar capacities throughout neuronal lineage development. Differentiating neurons, but not precursors expressed Ca(2+)(i) stores with ryanodine and caffeine sensitivity and baseline Ca(2+)(c) levels that depended on Na(+)-Ca(2+) exchange activity. Voltage-dependent Ca(2+)(o) entry was not detected in precursors, but emerged during neuronal differentiation, with most of the neurons expressing functional L-type Ca(2+) channels. Ca(2+) imaging of individually immunoidentified cells acutely recovered in culture confirmed that precursors differentiate into neurons which stereotypically exhibit Ca(2+)(o) entry at the level of the membrane with increased Ca(2+)(i) release mechanisms on Ca(2+)(i) stores, Na(+)-Ca(2+) exchange activity and expression of voltage-dependent Ca(2+) channels.

Animals↗

PubMed2000

Stereotypical physiological properties emerge during early neuronal and glial lineage development in the embryonic rat neocortex.

Surface immunolabeling was used together with membrane potential and/or Ca(2+) indicator dyes to characterize physiological properties emerging among precursors, neuroglial progenitors and differentiating neurons during neurogenesis of embryonic rat neocortex. Cells were immunoidentified with tetanus toxin (TnTx), which binds to gangliosides expressed by neurons, and anti-A2B5, which reacts with gangliosides expressed by neuroglial progenitors. Microdissection of the neocortex into ventricular/subventricular zone (VZ/SVZ) and cortical plate/subplate (CP/SP) regions further resolved the TnTx/A2B5-immunoidentified cells into pre- and post-migratory subpopulations. Quantitative immunocytochemistry revealed mainly proliferative (BrdU(+)) and immature (nestin(+)) elements among TnTx(-)A2B5(-) precursors and TnTx(-)A2B5(+) progenitors in the VZ/SVZ, and the appearance of neuron-specific antigens among post-mitotic TnTx(+) subpopulations of the CP/SP. Flow cytometry of acutely prepared cells in suspension and dual-imaging of cells in culture revealed that ionotropic amino acid receptors and metabotropic acetylcholine receptors closely paralleled the emergence of voltage-dependent Na(+) and Ca(2+) channels and Na(+)-Ca(2+) exchange activity among TnTx(+) neuronal progenitors migrating from VZ/SVZ to CP/SP. During this period, TnTx(-)A2B5(-) precursors and TnTx(-)A2B5(+) neuroglial progenitors from VZ/SVZ predominantly exhibited Ca(2+) responses to ATP. Thus, stereotypical and contrasting physiologies emerge among embryonic cortical cells in vivo as they initially progress from proliferating precursors and progenitors along neuronal and glial cell lineages.

Animals↗

PubMed2000

GABA receptor antagonists modulate postmitotic cell migration in slice cultures of embryonic rat cortex.

Recent studies indicate that GABA acts as a chemoattractant during rat cortical histogenesis. In vivo, GABA localizes in appropriate locations for a chemoattractant, along migratory routes and near target destinations for migrating cortical neurons. In vitro, GABA induces dissociated embryonic cortical neurons to migrate. Here, embryonic rat cortical slices were cultured in the presence or absence of GABA receptor (GABA-R) antagonists to assess GABA's effects on neuronal migration in situ. Gestational day 18 (E18) cortical slices were incubated overnight in bromodeoxyuridine (BrdU)-containing medium to label ventricular zone (vz) cells as they underwent terminal mitosis. The slices were then cultured in BrdU-free medium with or without GABA-R antagonists. In control slices, most BrdU(+) cells were observed in the cortical plate (cp) after 48 h. In contrast, cultures maintained in either saclofen (a GABA(B)-R antagonist) or picrotoxin (a GABA(A/C)-R antagonist) had few BrdU-labeled cp cells. However, the effects of the two antagonists were distinct. In the picrotoxin-treated slices, nearly half of all BrdU(+) cells remained in the vz and subventricular zone (svz), whereas saclofen treatment resulted in an accumulation of BrdU(+) cells in the intermediate zone (iz). Bicuculline, a GABA(A)-R antagonist, did not block, but rather enhanced migration of BrdU(+) cells into the cp. These results provide evidence that picrotoxin-sensitive receptors promote the migration of vz/svz cells into the iz, while saclofen-sensitive receptors signal cells to migrate into the cp. Thus, as cortical cells differentiate, changing receptor expression appears to modulate migratory responses to GABA.

Animals↗

PubMed2000

The virulence regulatory protein ToxR mediates enhanced bile resistance in Vibrio cholerae and other pathogenic Vibrio species.

The transmembrane regulatory protein ToxR is required for expression of virulence factors in the human diarrheal pathogen Vibrio cholerae, including cholera toxin (CT) and the toxin coregulated pilus (TCP). ToxR is necessary for transcription of the gene encoding a second regulatory protein, ToxT, which is the direct transcriptional activator of CT and TCP genes. However, ToxR, independent of ToxT, directly activates and represses transcription of the outer membrane porins OmpU and OmpT, respectively. The genes encoding TCP and CT (and including ToxT) lie on horizontally acquired genetic elements, while the toxR, ompU, and ompT genes are apparently in the ancestral Vibrio chromosome. The contribution of ToxR-dependent modulation of outer membrane porins to cholera pathogenesis has remained unknown. We demonstrate that ToxR mediates enhanced bile resistance in a ToxT-independent manner. In both classical and El Tor biotypes of V. cholerae, a toxR mutant strain has a reduced minimum bactericidal concentration (MBC) of bile, the bile component deoxycholate (DC), and the anionic detergent sodium dodecyl sulfate (SDS) compared to both wild-type and toxT mutant strains. Classical and El Tor toxR mutant strains also exhibit reduced growth rates at subinhibitory concentrations of DC and SDS. Growth of either V. cholerae biotype in subinhibitory concentrations of bile or DC induces increased ToxR-dependent production of a major 38-kDa outer membrane protein, which was confirmed to be OmpU by Western blot. Measurement of transcription of a ompUp-lacZ fusion in both biotypes reveals stimulation (about two- to threefold) of ToxR-dependent ompU transcription by the presence of bile or DC, suggesting that ToxR may respond to the presence of bile. The toxR mutant strains of three additional human intestinal pathogenic Vibrio species, V. mimicus, V. fluvialis, and V. parahaemolyticus, display lower MBCs of bile, DC, and SDS and have altered outer membrane protein profiles compared to the parental wild-type strains. Our results demonstrate a conserved role for ToxR in the modulation of outer membrane proteins and bile resistance of pathogenic Vibrio species and suggest that these ToxR-dependent outer membrane proteins may mediate enhanced resistance to bile. We speculate that ToxR-mediated bile resistance was an early step in the evolution of V. cholerae as an intestinal pathogen.

Adhesins, Bacterial↗

PubMed2000

Persistent activation of GABA(A) receptor/Cl(-) channels by astrocyte-derived GABA in cultured embryonic rat hippocampal neurons.

Whole cell patch-clamp recordings using Cl(-)-filled pipettes revealed more negative levels of baseline current and associated current variance in embryonic rat hippocampal neurons co-cultured on a monolayer of astrocytes than those cultured on poly-D-lysine. These effects were mimicked by culturing neurons on poly-D-lysine in astrocyte-conditioned medium (ACM). The baseline current and variance decreased immediately in all cells after either local perfusion with saline or exposure to bicuculline, an antagonist of GABA at GABA(A) receptor/Cl(-) channels. Baseline current and variance in all cells reached a nadir at approximately 0 mV, the calculated equilibrium potential for Cl(-). Perfusion of ACM rapidly induced a sustained current in neurons, which also reversed polarity at approximately 0 mV. Bicuculline attenuated or eliminated the ACM-induced current at a concentration that completely blocked micromolar GABA-induced current. Quantitative analyses of spontaneously occurring fluctuations superimposed on the ACM-induced current revealed estimated unitary properties of the underlying channel activity similar to those calculated for GABA's activation of GABA(A) receptor/Cl(-) channels. Bicuculline-sensitive synaptic-like transients, which reversed at approximately 0 mV, were also detected in neurons cultured in ACM, and these were immediately eliminated along with the negative baseline current and superimposed current fluctuations by perfusion. Furthermore bicuculline-sensitive synaptic-like transients were rapidly and reversibly triggered when ACM was acutely applied. ACM induced an increase in cytoplasmic Ca(2+) in cultured embryonic hippocampal neurons that was completely blocked by bicuculline and strychnine. We conclude that astrocytes release diffusible substances, most likely GABA, that persistently activate GABA(A) receptor/Cl(-) channels in co-cultured neurons.

3-Mercaptopropionic Acid↗

PubMed1999

Separation of dorsal and ventral dopaminergic neurons from embryonic rat mesencephalon by buoyant density fractionation: disassembling pattern in the ventral midbrain.

The dopaminergic neurons of the ventral mesencephalon, though physically mixed with non-dopamine neurons, are organized into dorsal and ventral 'tiers' with regard to their ontogeny, efferent projections and their relative position in the various mesencephalic sub-nuclei. We have employed buoyant density fractionation to separate the dopaminergic neurons of the two compartments and compare their subsequent phenotype development with respect to their expression of the gene encoding tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine biosynthetic pathway. Using immunocytochemistry, separately and combined with in situ hybridization, we demonstrate here that sedimentation of cell suspensions from E19 rat ventral mesencephalon on 5-step Percoll gradients produces cell fractions enriched in ventral and dorsal tier DA neurons, respectively.

Animals↗

PubMed1999

GABAA receptor subunit composition and functional properties of Cl- channels with differential sensitivity to zolpidem in embryonic rat hippocampal cells.

Using flow cytometry in conjunction with a voltage-sensitive fluorescent indicator dye (oxonol), we have identified and separated embryonic hippocampal cells according to the sensitivity of their functionally expressed GABAA receptors to zolpidem. Immunocytochemical and RT-PCR analysis of sorted zolpidem-sensitive (ZS) and zolpidem-insensitive (ZI) subpopulations identified ZS cells as postmitotic, differentiating neurons expressing alpha2, alpha4, alpha5, beta1, beta2, beta3, gamma1, gamma2, and gamma3 GABAA receptor subunits, whereas the ZI cells were neuroepithelial cells or newly postmitotic neurons, expressing predominantly alpha4, alpha5, beta1, and gamma2 subunits. Fluctuation analyses of macroscopic Cl- currents evoked by GABA revealed three kinetic components of GABAA receptor/Cl- channel activity in both subpopulations. We focused our study on ZI cells, which exhibited a limited number of subunits and functional channels, to directly correlate subunit composition with channel properties. Biophysical analyses of GABA-activated Cl- currents in ZI cells revealed two types of receptor-coupled channel properties: one comprising short-lasting openings, high affinity for GABA, and low sensitivity to diazepam, and the other with long-lasting openings, low affinity for GABA, and high sensitivity to diazepam. Both types of channel activity were found in the same cell. Channel kinetics were well modeled by fitting dwell time distributions to biliganded activation and included two open and five closed states. We propose that short- and long-lasting openings correspond to GABAA receptor/Cl- channels containing alpha4beta1gamma2 and alpha5beta1gamma2 subunits, respectively.

Animals↗

PubMed1999

Glutamate acting at NMDA receptors stimulates embryonic cortical neuronal migration.

During cortical development, embryonic neurons migrate from germinal zones near the ventricle into the cortical plate, where they organize into layers. Mechanisms that direct neuronal migration may include molecules that act as chemoattractants. In rats, GABA, which localizes near the target destination for migrating cortical neurons, stimulates embryonic neuronal migration in vitro. In mice, glutamate is highly localized near the target destinations for migrating cortical neurons. Glutamate-induced migration of murine embryonic cortical cells was evaluated in cell dissociates and cortical slice cultures. In dissociates, the chemotropic effects of glutamate were 10-fold greater than the effects of GABA, demonstrating that for murine cortical cells, glutamate is a more potent chemoattractant than GABA. Thus, cortical chemoattractants appear to differ between species. Micromolar glutamate stimulated neuronal chemotaxis that was mimicked by microM NMDA but not by other ionotropic glutamate receptor agonists (AMPA, kainate, quisqualate). Responding cells were primarily derived from immature cortical regions [ventricular zone (vz)/subventricular zone (svz)]. Bromodeoxyuridine (BrdU) pulse labeling of cortical slices cultured in NMDA antagonists (microM MK801 or APV) revealed that antagonist exposure blocked the migration of BrdU-positive cells from the vz/svz into the cortical plate. PCR confirmed the presence of NMDA receptor expression in vz/svz cells, whereas electrophysiology and Ca2+ imaging demonstrated that vz/svz cells exhibited physiological responses to NMDA. These studies indicate that, in mice, glutamate may serve as a chemoattractant for neurons in the developing cortex, signaling cells to migrate into the cortical plate via NMDA receptor activation.

Animals↗

PubMed1999

Kir 4.1 channel expression in neuroblastomaxglioma hybrid NG108-15 cell line.

To study a possible involvement of inwardly rectifying K+ 4.1 (Kir 4. 1) channels in neural cell development, RT-PCR, immunocytochemistry and whole-cell patch-clamp techniques were used to assess expression of Kir 4.1 channels in proliferating and differentiated NG108-15 cells. RT-PCR revealed co-expression of Kir 4.1 and rat ether-a-go-go-related gene (R-ERG) mRNAs in both proliferating and differentiated cells. The relative Kir 4.1 mRNA concentration increased markedly as cells progressed from undifferentiated to differentiated cells. Kir 4.1-immunoreactivity was barely detectable in undifferentiated cells, but clearly detected in differentiated cells, indicating that Kir 4.1 gene and protein expressions are developmentally regulated. However, corresponding Kir 4.1 current could not be detected in differentiated cells using whole-cell patch-clamp recording. The 'silent' channel/receptor, often found in tumor cells, may carry genetic defects, which prevent functional expression of the channel. NG108-15 may serve as unique model for studying the relationship between the expression of an ion channel gene and the electrophysiological phenotype it encodes.

Animals↗

PubMed1999

The expression of GABA(A) receptor alpha2 subunit is upregulated by testosterone in rat cerebral cortex.

The GABAergic system is sexually dimorphic in certain brain regions and can be regulated by testosterone (T). However, the contribution of T to sex-specific developmental processes in the brain is less clear. We have examined whether T regulates expression of GABA(A) receptor alpha2 subunit in the cerebral cortex of embryonic and postnatal female rats using in situ hybridization and Western blotting. We found that both alpha2 mRNA and protein levels are significantly increased by T treatment at embryonic day 20 (E20) and birth (P0). The observed modulation of the expression of GABA(A) receptor alpha2 subunit by T may be translated into changes in the levels or composition of GABA(A) receptor, either of which would be expected to alter neuronal functional response to GABA activation. As the effects of T are developmental-stage-specific, they may have an organizational impact on brain development.

Analysis of Variance↗

PubMed1999

Sex differences in expression of serotonin receptors (subtypes 1A and 2A) in rat brain: a possible role of testosterone.

Sexual differences in the expression of messenger RNA and in the binding of serotonin receptors (subtypes 1A and 2A) were studied by in situ hybridization and autoradiography ¿[3H]8-hydroxy-2(di-n-propylamino)tetralin and [3H]ketanserin binding) in the rat brain. Serotonin-1A receptor messenger RNA showed distinct expression patterns for female and male rats. Expression of serotonin-1A receptor messenger RNA was greater in males in subregions of the hypothalamus and amygdala, and less in males in subregions of the hippocampus. No significant differences in the distribution of serotonin-1A receptor binding sites were found between the sexes. Serotonin-2A receptor messenger RNA expression was comparable in males and females in all brain regions except the ventromedial hypothalamic nuclei, where lower levels were seen in females. However, the binding of serotonin-2A receptor measured with [3H]ketanserin was significantly higher in females in all regions of the hippocampus. In a separate study, gonadectomy in males significantly increased serotonin-1A messenger RNA content in the cortex, hypothalamus, hippocampus, amygdala and dorsal raphe, and decreased serotonin-2A messenger RNA in ventromedial hypothalamic nuclei only. Almost all gonadectomy-induced changes were reversed by concomitant administration of testosterone. Our data provide evidence for region-specific sex differences in serotonin receptor subtype 1A and 2A transcription and concentration in the rat brain, and further suggest a modulatory role of testosterone in serotonin (particularly subtype 1A) receptor expression. Gender and gonadal steroid effects on central serotonergic systems may underlie the reported sexual dimorphisms in affective state regulation, response to psychopharmacological agonists or pituitary adrenal activation.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1999

Astrocytes regulate the developmental appearance of GABAergic and glutamatergic postsynaptic currents in cultured embryonic rat spinal neurons.

The effects of astrocytes on the emergence of synaptic transients and excitable membrane properties in cultured, embryonic, rat ventral spinal neurons were studied with electrical and optical recording techniques. Neurons on astrocytes had significantly longer neurites and an accelerated rate of growth in surface membrane during the initial 24 h in culture compared to neurons on poly-D-lysine (PDL). GABAergic (GABA, gamma-aminobutyric acid) and glutamatergic transients appeared spontaneously in co-cultured neurons by 24 h. GABAergic quanta did not appear in neurons on PDL until 4 days in culture, and glutamatergic transients did not emerge until 7 days in culture. Astrocyte-conditioned medium (ACM) partially mimicked the effects of direct astrocytic contact. GABAergic transients appeared by 2 days, and glutamatergic signals by 4 days in neurons on PDL exposed to ACM. All of the spontaneous, synaptic-like transients were eliminated by tetrodotoxin or Ca2+o-free saline, implicating voltage-dependent cation channels in their generation. Astrocytes immediately and significantly increased the density of voltage-dependent Na+ currents compared to neurons on PDL, but by the end of 24 h, Na+ current densities were identical. Electrophysiological and optical recording revealed comparable densities of high-voltage-activated (HVA) Ca2+ currents on both co-cultured neurons and neurons on PDL throughout the first week. However, neurons on astrocytes had significantly greater contributions of P/Q-type currents and lesser contributions of L-type currents beginning at 24 h and continuing for 7 days. The contribution of N-type current was significantly more in co-cultured neurons only at 24 h. Thus, in vitro, astrocytes help to differentiate specific excitable membrane properties in spinal neurons, along with GABAergic and glutamatergic forms of synaptic transmission.

Amino Acids↗