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Ion-channel blockers are molecules that obstruct the path used by ions to cross the membrane through a protein channel. Many of these are local anesthetics, toxins or drugs of abuse, and the knowledge of their mechanism of action at the atomic level is an important step towards the development of new compounds on a structural basis. A molecular model of the transmembrane region of the nicotinic acetylcholine receptor, an important brain and muscle fast signaling protein, was used as a target for docking several channel blockers by means of an automatic docking method. The combination of the independent docking method and molecular models (of the receptor and blockers) reproduced or explained quite accurately experimental data (photoaffinity labeling, site-directed mutagenesis, binding assays). This represents a strong support for the validity of the predictions made for those molecules for which no experimental data is available and also for the models and methods on which are based.

Pyrilene acts as a central H-cholinoblocker upon intramuscular injection at a dose of 0.02-0.08 mg/kg, and as an NMDA-blocker, when the dose is increased to 0.2-0.8 mg/kg. Similarly, amantadine exhibits the properties of H-cholinoblocker and NMDA-blocker in the dose intervals 10-15 mg/kg and 120-180 mg/kg, respectively. The activity of MK-801 markedly exceeds that of memantine, although close doses of both NMDA-blockers inhibit the NMDA and corazole effects, as well as the central effects (analgesia and seizure) of nicotine, thus showing no significant selectivity with respect to NMDA. IEM-1754 tested on intact animals exhibited a selective action upon the NMDA receptors, preventing the NMDA-induced analgesia and lethality and the corazole-induced convulsions at doses 10-100 times lower as compared to those preventing nicotine-induced seizure and analgesia.

1. Some nicotinic antagonists (piperidine and quinuclidine derivatives and bis-quaternary compounds) protect early embryos of the sea urchin Lytechinus pictus against a calcium shock evoked by ionomycin or a mixture of phorbol myristate acetate and nicotine. 2. Maximal protective potency was found for drugs that did not penetrate the plasma membrane. 3. Early sea urchin embryos have nicotinic acetylcholine receptors (nAChR) or nAChR-like structures localized on the cell surface that, apparently, take part in the control of Ca2+ influx.

A study was undertaken to assess the receptor binding characteristics of [3H]4-benzylpempidine to an allosteric site on calf brain membranes associated with nicotinic cholinergic receptors and to compare the binding affinity of novel arylpempidine analogs with their ability to antagonize the behavioral effects of nicotine in mice. Scatchard analysis of the binding yielded a K(d) of 20 nM and a B(max) of 330 fmols/mg membrane protein. [3H]4-benzylpempidine appears to be a more satisfactory ligand than [3H]mecamylamine, since it possessed a 50-fold greater affinity and its binding was far less sensitive to inorganic ions and Tris. Among the arylpempidine analogs 4-m-chlorobenzylidenepempidine and 4-benzylidenepempidine had the lowest K(i) values (1.4 nM and 5.0 nM, respectively) and were the most potent in antagonizing nicotine-induced seizures in mice. Although the K(i) values for pempidine and mecamylamine were 1-2 orders of magnitude greater than any of the arylpempidines, the dose required to antagonize nicotine-induced seizures in mice was comparable to the arylpempidines. One explanation for this apparent discrepancy in the correlation of binding affinity and nicotine antagonism is the lower brain penetration of arylpempidines compared to mecamylamine, following their systemic administration to mice.

Effects of different pharmacons on the non-excitable period (NEP) and on the relative excitable period (REP) was studied in the sympathetic ganglionic synapses of the frog (Rana esculenta). Using paired stimulation we demonstrated that hexamethonium, magnesium, pempidine, tetraethylammonium (TEA) and d-tubocurarine chlorides significantly prolonged both NEP and REP at ganglion blocking threshold concentrations. Their maximum effect occurred within 30-60 min after the start of the exposition. Hemicholine and neostigmine prolonged only NEP but not REP while lidocaine influenced neither period applying continuous repeated stimulation at low frequencies (0.1-12.5 Hz). TEA showed no effect, however, at higher frequencies (14.3-20.0 Hz) it exerted a frequency-dependent depressant effect on the amplitude of the compound action potential.

The modulation of [3H]ACh release by nicotinic compounds was studied in superfused rat hippocampal synaptosomes loaded with [3H]choline, (-)-Nicotine (0.1-10 microM) evoked a dose-dependent increase in [3H]ACh release; higher concentrations were less effective. Nicotine-evoked release was Ca(2+)-dependent, and blocked by the nicotinic antagonists dihydro-beta-erythroidine, mecamylamine, and pempidine. The alpha 7-selective antagonist methyllycaconitine did not inhibit nicotine-evoked release when tested at 1 microM, although at 10 microM some attenuation of the response was observed. Six agonists tested were equally efficacious in stimulating [3H]ACh release, as judged by the maximum responses, and gave the following EC50 values: (+/-)-epibatidine 0.12 microM; (+)-anatoxin-a 0.14 microM; (-)-nicotine 0.99 microM; (-)-cytisine 1.06 microM; ABT-418 2.6 microM; isoarecolone 43 microM. Each agonist generated a "bell-shaped" dose response curve, suggesting desensitisation at higher concentrations. This is supported by analysis of repetitive stimulation with (-)-nicotine and (-)-cytisine: S2/S1 ratios declined sharply with increasing concentration, whereas subsequent KC1-evoked release remained constant. These results are discussed in terms of possible nicotinic receptor subtypes that might be present on hippocampal nerve terminals.

Using a sensitive in vitro microperfusion method, the effects of selective and potent agonists of NK1, NK2, and NK3 tachykinin receptors ([Pro9]SP, ([Lys5,MeLeu9,Nle10]NKA-(4-10), and [Pro7]NKB, respectively) on the presynaptic control of dopamine release were investigated in striosomal-enriched (area rich in [3H]naloxone binding sites) and matrix-enriched areas of the rat striatum. Marked differences could be demonstrated as follows: (i) when used at 0.1 microM, the NK1 agonist stimulated the release of [3H]dopamine continuously synthesized from [3H]tyrosine in both compartments, while the NK2 and NK3 agonists enhanced the release of [3H]dopamine only in the matrix; (ii) the stimulatory effect of the NK3 agonist was less pronounced than those of the NK1 and NK2 agonists; (iii) the NK1 agonist-evoked responses were tetrodotoxin (1 microM) sensitive, while those of the NK2 and NK3 agonists were, respectively, partially and totally tetrodotoxin resistant; (iv) specific receptors are involved in these responses since the stimulatory effects of the NK1 and NK2 agonists were, respectively, blocked by potent antagonists of NK1 (RP-67580; 1 microM) and NK2 (SR-48968; 1 microM) receptors, while these antagonists did not affect the NK3 agonist-evoked response; (v) the indirect stimulatory effect of the NK1 agonist was partially reduced under local blockade of cholinergic transmission in the matrix but not in the striosomal-enriched area. Interestingly, this study also revealed mismatches between autoradiographic data and receptor-mediated responses, since NK2 binding sites could not be observed in the striatum while NK3 but not NK1 binding sites were visualized in the striosomal-enriched area.

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.

The ultrastructural effects of drugs enhancing, by different mechanisms, cholinergic transmission in the crop-sac (the target for prolactin secretion in birds) and the anterior pituitary lactotrophs, were studied in pigeons (Columba livia). The systemic or intraventricular administration of physostigmine, carbachol and muscarine produced maximal crop-sac stimulation with milk-like secretion, as demonstrated by the observation of ultrastructural changes in the lactiferous areas through scanning and transmission electron microscopy of the crop-sac mucosa. A marked activation was also observed in anterior pituitary lactotrophs. Crop-sac and anterior pituitary lactotrophs stimulatory effects were prevented by an atropine pretreatment, but not by mecamylamine and pempidine pretreatments. The present results suggest that muscarinic receptors at the hypothalamic and/or anterior pituitary level are involved in avian species in the control of prolactin secretion.

The nature of mecamylamine's and pempidine's antagonism of nicotine in the central nervous system has not been defined clearly. Although these compounds are thought to be noncompetitive antagonists in the brain due to the fact that they do not compete effectively for agonist binding to brain tissue in vitro, pharmacological evidence is lacking. The alteration of nicotine's dose-response curves for depression of spontaneous activity and antinociception was determined in the presence of increasing concentrations of pempidine. Pempidine was found to increase the ED50 of nicotine (0.73 mg/kg) for depression of spontaneous activity in a dose-related manner. At a dose of 3 mg/kg, pempidine increased nicotine's ED50 4.7-fold. The maximum effect of nicotine was achieved in the presence of the highest dose of pempidine, suggesting competitive antagonism. However, pempidine did decrease the maximum effect of nicotine in producing antinociception at doses that increased the ED50 13.7-fold which suggests a noncompetitive action. The structural requirements for mecamylamine's antagonism of these nicotine effects was also determined in order to address the question of whether the antagonists are interacting at a receptor site. The structure-activity relationships of the mecamylamine analogs revealed that the N-, 2- and 3-methyl groups were important for optimal potency. Optical isomerism was found to have little effect on potency. Addition of pyridinyl groups to the nitrogen abolished the activity of these compounds. The structural requirements for the agonists and antagonists therefore appear to be quite different. The alterations produced similar results for antagonism of both effects of nicotine. Mecamylamine and pempidine therefore appear to exhibit both competitive and noncompetitive properties in antagonizing the central effects of nicotine.

Both presynaptic and postsynaptic blockade of ganglionic transmission during the period of naturally occurring ganglion cell death reduced the number of surviving neurons in the sympathetic ganglia (SG) and ciliary ganglion (CG). The CG was chosen for analysis because there was a temporal separation between cell proliferation and death in the CG but not in the SG. Ganglion cell proliferation and migration were unaffected by ganglionic blockade. The increased ganglion cell loss that followed ganglionic blockade was accompanied by an increased number of degenerating cells. These results indicate that the decreased number of healthy ganglion cells that followed ganglionic blockade was the result of enhanced naturally occurring cell death.

Decentralization of the superior cervical ganglion (S.C.G.) of the rat elevated the neuropeptide-Y immunoreactivity (NPY-ir) content of the ganglion on day 1 (+43%) but not on day 3 post-surgery. The content of NPY-ir in the iris was increased by decentralization (+40%) 3 days post-surgery, and treatment with clonidine (+43%), and pempidine (+82%). The levels of NPY-ir in the rat vas deferens were not affected by either surgical or pharmacological treatment. These results suggest NPY is released from sympathetic nerves in the iris but not vas deferens during normal sympathetic activity.

Young rats, 11, 16, and 20 days of age, received bilateral injections of three antinicotinic agents into the posteroventral hippocampo-subiculo-entorhinal area, and were trained to learn a cool-draft-stimulus, passive-avoidance task shortly after (17 min). Gallamine triethiodide had no action at low doses and provoked convulsions at higher concentrations. Pempidine tartrate produced age- and dose-dependent impairments of the passive avoidance, and was much more effective in younger groups (11 and 16 days) than at 20 days. alpha-bungarotoxin also induced dose-dependent deficits. These results, together with the mecamylamine-induced deficits already reported, suggest that nicotinic cholinergic synapses located in the posteroventral part of the hippocampal complex play a role in passive-avoidance learning in the young rat as soon as this type of conditioning is possible, but become relatively less important at older ages, when muscarinic mechanisms also become involved.

Rat striatal slices (two) were superfused continuously with L-3,5-3H tyrosine and 3H-dopamine (3H-DA) release was estimated in serial fractions of superfusates. The spontaneous release of 3H-DA was reduced by about 50% when slices were superfused with a calcium-free medium containing ethylene glycol bis (beta-aminoethyl ether)- N,N'-tetraacetic acid (EGTA) (10(-4) M) or with a medium containg tetrodotoxin (5 x 10(-7) M). These effects were not related to a change in 3H-DA synthesis since the rate of L-3,5-3H tyrosine hydroxylation, as measured by 3H-H2O formation was not significantly reduced. Acetylcholine (ACh) (10(-5) M) stimulated the release of 3H-DA (about 100%). This effect was abolished in the absence of calcium; it was partially blocked by pempidine (10(-5) M), atropine (10(-6) M) or scopolamine (10(-5), 10(-6) M). Oxotremorine (10(-5) M) enhanced 3H-DA release but to a lesser extent (60%) than ACh (10(-5) M); its action was completely blocked by atropine (10(-6) M) and unaffected by pempidine (10(-5) M). The ACh- (10(-5) M) and oxotremorine- (10(-5) M) stimulatine effects on 3H-DA spontaneous release were still detected in slices superfused in the presence of tetrodotoxin (5 x 10(-7) M). In the presence of the neurotoxin, the effect of ACh (10(-5) M) was significantly reduced by pempidine (10(-5) M) and the effect of oxotremorine (10(-5) M) was blocked by atropine (10(-6) M). These results suggest the presence of cholinergic presynaptic receptors of the nicotinic and muscarinic types on striatal dopaminergic terminals.

1. Isoprenaline, 3.5-20 ng, injected intracerebroventricularly in atropinized mice under pentobarbitone anaesthesia produced a dose-dependent tachycardia. 2. Pretreatment with either reserpine or pempidine blocked nervously-mediated tachycardia as shown by marked reduction of that due to stimulation of the spinal outflow in pithed mice. After pretreatment with these drugs, intracerebroventricular isoprenaline caused tachycardia of a similar degree and time course to that in mice not so pretreated. 3. Pretreatment with either reserpine or pempidine caused supersensitivity to the tachycardia due to intravenous isoprenaline. 4. When allowance was made for this supersensitivity in the effect of intracerebroventricular isoprenaline in pretreated mice, a small dose-dependent residual effect remained that could be attributed to leakage of isoprenaline into the peripheral circulation. 5. This was confirmed by the appearance of a late-developing tachycardia on intracerebroventricular injection of isoprenaline in spinal mice. 6. It is therefore concluded that the tachycardia caused by intracerebroventricular isoprenaline in mice is, at least initially, of central origin.

By use of a sensitive in vitro microsuperfusion method, the cholinergic prsynaptic control of dopamine release was investigated in a prominent striosome (areas poor in acetylcholinesterase activity) located within the core of cat caudate nucleus and also in adjacent matrix area. The spontaneous release of [3H]dopamine continuously synthesized from [3H]tyrosine in the matrix area was found to be twice that in the striosomal area; the spontaneous and potassium-evoked releases of [3H]dopamine were calcium-dependent in both compartments. With 10(-6) M tetrodotoxin, 5 x 10(-5) M acetylcholine stimulated [3H]dopamine release in both striosomal and matrix areas, effects completely antagonized by atropine (10(-6) M), thus showing the involvement of muscarinic receptors located on dopaminergic nerve terminals. Experiments without tetrodotoxin revealed a more complex regulation of dopamine release in the matrix: (i) In contrast to results seen in the striosome, acetylcholine induced only a transient stimulatory effect on matrix dopamine release. (ii) Although 10(-6) M atropine completely abolished the cholinergic stimulatory effect on [3H]dopamine release in striosomal area, delayed and prolonged stimulation of [3H]dopamine release was seen with atropine in the matrix. The latter effect was completely abolished by the nicotinic antagonist pempidine (10(-5) M). Therefore, in the matrix, in addition to its direct (tetrodotoxin-insensitive) facilitatory action on [3H]dopamine release, acetylcholine exerts two indirect (tetrodotoxin-sensitive) opposing effects: an inhibition and a stimulation of [3H]dopamine release mediated by muscarinic and nicotinic receptors, respectively.

Isopropylnoradrenaline (ISO), 3',5'-AMP and dibutyryl-3',5'-AMP decreased the oxygen tension (pO2) in the liver and the spleen and increased the body oxygen consumption (VO2). Time dynamics of these two effects was closely correlated for ISO and 3',5'-AMP. An increase of heat output was not accompanied by any significant changes in the respiration coefficient. Pempidine and dihydroergotamine failed to prevent 3',5'-AMP effects; inderal somewhat decreased these effects. Apparently, the catecholamine influence upon pO2 was a result of the VO2 increase through 3'5'-AMP effects are largely direct, but they include the in vivo and beta-receptor component; 2',3'-AMP decreased pO2 and VO2.

The messenger RNAs coding for opioid peptide precursors have been detected and mapped in histological sections by "in situ' hybridization using specific DNA probes labelled with 32P. Using bovine preproenkephalin A (PPA) cDNA, PPA mRNA was detected in adrenal medulla of bull, hamster and guinea pig. No signal was detected in adrenal of man, rat and cat. The pro-opiomelanocortin (POMC) mRNA was detected in pituitary of man, bull, cat, rat and pig, in all cells of the intermediate lobe as well as in scattered cells of the anterior lobe producing POMC. Adequate controls demonstrated the specificity of the labelling. These results provide evidence of the expression of the gene coding for PPA in the adrenal and for POMC in the pituitary. They show cross-hybridization of one DNA probe with mRNAs of various mammals and then provide evidence that one single probe can be used to analyze expression of a given gene in tissues of several animal species by "in situ' hybridization.

1. Angiotensin I, II and hog renin, infused into the lateral cerebral ventricles (I.C.V.) of water replete cats, each induced water drinking behaviour. 2. Intravenous infusion of high doses of angiotensin I or II also elicited a drinking response. The dipsogenic effect of I.V. renin was not marked. 3. Drinking in response to I.C.V. angiotensin II was abolished after autonomic ganglion blockade with I.V. hexamethonium or pempidine and was significantly reduced after I.V. atropine methonitrate. 4. The dipsogenic response to I.C.V. angiotensin II was unaffected by either peripheral adrenergic neurone blockade with I.V. bethanidine, alpha-adrenoceptor blockade with phentolamine or beta-adrenoceptor blockade with sotalol. 5. Atropine, atropine methonitrate, hexamethonium and pempidine given I.C.V did not inhibit the diposgenic response to I.C.V. angiotensin II. 6. Bethanidine I.C.V. produced a dose related reduction in the dipsogenic response to I.C.V. angiotensin II. 7. The alpha-adrenoceptor blocking agents tolazoline and phenoxybenzamine given I.C.V did not affect angiotensin induced drinking but the response was regularly inhibited by phentolamine I.C.V. 8. The beta-adrenoceptor blocking agents propranolol and practolol given I.C.V. each inhibited angiotensin induced drinking. The L-isomer of propranolol was a more effective blocker than the D-isomer. 9. Isoprenaline given I.C.V induced drinking in ten of sixteen cats. Subcutaneous administration of isoprenaline also elicited drinking but the onset of the response was delayed and the amount consumed slightly less than after I.C.V infusion.

We have found a selective inhibition of nicotine-induced antinociception in mice by neosurugatoxin (NSTX, 0.4-3.8 nmol/kg), a neurotoxin with a high affinity for ganglionic nicotinic receptors (ED50 = 0.65 nmol/kg). The toxin also reduced specific [3H]nicotine binding in mouse brain membranes (IC50 = 95 nM). The anti-nicotinic activity of NSTX was markedly greater than that of mecamylamine and pempidine. These data indicate that NSTX may block functional nicotinic cholinoceptors possibly in the central nervous system.

1 Thermoregulatory responses have been recorded from Welsh Mountain sheep exposed to warm, neutral or cold environments while injections of cholinomimetic drugs and/or their antagonists have been given into a lateral cerebral ventricle. 2. Carbachol and physostigmine inhibited panting of animals at high ambient temperature (ta), caused vasoconstriction and initiated shivering at neutral ta, and accentuated shivering at low ta. Rectal temperature (tre) invariably increased. Oxotremorine had apparently identical effects. 3. Nicotine and another ganglionic stimulant, the quaternary methyl derivative of dopamine, had no effects on thermoregulation. 4. Atropine given 10 min before injections of carbachol, physostigmine or oxotremorine completely inhibited their hyperthermic effects, but pretreatment with the ganglion-blocking drug, pempidine, caused no inhibition. The cholinergic synapses that respond to cholinomimetic drugs injected into the lateral cerebral ventricles of sheep are therefore muscarinic and not nicotinic. 5. When atropine was given to sheep exposed to cold, no detectable reduction of shivering occurred and tre decreased only slightly, even with doses of atropine far greater than needed to inhibit shivering induced by physostigmine. This may be because shivering is controlled by neural pathways unaffected by drugs administered intracerebroventricularly or because the cholinergic synapses activated by physostigmine do not carry the input from cold sensors.

The ganglionic blocking effects of the secondary and tertiary amines, mecamylamine and pempidine, on the spinal reflex of cats of both sexes were investigated. These blocking effects were then compared with findings in the quaternary ammonium compounds such as tetraethylammonium (TEA) and decamethonium (C10). Mecamylamine (5 mg/kg) and pempidine (1 mg/kg) inhibited spinal reflex potentials such as the monosynaptic reflex (MSR), the polysynaptic reflex (PSR) and the dorsal root reflex (DRR). Maximal inhibition occurred 40 min after intravenous administration these drugs. In the case of mecamylamine, the inhibited potentials recovered gradually after reaching the maximum inhibition. However, the inhibitory effect of pempidine was prolonged, and recovery of the potentials did not occur for 6 min or longer. Although 10 mg/kg of C10 and 0.025 mg/kg of nicotine transiently inhibited the MSR and PSR, these compounds had no effect on the DDR. TEA produced prolonged inhibition of the MSR and PSR, and slightly enhanced the DRR. These results demonstrated the differences in DRR responses to secondary and tertiary amines, and quaternary ammoniums.

1 Transmural stimulation of rat isolated uterine horns at low pulse width produced contractions. These were antagonized by hyoscine or tetrodotoxin and potentiated by physostigmine. 2 In the presence of hyoscine, and during bradykinin-induced contractions, transmural stimulation produced inhibition. This inhibition was antagonized by guanethidine, propranolol or tetrodotoxin. 3 Hexamethonium or pempidine did not affect responses to transmural stimulation. 4 It is suggested that transmural stimulation is a method of exciting cholinergic motor and noradrenergic inhibitory postganglionic neurones to the rat myometrium.

Administration of serotonin into animals and incubation of serotonin with homogenates stimulated disulphide reductase in liver and spleen tissues. The effect of serotonin in vivo was probably mediated by liberation of catecholamines; it was eliminated by pyrilene and reserpine. The reflex mechanisms of catecholamines liberation were mediated by serotonin through serotonin-receptors of T-type. Alteration in the disulphide reductase activity correlated with the increased content of thiols after administration of serotonin.

For studying the interactions of the cholinergic and noradrenergic systems in the central nervous system rats were given muscarine or nicotine and the peripheral receptors were blocked with atropine or pempidine. After killing the animals the level of biogenic amines was determined in various parts of the brain. Evident changes were found in the levels of biogenic amines after stimulation or blockade of muscarinic or nicotinic receptors.

3 x 10(-6)M praziquantel fails to completely paralyse miracidia and cercariae in a short time but they are not infective when maintained in the solution. 3 x 10(-5)M praziquantel prevents infected snails shedding cercariae but does not kill daughter sporocyts or developing cercariae. As the action of praziquantel on adult worms is not blocked by 10(-2)M mecamylamine, pempidine or carbachol, but is reduced by calcium depletion, it is suggested that praziquantel may act by permitting calcium influx to muscle cells causing them to contract.

Secretion of corticotropin releasing factor (CRF) from the hypothalamic paraventricular nuclei into the hypophysial-portal circulation is modulated by a variety of neuronal afferents. Effects of intracerebroventricular acetylcholine (ACH), gamma-aminobutyric acid (GABA) and epinephrine (EPI) on immunoreactive (ir) CRF concentration in portal plasma were directly evaluated in urethanized male rats. ACH (0.1-10 nmole) administration was associated with a dose-dependent elevation of portal irCRF which was attenuated by pretreatment with either muscarinic or nicotinic receptor antagonists. GABA (0.1-10 nmole) also caused inhibition of irCRF concentration in the portal plasma which was prevented by bicuculline pretreatment. Finally, EPI (0.1-10 nmole) facilitated irCRF secretion via alpha 1- and beta-adrenergic mechanisms. These observations provide the first direct information on possible neurotransmitter actions on hypothalamic CRF secretion.

The ability of nicotinic receptor blockers, mecamylamine and pempidine, to antagonize the changes in striatal dopamine (DA) metabolism induced by repeated nicotine administration was studied. The contents of DA and its metabolites 3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured. Mice kept at 20-22 degrees C were given nicotine, 3 mg/kg, s.c., four times, at 30 min intervals, and sacrificed 20 min after the last dose. Hexamethonium, 10 mg/kg, i.p., was administered at 30 min before the first nicotine dose in order to prevent the peripheral effects of nicotine. Mecamylamine, 0.6 or 10 mg/kg, i.p., and pempidine, 0.6 or 20 mg/kg, i.p., were given at 60 min before sacrifice. Mecamylamine and pempidine decreased clearly the striatal 3-MT content, which suggests that the nigrostriatal dopaminergic neurons are physiologically controlled by a stimulatory nicotinic mechanism. The repeatedly administered nicotine caused deep hypothermia, and increased the striatal DOPAC content but decreased the 3-MT and HVA contents. The small dose of mecamylamine, which was the only dose found to effectively antagonize the nicotine-induced hypothermia, antagonized the decrease of HVA content. The large but not the small doses of mecamylamine and pempidine antagonized the nicotine-induced increase of DOPAC content but none of the doses studied antagonized the decrease of 3-MT content. Thus it seems that nicotine decreases the 3-MT content by a mechanism distinct from the mechanism mediating the increase of the DOPAC content. The decreased 3-MT content most probably results from desensitization of nicotinic cholinergic receptors (nAChR) and following decrease of cholinergic regulation of nigrostriatal dopaminergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Both the naturally occurring (-)-isomer and the synthetic (+)-isomer of nicotine caused release of 3H from a crude synaptosomal fraction of rat brain preincubated with [3H]dopamine. The isomers were equipotent in producing this response, which was concentration-dependent, a significant effect on the fractional release of dopamine being observed at 10(-4) M nicotine. The effect did not appear to be the result of synaptosomal damage, as levels of the intrasynaptosomal marker lactate dehydrogenase did not increase in the supernatant. Nicotine-induced release was inhibited by removal of external Ca2+ and by the presence in vitro of pempidine (230 microM). Neither hexamethonium (500 microM) in vitro nor the chronic administration of (-)-nicotine in vivo had any effect on the nicotine-induced release of [3H]dopamine. It is concluded that nicotine exerts this effect via a presynaptic nicotinic receptor of the "ganglionic" type, but that this receptor differs from that in the periphery by showing a relative lack of stereospecificity. There is no evidence of a functional "down regulation" in this receptor on chronic exposure to nicotine in vivo.