Cholinergic neurotransmission from mechanosensory afferents to giant interneurons in the terminal abdominal ganglion of the cricket Gryllus bimaculatus

Crickets respond to air currents with quick avoidance behavior. The terminal abdominal ganglion (TAG) has a neuronal circuit for a wind-detection system to elicit this behavior. We investigated neuronal transmission from cercal sensory afferent neurons to ascending giant interneurons (GIs). Pharmacological treatment with 500 muM acetylcholine (ACh) increased neuronal activities of ascending interneurons with cell bodies located in the TAG. The effects of ACh antagonists on the activities of identified GIs were examined. The muscarinic ACh antagonist atropine at 3-mM concentration had no obvious effect on the activities of GIs 10-3, 10-2, or 9-3. On the other hand, a 3-mM concentration of the nicotinic ACh antagonist mecamylamine decreased spike firing of these interneurons. Immunohistochemistry using a polyclonal anti-conjugated acetylcholine antibody revealed the distribution of cholinergic neurons in the TAG. The cercal sensory afferent neurons running through the cercal nerve root showed cholinergic immunoreactivity, and the cholinergic immunoreactive region in the neuropil overlapped with the terminal arborizations of the cercal sensory afferent neurons. Cell bodies in the median region of the TAG also showed cholinergic immunoreactivity. This indicates that not only sensory afferent neurons but also other neurons that have cell bodies in the TAG could use ACh as a neurotransmitter.     

Gain modulation by nicotine in macaque v1

Acetylcholine is a ubiquitous cortical neuromodulator implicated in cognition. In order to understand the potential for acetylcholine to play a role in visual attention, we studied nicotinic acetylcholine receptor (nAChR) localization and function in area V1 of the macaque. We found nAChRs presynaptically at thalamic synapses onto excitatory, but not inhibitory, neurons in the primary thalamorecipient layer 4c. Furthermore, consistent with the release enhancement suggested by this localization, we discovered that nicotine increases responsiveness and lowers contrast threshold in layer 4c neurons. We also found that nAChRs are expressed by GABAergic interneurons in V1 but rarely by pyramidal neurons, and that nicotine suppresses visual responses outside layer 4c. All sensory systems incorporate gain control mechanisms, or processes which dynamically alter input/output relationships. We demonstrate that at the site of thalamic input to visual cortex, the effect of this nAChR-mediated gain is an enhancement of the detection of visual stimuli.     

Ubiquilin-1 regulates nicotine-induced up-regulation of neuronal nicotinic acetylcholine receptors

Chronic exposure to nicotine, as in tobacco smoking, up-regulates nicotinic acetylcholine receptor surface expression in neurons. This up-regulation has been proposed to play a role in nicotine addiction and withdrawal. The regulatory mechanisms behind nicotine-induced up-regulation of surface nicotinic acetylcholine receptors remain to be determined. It has recently been suggested that nicotine stimulation acts through increased assembly and maturation of receptor subunits into functional pentameric receptors. Studies of muscle nicotinic acetylcholine receptors suggest that the availability of unassembled subunits in the endoplasmic reticulum can be regulated by the ubiquitin-proteosome pathway, resulting in altered surface expression. Here, we describe a role for ubiquilin-1, a ubiquitin-like protein with the capacity to interact with both the proteosome and ubiquitin ligases, in regulating nicotine-induced up-regulation of neuronal nicotinic acetylcholine receptors. Ubiquilin-1 interacts with unassembled alpha3 and alpha4 subunits when coexpressed in heterologous cells and interacts with endogenous nicotinic acetylcholine receptors in neurons. Coexpression of ubiquilin-1 and neuronal nicotinic acetylcholine receptors in heterologous cells dramatically reduces the expression of the receptors on the cell surface. In cultured superior cervical ganglion neurons, expression of ubiquilin-1 abolishes nicotine-induced up-regulation of nicotinic acetylcholine receptors but has no effect on the basal level of surface receptors. Coimmunostaining shows that the interaction of ubiquilin-1 with the alpha3 subunit draws the receptor subunit and proteosome into a complex. These data suggest that ubiquilin-1 limits the availability of unassembled nicotinic acetylcholine receptor subunits in neurons by drawing them to the proteosome, thus regulating nicotine-induced up-regulation.     

Cholinergic interneuron characteristics and nicotinic properties in the striatum

The neostriatum (dorsal striatum) is composed of the caudate and putamen. The ventral striatum is the ventral conjunction of the caudate and putamen that merges into and includes the nucleus accumbens and striatal portions of the olfactory tubercle. About 2% of the striatal neurons are cholinergic. Most cholinergic neurons in the central nervous system make diffuse projections that sparsely innervate relatively broad areas. In the striatum, however, the cholinergic neurons are interneurons that provide very dense local innervation. The cholinergic interneurons provide an ongoing acetylcholine (ACh) signal by firing action potentials tonically at about 5 Hz. A high concentration of acetylcholinesterase in the striatum rapidly terminates the ACh signal, and thereby minimizes desensitization of nicotinic acetylcholine receptors. Among the many muscarinic and nicotinic striatal mechanisms, the ongoing nicotinic activity potently enhances dopamine release. This process is among those in the striatum that link the two extensive and dense local arbors of the cholinergic interneurons and dopaminergic afferent fibers. During a conditioned motor task, cholinergic interneurons respond with a pause in their tonic firing. It is reasonable to hypothesize that this pause in the cholinergic activity alters action potential dependent dopamine release. The correlated response of these two broad and dense neurotransmitter systems helps to coordinate the output of the striatum, and is likely to be an important process in sensorimotor planning and learning.     

Timing and location of nicotinic activity enhances or depresses hippocampal synaptic plasticity

This study reveals mechanisms in the mouse hippocampus that may underlie nicotinic influences on attention, memory, and cognition. Induction of synaptic plasticity, arising via generally accepted mechanisms, is modulated by nicotinic acetylcholine receptors. Properly timed nicotinic activity at pyramidal neurons boosted the induction of long-term potentiation via presynaptic and postsynaptic pathways. On the other hand, nicotinic activity on interneurons inhibited nearby pyramidal neurons and thereby prevented or diminished the induction of synaptic potentiation. The synaptic modulation was dependent on the location and timing of the nicotinic activity. Loss of these synaptic mechanisms may contribute to the cognitive deficits experienced during Alzheimer's diseases, which is associated with a loss of cholinergic projections and with a decrease in the number of nicotinic receptors.     

A Novel Agonist Binding Site on Nicotinic Acetylcholine Receptors

Abstract

This report provides evidence that physostigmine (Phy) and benzoquinonium (BZQ) are able to activate nicotinic acetylcholine receptors (nAChRs) through binding site(s) distinct from those of the natural transmitter, ACh. Such findings are in agreement with a second pathway of activation of nAChRs. Receptor activation may be modulated through the novel site, and, consequently, physiological processes involving nicotinic synapses could be controlled. Using patch clamp techniques, single channel currents activated by ACh and anatoxin were recorded from frog interosseal muscle fibers under cell-attached condition and outside-out patches excised from cultured rat hippocampal neurons. Whole cell nicotinic currents were also studied in the cultured neurons. In most of the neurons, nicotinic responses were blocked by the nicotinic antagonists methyllycaconitine (MLA) and α-bungarotoxin (α-BGT). Evaluation of the effects of Phy and BZQ on the muscle and on the α-BGT- and MLA-sensitive neuronal nAChRs demonstrated that both compounds were open channel blockers at these receptors. Furthermore, at low micromolar concentrations, Phy and BZQ activated the nAChRs of all preparations tested, such an effect being unexpectedly resistant to α-BGT or MLA. Thus, the nAChRs could be activated via two distinct binding sites: one for ACh and the other for Phy and BZQ. These findings and previous biochemical results led us to suggest that a putative endogenous ligand could bind to the new site and thereby regulate the activation of nAChRs in nicotinic synapses.     

Immunolocalization of laminin-alpha1-like antigens around synapses in mouse cerebellar perineuronal nets

The hypothesis that extracellular matrix components may be related to neuronal development in the mouse cerebellar cortex was verified with immunohistochemistry by using an antibody against laminin-alpha1, a major extracellular matrix protein in various tissues. A commercially available polyclonal antibody, raised against the carboxyl-terminal 20-amino acid peptide of laminin-alpha1 was used. Some positive immunoreaction products were localized around large GABAergic interneurons in granular layers and others were around neurons in deep cerebellar nuclei. At the electron microscope level, diaminobenzidine immunoreaction products were localized around presynaptic boutons and in intercellular matrices around interneurons. Such immunoreaction products could be detected at postnatal day 20, when most of cerebellar synapses are assumed to be established. It has been known that a special feature of extracellular matrix, termed perineuronal nets, exists around specific subpopulation of neurons. In the mouse cerebellum, the present findings suggest that laminin itself or laminin-like-antigens exists in the perineuronal nets in relation to inhibitory neuron synapses.     

Studies on rat sympathetic neurons developing in cell culture. III. Cholinergic transmission.

Principal neurons were dissociated from the superior cervical ganglia of newborn rats and grown in culture with several types of non-neuronal cells. As described in the second paper of this series, the neurons in such mixed cultures formed two types of excitatory synapses with each other, electrical and chemical. Evidence is presented here that transmission at the chemical synapses was cholinergic. Four nicotinic ganglionic blocking agents (curare, hexamethonium, tetraethylammonium, and mecamylamine) strongly attenuated or eliminated the excitatory postsynaptic potentials (e.p.s.p.'s) at moderate concentrations; atropine at relatively high concentrations also blocked transmission. Iontophoretic application of acetylcholine (ACh) to the surface of the neurons gave rise to depolarizations that could be made to resemble the e.p.s.p.'s in size and time course; the ACh potentials and the e.p.s.p.'s were then similarly affected by nicotinic blocking agents. The sensitivity to ACh was often distributed nonuniformly on the neuronal surface; it was common to find small, sharply localized regions of high sensitivity. Catecholamines (norepinephrine, epinephrine, and dopamine) had only inhibitory actions; in a few experiments adrenergic blocking agents (phenoxybenzamine, propranolol) were found to have no effect on the e.p.s.p.'s. These observations leave no doubt that the neurons released ACh and had ganglionic, nicotinic ACh receptors on their surfaces. The significance of the fact that a high proportion of the sympathetic neurons in mixed cultures formed cholinergic synapses is discussed.     

Immunolocalization of laminin-α1-like antigens around synapses in mouse cerebellar perineuronal nets

The hypothesis that extracellular matrix components may be related to neuronal development in the mouse cerebellar cortex was verified with immunohistochemistry by using an antibody against laminin-α1, a major extracellular matrix protein in various tissues. A commercially available polyclonal antibody, raised against the carboxyl-terminal 20-amino acid peptide of laminin-α1 was used. Some positive immunoreaction products were localized around large GABAergic interneurons in granular layers and others were around neurons in deep cerebellar nuclei. At the electron microscope level, diaminobenzidine immunoreaction products were localized around presynaptic boutons and in intercellular matrices around interneurons. Such immunoreaction products could be detected at postnatal day 20, when most of cerebellar synapses are assumed to be established. It has been known that a special feature of extracellular matrix, termed perineuronal nets, exists around specific subpopulation of neurons. In the mouse cerebellum, the present findings suggest that laminin itself or laminin-like-antigens exists in the perineuronal nets in relation to inhibitory neuron synapses.     

Target-Dependent Regulation of Retinal Nicotinic Acetylcholine Receptor and Tubulin RNAs During Optic Nerve Regeneration in Goldfish

A fundamental issue in central nervous system development regards the effect of target tissue on the differentiation of innervating neurons. We address this issue by characterizing the role the retinal ganglion cell target, i.e., the optic tectum, plays in regulating expression of tubulin and nicotinic acetylcholine receptor genes in regenerating retinal ganglion cells. Tubulins are involved in axonal growth, whereas nicotinic acetylcholine receptors mediate communication across synapses. Retinal ganglion cell axons were induced to regenerate by crushing the optic nerve. Following crush, there was a rapid increase in alpha-tubulin RNAs (3 days), which preceded the increase in nicotinic acetylcholine receptor RNAs (10-15 days). Both classes of RNAs approached control levels by the time retinotectal synapses and functional recovery were restored (4-6 weeks). If the optic nerve was repeatedly crushed or its target ablated, tubulin RNAs remained elevated, and the increase in receptor RNAs that would otherwise be seen 2 weeks after a single nerve crush did not occur. The interaction of retinal ganglion cell axons with their targets in the optic tectum appears, then, to exert a suppressive effect on the RNA encoding a cytoskeletal protein, tubulin, and an inductive effect on RNAs encoding nicotinic acetylcholine receptors involved in synaptic communication.     

Heartbeat control in the medicinal leech: A model system for understanding the origin,coordination, and modulation of rhythmic motor patterns

We have analyzed in detail the neuronal network that generates heartbeat in the leech. Reciprocally inhibitory pairs of heart interneurons form oscillators that pace the heartbeat rhythm. Other heart interneurons coordinate these oscillators. These coordinating interneurons, along with the oscillator interneurons, form an eight-cell timing oscillator network for heartbeat. Still other interneurons, along with the oscillator interneurons, inhibit heart motor neurons, sculpting their activity into rhythmic bursts. Critical switch interneurons interface between the oscillator interneurons and the other premotor interneurons to produce two alternating coordination states of the motor neurons. The periods of the oscillator interneurons are modulated by endogenous RFamide neuropeptides. We have explored the ionic currents and graded and spike-mediated synaptic transmission that promote oscillation in the oscillator interneurons and have incorporated these data into a conductance-based computer model. This model has been of considerable predictive value and has led to new insights into how reciprocally inhibitory neurons produce oscillation. We are now in a strong position to expand this model upward, to encompass the entire heartbeat network, horizontally, to elucidate the mechanisms of FMRFamide modulation, and downward, to incorporate cellular morphology. By studying the mechanisms of motor pattern formation in the leech, using modeling studies in conjunction with parallel physiological experiments, we can contribute to a deeper understanding of how rhythmic motor acts are generated, coordinated, modulated, and reconfigured at the level of networks, cells, ionic currents, and synapses. © 1995 John Wiley & Sons, Inc.     

Single Particle Tracking of α7 Nicotinic AChR in Hippocampal Neurons Reveals Regulated Confinement at Glutamatergic and GABAergic Perisynaptic Sites

α7 neuronal nicotinic acetylcholine receptors (α7-nAChR) form Ca²⁺-permeable homopentameric channels modulating cortical network activity and cognitive processing. They are located pre- and postsynaptically and are highly abundant in hippocampal GABAergic interneurons. It is unclear how α7-nAChRs are positioned in specific membrane microdomains, particularly in cultured neurons which are devoid of cholinergic synapses. To address this issue, we monitored by single particle tracking the lateral mobility of individual α7-nAChRs labeled with α-bungarotoxin linked to quantum dots in live rat cultured hippocampal interneurons. Quantitative analysis revealed different modes of lateral diffusion of α7-nAChR dependent on their subcellular localization. Confined receptors were found in the immediate vicinity of glutamatergic and GABAergic postsynaptic densities, as well as in extrasynaptic clusters of α-bungarotoxin labeling on dendrites. α7-nAChRs avoided entering postsynaptic densities, but exhibited reduced mobility and long dwell times at perisynaptic locations, indicative of regulated confinement. Their diffusion coefficient was lower, on average, at glutamatergic than at GABAergic perisynaptic sites, suggesting differential, synapse-specific tethering mechanisms. Disruption of the cytoskeleton affected α7-nAChR mobility and cell surface expression, but not their ability to form clusters. Finally, using tetrodotoxin to silence network activity, as well as exposure to a selective α7-nAChR agonist or antagonist, we observed that α7-nAChRs cell surface dynamics is modulated by chronic changes in neuronal activity. Altogether, given their high Ca²⁺-permeability, our results suggest a possible role of α7-nAChR on interneurons for activating Ca²⁺-dependent signaling in the vicinity of GABAergic and glutamatergic synapses.     

Rabies virus binding to an acetylcholine receptor alpha-subunit peptide

The binding of 125I-labeled rabies virus to a synthetic peptide comprising residues 173-204 of the alpha 1-subunit of the nicotinic acetylcholine receptor was investigated. Binding of rabies virus to the receptor peptide was dependent on pH, could be competed with by unlabeled homologous virus particles, and was saturable. Synthetic peptides of snake venom, curaremimetic neurotoxins and of the structurally similar segment of the rabies virus glycoprotein, were effective in competing with labeled virus binding to the receptor peptide at micromolar concentrations. Similarly, synthetic peptides of the binding domain on the acetylcholine receptor competed for binding. These findings suggest that both rabies virus and neurotoxins bind to residues 173-204 of the alpha 1-subunit of the acetylcholine receptor. Competition studies with shorter alpha-subunit peptides within this region indicate that the highest affinity virus binding determinants are located within residues 179-192. A rat nerve alpha 3-subunit peptide, that does not bind alpha-bungarotoxin, inhibited binding of virus to the alpha 1 peptide, suggesting that rabies binds to neuronal nicotinic acetylcholine receptors. These studies indicate that synthetic peptides of the glycoprotein binding domain and of the receptor binding domain may represent useful antiviral agents by targeting the recognition event between the viral attachment protein and the host cell receptor, and inhibiting attachment of virus to the receptor.     

Alcohol is a potent stimulant of immature neuronal networks: implications for fetal alcohol spectrum disorder

Ethanol consumption during development affects the maturation of hippocampal circuits by mechanisms that are not fully understood. Ethanol acts as a depressant in the mature CNS and it has been assumed that this also applies to immature neurons. We investigated whether ethanol targets the neuronal network activity that is involved in the refinement of developing hippocampal synapses. This activity appears during the growth spurt period in the form of giant depolarizing potentials (GDPs). GDPs are generated by the excitatory actions of GABA and glutamate via a positive feedback circuit involving pyramidal neurons and interneurons. We found that ethanol potently increases GDP frequency in the CA3 hippocampal region of slices from neonatal rats. It also increased the frequency of GDP-driven Ca2+ transients in pyramidal neurons and increased the frequency of GABA(A) receptor-mediated spontaneous postsynaptic currents in CA3 pyramidal cells and interneurons. The ethanol-induced potentiation of GABAergic activity is probably the result of increased quantal GABA release at interneuronal synapses but not enhanced neuronal excitability. These findings demonstrate that ethanol is a potent stimulant of developing neuronal circuits, which might contribute to the abnormal hippocampal development associated with fetal alcohol syndrome and alcohol-related neurodevelopmental disorders.     

Postural interneurons in the abdominal nervous system of lobster

Using intracellular recording and dye-filling techniques, a survey of postural interneurons was undertaken by impaling their somata in the 2nd abdominal ganglion of lobster. During the course of study approximately fourty different intersegmental interneurons in this ganglion were sampled. Of these, 8 evoked unique, patterned responses in the postural (superficial) motoneurons; each could be identified morphologically. Five of the 8 interneurons had caudally directed axons; 4 of these projected beyond the 4th abdominal ganglion. The remainder projected rostrally, beyond the 1st abdominal ganglion. The postural interneurons were classified according to the motor program they elicited. Five were flexion producing interneurons (FPIs), one was extension producing (EPI), and two generated only inhibitory motor outputs. All motor responses were bilateral and occurred in several segments, including A2. Two neurons, FPIs 201 and 301, produced the full motor reciprocity that typically is observed when flexion command fibers are stimulated. However, three of the FPIs and the single EPI did not express complete reciprocity in synergistic and antagonistic motoneurons. The results indicate that some interneurons displaying all of the properties of command neurons are located entirely within the abdominal nervous system. The overall organization of posture-evoking interneurons appears to be similar to that found in crayfish, suggesting an even more fundamental homology in the neuronal connectivities of these two species than has been established previously.     

Evidence that synaptic transmission between giant interneurons and identified thoracic interneurons in the cockroach is cholinergic.

In the cockroach, a population of thoracic interneurons (TIs) receives direct inputs from a population of ventral giant interneurons (vGIs). Synaptic potentials in type-A TIs (TIAs) follow vGI action potentials with constant, short latencies at frequencies up to 200 Hz. These connections are important in the integration of directional wind information involved in determining an oriented escape response. The physiological and biochemical properties of these connections that underlie this decision-making process were examined. Injection of hyperpolarizing or depolarizing current into the postsynaptic TIAs resulted in alterations in the amplitude of the post-synaptic potential (PSP) appropriate for a chemical connection. In addition, bathing cells in zero-calcium, high-magnesium saline resulted in a gradual decrement of the PSP, and ultimately blocked synaptic transmission, reversibly. Single-cell choline acetyltransferase (ChAT) assays of vGI somata were performed. These assays indicated that the vGIs can synthesize acetylcholine. Furthermore, the pharmacological specificity of transmission at the vGI to TIA connections was similar to that previously reported for nicotinic, cholinergic synapses in insects, suggesting that the transmitter released by vGIs at these synapses is acetylcholine.     

Co-Expression of Glutamic Acid Decarboxylase Isoform 67, Membrane Nicotinic Acetylcholine Receptors,and Connexin 36 in Ischemia-Resistant Hippocampal Interneurons

As is known, hippocampal pyramidal neurons are highly sensitive to cerebral ischemia, while some other hippocampal neurons (particularly, interneurons) survive and keep their functional activity under these conditions for a longer time. We studied interneurons of the rat hippocampal organotypic culture after 30-min-long oxygen-glucose deprivation (OGD) using immunohistochemical approaches. Four and 24 h after OGD, the somata of interneurons with no signs of degeneration (revealed by propidium iodide, PI, staining) were immunopositive to antibodies against glutamic acid decarboxylase isoform 67 (GAD67) and to an extracellular domain of a7 nicotinic acetylcholine receptor (nAChR) but negative with respect to choline acetyltransferase (ChAT). GAD67/nAChR-positive interneurons were abundant within all layers of the hippocampal CA1-CA4 zones and also in the dentate gyrus. Co-localized GAD67/nAChR immunopositivity was also observed on numerous punctuate terminals close to the somata of pyramidal neurons stained by PI. After OGD followed by incubation with a blocker of gap junctions, carbenoxolone, only single PI-stained units were revealed in the pyramidal layer. In experiments with connexin 36 cyan fluorescent protein (Cx36-CFP) on gene-reporter mice, we have found that the combination of GAD67/nAChR immunopositivity and ChAT negativity in the hippocampus is specific for the interneuronal somata expressing Cx36-CFP, a component of electrotonic gap contacts in the neuronal networks. Our results indicate that OGD-resistant hippocampal interneurons display co-localization of GAD67, a7 nAChR, and Cx36-CFP. By these neurochemical features, OGD-resistant neurons can be classified as inhibitory GABA-ergic acetylcholine-sensitive interneurons able to couple electrotonically with other hippocampal units through Cx36-CFP-containing gap junctions. The existence of hippocampal interneurons coexpressing the above factors shows that further investigations towards elucidation of cooperative endogenic mechanisms responsible for cerebral neuroresistance are expedient.     

Neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes have a pentameric quaternary structure

We have determined the subunit stoichiometry of chicken neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes by quantitation of the amount of radioactivity in individual subunits of [35S] methionine-labeled receptors. The chicken neuronal nicotinic acetylcholine receptor appears to be a pentamer of two alpha 4 acetylcholine-binding subunits and three beta 2 structural subunits. We also show that these expressed receptors bind L-[3H]nicotine with high affinity, are transported to the surface of the oocyte outer membrane, and cosediment on sucrose gradients with acetylcholine receptors isolated from chicken brain. Using this unique and generally applicable method of determining subunit stoichiometry of receptors expressed in oocytes, we obtained the expected (alpha 1) 2 beta 1 gamma delta stoichiometry for muscle-type acetylcholine receptors assembled from coexpression of either Torpedo alpha 1 or human alpha 1 subunits, with Torpedo beta 1, gamma, and delta subunits.     

Purification and characterization of a nicotinic acetylcholine receptor from chick brain

Immunohistochemical studies have previously shown that both the chick brain and chick ciliary ganglion neurons contain a component which shares antigenic determinants with the main immunogenic region of the nicotinic acetylcholine receptor from electric organ and skeletal muscle. Here we describe the purification and initial characterization of this putative neuronal acetylcholine receptor. The component was purified by monoclonal antibody affinity chromatography. The solubilized component sediments on sucrose gradients as a species slightly larger than Torpedo acetylcholine receptor monomers. It was affinity labeled with bromo[3H]acetylcholine. Labeling was prevented by carbachol, but not by alpha-bungarotoxin. Two subunits could be detected in the affinity-purified component, apparent molecular weights 48 000 and 59 000. The 48 000 molecular weight subunit was bound both by a monoclonal antibody directed against the main immunogenic region of electric organ and skeletal muscle acetylcholine receptor and by antisera raised against the alpha subunit of Torpedo receptor. Evidence suggests that there are two alpha subunits in the brain component. Antisera from rats immunized with the purified brain component exhibited little or no cross-reactivity with Torpedo electric organ or chick muscle acetylcholine receptor. One antiserum did, however, specifically bind to all four subunits of Torpedo receptor. Experiments to be described elsewhere (J. Stollberg et al., unpublished results) show that antisera to the purified brain component specifically inhibit the electrophysiological function of acetylcholine receptors in chick ciliary ganglion neurons without inhibiting the function of acetylcholine receptors in chick muscle cells. All of these properties suggest that this component is a neuronal nicotinic acetylcholine receptor with limited structural homology to muscle nicotinic acetylcholine receptor.     

The physiological action of analogues of philanthotoxin-4.3.3 at insect nicotinic acetylcholine receptors

1. The blocking action of δ-philanthotoxin (PhTX-4.3.3), a polyamine amide wasp toxin, and 33 structural analogues was studied at the nicotinic acetylcholine receptor of isolated neuronal somata from locust thoracic ganglia and at the cockroach cercal nerve-giant interneuron nicotinic cholinergic synapse.2. A comparison of the structure-activity relationships reported here for the locust somal and cockroach synaptic nicotinic receptors and for the glutamatergic neuromuscular synapses of housefly larvae reported previously suggests a generally similar pharmacology for the channel-blocking action at ligand-activated ion channels, but with differences that might be due to variation in accessibility between synaptic receptors and those on the neuronal somata or to genuine divergence in ligand-activated ion channel pharmacology.