Role of pertussis toxin-sensitive G-proteins in synaptic transmission and plasticity at corticostriatal synapses

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without a liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels, but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Predicting the response of striatal spiny neurons to sinusoidal input

Spike-timing effects of small-amplitude sinusoidal currents were measured in mouse striatal spiny neurons firing repetitively. Spike-timing reliability varied with the stimulus frequency. For frequencies near the cell's firing rate, the cells altered firing rate to match the stimulus and became phase locked to it. The stimulus phase of firing during lock depended on the stimulus frequency relative to the cell's unperturbed firing rate. Interspike intervals during sinusoidal stimulation were predicted using an iterative map constructed from the cells' phase-resetting curve. Variability of interspike intervals was reduced by stimulation at all frequencies higher than about half the cell's unperturbed rate, and interspike intervals were accurately predicted by the map. Long sequences of spike times were predicted by iterating on the map. The accuracy of that prediction varied with frequency. Spike time predictability was highest near and during phase lock. The map predicted the phase of firing on the input and its dependence on stimulus frequency. Prediction errors, when they occurred, were of two kinds: unpredicted variation in interspike interval from intrinsic cell noise and accumulation of prediction errors from previous interspike intervals. Each type of prediction error arose from a different mechanism, and their impact was also predicted from the phase model. When two oscillatory input currents were presented simultaneously, striatal neurons responded selectively to only one of them, the one closest in frequency to the cell's unperturbed firing rate. Their spike times encoded the frequency and phase of that single oscillatory input.NEW & NOTEWORTHY During repetitive firing, the timing of action potentials is determined by the interaction between the input and voltage-sensitive currents throughout the interspike interval. This interaction is encapsulated in the neuron's phase-resetting curve. The phase-resetting curve predicted spike timing to small sinusoidal currents over a wide range of stimulus frequencies. Firing patterns were most sensitive to oscillatory components near the cell's own firing rate, even in the presence of noise and other inputs.

An adaptive role of TNFα in the regulation of striatal synapses

Elevation of inflammatory cytokines in the striatum precedes symptoms in a number of motor dysfunctions, but it is unclear whether this is part of the disease process or an adaptive response to the pathology. In pyramidal cells, TNFα drives the insertion of AMPA-type glutamate receptors into synapses, and contributes to the homeostatic regulation of circuit activity in the developing neocortex. Here we demonstrate that in the mouse dorsolateral striatum, TNFα drives the internalization of AMPARs and reduces corticostriatal synaptic strength, dephosphorylates DARPP-32 and GluA1, and results in a preferential removal of Ca(2+)-permeable AMPARs. Striatal TNFα signaling appears to be adaptive in nature, as TNFα is upregulated in response to the prolonged blockade of D2 dopamine receptors and is necessary to reduce the expression of extrapyramidal symptoms induced by chronic haloperidol treatment. These data indicate that TNFα is a regulator of glutamatergic synaptic strength in the adult striatum in a manner distinct from its regulation of synapses on pyramidal cells and mediates an adaptive response during pathological conditions.

Neonatal exposure to antiepileptic drugs disrupts striatal synaptic development

OBJECTIVE

Drug exposure during critical periods of brain development may adversely affect nervous system function, posing a challenge for treating infants. This is of particular concern for treating neonatal seizures, as early life exposure to drugs such as phenobarbital is associated with adverse neurological outcomes in patients and induction of neuronal apoptosis in animal models. The functional significance of the preclinical neurotoxicity has been questioned due to the absence of evidence for functional impairment associated with drug-induced developmental apoptosis.

METHODS

We used patch-clamp recordings to examine functional synaptic maturation in striatal medium spiny neurons from neonatal rats exposed to antiepileptic drugs with proapoptotic action (phenobarbital, phenytoin, lamotrigine) and without proapoptotic action (levetiracetam). Phenobarbital-exposed rats were also assessed for reversal learning at weaning.

RESULTS

Recordings from control animals revealed increased inhibitory and excitatory synaptic connectivity between postnatal day (P)10 and P18. This maturation was absent in rats exposed at P7 to a single dose of phenobarbital, phenytoin, or lamotrigine. Additionally, phenobarbital exposure impaired striatal-mediated behavior on P25. Neuroprotective pretreatment with melatonin, which prevents drug-induced neurodevelopmental apoptosis, prevented the drug-induced disruption in maturation. Levetiracetam was found not to disrupt synaptic development.

INTERPRETATION

Our results provide the first evidence that exposure to antiepileptic drugs during a sensitive postnatal period impairs physiological maturation of synapses in neurons that survive the initial drug insult. These findings suggest a mechanism by which early life exposure to antiepileptic drugs can impact cognitive and behavioral outcomes, underscoring the need to identify therapies that control seizures without compromising synaptic maturation.

Convergent evidence for abnormal striatal synaptic plasticity in dystonia

Dystonia is a functionally disabling movement disorder characterized by abnormal movements and postures. Although substantial recent progress has been made in identifying genetic factors, the pathophysiology of the disease remains a mystery. A provocative suggestion gaining broader acceptance is that some aspect of neural plasticity may be abnormal. There is also evidence that, at least in some forms of dystonia, sensorimotor "use" may be a contributing factor. Most empirical evidence of abnormal plasticity in dystonia comes from measures of sensorimotor cortical organization and physiology. However, the basal ganglia also play a critical role in sensorimotor function. Furthermore, the basal ganglia are prominently implicated in traditional models of dystonia, are the primary targets of stereotactic neurosurgical interventions, and provide a neural substrate for sensorimotor learning influenced by neuromodulators. Our working hypothesis is that abnormal plasticity in the basal ganglia is a critical link between the etiology and pathophysiology of dystonia. In this review we set up the background for this hypothesis by integrating a large body of disparate indirect evidence that dystonia may involve abnormalities in synaptic plasticity in the striatum. After reviewing evidence implicating the striatum in dystonia, we focus on the influence of two neuromodulatory systems: dopamine and acetylcholine. For both of these neuromodulators, we first describe the evidence for abnormalities in dystonia and then the means by which it may influence striatal synaptic plasticity. Collectively, the evidence suggests that many different forms of dystonia may involve abnormal plasticity in the striatum. An improved understanding of these altered plastic processes would help inform our understanding of the pathophysiology of dystonia, and, given the role of the striatum in sensorimotor learning, provide a principled basis for designing therapies aimed at the dynamic processes linking etiology to pathophysiology of the disease.

A proGDNF-related peptide BEP increases synaptic excitation in rat hippocampus

The glial cell-derived neurotrophic factor (GDNF) precursor contains several putative sites for prohormone convertase-mediated excision of short peptides. Here, we show that one of the predicted peptides, named BEP (brain excitatory peptide), induces a substantial increase in the synaptic excitability in rat CA1 pyramidal neurons. The excitation is sensitive to N-ethylmaleimide, suggesting involvement of a G-protein-coupled receptor.

Reliable long-lasting depression interacts with variable short-term facilitation to determine corticostriatal paired-pulse plasticity in young rats

Synaptic plasticity at corticostraital synapses is proposed to fine tune movment and improve motor skills. We found paired-pulse plasticity at corticostriatal synapses reflected variably expressed short-term facilitation blended with a consistent background of longer-lasting depression. Presynaptic modulation via neuotransmitter receptor activation was ruled out as a mechanism for long-lasting paired-pulse depression by examining the effect of selective receptor antagonists. EPSC amplitude and paired-pulse plasticity, however, was influenced by block of D2 dopamine receptors. Block of glutamate transport with l-transdicarboxylic acid (PDC) reduced EPSCs, possibly through a mechanism of AMPA receptor desensitization. Removal of AMPA receptor desensitization with cyclothiazide reduced the paired-pulse depression at long-duration interstimulus intervals (ISIs), indicating that AMPA receptor desensitization participates in corticostriatal paired-pulse plasticity. The low-affinity glutamate receptor antagonist cis-2,3-piperidine dicarboxylic acid (PDA) increased paired-pulse depression, suggesting that a presynaptic component also exists for long-lasting paired-pulse depression. Low Ca(2+)-high Mg(2+) or BAPTA-AM dramatically reduced the amplitude of corticostriatal EPSCs and both manipulations increased the expression of facilitation and, to a lesser extent, they reduced long-lasting paired-pulse depression. EGTA-AM produced a smaller reduction in EPSC amplitude and it did not alter paired-pulse facilitation, but in contrast to low Ca(2+) and BAPTA-AM, EGTA-AM increased long-lasting paired-pulse depression. These experiments suggest that facilitation and depression are sensitive to vesicle depletion, which is dependent upon changes in peak Ca(2+) (i.e. low Ca(2+)-high Mg(2+) or BAPTA-AM). In addition, the action of EGTA-AM suggests that basal Ca(2+) regulates the recovery from long-lasting paired-pulse depression, possibly thourgh a Ca(2+)-sensitive process of vesicle delivery.

The phospholipid mediator platelet-activating factor mediates striatal synaptic facilitation

The phospholipid mediator platelet-activating factor (PAF), an endogenous modulator of glutamatergic neurotransmission, can also be secreted by brain mononuclear phagocytes during HIV-1 infection. Platelet-activating factor can induce neuronal apoptosis by NMDA receptor-dependent and independent mechanisms. We now demonstrate that acute administration of sublethal doses of PAF to striatal slices augments synaptic facilitation in striatal neurons following high-frequency stimulation, which can be blocked by PAF receptor antagonists, suggesting that striatal synaptic facilitation can be augmented by PAF receptor agonism. We also demonstrate that repeated sublethal doses of PAF during tetanic stimulation can greatly increase the magnitude of postsynaptic potentials and action potentials, but a lethal dose of PAF destroys the capacity of corticostriatal synapses to achieve this augmented synaptic facilitation. Thus, the relative concentration and temporal pattern of PAF expression at glutamatergic synapses may govern whether it acts in a physiologic or pathophysiologic manner during striatal neurotransmission.

Acute inhibition of corticostriatal synaptic transmission in the rat dorsal striatum by ethanol

The purpose of this study was to examine the effects of ethanol on synaptic transmission in the dorsal striatum in rat brain slices. The effects of ethanol on corticostriatal synaptic transmission were tested by whole-cell voltage-clamp recording. Ethanol significantly decreased corticostriatal excitatory postsynaptic currents (EPSCs) in a dose-dependent manner (10-200 mM). However, the paired-pulse ratio was not affected by the ethanol (100 mM) treatment. The amplitude of miniature EPSCs (mEPSCs) from these neurons, recorded without cortical stimulation, was decreased, but the frequency of the mEPSCs remained unchanged. Ethanol also decreased currents induced by the local pressure injection of glutamate into dorsal striatal neurons. These results suggest that ethanol inhibits glutamatergic synaptic transmission in the dorsal striatum, possibly through a postsynaptic mechanism.

Modulation of Corydalis tuber on glycine-induced ion current in acutely dissociated rat periaqueductal gray neurons

Traditionally, Corydalis tuber has been used for the control of pain including headache, stomach ache, and neuralgia. In the present study, modulation of the Corydalis tuber on glycine-activated ion current in the acutely dissociated periaqueductal gray (PAG) neurons was studied by a nystatin-perforated patch-clamp technique. High concentrations of Corydalis tuber elicited ion current, which was suppressed by strychnine application, while low concentrations of Corydalis tuber reduced glycine-induced ion current in the PAG neurons. Inhibitory action of Corydalis tuber on glycine-activated ion current was partially abolished by treatment with naltrexone, a non-selective opioid antagonist. Application of N-methylmalemide (NEM), a sulfhydryl alkylating agent, also partially abolished the inhibitory action of Corydalis tuber on glycine-activated ion current in the PAG neurons. These results suggest that the inhibitory effect of Corydalis tuber on glycine-activated ion current in the PAG neurons is one of the analgesic mechanisms of the Corydalis tuber.

Induction of striatal long-term synaptic depression by moderate frequency activation of cortical afferents in rat

The striatum regulates motor output, and it is thought that changes in the synaptic efficacy of inputs to the striatum contribute to motor learning and habit formation. Previously, several laboratories have observed that brief high frequency stimulation (HFS) of cortical afferents innervating the dorsolateral striatum induces a long-term decrease in synaptic efficacy called long-term depression (LTD). We recently showed that HFS-induced striatal LTD requires retrograde signalling involving postsynaptic release of endocannabinoids and activation of presynaptic CB1 cannabinoid receptors. In the present study we have employed whole-cell recording in brain slices to examine a new form of LTD at corticostriatal synapses that can be induced by a 10 Hz, 5 min train. The decrease in synaptic efficacy is associated with a decrease in presynaptic release probability, as demonstrated by a decrease in frequency but not amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) and an increase in the paired pulse ratio (PPR). This form of LTD is blocked by antagonists for CB1 and D2 dopamine receptors and impaired by blockers of L-type calcium channels. However, 10 Hz-induced LTD does not depend on postsynaptic depolarization, unlike HFS-induced LTD. Furthermore, this new form of LTD is not prevented by treatments known to block HFS-induced LTD, including antagonism of metabotropic glutamate receptors (mGluRs), chelation of postsynaptic calcium, or intracellular application of an anandamide membrane transport inhibitor (VDM11). From these findings it is not clear that the endocannabinoid responsible for this form of LTD acts in a retrograde fashion, and the cellular source of endocannabinoid necessary for 10 Hz-induced LTD is as yet unknown. Our results demonstrate that a prolonged moderate frequency train induces cannabinoid-dependent LTD, further supporting the idea that endocannabinoids play a prominent role in the regulation of long-lasting changes in striatal output.

Involvement of GABAA receptors in the regulation of the prefrontal cortex on dopamine release in the rat dorsolateral striatum

The characteristics of the prefrontal cortex regulation of dopamine release in the rat dorsolateral striatum were investigated in focusing on the corticostriatal pathway, using dual-probe microdialysis in combination with simple behavioral procedures. Intracortical perfusion of the GABA(A) receptor antagonist bicuculline (0.03 and 0.1 mM) increased the striatal dopamine release, whereas the GABA(A) receptor agonist muscimol (0.1 and 1 mM) reduced the release dose dependently. Co-perfusion of muscimol (0.01 mM), which did not by itself affect the dopamine release, completely prevented the glutamate (1 mM)-stimulated dopamine release and behavioral activities, including locomotion and rearing. Muscimol (0.01 mM) also prevented the N-methyl-D-aspartate (NMDA; 1 mM)-induced increases in glutamate, as well as dopamine levels. These findings suggest that the prefrontal cortex functionally regulates dopamine release in the dorsolateral striatum, which is mediated via GABA(A) receptors. This cortical GABAergic system underlying the prefrontal cortex regulatory mechanism appears to be associated with the corticostriatal pathway.

Modulation of Chelidonii herba on glycine-activated and glutamate-activated ion currents in rat periaqueductal gray neurons

BACKGROUND

Chelidonii herba is classified as Papaver somniferum L. Aqueous extract from C. herba is traditionally used for disorders with symptoms like pain, bloating, abdominal cramp after meals.

METHODS

Modulation of C. herba on glycine-activated and glutamate-activated ion currents in the acutely dissociated periaqueductal gray (PAG) neurons was investigated by the nystatin-perforated patch-clamp technique.

RESULTS

C. herba inhibited glycine-activated ion current and increased glutamate-activated ion current. C. herba-induced inhibition on glycine-activated ion current is implicated in opioid receptors and GTP-binding proteins (G-proteins). Increased glutamate-activated ion current induced by C. herba is linked neither by opioid receptors nor GTP-binding proteins.

CONCLUSIONS

Suppressed glycine-induced response and elevated glutamate-induced response by C. herba may increase neuronal excitability in PAG, results in activation of descending pain control system, and this mechanism can be suggested as one of the analgesic actions of C. herba.

Retrograde signaling in the regulation of synaptic transmission: focus on endocannabinoids

This review covers recent developments in the cellular neurophysiology of retrograde signaling in the mammalian central nervous system. Normally at a chemical synapse a neurotransmitter is released from the presynaptic element and diffuses to the postsynaptic element, where it binds to and activates receptors. In retrograde signaling a diffusible messenger is liberated from the postsynaptic element, and travels "backwards" across the synaptic cleft, where it activates receptors on the presynaptic cell. Receptors for retrograde messengers are usually located on or near the presynaptic nerve terminals, and their activation causes an alteration in synaptic transmitter release. Although often considered in the context of long-term synaptic plasticity, retrograde messengers have numerous roles on the short-term regulation of synaptic transmission. The focus of this review will be on a group of molecules from different chemical classes that appear to act as retrograde messengers. The evidence supporting their candidacy as retrograde messengers is considered and evaluated. Endocannabinoids have recently emerged as one of the most thoroughly investigated, and widely accepted, classes of retrograde messenger in the brain. The study of the endocannabinoids can therefore serve as a model for the investigation of other putative messengers, and most attention is devoted to a discussion of systems that use these new messenger molecules.

The sulphydryl reagent, N-ethylmaleimide, disrupts sleep and blocks A1 adenosine receptor-mediated inhibition of intracellular calcium signaling in the in vitro ventromedial preoptic nucleus

To explore the neuronal signaling mechanisms underlying sleep regulation in the rat, the present study examined continuous intra-third ventricle infusion of N-ethylmaleimide (NEM), a sulphydryl reagent that inhibits G(i/o) protein-coupled receptor-mediated signaling pathways. The diurnal infusion of NEM (0.01-10 micromol/10 h) dose-dependently inhibited both non-rapid eye movement sleep and rapid eye movement sleep. A maximal dose of NEM (10 micromol/10 h) dramatically inhibited day-time sleep (-57% for non-rapid eye movement sleep and -89% for rapid eye movement sleep) with a compensatory increase of sleep during the subsequent night-time (+33% for non-rapid eye movement sleep and +259% for rapid eye movement sleep). The day-time brain temperature was also increased by NEM, demonstrating effects of NEM on both sleep and body temperature levels. Immunostaining of the rat hypothalamus with a monoclonal antibody against the A1 adenosine receptor (A1R) was used to explore the distribution of a sleep-related G(i/o) protein-coupled receptor. Robust A1R-like immunoreactivity was found in the ventromedial preoptic nucleus and the supraoptic nucleus. Fura-2-based Ca(2+) imaging analysis of acute hypothalamic slices further demonstrated that the A1R agonist N(6)-cyclopentyladenosine (CPA; 200 nM) inhibited spontaneous Ca(2+) oscillations and high potassium (80 mM)-induced Ca(2+) flux in the ventromedial preoptic nucleus, while NEM (100-300 microM) and an A1R antagonist 8-cyclopentyl-dipropylxanthine (300 nM) blocked the CPA actions and increased the high potassium-induced Ca(2+) flux. From these results we suggest that NEM-sensitive G protein-coupled receptor(s) may play an important role in the regulation of sleep and body temperature in the rat and one possible mechanism is an A1R-mediated regulation of intracellular Ca(2+) concentrations in the ventromedial preoptic nucleus.

Modulation of Chelidonii herba on GABA activated chloride current in rat PAG neurons

Modulation of Chelidonii herba on gamma-aminobutyric acid (GABA) activated chloride current in the acutely dissociated periaqueductal gray (PAG) neuron was studied by nystatin-perforated patch-clamp technique. High concentrations of Chelidonii herba elicited ion current, that was blocked by bicuculline. Low concentrations reduced the GABA activated current in PAG. Two types of inhibitory action of Chelidonii herba on GABA activated current have been implicated in PAG. One is the inhibitory action of Chelidonii herba on GABA was abolished by naltrexone and the other is that of Chelidonii herba was potentiated by naltrexone. In addition, all of two types of action of Chelidonii herba are linked to pertussis toxin-sensitive GTP-binding proteins. These results suggest that the inhibitory modulation of Chelidonii herba on GABA activated current via G-proteins in PAG neuron is an important analgesic mechanism.

Activation of group I mGluRs is necessary for induction of long-term depression at striatal synapses

Activation of metabotropic glutamate receptors (mGluRs), which are coupled to G proteins, has important roles in certain forms of synaptic plasticity including corticostriatal long-term depression (LTD). In the present study, extracellular field potential and whole cell voltage-clamp recording techniques were used to investigate the effect of mGluR antagonists with different subtype specificity on high-frequency stimulation (HFS)-induced LTD of synaptic transmission in the striatum of brain slices obtained from 15-to 25-day-old rats. Induction of LTD was prevented during exposure to the nonselective mGluR antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (500 microM). The group I mGluR-selective antagonists (S)-4-carboxy-phenylglycine (50 microM) and (RS)-1-aminoindan-1,5-dicarboxylic acid (100 microM) prevented induction of LTD when applied before and during HFS. The mGluR1-selective antagonist 7-(Hydroxyimino) cyclopropa[b]chromen-1a-carboxylate ethyl ester (80 microM) also blocked LTD induction. Unexpectedly, the mGluR5-selective antagonist 2-methyl-6-(phenylethyl)-pyridine (10 microM) also prevented LTD induction. The group II mGluR antagonist LY307452 (10 microM) did not block LTD induction at corticostriatal synapses, but LY307452 was able to block transient synaptic depression induced by the group II agonist LY314593. None of the antagonists had any effect on basal synaptic transmission at the concentrations used, and mGluR antagonists did not reverse LTD when applied beginning 20 min after HFS. These results suggest that both group I mGluR subtypes contribute to the induction of LTD at corticostriatal synapses.

Dopaminergic control of synaptic plasticity in the dorsal striatum

Cortical glutamatergic and nigral dopaminergic afferents impinge on projection spiny neurons of the striatum, providing the most significant inputs to this structure. Isolated activation of glutamate or dopamine (DA) receptors produces short-term effects on striatal neurons, whereas the combined stimulation of both glutamate and DA receptors is able to induce long-lasting modifications of synaptic excitability. Repetitive stimulation of corticostriatal fibres causes a massive release of both glutamate and DA in the striatum and, depending on the glutamate receptor subtype preferentially activated, produces either long-term depression (LTD) or long-term potentiation (LTP) of excitatory synaptic transmission. D1-like and D2-like DA receptors interact synergistically to allow LTD formation, while they operate in opposition during the induction phase of LTP. Corticostriatal synaptic plasticity is severely impaired after chronic DA denervation and requires the stimulation of DARPP-32, a small protein expressed in dopaminoceptive spiny neurons which acts as a potent inhibitor of protein phosphatase-1. In addition, the formation of LTD and LTP requires the activation of PKG and PKA, respectively, in striatal projection neurons. These kinases appear to be stimulated by the activation of D1-like receptors in distinct neuronal populations.

Dopamine-dependent synaptic plasticity in striatum during in vivo development

The neurotransmitters dopamine (DA) and glutamate in the striatum play key roles in movement and cognition, and they are implicated in disorders of the basal ganglia such as Parkinson's disease. Excitatory synapses in striatum undergo a form of developmental plasticity characterized by a decrease in glutamate release probability. Here we demonstrate that this form of synaptic plasticity is DA and DA D2 receptor dependent. Analysis of spontaneous synaptic responses indicates that a presynaptic mechanism involving inhibition of neurotransmitter release underlies the developmental plasticity. We suggest that a major role of DA in the striatum is to initiate mechanisms that regulate the efficacy of excitatory striatal synapses, producing a decrease in glutamate release.

Dopamine-dependent synaptic plasticity in striatum during in vivo development

The neurotransmitters dopamine (DA) and glutamate in the striatum play key roles in movement and cognition, and they are implicated in disorders of the basal ganglia such as Parkinson's disease. Excitatory synapses in striatum undergo a form of developmental plasticity characterized by a decrease in glutamate release probability. Here we demonstrate that this form of synaptic plasticity is DA and DA D2 receptor dependent. Analysis of spontaneous synaptic responses indicates that a presynaptic mechanism involving inhibition of neurotransmitter release underlies the developmental plasticity. We suggest that a major role of DA in the striatum is to initiate mechanisms that regulate the efficacy of excitatory striatal synapses, producing a decrease in glutamate release.

Regional and postnatal heterogeneity of activity-dependent long-term changes in synaptic efficacy in the dorsal striatum

High-frequency activation of excitatory striatal synapses produces lasting changes in synaptic efficacy that may contribute to motor and cognitive functions. While some of the mechanisms responsible for the induction of long-term potentiation (LTP) and long-term depression (LTD) of excitatory synaptic responses at striatal synapses have been characterized, much less is known about the factors that govern the direction of synaptic plasticity in this brain region. Here we report heterogeneous activity-dependent changes in the direction of synaptic strength in subregions of the developing rat striatum. Neurons in the dorsolateral region of the anterior striatum tended to express LTD after high-frequency afferent stimulation (HFS) in slices from animals aged P15-P34. However, HFS in dorsolateral striatum from P12-P14 elicited an N-methyl-D-aspartate (NMDA) receptor-dependent form of LTP. Synapses in the dorsomedial anterior striatum exhibited a propensity to express an NMDA-receptor dependent form of LTP across the entire developmental time period examined. The NMDA receptor antagonist (+/-)-2-amino-5-phosphopentanoic acid (APV) inhibited evoked excitatory postsynaptic potentials recorded in striatum obtained from P12-P15 rats but had little effect in striatum from older animals. The expression of multiple forms of synaptic plasticity in the striatum suggests mechanisms by which this brain region plays pivotal roles in the acquisition or encoding of some forms of motor sequencing and stereotypical behaviors.

Studying heterotrimeric G-protein-linked signal transduction using replication-deficient adenoviruses

Plasma membrane-spanning G-protein-linked receptors transduce approximately 60% of all extracellular stimuli in higher animals. Many G-protein-linked receptor pathways are yet to be elucidated, with the receptor, G-protein or effector system as yet unidentified. In addition, many fundamental issues pertaining to G-protein signalling remain unresolved, such as the factors governing the specificity of G-protein receptor coupling and the control of signal amplitude in response to G-protein activation. In order to address some of these issues, the use of replication-deficient adenoviruses as gene transfer vectors for investigations of G-protein signalling has been developed, facilitating dissection of G-protein-linked signal transduction pathways in an extensive range of cultured cells, as well as in vivo. The present review focuses on the versatility and utility of adenoviruses for the investigation of signalling by heterotrimeric G-proteins and explores some of the recent advances in adenoviral technology as they relate to the study of signal transduction.