Nicotinic depolarization activates calcium dependent gK in myenteric neurons

Intracellular recordings were made from S type neurons in the myenteric plexus of the guinea-pig ileum. Acetylcholine (ACh) was applied directly onto the soma membrane by iontophoresis with visual placement of the iontophoretic pipette. Fast nicotinic depolarizations were evoked which were followed by slow muscarinic depolarizations. After application of hyoscine to block the slow muscarinic depolarization, the nicotinic depolarization was found to be followed by a hyperpolarization. This hyperpolarization was several mV in amplitude and 1-5 s in total duration. It disappeared when the preceding nicotinic depolarization was blocked by hexamethonium. The ACh induced by hyperpolarization was due to calcium entry and subsequent opening of potassium channels.     

Facilitation of cholinergic transmission by substance P methyl ester in the mouse hippocampal slice preparation

Using sharp microelectrode recording from CA1 pyramidal neurons of the adult mouse hippocampal slice preparation, we studied the modulatory action of the selective neurokinin 1 (NK1) receptor agonist substance P methyl ester (SPME), a peptidase-resistant analogue of the peptide substance P (SP), on cholinergic responses. While SPME (0.1-1 microM) had only slight effects on membrane potential and input resistance of CA1 neurons, it largely and reversibly enhanced the membrane depolarization and oscillatory activity induced by the cholinergic agonist carbachol (CCh; 0.1-100 microM). This effect of SPME was prevented by the selective NK1 receptor antagonist SR 140333 (4 microM). In about half of the tested neurons the action of SPME was preserved in tetrodotoxin (TTX) solution, suggesting that it partly occurred at the level of pyramidal cells. Cholinergic slow excitatory postsynaptic potentials (sEPSPs) were reversibly enhanced by SPME which increased their amplitude and prolonged any associated bursting activity. This action was also blocked by SR 140333. The present results suggest that SPME largely enhances cholinergic activity in the mouse hippocampus, an effect which can help to explain, in this brain area, the recently reported facilitation of seizures by SP.     

Involvement of prolactin, vasopressin and opioids in post-ictal antinociception induced by electroshock in rats

The local and endogenous nicotinic neuronal transmissions of dopaminergic neurons in the substantia nigra were confirmed electrophysiologically using a slice-patch technique. After identifying dopaminergic neurons based on their electrophysiological characteristics, miniature postsynaptic inward currents were recorded in the presence of atropine (a muscarinic acetylcholine receptor antagonist), bicuculline (a GABA receptor antagonist) and L-glutamic acid diethyl ester (GDEE) (a non-selective glutamate receptor antagonist). Under conditions that eliminated muscarinic, GABAergic and glutamatergic synaptic transmissions, we found miniature currents that were inhibited by the specific neuronal nicotinic receptor antagonists, dihydro-beta-erythroidine (DHbetaE) and/or methyllycaconitine (MLA) (selective alpha4beta2 and/or alpha7 nicotinic acetylcholine receptor antagonists, respectively). Under the same extracellular conditions, local stimulations in the vicinity of a target neuron evoked excitatory postsynaptic inward currents (EPSCs). These EPSCs were elicited in an extracellular Ca(2+) dependent manner and were also blocked by DHbetaE and/or MLA. These results suggest that dopaminergic neurons in the substantia nigra receive excitatory cholinergic inputs that are mediated via at least two types of postsynaptic nicotinic receptors, namely alpha7 and alpha4beta2 subtypes.     

大鼠大脑皮质神经元一种新型去极化电位

５—ＨＴ灌流大鼠脑片并刺激丘脑内髓板时，２４．３％的大脑皮质额叶后部Ⅳ层神经元出现一种阵发性的潜伏期长、幅度大的会极化电位（Ｌａｒｇｅｄｅｐｏｌａｒｉｚａｔｉｏｎｐｏｔｅｎｔｉａｌ，ＬＤＰ）。５－ＨＴ１Ｂ激动剂ＴＦＭＰＰ、ＧＡＢＡＡ拮抗剂ｂｉｃｕｃｕｌｌｉｎｅ灌流并刺激内髓板时，也有类似诱发效应、ＬＤＰ伴膜电阻降低，随胞膜超极化而幅度增大，去极化而减小，其平衡电位近似钠平衡电位。ＬＤＰ为５－ＨＴ１拮抗剂Ｍｅｔｈｉｏｔｈｅｐｉｎ所抑制，几乎不受５－ＴＨ１ｃ／２、５—ＨＴ。拮抗剂Ｋｅｔａｎｓｅｒｉｎｅ、ＭＤＬ—７２２２２以及ＮＭＤＡ、非ＮＭＤＡ拮抗剂ＡＰＶ、ＤＮＱＸ所影响。提示ＬＤＰ可能与钠内流有关，是一种不同于已知突触电位的新发现电位，可能与丘脑－皮质非特异投射有关。     

Acetylcholine causes nicotinic depolarization in rat dorsal motor nucleus of the vagus, in vitro

Action of acetylcholine (ACh) on the electrophysiologically identified preganglionic neurons in the dorsal motor nucleus of the vagus (DMV) were investigated in slice preparations of rat medulla oblongata by using conventional intracellular recording technique. Applications of ACh to the DMV neurons resulted in a marked depolarization, which was not abolished in Ca-free superfusing solution, indicating the direct action of ACh on the cells. This depolarization was associated with an increase in membrane conductance and markedly reduced in the Na-free superfusate. The extrapolated reversal potential of ACh response was about -35 mV, indicating that both sodium and potassium conductances are likely responsible for the ACh depolarization. Application of nicotine caused similar depolarization to that of ACh, while muscarinic agonists (muscarine and oxotremorine) did not have any effect. Additions of the nicotinic antagonists hexamethonium and D-tubocurarine to the bathing solution reversibly attenuated the ACh-induced depolarization, while the muscarinic antagonist atropine did not have any effect. The nicotinic properties of ACh action in the DMV neurons presented here form a striking contrast to previous autoradiographic findings. Though endogenous cholinergic inputs to the DMV have not been identified, ACh may have a strong influence on vagal control by depolarization through nicotinic receptors of the DMV preganglionic neurons.     

Intracellular recordings from lateral horn cells fo the spinal cord in vitro

Intracellular recording was used in studies of the preganglionic neurons of the autonomic nervous system. These were carried out on isolated segments of the cat spinal cord. It was found that the lateral horn cells have electrical membrane characteristics similar to postganglionic neurons, but many of them have a much longer afterhyperpolarization. 5-Hydroxytryptamine, noradrenaline and aspartate induce depolarizations in lateral horn cells which are characteristically associated with an increased membrane resistance. EPSPs in lateral horn cells are not cholinergic in nature, though many cells are endowed with excitatory nicotinic receptors. Some interneurons also appear to have excitatory muscarinic receptors. Glutamate can depolarize many lateral horn cells. This excitatory amine does not seem to be responsible for the production of an EPSP, since the EPSP persisted during the continued presence of glutamate in the superfusing medium. All the neurons examined in the lateral horn are susceptible to the hyperpolarizing and shunting actions of GABA and glycine. In a small group of neurons, noradrenaline caused a hyperpolarization.     

Calcitonin gene-related peptide evokes distinct types of excitatory response in guinea pig coeliac ganglion cells

Pressure application of calcitonin gene-related peptide (CGRP) evoked in a population of guinea pig coeliac neurons 3 types of response: a fast, a slow and a biphasic depolarization. The responses were not appreciably affected in low Ca/high Mg or tetrodotoxin-containing Krebs solution. The fast depolarization was associated with a fall in membrane resistance; it was made larger on hyperpolarization and the estimated reversal potential was -24 mV. The fast response was reversibly blocked in a Na-free medium as well as by relatively high concentrations of d-tubocurarine (50-100 microM) but not by hexamethonium. The slow, CGRP-induced depolarization resistant to nicotinic and muscarinic antagonists, was associated with either a small increase or decrease of input resistance. Membrane hyperpolarization increased the slow response in the majority of coeliac neurons, with an estimated reversal potential of -44 mV. The biphasic depolarization displayed electrophysiological and pharmacological characteristics resembling the fast and slow responses. These results raise the possibility that CGRP acting via two distinct types of receptor elicits, respectively, a fast, Na-dependent excitatory response and a slow response, the mechanism of which remains to be established.     

Cholinergic activation of medial pontine reticular formation neurons in vitro

Direct microinjection of cholinergic compounds into pontine reticular formation furnishes an excellent phenomenological model of the rapid eye movement phase of sleep (REM), but the mechanisms underlying this effect and whether they mimic the cellular events of natural REM remain unknown. Data presented here from intracellular recordings in vitro in the rat demonstrate that two-thirds of medial pontine reticular formation neurons respond to application of 0.5-1.0 microM carbachol with a depolarization characterized by a decreased conductance and a linear I/V curve. The resultant mimicry of REM cellular events by carbachol extends to membrane potential depolarization, increased cellular excitability, enhancement of PSPs from reticular stimulation, and the absence of a burst discharge pattern. The presence of these effects with tetrodotoxin and their blockade by atropine imply a direct, muscarinic cholinergic mediation. Other neurons tested responded with either a biphasic hyperpolarization-depolarization or a hyperpolarization. The hyperpolarization was associated with an increased conductance which exhibited pronounced inward rectification, an effect novel for cholinergic agonists in vertebrate CNS but described in heart cells.     

Identification of the nicotinic and muscarinic cholinoreceptors of the soma of the RPa4 neuron in the edible snail

Intracellular recording of potentials was employed to identify cholinoreceptors of the somatic membrane in Helix lucorum RPa4 neuron. A local application under pressure of specific agonists of nicotinic (nicotine, cytisine) and muscarinic (muscarine, arecoline) cholinoreceptors to the soma produced cell depolarization. Depolarization to acetylcholine application was short and was often followed by hyperpolarization. Selective desensitization of receptors by nicotine and muscarine as well as occupation of receptors by cytisine and arecoline reduced depolarization in response to acetylcholine. Nicotinic cholinergic blocker, d-tubocurarine, inhibited to a greater extent responses to nicotinic cholinomimetics, while atropine, muscarinic cholinergic blocker, inhibited responses to muscarinic cholinomimetics. Acetylcholine exhibited a mixed cholinomimetic effect: acetylcholine-induced responses were almost equally inhibited by d-tubocurarine and atropine. A hypothesis is suggested that somatic membrane of RPa4 neuron contains classical nicotinic and muscarinic acetylcholine receptors similar to those of the vertebrates.     

D2-like dopamine receptor activation excites rat dorsal raphe 5-HT neurons in vitro

The aim of the present study was to investigate the effect of dopamine (DA) on the excitability of dorsal raphe nucleus (DRN) 5-hydroxytryptamine (5-HT) neurons using the patch-clamp technique in brain slices. Bath application of DA (1-300 microM) produced a concentration-dependent membrane depolarization in all 5-HT neurons examined. This effect persisted in the presence of tetrodotoxin (TTX; 1 microM) and low extracellular calcium. Moreover, blockade of ionotropic glutamate receptors with 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 2-amino-5-phosphonopentanoic acid (AP5) did not prevent DA-induced depolarization, indicating that it was mediated by a direct effect of DA on 5-HT neurons. The DA-induced depolarization was not antagonized by selective alpha1-adrenergic receptor antagonists, prazosin and WB 4101, but by a nonselective DA receptor antagonist, haloperidol. In addition, the selective D2-like receptor agonist quinpirole and antagonist sulpiride mimicked and blocked DA-induced depolarization, respectively. These results indicate that DA-induced membrane depolarization in DRN 5-HT neurons is mediated by the activation of D2-like DA receptors. The DA-induced membrane depolarization and inward current were associated with an increase in membrane conductance. Examination of the current-voltage (I-V) relationship for the DA-induced inward current revealed that the amplitude of the current increased with membrane hyperpolarization and reversed polarity at a potential near -15 mV. These data suggest that DA-induced depolarization in DRN 5-HT neurons is not mediated by a decrease in potassium conductance, but most likely by the activation of a nonselective cation current.     

Two types of acetylcholine receptors on the soma of primary afferent neurons

Acetylcholine (ACh) caused two types of depolarizations of the soma membrane of bullfrog primary afferent neurons (dorsal root ganglion cells); the one, a rapid transient depolarization, was nicotinic and other, a long-lasting one, as muscarinic in nature, respectively. The rapid transient depolarization was due to a simultaneous increase in sodium and potassium conductance, whereas the slow one was caused by a decrease in membrane potassium conductance. These results indicate that the soma of bullfrog primary afferent neuron is endowed with nicotinic and muscarinic receptors.     

Disparate cholinergic currents in rat principal trigeminal sensory nucleus neurons mediated by M1 and M2 receptors: a possible mechanism for selective gating of afferent sensory neurotransmission

Neurons situated in the principal sensory trigeminal nucleus (PSTN) convey orofacial sensory inputs to thalamic relay regions and higher brain centres, and the excitability of these ascending tract cells is modulated across sleep/wakefulness states and during pain conditions. Moreover, acetylcholine release changes profoundly across sleep/wakefulness states and ascending sensory neurotransmission is altered by cholinergic agonists. An intriguing possibility is, therefore, that cholinergic mechanisms mediate such state-dependent modulation of PSTN tract neurons. We tested the hypotheses that cholinergic agonists can modulate PSTN cell excitability and that such effects are mediated by muscarinic receptor subtypes, using patch-clamp methods in rat and mouse. In all examined cells, carbachol elicited an electrophysiological response that was independent of action potential generation as it persisted in the presence of tetrodotoxin. Responses were of three types: depolarization, hyperpolarization or a biphasic response consisting of hyperpolarization followed by depolarization. In voltage-clamp mode, carbachol evoked corresponding inward, outward or biphasic currents. Moreover, immunostaining for the vesicle-associated choline transporter showed cholinergic innervation of the PSTN. Using muscarinic receptor antagonists, we found that carbachol-elicited PSTN neuron hyperpolarization was mediated by M2 receptors and depolarization, in large part, by M1 receptors. These data suggest that acetylcholine acting on M1 and M2 receptors may contribute to selective excitability enhancement or depression in individual, rostrally projecting sensory neurons. Such selective gating effects via cholinergic input may play a functional role in modulation of ascending sensory transmission, including across behavioral states typified by distinct cholinergic tone, e.g. sleep/wakefulness arousal levels or neuropathic pain conditions.     

Serotonin receptor subtypes that depolarize guinea pig inferior mesenteric ganglion neurons

Our previous studies indicated that serotonin (5-HT) depolarized a majority of guinea pig inferior mesenteric ganglion (IMG) neurons and may be another transmitter for the noncholinergic late slow excitatory postsynaptic potential (ls-EPSP) in the IMG. However, the subtypes of 5-HT receptor mediating these responses have not yet been identified. Using intracellular recording, we examined the effect of 5-HT receptor antagonists with specificity to various 5-HT receptor subtypes on the 5-HT-mediated depolarization and ls-EPSP in IMG neurons in vitro. Cyproheptadine, a 5-HT(1/2) receptor antagonist, reversibly inhibited the slow, but not the fast, depolarization and ls-EPSP in the 5-HT-sensitive neurons. Both mianserin and spiperone, 5-HT(2) and 5-HT(1A) receptor antagonists, did not significantly alter either the fast or slow depolarizing responses or the ls-EPSP. The 5-HT(3) receptor antagonist MDL 72222 (Bemesetron) completely inhibited the fast depolarization with little diminution of the slow depolarization and ls-EPSP. Superfusion of putative 5-HT(1P) receptor antagonist, BRL 24924 (Renzapride), reversibly attenuated both the depolarization and ls-EPSP. However, 5-HT-insensitive neurons with ls-EPSP were found to be insensitive to both cyproheptadine and BRL 24924. In most 5-HT-sensitive neurons, the 5-HT(3) receptor agonist, 2-methyl-5-HT, and the selective 5-HT(1P) agonist, MCPP or 5-OHIP, evoked a fast and a slow depolarization in 55.6 and 71.4% of the neurons, respectively, without a significant effect on the membrane potential in 85.7 and 100% of the 5-HT-insensitive neurons. In 5-HT-sensitive neurons, MDL 72222 reversibly abolished the fast depolarization induced by 2-methyl-5-HT; BRL 24924 significantly inhibited the slow depolarization induced by MCPP or 5-OHIP, but not by SP. Prolonged superfusion of 5-HT-sensitive neurons with MCPP abolished the evoked ls-EPSP without inhibition of action potential. These results suggest that the fast and slow depolarizations in these neurons are mediated by 5-HT(3) and 5-HT(1P) receptor subtypes, respectively. The latter may also mediate the ls-EPSP in 5-HT-sensitive neurons.     

Acetylcholine causes rapid nicotinic excitation in the medial habenular nucleus of guinea pig, in vitro

The actions of ACh in the medial habenular nucleus (MHb) were investigated using extra- and intracellular recording techniques in guinea pig thalamic slice maintained in vitro. Applications of ACh to MHb neurons resulted in rapid excitation followed by inhibition. Neither of these responses was abolished by blockade of synaptic transmission, indicating that they are consequences of ACh action directly on MHb cells. Local applications of the nicotinic agonists nicotine and cytisine caused long-lasting excitation, while applications of another nicotinic agonist, 1,1-dimethyl-4-phenylpiperazinium caused both the excitatory and inhibitory responses. Applications of the muscarinic agonists DL-muscarine and acetyl-beta-methylcholine did not consistently cause either the excitatory or inhibitory response. Adding the nicotinic antagonist hexamethonium to the bathing medium blocked both the excitatory and inhibitory ACh responses, while addition of the muscarinic antagonists atropine or scopolamine had no effect. These results indicate that the effects of ACh on MHb neurons are mediated by nicotinic receptors. Intracellular recordings revealed that ACh or nicotine cause an increase in membrane conductance associated with depolarizations that had an average reversal potential of -16 to -11 mV. These results indicate that the ACh-induced excitation is due to an increase in membrane cation conductance. The inhibitory response that follows ACh-induced depolarization and repetitive firing was associated with a hyperpolarization and an increase in membrane conductance. Similar postexcitatory inhibition could also be elicited by direct depolarization or by applications of glutamate, indicating that the hyperpolarizing response to ACh may be an endogenous postexcitatory potential that is not directly coupled to activation of nicotinic receptors. These results suggest that cholinergic transmission in the MHb may be largely of the nicotinic type. This nucleus may be of one of the major regions of the nervous system through which nicotine mediates its central effects.     

Nicotinic and muscarinic synaptic transmission in canine intracardiac ganglion cells innervating the sinoatrial node

Nicotinic and muscarinic mediated synaptic mechanisms were investigated in isolated, canine intracardiac ganglia taken from the right atrial fat pad. Using conventional intracellular microelectrode recording techniques on 216 neurons fast, and slow synaptic potentials were evoked by single or trains of stimulation of presynaptic fibers in interganglionic nerves. By varying the stimulus intensity, single or multiple fast excitatory postsynaptic potentials (f-EPSPs) were evoked, indicating the convergence of synaptic inputs on these cells. These f-EPSPs often reached the action potential threshold, were enhanced by the acetelcholinesterase inhibitor physostigmine and were blocked by the nicotinic antagonist hexamethonium. The f-EPSPs were accompanied by a decreased input resistance and had an extrapolated reversal potential of −7.1 mV, suggesting increased conductances to more than one cation. Repetitive presynaptic stimulation evoked slow excitatory postsynaptic potentials (s-EPSPs) in 41% of the cells while slow inhibitory postsynaptic potentials (s-IPSPs) or s-IPSPs followed by s-EPSPs were evoked in 19% of the cells. All slow potentials were abolished by atropine and low Ca²⁺/high Mg²⁺ solutions and enhanced by physostigmine. Hexamethonium and adrenergic receptor antagonists had no effects on s-EPSP and s-IPSP. The M₁ receptor antagonist pirenzepine reversibly blocked the s-EPSP but not the s-IPSP. On the other hand, the M₂ receptor blocker 4-diphenyl-acetoxy-N-methyl piperidine methiodide (4-DAMP) had no effects on the s-EPSP. These observations suggest that s-EPSPs and s-IPSPs are mediated by distinct muscarinic by increased input resistance. These responses were decreased in amplitude by membrane hyperpolarization and either reversed polarity or declined to zero amplitude at about −80 mV, suggesting the inhibition of a potassium conductance.     

Serotonin mediates a slow excitatory potential in mammalian celiac ganglia

Neuropharmacological and histochemical evidence presented here indicates that serotonin (5-HT) is the transmitter mediating one of the postsynaptic potentials in the guinea pig celiac ganglion. Repetitive stimulation elicited in celiac neurons, in addition to the nicotinic fast excitatory postsynaptic potential (EPSP), a slow EPSP that was resistant to cholinergic antagonist. Application of 5-HT caused a depolarization with membrane characteristics similar to those of the slow EPSP, furthermore, the latter was reversibly suppressed by 5-HT. The slow depolarization evoked by either nerve stimulation or 5-HT was augmented by fluoxetine, a 5-HT reuptake blocker, and depressed by cyproheptadine, a 5-HT receptor blocker; in addition, tryptophan, a precursor of 5-HT, enhanced differentially the slow EPSP. Lastly, histochemical study revealed dense networks of 5-HT immunoreactivity nerve fibers encircling many ganglionic neurons.     

Chemoreceptors for serotonin (5-HT), acetylcholine (ACh), bradykinin (BK), histamine (H) and γ-aminobutyric acid (GABA) on rabbit visceral afferent neurons

The somata of type ‘C’ neurons in rabbit nodose ganglion are endowed with receptor sites for 5-HT, BK, ACh, II and GABA. 5-HT and ACh application to type ‘C’ neurons in the nodose ganglion of rabbits produced a rapid depolarization associated with an increased membrane conductance, most likely to Na⁺ and K⁺. BK and H elicited slow depolarizations accompanied by a decreased membrane conductance probably to K⁺. GABA induced a rapid depolarization associated with an increased conductance to Cl⁻. In contrast, type ‘A’ neurons were insensitive to the four algesic agents but responded to GABA. d-Tubocurarine or picrotoxin at relatively low concentrations blocked ACh, 5-HT and GABA depolarizations without affecting membrane properties. Hexamethonium blocked ACh responses but not 5-HT responses. In addition, no desensitization occurred between the substances 5-HT, ACh or BK. The results suggest that the depolarizing effect of these agents on visceral neurons might be exerted via different receptors.     

Postsynaptic M1 and M3 receptors are responsible for the muscarinic enhancement of retrograde endocannabinoid signalling in the hippocampus

The cholinergic system is crucial for higher brain functions including learning and memory. These functions are mediated primarily by muscarinic acetylcholine receptors (mAChRs) that consist of five subtypes (M(1)-M(5)). A recent study suggested a novel role of acetylcholine as a potent enhancer of endocannabinoid signalling that acts retrogradely from postsynaptic to presynaptic neurons. In the present study, we further investigated the mechanisms of this cholinergic effect on endocannabinoid signalling. We made paired whole-cell recordings from cultured hippocampal neurons, and monitored inhibitory postsynaptic currents (IPSCs). The postsynaptic depolarization induced a transient suppression of IPSCs (DSI), a phenomenon known to involve retrograde signalling by endocannabinoids. The cholinergic agonist carbachol (CCh) markedly enhanced DSI at 0.01-0.3 microM without changing the presynaptic cannabinoid sensitivity. The facilitating effect of CCh on DSI was mimicked by the muscarinic agonist oxotremorine-M, whereas it was eliminated by the muscarinic antagonist atropine. It was also blocked by a non-hydrolizable analogue of GDP (GDP-beta-S) that was applied intracellularly to postsynaptic neurons. The muscarinic enhancement of DSI persisted to a substantial degree in the neurons prepared from M1-knockout and M3-knockout mice, but was virtually eliminated in the neurons from M1/M3-compound-knockout mice. CCh still enhanced DSI significantly under the blockade of postsynatpic K(+) conductance, and did not significantly influence the depolarization-induced Ca(2+) transients. These results indicate that the activation of postsynaptic M1 and M3 receptors facilitates the depolarization-induced release of endocannabinoids.     

Differential regulation of muscarinic and nicotinic cholinergic receptors and their mRNAs in cultured sympathetic neurons.

Mechanisms regulating expression of neuronal muscarinic and nicotinic receptors were examined in cultures of neonatal rat sympathetic neurons. Two factors known to stimulate cholinergic transmitter development in sympathetic neurons were examined for their effects on cholinergic receptor expression. A membrane associated factor (MANS46) and a diffusible factor produced by cultured rat fibroblasts (RFCM) each decreased muscarinic receptor number. By contrast, neither treatment altered levels of nicotinic receptors. Levels of muscarinic (m2) receptor mRNA were decreased by MANS but not by RFCM, indicating that effects of the two treatments were mediated by different mechanisms. Neither MANS nor RFCM altered levels of nicotinic alpha 3 or beta 2 mRNAs, consistent with the lack of change in numbers of nicotinic receptors. These observations indicate that receptor phenotype in developing neurons is subject to regulation by multiple epigenetic factors. Further, the same signals which regulate transmitter development may also regulate receptor expression in sympathetic neurons.