Presynaptic muscarinic receptors in guinea pig superior cervical ganglion

This study characterizes the presynaptic muscarinic cholinergic receptors associated with the modulation of the electrically-evoked acetylcholine output from guinea pig superior cervical ganglion preincubated with [3H]choline. The M1-selective agonist pilocarpine had no effect while carbachol and oxotremorine strongly decreased the evoked outflow of tritium. Atropine increased such evoked release of [3H]acetylcholine whereas the M1-selective antagonist pirenzepine was ineffective. Moreover, atropine but not pirenzepine antagonized the inhibitory effect of carbachol. These results suggest that the guinea-pig superior cervical ganglion is equipped with presynaptic inhibitory muscarinic receptors of the M2 subtype.     

Muscarinic inhibition of quantal transmitter release from the magnesium-paralysed frog sartorius muscle

The existence of presynaptic muscarinic acetylcholine receptors on motor nerve terminals of the isolated frog sartorius muscle was investigated. The modulatory role of these receptors was studied by observing the effects of muscarinic ligands on the frequency of miniature endplate potentials and on the quantal content of endplate potentials. The agonist oxotremorine reduced in concentration-dependent fashion the frequency of spontaneous potentials and the amplitude of evoked potentials. Also, high concentrations of oxotremorine depolarized the postsynaptic membrane and reduced the amplitude of the miniature endplate potentials. The depolarizing action of the drug was blocked byd-tubocurarine. The muscarinic antagonist atropine attenuated agonist-induced reductions in endplate potential amplitude and miniature endplate potential frequency but did not affect the depression in amplitude of the spontaneous potentials evoked by oxotremorine. It is concluded that activation of presynaptic muscarinic receptors inhibits the release of acetylcholine from motor nerve terminals.

Atropine itself had no effect on the quantal content of evoked potentials or on the frequency of spontaneous potentials suggesting that the nerve terminal is not affected by non-quantal acetylcholine.     

Characterization and quantitative autoradiographic distribution of [3H]acetylcholine muscarinic receptors in mammalian brain. Apparent labelling of an M2-like receptor sub-type

[3H]Acetylcholine receptor binding characteristics (under muscarinic conditions) have been investigated using membrane binding assays and in vitro receptor autoradiography. In rat, guinea-pig and monkey brain membrane preparations, [3H]acetylcholine binds with high affinity (25-50 nM) to an apparently single class of sites which is differentially distributed across brain regions. The ligand selectivity pattern reveals that the potency of (-)quinuclidinyl benzylate is greater than (greater than) atropine greater than scopolamine greater than oxotremorine greater than carbamylcholine greater than pirenzepine greater than methylcarbamyl-choline = nicotine in competing for [3H]acetylcholine binding sites, indicating that [3H]acetylcholine selectively binds to muscarinic sites under these incubation conditions. Moreover, the low potency of pirenzepine suggests that [3H]acetylcholine does not label a significant proportion of the M1 receptor sub-type but most likely binds to putative M2-like receptor sites. This hypothesis is also supported by the autoradiographic distribution of [3H]acetylcholine binding sites in all species studied here. High densities of [3H]acetylcholine binding sites are seen in various nuclei of the medulla and pons, certain thalamic nuclei, medial septum, laminae III, V and VI of the cortex and just above the pyramidal cell layer of the hippocampus. Such localization is much different from that seen with the non-selective antagonist [3H]quinuclidinyl benzylate and the selective M1 receptor ligand [3H]pirenzepine, although it resembles that of the selective M2 receptor antagonist [3H]AF-DX 116. Thus, [3H]acetylcholine apparently mostly binds with high affinity mainly to non-M1 muscarinic receptor types in mammalian brain tissues. Moreover, the ligand selectivity pattern and in vitro receptor autoradiographic data suggest that at low concentrations (10-20 nM) most of [3H]actylcholine labelled sites are of the M2-like receptor class.     

Muscarinic receptors mediate direct inhibition of GABA release from rat striatal nerve terminals

The effects of acetylcholine (ACh) on the depolarization-evoked release of [3H]gamma-aminobutyric acid ([3H]GABA) have been investigated using synaptosomes prepared from rat corpus striatum and depolarized by superfusion with 9 mM KCl. Acetylcholine inhibited the [3H]GABA overflow in a concentration-dependent manner. The maximal effect was about 50%. The IC50 value (concentration producing half-maximal effect) amounted to 1 microM, in the absence of acetylcholinesterase inhibitors. The effect of ACh on the K(+)-evoked [3H]GABA release was counteracted by the muscarinic receptor antagonist atropine, but not by the nicotinic receptor antagonist mecamylamine or by the selective M1 antagonist pirenzepine. The data show that muscarinic receptors with low affinity for pirenzepine are localized on GABAergic nerve endings in rat corpus striatum where they may directly inhibit the release of GABA.     

Functional heterogeneity of the matrix compartment in the cat caudate nucleus as demonstrated by the cholinergic presynaptic regulation of dopamine release.

Previously, using a new in vitro microsuperfusion procedure, we have demonstrated marked differences in the cholinergic presynaptic regulation of the release of [3H]dopamine continuously synthesized from [3H]tyrosine in two close striosomal- and matrix-enriched areas of the cat caudate nucleus. A tetrodotoxin-resistant stimulatory effect of acetylcholine mediated by muscarinic receptors was observed in both compartments. However, in addition, two opposing types of tetrodotoxin-sensitive acetylcholine-evoked regulation of [3H]dopamine release were only seen in the matrix: one facilitatory, involving nicotinic receptors located on as yet unidentified neurons, and the other inhibitory, mediated by muscarinic receptors located on dynorphin-containing neurons. In the present study, using the same approach, a functional heterogeneity was demonstrated in the matrix. Indeed, in various conditions the effects of acetylcholine (50 microM) on the release of [3H]dopamine were different in a matrix-enriched area (matrix 2) distinct from that previously investigated (matrix 1); these areas being characterized by the presence or absence of islands of striatonigral cells, respectively. As in matrix 1, acetylcholine induced a short-lasting stimulation of [3H]dopamine release in matrix 2 but, in contrast to that observed in matrix 1, the acetylcholine-evoked response in matrix 2 was not modified in the presence of tetrodotoxin (1 microM). Experiments made in the presence of the tetrodotoxin and atropine (1 microM) indicated that both muscarinic and nicotinic receptors are located on dopaminergic nerve terminals in matrix 2 while muscarinic receptors are only present in matrix 1. In the absence of tetrodotoxin, the short-lasting stimulation of [3H]dopamine release was transformed into a long-lasting response in the presence of pempidine (50 microM), in matrix 2 but not in matrix 1 while prolonged responses were seen in both matrix areas in the presence of atropine. Finally, the acetylcholine short stimulatory effect on [3H]dopamine release was transformed into a long stimulatory response in the presence of bicuculline (50 microM) but not naloxone (1 microM) in matrix 2 while the reverse was observed in matrix 1. By providing further evidence for a functional heterogeneity of the matrix, our results suggest that depending on the matrix area investigated, dynorphin- or GABA-containing neurons are involved in the indirect cholinergic inhibitory control of dopamine release.     

Presynaptic inhibition of acetylcholine release

High potassium (51 mM) has been shown to evoke release of acetylcholine ([3H]ACh and endogenous ACh) from cholinergic nerves in rat bronchial smooth muscle. The release of [3H]ACh was reduced by 85% when the Ca2+ concentration was changed from 2 to 0.1 mM. The veratridine-induced release was completely inhibited by tetrodotoxin, but tetrodotoxin did not reduce the potassium-evoked release. The muscarinic agonist, oxotremorine, reduced the potassium stimulated release of [3H]ACh, without affecting the basal release. In contrast, scopolamine substantially potentiated the potassium-evoked release. Adenosine had a dual effect in the rat bronchi. Adenosine inhibited the potassium-evoked release of [3H]ACh and this presynaptic effect of adenosine was antagonized by 8-phenyltheophylline. Adenosine also induced contraction of the bronchial smooth muscle and there was potentiation by adenosine of the ACh-induced contraction. The results indicate that cholinergic nerve terminals in the rat bronchi possess muscarinic receptors which inhibit the release of ACh. Adenosine may have analogous effects, e.g. presynaptic inhibition of transmitter release in addition to postsynaptic enhancement of bronchial smooth muscle contraction.     

Evidence for a nicotinic component to the actions of acetylcholine in cat visual cortex

Summary Radioligand binding assays, receptor autoradiography and iontophoresis have been used to look for evidence of a nicotinic component to the actions of acetylcholine in cat visual cortex. [³H]Nicotine bound to a uniform population of high affinity binding sites in cat primary visual cortex. This binding was inhibited by nicotine agonists and antagonists but not muscarinic antagonists. The concentration of nicotinic binding sites was about 10% of that of muscarinic binding sites measured with [³H]N-methylscopolamine. The muscarinic sites were resolved into M1 and M2 subtypes. Quantitative receptor autoradiography showed that there were muscarinic sites in all layers, although they were least abundant in layer IV of area 17. In contrast, the nicotinic sites were most concentrated in layer IV in area 17. The concentration of this labelling was reduced at the 17/18 border and also at the 18/19 border. Layer I of the cingulate and suprasylvian gyri were also labelled. Electrolytic lesions of the lateral geniculate nucleus (LGN) led to a loss of nicotinic binding sites in layer IV of area 17, indicating that these sites are most likely located on the LGN terminals. Iontophoresis of mecamylamine, a nicotinic antagonist, decreased evoked responses in visual cortex, providing evidence that the [³H]nicotine binding sites are functional receptors and suggesting that the release of acetylcholine onto these receptors on the LGN terminals facilitates the input of visual information into visual cortex.     

Evaluation of autoreceptor-mediated control of [3H]acetylcholine release in rat and human neocortex

In order to assess the autoinhibitory control of endogenous acetylcholine (ACh) in rat and human neocortex, slices of these tissues were prelabelled with [³H]choline, superfused continuously and stimulated electrically using various frequencies in the presence or absence of drugs. The autoinhibitory feedback control of [³H]ACh release was operative – despite the absence of blockers of ACh esterase – at stimulation frequencies ≥3 Hz in rat and ≥6 Hz in human neocortex tissue. At these frequencies the muscarinic antagonist atropine (0.1 μM) disinhibited the release of [³H]ACh in both species. Estimation of the biophase concentration of ACh near the autoreceptor in the rat neocortex from concentration-response curves of the muscarinic agonist oxotremorine revealed that at 3 Hz about 25% of the autoreceptors were activated by endogenously released ACh. This estimation is consistent with an increase in [³H]ACh release to about 120% of control values by complete blockade of autoreceptors with atropine. The observation that in human neocortical tissue presynaptic autoinhibition of [³H]ACh release is operative at stimulation frequencies ≥6 Hz suggests that selective blockade of autoinhibition may also increase ACh release in the cortex of Alzheimer’s disease patients, without additional blockade of the enzyme acetylcholinesterase. Received: 22 September 1998 / Accepted: 27 April 1999     

Investigations of the cholinergic modulation of GABA release in rat thalamus slices

The thalamus receives a dense cholinergic projection from the pedunculopontine tegmentum. A number of physiological studies have demonstrated that this projection causes a dramatic change in thalamic activity during the transition from sleep to wakefulness. Previous anatomical investigations have found that muscarinic type 2 receptors are densely distributed on the dendritic terminals of GABAergic interneurons, as well as the somata and proximal dendrites of GABAergic cells in the thalamic reticular nucleus. Since these structures are the synaptic targets of cholinergic terminals in the thalamus, it appears likely that thalamic pedunculopontine tegmentum terminals can activate muscarinic type 2 receptors on GABAergic cells. To test whether activation of muscarinic type 2 receptors affects the release of GABA in the thalamus, we have begun pharmacological studies using slices prepared from the rat thalamus. We have found that the application of the nonspecific muscarinic agonist, methacholine, and the muscarinic type 2-selective agonist, oxotremorine.sesquifumarate, diminished both the baseline, and K(+) triggered release of [(3)H]GABA from thalamic slices. This effect was calcium dependent, and blocked by the nonselective muscarinic antagonist atropine, the muscarinic type 2-selective antagonist, methoctramine, but not the muscarinic type 1 antagonist, pirenzepine. Thus, it appears that one function of the pedunculopontine tegmentum projection is to decrease the release of GABA through activation of muscarinic type 2 receptors. This decrease in inhibition may play an important role in regulating thalamic activity during changes in states of arousal.     

Ranitidine but not famotidine releases acetylcholine from the guinea pig myenteric plexus

The effects of the histamine H2-receptor antagonists ranitidine and famotidine on acetylcholine release have been studied in the guinea pig myenteric plexus longitudinal muscle preparation incubated with [³H]-choline. Ranitidine (3×10^–5–3×10^–4 M) dose-dependently increased the resting release of acetylcholine and that evoked by electrical stimulation. The effect was present only in strips perfused with 10^–5 M physostigmine. The effect of ranitidinc was inhibited by tetrodotoxin and hexamethonium. Famotidine (10^–5–3×10^–4 M) was totally ineffective in modifying both the resting release and that evoked by field stimulation. Ranitidine did not antagonize the inhibitory effect of oxotremorine, which specifically activates negative feedback mechanisms via presynaptic muscarinic receptors.     

Muscarinic receptor activation attenuates D2 dopamine receptor mediated inhibition of acetylcholine release in rat striatum: indications for a common signal transduction pathway

In the present investigations, we used a superfusion system to study the effect of simultaneous activation of D2 dopamine receptors and so-called muscarinic "autoreceptors" on the K(+)-evoked in vitro release of [3H]acetylcholine from rat striatal tissue slices. Activation of D2 receptors with the selective agonist LY 171555 (0.01-1 microM) clearly decreased the evoked release of [3H]acetylcholine. This effect was markedly attenuated in the presence of either the selective muscarinic receptor agonist oxotremorine (3 microM) or the cholinesterase inhibitor physostigmine (1 microM). Conversely, D2 receptor activation with LY 171555 (1 microM) completely abolished the muscarinic receptor mediated inhibition of evoked [3H]acetylcholine release induced by oxotremorine (0.03-10 microM). These results show that the inhibitory effects of D2 dopamine receptor and muscarinic receptor activation on striatal acetylcholine release are non-additive and therefore are interdependent processes. In addition, we investigated some aspects of the signal transduction mechanism by which the muscarinic receptor mediates inhibition of K(+)-evoked in vitro release of [3H]acetylcholine from rat striatal tissue slices. It appeared that the effect of muscarinic receptor activation was not significantly influenced either by a lowering of the extracellular Ca2+ concentration from the usual 1.2-0.12 mM or by an increase of the intracellular cyclic adenosine-3',5'-monophosphate content. However, increasing extracellular K+ strongly decreased the inhibition of evoked [3H]acetylcholine release mediated by activation of muscarinic receptors. This set of results indicates that the muscarinic "autoreceptor" mediates the decrease of depolarization induced [3H]acetylcholine release from rat striatum to a large extent through stimulation of K+ efflux (opening of K+ channels) in a cyclic adenosine-3',5'-monophosphate independent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition by acetylcholine of the stimulation-evoked release of [3H]acetylcholine from the guinea-pig myenteric plexus

The longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum was incubated with [³H]choline and then superfused with Tyrode's solution. Exposure to [³H]choline resulted in the formation of [³H]acetylcholine which was released upon electrical field stimulation. The effects of exogenous acetylcholine, physostigmine and scopolamine on the stimulation-evoked release of [³H]acetylcholine were studied.In the absence of a cholinesterase inhibitor exogenous acetylcholine (10^?5 M) only slightly inhibited (by 26%) the evoked release of [³H]acetylcholine. If the cholinesterase activity of the preparation was reduced by about 50% in the presence of 10^?7M physostigmine, exogenous acetylcholine caused a concentration-dependent depression of the release evoked at 1 Hz. At a concentration of 10^?5 M acetylcholine the release was reduced by 76%. Scopolamine (10^?9 M) shifted the concentration-response curve for the inhibitory action of acetylcholine in a parallel manner to the right. From the dose ratio a pA₂ value of 9.8 for scopolamine against the release-inhibitory effect of acetylcholine was calculated. Physostigmine also inhibited the stimulation-evoked release of [³H]acetylcholine in a concentration-dependent manner, the maximal effect measured being an 85% reduction by 10^?5 M physostigmine. In the absence of a cholinesterase inhibitor scopolamine enhanced the evoked release of [³H]acetylcholine. The facilitatory effect was more marked at a stimulation frequency of 3 Hz (2-fold increase) than at 1 Hz (1.4-fold increase).It is concluded that extracellular acetylcholine decreases the stimulation-evoked release of neuronal acetylcholine. This inhibition is specifically mediated by a stimulation of presynaptic muscarinic receptors. The increase by scopolamine of the evoked release of [³H]acetylcholine suggests that previously liberated acetylcholine may trigger the negative feedback mechanism of acetylcholine release even if the cholinesterase activity is not inhibited, and that the presynaptic muscarinic receptors of the myenteric plexus have a physiological role in regulating the release of acetylcholine.     

Effects of aging on rat cortical presynaptic cholinergic processes

We studied the effects of aging on the [³H]-choline uptake, acetylation, [³H]-ACh release and muscarinic modulation of [³H]-ACh release in cortical synaptosomes prepared from Fischer 344 male rats. Our results indicate that 6 and 24 month old rats take up and acetylate [³H]-choline to a similar extent, but that the older animals release significantly less [³H]-ACh in response to K⁺-depolarization than the young adults do. This difference in K⁺-induced release is not due to a difference in presynaptic muscarinic receptor inhibitory activity since the older animals appear to be, if anything, slightly less sensitive to oxotremorine than the younger animals are. Atropine (1 μM) had no effect on ACh-release but blocked oxotremorine-induced modulation. Our results suggest that acetylcholine release is decreased in synaptosomes prepared from old rats although the presynaptic muscarinic regulation of release is functional. Thus, muscarinic receptor-mediated release-modulation is a potential site for pharmacologically altering ACh release.     

Dopamine prevents muscarinic-induced decrease of glutamate release in the auditory cortex

Acetylcholine and dopamine are simultaneously released in the cortex at the occurrence of novel stimuli. In addition to a series of excitatory effects, acetylcholine decreases the release of glutamate acting on presynaptic muscarinic receptors. By recording evoked excitatory postsynaptic currents in layers II/III neurons of the auditory cortex, we found that activation of muscarinic receptors by oxotremorine reduces the amplitude of glutamatergic current (A(oxo)/A(ctr) = 0.53 +/- 0.17) in the absence but not in the presence of dopamine (A(oxo)/A(ctr) = 0.89 +/- 0.12 in 20 microM dopamine). These data suggested that an excessive sensitivity to dopamine, such as postulated in schizophrenia, could prevent the decrease of glutamate release associated with the activation of cholinergic corticopetal nuclei. Thus, a possible mechanism of action of antipsychotic drugs could be through a depression of the glutamatergic signal in the auditory cortex. We tested the capability of haloperidol, clozapine and lamotrigine to affect glutamatergic synaptic currents and their muscarinic modulation. We found that antipsychotics not only work as dopamine receptor antagonists in re-establishing muscarinic modulation, but also directly depress glutamatergic currents. These results suggest that presynaptic modulation of glutamate release can account for a dual route of action of antipsychotic drugs.     

Pharmacology, distribution and development of muscarinic acetylcholine receptor subtypes in the optic tectum of Rana pipiens

Visually evoked behaviors mediated by the frog optic tectum require cholinergic activity, but the receptor subtypes through which acetylcholine acts are not yet identified. Using quantitative autoradiography and scintillation spectrometry, we examined the binding of [3H]pirenzepine and [3H]AF-DX 384 in the laminated optic tectum of the frog. In mammalian systems, these substances bind excitatory (m1 and m3 subtypes) and inhibitory (m2 and m4 subtypes) muscarinic acetylcholine receptors, respectively. Pharmacological analyses, including the use of specific muscarinic toxins, confirmed the subtype selectivity of the radioligands in the frog brain. Binding sites for [3H]pirenzepine were distinct from those for [3H]AF-DX 384. In the adult tectum, [3H]pirenzepine demonstrated specific binding in tectal layers 5-9. [3H]Pirenzepine binding was also present in tadpoles as young as stage V, but all sampled stages of tadpole tectum had significantly less binding when compared to adults. Lesioning of the optic nerve had no effect on [3H]pirenzepine binding. Specific [3H]AF-DX 384 binding was found in all layers of the adult tectum. All sampled tadpole stages exhibited binding sites for [3H]AF-DX 384, but the densities of these sites were also significantly higher in adults than they were in developing stages. Short-term lesions of the optic nerve reduced [3H]AF-DX 384 binding in all tectal layers of the deafferented lobe when compared to the afferented one. Long-term lesions decreased [3H]AF-DX 384 sites in both lobes.These results indicate that multiple muscarinic acetylcholine receptor binding sites reside in the frog optic tectum at all stages of development, and their pharmacology resembles that of mammalian m1/m3, m2 and m4 subtypes. Our data indicate that few, if any, of these receptors are likely to be located on retinal ganglion cell terminals. Furthermore, the expression of inhibitory muscarinic subtypes seems to be regulated by different mechanisms than that for excitatory subtypes.     

Pre-junctional muscarinic autoreceptors in bovine airways

We searched for pre-junctional inhibitory muscarinic receptors in isolated bovine trachealis strips and bronchial rings. Electric stimulation (ES)-induced tritiated acetylcholine ([³H]-ACh)-release and isometric contractions were determined in muscles incubated with the non-selective muscarinic agonist pilocarpine, the non-selective muscarinic antagonist atropine, the selective M₂-receptor antagonists methoctramine and gallamine, or the selective M₄-receptor antagonist PD102807. Electric field stimulation (EFS)-induced isometric contractile responses were assessed in trachealis strips and bronchial rings treated with 10⁻⁹-10⁻⁵ M methoctramine, gallamine or PD102807. Pilocarpine (10⁻⁶ and 10⁻⁵ M) and atropine (10⁻⁷ M) significantly decreased and increased ES-evoked [³H]-ACh-release, respectively. The enhancing effect of atropine on [³H]-ACh-release prevailed over the inhibitory effect of pilocarpine. M₂- and M₄-receptor antagonists did not increase EFS-induced contraction or ES-induced [³H]-ACh-release. However, 10⁻⁷ M methoctramine, gallamine or PD102807 significantly attenuated the inhibitory effects of pilocarpine 10⁻⁵ M on ES-induced [³H]-ACh-release. Conclusions: Muscarinic autoregulation is present in bovine airways but is not fully accounted for by M₂- and M₄-receptor subtypes.     

Reduced number of [3H]nicotine and [3H]acetylcholine binding sites in the frontal cortex of Alzheimer brains

Nicotinic cholinergic receptors were measured in human frontal cortex using [3H]nicotine and [3H]acetylcholine (in the presence of atropine) as receptor ligands. A parallel marked reduction in number of [3H]nicotine (52%; P less than 0.01) and [3H]acetylcholine (-55%; P less than 0.05) binding was found in the frontal cortex of Alzheimer brains (AD/SDAT) when compared to age-matched control brains. As a comparison the number of muscarinic receptors was quantified using [3H]quinuclidinyl benzilate and found to be significantly increased (+23%; less than 0.01) in AD/SDAT compared to controls.     

Muscarinic cholinergic receptor binding in rat mast cells

Specific [³H]-QNB binding was present in isolated, purified, intact rat mast cells and in crude membrane preparations. The binding is saturable, time- and temperature-dependent. Cholinergic agents inhibit selectively the binding: atropine is the most effective of the antagonists while oxotremorine is the most potent of the muscarinic agonists. It is concluded that rat mast cells are provided with muscarinic cholinergic receptors.     

Cutaneous responses to anticholinergics: evidence for muscarinic receptor subtype participation

We conducted a series of experiments to determine if anticholinergics induce immediate cutaneous wheal-and-flare responses in normal volunteers. We performed intradermal skin testing in seven healthy volunteers (three atopic and four nonatopic) with 20 nmol of atropine. All subjects had an immediate wheal-and-flare response to atropine. To determine if this cutaneous response was due to anticholinergics in general, skin testing was also performed to scopolamine and ipratropium. These agents also produced immediate wheal-and-flare responses in all subjects, but they less potent than atropine. Pretreatment with antihistamines equivalently inhibited wheal-and-flare responses to both histamine and atropine, indicating a possible mast cell role. The potential role of M1, M2, and M3 muscarinic receptor subtypes was evaluated by use of the selective antagonists, pirenzepine (M1), 11[[2-1[(diethylamino)methyl]-1-piperidinyl]-acetyl]-5, 11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one (AFDX-116) (M2), and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) (M3). Cutaneous wheal responses induced by pirenzepine and 4-DAMP were relatively equivalent and larger than responses induced by AFDX-116 at doses less than 200 nmol. At 200 nmol, all three muscarinic receptor subtype antagonists induced equivalent wheal formation. We then compared the cutaneous wheal responses to these specific muscarinic receptor antagonists based on their relative affinity for their respective muscarinic receptor subtype. This comparison suggested that M1 or M2, but not M3, muscarinic receptor subtypes may be important in anticholinergic-induced cutaneous wheal-and-flare responses. We propose that there may be an M1 or M2 muscarinic autoreceptor that inhibits the release of acetylcholine and other neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of dynorphin-containing neurons in the presynaptic inhibitory control of the acetylcholine-evoked release of dopamine in the striosomes and the matrix of the cat caudate nucleus.

The roles of acetylcholine and dynorphin (1-13) in the presynaptic control of the release of [3H]dopamine continuously synthesized from [3H]tyrosine were examined in a prominent striosomal enriched area and in an adjacent matrix enriched area of the cat caudate nucleus. This was achieved using microsuperfusion devices applied vertically onto coronal slices of cat brain. These devices were placed in a striosomal enriched area located in the core of the structure (acetylcholinesterase-poor zone) and in an adjacent matrix enriched area (acetylcholinesterase-rich zone). [3H]Tyrosine was delivered continuously to each microsuperfusion device and [3H]dopamine released was estimated in the superfusate. As previously shown, in the presence of tetrodotoxin (1 microM), acetylcholine (50 microM) induces a prolonged stimulation of [3H]dopamine release in both compartments through an interaction with muscarinic receptors. Our present study indicates that both dynorphin 1-13 (1 microM) and the selective kappa agonist trans-3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl)cyclohexyl]benzeneace tamine (U50488) (1 microM) inhibit the tetrodotoxin-resistant acetylcholine-evoked release of [3H]dopamine, these effects being slightly more pronounced in the matrix than in the striosomal enriched area. Naloxone (1 microM) reversed the inhibitory effect of U50488 in both areas. These results suggest that dynorphin exerts an inhibitory presynaptic control of dopamine release through kappa opioid receptors located on dopamine nerve terminals in the striosome as well as in the matrix. However, the presynaptic cholinergic control of dopamine release is much more complex in the matrix than in the striosomal enriched area. Besides its tetrodotoxin-resistant stimulatory effect, acetylcholine exerts two opposing tetrodotoxin-sensitive effects on [3H]dopamine release, one facilitatory and the other inhibitory. We demonstrate here that in the superfused matrix enriched area, the indirect acetylcholine inhibitory response is mediated by dynorphin-containing neurons. Indeed, the short-lasting stimulatory effect of acetylcholine on [3H]dopamine release was converted into a long-lasting response in the presence of naloxone (1 microM), and, in this latter condition, the co-application of dynorphin 1-13 (1 microM) restored the short-lasting stimulatory effect.