Microglial diversity along the hippocampal longitudinal axis impacts synaptic plasticity in adult male mice under homeostatic conditions.

The hippocampus is a plastic brain area that shows functional segregation along its longitudinal axis, reflected by a higher level of long-term potentiation (LTP) in the CA1 region of the dorsal hippocampus (DH) compared to the ventral hippocampus (VH), but the mechanisms underlying this difference remain elusive. Numerous studies have highlighted the importance of microglia-neuronal communication in modulating synaptic transmission and hippocampal plasticity, although its role in physiological contexts is still largely unknown. We characterized in depth the features of microglia in the two hippocampal poles and investigated their contribution to CA1 plasticity under physiological conditions. We unveiled the influence of microglia in differentially modulating the amplitude of LTP in the DH and VH, showing that minocycline or PLX5622 treatment reduced LTP amplitude in the DH, while increasing it in the VH. This was recapitulated in Cx3cr1 knockout mice, indicating that microglia have a key role in setting the conditions for plasticity processes in a region-specific manner, and that the CX3CL1-CX3CR1 pathway is a key element in determining the basal level of CA1 LTP in the two regions. The observed LTP differences at the two poles were associated with transcriptional changes in the expression of genes encoding for Il-1, Tnf-α, Il-6, and Bdnf, essential players of neuronal plasticity. Furthermore, microglia in the CA1 SR region showed an increase in soma and a more extensive arborization, an increased prevalence of immature lysosomes accompanied by an elevation in mRNA expression of phagocytic markers Mertk and Cd68 and a surge in the expression of microglial outward K+ currents in the VH compared to DH, suggesting a distinct basal phenotypic state of microglia across the two hippocampal poles. Overall, we characterized the molecular, morphological, ultrastructural, and functional profile of microglia at the two poles, suggesting that modifications in hippocampal subregions related to different microglial statuses can contribute to dissect the phenotypical aspects of many diseases in which microglia are known to be involved.

ATP release during cell swelling activates a Ca2+-dependent Cl- current by autocrine mechanism in mouse hippocampal microglia.

Microglia cells, resident immune cells of the brain, survey brain parenchyma by dynamically extending and retracting their processes. Cl- channels, activated in the cellular response to stretch/swelling, take part in several functions deeply connected with microglia physiology, including cell shape changes, proliferation, differentiation and migration. However, the molecular identity and functional properties of these Cl- channels are largely unknown. We investigated the properties of swelling-activated currents in microglial from acute hippocampal slices of Cx3cr1 +/GFP mice by whole-cell patch-clamp and imaging techniques. The exposure of cells to a mild hypotonic medium, caused an outward rectifying current, developing in 5-10 minutes and reverting upon stimulus washout. This current, required for microglia ability to extend processes towards a damage signal, was carried mainly by Cl- ions and dependent on intracellular Ca2+. Moreover, it involved swelling-induced ATP release. We identified a purine-dependent mechanism, likely constituting an amplification pathway of current activation: under hypotonic conditions, ATP release triggered the Ca2+-dependent activation of anionic channels by autocrine purine receptors stimulation. Our study on native microglia describes for the first time the functional properties of stretch/swelling-activated currents, representing a key element in microglia ability to monitor the brain parenchyma.

KCa3.1 inhibition switches the phenotype of glioma-infiltrating microglia/macrophages.

Among the strategies adopted by glioma to successfully invade the brain parenchyma is turning the infiltrating microglia/macrophages (M/MΦ) into allies, by shifting them toward an anti-inflammatory, pro-tumor phenotype. Both glioma and infiltrating M/MΦ cells express the Ca(2+)-activated K(+) channel (KCa3.1), and the inhibition of KCa3.1 activity on glioma cells reduces tumor infiltration in the healthy brain parenchyma. We wondered whether KCa3.1 inhibition could prevent the acquisition of a pro-tumor phenotype by M/MΦ cells, thus contributing to reduce glioma development. With this aim, we studied microglia cultured in glioma-conditioned medium or treated with IL-4, as well as M/MΦ cells acutely isolated from glioma-bearing mice and from human glioma biopsies. Under these different conditions, M/MΦ were always polarized toward an anti-inflammatory state, and preventing KCa3.1 activation by 1-[(2-Chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), we observed a switch toward a pro-inflammatory, antitumor phenotype. We identified FAK and PI3K/AKT as the molecular mechanisms involved in this phenotype switch, activated in sequence after KCa3.1. Anti-inflammatory M/MΦ have higher expression levels of KCa3.1 mRNA (kcnn4) that are reduced by KCa3.1 inhibition. In line with these findings, TRAM-34 treatment, in vivo, significantly reduced the size of tumors in glioma-bearing mice. Our data indicate that KCa3.1 channels are involved in the inhibitory effects exerted by the glioma microenvironment on infiltrating M/MΦ, suggesting a possible role as therapeutic targets in glioma.

Acetylcholine-activated inward current induces cytosolic Ca2+ mobilization in mouse C2C12 myotubes.

We examined the spatiotemporal pattern of intracellular Ca2+ liberation in mouse myotubes by means of fluorescence imaging of cytosolic free Ca2+ together with the simultaneous recording of membrane whole-cell currents. Acetylcholine (ACh) applications to C2C12 myotubes equilibrated in Ca(2+)-free medium and voltage clamped at -50 mV evoked localized fluorescence transients of variable amplitude with less than 0.5 s delay. Under the same experimental conditions, fluorescence transients were elicited by ACh also in mouse primary myotubes. Ca2+ transients were inhibited in myotubes clamped at depolarized potentials (-10 mV to +50 mV), or equilibrated in a Na+,Ca(2+)-free medium as well as in cells loaded with heparin, or with inositol (1,4,5) trisphosphate (InsP3). To investigate whether InsP3 could induce Ca2+ mobilization, [Ca2+]i determinations were carried out in myotubes loaded with InsP3 through the whole-cell patch-clamp recording pipette or by extracellular application in permeabilized cells. InsP3 diffusion into the myoplasm caused Ca2+ spikes with 5 +/- 1 s (mean +/- SEM) delay from the rupture of the membrane patch. Spikes were followed by sustained increases in fluorescence or by damped oscillations. In permeabilized myotubes, InsP3 induced the release of sequestered 45Ca2+ with a half-maximally effective concentration (EC50) of 0.28 +/- 0.05 microM, and Hill coefficient of 0.79 +/- 0.09. It is concluded that the ACh-activated inward current in mouse myotubes is coupled to cytosolic Ca2+ mobilization from internal InsP3-sensitive pools.

Chemokine receptor CXCR2 regulates the functional properties of AMPA-type glutamate receptor GluR1 in HEK cells.

Experiments were conducted in both HEK cells and cerebellar neurons to investigate whether CXC chemokine receptor 2 (CXCR2) is functionally coupled to GluR1. The co-expression of CXCR2 with GluR1 in HEK cells increased (i) the GluR1 "apparent" affinity for the transmitter; (ii) the GluR1 channel open probability; and (iii) GluR1 binding site cooperativity upon CXCR2 stimulation with CXC chemokine ligand 2 (CXCL2). The affinity of C-terminal-deleted GluR1 for glutamate (Glu) remained stable instead. Furthermore, CXCL2 increased the binding site cooperativity of AMPA receptors in rat cerebellar granule cells; and the amplitude of spontaneous excitatory postsynaptic current (sEPSCs) in Purkinje neurons (PNs). Our findings indicate that the coupling of CXCR2 with GluR1 may modulate glutamatergic synaptic transmission.

CXC chemokines interleukin-8 (IL-8) and growth-related gene product alpha (GROalpha) modulate Purkinje neuron activity in mouse cerebellum.

We give here evidence that Purkinje neurons (PNs) of mouse cerebellar slices studied with patch clamp technique combined with laser confocal microscopy, respond to human IL-8 and GROalpha by (i) a cytosolic Ca2+ transient compatible with inositol (1,4,5) trisphosphate (InsP3) formation; (ii) an enhancement of the neurotransmitter release; and (iii) an impairment of the long-term depression of synaptic strength (LTD). It was also found the expression of IL-8 receptor type 2 in PN and granule cells by immunofluorescence, immunoblotting and RT-PCR analysis. Considered together these findings suggest that IL-8 and GROalpha may play a neuromodulatory role on mouse cerebellum.

Kinetics and Mg2+ block of N-methyl-D-aspartate receptor channels during postnatal development of hippocampal CA3 pyramidal neurons.

Voltage-dependent magnesium block of N-methyl-D-aspartate-activated channels, and the N-methyl-D-aspartate component of excitatory synaptic currents were studied in CA3 pyramidal neurons of hippocampal slices from immature (postnatal day 3-8) and adult (postnatal day 25-60) rats. In all neurons studied the kinetics of single-channel openings in cell-attached and inside-out configurations was strongly modulated by extracellular Mg2+, in a voltage-dependent manner. No age-dependent difference in the Mg2+ sensitivity of N-methyl-D-aspartate channels was observed. At physiological concentrations of external Mg2+ (1.3 mM), N-methyl-D-aspartate components of excitatory synaptic currents measured from immature and adult rats displayed a similar voltage-dependence. In immature neurons (postnatal day 3-6), the N-methyl-D-aspartate component of excitatory postsynaptic currents decay time-course was a single-exponential with an average time-constant of about 300 ms. In neurons from older animals the decay was described by a double-exponential function with both a fast component (tau f, 54-130 ms) and a slow component (tau s, 275-400 ms). With age, the contribution of the fast component increased and the decay time-course of the N-methyl-D-aspartate component of excitatory postsynaptic currents accelerated. It is concluded that the Mg2+ block of N-methyl-D-aspartate channels in CA3 pyramidal neurons does not change with development, but the kinetic properties of N-methyl-D-aspartate receptor channels are developmentally regulated.

Modulation of the neurotransmitter release in rat cerebellar neurons by GRO beta.

We report here that, in cultured cerebellar granule cells, the CXC chemokine GRObeta stimulates the signaling pathway of the extracellular signal-regulated kinases, and enhances both evoked and spontaneous postsynaptic currents in patch clamped Purkinje neurons from rat cerebellar slices. The GRObeta-induced enhancement of the excitatory post-synaptic currents evoked by stimulating the parallel fibres is blocked by the inhibitor of the extracellular signal-regulated kinases pathway PD98059, which also reduces both basal frequency of spontaneous post-synaptic currents and mean amplitude of evoked excitatory post-synaptic currents. Our results suggest that GRObeta modulates neurotransmitter release in the cerebellum through the activation of the extracellular signal-regulated kinases pathway.

Inhibition of GABA and glycine responses by glutamate in rat hippocampal neurons.

Currents elicited by activation of GABAA, glycine (GLY) and glutamate (GLU) receptors (R) in pyramidal neurons of CA1 region from thin slices of rat hippocampus were studied using the tight-seal whole-cell recording techniques. GLU (100 mM) induced a long-lasting depression of GABA- and GLY-activated currents (IGABA and IGLY) when using standard saline in conjunction with depolarization. The long-lasting depression was not observed: (1) in neurons held at -70 mV during GLU application; (2) in neurons depolarized by current injection but not exposed to GLU; (3) when GLU/depolarization protocol was performed in Ca(2+)-free medium; or (4) by using recording patch-pipettes filled with a medium that tightly controlled cytosolic Ca2+ transients. Sphingosine (10 mM), staurosporine (1 mM) and the specific inhibitor of protein kinase C (PKC(19-36) (200 mM in the patch-pipette solution), blocked the long-lasting depression of IGABA. IGABA was depressed even when the treatment with GLU was performed before patch-clamping the neuron. We conclude that the sustained IGABA and IGLY depression is mediated by cytosolic events triggered by the activation of GLUR.

Interferon inhibits synaptic potentiation in rat hippocampus.

The effects of rat interferon (IFN) on the electrically-induced potentiation of the synaptic transmission were studied in rat hippocampal slices by using extracellular field potential recordings. The treatment with rat IFN (120 U/ml) reduced the size of short-term potentiation (STP) and suppressed long-term potentiation (LTP). These IFN-induced effects were dose-dependent in the range of 50-500 U/ml. In addition, IFN slightly attenuated the potentiation when applied during the maintenance of LTP. Basal synaptic transmission was affected by IFN at concentrations greater than or equal to 250 U/ml. Following an acute exposure to IFN (500-200 U/ml), cultured embryonic neurones from rat hippocampus often exhibited an attenuation of N-methyl-D-aspartate-induced currents and a variation (increase or decrease) of voltage-activated Ca2+ current amplitude. A possible role of IFN as neuromodulator in mammalian brain during immune responses is discussed.

A role for intracellular zinc in glioma alteration of neuronal chloride equilibrium.

Glioma patients commonly suffer from epileptic seizures. However, the mechanisms of glioma-associated epilepsy are far to be completely understood. Using glioma-neurons co-cultures, we found that tumor cells are able to deeply influence neuronal chloride homeostasis, by depolarizing the reversal potential of γ-aminobutyric acid (GABA)-evoked currents (EGABA). EGABA depolarizing shift is due to zinc-dependent reduction of neuronal KCC2 activity and requires glutamate release from glioma cells. Consistently, intracellular zinc loading rapidly depolarizes EGABA in mouse hippocampal neurons, through the Src/Trk pathway and this effect is promptly reverted upon zinc chelation. This study provides a possible molecular mechanism linking glioma invasion to excitation/inhibition imbalance and epileptic seizures, through the zinc-mediated disruption of neuronal chloride homeostasis.

CX3CL1-induced modulation at CA1 synapses reveals multiple mechanisms of EPSC modulation involving adenosine receptor subtypes.

We characterized the role of adenosine receptor (AR) subtypes in the modulation of glutamatergic neurotransmission by the chemokine fractalkine (CX3CL1) in mouse hippocampal CA1 neurons. CX(3)CL1 causes a reversible depression of excitatory postsynaptic current (EPSC), which is abolished by the A(3)R antagonist MRS1523, but not by A(1)R (DPCPX) or A(2A)R (SCH58261) antagonists. Consistently, CX3CL1-induced EPSC depression is absent in slices from A(3)R(-/-) but not A(1)R(-/-) or A(2A)R(-/-) mice. Further, A(3)R stimulation causes similar EPSC depression. In cultured neurons, CX3CL1-induced depression of AMPA current shows A(1)R-A(3)R pharmacology. We conclude that glutamatergic depression induced by released adenosine requires the stimulation of different ARs.

Anomalous levels of Cl- transporters in the hippocampal subiculum from temporal lobe epilepsy patients make GABA excitatory.

The mRNA levels of NKCC1, an inwardly directed Na(+), K(+)-2Cl(-) cotransporter that facilitates the accumulation of intracellular Cl(-), and of KCC2, an outwardly directed K(+)-Cl(-) cotransporter that extrudes Cl(-), were studied in surgically resected brain specimens from drug-resistant temporal lobe (TL) epilepsy (TLE) patients. Quantitative RT-PCR analyses of the mRNAs extracted from the human TLE-associated brain regions revealed an up-regulation of NKCC1 mRNA and a down-regulation of KCC2 mRNA in the hippocampal subiculum, compared with the hippocampus proper or the TL neocortex, suggesting an abnormal transcription of Cl(-) transporters in the TLE subiculum. In parallel experiments, cell membranes isolated from the same TLE-associated brain regions were injected into Xenopus oocytes that rapidly incorporated human GABA(A) receptors into their surface membrane. The GABA currents elicited in oocytes injected with membranes from the subiculum had a more depolarized reversal potential (E(GABA)) compared with the hippocampus proper or the neocortex. The NKCC1 blocker bumetanide or a temperature decrease of 10 degrees C shifted the GABA-current E(GABA) more negative in oocytes injected with membranes from TLE hippocampal subiculum, matching the E(GABA) of TL neocortex-injected oocytes. We conclude that the anomalous expression of both Cl(-) transporters, NKCC1 and KCC2 [corrected] in TLE hippocampal subiculum probably causes altered Cl(-) transport in the "epileptic" neurons, as revealed in the microtransplanted Xenopus oocytes, and renders GABA aberrantly "exciting," a feature that may contribute to the precipitation of epileptic seizures.

Rundown of GABA type A receptors is a dysfunction associated with human drug-resistant mesial temporal lobe epilepsy.

Pharmacotherapeutic strategies have been difficult to develop for several forms of temporal lobe epilepsy, which are consequently treated by surgical resection. To examine this problem, we have studied the properties of transmitter receptors of tissues removed during surgical treatment. We find that when cell membranes, isolated from the temporal neocortex of patients afflicted with drug-resistant mesial temporal lobe epilepsy (TLE), are injected into frog oocytes they acquire GABA type A receptors (GABA(A)-receptors) that display a marked rundown during repetitive applications of GABA. In contrast, GABA(A)-receptor function is stable in oocytes injected with cell membranes isolated from the temporal lobe of TLE patients afflicted with neoplastic, dysgenetic, traumatic, or ischemic temporal lesions (lesional TLE, LTLE). Use-dependent GABA(A)-receptor rundown is also found in the pyramidal neurons of TLE neocortical slices and is antagonized by BDNF. Pyramidal neurons in cortical slices of a traumatic LTLE patient did not show GABA(A)-receptor rundown. However, the apparent affinity of GABA(A)-receptor in oocytes microtransplanted with membranes from all of the epileptic patients studied was smaller than the affinity of receptors transplanted from the nonepileptic brain. We conclude that the use-dependent rundown of neocortical GABA(A)-receptor represents a TLE-specific dysfunction, whereas the reduced affinity may be a general feature of brains of both TLE and LTLE patients, and we speculate that our findings may help to develop new treatments for TLE and LTLE.

[Contribution of the Aversa school to the birth and progress of criminal anthropology]. / Contributo della scuola aversana alla nascita e progresso dell'antropologia criminale

In this historical research the author highlights the contribution made by the Aversa school in the birth and progress of criminal Anthropology. He describes in particular the scientific work of Gaspare Virgilio who with his intuitions contributed to a notable extent in the evolution of the though of Lombroso, of whom he was a friend, and also the work of his successor, Fillipo Saporito, who, in dealing with the treatment of criminals, advocated the necessity of replacing the punishment-chastisement by the punishment-treatment, thus forestalling the principles set forth in the new prison reform.

Ca2+ permeability of mouse and chick nicotinic acetylcholine receptors expressed in transiently transfected human cells.

1. Combinations of cDNAs encoding mouse and chick nicotinic acetylcholine receptor (nAChR) subunits were transiently transfected into human BOSC 23 cells, and the expressed receptors were studied by simultaneously recording transmembrane currents and fluorescence transients using the whole-cell patch-clamp technique, and confocal microscopy with the Ca2+ indicator dye fluo-3. 2. The fractional Ca2+ current, Pf, of nAChRs was evaluated as the normalized ratio of nicotine-evoked fluorescence transient over total charge entering the cell (F/Q ratio). Mouse fetal muscle nAChR channels had a Pf, alphabetagammadelta value of 2.1 %. The substitution of the gamma subunit with the epsilon subunit resulted in a 2-fold increase in Pf (4.2 %). The difference in Ca2+ permeability was confirmed by determination of Ca2+/Cs+ permeability ratios. 3. Among the chick neuronal nAChRs tested, Pf,alpha3beta4 was 4.6 %, while Pf, alpha4beta4 and Pf,alpha4beta2 were 3.0 % and 2.9 %, respectively. 4. The amplitude of the current elicited by the activation of alpha3beta4 nAChRs increased as the external Ca2+ concentration was raised from 2 to 110 mM, whereas currents flowing through all other nAChRs tested were reduced to various extents. 5. Our findings indicate that the adult-type muscle nAChR (alphabetaepsilondelta) is more permeable to Ca2+ than the fetal-type (alphabetagammadelta), while ganglionic-like alpha3beta4 nAChR is more permeable to Ca2+ than the examined alpha4-containing nAChRs. The functional significance is discussed.

Design and in vitro pharmacology of a selective gamma-aminobutyric acidC receptor antagonist.

In mammals, receptors for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) are divided into three pharmacological classes, which are denoted GABAA, GABAB, and GABAC. GABAC receptors are defined by their insensitivity to the GABAA receptor antagonist bicuculline and the GABAB receptor agonist (-)-baclofen. GABAC receptors probably are a heterogeneous group of proteins. The most extensively studied mammalian GABAC receptors are those found in neurons of the outer retina. These receptors are GABA-gated Cl- channels comprised of p subunits, of which there are two subtypes. The physiological functions served by GABAC receptors are largely unknown; to determine the functions, it would be useful to have GABAC-selective ligands. In a previous study, we found that isoguvacine, a GABAA-selective agonist, and 3-aminopropyl-(methyl)phosphinic acid (3-APMPA), a GABAB-selective agonist, show affinity for retinal GABAC receptors. In particular, 3-APMPA is an antagonist with low micromolar potency (Kb approximately 1 microM). Here, we report the synthesis and pharmacological characterization of (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid (TPMPA), a hybrid of isoguvacine and 3-APMPA designed to retain affinity for GABAC receptors but not to interact with GABAA or GABAB receptors. Electrical assays show that TPMPA is a competitive antagonist of cloned human mu 1 GABAC receptors expressed in Xenopus laevis oocytes (Kb approximately 2 microM). TPMPA is > 100-fold weaker as an inhibitor of rat brain GABAA receptors expressed in oocytes (Kb approximately 320 microM) and has only weak agonist activity on GABAB receptors assayed in rat hippocampal slices (EC50 approximately 500 microM). TPMPA should be a useful pharmacological probe with which to investigate GABAC receptor function in the outer retina and in any other areas of the nervous system in which these types of receptor are present.

Spontaneous and repetitive calcium transients in C2C12 mouse myotubes during in vitro myogenesis.

Fluorescence videomicroscopy was used to monitor changes in the cytosolic free Ca2+ concentration ([Ca2+]i) in the mouse muscle cell line C2Cl2 during in vitro myogenesis. Three different patterns of changes in [Ca2+]i were observed: (i) [Ca2+]i oscillations; (ii) faster Ca2+ events confined to subcellular regions (localized [Ca2+]i spikes) and (iii) [Ca2+]i spikes detectable in the entire myotube (global [Ca2+]i spikes). [Ca2+]i oscillations and localized [Ca2+]i spikes were detectable following the appearance of caffeine-sensitivity in differentiating C2Cl2 cells. Global [Ca2+]i spikes appeared later in the process of myogenesis in cells exhibiting coupling between voltage-operated Ca2+ channels and ryanodine receptors. In contrast to [Ca2+]i oscillations and localized [Ca2+]i spikes, the global events immediately stopped when cells were perfused either with a Ca2+-free solution, or a solution with TTX, TEA and verapamil. To explore further the mechanism of the global [Ca2+]i spikes, membrane currents and fluorescence signals were measured simultaneously. These experiments revealed that global [Ca2+]i spikes were correlated with an inward current. Moreover, while the depletion of the Ca2+ stores blocked [Ca2+]i oscillations and localized [Ca2+]i spikes, it only reduced the amplitude of global [Ca2+]i spikes. It is suggested that, during the earlier stages of the myogenesis, spontaneous and repetitive [Ca2+]i changes may be based on cytosolic oscillatory mechanisms. The coupling between voltage-operated Ca2+ channels and ryanodine receptors seems to be the prerequisite for the appearance of global [Ca2+]i spikes triggered by a membrane oscillatory mechanism, which characterizes the later phases of the myogenic process.

Zinc permeates mouse muscle ACh receptor channels expressed in BOSC 23 cells and affects channel function.

1. The influx of Zn2+ through the channels of fetal and adult mouse muscle nicotinic acetylcholine receptors (gamma- and epsilon-AChRs) and its effects on receptor function were studied in transiently transfected human BOSC 23 cells, by combining patch-clamp recordings with digital fluorescence microscopy. 2. ACh-induced whole-cell currents were reversibly reduced by external ZnCl2, with half-maximal inhibitory concentrations of 3 and 1 mM for gamma- and epsilon-AChRs, respectively. 3. Both gamma- and epsilon-AChR channels were permeable to Zn2+, as shown by fluorescence measurements using Zn2+-sensitive dyes. The fractional current carried by Zn2+ (Pf,Zn; 0.5 mM Zn2+ in Ca2+- and Mg2+-free medium) through gamma- and epsilon">-AChR channels was 1.7 and 4 %, respectively. 4. Pf,Zn increased with the concentration of ZnCl2, but was little affected by physiological concentrations of Ca2+ and Mg2+ in the external medium. 5. The conductance of ACh-evoked unitary events, measured by cell-attached or outside-out recordings, decreased when the patched membrane was exposed to ZnCl2 (1 or 3 mM). Simultaneous application of ACh and Zn2+ to the extra-patch membrane lengthened channel open duration (tau op) by 50%. No obvious increment of tau op was observed following exposure of inside-out patches to Zn2+. 6. The possible physiological relevance of zinc-induced modulation of AChR channels is discussed.