Association between information provision and decisional conflict in cancer patients

BACKGROUND

In this study, we aimed to identify demographic and clinical variables that correlate with perceived information provision among cancer patients and determine the association of information provision with decisional conflict (DC).

PATIENTS AND METHODS

We enrolled a total of 625 patients with cancer from two Korean hospitals in 2012. We used the European Organization for Research and Treatment of Cancer (EORTC) quality-of-life questionnaire (QLQ-INFO26) to assess patients' perception of the information received from their doctors and the Decisional Conflict Scale (DCS) to assess DC. To identify predictive sociodemographic and clinical variables for adequate information provision, backward selective logistic regression analyses were conducted. In addition, adjusted multivariate logistic regression analyses were carried out to identify clinically meaningful differences of perceived level of information subscales associated with high DC.

RESULTS

More than half of patients with cancer showed insufficient satisfaction with medical information about disease (56%), treatment (73%), other services (83%), and global score (80%). In multiple logistic regression analyses, lower income and education, female, unmarried status, type of cancer with good prognosis, and early stage of treatment process were associated with patients' perception of inadequate information provision. In addition, Information about the medical tests with high DCS values clarity [adjusted odds ratio (aOR), 0.54; 95% confidence interval (CI) 0.30-0.97] and support (aOR, 0.53; 95% CI 0.33-0.85) showed negative significance. For inadequate information perception about treatments and other services, all 5 DCS scales (uncertainty, informed, values clarity, support, and effective decision) were negatively related. Global score of inadequate information provision also showed negative association with high DCS effective decision (aOR, 0.43; 95% CI 0.26-0.71) and DCS uncertainty (aOR, 0.46; 95% CI 0.27-0.77).

CONCLUSION

This study found that inadequate levels of perceived information correlated with several demographic and clinical characteristics. In addition, sufficient perceived information levels may be related to low levels of DC.

Effect of the intra-abdominal pressure and the center of segmental body mass on the lumbar spine mechanics - a computational parametric study

Determination of physiological loads in human lumbar spine is critical for understanding the mechanisms of lumbar diseases and for designing surgical treatments. Computational models have been used widely to estimate the physiological loads of the spine during simulated functional activities. However, various assumptions on physiological factors such as the intra-abdominal pressure (IAP), centers of mass (COMs) of the upper body and lumbar segments, and vertebral centers of rotation (CORs) have been made in modeling techniques. Systematic knowledge of how these assumptions will affect the predicted spinal biomechanics is important for improving the simulation accuracy. In this paper, we developed a 3D subject-specific numerical model of the lumbosacral spine including T12 and 90 muscles. The effects of the IAP magnitude and COMs locations on the COR of each motion segment and on the joint/muscle forces were investigated using a global convergence optimization procedure when the subject was in a weight bearing standing position. The data indicated that the line connecting the CORs showed a smaller curvature than the lordosis of the lumbar spine in standing posture when the IAP was 0 kPa and the COMs were 10 mm anterior to the geometric center of the T12 vertebra. Increasing the IAP from 0 kPa to 10 kPa shifted the location of CORs toward the posterior direction (from 1.4 ± 8.9 mm anterior to intervertebral disc (IVD) centers to 40.5 ± 3.1 mm posterior to the IVD centers) and reduced the average joint force (from 0.78 ± 0.11 Body weight (BW) to 0.31 ± 0.07 BW) and overall muscle force (from 349.3 ± 57.7 N to 221.5 ± 84.2 N). Anterior movement of the COMs from -30 mm to 70 mm relative to the geometric center of T12 vertebra caused an anterior shift of the CORs (from 25.1 ± 8.3 mm posterior to IVD centers to 7.8 ± 6.2 mm anterior to IVD centers) and increases of average joint forces (from 0.78 ± 0.1 BW to 0.93 ± 0.1 BW) and muscle force (from 348.9 ± 47.7 N to 452.9 ± 58.6 N). Therefore, it is important to consider the IAP and correct COMs in order to accurately simulate human spine biomechanics. The method and results of this study could be useful for designing prevention strategies of spinal injuries and recurrences, and for enhancing rehabilitation efficiency.

'Out of two bad choices, I took the slightly better one': vaccination dilemmas for Scottish and Polish migrant women during the H1N1 influenza pandemic

OBJECTIVES

Pregnancy has been identified as a risk factor for complications from pandemic H1N1 influenza, and pregnant women were identified as a target group for vaccination in the UK in the 2009 pandemic. Poland took a more conservative approach, and did not offer vaccination to pregnant women. Poland accounts for the largest wave of recent migrants to the UK, many of whom are in their reproductive years and continue to participate actively in Polish healthcare systems after migration. The authors speculated that different national responses may shape differences in approaches to the vaccine between Scottish and Polish women. This study therefore aimed to assess how pregnant Polish migrants to Scotland weighed up the risks and benefits of the vaccine for pandemic H1N1 influenza in comparison with their Scottish counterparts.

STUDY DESIGN

A qualitative interview-based study comparing the views of Scottish and Polish pregnant women on H1N1 vaccination was carried out in 'real time' during the first 2 weeks of the vaccination programme in November 2009.

METHODS

One-to-one interviews were conducted with 10 women (five Polish and five Scottish) in their native language. Interviews were transcribed, translated, coded and analysed for differences and similarities in decision-making processes between the two groups.

RESULTS

Contrary to expectations, Scottish and Polish women drew on a strikingly similar set of considerations in deciding whether or not to accept the vaccine, with individual women reaching different conclusions. Almost all of the women adopted a critical stance towards the vaccine. While most women understood that pregnancy was a risk factor for complications from influenza, their primary concern was protecting family health overall and their fetus in particular. Deciding whether or not to accept the vaccine was difficult for women. Some identified a contradiction between the culture of caution which characterizes pregnancy-related advice, and the fact that they were being urged to accept what was perceived as a relatively untested vaccine. Their health histories, individual constitutions, and whether their everyday routines exposed them to sources of infection combined to establish their perceived 'candidacy' for contracting infection. Neither Scottish nor Polish women felt that 'official' information addressed their concerns in sufficient detail, and almost all of the women sought information from a variety of sources. Polish women found it more difficult to access information and advice from the National Health Service than their Scottish counterparts. For most respondents, deciding whether or not to accept the vaccine was an attenuated process, culminating for many in choosing the 'least worst' option in the context of competing risks.

CONCLUSIONS

To the authors' knowledge, this is the first study to assess perceptions of H1N1 immunization risk in pregnant women in 'real time'. It highlights the important unmet needs for information that women need to be able to make informed vaccination choices, and the challenges of producing such information in a context of uncertainty. This is of particular relevance as many countries, including the UK, are actively reviewing their plans for vaccination programmes during pregnancy.

Amitriptyline does not block the action of ATP at human P2X4 receptor

BACKGROUND AND PURPOSE

Amitriptyline is a tricyclic antidepressant that is also widely used to treat neuropathic pain in humans, but the mechanism of this anti-hyperalgesic effect is unknown. Microglia in the mouse spinal cord become activated in neuropathic pain, and expression of P2X4 receptors by these microglia is increased. Antisense RNA targeting P2X4 receptors suppresses the development of tactile allodynia in rats. This suggests that blockade of P2X4 receptors might be the mechanism by which amitriptyline relieves neuropathic pain.

EXPERIMENTAL APPROACH

We expressed human, rat and mouse P2X receptors (P2X2, P2X4, P2X7) in human embryonic kidney cells and evoked inward currents by applying ATP. We compared the action of ATP on control cells and cells treated with amitriptyline.

KEY RESULTS

Amitriptyline (10 microM), either applied acutely or by pre-incubation for 2-6 h, had no effect on inward currents evoked by ATP (0.3-100 microM) at human P2X4 receptors. At rat and mouse receptors, amitriptyline (10 microM) caused a modest reduction in the maximum responses to ATP, without changes in EC(50) values, but it had no effect at 1 microM. Amitriptyline also had no effects on currents evoked by ATP at rat P2X2 receptors, or at rat or human P2X7 receptors.

CONCLUSION AND IMPLICATIONS

The results do not support the view that amitriptyline owes its pain-relieving actions in man to the direct blockade of P2X4 receptors.

P2X1 and P2X4 receptor currents in mouse macrophages

BACKGROUND AND PURPOSE

Activation of P2X receptors on macrophages is an important stimulus for cytokine release. This study seeks evidence for functional expression of P2X receptors in macrophages that had been only minimally activated.

EXPERIMENTAL APPROACH

Whole-cell recordings were made from macrophages isolated 2-6 h before by lavage from mouse peritoneum, without further experimental activation. ATP (1-1000 muM) elicited inward currents in all cells (holding potential -60 mV). The properties of this current were compared among cells from wild type, P2X1 (-/-) and P2X4 (-/-) mice.

KEY RESULTS

Immunoreactivity for P2X1 and P2X4 receptors was observed in wild type macrophages but was absent from the respective knock-out mice. In cells from wild type mice, ATP and alpha beta methyleneATP (alpha beta meATP) evoked inward currents rising in 10-30 ms and declining in 100-300 ms: these were blocked by pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 microM). ATP also elicited a second, smaller ( approximately 10% peak amplitude), more slowly decaying (1-3 s) at concentrations > or =10 microM: this was resistant to PPADS and prolonged by ivermectin. Macrophages from P2X1 (-/-) mice responded to ATP (>100 microM) but not alpha beta meATP: these small currents were prolonged by ivermectin. Macrophages from P2X4 (-/-) mice responded to ATP and alpha beta meATP as cells from wild type mice, except that ATP did not evoke the small, slowly decaying component: these currents were blocked by PPADS.

CONCLUSION

Mouse peritoneal macrophages that are minimally activated demonstrate membrane currents in response to ATP and alpha beta meATP that have the predominate features of P2X1 receptors.

Evidence Against a Role for Protein Kinase C in the Inhibition of the Calcium-activated Potassium Current IAHP by Muscarinic Stimulants in Rat Hippocampal Neurons

The possible role of protein kinase C activation in the inhibitory action of cholinergic transmitters on the slow Ca-dependent afterhyperpolarizing current (IAHP) in hippocampal CA3 pyramidal neurons was investigated using hippocampal slice cultures. IAHP was inhibited reversibly by methacholine (100 - 600 nM) and irreversibly by the protein kinase C activator, phorbol-12,13-dibutyrate (PDBu, 10 nM to 1 microM). The inhibitory action of PDBu was antagonized by prior (15 - 60 min) exposure to staurosporin (1 microM). In contrast, the inhibitory effect of methacholine on IAHP was not reduced after up to 3 h of exposure to this compound. In addition, methacholine produced a reversible inward current at the holding potential, which was augmented by staurosporin. However, prior exposure to PDBu reduced the effect of methacholine on IAHP and occluded the methacholine-induced inward current. This effect of PDBu was also observed in the presence of staurosporin, suggesting that it might be exerted through a protein kinase C-independent pathway. Noradrenalin (2 - 5 microM) and 8-bromo cyclic adenosine 3',5'monophosphate (8-Br-cAMP, 1 mM) also produced a reversible block of IAHP. Their action was antagonized by staurosporin, probably via its effect on protein kinase A. Thus the present experiments suggest that the action of muscarinic agonists on IAHP cannot be explained by an effect on protein kinase C, but support a role for protein kinase A in mediating the action of noradrenalin.

Reduction of Potassium Conductances Mediated by Metabotropic Glutamate Receptors in Rat CA3 Pyramidal Cells Does Not Require Protein Kinase C or Protein Kinase A

Metabotropic glutamate receptors, unlike ionotropic receptors, exert their actions on ion channels via G-proteins coupled to second messenger systems. In the hippocampus stimulation of metabotropic receptors can lead to decreased potassium channel conductance, decreased accommodation of cell firing and inhibition of the slow calcium-dependent afterhyperpolarizing current (IAHP). Using the single-electrode voltage-clamp technique in hippocampal slice cultures of the rat, the role of protein kinases in mediating these metabotropic glutamate responses was investigated. In the presence of staurosporin, protein kinase C activation by phorbol esters and protein kinase A activation by 8-bromo-cyclic adenosine monophosphate were blocked. Under these conditions, the inhibition of IAHP by 1-amino-cyclopentyl-trans-dicarboxylate (ACPD), a metabotropic agonist, was unchanged, whilst the inward current elicited by ACPD was enhanced. These results demonstrate that, in the hippocampus, metabotropic glutamate responses persist during inhibition of protein kinase A and C activation. Furthermore, these responses are insensitive to pertussis toxin, confirming previous observations.

Molecular and cellular properties of GnRH neurons revealed through transgenics in the mouse

Recent advances in the use of gonadotropin-releasing hormone (GnRH) promoter-driven transgenics in the mouse are beginning to open up the once elusive GnRH neuronal phenotype to detailed molecular and cellular investigation. This review highlights progress in the development of GnRH promoter transgenic constructs and the understanding of murine gene sequences required for the correct temporal and spatial targeting of transgenes to the GnRH phenotype in vivo. Strategies enabling the identification of single, living GnRH neurons in the acute brain slice preparation are allowing gene profiling and electrophysiological experiments to be undertaken. Results so far indicate that, like other neurons, GnRH cells express a variety of sodium, potassium and calcium channels as well as GABAergic and glutamatergic receptors which are responsible for determining the membrane properties and firing characteristics of the GnRH neuron. Many of these receptors and channels appear to be expressed heterogeneously within the GnRH phenotype. Furthermore, several display distinct postnatal developmental expression profiles which are likely to be of consequence to the development of synchronized, pulsatile GnRH secretion in the adult animal.

Profiling gamma-aminobutyric acid (GABA(A)) receptor subunit mRNA expression in postnatal gonadotropin-releasing hormone (GnRH) neurons of the male mouse with single cell RT-PCR

The present investigation has examined which subunits of the GABA(A) receptor are expressed by gonadotropin-releasing hormone (GnRH) neurons in the juvenile and adult male mouse. Cells of defined morphology, located in the medial septum (MS) and rostral preoptic area (POA), were patch-clamped in the acute brain slice preparation and their cell contents extracted. A reverse transcriptase polymerase chain reaction (RT-PCR) procedure using nested primers was used to establish individual GnRH mRNA-expressing cells which were then evaluated for eleven GABA(A) receptor (alpha1-5, beta1-3, gamma1-3) subunit transcripts. Single and multiple GABA(A) receptor subunit mRNAs were detected in approximately 70% of all GnRH neurons. A range of different subunit mRNAs (alpha1, alpha2, alpha5, beta1, beta2, beta3, gamma2) were found in juvenile GnRH neurons, with the alpha1gamma2 and alpha5gamma2 combinations encountered most frequently within individual cells. The expression profile in adult GnRH neurons was more extensive than that detected in juveniles with alpha1, alpha2, alpha3, alpha5, beta1, beta2, beta3, gamma1 and gamma2 subunits all being detected. The major difference in subunit profile between GnRH neurons located in the MS and POA involved the beta subunits. The principal postnatal developmental change was one of increasing overall subunit heterogeneity in maturing POA GnRH neurons. The profile of GABA(A) receptor subunit mRNAs detected in male GnRH neurons was quite different to that reported by us for female GnRH neurons in the mouse using the same RT-PCR approach. Together, these findings indicate that postnatal GnRH neurons are likely to express a range of GABA(A) receptor subunit mRNAs in a sexually dimorphic and developmentally-regulated manner.

Direct regulation of postnatal GnRH neurons by the progesterone derivative allopregnanolone in the mouse

The mechanisms through which gonadal steroids exert critical feedback actions upon the activity of the GnRH neurons are not understood. We have examined here whether progesterone may modulate the electrical activity of the GnRH neurons following its rapid metabolism to the neuroactive steroid allopregnanolone within the brain. Using an acute brain slice preparation, whole-cell, patch-clamp recordings were made from GnRH neurons of juvenile (postnatal d 15-20) and adult (postnatal d 60-70) female mice in the presence of tetrodotoxin. Progesterone (1 microM) was not observed to have any actions (up to 5 min exposure) upon GnRH neurons. However, allopregnanolone (500 nM-1 microM) exerted rapid (<1 min) effects upon the baseline membrane potential of all GnRH neurons and also significantly (P < 0.01) enhanced their GABA responses by up to 4-fold. All GABA and allopregnanolone responses were abolished by the GABA(A) receptor antagonist bicuculline. No differences were detected in the allopregnanolone sensitivity of GnRH neurons recorded from juvenile and adult GnRH neurons. These results provide the first evidence for a direct action of the neurosteroid allopregnanolone on postnatal GnRH neurons and suggest a new mechanism through which fluctuating progesterone levels may influence the secretory activity of these important neurons in the female mouse.

Heterogeneity in the basic membrane properties of postnatal gonadotropin-releasing hormone neurons in the mouse

The electrophysiological characteristics of unmodified, postnatal gonadotropin-releasing hormone (GnRH) neurons in the female mouse were studied using whole-cell recordings and single-cell RT-PCR methodology. The GnRH neurons of adult animals fired action potentials and exhibited distinguishable voltage-current relationships in response to hyperpolarizing and depolarizing current injections. On the basis of their patterns of inward rectification, rebound depolarization, and ability to fire repetitively, GnRH neurons in intact adult females were categorized into four cell types (type I, 48%; type II, 36%; type III, 11%; type IV, 5%). The GnRH neurons of juvenile animals (15-22 d) exhibited passive membrane properties similar to those of adult GnRH neurons, although only type I (61%) and type II (7%) cells were encountered, in addition to a group of "silent-type" GnRH neurons (32%) that were unable to fire action potentials. A massive, action potential-independent tonic GABA input, signaling through the GABA(A) receptor, was present at all ages. Afterdepolarization and afterhyperpolarization potentials (AHPs) were observed after single action potentials in subpopulations of each GnRH neuron type. Tetrodotoxin (TTX)-independent calcium spikes, as well as AHPs, were encountered more frequently in juvenile GnRH neurons compared with adults. These observations demonstrate the existence of multiple layers of functional heterogeneity in the firing properties of GnRH neurons. Together with pharmacological experiments, these findings suggest that potassium and calcium channels are expressed in a differential manner within the GnRH phenotype. This heterogeneity occurs in a development-specific manner and may underlie the functional maturation and diversity of this unique neuronal phenotype.

Late postnatal reorganization of GABA(A) receptor signalling in native GnRH neurons

The molecular and cellular characteristics of the gonadotropin-releasing hormone (GnRH) neurons have been difficult to ascertain due to their scattered distribution within the basal forebrain. Using morphological criteria coupled with single cell RT-PCR postidentification, we have developed a method for investigating native GnRH neurons in the mouse brain and used it to examine the development of GABA(A) receptor signalling in this phenotype. Following the harvesting of the cytoplasmic contents of individual GnRH neurons, single cell multiplex RT-PCR experiments demonstrated that GABAA receptor alpha1-5, beta1-3 and gamma2 & 3 subunit transcripts were expressed by both neonatal (postnatal day 5) and juvenile (day 15-20) GnRH neurons in a heterogeneous manner. Following puberty, this profile was reduced to a predominant alpha1, alpha5, beta1, gamma2 subunit complement in rostral preoptic area GnRH neurons of the adult female. Whole-cell patch-clamp recordings revealed little difference between juvenile and adult GnRH neurons in their resting membrane potential and spontaneous firing rates. All GnRH neurons were found to be subjected to a tetrodotoxin-insensitive, tonic GABAergic barrage signalling through the GABA(A) receptor. However, marked heterogeneity in the sensitivity of individual juvenile GnRH neurons to GABA was revealed and, in parallel with the change in subunit mRNA profile, this was dramatically reduced in the reproductively competent adult GnRH neurons. These findings provide the first electrical and molecular characterization of the GnRH phenotype and demonstrate a novel pattern of late postnatal reorganization of native GABA(A) receptor gene expression and signalling in the GnRH neuronal population.

Detection of estrogen receptor alpha and beta messenger ribonucleic acids in adult gonadotropin-releasing hormone neurons

The behavior of the gonadotropin-releasing hormones (GnRH) neurons controlling fertility is dependent upon cyclic fluctuations in circulating concentrations of estrogen. However, the nature of estrogen action upon these cells has remained controversial due to their dispersed distribution within the brain, and evidence indicating that they do not express nuclear estrogen receptors (ERs) in vivo. We report here an acute brain slice preparation that enables individual living GnRH neurons to be identified within the mouse brain and show, using single cell multiplex RT-PCR, that the greater than 50% of GnRH neurons in adult and prepubertal females contain ERalpha messenger RNA. Approximately 10% of GnRH neurons contained ERbeta transcripts that were always coexistent with ERalpha. Single cell RT-PCR analysis of nonGnRH cells located in the medial preoptic area revealed a similar coexpression pattern of ERalpha and ERbeta transcripts. In contrast, single striatal cells were not found to contain ERbeta despite ERalpha being present in approximately 25% of cells. The analysis of single GnRH neurons in cycling female mice revealed that the detection of ERalpha and ERbeta transcripts was lowest on proestrus (ERalpha, 18% of all GnRH neurons; ERbeta, 0%) compared with diestrus (44% and 6%) and estrus (75% and 19%, respectively). Using a novel approach that enables single cell RT-PCR analysis of GnRH neurons, we present here evidence for the cyclic expression of ERalpha and ERbeta messenger RNAs within prepubertal and adult female GnRH neurons.

Promoter transgenics reveal multiple gonadotropin-releasing hormone-I-expressing cell populations of different embryological origin in mouse brain

Gonadotropin-releasing hormone-I (GnRH-I) is thought to be expressed by a single, highly spatially restricted group of neurons, which originate in the olfactory placode and migrate through the nose into the medial septum and hypothalamus from where they control fertility. Transgenic mice bearing a 13.5 kb GnRH-I-lacZ reporter construct were derived and found to express high levels of beta-galactosidase mRNA and protein within the septohypothalamic GnRH neurons in a correct temporal and spatial manner. Unexpectedly, low levels of beta-galactosidase were also present in three further populations of cells within the lateral septum, bed nucleus of the stria terminalis, and tectum. Analysis of wild-type mice with three different GnRH-I antibodies revealed distinct and transient patterns of GnRH-I peptide expression during development in all three of these populations revealed by transgenics. The synthesis of GnRH by cells of the lateral septum was the most persistent and remained until the third postnatal week. Embryonic "small eye" Pax-6 null mice, which fail to develop an olfactory placode, were also examined and shown to have equivalent populations of GnRH-I-immunoreactive cells in the lateral septum, tectum, and bed nucleus of the stria terminalis but none of the migrating cells that form the septohypothalamic GnRH population. These results prove that so-called "ectopic" expression in promoter transgenic lines can reflect authentic developmental patterns of gene expression. They further provide the first demonstration in mammalian brain that multiple neuronal populations of different embryological origin express GnRH-I peptide during embryonic and postnatal development.

Small (SKCa) Ca2+-activated K+ channels in cultured rat hippocampal pyramidal neurones

Small (SKCa) Ca2+-activated K+ channels were identified in membrane patches excised from cultured CA1-CA3 pyramidal neurones of the neonatal rat hippocampus. When recorded in low-K+ extracellular solution ([K+]o=2.5 mM), SKCa channels had a low conductance (@3 pS at 0 mV), were activated by >/=175 nM Ca2+ (Po=0.54 at 500 nM Ca2+) and there were two open-time components (2.1 and @70 ms) to their activity. These properties of single SKCa channels are similar to those of slow after-hyperpolarization channels (sAHP) previously inferred from fluctuation analysis of the sAHP current. It is concluded that the SKCa channel reported here may be the channel that generates the sAHP in hippocampal pyramidal neurones.

Morphological and membrane properties of rat magnocellular basal forebrain neurons maintained in culture

Morphological and electrophysiological characteristics of magnocellular neurons from basal forebrain nuclei of postnatal rats (11-14 days old) were examined in dissociated cell culture. Neurons were maintained in culture for periods of 5-27 days, and 95% of magnocellular (>23 micron diam) neurons stained positive with acetylcholinesterase histochemistry. With the use of phase contrast microscopy, four morphological subtypes of magnocellular neurons could be distinguished according to the shape of their soma and pattern of dendritic branching. Corresponding passive and active membrane properties were investigated with the use of whole cell configuration of the patch-clamp technique. Neurons of all cell types displayed a prominent (6-39 mV; 6.7-50 ms duration) spike afterdepolarization (ADP), which in some cells reached firing threshold. The ADP was voltage dependent, increasing in amplitude and decreasing in duration with membrane hyperpolarization with an apparent reversal potential of -59 +/- 2.3 (SE) mV. Elevating [Ca2+]o (2.5-5.0 mM) or prolonging spike repolarization with 10 mM tetraethylammonium (TEA) or 1 mM 4-aminopyridine (4-AP), potentiated the ADP while it was inhibited by reducing [Ca2+]o (2.5-1 mM) or superfusion with Cd2+ (100 microM). The ADP was selectively inhibited by amiloride (0.1-0.3 mM or Ni2+ 10 microM) but unaffected by nifedipine (3 microM), omega-conotoxin GVIA (100 nM) or omega-agatoxin IVA (200 nM), indicating that Ca2+ entry was through T-type Ca2+ channels. After inhibition of the ADP with amiloride (300 microM), depolarization to less than -65 mV revealed a spike afterhyperpolarization (AHP) with both fast and slow components that could be inhibited by 4-AP (1 mM) and Cd2+ (100 microM), respectively. In all cell types, current-voltage relationships exhibited inward rectification at hyperpolarized potentials >/=EK (approximately -90 mV). Application of Cs+ (0.1-1 mM) or Ba2+ (1-10 microM) selectively inhibited inward rectification but had no effect on resting potential or cell excitability. At higher concentrations, Ba2+ (>10 microM) also inhibited an outward current tonically active at resting potential (VH -70 mV), which under current-clamp conditions resulted in small membrane depolarization (3-10 mV) and an increase in cell excitability. Depolarizing voltage commands from prepulse potential of -90 mV (VH -70 mV) in the presence of tetrodotoxin (0.5 microM) and Cd2+ (100 microM) to potentials between -40 and +40 mV cause voltage activation of both transient A-type and sustained delayed rectifier-type outward currents, which could be selectively inhibited by 4-AP (0.3-3 mM) and TEA (1-3 mM), respectively. These results show that, although acetylcholinesterase-positive magnocellular basal forebrain neurons exhibit considerable morphological heterogeneity, they have very similar and characteristic electrophysiological properties.

Ca2+-inhibited non-inactivating K+ channels in cultured rat hippocampal pyramidal neurones

1. Whole-cell perforated-patch recording from cultured CA1-CA3 pyramidal neurones from neonatal rat hippocampus (20-22 C; [K+]o = 2.5 mM) revealed two previously recorded non-inactivating (sustained) K+ outward currents: a voltage-independent 'leak' current (Ileak) operating at all negative potentials, and, at potentials >= -60 mV, a time- and voltage-dependent 'M-current' (IK(M)). Both were inhibited by 1 mM Ba2+ or 10 microM oxotremorine-M (Oxo-M). In ruptured-patch recording using Ca2+-free pipette solution, Ileak was strongly enhanced, and was inhibited by 1 mM Ba2+ but unaffected by 0.5 mM 4-aminopyridine (4-AP), 1 mM tetraethylammonium (TEA) or 1-10 nM margatoxin. 2. Single channels underlying these currents were sought in cell-attached patch recordings. A single class of channels of conductance approximately 7 pS showing sustained activity at resting potential and above was identified. These normally had a very low open probability (Po < 0. 1), which, however, showed a dramatic and reversible increase (to about 0.9 at approximately 0 mV) following the removal of Ca2+ from the bath. Under these (Ca2+-free) conditions, single-channel Po showed both voltage-dependent and voltage-independent components on patch depolarization from resting potential. The mean activation curve was fitted by a modified Boltzmann equation. When tested, all channels were reversibly inhibited by addition of 10 microM Oxo-M to the bath solution. 3. The channels maintained their high Po in patches excised in inside-out mode into a Ca2+-free internal solution and were strongly inhibited by application of Ca2+ to the inner face of the membrane (IC50 = 122 nM); this inhibition was observed in the absence of MgATP, and therefore was direct and unrelated to channel phosphorylation/dephosphorylation. 4. Channels in patches excised in outside-out mode were blocked by 1 mM Ba2+ but were unaffected by 4-AP or TEA. 5. Channels in cell-attached patches were inhibited after single spikes, yielding inward ensemble currents lasting several hundred milliseconds. This was prevented in Ca2+-free solution, implying that it was due to Ca2+ entry. 6. The properties of these channels (block by internal Ca2+ and external Oxo-M and Ba2+, and the presence of both voltage-dependent and voltage-independent components in their Po/V relationship) show points of resemblance to those expected for channels associated with both Ileak and IK(M) components of the sustained macroscopic currents. For this reason we designate them Ksust ('sustained current') channels. Inhibition of these channels by Ca2+ entry during an action potential may account for some forms of Ca2+-dependent after-depolarization. Their high sensitivity to internal Ca2+ may provide a new, positive feedback mechanism for cell excitation operating at low (near-resting) [Ca2+]i.

Modulation of inhibitory transmission by dopamine in rat basal forebrain nuclei: activation of presynaptic D1-like dopaminergic receptors

The effects of dopamine (DA) on inhibitory transmission onto identified magnocellular neurons were examined in rat basal forebrain slices using whole-cell recording. IPSCs evoked by focal stimulation within basal forebrain nuclei were reversibly blocked by 10 microM bicuculline and had a decay time constant of 20.1 +/- 0.77 msec in the presence of 6-cyano-7-nitroquinoxalline-2,3-dione (5 mM). Bath application of DA reduced the amplitude of IPSCs up to 71.1 +/- 1.49% in a concentration-dependent manner between 0.003 and 1 mM (the IC50 value being 6.6 microM), without any effect on the holding current at -70 mV. DA (10 microM) reduced the frequency of miniature IPSCs (mIPSCs) recorded in the presence of TTX (0.5 microM), without affecting their mean amplitude, rise time, and decay time constant. Furthermore, the DA-induced effect on mIPSCs remained unaffected by 100 microM cadmium, suggesting a presynaptic mechanism independent of calcium influx. SKF 81297, a D1-like agonist, mimicked DA-induced effect on evoked IPSCs (IC50, 10.9 microM), whereas R(-)-TNPA or (-)-quinpirole, D2-like agonists (30 microM), had little or no effect on the amplitude of evoked IPSCs. R(+)-SCH 23390, a D1-like antagonist, antagonized the DA-induced effect on IPSCs (K(B) 0.82 microM), whereas S(-)-eticlopride, a D2-like antagonist, showed slight antagonism (K(B) 7.8 microM). Forskolin (10 microM) reduced the amplitude of evoked IPSCs to approximately 58% of the control and occluded the inhibitory effect of DA. These findings indicate that DA reduces inhibitory transmission onto magnocellular basal forebrain neurons by activating presynaptic D1-like receptors.

Dopamine D1-like receptor-mediated presynaptic inhibition of excitatory transmission onto rat magnocellular basal forebrain neurones

1. Excitatory postsynaptic currents (EPSCs) following focal afferent stimulation were recorded from patch-clamped magnocellular neurones in a thin-slice preparation of the rat basal forebrain. Evoked EPSCs had a mean decay time constant of 3.81 +/- 0.09 ms and were reversibly blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5 microM). 2. Bath-applied dopamine (DA) reduced evoked EPSC amplitude by up to 54.2 +/- 2.3% with an IC50 of 19.9 microM in normal Krebs solution (2.5 mM Ca2+, 1.2 mM Mg2+) without effect on postsynaptic holding current. 3. DA (30 microM) reduced the mean frequency of spontaneous miniature EPSCs recorded in 0.5 microM tetrodotoxin without affecting their mean amplitude, rise time or decay time constant. This effect was diminished by 100 microM Cd2+. 4. The effect of DA on evoked EPSCs was mimicked by the D1-like receptor agonist, SKF 81297 (IC50 25.6 microM), but not by the D2-like receptor agonist R(-)-TNPA (30 microM) or (-)-quinpirole (30 microM), and was antagonized by the D1-like receptor antagonist R(+)-SCH 23390 (estimated dissociation constant KB = 1.7 microM) but not by the D2-like receptor antagonist S(-)-eticlopride (10 microM). 5. Forskolin (10 microM) reduced evoked EPSCs to approximately 60% of the control amplitude, and occluded the effect of subsequent application of DA. 6. These results suggest that glutamatergic afferents to magnocellular basal forebrain neurones possess presynaptic D1-like DA receptors, and that activation of these receptors reduces excitatory glutamatergic transmission, probably via an adenylyl cyclase-dependent pathway.

Muscarinic inhibition of glutamatergic transmissions onto rat magnocellular basal forebrain neurons in a thin-slice preparation

We have examined excitatory and inhibitory transmission in visually identified rat magnocellular basal forebrain neurons using whole-cell patch-clamp recordings in a thin-slice preparation of the rat brain. In most cells, spontaneous excitatory and inhibitory synaptic activities could be recorded from their resting membrane potential. Following focal stimulation within the basal forebrain nucleus or directly onto visualized neighbouring neurons, postsynaptic currents were elicited in magnocellular basal forebrain cells held at -70 mb (a value close to their resting membrane potential). The synaptic responses were complex, consisting either mainly of excitatory postsynaptic currents (EPSCs), or inhibitory postsynaptic currents (IPSCs), or an EPSC-IPSC sequence. The EPSC component was consistent with the activation of AMPA/KA receptors, as it could be selectively blocked by CNQX. The IPSC component resulted in the activation of GAGAA receptors, and could be blocked by bicuculline. Since GABA-mediated trasmissions were not frequently recorded, we focused on the glutamate-mediated transmission. Studies using specific calcium channel blockers suggested that both omega-conotoxin GVIA-sensitive and omega-agatoxin VIA-sensitive calcium channels contribute to the glutamatergic transmission onto magnocellular basal forebrain neurons. Carbachol (0.3-30 microM) had no observable effect on holding current, but produced a dose-dependent inhibition of the amplitude of evoked EPSCs. This cholinergic modulation was mediated by muscarinic receptors, as it could be antagonized by atropine. The inhibitory effect of carbachol on the amplitude of EPSCs could be significantly antagonized by 100 nM methoctramine, an M2-receptor antagonist. In contrast, only a small degree of antagonism could be obtained with pirenzepine, and M1-muscarinic receptor antagonist, when present at relatively high concentration of 1 microM. Moreover, the action of carbachol was presynaptic, since the frequency of miniature postsynaptic currents was reduced without affecting their amplitude. In conclusion, the present findings indicate that glutamate-mediated transmission onto magnocellular basal forebrain neurons appeared to involve both N- and P/Q-type calcium channels, and that muscarinic modulation of glutamatergic transmission to MBF neurons is mediated by a presynaptic M2-muscarinic receptor subtypes.

Single-channel activity correlated with medium-duration, Ca-dependent K current in cultured rat hippocampal neurones

Whole-cell voltage- and patch-clamp techniques were used to record the calcium-dependent component of ImAHP and correlated single-channel activity in postnatal cultured rat hippocampal neurons. The Ca-dependent ImAHP was elicited by voltage steps to + 10 mV from a holding potential of -50 mV in the whole-cell mode. In cell-attached patches, single currents of approximately 2 pA were observed following spontaneous action currents. The duration of ensemble-averaged single-channel activity was very similar to that of the whole-cell ImAHP, approximately 100 ms. Both whole-cell current and single-channel activity could be blocked by bath-applied cadmium, 200 microM. Vigorous channel activity was evoked by bursts of action potentials that are known to elicit Ca-dependent AHPs. We conclude that this channel is a candidate for mediating ImAHP.

The whole-cell calcium current in acutely dissociated magnocellular cholinergic basal forebrain neurones of the rat

1. The electrophysiological and pharmacological characteristics of the calcium current (ICa) in acutely dissociated magnocellular cholinergic basal forebrain neurones from 11- to 14-day-old post-natal rats were studied using the whole-cell patch-clamp technique. 2. All cells exhibited a small transient low-voltage-activated (LVA) current with half-activation and half-inactivation potentials of -40.2 and -49.3 mV and slope factors for activation and inactivation of 4.82 and 3.85 mV per e-fold change in membrane potential (Vm) respectively. Activation and inactivation rates for the LVA current were highly voltage dependent. For test potential changes from -50 to -20 mV, the time-to-peak of the current decreased from 39.1 to 6.4 ms, and the time constant of current decay decreased from 81.7 to 15.5 ms. 3. A high-voltage-activated (HVA) component of ICa could be elicited at threshold voltages between -46 and -30 mV from a holding potential (VH) of -80 mV. The HVA current peaked around 0 mV; a 10-fold increase in [Ca2+]o produced a 13 mV positive shift in the peak, whilst the amplitude of the current showed an approximately hyperbolic relationship to [Ca2+]o with half-saturation at 2.5 mM. The transient phase of the HVA current could be described by two exponential functions with time constants tau fast and tau slow of 16.2 and 301 ms. Steady-state inactivation of the transient and extrapolated true sustained (pedestal) components of HVA current were described by Boltzmann equations, with half-inactivation potentials (slope factors) of -47.3 mV, (9.04) and -29.2 mV (11.8) respectively. 4. omega-Conotoxin (omega-CgTX; 100 nM) irreversibly inhibited a kinetically distinct component of HVA current but had no effect upon the transient LVA current. The omega-CgTX-sensitive current could not be distinguished from the control HVA current by the voltage dependence of its activation or inactivation rates. 5. Low concentrations of amiloride (< or = 300 microM) or Ni2+ (< or = 5 microM) selectively inhibited the transient LVA current, with IC50 values of 97 and 5 microM respectively. Cd2+ (< or = 1 microM) selectively blocked a component of HVA current. At higher concentrations, Cd2+ and Ni2+ were non-selective and totally blocked all components of ICa. 6. The lanthanide ions Gd3+ and La3+ produced saturable incomplete block of the HVA current. Maximally effective concentrations of Gd3+ (100 microM) or La3+ (30 microM) inhibited 76.5 and 41.2% respectively of the sustained component of HVA current with corresponding IC50 values of 2.2 and 1.1 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscarinic agonists block a late-afterhyperpolarization in medial septum/diagonal band neurons in vitro

Intracellular recordings were made from neurons located in the medial septum (MS), and nucleus of the diagonal band (nDB) from slices of guinea pig brain. These forebrain nuclei contain both cholinergic and noncholinergic neurons that project to the cortex and hippocampus and are involved in many cortical functions. Muscarinic agonists (bethanechol, 2-30 microM) had the specific action to reduce a long-duration afterhyperpolarization (long-AHP) while leaving other shorter duration AHPs intact. Since the long-AHP was observed in both cholinergic and non-cholinergic neurons, muscarinic agonists were not selective for any one cell type. Block of a long-AHP was not associated with a consistent increase in cell excitability and therefore can not fully explain the excitatory actions of acetylcholine (ACh) observed in vivo within the MS/nDB.

The naphthalenesulphonamide calmodulin antagonist W7 and its 5-iodo-1-C8 analogue inhibit potassium and calcium currents in NG108-15 neuroblastoma x glioma cells in a manner possibly unrelated to their antagonism of calmodulin

Patch clamp techniques were used to record voltage-sensitive calcium and potassium currents from NG108-15 cells. N-(6-aminohexyl)-5-chloro-1-naphthalene- sulphonamide (W7), a calmodulin (CaM) antagonist and its more potent (10 times) 5-iodo-1-C8 analogue (J8) inhibited these currents in a dose-dependent manner. The inhibition was not dependent on internal or external Ca2+. W7 was about four times more potent as an inhibitor of the transient potassium current (IC50 = 8 microM) than of the M-current or of the calcium current. J8 was also selective for the potassium currents (IC50 values: transient current 4 microM, M-current 11 microM) compared to the calcium current (IC50 36 microM). It is suggested that the inhibition does not result from an anti-CaM action of the compounds.

Electrophysiologic characteristics of basal forebrain neurons in vitro

Our data show that different cell types recorded in vitro can be identified by their intrinsic membrane properties. One type of neuron, namely S-AHP cells, have the ability to fire single action potentials in a rhythmic fashion following sufficient membrane depolarization. The rate is apparently controlled by several voltage-dependent conductances. S-AHP cells are normally quiescent at their resting potentials but will discharge once threshold is reached (-55 to -60 mV). Importantly, S-AHP (or F-AHP) cells will not convert into burst-firing neurons merely with changes in membrane potential. On the other hand, burst-firing cells have the ability to switch to a repetitive-firing pattern following membrane depolarization. All of these data provide a first step in an understanding of the firing rates of basal forebrain neurons, however, our results must be consolidated with existing in vivo studies for a more general understanding of basal forebrain function. Comparing our data to an in vivo preparation of the MS/nDB with synaptic afferents surgically removed may be one approach to correlating in vitro and in vivo studies. Vinogradova et al. (1980) used single unit recording techniques in unanesthetized chronic rabbits and compared the firing rates of cells before and after deafferentation. These authors reported a preservation of burst-firing neurons (25% of the cells) after deafferentation but with a significant reduction in the mean frequency of bursts. In addition a higher percentage of regularly firing cells also occurred following deafferentation (Vinogradova et al., 1980). It is interesting to speculate that these regularly firing cells may correspond to S-AHP cells in our in vitro studies, and some of the burst-firing units may correspond to the burst-firing cells we record in slices. Nevertheless, the in vivo data strongly suggests that endogenous regular spiking as well as rhythmic burst capabilities are present in some MS/nDB cells, however, the firing rates of most MS/nDB neurons are strongly influenced by synaptic afferents (see also Vinogradova et al., 1980; 1987). The endogenous activity in vivo can be explained, in part, by the intrinsic properties elucidated in our in vitro studies. How the synaptic afferents control MS/nDB circuitry and integrative output is premature to speculate without a more thorough understanding of the synaptic mechanisms involved. It is possible that future in vitro studies will help define these mechanisms and again contribute to an understanding of basal forebrain function.

Comparison of 4-aminopyridine and tetrahydroaminoacridine on basal forebrain neurons

This study was designed to investigate the ability of 4-aminopyridine (4-AP) and tetrahydroaminoacridine (THA) to reduce several potassium conductances in cells of the medial septum and nucleus of the diagonal band. Intracellular recording and single electrode voltage-clamp techniques were used in an in vitro brain slice preparation. Both 4-AP (100-300 microM) and THA (300 microM) reduced a transient outward current (A-current), whereas only 4-AP increased the release of spontaneous postsynaptic potentials and significantly prolonged action potential duration. High concentrations of THA (1 mM) were needed to significantly increase action potential duration but these levels of THA were still ineffective in eliciting spontaneous postsynaptic potentials. THA (300 microM), but not 4-AP, had the additional effect of reducing time-dependent membrane rectification (Q-current) in one cell type. Our results demonstrate that both cholinergic and non-cholinergic cells are sensitive to pharmacological concentrations of both compounds.

Neuronal properties and trophic activities of immortalized hippocampal cells from embryonic and young adult mice

The hippocampal formation elaborates trophic factors such as nerve growth factor (NGF) to support the cholinergic innervation it receives from the septal region. To further study the trophic interactions of this pathway, hippocampal cells from embryonic day 18 and postnatal day 21 mice were immortalized via somatic cell fusion to N18TG2 neuroblastoma cells. The hippocampal cell lines exhibit morphological and cytoskeletal features which are typical of their neuronal parents but which are not expressed by the neuroblastoma parent. When differentiated with retinoic acid, the hippocampal cell lines exhibit electrophysiological features similar to cultured hippocampal neurons. Many of the lines constitutively express high levels of NGF, and at least one cell line exerts a non-NGF trophic effect on the expression of choline acetyltransferase by septal neurons in vitro. These cell lines are potentially useful for investigating the neurochemical and excitable properties of hippocampal neurons and identifying novel trophic activities that promote the development and maintenance of the septohippocampal pathway.

A transient outward current in NG108-15 neuroblastoma x glioma hybrid cells

Outward currents were recorded from voltage-clamped NG108-15 mouse neuroblastoma X rat glioma hybrid cells, differentiated with prostaglandin E1. Depolarising voltage steps from -70 mV, evoked a transient outward current from a threshold of -30 mV. The outward current showed complete inactivation at potentials positive to -10 mV. Inactivation was removed by hyperpolarisation with half-inactivation at -53 mV. The time course of the inactivation could be best fitted by two exponentials with mean time constants of 280 ms and 1.6 s at +80 mV. Tail current measurements showed a shift in the reversal potential with changes in external K+ concentration, consistent with K+ as the current-carrying ion. The outward current amplitude was reversibly reduced by 4-aminopyridine, and the time course of inactivation modified. In the presence of other K+ channel blockers (tetraethylammonium, barium and tetrahydroaminoacridine) the amplitude of the outward current was also reversibly reduced, but with a negligible effect on its time course. The current was unaffected by dendrotoxin, d-tubocurarine, apamin, Cd2+ and Ni2+, and by replacing external Ca2+ with Co2+ or Mg2+. In current clamp, action potential duration was greatly increased by 4-aminopyridine. The findings show that the NG108-15 cell line displays a transient outward current that resembles IK(A) but with a higher than usual threshold and relatively slow inactivation, and that this current is likely to be important for action potential repolarisation.

Submicromolar concentrations of zinc irreversibly reduce a calcium-dependent potassium current in rat hippocampal neurons in vitro

The action of the endogenous divalent cation zinc on Ca2+ and Ca2(+)-dependent currents was studied in rat hippocampal CA1 and CA3 neurons in vitro, by means of a single electrode voltage clamp technique. Bath application of zinc (0.5-1 microM) produced a small membrane depolarization associated with an increase in synaptic noise and cell excitability and a depression of the afterhyperpolarization following a train of action potentials. The effects on the afterhyperpolarization, could not be reversed on washout. In voltage-clamped neurons, zinc induced a steady inward current and reduced, at resting membrane potential, the peak amplitude of the outward current underlying the afterhyperpolarization, IAHP. In caesium loaded neurons (in the presence of tetrodotoxin and tetraethylammonium), zinc reduced the slow inactivating Ca2+ current activated from a holding potential of -40 mV. Similar results were observed with nickel and cobalt at comparable concentrations, with Zn2+ greater than Ni2+ greater than Co2+, in their order of potency. In contrast to nickel and cobalt the effects of zinc did not reverse on washout. These results suggest that low concentrations of zinc enhance cell excitability by reducing IAHP. In addition, zinc reduces the slow inactivating voltage-dependent Ca2+ current. The irreversible effect of this metal ion is compatible with a toxic, intracellular site of action.

Calcium-dependent potassium conductance in guinea-pig olfactory cortex neurones in vitro

1. Guinea-pig olfactory cortex neurones in vitro (23-25 degrees C) were voltage clamped by means of a single-micro-electrode sample-and-hold technique. 2. Under current clamp at the resting potential (approximately -80 mV), brief depolarizing stimuli evoked trains of action potentials with little visible after-potential. However, in 90% of recorded cells held at membrane potentials between -70 and -45 mV, depolarizing current pulses evoked a slow after-hyperpolarization (a.h.p.) (approximately 8 mV) lasting several seconds and accompanied by an increase in input conductance. 3. The outward membrane current underlying the a.h.p. was revealed either by switching rapidly to voltage clamp at the end of a spike train ('hybrid' clamp) or by applying brief depolarizing commands from potentials between -60 to -45 mV. The tail current showed a distinct rising phase (time to peak approximately 1 s) and exponential decay (tau approximately 3 s) and was suppressed by removal of external Ca2+, or adding Co2+ (1-2 mM), Cd2+ (200 microM) or Mg2+ (6 mM). The a.h.p. current reversal potential was -96 mV in 3 mM-K+ medium. 4. Low concentrations (1-2 microM) of muscarine, carbachol, oxotremorine or the muscarinic ganglion stimulant, McN-A-343 (1-10 microM) reduced the a.h.p. current and leak conductance and induced a steady inward current, without affecting M-current (IM) relaxations. IM inhibition generally required higher (greater than 10 microM) agonist concentrations, although oxotremorine remained ineffective at up to 50 microM. 5. The a.h.p. current was reduced by noradrenaline and tetraethylammonium (TEA), but not by apamin or tubocurarine. Apart from TEA, these agents had no effect on IM. 6. Addition of tetrodotoxin (TTX, 1 microM) or removing external Na+ depressed the a.h.p. current amplitude recorded under voltage clamp. The residual tail current could be further reduced by adding Cd2+ or muscarinic agonists. 7. Repolarizing tail currents induced following positive voltage commands consisted mainly of IM and slow a.h.p. current with little evidence of a 'fast' Ca2+-activated K+ current (IC). 8. It is concluded that the slow a.h.p. current that underlies the post-burst after-hyperpolarization of olfactory neurones, is a Ca2+-dependent K+ current distinct from IM. It is suggested that the cholinergic modulation of this current (rather than IM) may provide a more subtle control of cell excitability in cortical neurones.

Muscarinic receptors mediating suppression of the M-current in guinea-pig olfactory cortex neurones may be of the M2-subtype

Guinea-pig olfactory cortical neurones in vitro were voltage clamped by means of a single intracellular microelectrode technique. Hyperpolarizing voltage commands from holding potentials between -40 to -50 mV produced slow inward current relaxations reflecting deactivation of the M-current (IM). IM was reversibly suppressed by 30 microM muscarine or carbachol; this suppression was insensitive to pirenzepine (up to 300 nM) but was inhibited by gallamine (10-20 microM) or 4-diphenyl-acetoxy-N-methylpiperidine (100, 500 nM), suggesting the involvement of the M2-type muscarinic receptor.

A comparison between mechanisms of action of different nicotinic blocking agents on rat submandibular ganglia

The blocking properties of tubocurarine, decamethonium, hexamethonium and trimetaphan on nicotinic agonists applied by repetitive ionophoretic pulses were examined in rat submandibular ganglion cells using a two-microelectrode voltage-clamp technique at 30 degrees C. Hexamethonium, a proposed slowly dissociating, open-channel blocker at concentrations of 2-20 microM did not produce a 'use-dependent' run-down of responses, but its antagonism was clearly dependent on membrane potential. The voltage-dependent reduction of agonist response by hexamethonium was not dependent on the nature of agonist used. Similar results were obtained with acetylcholine (ACh) and carbamylcholine (CCh) ionophoresis. (+)-Tubocurarine (5 microM) and decamethonium (10 microM) produced 'use-dependent' run-down of agonist responses which became more pronounced at higher frequency and as the cell was hyperpolarized, consistent with open-channel blockade. In contrast, trimetaphan (2.5 microM), a receptor antagonist did not cause 'use-dependent' run-down of responses. Hence, the antagonism produced by hexamethonium, unlike tubocurarine and decamethonium, could not be accounted for in terms of open-channel blockade but requires an alternative mechanism, the nature of which is discussed.

Calcium-dependent inward currents in voltage-clamped guinea-pig olfactory cortex neurones

Guinea-pig olfactory cortex neurones in vitro (23 degrees C--25 degrees C) were voltage clamped by means of a single microelectrode sample-and-hold technique. In most Cs+-loaded neurones (in the presence of tetrodotoxin), membrane depolarization beyond -60 mV elicited inward currents, which had rapid activation kinetics. The steady-state current-voltage relationship was N-shaped with a region of negative slope conductance between - 50 mV and - 20 mV. The rate of inactivation varied according to the holding potential and the command potential. The inward currents were maintained when external Ca2+ was replaced by Ba2+, and were blocked by Cd2+, suggesting that Ca2+ was the principal charge carrier. The results demonstrate the existence of calcium current in olfactory cortex neurones.

The effect of extracellular sodium ion concentration on the action of opiates to inhibit potassium-evoked release of [3H]noradrenaline from the mouse vas deferens

Opiates depress the potassium-induced efflux of [3H]noradrenaline from the mouse vas deferens in a concentration-dependent (the IC50 for normorphine was 1.5 microM), stereospecific and naloxone-reversible manner. As the concentration of sodium in the extracellular fluid was reduced, the inhibitory action of opiates was also reduced. This attenuation of opiate action is the converse of that predicted by the 'sodium-shift' observed in opiate binding studies in which lowering the sodium concentration potentiates opiate agonist binding. The relevance of sodium to the pharmacological actions of opiates is discussed.