Regulation of opiate receptors in mouse brain: arcuate nuclear lesion induces receptor up-regulation and supersensitivity to opiates

Lesion of the hypothalamic arcuate nucleus of the mouse by neonatal application of monosodium glutamate (MSG) increased the binding of [3H]dihydromorphine to membranes prepared from the midbrain. A saturation curve of [3H]dihydromorphine binding indicated that MSG increased the number of the opiate receptors. The MSG-treated mice also exhibited an enhanced response to morphine and naltrexone regarding thermal pain sensitivity. The physiological implications of opiate receptors up-regulations upon arcuate nuclear lesion are discussed.

Down-regulation of opiate receptors in serum-free cultures of aggregating fetal brain cells

Brain cells from rat embryos that were cultured in serum-free medium form aggregates which possess stereospecific binding of radioactive opiates. The specificity of these opiate receptors and their regulation by opiate alkaloids and enkephalin was studied. D-ala2, D-leu5-enkephalin (DADL) induced down-regulation of opiate receptors in aggregates prepared from the forebrain but had no effect on hindbrain aggregates, whereas the potent alkaloid etorphine induced down-regulation of the receptors in both tissues. Interestingly, morphine did not induce down-regulation in both tissues. The significance of these findings and their relationship to the control of different types of opiate receptors are discussed.

Enkephalins and opiate antagonists control calmodulin distribution in neuroblastoma-glioma cells

The calcium binding protein calmodulin and the opiate receptor binding sites are unevenly distributed in various subcellular fractions of neuroblastoma-glioma NG108-15 cells. The crude mitochondrial-membrane fraction of these cells contains two membrane fractions that are separable by sucrose gradient centrifugation. These two differ in the content of both calmodulin and opiate receptors. Leucine enkephalin and D-Ala2-methionine enkephalinamide decrease the amount of membrane-bound calmodulin in the NC108-15 cells in a time- and dose-dependent manner, whereas the opiate antagonists naloxone and levallorphan have an opposite effect. Naloxone blocks the effect of leucine enkephalin and dextrallorphan has no significant effect. The opiate alkaloids entorphine and phenazocine induce changes similar to that of the enkephalins whereas morphine is inactive even at high concentrations. The alteration in the amount of membrane-bound calmodulin after a short incubation (15 min) with the enkephalins or with naloxone is reflected as an opposite change in the amount of calmodulin in the cell cytosol. Naloxone and levallorphan also increase the number of opiate receptors in NG108-15 cells but dextrallorphan has no such effect. Modulation of the intracellular distribution of calmodulin by opioid peptides and alkaloids may control the activity of various membrane-bound and cytosolic systems that are calmodulin- and/or calcium-dependent.

Down regulation of enkephalin (delta) receptors. Demonstration in membrane-bound and solubilized receptors

The pentapeptide leucine enkephalin induced down-regulation of enkephalin receptors in neuroblastoma-glioma NG108-15 hybrid cells in a reversible fashion, whereas the stable enkephalin analogue D-Ala2-Met-enkephalinamide (AMEA), and the potent opiate alkaloid, etorphine, had a prolonged effect. The opiate alkaloid, morphine, which has low affinity to delta-type enkephalin receptors of these cells did not induce down-regulation, whereas AMEA decreased the binding of both opiate agonists and antagonists but had no effect on the binding of the alpha 2-adrenergic ligand, [3H]yohimbine. From several experiments that were designed to remove the tightly bound AMEA, and from experiments with solubilized receptor we ruled out the possibility that the decreased binding capacity of enkephalin-treated cells reflects only receptor masking. The study suggests that down-regulation of enkephalin receptors that may also occur in vivo can account for some of the abnormal physiological responses of subjects treated chromically with opiates. However, since opiates from the morphine type can induce opiate tolerance in vivo, but not down-regulation of enkephalin receptors in the cultured cells, we suggest that down-regulation of delta-type opiate receptors may not be prerequisite for the development of the physiological tolerance/dependence on these alkaloids.

A genetic approach to reveal the action of the opiate receptor in selected neuroblastoma-glioma cells. Interaction with alpha-adrenoceptors, calmodulin and Ca2+-ATPase

Three clones of neuroblastoma-glioma cells that contain low amounts of calmodulin were selected from the NG108-15 cells after several treatments with high concentrations of chlorpromazine. Purified membranes of the three clones had decreased numbers of both alpha-adrenergic and opiate receptors, monitored with [3H]yohimbine and [3H,D-Ala2]methionine encephalinamide, respectively. No changes were observed in the affinity of these radioactive ligands to the receptors of the selected cells as compared to the parent cells. Addition of bovine brain calmodulin did not affect the binding of [3H,D-Ala2]methionine encephalinamide to the membranes of the selected cells and they had the same number of acetylcholine receptors, determined with 1-quinuclidinyl-[phenyl-4-3H]-benzilate, as the parent NG108-15 cells. The basal ATPase activity in the membranes of the selected cells was 35-50% of the parent cells, with a decreased V value and no significant change in the affinity constant Ka to ATP. Addition of Ca2+ to the purified membranes increased the V of the ATPase in the selected as well as the parent cells but the V of the selected cells remained lower than that of the parent cells. Ca2+ had no effect on the Ka to ATP in either cell type. The Ca2+-dependent ATPase activity of both the parent and the selected cells was also calmodulin-dependent dependent since it was blocked in vitro by chlorpromazine. The co-regulation of opiate and adrenergic receptors and their interaction with calmodulin and Ca2+-ATPase is discussed in view of recent observations indicating biochemical and physiological association between opiates, Ca2+ and adrenergic compounds.

Enkephalin and alpha-adrenergic receptors: evidence for both common and differentiable regulatory pathways and down-regulation of the enkephalin receptor

Several clones of neuroblastoma-glioma NG108-15 hybrid cells were used to reveal whether the regulation of opiate receptor density interacts with the regulation of alpha-adrenergic or acetyl-choline receptors. Low density of alpha-adrenergic receptors in 3 selected clones was accompanied with similar reduction in the density of enkephalin receptors but not in muscarinic acetyl-choline receptors. Yet opiate antagonists that increased the number of opiate receptors in the parent NG108-15 cells in a stereospecific manner had no similar effect on the number of alpha-adrenergic receptors. Moreover, the stable enkephalin analogue D-ala-2-methionine enkephalinamide, but not the opiate alkaloid morphine, decreased the binding of 3H-DAMEA to the membranes and induced down-regulation of enkephalin receptors. Yet DAMEA had no effect on the binding of the alpha-adrenergic antagonist 3H-yohimbine. The study suggests that alpha-adrenergic and enkephalin receptors may share some common regulatory pathways but opiate peptides and antagonists selectively decrease or increase the density of enkephalin receptors, respectively, with no effect on alpha-adrenergic receptor density.

Effects of acute and chronic morphine treatment of calmodulin activity of rat brain

The cyclic AMP-phosphodiesterase assay was used to quantitate the amount of calmodulin activity in various brain areas of male rats treated acutely or chronically for 5 days with morphine. The acute treatment with morphine decreased calmodulin activity in the mitochondrial-synaptosomal P2 fraction of the striatum, midbrain, and thalamus but had no effect on the cerebellum, which contains a low density of opiate receptors. The decrease in calmodulin activity by morphine was dose-dependent and was blocked by the opiate antagonist naloxone. In contrast, chronic treatment of rats with morphine increased calmodulin activity in the mitochondrial-synaptosomal P2 of the striatum, midbrain, cerebral cortex, and thalamus. A highly sensitive Ca2+/Mg2+-ATPase assay was also used to quantitate the amount of calmodulin activity in subcellular fractions obtained from the striatum. Chronic morphine treatment caused a significant increase in calmodulin activity in the membrane containing microsomal, synaptosomal, and mitochondrial layers but only a small change in the layer that contained the soluble proteins and the synaptic vesicles. It is suggested that alteration of the content of calmodulin in specific subcellular sites may have a central role in opiate action and addiction via regulation of multiple calmodulin-sensitive biochemical pathways.

Local electrographic effects of leu-enkephalin microinjections into the brain

Microinjections of Leu-enkephalin were made in dorsal hippocampus, caudate nucleus, amygdala, nucleus accumbens and parietal cortex in rats. The effects of enkephalin on the local electrical activity recorded from the area of the microinjection are described. Depression effects (attenuation of amplitudes and slowing) were recorded in caudate nucleus, nucleus accumbens, amygdala and parietal cortex, but not in hippocampus. Activation and epileptiform effects (spikes, seizures) were recorded from all structures studied.

Enhancement of hormone action by a phorbol ester and anti-tubulin alkaloids involves different mechanisms

The tumor-promoting phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) enhanced 1-isoproterenol and prostaglandin E1 stimulated cyclic AMP formation in clones of mouse myeloid leukemic cells. The enhancement was found up to 3h after TPA treatment and had disappeared after 24h, indicating its reversibility. The effect of TPA was not inhibited by removal of extracellular Ca2+ or pre-treatment with the calcium ionophore A23187. This enhancement by TPA seems to involve a different pathway than enhancement of response to the same hormones after treatment with the anti-tubulin alkaloids colchicine or vinblastine, since a myeloid leukemic cell mutant clone that was non-responsive to the anti-tubulin alkaloids responded to TPA. Furthermore, combined treatment of colchicine-sensitive cells with TPA and colchicine showed an additive stimulating effect. The enhancement of cell response to hormones by TPA was found in myeloid leukemic cell clones that either were or were not induced to differentiate after treatment with TPA. This suggests that enhancement of the effect of these and possibly other hormones by TPA may be an initial step of TPA action, but that this enhancement is not sufficient to induce the wide repertoire of TPA effects including induction of differentiation.

Role of phospholipase A2 and prostaglandin E in growth and differentiation of myeloid leukemic cells

Phospholipase A2 activity and prostaglandin E synthesis have been studied in different clones of myeloid leukemic cells, which differ in their competence to be induced to differentiate by the macrophage and granulocyte differentiation-inducing protein or the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA). Clones that could be induced to differentiate by this protein showed a higher basal phospholipase A2 activity than clones that could not be induced to differentiate by this protein inducer. Cell competence to be induced to differentiate by TPA did not show this correlation, and the clone with the least ability to respond to TPA showed the lowest number of binding sites for [20-3H]phorbol 12,13-dibutyrate. Differentiation induced by the protein was accompanied by a 7-14-fold increase in prostaglandin E synthesis, whereas differentiation induced by TPA did not show this increase. Externally added prostaglandin E1 did not induce differentiation but inhibited cell proliferation and the degree of inhibition in the different clones was related to the basal phospholipase A2 activity. The results indicate that increase of prostaglandin E synthesis was not an essential pre-requisite for differentiation, that prostaglandin E seems to be involved in the inhibition of cell proliferation in association with phospholipase A2, and that the differentiation-inducing protein and TPA can induce differentiation by different pathways. The amount of basal phospholipase A2 activity was also related to previously found differences in the ability of the clones to develop desensitization to beta-adrenergic hormones or prostaglandin E1.

Influence of body temperature on the epileptogenic effect of enkephalin microinjections into the hippocampus

The influence of different body temperatures on the epileptiform discharges induced in hippocampus by local microinjections of leu-enkephalin was studied in rats. In the absence of enkephalin, changes in body temperature by either cooling or heating induced epileptiform discharges that disappeared after temperature stabilization. The epileptiform episode induced by enkephalin microinjections was of longer duration at temperature below normal (29-30 degrees C). At body temperature above normal (39-40 degrees C) the epileptiform discharge was less intense and of shorter duration. In vitro testing led to parallel results: the destruction of enkephalin by the brain tissue was faster at higher temperatures. It is proposed that in conditions of hyperthermia enkephalin has a weaker activity due to acceleration of the activity of peptidases involved in its breakdown.

Opiate receptor binding in the brain of the hypertensive rat

Experimental and genetic hypertension in male rate is accompanied by a lower specific [3H]naloxone binding in the dorsal horn of the spinal cord, and in the hippocampus as compared to controls. Rats which are genetically resistant to hypertensive stimuli have a higher specific [3H]naloxone binding in the nucleus tractus solitarius and lower opiate receptor binding in the dorsal horn. Together with previous studies which demonstrated a correlation between blood pressure and pain sensitivity, these results support the notion that specific brain loci participate in co-regulation of pain perception and blood pressure.

Sexual behavior decreases pain sensitivity and stimulated endogenous opioids in male rats

In male rats copulation has antinociceptive effects as measured either by shock-induced vocalizations or hindlimb withdrawal to pinch. Prolonged mating reduces the content of endogenous opioids in midbrain but not in hypothalamus or caudate nucleus. Blockage of opiate receptors with the narcotic antagonist naloxone (4 mg/kg) significantly extends the postejaculatory interval. The results indicate that mating is a biological stimulus for the release of endogenous opoids, possibly to (a) prevent intense sexual stimulation from becoming aversive, and (b) increase its reward value.

Desensitization of enucleated cells to hormones and role of cytoskeleton in control of normal hormonal response

Prostaglandin E1 and the beta-adrenergic hormone l-isoproterenol stimulated cyclic AMP formation in both nucleated and enucleated myeloid leukemic cells that could be induced to differentiate normally to mature cells by the macrophage- and granulocyte-inducing protein MGI (MGI+D+ cells). Enucleated as well as nucleated MGI+D+ cells also desensitized to these hormones, indicating that this desensitization is an extranuclear process. Nucleated or enucleated mutant myeloid leukemic cells that are not induced to differentiate (MGI-D- cells) were not desensitized to these hormones. The antitubulin alkaloids colchicine and vinblastine, but not the antimicrofilament compound cytochalasin B, increased the maximal hormone-induced formation of cyclic AMP in nucleated MGI+D+ cells but not in the MGI-D- cells. These alkaloids also inhibited the development of desensitization to l-isoproterenol and prostaglandin E1 in enucleated MGI+D+ cells. The results indicate that in MGI+D+ cells the cytoskeletal system puts constraints on the cells' ability to respond to these hormones and that these constraints are absent in the mutant MGI-D- cells. Because MGI+D+ but not MGI-D- cells can be induced to differentiate by the macrophage- and granulocyte-inducing protein, cytoskeletal constraints, which are also found in normal myeloid cells, may be necessary for cell competence to differentiate. The results support the suggestion that membrane cytoskeletal constraints generate may control the normal response and desensitization to membrane-mediated cell inducers.

Pain sensitivity and opioid activity in genetically and experimentally hypertensive rats

Pain sensitivity was studied in renal and DOCA-salt hypertensive rats, and in two strains of rats derived from the same parental strain for their sensitivity (H) or immunity (N) to hypertension induced by DOCA-salt treatment. Experimentally hypertensive rats, and H and N rats were less sensitive to painful stimuli than their appropriate controls, as assessed in the hot-plate and paw pinch tests. Naloxone reversed this hypoalgesia in both experimentally and genetically hypertensive rats while it did not affect blood pressure in any rat-type tested. Opioid activity was measured with the radioreceptor assay in several brain regions and pituitary gland of both experimentally and genetically hypertensive rats. Experimentally hypertensive rats had a 45% higher level of opioid activity in the spinal cord compared to control. Rats of the H and N strains both exhibited higher levels of opioid activity in the spinal cord, hypothalamus and pituitary. It is suggested that control systems for blood pressure and pain sensitivity are closely associated in the rat.

Differential desensitization of functional adrenergic receptors in normal and malignant myeloid cells: relationship to receptor-mediated hormone cytotoxicity

Malignant myeloid leukemic cells and normal macrophages and granulocytes have functional beta-adrenergic receptors, which have been quantitated by radioreceptor binding with the beta-adrenergic antagonist [(3)H]dihydroalprenolol and by induction of cyclic AMP by adrenergic hormones. Both the normal and leukemic cells have beta(2)-adrenergic receptors, and the [(3)H]dihydroalprenolol binding was saturable, reversible, and stereospecific. The leukemic cells consisted of clones that could be induced to differentiate (MGI(+)D(+)) and clones that could not be induced to differentiate to mature macrophages and granulocytes by the protein inducer MGI. The different types of leukemic clones all had 1100-2300 receptor sites per cell, whereas normal macrophages had 7000 receptors per cell. The differentiation of MGI(+)D(+) leukemic cells was associated with an increase in receptors to a number similar to that found with normal macrophages. MGI(+)D(+) leukemic cells and normal macrophages were able to densensitize to the beta-adrenergic agonist (-)isoproterenol, shown by termination of cyclic AMP induction within 10-15 min and the lack of a second induction. The leukemic cells that could not be induced to differentiate lacked this capacity for desensitization, possibly due to an alteration in the uncoupling system between the receptor and adenylate cyclase. The lack of desensitization in these leukemic cells was associated with a higher sensitivity to the receptor-mediated cytotoxic effects of adrenergic hormones. It is suggested that cells, like some leukemic cells, that are unable to desensitize to adrenergic and possibly other hormones may be appropriate targets for differential destruction by hormones under conditions that do not affect normally desensitizing cells.

The opiate receptor binding interactions of 3H-methionine enkephalin, an opioid peptide

3H-Methionine enkephalin binds stereospecifically with high affinity to opiate receptors in rat brain membranes. Equilibrium experiments indicate two distinct dissociation constants with KD values of 1.8 and 5.8 nM respectively. 3H-Methionine enkephalin associates and dissociates from the opiate receptor with 8--10 fold slower kinetics than 3H-opiates. Though several opiates have similar affinities for sites labeled by 3H-methionine enkephalin, 3H-dihydromorphine and 3H-naloxone, some opiates such as morphine, dihydromorphine and oxymorphone are only one tenth as potent in competing for 3H-methionine enkephalin as for 3H-dihydromorphine and 3H-naloxone binding. As with other opiate agonists, 5--10 mM sodium selectively decreases the binding of 3H-methionine enkephalin. At 26 degrees C, 0.1--1.0 mM manganese but not magnesium or calcium increases the binding of 3H-methionine enkephalin, while at 0 degrees C manganese decreases the binding of methionine enkephalin.

Enkephalin: radioimmunoassay and radioreceptor assay in morphine dependent rats

A sensitive and specific radioimmunoassay for enkephalins is described which discriminates between leucineenkephalin and methionine-enkephalin. Total opioid peptide activity was assayed by the ability of brain extracts to compete for opiate receptor binding. In rats treated with morphine and/or naloxone, opiates were separated from opioid peptides by Dowex AG-50W column chromatography prior to radioreceptor assay. Chronic administration of morphine failed to alter immunoreactive enkephalin levels or total opioid activity in radioreceptor assays.

A morphine-like factor in mammalian brain: analgesic activity in rats

A partially purified morphine-like peptide 'enkephalin' (PPE) extract from bovine brain elicited pronounced apparent analgesia after injection into the periaqueductal gray matter of rat brain. This analgesia was reversed by the opiate antagonist naloxone in a dose-dependent fashion. Analgesia was more rapid in onset and much shorter in duration after PPE than after morphine administration. Analgesia was elicited only by those ion exchange column fractions of PPE that competed potently for opiate receptor binding. No analgesia could be detected when PPE or morphine injections were administered at a site 2 mm lateral to the periaqueductal gray matter. The potencies of synthetic methionine- and leucine-enkephalin in eliciting analgesia were less than 1% of those of partially purified enkephalin extracts when doses of equivalent ability to compete for opiate receptor binding were compared.

Opioid peptide enkephalin: immunohistochemical mapping in rat central nervous system

Using specific antisera to methionine-enkephalin and leucine-enkephalin, we have visualized apparent enkephalin-containing neuronal fibers and terminals throughout the central nervous system of the rat. Immunoreactive enkephalin displays sharply defined localizations. Regions of highest immunofluorescent density include the laminae I and II of the spinal cord, the substantia gelatinosa of the caudal nucleus of nerve V, the vagal nuclei of the medulla, the periventricular and periaqueductal areas of the upper medulla and midbrain, dorsomedial thalamic regions, specific hypothalamic nuclei, the basal ganglia, particularly the globus pallidus and the central nucleus of the amygdala, and the lateral septum. In certain regions enkephalin immunofluorescence corresponds closely with the distribution of autoradiographic opiate receptor grains.

Morphine-like peptides in mammalian brain: isolation, structure elucidation, and interactions with the opiate receptor

A substance that competes for opiate receptor binding has been isolated from calf brain and identified as two pentapeptides, H-Tyr-Gly-Gly-Phe-Met-OH (methionine enkephalin) and H-Tyr-Gly-Gly-Phe-Leu-OH (leucine enkephalin), with about four times more leucine enkephalin than methionine enkephalin. Sodium and manganese effects on opiate receptor interactions show that both peptides are agonists, whereas leucine enkephalin may be a "purer" agonist than methionine enkephalin.

Temperature sensitivity of cyclic-adenosine-3':5'-monophosphate-binding proteins, activity of protein kinases and the regulation of cell growth

A clone of neuroblastoma cells has been selected for its ability to survive and multiply at 40 degrees C. This temperature-resistant clone, like clones of neuroblastoma cells selected for resistance to dibutyryladenosine 3':5'-monophosphate (Bt2-Ado-3':5'-P) showed an increased tumorogenicity in animals and an increased saturation density at 37 degrees C. The Ado-3':5'-P-binding proteins and Ado-3':5'-P-dependent protein kinases from the temperature-resistant and non-resistant cells have been partially purified by chromatography on a DEAE-cellulose column. The Ado-3':5'-P-binding proteins from temperature-resistant cells were more sensitive to temperature than the binding proteins from non-resistant cells. After incubation of binding proteins from resistant cells at 37 degrees C, the specific activity of Ado-3':5'-P-binding to proteins was decreased about 50% and the apparent association constant (Ka) for Ado-3':5-p-binding was decreased from 7.4 X 10(7)M-1 to 4.4 x 10(7)M-1. There was no such decrease with binding proteins from non-resistant cells. A decrease in the activity of binding proteins from the temperature-resistant cells, but not of those from non-resistant cells, was also found when the proteins were stored at 2 degrees C. Treatment with 2-mercaptoethanol made binding proteins from the resistant cells less temperature-sensitive. In the absence of added Ado-3:5-P the protein kinase activity from the temperature-resistant cells was about 50% of the activity from non-resistant cells. Kinase activity was increased by addition of Ado-3:5-P and there was a greater increase with kinases from resistant cells. The maximum protein kinase activity was found in the presence of 10muM Ado-3':5'-P for the temperature-resistant cells and 0.1 muM Ado-3':5'-P for the non-resistant cells. The results indicate that the temperature sensitivity of Ado-3':5'-P-binding proteins, and the activity of protein kinase from cells selected for resistance to high temperature, are similar to those of cells selected for resistance to Bt2-Ado-3':5'-P. It is suggested that the temperature sensitivity of Ado-3':5'-P-binding proteins and the activity of Ado-3':5'-P-dependent protein kinases are involved in the regulation of malignancy and of cell growth at different temperatures.

Induction of polyadenylate polymerase and differentiation in neuroblastoma cells

Treatment of neuroblastoma cells with dibutyryl-adenosine 3':5'-monophosphate or adenine induced axon formation and a three-fold increase in the polyadenylate, poly(A), content of the polysomal mRNA. The extracted poly(A) contained 90% adenylic acid and showed a mobility of 6--7 S in dodecylsulfate-polyacrylamide gel electrophoresis. Treatment with dibutyryl-adenosine 3':5'-monophosphate or adenine, also induced a 4--6 fold increase in a nuclear enzymic activity that incorporated [3H]ATP to an acid-insoluble polymer in a cell-free system. This polymer, like poly(A) extracted from the polysomal mRNA, was bound at high salt concentration to nitrocellulose filters. [3H]ATP incorporation was Mg2+-dependent, sensitive to ribonuclease and EDTA and resistant to deoxyribonuclease and actinomycin D. There was no incorporation of [3H]UTP or [3H]dTTP and addition of TUP, CTP and GTP did not increase the incorporation of [3H]ATP. 5-Bromodeoxyuridine induced axon formation of neuroblastoma cells and poly(A) polymerase activity, without increasing the poly(A) content in the polysomal mRNA. The results indicate that induction of axon formation of neuroblastoma cells is associated with an increase in the activity of poly(A) polymerase. It is suggested that the induction of this enzyme may be generally involved in cell differentiation.

Temperature sensitivity of cyclic adenosine 3':5'-monophosphate-binding proteins and the regulation of growth and differentiation in neuroblastoma cells

The apparent association constant (K-a) of cAMP to the binding proteins from resistant and nonresistant cells was 7.4 times 10-7 M-1 and 8.2 times 10-7 M-1, respectively, and the specific activity of cAMP BINDING TO THESE PROTEINS WAS SIMILAR FOR BOTH TYPES OF CELLS.

Regulation of acetylcholine receptors in relation to acetylcholinesterase in neuroblastoma cells

Purified alpha-toxin from Naja nigricollis snake venom labeled by [(3)H]acetylation binds specifically to the acetylcholine receptors of mouse neuroblastoma cells. Toxin binding was inhibited by inhibitors for nicotinic and muscarinic acetylcholine receptors. Clones of neuroblastoma cells were selected for low acetylcholinesterase (EC 3.1.1.7) activity with antibodies against this enzyme. Selection for an 80-fold decrease in acetylcholinesterase activity was not associated with any decrease in the number of acetylcholine receptors (3.4 x 10(7) per cell). Removal or inactivation of 80% of the acetylcholine receptors by proteolytic enzymes or by compounds that block sulfhydryl groups did not change the activity of acetylcholinesterase on the cell surface. In addition to these results on the separation between acetylcholine receptors and acetylcholinesterase, a common regulation was found in that both the number of acetylcholine receptors and the activity of acetylcholinesterase were increased 5- to 10-fold when the cells stopped to multiply or were induced to differentiate by dibutyryl-cyclic AMP. It is suggested that there are different genes for the acetylcholine receptor and acetylcholinesterase, and that both are regulated during growth and differentiation by a common regulatory gene.