Muscarinic Cholinergic Receptors Research Articles

Prejunctional facilitatory effect of a thiol-alkylating agent N -Ethylmaleimide on neurogenic contractions in rat prostate smooth muscle

The effect of a non-specific thiol-alkylating agent N-ethylmaleimide (NEM) was studied on neurogenic contractile mechanisms in rat ventral prostate gland. Male Wistar albino rats were used. The rats were killed by cervical dislocation under sevoflurane anesthesia and ventral prostate gland was removed. Two preparations were obtained from each lobe. Neurally evoked isometric contractions were induced using trains of electrical field stimulation (EFS; 0.5, 1, 4, or 8 Hz). The effect of NEM on the contractions to EFS was examined in the absence or presence of adrenergic and/or purinergic antagonists. NEM enhanced the EFS-evoked contractions without altering the basal tone. These effects were significantly suppressed by an α(1) -adrenergic receptor antagonist (prazosin), a P2-purinergic antagonist (suramin), a specific P2X-receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS), an ATP analog (α,β-methylene ATP), or a calcium channel blocker (verapamil). This facilitating effect of NEM did not occur following the administration of L-cysteine or glutathione which saturated NEM with excess thiols. However, a thiol-oxidant diamide failed to affect the contractions to EFS. An adrenergic neuron blocker (guanethidine) completely suppressed the responses to NEM. On the other hand, an α(2) -adrenergic receptor blocker (yohimbine), a nitric oxide synthase inhibitor (N(ω) -nitro-L-arginine) or a cholinergic muscarinic receptor antagonist (atropine) did not significantly affect the facilitatory response of NEM. These findings suggest that NEM has a prejunctional facilitatory action on the adrenergic nerves in rat prostate tissue to enhance release of transmitters, noradrenaline, and ATP. NEM sensitive proteins involved in transmitter release mechanisms can play a role in this effect.

Muscarinic cholinergic receptors and odor discrimination and learning in mice.

Event Abstract Back to Event Muscarinic cholinergic receptors and odor discrimination and learning in mice. Ricardo C. Araneda1*, Robert K. Maurer1 and Wilson Chan1 1 University of Maryland, Biology, United States The olfactory system enables the proper execution of behaviors that are critical for survival of mammals and the olfactory bulb (OB) is the site where initial odor information processing occurs. Reciprocal and lateral inhibition mediated by dendrodendritic synapses between mitral (MCs) and granule cells (GCs) is an important mechanism in OB processing and modulation of these synapses by the cholinergic system is important for odor discrimination and olfactory learning. Acetylcholine modulates several brain functions including learning and attention through the activation of two different receptor subtypes, nicotinic and muscarinic receptors (mAChR). Previous studies from our lab have shown that activation of the M1-mAChR subtype increases the excitability of GCs, which enhances the inhibitory input onto MCs, suggesting an important role for M1-mAChRs in olfactory behavior (Smith and Araneda, 2009). Here, we examine the behavioral consequences of disrupting cholinergic function in mice lacking specific mAChRs subtypes. To evaluate olfactory function we utilized two testing paradigms, the habituation-dishabituation (H-D) and the hidden-cookie tests, which rely on short and long-term memory, respectively. Using the H-D test we find that unlike the wild-type, mice lacking the M1 mAChR subtype fail to discriminate odor molecules differing by one single carbon. Moreover, wild-type and M1 k.o. mice cannot discriminate between pairs of enantiomers of carvone. However, the M1 k.o. mice can learn to discriminate these odors when they are associated with a reward in the hidden-cookie test albeit with a slower learning curve than wild type. Visual discrimination, response to aversive odors and response to complex social odors was not affected in the M1 k.o. mice, indicating that disruption of these receptors does not impair general sensory function. These results further support the involvement of M1 mAchRs in olfactory discrimination, a sensory property emerging from the concerted activity of neuronal circuitry in the OB. Our results suggest that activation of these receptors is necessary for the short term odor memory. Acknowledgements NIDCD Grant DC RO1-DC-009817 to R.C. Araneda and HHMI Undergraduate Research Fellowship to R. K. Maurer References Smith, R.S. and Araneda, RC (2010). "Cholinergic modulation of neuronal excitability in the accessory olfactory bulb." J. Neurophys. 104(6): 2963-74. Keywords: Acetylcholine, dendrodendritc synapses, granule cell, Neuromodulation, Olfactory Bulb Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for Participant Symposium) Topic: Sensory: Olfaction and Taste Citation: Araneda RC, Maurer RK and Chan W (2012). Muscarinic cholinergic receptors and odor discrimination and learning in mice.. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00369 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 01 May 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Ricardo C Araneda, University of Maryland, Biology, College Park, MD, 20742, United States, raraneda@umd.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Ricardo C Araneda Robert K Maurer Wilson Chan Google Ricardo C Araneda Robert K Maurer Wilson Chan Google Scholar Ricardo C Araneda Robert K Maurer Wilson Chan PubMed Ricardo C Araneda Robert K Maurer Wilson Chan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Role of Various Subtypes of Muscarinic Cholinergic Receptors in the Development of Posthemorrhagic Abnormalities in Systemic and Portal Circulation in Rats

The experiments employing high-frequency ultrasonic technique and selective blockers of M1, M3, and M4 muscarinic cholinergic receptors pirenzepine, 4-DAMP, and tropicamide, respectively, revealed individual roles of these receptors in the development of severe posthemorrhagic hypotension in rats with low or high individual resistance to circulatory hypoxia. The study showed that M1 and M4 muscarinic receptors are involved in shock-limiting and shock-activating processes, respectively, while M3 receptors exert no effect on the course of posthemorrhagic abnormalities in systemic and hepatic portal circulation and on the posthemorrhagic lifespan. Poor resistance of the cardiovascular system to circulatory hypoxia during shock development is considered to be dysregulatory pathology.

Application of Neurochemical Markers for Assessing Health Effects after Developmental Methylmercury and PCB Coexposure

Cholinergic muscarinic receptors (MRs) and monoamine oxidase activity (MAO-B), expressed both in brain and blood cells, were investigated in animals and exposed subjects to assess (i) MeHg (0.5–1 mg/kg/day GD7-PD7) and/or PCB153 (20 mg/kg/day GD10–GD16) effects on cerebellar MAO-B and MRs, and lymphocyte MRs, in dams and offspring 21 days postpartum; (ii) MAO-B in platelets and MRs in lymphocytes of a Faroese 7-year-old children cohort, prenatally exposed to MeHg/PCBs. Animal Data. MAO-B was altered in male cerebellum by MeHg, PCB153, and their combination (35%, 45%, and 25% decrease, resp.). Cerebellar MRs were enhanced by MeHg alone in dams (87%) and male pups (27%). PCB153 alone and in mixture did not modify cerebellar MRs. Similarly to brain, lymphocyte MRs were enhanced in both dams and offspring by MeHg alone. All changes were caused by 1 MeHg mg/kg/day, the lower dose was ineffective. Human Data. Both biomarkers showed homogeneous distributions within the cohort (MRs, range 0.1–36.78 fmol/million cells; MAO-B, 0.95–14.95 nmol/mg protein/h). No correlation was found between the two biomarkers and neurotoxicant concentrations in blood (pre- and postnatally).

Cholinergic Fibers and Muscarinic Receptors in the Central Auditory System

アルツハイマー病では中枢聴覚系の機能障害を示唆する症状を合併する場合が少なくない．また細胞変性等の病変が疾病脳の聴覚上行路各部位にも確認されている．本研究ではマウス脳のこれらの部位におけるコリン線維とムスカリン性受容体（m2，m3タイプ）の発現分布密度を測定した．聴覚上行路諸核で，これらコリン線維・受容体を介する情報伝達・変換が聴覚の伝達に一定の意義を有することが，本研究から強く示唆された．

Regulation of Fear Memory by Glucocorticoid and Cholinergic Receptors within the Dorsal Striatum

GENERAL COMMENTARY article Front. Behav. Neurosci., 19 July 2012Sec. Learning and Memory Volume 6 - 2012 | https://doi.org/10.3389/fnbeh.2012.00042

Effects of Autonomic Agents on Ca2+ Cycling in Canine Atrial Myocytes during Rapid Pacing

Atrial fibrillation (AF), or conditions conducive to it, often occur(s) in conjunction with high and/or unbalanced sympathetic/parasympathetic (autonomic) activity, which has profound effects on myocyte Ca2+ cycling. Using confocal microscopy, we have begun scrutinizing the effects various autonomic agents–including but not limited to isoproterenol (ISO; ∗-adrenergic receptor (AR) agonist), phenylephrine (PE; ∗-AR agonist) norepinephrine (NE, ∗- and ∗-AR agonist), and carbachol (CCh; muscarinic cholinergic receptor agonist)–have on Ca2+ cycling in isolated canine atrial myocytes paced at cycle lengths (CLs) ranging from 5000-200ms. In general, Ca-transient amplitudes were increased by ISO and NE; decreased by CCh; and varying decreased, increased or unaffected by PE–although PE only increased Ca-transients after PTX-treatment. However, considerable cell-to-cell variability in magnitude/dose-response for such effects was notable. The effects these agents had on irregular Ca-release events (ICREs)–i.e., Ca-alternans triggered-Ca-waves occurring during pacing (t-CaWs), and spontaneous-Ca-waves occurring during a pause after pacing (s-CaWs)–consequent to rapid pacing (CLs≤300ms) were interestingly distinct. CCh significantly reduced the appearance of all ICREs, yet were often accentuated upon CCh withdrawal. ISO often induced s-CaWs, but suppressed t-CaWs–with Ca-alternans often appearing in their stead. NE mimicked ISO regarding ICREs in some cells, but in others did not suppress and sometimes accentuated t-CaWs. PE accentuating t-CaWs and/or subcellular Ca-alternans in some cells, while suppressing or having no apparent effect on them in others. However, after PTX-treatment, PE mimicked ISO regarding ICREs without s-CaWs induction. These findings not only underscore the complexity of atrial autonomic modulation and its differences with that in ventricle, but also particulars evident only during rapid pacing–i.e., that during or conducive to the onset of AF.

Modulation of inflammatory pathways by the immune cholinergic system

Research done in the past years pointed to a novel function of cholinergic transmission. It has been shown that cholinergic transmission can modulate various aspects of the immune function, whether innate or adaptive. Cholinergic transmission affects immune cell proliferation, cytokine production, T helper differentiation and antigen presentation. Theses effects are mediated by cholinergic muscarinic and nicotinic receptors and other cholinergic components present in immune cells, such as acetylcholinesterase (AChE) and cholineacetyltransferase. The α7 nicotinic acetylcholine receptor was designated anti-inflammatory activity and has shown promise in pre-clinical models of inflammatory disorders. We herein describe the various components of the immune cholinergic system, and specifically the immune suppressive effects of α7 activation. This activation can be accomplished either by direct stimulation or indirectly, by inhibition of AChE. Thus, the presence of the immune cholinergic system can pave the way for novel immunomodulatory agents, or to the broadening of use of known cholinergic agents.

Reversal of scopolamine-induced disruption of prepulse inhibition by clozapine in mice

Prepulse inhibition (PPI) of the acoustic startle reflex refers to the reduction of the startle response to an intense acoustic pulse stimulus when it is shortly preceded by a weak non-startling prepulse stimulus and provides a cross-species measure of sensory-motor gating. PPI is typically impaired in schizophrenia patients, and a similar impairment can be induced in rats by systemic scopolamine, a muscarinic cholinergic receptor antagonist that can evoke a range of cognitive and psychotic symptoms in healthy humans that are commonly referred to as the “anti-muscarinic syndrome” resembling some clinical features of schizophrenia. Scopolamine-induced PPI disruption has therefore been proposed as an anti-muscarinic animal model of schizophrenia, but parallel investigations in the mouse remain scant and the outcomes are mixed and often confounded by an elevation of startle reactivity. Here, we distinguished the PPI-disruptive and the confounding startle-enhancing effects of scopolamine (1 and 10mg/kg, i.p.) in C57BL/6 wild-type mice by showing that the latter partly stemmed from a shift in spontaneous baseline reactivity. With appropriate correction for between-group differences in startle reactivity, we went on to confirm that the PPI-disruptive effect of scopolamine could be nullified by clozapine pre-treatment (1.5mg/kg, i.p.) in a dose-dependent manner. This is the first demonstration that scopolamine-induced PPI disruption is sensitive to atypical antipsychotic drugs. In concert with previous data showing its sensitivity to haloperidol the present finding supports the predictive validity of the anti-muscarinic PPI disruption model for both typical and atypical antipsychotic drug action.

Participation of hippocampal cholinergic system in memory persistence for inhibitory avoidance in rats

Memory persistence needs a new event of consolidation 12h after the acquisition. We investigated the role of the cholinergic activity on the persistence of memory. For this purpose, we performed the treatments 9 or 12h after acquisition and the memory tested 2 or 7days after inhibitory avoidance (IA) training. Here we report that activity of medial septum, by transitorily inactivating this structure with lidocaine 12h after IA training, is essential for memory persistence at the 7th day, but not for the formation at the 2nd day. We also report that muscarinic and nicotinic cholinergic receptors of CA1 area are engaged on memory persistence. Since scopolamine (mAChRs antagonist) and mecamylamine (nAChRs blocker) infusions, 12h post-training, demonstrated impairment on long term memory (LTM), persistence on the 7th day but no effect on LTM formation was found on the 2nd day in the IA test. The same effects were found with pirenzepine, an M1 antagonist. No effects on the formation and persistence of memory on the 2nd and 7th days were demonstrated after DHβE infusions (nAChRs subtype antagonist α4β2, α3β2). These findings suggest that mAChR and nAChR at the CA1 area, and also MS activation, are required for the persistence of memory.

Advances in understanding fragile X syndrome and related disorders

Fragile X syndrome is the most common form of inherited intellectual disability. Over the past 2 decades, insights into the cause of this disease have increased tremendously. This review will highlight recent discoveries with an emphasis on biochemical pathways affected in the disorder that are potentially amenable to treatment. Recent work in the field demonstrated that multiple pathways are deregulated as a consequence of the FMR1 gene inactivation in patients with fragile X syndrome. In fragile X patients, no fragile X mental retardation protein is formed and thereby protein translation is compromised. As a consequence, a variety of biological pathways are disturbed. These pathways include mainly the metabotropic glutamate receptor and gamma-aminobutyric acid (GABA)ergic pathways, but recently potassium channels and the muscarinic cholinergic receptor have also been implied in fragile X syndrome. An overview is given of the potential therapeutic targets and clinical studies that have been performed. The gene defect underlying fragile X syndrome was discovered back in 1991. Since then, there has been enormous progress in our understanding of the molecular basis of the disease. Excitingly, our insights have now reached a next phase in which therapy specifically targeting the underlying molecular defect becomes feasible.

Inhibition of granulocyte migration by tiotropium bromide.

Study objectivesNeutrophil influx into the airways is an important mechanism in the pathophysiology of the inflammatory process in the airways of patients with chronic obstructive pulmonary disease (COPD). Previously it was shown that anticholinergic drugs reduce the release of non-neuronal paracrine mediators, which modulate inflammation in the airways. On this basis, we investigated the ability of the long-acting anticholinergic tiotropium bromide to inhibit a) alveolar macrophage (AM)-mediated chemotaxis of neutrophils, and b) cellular release of reactive oxygen species (ROS).MethodAM and neutrophils were collected from 71 COPD patients. Nanomolar concentrations of tiotropium bromide were tested in AM cultured up to 20 h with LPS (1 μg/ml). AM supernatant was tested for TNFα, IL8, IL6, LTB4, GM-CSF, MIPα/β and ROS. It was further used in a 96-well chemotaxis chamber to stimulate the migration of fluorescence labelled neutrophils. Control stimulants consisted of acetylcholine (ACh), carbachol, muscarine or oxotremorine and in part PMA (phorbol myristate acetate, 0.1 μg/ml). Potential contribution of M1-3-receptors was ascertained by a) analysis of mRNA transcription by RT-PCR, and b) co-incubation with selective M-receptor inhibitors.ResultsSupernatant from AM stimulated with LPS induced neutrophilic migration which could be reduced by tiotropium in a dose dependent manner: 22.1 ± 10.2 (3 nM), 26.5 ± 18,4 (30 nM), and 37.8 ± 24.0 (300 nM, p < 0.001 compared to non-LPS activated AM). Concomitantly TNFα release of stimulated AM dropped by 19.2 ± 7.2% of control (p = 0.001). Tiotropium bromide did not affect cellular IL8, IL6, LTB4, GM-CSF and MIPα/β release in this setting. Tiotropium (30 nM) reduced ROS release of LPS stimulated AM by 36.1 ± 15.2% (p = 0.002) and in carbachol stimulated AM by 46.2 ± 30.2 (p < 0.001). M3R gene expression dominated over M2R and M1R. Chemotaxis inhibitory effect of tiotropium bromide was mainly driven by M3R inhibition.ConclusionOur data confirm that inhibiting muscarinic cholinergic receptors with tiotropium bromide reduces TNFα mediated chemotactic properties and ROS release of human AM, and thus may contribute to lessen cellular inflammation.

Extracts from hardwood trees used in commercial paper mills contain biologically active neurochemical disruptors

Following on our discovery that pulp and paper mill effluents can interact with, and disrupt, various neurotransmitter receptors and enzymes important to fish reproduction, we tested wood and bark extracts of 14 Eastern North American hardwood trees used in pulp and paper production. Radioligand binding to neurotransmitter receptors, including the dopamine-2 receptor (D2), the gamma aminobutyric acid receptor A (GABA(A)), N-methyl-d-aspartic acid (NMDA) receptor, and muscarinic cholinergic receptor (mACh-R), were significantly changed following in vitro incubations with many but not all extracts. Activities of neurotransmitter-related enzymes monoamine oxidase (MAO), GABA-transaminase (GABA-T), acetylcholinesterase (AChE) and glutamic acid decarboxylase (GAD) were also significantly altered. Butternut wood extracts and the isolated compound juglone significantly inhibited the enzymatic activities of MAO and GAD which we suggest may be part of a mechanism that may negatively affect fish reproduction. Besides giving credence to the hypothesis that neuroactive compounds in pulp and paper effluent may originate in the trees used by mills, the results reported here also indicate important neuropharmacological activities in hardwoods which may help identify new sources of biologically active natural products.

Involvement of cholinergic-muscarinic receptor in &lt;i&gt;Anaphe venata&lt;/i&gt;-induced stretching-ataxia behavioral effects in rats

Anaphe venata entomophagy has previously been implicated in the aetiopathogenesis of seasonal ataxia in humans and altered motor function in rodents. Thus, we investigated the effect of A. venata PhosphateBuffer Saline (PBS) extract on stretching, ataxia and the possible mechanism(s) of action. Animals were divided into four groups (n = 6-12 per group) and graded doses of extract (100, 200 or 400 mg/kg) wereadministered intraperitoneally (i.p.) while the control group received saline. Behavioral scores were recorded for a period of 30 min immediately after the administration of saline or extract. The role of various receptors inthe extract induced stretching and ataxia was evaluated using known receptor antagonists in other groups of rats. The in-vitro cholinesterase inhibition assay of the extract was also performed. The protein profile of theextract was evaluated using the Sodium Dodecyl Sulphate&nbsp; (SDS)-Polyacrylamide gel electrophoresis. Results showed that the extract induced significant (p&lt;0.01) stretching and ataxia behavioural effects dose-dependently when compared to vehicle-treated rats. Pretreatment with the non-selective muscarinic antagonist, scopolamine, significantly (p&lt;0.05) reversed both stretching and ataxia-induced behaviour of PBS extract at alldose levels however both flumazenil and naloxone did not show any significant effects. Anticholinesterase assay also provided evidence that the extract has inhibitory effect on acetylcholinesterase enzyme. Electrophoresis assay suggested that the major proteins in the extract are probably of small molecular weight. In conclusion, the A. venata PBS extract induced-behaviours are probably mediated via the activation of cholinergic-muscarinic receptor systems.

Plasticity of Prefrontal Attention Circuitry: Upregulated Muscarinic Excitability in Response to Decreased Nicotinic Signaling Following Deletion of α5 or β2 Subunits

Attention depends on cholinergic stimulation of nicotinic and muscarinic acetylcholine receptors in the medial prefrontal cortex. Pyramidal neurons in layer VI of this region express cholinergic receptors of both families and play an important role in attention through their feedback projections to the thalamus. Here, we investigate how nicotinic and muscarinic cholinergic receptors affect the excitability of these neurons using whole-cell recordings in acute brain slices of prefrontal cortex. Since attention deficits have been documented in both rodents and humans having genetic abnormalities in nicotinic receptors, we focus in particular on how the cholinergic excitation of layer VI neurons is altered by genetic deletion of either of two key nicotinic receptor subunits, the accessory α5 subunit or the ligand-binding β2 subunit. We find that the cholinergic excitation of layer VI neurons is dominated by nicotinic receptors in wild-type mice and that the reduction or loss of this nicotinic stimulation is accompanied by a surprising degree of plasticity in excitatory muscarinic receptors. These findings suggest that disrupting nicotinic receptors fundamentally alters the mechanisms and timing of excitation in prefrontal attentional circuitry.

Effects of olanzapine on muscarinic M3 receptor binding density in the brain relates to weight gain, plasma insulin and metabolic hormone levels

The second generation antipsychotic drug (SGA) olanzapine has an efficacy to treat schizophrenia, but can cause obesity and type II diabetes mellitus. Cholinergic muscarinic M3 receptors (M3R) are expressed on pancreatic β-cells and in the brain where they influence insulin secretion and may regulate other metabolic hormones via vagal innervation of the gastrointestinal tract. Olanzapine's M3R antagonism is an important risk factor for its diabetogenic liability. However, the effects of olanzapine on central M3Rs are unknown. Rats were treated with 0.25, 0.5, 1.0 or 2.0mg olanzapine/kg or vehicle (3×/day, 14-days). M3R binding densities in the hypothalamic arcuate (Arc) and ventromedial nuclei (VMH), and dorsal vagal complex (DVC) of the brainstem were investigated using [3H]4-DAMP plus pirenzepine and AF-DX116. M3R binding correlations to body weight, food intake, insulin, ghrelin and cholecystokinin (CCK) were analyzed. Olanzapine increased M3R binding density in the Arc, VMH and DVC, body weight, food intake, circulating plasma ghrelin and CCK levels, and decreased plasma insulin and glucose. M3R negatively correlated to insulin, and positively correlated to ghrelin, CCK, food intake and body weight. Increased M3R density is a compensatory up-regulation in response to olanzapine's M3R antagonism. Olanzapine acts on M3R in regions of the brain that control food intake and insulin secretion. Olanzapine's M3R blockade in the brain may inhibit the acetylcholine pathway for insulin secretion. These findings support a role for M3Rs in the modulation of insulin, ghrelin and CCK via the vagus nerve and provide a mechanism for olanzapine's diabetogenic and weight gain liability.

Muscarinic receptor activation enables persistent firing in pyramidal neurons from superficial layers of dorsal perirhinal cortex

Persistent-firing neurons in the entorhinal cortex (EC) and the lateral nucleus of the amygdala (LA) continue to discharge long after the termination of the original, spike-initiating current. An emerging theory proposes that endogenous persistent firing helps support a transient memory system. This study demonstrated that persistent-firing neurons are also prevalent in rat perirhinal cortex (PR), which lies immediately adjacent to and is reciprocally connected with EC and LA. Several characteristics of persistent-firing neurons in PR were similar to those previously reported in LA and EC. Persistent firing in PR was enabled by the application of carbachol, a nonselective cholinergic agonist, and it was induced by injecting a suprathreshold current or by stimulating suprathreshold excitatory synaptic inputs to the neuron. Once induced, persistent firing lasted for seconds to minutes. Persistent firing could always be terminated by a sufficiently large and prolonged hyperpolarizing current; it was prevented by antagonists of muscarinic cholinergic receptors (mAChRs); and it was blocked by flufenamic acid. The latter has been suggested to inhibit a Ca(2+) -activated nonspecific cation conductance (G(CAN) ) that normally furnishes the sustained depolarization during persistent firing. In many PR neurons, the discharge rate during persistent firing was a graded function of depolarizing and/or hyperpolarizing inputs. Persistent firing was not prevented by blocking fast excitatory and inhibitory synaptic transmission, demonstrating that it can be generated endogenously. We suggest that persistent-firing neurons in PR, EC, LA, and certain other brain regions may cooperate in support of a transient-memory system.

Acute restraint stress enhances hippocampal endocannabinoid function via glucocorticoid receptor activation

Exposure to behavioural stress normally triggers a complex, multilevel response of the hypothalamic-pituitary-adrenal (HPA) axis that helps maintain homeostatic balance. Although the endocannabinoid (eCB) system (ECS) is sensitive to chronic stress, few studies have directly addressed its response to acute stress. Here we show that acute restraint stress enhances eCB-dependent modulation of GABA release measured by whole-cell voltage clamp of inhibitory postsynaptic currents (IPSCs) in rat hippocampal CA1 pyramidal cells in vitro. Both Ca(2+)-dependent, eCB-mediated depolarization-induced suppression of inhibition (DSI), and muscarinic cholinergic receptor (mAChR)-mediated eCB mobilization are enhanced following acute stress exposure. DSI enhancement is dependent on the activation of glucocorticoid receptors (GRs) and is mimicked by both in vivo and in vitro corticosterone treatment. This effect does not appear to involve cyclooxygenase-2 (COX-2), an enzyme that can degrade eCBs; however, treatment of hippocampal slices with the L-type calcium (Ca(2+)) channel inhibitor, nifedipine, reverses while an agonist of these channels mimics the effect of in vivo stress. Finally, we find that acute stress produces a delayed (by 30 min) increase in the hippocampal content of 2-arachidonoylglycerol, the eCB responsible for DSI. These results support the hypothesis that the ECS is a biochemical effector of glucocorticoids in the brain, linking stress with changes in synaptic strength.

Task demands dissociate the effects of muscarinic M1 receptor blockade and protein kinase C inhibition on attentional performance in rats

The cholinergic system is known to be necessary for normal attentional processing. However, the receptors and mechanisms mediating the effects of acetylcholine on attention remain unclear. Previous work in our laboratory suggested that cholinergic muscarinic receptors are critical for maintaining performance in an attention-demanding task in rats. We examined the role of the muscarinic M(1) receptor and protein kinase C (PKC), which is activated by the M(1) receptor, in attention task performance. Rats were trained in an attention-demanding task requiring discrimination of brief (500, 100, 25 ms) visual signals from trials with no signal presentation. The effects of muscarinic M(1) receptor blockade were assessed by administering dicyclomine (0-5.0 mg/kg). The effects of PKC inhibition were assessed by administering chelerythrine chloride (0-2.0 mg/kg). Dicyclomine decreased the accuracy of detecting longer signals in this attention task, including when attentional demands were increased by flashing a houselight throughout the session. Chelerythrine chloride decreased the accuracy of signal detection in the standard version of the task but not when the houselight was flashed throughout the session. The present findings indicate that muscarinic M(1) receptors are critical for maintaining performance when attentional demands are increased, and that PKC activity may contribute to some aspects of attentional performance.

Object-selective responses evoked by phase-shift motion stimuli in macaque inferior temporal cortex: A case study using chronically implanted multielectrode arrays

In frogs, the horizontal monocular optokinetic nystagmus (OKN) is asymmetrical, with only the temporal-nasal (T-N) stimulation being efficient to evoke the reflex. Coil recordings showed that, in adult animals, prolonged monocular visual deprivation by unilateral eyelid suture provoked the appearance of the N-T component. A unique microinjection of GABAA agonist THIP or of muscarinic antagonist atropine into the nucleus lentiformis mesencephali (nLM), the pretectal mesencephalic structure involved in OKN, transiently abolished the presence of the N-T component. Daily microinjections of the NMDA antagonist APV into the nLM, during the week of monocular deprivation, prevented the appearance of the N-T component. The results suggest that this phenomenon of visual plasticity can be due to reduction in pretectal GABAergic inhibition, and to concomitant activation of both cholinergic muscarinic and NMDA receptors.