Chronic exposure to alcohol during development alters the responses to excitatory amino acids in cultured Purkinje neurons

Homer proteins control neuronal differentiation through IP(3) receptor signaling

Neurons expand, sustain or prune their dendritic trees during ontogenesis [Cline, H.T. (2001). Dendritic arbor development and synaptogenesis. Curr. Opin. Neurobiol. 11, 118-126; Wong, W.T. and Wong, R.O.L. (2000) Rapid dendritic movements during synapse formation and rearrangement. Curr. Opin. Neurobiol. 10, 118-124] which critically depends on neuronal activity [Wong, W.T., Faulkner-Jones, B.E., Sanes, J.R. and Wong, R.O.L. (2000) Rapid dendritic remodeling in the developing retina: dependence on neurotransmission and reciprocal regulation by Rac and Rho. J. Neurosci. 20, 5024-5036; Li, Z., Van Aelst, L. and Cline, H.T. (2000) Rho GTPases regulate distinct aspects of dendritic arbor growth in Xenopus central neurons in vivo. Nat. Neurosci. 3, 217-225; Wong, W.T. and Wong, R.O.L. (2001) Changing specificity of neurotransmitter regulation of rapid dendritic remodeling during synaptogenesis. Nat. Neurosci. 4, 351-352.] and sub-cellular Ca(2+) signals [Lohmann, C., Myhr, K.L. and Wong, R.O. (2002) Transmitter-evoked local calcium release stabilizes developing dendrites, Nature 418, 177-181.]. The role of synaptic clustering proteins connecting both processes is unclear. Here, we show that expression levels of Vesl-1/Homer 1 isoforms critically control properties of Ca(2+) release from intracellular stores and dendritic morphology of CNS neurons. Vesl-1L/Homer 1c, an isoform with a functional WH1 and coiled-coil domain, but not isoforms missing these features were capable of potentiating intracellular calcium signaling activity indicating that such regulatory interactions function as a general paradigm in cellular differentiation and are subject to changes in expression levels of Vesl/Homer isoforms.

Early chronic ethanol exposure in rats disturbs respiratory network activity and increases sensitivity to ethanol

Chronic ethanol exposure during the fetal period alters spontaneous neuronal discharge, excitatory and inhibitory amino acid neurotransmission and neuronal sensitivity to ethanol in the adult brain. However, nothing is known about the effects of such exposure on the central respiratory rhythmic network, which is highly dependent on ethanol-sensitive amino acid neurotransmission. In 3- to 4-week-old rats, we investigated (1) the effects of chronic ethanol exposure (10% v/v as only source of fluid) during gestation and lactation on phrenic (Phr) and hypoglossal (XII) nerve activity using an in situ preparation and on spontaneous breathing at rest in unanaesthetized animals using plethysmography; (2) the sensitivity of the respiratory system to ethanol re-exposure in situ; and (3) the phrenic nerve response to muscimol, a GABA(A) receptor agonist, applied systemically in an in situ preparation. In control rats, ethanol (10-80 mm) induced a concentration-dependent decrease in the amplitude of both XII and Phr motor outflows. At 80 mm ethanol, the amplitude of the activity of the two nerves displayed a difference in sensitivity to ethanol and respiratory frequency increased as a result of shortening of postinspiratory duration period. After chronic ethanol exposure, respiratory frequency was significantly reduced by 43% in situ and by 23% in unanaesthetized animals, as a result of a selective increase in expiratory duration. During Phr burst, the ramp was steeper, revealing modification of inspiratory patterning. Interestingly that re-exposure to ethanol in situ elicited a dramatic inhibitory effect. At 80 mm, ethanol abolished rhythmic XII nerve outflow in all cases and Phr nerve outflow in only 50% of cases. Furthermore, administration of 50 microm muscimol abolished Phr nerve activity in all control rats, but only in 50% of ethanol-exposed animals. Our results demonstrate that chronic ethanol exposure at an early stage of brain development depresses breathing in juvenile rats, and sensitizes the respiratory network to re-exposure to ethanol, which does not seem to involve GABAergic neurotransmission.

Characteristics of endothelial cells derived from the blood-brain barrier and of astrocytes in culture

In this study, cultures of astrocytes and capillary endothelial cells from the blood-brain barrier (BBB) of the postnatal (P1) mouse cerebral cortex were analyzed with the aim of acquiring information on the distinguishing characteristics of each cell type. For isolation and purification of astrocyte cells, the methods of McCarthy and DeVellis [J. Cell Biol. 85 (1980) 890] were employed. The methods of Chen et al. [Lab. Invest. 78 (1998) 353], Duport et al. [Proc. Natl. Acad. Sci. USA 95 (1998) 1840], Rubin et al. [J Cell Biol. 115 (1991) 1725] and Tontsch and Bauer [Microvasc. Res. 37 (1989) 148] were utilized for culturing of cells from the BBB. A simple protocol was also created for isolating and purifying brain endothelial cells with 10 mM sodium cyanide. The vascular system of the cerebral cortex is derived from the leptomeningeal blood vessels [Qin and Sato, Dev. Dyn. 202 (1995) 172; Risau et al., EMBO J. 5 (1986) 3179]. With this in mind, cultures of the P1 mouse meninges were used as a comparative cell type in order to differentiate between BBB cells and astrocytes. In this regard, the expression of a number of markers were correlated, and an antibody double labeling technique was employed. The staining of these markers was then compared to cells cultured from leptomeninges and to two other types of endothelial cells, human umbilical vein and bovine aortic. Reverse transcription-polymerase chain reaction (RT-PCR) was performed on total RNA isolated from adult mouse brain, cells cultured from P1 mouse cortex or meninges, bovine aortic endothelial cells and human umbilical vein endothelial cells (HUV-EC) to detect the expression of glial fibrillary acidic protein (GFAP), Von Willebrand factor (factor VIII-related antigen) and fibronectin. These analyses revealed the presence of GFAP mRNA in the cultures of cortical and leptomeningeal cells and of protein in all cell types; Von Willebrand factor mRNA was detectable in HUV-EC cells but undetectable in cortical, leptomeningeal and bovine aortic endothelial cells. Fibronectin mRNA and protein were present in all of the cell types. Given the results of our investigations we conclude that in culture, astrocytes are actually brain endothelial cells.

The contribution of electrophysiology to knowledge of the acute and chronic effects of ethanol

This review describes the effects of ethanol on the components of neuronal transmission and the relationship of such effects to the behavioural actions of ethanol. The concentrations of ethanol with acute actions on voltage-sensitive ion channels are first described, then the actions of ethanol on ligand-gated ion channels, including those controlled by cholinergic receptors, 5-hydroxytryptamine receptors, the various excitatory amino acid receptors, and gamma-aminobutyric acid receptors. Acute effects of ethanol are then described on brain areas thought to be involved in arousal and attention, the reinforcing effects of ethanol, the production of euphoria, the actions of ethanol on motor control, and the amnesic effects of ethanol; the acute effects of ethanol demonstrated by EEG studies are also discussed. Chronic effects of alcohol on neuronal transmission are described in the context of the various components of the ethanol withdrawal syndrome, withdrawal hyperexcitability, dysphoria and anhedonia, withdrawal anxiety, craving, and relapse drinking. Electrophysiological studies on the genetic influences on the effects of ethanol are discussed, particularly the acute actions of ethanol and electrophysiological differences reported in individuals predisposed to alcoholism. The conclusion notes the concentration of studies on the classical transmitters, with relative neglect of the effects of ethanol on peptides and on neuronal interactions between brain areas and integrated patterns of neuronal activity.

Postnatal ethanol exposure blunts upregulation of GABAA receptor currents in Purkinje neurons

Recently, we found that early postnatal ethanol exposure inhibits the maturation of GABAA receptors (GABAARs) in developing medial septum/diagonal band (MS/DB) neurons, suggesting that these receptors may represent a target for ethanol related to fetal alcohol syndrome (FAS). To determine whether GABAARs on other neurons are also sensitive to a postnatal ethanol insult, postnatal day (PD) 4-9, rat pups were artificially reared and exposed to ethanol (4.5 g kg-1 day-1, 10.2% v/v). The pharmacological profile of acutely dissociated cerebellar Purkinje cell GABAARs from untreated, artificially reared controls and ethanol-treated animals was examined with conventional whole-cell patch clamp recordings during PD 12-16 (juveniles) and PD 25-35 (young adults). For untreated animals, GABA (0.3-100 microM) consistently induced inward Cl- currents in a concentration-dependent manner showing an age-related increase in maximum response without change in EC50 or slope value. Acute ethanol (100 mM) consistently inhibited 3 microM GABA currents (10-20%); positive modulators, pentobarbital (10 microM), midazolam (1 microM) and loreclezole (10 microM), consistently potentiated; the negative modulator, Zn2+ (30 microM), inhibited GABA currents across both juvenile and young adult groups. Loreclezole potentiation increased while Zn2+ inhibition decreased with age in untreated Purkinje neurons. Postnatal ethanol exposure (PD 4-9) decreased GABAAR maximum current density in young adult Purkinje cells but not in juvenile neurons. However, sensitivity to allosteric modulators did not change after ethanol. These data are consistent with the hypothesis that postnatal ethanol exposure during the brain growth spurt can disturb GABAAR development across the brain, although the mechanism(s) underlying this action remains to be determined.

Chronic ethanol treatment alters AMPA-induced calcium signals in developing Purkinje neurons

Cerebellar Purkinje neurons developing in culture were treated chronically with 30 mM (140 mg%; 3-11 days in vitro) ethanol to study the actions of prolonged ethanol exposure on responses to exogenous application of AMPA, a selective agonist at the AMPA subtype of ionotropic glutamate receptors. There was no consistent difference between control and chronic ethanol-treated neurons in resting membrane potential, input resistance, or the amplitude or duration of the membrane responses to AMPA (1 or 5 microM applied by brief microperfusion) as measured using the nystatin patch method of whole cell recording. In additional studies, the Ca2+ signal to AMPA was examined using the Ca2+ sensitive dye fura-2. The mean peak Ca2+ signal elicited by 5 microM AMPA was enhanced in the dendritic region (but not the somatic region) of chronic ethanol-treated Purkinje neurons compared to control neurons. In contrast, there was no difference between control and chronic ethanol-treated neurons in the peak amplitude of the Ca2+ signal to 1 microM AMPA, whereas the recovery of the Ca2+ signals was more rapid in both somatic and dendritic regions of ethanol-treated neurons. Resting Ca2+ levels in the somatic and dendritic regions were similar between control and ethanol-treated neurons. These data show that the membrane and Ca2+ responses to AMPA in Purkinje neurons are differentially affected by prolonged ethanol exposure during development. Moreover, chronic ethanol exposure produces a selective enhancement of AMPA-evoked dendritic Ca2+ signals under conditions reflecting intense activation (i.e., 5 microM AMPA), whereas both somatic and dendritic Ca2+ signals are attenuated with smaller levels of activation (i.e., 1 microM AMPA). Because Ca2+ is an important regulator of numerous intracellular functions, chronic ethanol exposure during development could produce widespread changes in the development and function of the cerebellum.

Chronic alcohol reduces calcium signaling elicited by glutamate receptor stimulation in developing cerebellar neurons

The effect of chronic alcohol (33 mM ethanol) on Ca2+ signals elicited by glutamate receptor agonists (quisqualate and NMDA) was examined in developing cerebellar Purkinje and granule neurons in culture. The neurons were exposed to alcohol during the second week in culture, the main period of morphological and physiological development. The Ca2+ signals were measured with fura-2 based microscopic video imaging. Chronic exposure to alcohol during development significantly reduced the peak amplitude of the Ca2+ signals to quisqualate (1 microM; Quis) in both the somatic and dendritic regions of the Purkinje neurons. The dendritic region was affected to a greater extent than the somatic region. Granule neurons also showed a reduced somatic Ca2+ signal to Quis (dendrites not measured) in the alcohol-treated cultures, indicating that the effect was not limited to Purkinje neurons. In addition to the effects on in the response to Quis, the peak amplitude of the Ca2+ signals to NMDA (100 microM) was reduced by chronic alcohol exposure during development in both the cultured Purkinje and granule neurons. Resting Ca2+ levels were not consistently affected by alcohol treatment in either neuronal type. These results indicate that Ca2+ signaling linked to glutamate receptor activation is an important target of alcohol in the developing nervous system and could be a contributing factor in the altered CNS function and development observed in animal models of fetal alcohol syndrome.

Alterations in responsiveness to ethanol and neurotrophic substances in fetal septohippocampal neurons following chronic prenatal ethanol exposure

Pregnant Long-Evans rats were maintained on three diets: a liquid diet in which ethanol accounted for 35-39% of the total calories, a similar diet with the isocaloric substitution of sucrose for ethanol, and a lab chow control diet. At gestation day 18, the fetuses were taken and cultures of septal and hippocampal neurons prepared. Neuronal survival and neurite outgrowth were compared in cultures from the three diet groups, using the following media supplements: ethanol (1.2, 1.8 or 2.4 g/dl), neurotrophic factors (nerve growth factor [NGF] with the septal cultures, basic fibroblast growth factor [bFGF] with the hippocampal cultures), or ethanol plus neurotrophic factors. Both the septal and hippocampal neurons responded to ethanol in a dose-dependent manner. The neurons from both populations from fetuses which had been exposed prenatally to ethanol, however, tolerated considerably higher ethanol concentrations before decreases in survival or outgrowth were seen. These ethanol-exposed neuronal populations were also less responsive to neurotrophic factors: in hippocampal cultures, process outgrowth was significantly enhanced by bFGF in control but not ethanol-derived cultures, and in septal and hippocampal cultures, the neurotrophic factors significantly ameliorated ethanol neurotoxicity in control cultures, but not in those from the ethanol-exposed fetuses. The possible relevance of these observations to the fetal alcohol syndrome is discussed.

Calcium signals elicited by quisqualate in cultured Purkinje neurons show developmental changes in sensitivity to acute alcohol

The effect of acute alcohol (33 mM ethanol) on calcium signaling evoked by glutamate receptor activation was studied in cultured cerebellar Purkinje and granule neurons at different stages of development. Calcium signals were measured by microscopic imaging using the calcium sensitive dye fura-2. At an early stage in development (10 days in vitro), acute alcohol enhanced the calcium signals evoked in Purkinje neurons by exogenous application of quisqualate, an agonist at ionotropic and metabotropic glutamate receptors. In contrast, in mature cultured Purkinje neurons (21-24 days in vitro) the calcium signals produced by quisqualate were reduced by alcohol. At an intermediate stage of development (14 days in vitro) reflecting the main period of morphological and physiological maturation, alcohol had no significant effect on the response to quisqualate. Alcohol's actions were significantly altered by manipulation of the intracellular stores with caffeine, implicating intracellular stores in alcohol's actions. Calcium signals produced by quisqualate in the cultured granule neurons were also altered by acute alcohol, in a manner similar to that observed in the Purkinje neurons. These data demonstrate that calcium signaling pathways are a site of alcohol action in developing CNS neurons and that the cellular consequences of alcohol exposure can change with development. Such actions of alcohol could have significant effects on the immature nervous system, where the precise timing of appropriate signaling levels are important aspects of the maturation process.

Chronic exposure to alcohol during development alters the calcium currents of cultured cerebellar Purkinje neurons

The effect of chronic exposure to alcohol during development on the calcium currents of rat cerebellar Purkinje neurons was studied in a culture model system using voltage clamp techniques. The neurons were exposed to 30 mM alcohol (ethanol) during the main period of morphological and physiological development. The calcium currents were measured at the end of the treatment period, which lasted for 8-10 days. The currents were evoked by a series of depolarizing test commands from holding potentials of -62 mV and -90 mV. The evoked currents were qualitatively similar in control and alcohol-treated neurons and were comprised of a high threshold slowly inactivating calcium current and a low threshold rapidly inactivating calcium current. The low threshold current could be observed in isolation at test potentials ranging from -50 to -30 mV. The mean peak amplitude of this current was significantly smaller in the alcohol-treated neurons compared to controls. At more depolarized test potentials, the high threshold current dominated the current response, which was characterized by an initial peak that slowly declined to a smaller relatively sustained level. The mean amplitude of the high threshold current at both peak and sustained levels was significantly larger in the alcohol-treated neurons compared to controls. Measurement of cell size indicated that alcohol-treated neurons were approximately 25% smaller than control neurons, a difference that could contribute to the smaller low threshold current observed in these neurons. These data show that chronic exposure to alcohol during the development can significantly influence the amplitude of calcium currents of the cultured Purkinje neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol dose-dependently attenuates NMDA-mediated thermal hyperalgesia in the rat

Recent observations using acute and persistent pain models have suggested that activation of the N-methyl-D-aspartate (NMDA) receptor is required for mechanisms that underly the development and maintenance of thermal hyperalgesia. The present results document that both NMDA-mediated thermal hyperalgesia produced after acute intrathecal NMDA administration and NMDA-mediated thermal hyperalgesia produced in a model of neuropathic pain are dose-dependently and reversibly attenuated by intrathecal administration of ethanol (0.5-1.0%; total dose, 106-213 nmol, i.t.). This is consistent with recent reports that ethanol may function as a selective NMDA receptor antagonist at low concentrations and further extends the evidence that thermal hyperalgesia is mediated by NMDA receptors.