- Neurosci Lett. 2007 Aug 10; [Epub ahead of print]
Cholinergic modulation of intrinsic fibre-evoked excitatory transmission contains a nicotinic component in immature but not adult rat piriform cortex, in vitro.
Department of Pharmacology, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, UK.
The piriform cortex (PC) is highly prone to epileptogenesis, particularly in immature animals, where decreased muscarinic modulation of PC intrinsic fibre excitatory neurotransmission is implicated as a likely cause. However, whether higher levels of acetylcholine (ACh) release occur in immature vs. adult PC remains unclear. We investigated this using in vitro extracellular electrophysiological recording techniques. Intrinsic fibre-evoked extracellular field potentials (EFPs) were recorded from layers II to III in PC brain slices prepared from immature (P14-18) and adult (P>40) rats. Adult and immature PC EFPs were suppressed by eserine (1muM) or neostigmine (1muM) application, with a greater suppression in immature ( approximately 40%) than adult ( approximately 30%) slices. Subsequent application of atropine (1muM) reversed EFP suppression, producing supranormal ( approximately 12%) recovery in adult slices, suggesting that suppression was solely muscarinic ACh receptor-mediated and that some 'basal' cholinergic 'tone' was present. Conversely, atropine only partially reversed anticholinesterase effects in immature slices, suggesting the presence of additional non-muscarinic modulation. Accordingly, nicotine (50muM) caused immature field suppression ( approximately 30%) that was further enhanced by neostigmine, whereas it had no effect on adult EFPs. Unlike atropine, nicotinic antagonists, mecamylamine and methyllycaconitine, induced immature supranormal field recovery ( approximately 20%) following anticholinesterase-induced suppression (with no effect on adult slices), confirming that basal cholinergic 'tone' was also present. We suggest that nicotinic inhibitory cholinergic modulation occurs in the immature rat PC intrinsic excitatory fibre system, possibly to complement the existing, weak muscarinic modulation, and could be another important developmentally regulated system governing immature PC susceptibility towards epileptogenesis.
Friday 31 August 2007
Latest publication
Plateau potentials and Ca
| Related Articles |
Computational model predicts a role for ERG current in repolarizing plateau potentials in dopamine neurons: implications for modulation of neuronal activity.
J Neurophysiol. 2007 Aug 15;
Authors: Canavier CC, Oprisan S, Callaway J, Ji H, Shepard PD
Blocking the small conductance (SK) calcium-activated potassium channel promotes burst firing in dopamine neurons both in vivo and in vitro. In vitro, the bursting is unusual in that spiking persists during the hyperpolarized trough and frequently terminates via depolarization block during the plateau. We focus on the underlying plateau potential oscillation generated in the presence of both apamin and TTX, so that action potentials are not considered. We find that although the plateau potentials are mediated by a voltage-gated Ca(2+) current, they do not depend on the accumulation of cytosolic Ca(2+) , then utilize a computational model to test the hypothesis that the slowly voltage-activated ether-a-go-go related gene (ERG) potassium current repolarizes the plateaus. The model, which includes a material balance on calcium, is able to reproduce the time course of both membrane potential and somatic calcium concentration, and can also mimic the induction of plateau potentials by the calcium chelator BAPTA. The principle of separation of time scales was used to gain insight into the mechanisms of oscillation and its modulation using nullclines in the phase space. The model predicts that the plateau will be elongated and ultimately result in a persistent depolarization as the ERG current is reduced. This study suggests that the ERG current may play a role in burst termination and the relief of depolarization block in vivo.
PMID: 17699694 [PubMed - as supplied by publisher]
Hypothalamus neuroendocrine
 | Related Articles |
Differences in spike train variability in rat vasopressin and oxytocin neurons and their relationship to synaptic activity.
J Physiol. 2007 May 15;581(Pt 1):221-40
Authors: Li C, Tripathi PK, Armstrong WE
The firing pattern of magnocellular neurosecretory neurons is intimately related to hormone release, but the relative contribution of synaptic versus intrinsic factors to the temporal dispersion of spikes is unknown. In the present study, we examined the firing patterns of vasopressin (VP) and oxytocin (OT) supraoptic neurons in coronal slices from virgin female rats, with and without blockade of inhibitory and excitatory synaptic currents. Inhibitory postsynaptic currents (IPSCs) were twice as prevalent as their excitatory counterparts (EPSCs), and both were more prevalent in OT compared with VP neurons. Oxytocin neurons fired more slowly and irregularly than VP neurons near threshold. Blockade of Cl- currents (including tonic and synaptic currents) with picrotoxin reduced interspike interval (ISI) variability of continuously firing OT and VP neurons without altering input resistance or firing rate. Blockade of EPSCs did not affect firing pattern. Phasic bursting neurons (putative VP neurons) were inconsistently affected by broad synaptic blockade, suggesting that intrinsic factors may dominate the ISI distribution during this mode in the slice. Specific blockade of synaptic IPSCs with gabazine also reduced ISI variability, but only in OT neurons. In all cases, the effect of inhibitory blockade on firing pattern was independent of any consistent change in input resistance or firing rate. Since the great majority of IPSCs are randomly distributed, miniature events (mIPSCs) in the coronal slice, these findings imply that even mIPSCs can impart irregularity to the firing pattern of OT neurons in particular, and could be important in regulating spike patterning in vivo. For example, the increased firing variability that precedes bursting in OT neurons during lactation could be related to significant changes in synaptic activity.
PMID: 17332000 [PubMed - indexed for MEDLINE]
Organotypic hypothalamic prep
 | Related Articles |
Organotypic slice culture of the hypothalamic paraventricular nucleus of rat.
J Vet Sci. 2007 Mar;8(1):15-20
Authors: Cho ES, Lee SY, Park JY, Hong SG, Ryu PD
Organotypic slice cultures have been developed as an alternative to acute brain slices because the neuronal viability and synaptic connectivity in these cultures can be preserved well for a prolonged period of time. This study evaluated a stationary organotypic slice culture developed for the hypothalamic paraventricular nucleus (PVN) of rat. The results showed that the slice cultures maintain the typical shape of the nucleus, the immunocytochemical signals for oxytocin, vasopressin, and corticotropin-releasing hormone, and the electrophysiological properties of PVN neurons for up to 3 weeks in vitro. The PVN neurons in the culture expressed the green fluorescent protein gene that had been delivered by the adenoviral vectors. The results indicate that the cultured slices preserve the properties of the PVN neurons, and can be used in longterm studies on these neurons in vitro.
PMID: 17322769 [PubMed - indexed for MEDLINE]
PC interneurones
 | Related Articles |
Inhibitory interneurons in the piriform cortex.
Clin Exp Pharmacol Physiol. 2007 Oct;34(10):1064-9
Authors: Suzuki N, Bekkers JM
1. The piriform cortex (PC) is the largest subdivision of the olfactory cortex and the first cortical destination of olfactory information. Despite the relatively simple anatomy of the PC and its obvious appeal as a model system for the study of cortical sensory processing, there are many outstanding questions about its basic cell physiology. In the present article, we review what is known about GABAergic inhibitory interneurons in the PC. 2. The GABA-containing neurons in the PC are morphologically diverse, ranging from small neurogliaform cells to large multipolar forms. Some of these classes are distributed across all three main layers of the PC, whereas others have a more restricted laminar expression. 3. Distinct and overlapping populations of GABAergic basket cells in Layers II and III of the PC express different combinations of calcium-binding proteins and neuropeptides. Few Layer I interneurons express any of the molecular markers so far examined. 4. The intrinsic firing properties of one or two types of putative PC interneurons have been measured and inhibitory post-synaptic responses have been recorded in PC pyramidal cells following extracellular stimulation. However, little is known about the physiology of the subtypes of interneurons identified. 5. In view of the likely importance of PC interneurons in olfactory learning, olfactory coding and epileptogenesis, further investigation of their properties is likely to be highly informative.
PMID: 17714095 [PubMed - in process]
PC Innervation
| | Related Articles |
Olfactory information converges in the amygdaloid cortex via the piriform and entorhinal cortices: observations in the guinea pig isolated whole-brain preparation.
Eur J Neurosci. 2007 Jun;25(12):3648-58
Authors: Kajiwara R, Tominaga T, Takashima I
The amygdaloid cortex (AC) has reciprocal connections with the entorhinal cortex (EC) and also receives projections from the olfactory bulb and the piriform cortex (PC). To assess the possibility that the AC and EC represent functionally coupled structures in the olfactory stream of information, we investigated the propagation pattern of neural activity in olfactory cortices--PC, AC and EC--using optical recordings with voltage-sensitive dyes in the guinea pig in vitro isolated whole-brain preparation. We observed two distinct pathways that convey neural activation evoked by olfactory nerve stimulation: a medial pathway from the PC to the AC, and a lateral pathway from the PC to the lateral EC along the rhinal sulcus. Besides being activated directly via the medial pathway, the AC was activated a second time via activity that propagated from the lateral EC. Lesion experiments revealed that the lateral pathway close to the rhinal sulcus is crucial for neural activation of the EC. Consistent with this activation pattern, we observed two separate, sharp downward deflections in field potential recordings, and we recorded synaptic potentials with multiple peaks from single neurons in the AC. Our findings suggest that the AC and EC are functionally coupled during olfactory information processing, and that this functional linkage may allow the AC to integrate olfactory sensation with information retained or processed in the EC.
PMID: 17610584 [PubMed - in process]
Synaptic modification in PC
| Related Articles |
Long-Term Modifications in the Strength of Excitatory Associative Inputs in the Piriform Cortex.
Chem Senses. 2007 Jul 18;
Authors: Young A, Sun QQ
Afferent olfactory information, in vivo and in vitro, can be rapidly adapted to through a metabotropic glutamate receptor (mGluR)-mediated attenuation of synaptic strength. Specific cellular and synaptic mechanisms underlying olfactory learning and habituation at the cortical level remain unclear. Through whole-cell recording, excitatory postsynaptic currents (EPSCs) were obtained from piriform cortex (PC) principal cells. Using a coincidental, pre- and postsynaptic stimulation protocol, long-term depression (LTD) in synaptic strength was induced at associative, excitatory synapses onto layer II pyramidal neurons of the mouse (P15-27) PC. LTD was mimicked and occluded by mGluR agonists and blocked by nonselective mGluR antagonist (RS)-alpha-methyl-4-sulfonophenylglycine (MSPG) but not by N-methyl-D-aspartic acid (NMDA) receptor antagonist 2-amino-5-phosphonovaleric acid (APV). Analysis of the paired-pulse ratio, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/NMDA current ratio, and spontaneous EPSCs indicate that electrically induced LTD was mediated predominantly by postsynaptic mechanisms. Additionally, presynaptic mGluRs were involved in agonist-mediated synaptic depression. Immunohistochemical analysis supports the presence of multiple subclasses of mGluRs throughout the PC, with large concentrations of several receptors present in layer II. These observations provide further evidence of activity-dependent, long-term modification of associative inputs and its underlying mechanisms. Cortical adaptation at associative synapses provides an additional link between cortical olfactory processing and subcortical centers that influence behavior.
PMID: 17634388 [PubMed - as supplied by publisher]
Cav2.3
| Related Articles |
The role of distal S6 hydrophobic residues in the voltage-dependent gating of Cav2.3 channels.
J Biol Chem. 2007 Jul 27;
Authors: Raybaud A, Baspinar EE, Dionne F, Dodier Y, Sauvé R, Parent L
The hydrophobic locus VAVIM is conserved in the S6 transmembrane segment of domain IV (IVS6) in Cav1 and Cav2 families. Herein we show that glycine substitution of the VAVIM motif in Cav2.3 produced whole-cell currents with inactivation kinetics that were either slower (A1719G = V1720G), similar (V1718G), or faster (I1721G = M1722G) than the wild-type channel. The fast kinetics of I1721G were observed with a = +10 mV shift in its voltage-dependence of activation (E(0.5,act)). In contrast, the slow kinetics of A1719G and V1720G were accompanied by a significant shift of = -20 mV in their E(0.5,act)indicating that the relative stability of the channel closed state was decreased in these mutants. Glycine scan performed in IS6 (V349), IIS6 (I701), and IIIS6 (L1420) at positions predicted to face V1720 (IVS6) also produced slow inactivating currents with hyperpolarizing shifts in the activation and inactivation potentials, again pointing out to a decrease in the stability of the channel closed state. Mutations to other hydrophobic residues at these positions nearly restored the channel gating. Altogether these data indicate that residues at positions equivalent to 1720 exert a critical control upon the relative stability of the channel closed and open states and more specifically, that hydrophobic residues at these positions promote the channel closed state. We discuss a 3-D homology model of Cav2.3 based upon Kv1.2 where hydrophobic residues at positions facing V1720 (IVS6) in IS6, IIS6, and IIIS6 play a critical role in stabilizing the closed state in Cav2.3.
PMID: 17660294 [PubMed - as supplied by publisher]
Worth thinking about how much is required to achieve functional complexity.
The man had a normal job and is a married father of two children.
Lionel Feuillet, Henry Dufour and Jean Pelletier. Brain of a white-collar worker. The Lancet, Volume 370, Issue 9583, 21 July 2007-27 July 2007, Page 262.
Tumours & cannabinoids
 | Related Articles |
The tumour suppressor protein, p53, is involved in the activation of the apoptotic cascade by Delta9-tetrahydrocannabinol in cultured cortical neurons.
Eur J Pharmacol. 2007 Jun 14;564(1-3):57-65
Authors: Downer EJ, Gowran A, Murphy AC, Campbell VA
Cannabis is the most commonly used illegal drug of abuse in Western society. Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of marijuana, regulates a variety of neuronal processes including neurotransmitter release and synaptic transmission. An increasing body of evidence suggests that cannabinoids play a key role in the regulation of neuronal viability. In cortical neurons tetrahydrocannabinol has a neurodegenerative effect, the mechanisms of which are poorly understood, but involve the cannabinoid receptor subtype, CB(1). In this study we report that tetrahydrocannabinol (5 muM) evokes a rapid phosphorylation, and thus activation, of the tumour suppressor protein, p53, in a manner involving the cannabinoid CB(1) receptor, and the stress-activated protein kinase, c-jun N-terminal kinase, in cultured cortical neurons. Tetrahydrocannabinol increased expression of the p53-transcriptional target, Bax and promoted Bcl phosphorylation. These events were abolished by the p53 inhibitor, pifithrin-alpha (100 nM). The tetrahydrocannabinol-induced activation of the pro-apoptotic cysteine protease, caspase-3, and DNA fragmentation was also blocked by pifithrin-alpha. A siRNA knockdown of p53 further verified the role of p53 in tetrahydrocannabinol-induced apoptosis. This study demonstrates a novel cannabinoid signalling pathway involving p53 that culminates in neuronal apoptosis.
PMID: 17379209 [PubMed - indexed for MEDLINE]
CB1 antags: pros and cons
| | Related Articles |
Antagonism of type-1 cannabinoid receptors: good for obesity, but is it safe for fertility?
Clin Endocrinol (Oxf). 2007 Mar;66(3):456-7
Authors: Maccarrone M, Wang H, Dey SK
PMID: 17302885 [PubMed - indexed for MEDLINE]
Cannabinoids and pain
| | Related Articles |
AM404 decreases Fos-immunoreactivity in the spinal cord in a model of inflammatory pain.
Brain Res. 2007 Jun 4;1152:87-94
Authors: Borsani E, Labanca M, Bianchi R, Rodella LF
Cannabinoids, such as anandamide, are involved in pain transmission. We evaluated the effects of AM404 (N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide), an anandamide reuptake inhibitor, monitoring the expression of c-fos, a marker of activated neurons and the pain-related behaviours using formalin test. The study was carried out in an experimental model of inflammatory pain made by a single injection of formalin in rat hind paws. Formalin test showed that the antinociceptive effect of AM404 was evident in phase I. We found that Fos-positive neurons in dorsal superficial and deep laminae of the lumbar spinal cord increased in formalin-injected animals and that AM404 significantly reduced Fos induction. Co-administration of cannabinoid CB(1) receptor antagonist (AM251), cannabinoid CB(2) receptor antagonist (AM630) and transient receptor potential vanilloid type 1 (TRPV-1) antagonist (capsazepine), attenuate the inhibitory effect of AM404 and this effect was higher using cannabinoid CB(2) and vanilloid TRPV-1 receptor antagonists. These results suggest that AM404 could be a useful drug to reduce inflammatory pain in our experimental model and that cannabinoid CB(2) receptor and vanilloid TRPV-1 receptor, and to a lesser extent, the cannabinoid CB(1) receptor are involved.
PMID: 17459353 [PubMed - indexed for MEDLINE]
Cannabinoid therapeutics
 | Related Articles |
Blocking the cannabinoid receptors: drug candidates and therapeutic promises.
Chem Biodivers. 2007 Aug;4(8):1805-27
Authors: Muccioli GG
The CB1 and CB2 cannabinoid receptors have been described as two prime sites of action for endocannabinoids. Both the localization and pharmacology of these two G-protein-coupled receptors are well-described, and numerous selective ligands have been characterized. The physiological effects of Cannabis sativa (cannabis) and a throughout study of the endocannabinoid system allowed for the identification of several pathophysiological conditions--including obesity, dyslipidemia, addictions, inflammation, and allergies--in which blocking the cannabinoid receptors might be beneficial. Many CB1 receptor antagonists are now in clinical trials, and the results of several studies involving the CB1 antagonist lead compound rimonabant (SR141716A) are now available. This review describes the pharmacological tools that are currently available and the animal studies supporting the therapeutic use of cannabinoid receptor antagonists and inverse agonists. The data available from the clinical trials are also discussed.
PMID: 17712820 [PubMed - in process]
Endocannabinoids and feeding
| | Related Articles |
Regulation of hypothalamic endocannabinoid levels by neuropeptides and hormones involved in food intake and metabolism: Insulin and melanocortins.
Neuropharmacology. 2007 Jun 29;
Authors: Matias I, Vergoni AV, Petrosino S, Ottani A, Pocai A, Bertolini A, Di Marzo V
Endocannabinoids are paracrine/autocrine lipid mediators with several biological functions. One of these, i.e. the capability to stimulate food intake via cannabinoid CB(1) receptors, has been particularly studied, thus leading to the development of the first CB(1) receptor blocker, rimonabant, as a therapeutic tool against obesity and related metabolic disorders. Hypothalamic endocannabinoids stimulate appetite by regulating the expression and release of anorexic and orexigenic neuropeptides via CB(1) receptors. In turn, the tone of the latter receptors is regulated by hormones, including leptin, glucocorticoids and possibly ghrelin and neuropeptide Y, by modulating the biosynthesis of the endocannabinoids in various areas of the hypothalamus. CB(1) receptor stimulation is also known to increase blood glucose during an oral glucose tolerance test in rats. Here we investigated in the rat if insulin, which is known to exert fundamental actions at the level of the mediobasal hypothalamus (MBH), and the melanocortin system, namely alpha-melanocyte stimulating hormone (alpha-MSH) and melanocortin receptor-4 (MCR-4), also regulate hypothalamic endocannabinoid levels, measured by isotope-dilution liquid chromatography coupled to mass spectrometry. No effect on anandamide and 2-arachidonoylglycerol levels was observed after 2h infusion of insulin in the MBH, i.e. under conditions in which the hormone reduces blood glucose, nor with intra-cerebroventricular injection of alpha-MSH, under conditions in which the neuropeptide reduces food intake. Conversely, blockade of MCR-4 receptors with HS014 produced a late (6h after systemic administration) stimulatory effect on endocannabinoid levels as opposed to a rapid and prolonged stimulation of food-intake (observable 2 and 6h after administration). These data suggest that inhibition of endocannabinoid levels does not mediate the effect of insulin on hepatic glucose production nor the food intake-inhibitory effect of alpha-MSH, although stimulation of endocannabinoid levels might underlie part of the late stimulatory effects of MCR-4 blockade on food intake.
PMID: 17675101 [PubMed - as supplied by publisher]
CB1s and desensitisation
| | Related Articles |
Rapid CB(1) cannabinoid receptor desensitization defines the time course of ERK1/2 MAP kinase signaling.
Neuropharmacology. 2007 Jun 26;
Authors: Daigle TL, Kearn CS, Mackie K
Molecular mechanisms regulating the development of physiological and behavioral tolerance to cannabinoids are not well understood. Two cellular correlates implicated in the development and maintenance of tolerance are CB(1) cannabinoid receptor internalization and uncoupling of receptor signal transduction. Both processes have been proposed as mediators of tolerance because of observations that chronic Delta(9)-tetrahydrocannabinol (THC) treatment causes both region-specific decreases in CB(1) receptors and G-protein coupling in the brain. To determine the balance of these two processes in regulating CB(1) receptor signaling during sustained receptor stimulation, we evaluated the parameters affecting ERK1/2 MAP kinase activity in HEK293 cells stably expressing CB(1) receptors. CB(1) receptor stimulation by the potent CB(1) receptor agonist, CP 55,940 transiently activated ERK1/2. To determine if CB(1) receptor desensitization or internalization was responsible for the transient nature of ERK1/2 activation, we evaluated ERK1/2 phosphorylation in HEK293 cells expressing a desensitization-deficient CB(1) receptor (S426A/S430A CB(1)). Here, the duration of S426A/S430A CB(1) receptor-mediated activation of ERK1/2 was markedly prolonged relative to wild-type receptors, and was dynamically reversed by SR141716A. Interestingly, the S426A/S430A CB(1) receptor was still able to recruit betaarrestin-2, a key mediator of receptor desensitization, to the cell surface following agonist activation. In contrast to a central role for desensitization, pharmacological and genetic approaches suggested CB(1) receptor internalization is dispensable in the transient activation of ERK1/2. This study indicates that the duration of ERK1/2 activation by CB(1) receptors is regulated by receptor desensitization and underscores the importance of G-protein uncoupling in the regulation of CB(1) receptor signaling.
PMID: 17681354 [PubMed - as supplied by publisher]
Raph's Book
 | Related Articles |
Cannabinoids as Therapeutics. Edited by Raphael Mechoulam. Birkhäuser Verlag, Basel, Switzerland. 2007. x + 272 pp. 16.5 x 24 cm. ISBN 3-7643-7055-6. 136.96 euros.
J Med Chem. 2007 Aug 8;
Authors: Makriyannis A
PMID: 17685506 [PubMed - as supplied by publisher]