Cerebral ischemia: Changes in brain choline,acetylcholine, and other monoamines as related to energy metabolism

The relationship of cerebral neurotransmitters acetylcholine (ACh), noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5HT) to the energy state of the brain was examined in mice at various times following complete ischemia produced by decapitation, in gerbils submitted to transient global ischemia (10 min bilateral carotid artery occlusion, 5 or 30 min recirculation), and in rats 24 hr after irreversible microembolism. Ischemia caused significant reductions in brain monoamine concentrations. The alterations in NA, DA, and 5HT levels persisted during recirculation and were unrelated to energy restoration. They were accompanied by an increase in the concentrations of related metabolites, suggesting that synthesis was unable to compensate for the release of the transmitters at early post-ischemic time periods. As described for the catecholamines and 5HT, ischemia resulted in a significant decrease in ACh level, but recirculation was associated with a rapid increase in ACh concentration. Impaired synthesis and/or increased release of ACh can be responsible for the decrease in ACh concentration during ischemia. Early post-ischemic elevation of ACh may be related to the large increase in brain choline brought about by ischemia.     

Enhancement of hippocampal cholinergic neurotransmission through 5-HT1A receptor-mediated pathways by repeated lithium treatment in rats

Hippocampal cholinergic neuronal activity is reported to be regulated, at least partly, through serotonin1A (5-HT1A) receptors. Chronic lithium treatment has been shown to alter both behavioral and neurochemical responses mediated by postsynaptic 5-HT1A receptors. We investigated whether long-term lithium treatment affects central cholinergic neurotransmission through 5-HT1A receptor-mediated pathways. Changes in acetylcholine (ACh) release induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, in the rat hippocampus were measured using a microdialysis technique and a radioimmunoassay for ACh. Administration of lithium for 21 days resulted in a serum lithium concentration of 1.03 mM and caused little change in density or affinity of [3H]8-OH-DPAT binding sites in the hippocampus. The local application of 8-OH-DPAT into the hippocampus of lithium treated rats increased the ACh efflux in both the absence and the presence of physostigmine, a cholinesterase (ChE) inhibitor, in the perfusion fluid. The basal ACh efflux of lithium treated rats was not different from that of the control rats under normal conditions, but was significantly higher than that of the controls when ChE was inhibited. These results demonstrate that chronic lithium treatment increases spontaneous ACh release in the hippocampus under conditions of ChE inhibition, but not under normal conditions, and enhances cholinergic neurotransmission through 5-HT1A receptor-mediated pathways, and suggest that activation of 5-HT1A receptor function by lithium is related to the enhancement of hippocampal cholinergic neurotransmission.     

Branchial musculature of a venerid clam: pharmacology,distribution, and innervation

This study was meant to analyze the neural control of the branchial muscles of the clam Mercenaria mercenaria. Gills isolated from the animal contract in response to 5-hydroxytryptamine (5HT), dopamine (DA), and acetylcholine (ACh); but the ACh contraction occurred only if the gills had been pretreated with the cholinesterase inhibitor eserine. The 5HT antagonists cyproheptadine and mianserin blocked the contractile effects of all of the agonists. However, gills exposed to the 5HT antagonists and eserine relaxed in response to ACh. The DA antagonist SCH-83566 inhibited the effects of DA, but had no effect on contractions induced by 5HT and ACh. The ACh antagonist hexamethonium inhibited both the excitatory and inhibitory effects of ACh, but had no effect on contractions induced by 5HT and DA. 5HT and DA in gill tissue were visualized by using immunohistochemistry. Within each gill filament are dorsoventral neurons running adjacent to the epithelium and containing immunoreactive 5HT and DA. A complex network of 5HT-positive fibers is associated with the septa, blood vessels, and muscles, whereas DA-positive fibers are restricted to the septa. We propose that 5HT is the excitatory transmitter to the gill muscles, and that DA and ACh exert their excitatory effects by stimulating 5HT motor nerves. ACh may also be an inhibitory transmitter of the muscles.     

Excitable membranes--object for evaluating the effect of heavy metal pollution

In acute experiments the interaction of heavy metals (CdCl2 and HgCl2) with neurotransmitters (ACh and 5HT) was studied on the excitable membrane of the identified neurons in the central nervous system of Helix pomatia L. (Gastropoda, Mollusca). It was shown that cadmium and mercury ions exert different influence on both resting and action potentials as well as on the responsiveness of the neural membranes to ACh and 5HT. The selective blocking effect of cadmium and mercury ions can be interpreted on the basis of specificity of postsynaptic receptor structures responsible for the transmitter action and of ion-channels involved in the excitatory processes. The heavy metal effect was not uniform for the different types of neurons, suggesting that pollutants can modify various functions to a different degree. The results show that testing on nerve cell membranes can serve as a useful method and model in investigating the effect of sublethal environmental contamination, as they may cause a profound modulation on the elements of the neural circuitry responsible for the regulation of the animal's behavior.     

Cholinergic transmission from mechanosensory afferents to an identified nonspiking interneuron in the crayfish Procambarus clarkii girard

Pharmacological properties of excitatory synaptic transmission from mechanosensory afferents to an identifiable nonspiking interneuron of crayfish were studied by drug perfusion experiments using acetylcholine (ACh) agonists and antagonists. Application of carbachol, a general agonist of ACh, caused sustained depolarization of the interneuron and a decrease in the peak amplitude of its excitatory synaptic response to sensory stimulation on the soma side. Similar depolarization was observed during application of carbachol under the low-Ca²⁺, high-Mg²⁺ condition. The peak amplitude was also reduced by application of nicotine and tetramethylammonium, both of which also caused sustained depolarization of the inter-neuron. By contrast, perfusion of muscarinic agonists, muscarine, oxotremorine and pilocarpine, reduced the peak amplitude without affecting the membrane potential of the interneuron. Perfusion of nicotonic antagonists of ACh, d-tubocurarine and hexamethonium, caused reduction of the peak amplitude without any change in the membrane potential. A muscarinic antagonist atropine was also effective in blocking the synaptic transmission but at higher concentration than d-tubocurarine. The results suggest that the ACh receptors on the nonspiking interneuron belong to a previously characterized class of crustacean cholinergic receptors resembling the nicotinic subtype of vertebrates.     

Effect of acetylcholine on ventrocaudal sensory neurons in the pleural ganglia ofAplysia

1. The effects of acetylcholine (ACh) on the soma of cultured ventrocaudal sensory neurons from the pleural ganglia of Aplysia kurodai were characterized. 2. Whole-cell recording was used for current and voltage clamping. ACh and other drugs were microapplied to the membranes of the cultured neurons. 3. Microapplication of ACh induced an outward current mediated by a conductance increase. No desensitization to repeated applications of ACh was detected. The threshold was 10(-7) M and the maximum response was at 10(-5) M. 4. The reversal potential in normal seawater is -80 mV, close to the K+ equilibrium potential. Increasing [K+]0 shifted the reversal potential by the amount predicted by the Nernst equation. Altering [Cl-]0 did not affect the reversal potential. Thus ACh opens a potassium channel in these sensory neurons and may act as a neurotransmitter on those neurons. 5. Atropine and d-tubocurarine partially blocked the ACh response. Hexamethonium had no obvious effect on this response. Tetraethylammonium reduced the response to 22% of control. Carbamylcholine and arecoline induced outward currents that were 71 and 12%, respectively, of the response to ACh. Nicotine and muscarine had almost no effect. 6. The ACh response was reduced by prior application of serotonin (5HT). The ACh response was also reduced by bath-applied 5HT, forskolin, and isobutylmethylxanthine. These data suggest that ACh activates an "S-like" channel in the ventrocaudal sensory neurons.     

调心滋肾中药组方对老年痴呆大鼠海马神经递质的影响

目的: 建立痴呆大鼠模型,观察调心滋肾中药组方对大鼠海马神经递质含量的影响.方法: 选用体重300～350 g的健康成年雄性Wistar大鼠, 参照大鼠脑立体定位图谱,双侧注入Ibotenic acid(IA)破坏大鼠Meynert基底核,建立痴呆大鼠模型.造模7 d后应用调心方、滋肾方和调心滋肾方治疗各20 d后,分光光度法检测海马乙酰胆碱含量,高效液相色谱法检测5-羟色胺和去甲肾上腺素的含量.结果: 经调心方、滋肾方和调心滋肾方治疗后,痴呆模型大鼠海马乙酰胆碱、5-羟色胺和去甲肾上腺素含量均明显提高.结论: 经调心方、滋肾方和调心滋肾方对痴呆模型大鼠海马降低的乙酰胆碱、5-羟色胺和去甲肾上腺素有上调作用.     

Distinct muscarinic mediation of suspected dopaminergic activity in sympathetic ganglions

The competitive neuromuscular blocking agents, gallamine and pancuronium, enhanced the nictitating membrane contraction, in the cat, resulting from muscarine ganglionic transmission. Inhibition of ganglionic muscarinic hyperpolarization, in response to short tetanic bouts of preganglionic cervical sympathetic stimulation, was an associated event and is considered by us to be causally related. The neuroleptic drug, haloperidol, enhanced ganglionic hyperpolarization under similar stimulatory conditions, and reduced the nictitating membrane contraction elicited via ganglionic muscarine pathways, effects opposite to those produced by the skeletal muscle relaxants. Apomorphine reduced both ganglionic hyperpolarization and the ganglionic muscarinic-induced nictitating membrane contractions. The action of gallamine and pancuronium conforms to a speculative cholinergic antagonism at the specific muscarinic receptors, termed Mi, on the ganglionic dopaminergic interneuron. Haloperiodol and apomorphine are anticipated to be exerting distinct antagonistic and agonistic actions, respectively, on prejunctional dopamine receptors of the ganglionic interneuron. Ganglionic slow depolarization mediated through the muscarinic receptors, termed Me, was unaltered by any of the agents studied.     

Norepinephrine-mediated Regulation of 5HT<Subscript>1</Subscript> Receptor Functioning in Human Platelets

Adaptive changes in serotonergic 5HT1 receptor signalling are believed to underlie the therapeutic effectiveness of antidepressant drugs. Since cells are continuously exposed to neurotransmitters/neuromodulators, spatially and temporally integrated, the responsiveness of a receptor system is dependent upon the physio-pathological state of the cell and the interaction between different neurotransmitters. In the present work, we investigated heterologous regulation of 5HT1 receptors induced by norepinephrine (NE) in human platelets. NE platelet treatment induced a time and concentration dependent 5HT1 receptor desensitisation mediated by both alpha and beta receptors through activation of intracellular protein kinases. In particular NE, through PKC activation, regulated 5HT1 receptor phosphorylation on threonine residues, causing in turn serotonin receptor-G protein uncoupling and functional responsiveness drop. These results suggest that high NE levels (released i.e. during stress disorders) may play an important role in regulating the 5HT1 responsiveness and in controlling effectiveness of drugs acting on these neurotransmitter systems.     

FACS-array gene expression analysis during early development of mouse telencephalic interneurons

Cortical interneuron dysfunction has been implicated in multiple human disorders including forms of epilepsy, mental retardation, and autism. Although significant advances have been made, understanding the biologic basis of these disorders will require a level of anatomic, molecular, and genetic detail of interneuron development that currently does not exist. To further delineate the pathways modulating interneuron development we performed fluorescent activated cell sorting (FACs) on genetically engineered mouse embryos that selectively express green fluorescent protein (GFP) in developing interneurons followed by whole genome microarray expression profiling on the isolated cells. Bioinformatics analysis revealed expression of both predicted and unexpected genes in developing cortical interneurons. Two unanticipated pathways discovered to be up regulated prior to interneurons differentiating in the cortex were ion channels/neurotransmitters and synaptic/vesicular related genes. A significant association of neurological disease related genes to the population of developing interneurons was found. These results have defined new and potentially important data on gene expression changes during the development of cortical interneurons. In addition, these data can be mined to uncover numerous novel genes involved in the generation of interneurons and may suggest genes/pathways potentially involved in a number of human neurological disorders.     

Calcium responses of circadian pacemaker neurons of the cockroach Rhyparobia maderae to acetylcholine and histamine

The accessory medulla (aMe) is the pacemaker that controls circadian activity rhythms in the cockroach Rhyparobia maderae. Not much is known about the classical neurotransmitters of input pathways to the cockroach circadian system. The circadian pacemaker center receives photic input from the compound eye, via unknown excitatory and GABAergic inhibitory entrainment pathways. In addition, neuropeptidergic inputs couple both pacemaker centers. A histamine-immunoreactive centrifugal neuron connects the ventral aMe with projection areas in the lateral protocerebrum and may provide non-photic inputs. To identify neurotransmitters of input pathways to the circadian clock with Fura-2-dependent Ca²⁺ imaging, primary cell cultures of the adult aMe were stimulated with acetylcholine (ACh), as the most prominent excitatory, and histamine, as common inhibitory neurotransmitter. In most of aMe neurons, ACh application caused dose-dependent increases in intracellular Ca²⁺ levels via ionotropic nicotinic ACh receptors. These ACh-dependent rises in Ca²⁺ were mediated by mibefradil-sensitive voltage-activated Ca²⁺ channels. In contrast, histamine application decreased intracellular Ca²⁺ levels in only a subpopulation of aMe cells via H2-type histamine receptor chloride channels. Thus, our data suggest that ACh is part of the light entrainment pathway while histamine is involved in a non-photic input pathway to the ventral circadian clock of the Madeira cockroach.     

Humoral factors released during trauma ofAplysia body wall

1. Preliminary, general chemical characteristics of substances in artificial sea water (ASW) washed through stimulated body wall (SBW) and in hemolymph taken from noxiously stimulated animals (SHL) were consistent with those of classical neurotransmitters, amino acids, and small- to medium-sized peptides. 2. 5-Hydroxytryptamine (5HT) and acetylcholine (ACh), unlike SBW and SHL, caused relaxation when perfused into isolated body wall. FMRFamide produced a biphasic response--brief contraction followed by prolonged relaxation. 3. Small cardioactive peptide (SCPB) caused body wall contractions similar to those produced by SBW and SHL, except that SCPB contractions displayed more desensitization and were completely blocked by 30 mM CoCl2. SCPB and SBW contractions were synergistic. 4. Dopamine caused persistent body wall contractions similar to those of SBW and SHL. Dopamine contractions were reduced but not blocked by 30 mM CoCl2. Unlike SBW activity, dopamine activity was reduced by alkalinization. 5. Glutamate and taurine produced strong but usually short-lasting body wall contractions. Adenosine, octopamine, arginine vasotocin, and cholecystokinin (CCK-8) caused weak or variable contractions. Met-enkephalin and somatostatin caused no obvious body wall responses. 6. When superfused over the fully sheathed abdominal ganglion, FMRFamide, met-enkephalin, glutamate, aspartate, and taurine reduced the magnitude of the gill-withdrawal reflex elicited by siphon nerve stimulation. 7. Taken together with earlier results, these data suggest a preliminary framework for trauma signal pathways. It is proposed that stress hormones (perhaps including FMRFamide, SCPs, 5HT, and dopamine) are released into hemolymph from neuroendocrine cells. Effective amounts of active intracellular solutes such as amino acids may also be released by extensive cellular rupture. Various humoral signals produce slow effects that contribute to hemostasis, balling up, increased cardiac output, and reflex suppression.     

A method for immunofluorescent demonstration of three coexisting neurotransmitters in rat brain and spinal cord, using the fluorophores fluorescein, lissamine rhodamine, and 7-amino-4-methylcoumarin-3-acetic acid.

Coexistence of neurotransmitters within single nerve fibers or terminals can be convincingly demonstrated by the use of multicolor immunofluorescence. The present study examined whether three-color immunocytochemical localization of coexisting neurotransmitters can be performed using the blue fluorophore AMCA. Spectrofluorometric examination of secondary antibodies conjugated with AMCA, fluorescein, and lissamine rhodamine showed that the peaks of excitation and emission were well separated and that dots of AMCA-conjugated IgG dried on slides were not visible when viewed using microscope filters for rhodamine and fluorescein. These findings suggest that AMCA might be suitable for three-color immunofluorescence. The usefulness of AMCA for triple labeling was tested directly by staining sections of rat brainstem and spinal cord for serotonin (5HT), substance P (SP), and either enkephalin (ENK) or prepro-thyrotropin-releasing hormone 160-169 (ppT), a marker peptide for thyrotropin-releasing hormone. Triple labeling for 5HT, SP, and ppT was observed in both brainstem and spinal cord but was only very rarely observed for 5HT,SP, and ENK. No evidence was found for artifactual triple labeling, although false negatives appeared to be possible in some circumstances. We conclude that AMCA can be combined with fluorescein and lissamine rhodamine for three-color immunofluorescent studies of coexisting neurotransmitters. In addition, the coexistence of 5HT with ENK appears to be much less common than the coexistence of 5HT with either SP or ppT.     

Aspects of the neuroendocrine control of ovulation and broodiness in the domestic hen

The neuroendocrine control of ovulation and broodiness in the domestic hen involves complex interactions between hypothalamic neuropeptides, neurotransmitters, and ovarian steroids which regulate the secretion of luteinizing hormone (LH) and prolactin. Nuclear progesterone receptor is localized in many neurons throughout the hypothalamus but is absent from LHRH neurons. Hence, the positive feedback action of progesterone on LH release is not mediated by a genomic mechanism within the LHRH neuron. Precursors of 5-hydroxytryptamine (5HT) and dopamine (DA) inhibit the preovulatory release of LH, while the turnover rates of these neurotransmitters in the anterior hypothalamus decrease when preovulatory levels of LH are at their highest. Further, a population of receptors for 5HT which occurs in the anterior hypothalamus in laying birds is absent in nonlaying, incubating hens. Taken together, these observations suggest that the preovulatory surge of LH is mediated by a transitory decrease in the inhibitory action of 5HT and possibly DA, on the secretion of LHRH. Neurons containing 5HT may play a role in the regulation of prolactin release and, more specifically, in the control of broodiness. Drugs which enhance the function of 5HT neurons stimulate prolactin release while increased prolactin secretion in incubating hens is associated with an increase in the turnover of 5HT in the anterior hypothalamus. No receptors for 5HT were demonstrable in the anterior pituitary gland, showing that the prolactin-releasing activity of 5HT must be mediated by a prolactin-releasing factor (PRF). A candidate for a physiological PRF is vasoactive intestinal polypeptide (VIP).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the Effects of a Convulsant Barbiturate on the Release of Endogenous and Radiolabeled Amino Acids from Slices of Mouse Hippocampus

The convulsant barbiturate 5-(2-cyclohexylidene-ethyl)-5-ethyl barbituric acid (CHEB) stimulates the spontaneous release of endogenous and radiolabeled acetylcholine (ACh) from mouse hippocampal slices in vitro. In order to determine if the ability of CHEB to release ACh was unique to this neurotransmitter, we have studied the action of this drug in vitro on the release of both radiolabeled and endogenous putative neurotransmitter and non-transmitter amino acids in the hippocampus. Although CHEB stimulated the spontaneous release of both [3H]gamma-n-aminobutyric acid (GABA) and endogenous GABA, CHEB had different effects on the spontaneous release of radiolabeled and endogenous L-glutamate and L-aspartate: L-[3H]glutamate release was inhibited by CHEB, but endogenous L-glutamate release was unaffected by CHEB, but endogenous L-aspartate release was stimulated. The spontaneous release of the amino acids L-alanine and glycine (not thought to be neurotransmitters in the hippocampus) was not affected by CHEB. The results of this study indicate that CHEB does not always stimulate the release of all putative neurotransmitters. The ability of this drug to release ACh, GABA, and L-aspartate may be the result of some specific interaction of CHEB with nerves using these neurotransmitters in the hippocampus. In addition, the results suggest some problems that may be encountered when radiolabeled substances are used to study neurotransmitter release.     

Segmental release of amino acid neurotransmitters from transcranial stimulation

The present study used microdialysis techniques in an intact rabbit model to measure the release of amino acids within the lumbar spinal cord in response to transcranial electrical stimulation. Dialysis samples from the extracellular space were obtained over a stimulation period of 90 minutes and were examined using high pressure liquid chromatography. Neuronal excitation was verified by recerding corticomotor evoked potentials (CMEPs) from the spinal cord. A significant increase in the release of glycine and taurine compared to sham animals was measured after 90 minutes of transcranial stimulation. Glutamate and aspartate release was not significantly elevated. GABA concentrations were consistently low. CMEP components repeatedly showed adequate activation of descending fiber pathways and segmental interneuron pools during dialysis sampling. Since glycine, and to a lesser extent taurine, have been shown to inhibit motor neuron activity and are closely associated with segmental interneuron pools, suprasegmental modulation of motor activity may be, in part, through these inhibitory amino acid neurotransmitters in the rabbit lumbar spinal cord.     

Interactions of morphine with putative neurotransmitters in the mesencephalic reticular formation

Acetylcholine (ACh) and norepinephrine (NE) have been identified previously as putative nociceptive neurotransmitters in the mesencephalic reticular formation (MRF) of the rat because they frequently mimic the change in neuronal firing (usually an increase) evoked by a noxious stimulus (NS). The purpose of this study was to determine if 1.) morphine (M) acts to prevent the increase in firing evoked by a NS by blocking the effects of either of these two neurotransmitters and 2.) if this effect is a specific narcotic effect. Using the technique of microiontophoresis in conjunction with extracellular recording, we located single units in the MRF in which 1.) neuronal firing was accelerated by a NS: 2.) M blocked this response; and 3.) either ACh or NE mimicked the effect of the NS. Neurons meeting these three criteria were studied further to determined if morphine would also block the response to either of the neurotransmitters and if this was a specific narcotic effect. We found that morphine blocked the increase in neuronal firing evoked by the NS and ACh or the NS and NE in over 50% of the cells meeting the above criteria. Some neurons were found in which both ACh and NE mimicked the NS and M blocked all three responses. This blockade of these neurotransmitters was a specific narcotic effect because it could be reversed by the systematic administration of naloxone. These data lead to the tentative hypothesis that M, acting via an opiate receptor, blocks the increase in neuronal firing evoked by a NS by blocking the postsynaptic effects of either ACh or NE. This may be one of the mechanisms by which morphine acts to produce analgesia.     

Neurotensin Regulation of Endogenous Acetylcholine Release from Rat Striatal Slices Is Independent of Dopaminergic Tone

The effects of neurotensin (NT) alone or in combination with the dopamine antagonist sulpiride were tested on the release of endogenous acetylcholine (ACh) from striatal slices. NT enhanced potassium (25 mM)-evoked ACh release from striatal slices in a dose-dependent manner. This effect was tetrodotoxin-insensitive, suggesting an action directly on cholinergic elements. The dopamine antagonist sulpiride (5 x 10(-5) M) significantly increased (63%) potassium-evoked ACh release from striatal slices; potassium-evoked ACh release was further increased (90%) in the presence of NT (10(-5) M) and sulpiride (5 x 10(-5) M). The second set of experiments tested the effects of 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra on NT-induced increases of potassium-evoked ACh release. These lesions did not alter the NT regulation of potassium-evoked ACh release from striatal slices, but did significantly increase spontaneous (33%) and potassium-evoked (40%) ACh release from striatal slices. Striatal choline acetyltransferase activity was not affected by 6-OHDA lesions. In addition, following 6-OHDA lesions, sulpiride was ineffective in altering ACh release from striatal slices. Furthermore, evoked ACh release in the presence of the combination of NT and sulpiride was not different from that in the presence of NT alone. These results suggest that in the rat striatum, NT regulates cholinergic interneuron activity by interacting with NT receptors associated with cholinergic elements. Moreover, the NT modulation of cholinergic activity is independent of either an interaction of NT with D2 dopamine receptors or the sustained release of dopamine.     

Acetylcholine Releases Prostaglandins from Brain Slices Incubated In Vitro

A variety of neurotransmitters elicit a phosphoinositide response in the CNS; however, their effects on prostaglandin (PG) formation in the brain are not well characterized. In the present study, we investigated the effect of acetylcholine (ACh) on the synthesis of PGs E and F in slices from various regions of guinea pig brain incubated in glucose-fortified Krebs-Henseleit bicarbonate saline. Slices were prewashed in the presence of 1% albumin to reduce basal PG levels followed by incubation for 30 min at 37 degrees C in the presence or absence of ACh. Under these conditions, 5 mM ACh significantly increased the efflux of PGE and PGF from brain regions enriched in muscarinic cholinergic receptors, i.e., cerebral cortex, temporal cortex, corpus striatum, and hippocampus. Depolarization by 45 mM KCl also significantly enhanced PG synthesis, and the relative magnitude of the effect was similar to that of ACh. The stimulation of PG synthesis by ACh was inhibited by 20 microM atropine, whereas the K+-induced stimulation was not. The effects of potassium and ACh were additive at maximally effective ACh concentrations, an observation that suggests that ACh and K+ increase PG efflux through independent mechanisms. Norepinephrine, histamine, and serotonin, three other neurotransmitters that evoke a phosphoinositide response in the brain, were ineffective in stimulating PG release from brain cortex slices.