Biomedical subjects

D J Surmeier

Publications and source records attributed to D J Surmeier.

At least 55 records · Page 3Linked to original sources

PubMed1996

Estradiol reduces calcium currents in rat neostriatal neurons via a membrane receptor.

Until recently, steroid hormones were believed to act only on cells containing intracellular receptors. However, recent evidence suggests that steroids have specific and rapid effects at the cellular membrane. Using whole-cell patch-clamp techniques, 17 beta-estradiol was found to reduce Ba2+ entry reversibly via Ca2+ channels in acutely dissociated and cultured neostriatal neurons. The effects were sex-specific, i.e., the reduction of Ba2+ currents was greater in neurons taken from female rats. 17 beta-Estradiol primarily targeted L-type currents, and their inhibition was detected reliably within seconds of administration. The maximum reduction by 17 beta-estradiol occurred at picomolar concentrations. 17 beta-Estradiol conjugated to bovine serum albumin also reduced Ba2+ currents, suggesting that the effect occurs at the membrane surface. Dialysis with GTP gamma S prevented reversal of the modulation, suggesting that 17 beta-estradiol acts via G-protein activation. 17 alpha-Estradiol also reduced Ba2+ currents but was significantly less effective than 17 beta-estradiol. Estriol and 4-hydroxyestradiol were found to reduce Ba2+ currents with similar efficacy to 17 beta-estradiol, whereas estrone and 2-methoxyestriol were less effective. Tamoxifen also reduced Ba2+ currents but did not occlude the effect of 17 beta-estradiol. These results suggest that at physiological concentrations, 17 beta-estradiol can have immediate actions on neostriatal neurons via nongenomic signaling pathways.

Animals↗

PubMed1996

Isolation and characterization of a persistent potassium current in neostriatal neurons.

1. Depolarization-activated, calcium-independent potassium (K+) currents were studied with the use of whole cell voltage-clamp recording from neostriatal neurons acutely isolated from adult (> or = 4 wk old) rats. The whole cell K+ current was composed of transient and persistent components. The aims of the experiments were to isolate the persistent component and then to characterize its voltage dependence and kinetics. 2. Application of 10 mM 4-aminopyridine (4-AP) completely blocked the transient currents while reducing the persistent current by approximately 40% [50% inhibitory concentration (IC50), of blockable current = 125 microM]. The persistent K+ current also was reduced by tetraethylammonium (TEA). Two components to the TEA block were present, having IC50s of 125 microM (23% of the blockable current) and 5.9 mM (77% of the blockable current). Collectively, these results suggested that the persistent components of the total K+ current was pharmacologically heterogeneous. The properties of the 4-AP-resistant, persistent K+ current (IKrp) were subsequently studied. 3. The kinetics of activation and deactivation of IKrp were voltage dependent. Examination of the entire activation/deactivation time constant profile showed that it was bell shaped, with time constants being moderately rapid (tau approximately 50 ms) at membrane potentials corresponding to the resting potential of neostriatal cells (approximately -80 mV), becoming considerably longer (tau approximately 100 ms) at potentials near the cells' spike thresholds (approximately -45 mV), and decreasing to a minimum (tau approximately 5 ms) at potentials associated with the peak of the cells' action potentials (approximately +20 mV). The inactivation kinetics of IKrp also were voltage dependent. The time constants of inactivation varied between 1 and 8 s at potentials between -10 and +35 mV. 4. Unlike persistent K+ currents in many other cell types, IKrp activated at relatively hyperpolarized membrane potentials (approximately -70 mV). The Boltzmann function describing activation had a half-activation voltage of -13 mV and a slope factor of 12 mV. In addition, the Boltzmann function describing the voltage dependence of inactivation of IKrp had a relatively depolarized half-inactivation voltage of -55 and a large slope factor of 19 mV, indicating that this current was available over a broad range of membrane potentials (between -100 and -10 mV). 5. Neostriatal neurons recorded in vivo exhibit subthreshold shifts in membrane potential of variable duration (tens of ms to s) from a hyperpolarized resting state to a depolarized state that is limited in amplitude just below spike threshold. The voltage dependence of activation and inactivation of IKrp indicates that it will be available on depolarization from the hyperpolarized state. However, the slow activation rate of this current suggests that it will contribute little either to limiting the amplitude of the initial depolarization associated with entry into the depolarized state or to depolarizing episodes of short duration (e.g., < 50 ms). However, IKrp should limit the amplitude of membrane depolarizations associated with prolonged excursions into the depolarized state.

4-Aminopyridine↗

PubMed1996

Voltage-dependent facilitation of calcium channels in rat neostriatal neurons.

1. Voltage-dependent facilitation of Ca2+ channels was studied in acutely isolated adult rat neostriatal neurons. Particular attention was paid to the facilitation of L-type channels. 2. In the absence of neuromodulators, the current-voltage relationship for whole cell Ba2+ currents was enhanced by a prepulse to +100 mV. The median enhancement at -20 mV was nearly 60%. The voltage dependence and kinetics of the processes underlying the facilitation were similar to those reported in other neurons. N-, P-, Q-, and L-type currents contributed to the observed facilitation. 3. Voltage-dependent facilitation of L-type currents was studied by subtracting nifedipine-insensitive currents from control currents. Although the kinetics were similar to those of the whole cell currents, the half-activation voltage for facilitation of L-type currents [half-activation voltage (Vh) = -0.6 mV, slope factors (Vc) = 11.8 mV, [n = 5] was significantly less depolarized than that of the pooled currents (Vh = 47.3 mV, Vc = 12.3 mV, n = 7). 4. Repetitive depolarization with spikelike waveforms was also able to induce facilitation of L-type currents, suggesting that facilitation was not simply a consequence of a modal shift in gating like that induced by Bay K 8644. 6. Combined whole cell recording and single-cell reverse transcription-polymerase chain reaction amplification revealed that neostriatal medium spiny neurons expressed detectable levels of either class C or class D L-type channel alpha 1, subunit mRNA. Both neurons expressing class C L-type channels and neurons expressing class D L-type channels exhibited voltage-dependent facilitation.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1996

Multiplicity of glutamate receptor subunits in single striatal neurons: an RNA amplification study.

The RNA amplification technique was used to examine the pattern of coexpression of mRNAs encoding 16 subtypes/subunits of the glutamate receptor (GluR) in acutely dissociated neurons from adult rat striata. THe signal intensity for each mRNA varied within single neurons, but the general pattern of low versus high expression signals was similar among neurons, except for the GluR4 subunit of the (+/-)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. The mRNAs for GluR1-3 subunits of the AMPA receptor were present in all cells, with the signal intensity of GluR1 mRNAs usually the lowest. The kainate receptor subunit mRNAs (GluR5-7) were present in most neurons, and the signal intensity for GluR6 mRNA was the highest. The signals for N-methyl-D-aspartate (NMDA)R1 and NMDAR2B mRNAs were high in most neurons; however, NMDAR2A and NMDAR2C mRNAs gave low or undetectable signals. For mRNAs encoding metabotropic GluRs (mGluRs), signals for mGluR1, mGluR2, and mGluR3 mRNAs were low or undetectable, whereas mGluR4 and mGluR5 mRNA signals were high in most neurons. In most cases (12 of 16 mRNAs), the results agreed with data from in situ hybridization experiments in which individual mRNAs were examined. All neurons expressed subtypes/subunits mRNAs for all four types of GluRs; however, there were differences in the relative intensity of the mRNA signals detected in individual cells, suggesting that these receptors could exist in various combinations within individual neurons and thus confer synapse-specific function for information processing in the striatum.

Animals↗

PubMed1995

Glutamate-mediated excitotoxic death of cultured striatal neurons is mediated by non-NMDA receptors.

Considerable interest has focused on the role of glutamate-mediated excitotoxicity in neurodegenerative disorders of the basal ganglia. The in vitro data on the receptor mechanisms involved in this process, however, have been inconclusive. Some studies have indicated that excitotoxins acting at NMDA receptors kill striatal neurons and others have indicated that NMDA receptor-mediated excitotoxic death of striatal neurons is minimal in the absence of cortex. In the present study, we used a pharmacological approach to carefully reexamine this issue in 2-week-old cultures of striatal neurons dissociated from E17 rat embryos. The sensitivity of these neurons to glutamate agonists and antagonists was determined by monitoring cell loss in identified regions of the growth dishes. We found that glutamate killed striatal neurons with an EC50 of 100 microM. This loss was not mediated by NMDA receptors, since it was not reduced by the NMDA receptor antagonist APV (0.1-1.0 mM). Consistent with this result, up to 50 mM NMDA receptor-specific excitotoxin quinolinic acid (QA) did not affect neuronal survival. Depolarizing the QA-exposed neurons with 35 mM potassium chloride to enhance NMDA receptor activation by QA also did not produce neuron loss. The metabotropic glutamate receptor antagonist AP3 (500 microM) also had no effect on the striatal neuron loss produced by 100 microM glutamate. In contrast, the non-NMDA antagonist GYKI 52466 (100 microM) did block the excitotoxic effect of glutamate (100 microM). Specific AMPA and KA receptor agonists and the non-NMDA antagonist GYKI 52466 revealed that the non-NMDA receptor-mediated excitotoxic effect of glutamate was mediated by KA receptors. These results suggest that cultured striatal neurons are directly vulnerable to non-NMDA glutamate agonists, but not to NMDA and metabotropic glutamate agonists. Thus, non-NMDA receptors may play a greater role in the excitotoxic death of striatal neurons in disease and experimental animal models than previously realized.

Animals↗

PubMed1995

Modulation of calcium currents by a D1 dopaminergic protein kinase/phosphatase cascade in rat neostriatal neurons.

In rat neostriatal neurons, D1 dopamine receptors regulate the activity of cyclic AMP-dependent protein kinase (PKA) and protein phosphatase 1 (PP1). The influence of these signaling elements on high voltage-activated (HVA) calcium currents was studied using whole-cell voltage-clamp techniques. The application of D1 agonists or cyclic AMP analogs reversibly reduced N- and P-type Ca2+ currents. Inhibition of PKA antagonized this modulation, as did inhibition of PP1, suggesting that the D1 effect was mediated by a PKA enhancement of PP1 activity directed toward Ca2+ channels. In a subset of neurons, D1 receptor-mediated activation of PKA enhanced L-type currents. The differential regulation of HVA currents by the D1 pathway helps to explain the diversity of effects this pathway has on synaptic integration and plasticity in medium spiny neurons.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Muscarinic receptors modulate N-, P-, and L-type Ca2+ currents in rat striatal neurons through parallel pathways.

Muscarinic modulation of calcium currents was studied in acutely isolated striatal neurons from the adult rat using the whole-cell configuration of the patch-clamp technique. Muscarinic agonists reduced calcium currents through two distinct signaling pathways. One pathway depended upon PTX-sensitive G-proteins and targeted N- and P-type currents. The other pathway depended upon PTX-insensitive G-proteins and was rendered inactive by high intracellular concentrations of BAPTA and targeted L-type currents. The modulation of N- and P-type currents was relieved by strong depolarizing prepulses, whereas the modulation of L-type currents was not. These findings support the proposition that parallel signaling pathways exist between muscarinic receptors and calcium channels.

Animals↗

PubMed1994

Opioids decrease high-voltage activated calcium currents in acutely dissociated neostriatal neurons.

Although the distribution of opioid receptors is central to the patch-matrix model of neostriatal organization, it has been unclear whether these receptors are located post-synaptically. Moreover, it has not yet been clarified whether opioid receptor activation in neostriatum results in the modulation of calcium and/or potassium conductances. To test this, neostriatal neurons were acutely isolated and their sensitivity to opioid receptor agonists determined. At nanomolar concentrations, both the mu-agonist [D-Ala2, MePhe4,Gly-ol5]-enkephalin (DAMGO) and the delta-agonist [D-Pen2, D-Pen5]-enkephalin (DPEPE) reversibly decreased whole-cell calcium currents in medium-sized neurons. These effects were blocked by the opiate antagonist naloxone. These findings argue that activation of post-synaptic, opioid receptors is capable of modulating the excitability of neostriatal neurons.

Calcium Channels↗

PubMed1994

Dopaminergic regulation of striatal efferent pathways.

In the past year there has been a growing debate about the distribution of dopamine receptors in striatal efferent pathways. As is often the case, different approaches lead to different perspectives. Nevertheless, the available data can be reconciled with a model in which D1 and D2 dopamine receptors are segregated in the distal dendrites and axonal terminal fields of striatonigral and striatopallidal neurons, but intermingled in the soma and proximal dendrites.

Animals↗

PubMed1994

Acutely isolated neurons of the rat globus pallidus exhibit four types of high-voltage-activated Ca2+ current.

1. Large, projection-like neurons from the adult (> 3 wk post-natal) rat globus pallidus (GP) were acutely isolated and subjected to whole-cell voltage-clamp (n = 37). Ca2+ currents were isolated pharmacologically in cells with whole-cell capacitances of 15-34 pF. 2. With 5 mM Ba2+ as a charge carrier, whole-cell currents began to activate near -40 mV and peaked near 0 mV. Based on activation threshold and inactivation kinetics, currents appeared to be of the high-voltage-activated type. 3. Cd2+ blocked whole-cell currents with an IC50 near 2 microM. Currents activated at negative potentials were not relatively resistant to Cd2+, supporting the inference that low-voltage-activated currents were not prominent in these neurons. 4. The dihydropyridine, L-channel antagonist, nifedipine (5 microM), reduced peak current by 21 +/- 4% (SD) (n = 10). The dihydropyridine agonist, BayK 8644 (1-2 microM) enhanced peak current and slowed current deactivation (n = 4). 5. The N-channel antagonist, omega-conotoxin GVIA (omega-CgTx, 2 microM) blocked 25 +/- 7% of the peak whole-cell current (n = 10). The blocks produced by omega-CgTx and nifedipine were additive, blocking an average of 46 +/- 8% of the current (n = 10). 6. The current resistant to the selective N- and L-channel antagonists was partially blocked by the P-channel antagonist omega-agatoxin IVA (omega-AgTx, 100 nM). omega-AgTx blocked about one-half of the current not attributable to N- and L-type channels (22 +/- 5% of the total current, n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Somatostatin- and substance P-like immunoreactivity in rat neostriatal cultures.

In the normal adult neostriatum, somatostatin immunoreactive interneurons constitute a few percent of the total neuronal population whereas substance P immunoreactive neurons, which project to the substantia nigra, constitute nearly half of the total. Primary monolayer neostriatal cultures derived from E17 rat brains displayed both somatostatin-like and substance P-like immunoreactivity (SOM-IR and SP-IR). However, the proportions of SOM-IR and SP-IR neurons in vitro were significantly different from those in vivo. At 4 days in vitro (DIV), SOM-IR neurons comprised 19% of all neurons and this percentage increased to 30% at 25 DIV. In contrast, SP-IR neurons were less common than expected at 4 DIV (20%) and declined in percentage to 13% at 27 DIV. These results suggest that survival in target-deprived neostriatal cultures is favored for SOM-IR interneurons.

Animals↗

PubMed1994

Cellular and molecular characterization of Ca2+ currents in acutely isolated, adult rat neostriatal neurons.

Ca2+ currents in acutely isolated, adult rat neostriatal neurons were studied with whole-cell voltage-clamp techniques. In the vast majority of neurons (approximately 90%, n > 250), currents were exclusively of the high-voltage-activated (HVA) type. HVA currents activated near -40 mV and reached their maximum amplitude near 0 mV. Quasi-steady-state inactivation curves in many neurons were well fitted only with a sum of Boltzmann functions, suggesting that the HVA currents were heterogeneous. Although the block of whole-cell current by Cd2+ was well fitted with a single isotherm having an IC50 of near 1 microM, experiments with organic channel antagonists suggested that at least four types of HVA channels were expressed by most cells. On average, the L-channel antagonist nifedipine (5-10 microM) blocked 31 +/- 10% of the whole-cell current (n = 20), the N-channel antagonist omega-conotoxin GVIA (omega-CgTx) (2-5 microM) blocked 27 +/- 11% (n = 20), and the P-channel antagonist omega-agatoxin IVA (100-500 nM) blocked 21 +/- 10% (n = 18). In many neurons, the block by omega-CgTx was partially or completely reversible. In cells tested with a combination of these antagonists, 34 +/- 17% of the peak Ca2+ current remained unblocked (n = 13). Single-cell expression profiling of medium-sized neurons revealed the presence of rbA and rbB Ca2+ channel alpha 1 subunit mRNAs but low or undetectable levels of rbC mRNA (n = 12). These findings suggest that although adult neostriatal projection neurons do not express significant levels of LVA Ca2+ current, they do express a pharmacologically and structurally heterogeneous population of HVA currents.

Animals↗

PubMed1993

Are neostriatal dopamine receptors co-localized?

The postsynaptic effects of dopamine in the neostriatum are mediated by five G-protein-coupled receptors. The extent to which these receptors are co-localized in neostriatal neurons has become controversial. This debate has far-reaching implications for treatment strategies in disorders of dopaminergic signaling, such as Parkinson's disease and schizophrenia. This review examines the molecular and cellular evidence for and against co-localization, including new information derived from single-cell mRNA amplification and patch-clamping of isolated neurons. It is concluded that this evidence is largely consistent with co-localization of functionally significant receptors of the D1 and D2 families in the majority of neostriatal efferent neurons. This conclusion has important implications for parallel processing models of the neostriatum.

Animals↗

PubMed1993

D1 and D2 dopamine receptor modulation of sodium and potassium currents in rat neostriatal neurons.

The potassium and sodium currents in acutely isolated neostriatal neurons are modulated by activation of both D1- and D2-class receptors. The amplification of mRNA in individual neurons supports this conclusion and has shown that striatonigral neurons express not only D1 and D2 receptors, but D3 receptors as well. The characteristics of the modulations produced by these receptors provide a foundation for both antagonistic and synergistic actions of D1 and D2 agonists in the neostriatum. Understanding precisely how these modulations interact in shaping excitability, however, will require a better characterization of spatial domains in which they operate.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1993

Voltage-gated potassium currents in acutely dissociated rat cortical neurons.

1. We describe three outward K+ current components in acutely dissociated neurons from rat sensorimotor cortex on the basis of inactivation kinetics and voltage dependence. 2. The fast A current (IAf) was completely inactivated at -40 mV and half-inactivated at -52 mV. It activated [time to peak (TTP) 8 ms at -10 mV] and was inactivated (tau inact = 12 ms at -10 mV) rapidly. Recovery from inactivation had a time constant of approximately 80 ms at -100 mV. It was insensitive to tetraethyl ammonium (TEA) and dendrotoxin but was blocked by 4-aminopyridine (4-AP, IC50 = 1 mM). 3. The slowly inactivating current (IKS) was the largest current seen in acutely dissociated adult neurons. It was completely inactivated at -40 mV, half-inactivated at -98 mV, and was kinetically slower (TTP = 130 ms at -10 mV; tau inact = 293 ms at -10 mV) than the fast A current. Deactivation tails were fit with the sum of two exponentials with time constants of 2-10 and 15-40 ms. IKS recovered from inactivation with a time constant of approximately 1,200 ms at -100 mV. 4. There were two components that inactivated with even slower kinetics. The very slowly inactivating current (IKSS) was operationally defined as the current remaining after a 5-s hold at -40 mV. One component inactivated with a time constant of 1,927 ms at -10 mV. The other component showed no inactivation over a 5-s test command, but in 40- to 50-s steps to -10 mV, inactivated with a tau of approximately 20 s. The very slowly inactivating current activated with similar kinetics to IKS (TTP = 121 ms at -10 mV), and two deactivation tails, with kinetics similar to those after the -100 mV prepulse, were observed after holding at -40 mV. 5. Both IKS and IKSS were sensitive to TEA. Seventy-six percent (76%) of IKSS was blocked by 30 mM TEA. Two components to the TEA block were present for IKSS, with IC50s of 88 microM (67% of blockable current) and 7 mM (33%). Seventy percent (70%) of IKS was blocked by 30 mM TEA. For the IKS current, there were also two effective concentrations, with IC50s of 8 microM (21% of blockade current) and 3 mM (79%). 6. IKS and IKSS were also sensitive to 4-AP. Seventy-six percent (76%) of IKSS was blocked by 3-5 mM 4-AP. IKSS exhibited two components of 4-AP block.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗

PubMed1993

Cholinergic and dopaminergic modulation of potassium conductances in neostriatal neurons.

Muscarinic and dopaminergic ligands exert their principal effects on excitability by modulating voltage-dependent conductances. Potassium currents activated by depolarization are among the conductances modulated. These currents can be divided into rapidly (Af) and slowly inactivating (A(s)) A-currents and a delayed rectifier current. The voltage-dependence and maximal conductance of the Af current are modulated by muscarinic agonists, presumably through a M1 receptor. This pharmacological class of receptors is coupled to phosphoinositide hydrolysis as well as the inhibition of cAMP accumulation. The nature of the muscarinic modulation of the Af current suggests that acetylcholine should not be viewed as excitatory or inhibitory but rather as enhancing state stability. Dopaminergic agonists appear to selectively modulate the A(s) current, rather than the Af current. This current is expressed late in the postnatal development of neostriatal neurons and plays an important part in regulating integrative behavior. Both D1 and D2 receptors mediate dopaminergic modulation. D1 agonists suppress this current whereas D2 agonists enhance it. The interaction of the dopaminergic modulation with the state transitions medium spiny neurons undergo in generating spike activity has yet to be fully explored. Nevertheless, it is clear that the modulation of the A(s) current provides a basis on which dopamine might interact with acetylcholine in controlling neostriatal excitability.

Acetylcholine↗

PubMed1992

Dopamine receptor subtypes colocalize in rat striatonigral neurons.

Dopaminergic neurons of the substantia nigra provide one of the major neuromodulatory inputs to the neostriatum. Recent in situ hybridization experiments have suggested that postsynaptic dopamine receptors are segregated in striatonigral and striatopallidal neurons. We have tested this hypothesis in acutely isolated, retrogradely labeled striatonigral neurons by examining the neuromodulatory effects of selective dopaminergic agonists on Na currents and by probing single-cell antisense RNA populations with dopamine receptor cDNAs. In most of the neurons examined (20/31), the application of the D1 dopamine receptor agonist SKF 38393 reduced evoked whole-cell Na+ current. The D2 agonists quinpirole and bromocriptine had mixed effects; in most neurons (23/42), whole-cell Na+ currents were reduced, but in others (8/42), currents were increased. In cell-attached patch recordings, bath application of SKF 38393 decreased currents as in whole-cell recordings, whereas quinpirole consistently (6/10) enhanced currents--suggesting that D2-like receptors could act through membrane delimited and non-delimited pathways. Changes in evoked current were produced by modulation of peak conductance and modest shifts in the voltage dependence of steady-state inactivation. Antisense RNA probes of dopamine receptor cDNA Southern blots consistently (5/5) revealed the presence of D1, D2, and D3 receptor mRNA in single striatonigral neurons. These findings argue that, contrary to a strict receptor segregation hypothesis, many striatonigral neurons colocalize functional D1, D2, and D3 receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1992

Grafted neostriatal neurons express a late-developing transient potassium current.

Previous anatomical and physiological studies of neostriatal grafts have suggested that transplanted neurons do not develop beyond an early postnatal stage. We have tested whether this hypothesis can be generalized by characterizing the developmentally regulated Ca-independent potassium currents in graft neurons. These currents were studied using a combination of the whole-cell voltage-clamp technique with acutely-dissociated neurons and intracellular recording in slices. In all of the graft neurons examined with voltage-clamp techniques (n = 13), evidence was found for a slowly-inactivating potassium current that is seen only beyond the third or fourth postnatal week in normal rats. A current resembling the delayed rectifier was also seen in all sample neurons. The rapidly inactivating A-current which dominates recordings from nearly all immature neurons was seen in only about half (54%, 7/13) of the graft neurons; in a sample of normal adult striatal neurons, the A-current was detected in a similar percentage of neurons (41%, 25/62). Recordings of graft neurons in slices corroborated the voltage-clamp findings in revealing a slowly inactivating outward current that acts in the subthreshold potential range. These findings suggest that graft neurons express the normal complement of depolarization-activated potassium channel proteins seen in adult neurons.

Animals↗