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PubMed2004

Releasing the peri-neuronal net to patch-clamp neurons in adult CNS.

The extracellular matrix of adult neural tissue contains chondroitin sulphated proteogylcans that form a dense peri-neuronal net surrounding the cell body and proximal dendrites of many neuronal classes. Development of the peri-neuronal net beyond approximately postnatal day 17 obscures visualization and often access by patch electrodes to neuronal membranes with the result that patch clamp recordings are most readily obtained from early postnatal animals. We describe a technique in which the surface tension of a sucrose-based medium promotes partial dissociation of thin tissue slices from adult tissue. Surface tension spreads the tissue and loosens the peri-neuronal net from neuronal membranes within minutes and in the absence of proteolytic enzymes. Furthermore, the extent of dissociation can be controlled so as to maintain the overall slice structure and allow identification of specific cell classes. Excellent structural preservation of neurons and dendrites can be obtained and full access by patch electrodes made possible for current- or voltage-clamp recordings in tissue well beyond the development of peri-neuronal nets. We demonstrate the feasibility of using this approach through patch recordings from neurons in the brainstem and cerebellum of adult gymnotiform fish and in deep cerebellar nuclei of rats as old as 6 months.

Animals↗

PubMed1989

The properties of 5-HT3 receptors in clonal cell lines studied by patch-clamp techniques.

1 The characteristics of transmembrane currents evoked by 5-hydroxytryptamine (5-HT) in the neuroblastoma x Chinese hamster brain cell line NCB-20 and neuroblastoma clonal cell line N1E-115 have been studied under voltage-clamp conditions by the whole-cell recording and outside-out membrane patch modes of the patch-clamp technique. 2 In 73% of NCB-20 cells examined (n = 221), and all N1E-115 cells studied (n = 80), 5-HT (10 microM) elicited a transient inward current at negative holding potentials, this being associated with an increase in membrane conductance. In both cell lines responses to 5-HT reversed in sign at a potential of approximately -2 mV and demonstrated inward rectification. 3 The reversal potential of 5-HT-induced currents (E5-HT) recorded from either NCB-20 or N1E-115 cells was unaffected by total replacement of internal K+ by Cs+. In N1E-115 cells, reducing internal K+ concentration from 140 to 20 mM produced a positive shift in E5-HT of approximately 28 mV, whereas reducing external Na+ from 143 to 20 mM was associated with a negative shift in E5-HT of about 37 mV. A large reduction in internal Cl- concentration (from 144 to 6 mM) had little effect on E5-HT. 4 5-HT-induced currents of NCB-20 cells were unaffected by methysergide (1 microM) or ketanserin (1 microM), but were reversibly antagonized by GR38032F (0.1-1.0 nM) with an IC50 of 0.25 nM. GR 38032F (0.3 nM) reduced 5-HT-induced currents in N1E-115 cells to approximately 26% of their control value. 5 On outside-out membrane patches excised from both NCB-20 and N1E-115 cells, 5-HT induced small inward currents which could not be clearly resolved into discrete single channel events. Such responses were: (i) reversibly antagonized by GR 38032F (1 nM) (ii) reversed in sign at 0 mV, and (iii) subject to desensitization. 6 Fluctuation analysis of inward currents evoked by 5-HT (1 microM) in N1E-115 cells suggests that 5-HT gates a channel with a conductance of approximately 310fS. Such a relatively small conductance could readily explain why the response of outside-out membrane patches to 5-HT cannot at present be resolved into clear single channel events.

Cell Membrane↗

PubMed2005

Calbindin-D28k content and firing pattern of hippocampal granule cells in amygdala-kindled rats: a perforated patch-clamp study.

The dentate gyrus is believed to play an important pathophysiological role during experimentally induced kindling. In this study, we investigated whether an altered content of the calcium binding protein calbindin-D(28k) or an increased intrinsic excitability of hippocampal granule cells contribute to the induction of the kindling phenomenon. We determined the firing pattern of granule cells in hippocampal slices using perforated patch-clamp recordings in current clamp mode. The expression of calbindin-D(28k) and glutamic acid decarboxylase (GAD(67)) by granule cells was analyzed immunohistochemically. Rats developed secondarily generalized limbic seizures within approximately 11 days of twice-daily stimulation of the amygdala. As reported for other kindling paradigms, this protocol induced a clear up-regulation of GAD(67) in granule cells, indicating their involvement in the induced neuronal activity. However, when comparing kindled and control rats, we could not detect any differences in intrinsic excitability: Firing frequency, after-hyperpolarisations, action potentials, input resistance and membrane potentials were nearly identical between both groups. Furthermore, we did not observe any differences in the calbindin-D(28k) immunoreactivity between groups. In every slice, virtually all granule cells were found to be strongly calbindin-D(28k) positive, and there was no apparent reduction in the general level of calbindin-D(28k) expression. We conclude that changes in intrinsic membrane properties or in the calbindin-D(28k) content of granule cells are not necessary for the development of amygdala kindling.

Action Potentials↗

PubMed2003

Patch-clamp fluorometry recording of conformational rearrangements of ion channels.

Conformational rearrangements are commonly observed in membrane proteins and constitute the molecular mechanisms through which they contribute to signal transduction. Information on structural changes in membrane proteins has mostly been inferred from functional studies. Recently, site-specific fluorescence recordings have made it possible to directly observe such molecular events in real time within the membrane environment. Here, we describe the patch-clamp fluorometry (PCF) technique that records simultaneously the local structural changes and the functional states of ion channels in isolated cell membranes. Combined with fluorescence resonance energy transfer (FRET), the technique should shed new light on ion channel activation, regulation, and interaction with other membrane proteins.

Animals↗

PubMed1995

Beta-adrenoceptor subtypes in young and old rat ventricular myocytes: a combined patch-clamp and binding study.

1. We used electrophysiological and binding techniques to assess the presence of beta 1- and beta 2-adrenoceptors (beta 1AR and beta 2AR) in rat cardiac myocytes and to determine their ratio during aging. Experiments were performed in left ventricular myocytes enzymatically dissociated from the heart of 3-(young) or 22-month-old (old) Wistar Kyoto rats. 2. In patch-clamp experiments, myocytes from old rats showed a prolonged action potential duration (at -20 mV: 41.7 +/- 3.6 vs 26.2 +/- 3.1 ms; at -60 mV: 154.4 +/- 17.7 vs 87.1 +/- 6.9 ms, P < 0.05) and an augmented membrane capacitance (an index of cell size) (271.7 +/- 20.2 vs 164.3 +/- 14.6 pF, P < 0.05) compared to young rats. beta 2AR stimulation, achieved by superfusing myocytes with the selective beta 2AR agonist, zinterol (10 microM) or with (-)-isoprenaline (1 microM) in the presence of the selective beta 1AR antagonist, CGP 20712A (0.1 microM), significantly increased L-type calcium current (ICa,L) in rat ventricular myocytes. The percentage increase was similar in both young and old rats, either with zinterol (26.9 +/- 3.6% and 24.2 +/- 2.8%, respectively) or isoprenaline plus CGP 20712A (30.4 +/- 3.7% and 22.4 +/- 4.1%, respectively). Isoprenaline alone (beta 1AR and beta 2AR stimulation) caused a much smaller increase in ICa,L in old rats (58.4 +/- 12.1%) than in younger ones (95.3 +/- 8.1%) (P = 0.067). 3 The number of ,BAR mg-' protein, measured with saturation binding assays of the non selective ,betaAR antagonist [3H]-CGP 12177 was 1989.4+/-189.5 for 3- and of 1580.7 +/-161.5 for 22-month-old rats.Competition for [3H]-CGP 12177 binding by CGP 20712A gave biphasic curves which demonstrated two classes of binding sites. Densities (as percentages of total PAR density), and affinities for the two binding sites were: 80.4 +/- 2.2% (Ki = 6.6 +/- 1.3 nM) betaAR and 19.6 +/- 2.2% (Ki = 6.9 +/- 2.2 microM) beta2AR in young rats and 66.1 +/- 1.2% (Ki=8.3+/- 1.1 nM) beta1 AR and 33.9+/- 1.2% (Ki=5.2+/-0.6 PM) P2AR in old rats. Thebeta1AR/beta2AR ratio was significantly (P<0.01) reduced in old rats with respect to the younger ones.4 By combining electrophysiological and binding measurements, we calculated beta1AR and beta2ARdensities as number of receptors per microM2 of cell surface. In old rats, beta1 density was significantly decreased compared to young rats (8.4+/-2.0 vs 15.4+/-3.7 receptors microM-2, P<0.05), while beta2AR density remained unchanged at both 3 and 22 months (3.8 +/- 0.7 and 4.2+/-1.1 receptors microM-2, respectively).5 Our results demonstrate that both beta1AR and beta2AR are functionally present in rat ventricular myocytes of young and old rats. The decreased responsiveness to betaAR stimulation during aging appears to be associated with a selective reduction in the density of beta1AR.

Action Potentials↗

PubMed1998

Physiological analysis of Rasmussen's encephalitis: patch clamp recordings of altered inhibitory neurotransmitter function in resected frontal cortical tissue.

Rasmussen's encephalitis (RE) is a progressive, rare childhood disease characterized by severe epilepsy, hemiplegia, dementia, and inflammation of the brain. While one mechanism underlying the pathogenesis of RE has been hypothesized to be mediated by production of excitotoxic GluR3 autoantibodies to the AMPA receptor, other neuropathological etiologies have also been indicated. Whole-cell patch clamp recordings of GABA(A) receptor mediated responses were conducted in neurons acutely isolated from an RE patient, and compared to properties of non-focal human temporal cortical neurons. RE neurons appeared similar anatomically to control cortical neurons. Significant differences in GABAergic responses were evident between RE and control neurons. GABA was significantly more potent in RE than in control cortical neurons (EC50 of 13 microM vs 23 microM, respectively). In addition, the overall efficacy of GABA was significantly decreased in RE neurons, associated with a decrease in postsynaptic GABA current density in RE neurons (5.1 pA/microm2) in comparison to controls (9.2 pA/microm2). Augmentation of GABA responses by the benzodiazepine, clonazepam (CNZ), was significantly reduced in RE in comparison to control neurons (34% vs 99% augmentation at 100 nM). The RE-associated reduced functional efficacy and altered pharmacology of neuronal GABA(A) receptors is consistent with overall disinhibition in RE neurons, and could contribute to the generation of the severe epileptic activity evident in this disorder.

Cell Size↗

PubMed2002

High-resolution scanning patch-clamp: new insights into cell function.

Cell specialization is often governed by the spatial distribution of ion channels and receptors on the cell surface. So far, little is known about functional ion channel localization. This is due to a lack of satisfactory methods for investigating ion channels in an intact cell and simultaneously determining the channels' positions accurately. We have developed a novel high-resolution scanning patch-clamp technique that enables the study of ion channels, not only in small cells, such as sperm, but in submicrometer cellular structures, such as epithelial microvilli, fine neuronal dendrites, and, particularly, T-tubule openings of cardiac myocytes. In cardiac myocytes, as in most excitable cells, action potential propagation depends essentially on the properties of ion channels that are functionally and spatially coupled. We found that the L-type calcium and chloride channels are distributed and colocalized in the region of T-tubule openings, but not in other regions of the myocyte. In addition, chloride channels were found in narrowly defined regions of Z-grooves. This finding suggests a new synergism between these types of channels that may be relevant for action potential propagation along the T-tubule system and excitation-contraction coupling.

Animals↗

PubMed1998

beta-Adrenergic regulation of ion transport in pancreatic ducts: patch-clamp study of isolated rat pancreatic ducts.

BACKGROUND & AIMS: In the intact pancreas, bicarbonate secretion is thought to be controlled by a number of regulators, including adrenergic agonists. The aim of this study was to investigate the effects of adrenergic agonists on pancreatic ducts, which are the site of bicarbonate secretion. METHODS: Small intralobular ducts were isolated from rat pancreas and studied in vitro by the whole-cell patch clamp technique. Cell membrane voltages and currents were indicators of cellular ion transport. In some ducts, intracellular Ca2+ activity was measured by fluorescence optical methods. RESULTS: Unstimulated duct cells had a membrane voltage (Vm) of about -50 mV. Isoproterenol had a concentration-dependent effect on Vm; at 10(-7) mol/L, it depolarized Vm by 20-25 mV and the cell conductance increased by 100 nanosiemens. These effects were a result of opening of luminal Cl- channels. Phenylephrine had much smaller effects. At comparable concentrations, it depolarized Vm by a few millivolts. Neither agonist had significant effects on intracellular Ca2+. CONCLUSIONS: This study provides the first direct evidence that adrenergic stimulation, namely, that of beta-adrenoceptors, controls ion transport in pancreatic ducts. Similar to secretin, isoproterenol stimulation leads to opening of luminal Cl- channels, and HCO3- enters the lumen in exchange for Cl-.

Adenosine Triphosphate↗

PubMed1995

Orphenadrine is an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist: binding and patch clamp studies.

Orphenadrine has been used as an antiparkinsonian, antispastic and analgesic drug for many years. Here we show that orphenadrine inhibits [3H]MK-801 binding to the phencyclidine (PCP) binding site of the N-methyl-D-aspartate (NMDA)-receptor in homogenates of postmortem human frontal cortex with a Ki-value of 6.0 +/- 0.7 microM. The NMDA receptor antagonistic effects of orphenadrine were assessed using concentration- and patch-clamp techniques on cultured superior colliculus neurones. Orphenadrine blocked open NMDA receptor channels with fast kinetics and in a strongly voltage-dependent manner. The IC50-value against steady state currents at -70 mV was 16.2 +/- 1.6 microM (n = 6). Orphenadrine exhibited relatively fast, concentration-dependent open channel blocking kinetics (Kon 0.013 +/- 0.002 10(6) M-1S-1) whereas the offset rate was concentration-independent (Koff 0.230 +/- 0.004 S-1). Calculation of the ratio Koff/Kon revealed an apparent Kd-value of 17.2 microM which is nearly identical to the IC50 calculated at equilibrium.

Aged↗

PubMed2001

A patch-clamp study on the physiology of aluminum toxicity and aluminum tolerance in maize. Identification and characterization of Al(3+)-induced anion channels.

The presence of Al(3+) in the rhizosphere induces citrate efflux from the root apex of the Al-tolerant maize (Zea mays) hybrid South American 3, consequently chelating and reducing the activity of toxic Al(3+) at the root surface. Because citrate is released from root apical cells as the deprotonated anion, we used the patch-clamp technique in protoplasts isolated from the terminal 5 mm of the root to study the plasma membrane ion transporters that could be involved in Al-tolerance and Al-toxicity responses. Acidification of the extracellular environment stimulated inward K(+) currents while inhibiting outward K(+) currents. Addition of extracellular Al(3+) inhibited the remaining K(+) outward currents, blocked the K(+) inward current, and caused the activation of an inward Cl(-) current (anion efflux). Studies with excised membrane patches revealed the existence of Al-dependent anion channels, which were highly selective for anions over cations. Our success in activating this channel with extracellular Al(3+) in membrane patches excised prior to any Al(3+) exposure indicates that the machinery required for Al(3+) activation of this channel, and consequently the whole root Al(3+) response, is localized to the root-cell plasma membrane. This Al(3+)-activated anion channel may also be permeable to organic acids, thus mediating the Al-tolerance response (i.e. Al-induced organic acid exudation) observed in intact maize root apices.

Aluminum↗

PubMed1996

Chloride channel properties of the uncoupling protein from brown adipose tissue mitochondria: a patch-clamp study.

The uncoupling protein (UCP) from brown adipose tissue mitochondria possesses H+ and Cl- transport activities [reviewed in Klingenberg, M. (1990) Trends Biochem. Sci. 15, 108-112]. Being a member of a mitochondrial carrier family, the transport of H+ and Cl- is carrier-like, i.e., much slower as compared to channels. Here we report that UCP reconstituted into giant liposomes displays stable chloride channel properties under patch-clamp conditions. The transport inhibitors (GTP, GDP, ATP, and ADP) also inhibit this channel in a reversible way, showing that the channel activity is associated with UCP. The slightly inward-rectifying chloride channel has a unit conductance of approximately 75 pS in symmetrical 100 mM KCl and closes at high positive potentials on the matrix side of UCP. Channel gatings switch from slow open-closure transitions to fast flickerings as the holding potential increases over +60 mV. Substitution experiments reveal a strong discrimination against cations [P(Cl-)/P(K+) approximately 17] and a permeability ratio order of Cl- > Br- > F- > SCN- > I- > NO3- > SO4(2-) > HPO4(2-) > gluconate. Nucleotide inhibition studies indicate that 70% UCP molecules had its matrix side oriented outside in the giant liposomes. Fatty acids, pH, divalent cations (Ca2+ and Mg2+), and mersalyl do not influence these Cl- currents. The Cl- channel can be blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) from the matrix side of UCP. The data are consistent with a dimer consisting of two monomeric 75-pS Cl- channels or with a monomeric 150-pS channel having a 50% subconductance state. The channel current increases with Cl- concentration showing a typical saturation curve with Km approximately 63 mM and gmax approximately 120 pS (100 mM KCl in the pipet). The Cl- conductance measured under these conditions is 6 orders of magnitude higher than the Cl- transport activity reported earlier, suggesting that the UCP has the potential of behaving as an anion channel.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed2004

The human mitochondrial KATP channel is modulated by calcium and nitric oxide: a patch-clamp approach.

ATP-sensitive potassium channels of the inner mitochondrial membrane (mtKATP) are blocked by ATP. They are suggested to be involved in protective mechanisms such as ischemic preconditioning (IPC). Here we identify this channel type for the first time in a human cell line (Jurkat cells). Vesicles of the inner mitochondrial membrane (mitoplasts) were prepared by hypoosmotic shock. Single-channel currents were measured by means of the patch-clamp technique. We identified an outward-rectifying channel with a slope conductance of 15 and 82 pS at negative and positive potentials, respectively. The block by 5-hydroxydecanoic acid and inhibition by ATP characterize this channel as the mtKATP channel. ATP also increased the frequency of events within the burst. This effect was modulated by the Ca2+-bath concentration. We also show that the human mtKATP channel is a direct target for nitric oxide that blocked the channel activity. Although the molecular structure of this channel type is still unknown, its characterization as an outward-rectifying channel and modulation by calcium ions and nitric oxide may help to elucidate its functional significance, which possibly implicates a role in cell survival after IPC.

Adenosine Triphosphate↗

PubMed2002

Melatonin effects on megakaryocyte membrane patch-clamp outward K+ current.

BACKGROUND: This study was carried out to evaluate the influence of melatonin concentration on rat bone marrow megakaryocyte outward K+ current and its implications with regard to platelet production. It is the Authors' view that the greatly extended development of megakaryocyte membrane, together with its ion channels, makes the choice of this topic particularly pertinent. MATERIAL/METHODS: Megakaryocytes from fresh Wistar rat bone marrow were clampaged with patch-clamp technique and the examination of membrane outward current was performed when melatonin dissolved in external or internal standard solution was used. RESULTS: On the basis of this study, melatonin does reduce outward K+ current intensity, the more the higher the melatonin concentration. In quantitative terms, whereas no change is noticed when dissolved melatonin concentration in external standard solution is smaller than 25 mM, at 50 mM only a delayed outward current decrease appears. The effect on the outward current intensity is reversible at least until melatonin concentration reaches 500 mM; when melatonin concentration is higher than 1000 mM the effect is demonstrably irreversible. The presence on the megakaryocyte membrane of internal standard melatonin solution does reduce the outward current even more sharply. CONCLUSIONS: There seems to be a positive correlation between cationic pump and megakaryocyte intimate processes of platelet production.

Animals↗

PubMed2002

Effect of magnetic field exposure on calcium channel currents using patch clamp technique.

Calcium influxes through the membrane of PC-12D cells were measured under exposure to DC biased AC magnetic fields in resonant conditions of the ion cyclotron and the ion parametric resonance hypotheses and compared with influxes in cells without exposure to the magnetic field. After cancellation of the geomagnetic field, the cells were exposed to the horizontal fields generated by a current sheet, a planar sheet of conductor which generated a satisfactorily homogeneous horizontal magnetic field on the stage of a microscope without hindering treatment of a cell under observation. At or near any resonant conditions, no change in calcium influx could be detected under standard patch clamp conditions.

Animals↗

PubMed1995

Use of Saccharomyces cerevisiae for patch-clamp analysis of heterologous membrane proteins: characterization of Kat1, an inward-rectifying K+ channel from Arabidopsis thaliana, and comparison with endogeneous yeast channels and carriers.

Transport-deficient strains of the yeast Saccharomyces cerevisiae have recently proven useful for cloning, by functional complementation, of cDNAs encoding heterologous membrane transporters: specifically, H(+)-amino acid symporters and K+ channels from the higher plant Arabidopsis thaliana. The present study uses whole-cell patch-clamp experiments to show that yeast strains which grow poorly on submillimolar K+ due to the deletion of two K(+)-transporter genes (TRK1 and TRK2) are in fact missing a prominent K+ inward current present in wild-type cells. Rescue of such strains for growth on low K+ by transformation with a gene (KAT1) encoding an inward-rectifying K+ channel from Arabidopsis is accompanied by the appearance of an inward current whose characteristics are in qualitative agreement with previous studies in the Xenopus oocyte system, but differ in quantitative details. The ability to make such measurements directly on Saccharomyces should facilitate structure-function studies of any electrogenic or electrophoretic ion transporters which can be expressed in the plasma membrane (or tonoplast) of that organism.

Animals↗

PubMed2006

Double patch clamp reveals that transient fusion (kiss-and-run) is a major mechanism of secretion in calf adrenal chromaffin cells: high calcium shifts the mechanism from kiss-and-run to complete fusion.

Transient fusion ("kiss-and-run") is accepted as a mode of transmitter release both in central neurons and neuroendocrine cells, but the prevalence of this mechanism compared with full fusion is still in doubt. Using a novel double patch-clamp method (whole cell/cell attached), permitting the recording of unitary capacitance events while stimulating under a variety of conditions including action potentials, we show that transient fusion is the predominant (>90%) mode of secretion in calf adrenal chromaffin cells. Raising intracellular Ca2+ concentration ([Ca]i) from 10 to 200 microM increases the incidence of full fusion events at the expense of transient fusion. Blocking rapid endocytosis that normally terminates transient fusion events also promotes full fusion events. Thus, [Ca]i controls the transition between transient and full fusion, each of which is coupled to different modes of endocytosis.

Action Potentials↗

PubMed2004

An improved method for acute isolation of neurons from the hippocampus of adult rats suitable for patch-clamping study.

An improved method is described for fast and reliable isolation of neurons from hippocampus of adult rats by a combination of mechanical and enzymatic means. The procedure allows the isolation of neurons from 500-600-d-old rats (over 300 g), preserving the proximal dendritic structure without impairing the electrical characteristics of the cells. Morphologically distinct neurons can be recognized. Using cell-attached, inside-out and whole-cell configurations of patch clamp technique, it was shown that the enzymatically isolated neurons in hippocampus from rats weighing more than 300 g exhibited voltage-gated calcium, sodium and potassium currents, outwardly rectifying chloride channel and large conductance Ca(2+)-activated potassium channel currents. Approximately, 95% of healthy cells allowed the formation of giga-ohm seals.

Animals↗

PubMed2003

The effects of nicotinic and muscarinic receptor activation on patch-clamped cells in the optic tectum of Rana pipiens.

Both nicotinic and muscarinic cholinergic receptors are present in the optic tectum. To begin to understand how the activation of these receptors affects visual activity patterns, we have determined the types of physiological responses induced by their activation. Using tectal brain slices from the leopard frog, we found that application of nicotine (100 microM) evoked long-lasting responses in 60% of patch-clamped tectal cells. Thirty percent of these responses consisted of an increase in spontaneous postsynaptic currents (sPSCs) and had both a glutamatergic and GABAergic component as determined by the use of 6-cyano-7-nitroquinoxaline-2,3-dione (50 microM) and bicuculline (25 microM), respectively. Remaining response types consisted of an inward membrane current (16%) and an increase in sPSCs combined with an inward membrane current (14%). All responses could be elicited in the presence of tetrodotoxin (0.5 microM). Muscarinic receptor-mediated responses, induced by carbachol (100 microM) application after nicotinic receptor desensitization, produced responses in 70% of tectal cells. In contrast to responses elicited by nicotine, carbachol-induced responses could be evoked multiple times without significant decrement. Responses consisted of either an outward current (57%), a decrease in sPSCs (5%) or an increase in sPSCs, with (almost 6%) or without (almost 3%) an outward current. The response elicited by carbachol was not predicted by the response of the cell to nicotine. Our results suggest that nicotinic receptors are found predominantly at presynaptic locations in the optic tectum while muscarinic receptors are most often present at postsynaptic sites. We conclude that both of these receptor types could substantially modulate visual activity by changing either the input to tectal neurons or the level of their response to that input.

Acetylcholine↗