On status badges and quality signals in the paper wasp Polistes dominulus: body size, facial colour patterns and hierarchical rank.

To establish a dominance order, social animals often rely on indicators of fighting to avoid costly aggressive encounters. In some species, individuals use colour patterns to signal their social status. Recent studies claimed that facial markings in the eusocial paper wasp Polistes dominulus are status badges that allow co-foundresses to form a linear hierarchy based on individual quality. Here, we evaluated facial patterns in natural populations of P. dominulus, in its native range, to observe whether the marks reflect overall wasp quality in different contexts. We used the same measures of clypeus patterns used by earlier studies, but did not find that they functioned as status badges. Our analyses showed no evidence that visual markers are related to: (i) size, (ii) probability of surviving winter, (iii) social rank in spring associations, or (iv) health status (assessed by the presence of strepsipteran endoparasites). Size, however, is important. Larger wasps are more likely to survive the winter and to acquire the dominant position in spring associations. Larvae infected with endoparasites become smaller adult wasps. These findings suggest that body size is a reliable quality indicator on which wasps build their social networks, and that clypeus patterning is not involved.

Non-sibling parasites (Strepsiptera) develop together in the same paper wasp.

Host discrimination by immature host-seeking endoparasites is a complex and somewhat unexplored topic. In the case of multiple infections, conflicts among conspecifics may occur to monopolize space and resources in the same host. Two or more 1st instar larvae of Xenos vesparum (Strepsiptera, Stylopidae) may enter into a Polistes dominulus (Hymenoptera, Vespidae) larva and develop together until the adult stage of both parasite and host. We carried out a screening of mitochondrial haplotypes in X. vesparum individuals extracted from superparasitized wasps taken in 5 naturally infected nests from different areas of Tuscany (Italy), to assess whether non-sibling parasites may infect the same colony and host. In total, we obtained 12 different haplotypes out of 122 genotyped individuals of both sexes: 17 of 34 superparasitized wasps hosted parasites that originated from females differing in their haplotypes. To date, this is the first described case of superparasitism with non-sibling host-seeking larvae infecting a single individual hymenopteran host. In addition, at least in heavily infected colonies, there is evidence of a male-biased sex-ratio and synchronous development of the parasites, regardless of their haplotypes. Finally, the distribution of haplotypes per nest is consistent with either phoretic infection or larvipositing on nests by means of superparasitized wasps.

Serotonin modulation of cell excitability and of [3H]GABA and [3H]D-aspartate efflux in primary cultures of rat cortical neurons.

The effects of 5-hydroxytryptamine (5-HT) on neuronal excitability, evaluated as depolarization-induced firing rate, and on amino acid release, measured as electrically-evoked [(3)H]GABA and [(3)H]d-aspartate efflux, were investigated in rat primary cortical neuronal cultures. 5-HT displayed a concentration-dependent, bimodal effect on neuronal excitability: at 3-10microM it increased excitability through 5-HT(2A) receptors, and was blocked by the selective 5-HT(2A) antagonist MDL 100907, whereas at 30-100microM it reduced excitability through 5-HT(1A) receptors, and was, in turn, blocked by the selective 5-HT(1A) antagonist WAY 100135. The electrically-evoked [(3)H]GABA efflux was concentration-dependently inhibited by 5-HT (pEC(50)=4.74) and such inhibition was prevented by WAY 100135, but not by GR 55562, a selective 5-HT(1D/B) receptor antagonist. Conversely, 5-HT concentration-dependently increased stimulus-evoked [(3)H]d-aspartate efflux (pEC(50)=4.71). The increase was facilitated by methiothepin and was reversed into inhibition by ICS 205930, a selective 5-HT(3) receptor antagonist. In the presence of ICS 205930, the inhibition induced by 5-HT was prevented by the selective 5-HT(1D/B) receptor antagonist GR 55562, but not by WAY 100135. These findings suggest that 5-HT inhibits GABA release through 5-HT(1A) receptors and exerts a dual modulation on glutamate release, mostly facilitatory (through 5-HT(3) receptors) but also inhibitory (through 5-HT(1D/B) receptors), leading to a prevalently positive modulation of the excitatory signal by amino acid neurotransmitter containing neurons.

Subtle effect of Xenos vesparum (Xenidae, Strepsiptera) on the reproductive apparatus of its male host: Parasite or parasitoid?

Parasitic castration is an adaptive strategy where parasites usurp the hosts' reproductive physiology to complete their life cycle. The alterations in the host traits vary in their magnitude, from subtle changes in the host morpho-physiology and behaviour to the production of complex aberrant phenotypes, which often depend on the host gender. The strepsipteran macroparasite Xenos vesparum induces dramatic behavioural and physiological changes in its female host, the paper wasp Polistes dominula, while its effect on the male phenotype is largely unknown. In this study we investigated how a single X. vesparum parasite influences the functional morphology of P. dominula male reproductive apparatus. We performed morphometry and ultrastructure characterization of corpora allata, testes, seminal vesicles and accessory glands in parasitized and unparasitized males, and also in young and old males to control for the effect of age on the natural deterioration of these organs. Our results show that age significantly affects the development of male reproductive apparatus. A low parasite load - one parasite per host is the common prevalence in the field - has only a marginal impact on the reproductive morphology of P. dominula males, affecting quantitatively but not qualitatively the protein content of male accessory glands. Thus, in male P. dominula wasps, X. vesparum appears to behave as a true "parasite", in clear opposition to the role of "parasitoid" that it takes in female hosts where castration causes the reproductive death.

Effects of chemical ischemia in cerebral cortex slices. Focus on nitric oxide.

Superfused rat cerebral cortex slices were submitted to a continuous electrical (5 Hz) stimulation and treated with sodium azide (1-10 mM) in the presence of 2 mM 2-deoxyglucose ("chemical ischemia"). Presynaptic cholinergic activity, evaluated as acetylcholine release, was inhibited depending on the sodium azide concentrations and on the length of application (5-30 min). Following a 5-min treatment with 10 mM sodium azide, acetylcholine release was reduced to 45+/-2.3%; simultaneously, there was a 15- and 10-fold increase in glutamate and nitric oxide effluxes, respectively. After restoring normal superfusion conditions, acetylcholine release recovered to 70+/-3.1% of the controls; the N-methyl-D-aspartate receptor antagonist MK-801 (10 microM) as well as the nitric oxide scavengers, haemoglobin (20 microM) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (150 microM), improved the recovery in presynaptic activity, showing that both glutamate and nitric oxide play detrimental roles in chemical ischemia. On the other hand, the post-ischemic recovery was worsened by the guanylylcyclase inhibitor 1H-[l,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (10 microM), suggesting that the activation of such a pathway plays a neuroprotective role and that the nitric oxide-induced harmful effects depend on different mechanisms. Chemical ischemia-evoked nitric oxide efflux partly derived from its calcium-dependent endogenous synthesis, since both the intracellular calcium chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (1 mM), and the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (100 microM), substantially prevented sodium azide effects. Nitric oxide efflux was only weakly reduced by MK-801 and was not modified by either the L-type calcium channel blocker, nifedipine (10 microM) or the N-type calcium channel blocker omega-conotoxin (0.5 microM), thus suggesting a prevailing intracellular calcium-dependence of nitric oxide production, although a partial extracellular calcium source cannot be ruled out. These findings show that sodium azide plus 2-deoxyglucose treatment is a useful protocol to induce brain ischemia in vitro and underline the involvement of nitric oxide in the complex events following the ischemic insult.

Mating of Xenos vesparum (Rossi) (Strepsiptera, Insecta) revisited.

The controversial mating of the strepsipteran Xenos vesparum was studied to investigate the possible sperm routes for fertilization. The female, which is a neotenic permanent endoparasite of Polistes wasps, extrudes only its anterior region, the "cephalothorax," from the host abdomen. This region has an opening where both mating and larval escape occur. Observations with scanning and transmission electron microscopy revealed spermatozoa not only in the hemocoel, but also in the "ventral canal" (an extragenital duct peculiar to strepsipteran females) and in the "genital ducts" (ectodermal invaginations connecting the ventral canal to the hemocoel) of recently mated females. Xenos vesparum spermatozoa can reach the oocytes either through the hemocoel as a result of a hypodermic insemination, or by moving along the extragenital ducts, which are later used by first instar larvae to escape. The hypothesis of hypodermic insemination is reconsidered in the light of behavioral and ultrastructural evidence.

The influence of 5-hydroxytryptamine on the release of acetylcholine from guinea-pig brain ex vivo and in vitro.

The effect of 5-hydroxytryptamine (5-HT) on the release of acetylcholine (ACh) from the brain of the guinea-pig was investigated in order to determine whether this amine plays a modulatory role on the cortical cholinergic projections. 5-Hydroxytryptamine (0.2-1 mumol), injected intracerebroventricularly (i.c.v.), caused mild excitation, stereotyped movements and ataxia. Simultaneously, it increased the output of ACh from the cortex in a dose-dependent manner. Methysergide (4.2 mumol Kg-1 i.p.) also increased the output of ACh by about 60-80%, but prevented the effect of 5-HT (1 mumol i.c.v.). Metitepine (1-4.2 mumol kg-1 i.p.) increased the output of ACh like methysergide but it changed the facilitation of the release of ACh by 5-HT into inhibition. At the same time the animals became hypothermic, sedated and their electroencephalogram (EEG) was synchronized. Pretreatment with 5,7-HT blocked the increase in release of ACh produced by 5-HT (1 mumol). D-Norfenfluramine (10.4 mumol kg-1) was ineffective alone but reduced the release of ACh in metitepine-pretreated animals. 5-Hydroxytryptamine (10-30 microM) did not affect the efflux of [3H]choline from electrically-stimulated slices of cerebral cortex. The increase in the release of ACh caused by 5-HT, abolished by pretreatment with methysergide and 5,7-HT, may be explained by activation of 5-HT autoreceptors, while the increase of transmitter outflow induced by methysergide may be due to a blockade of 5-HT receptors present on the cholinergic neurones. Metitepine appeared to unmask the tryptaminergic inhibition caused by injection of 5-HT intraventricularly or by the 5-HT-releasing drug, D-norfenfluramine, possibly by acting on the autoreceptors and preventing auto-inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of chronic chlorimipramine treatment on the serotonergic modulation of acetylcholine release from guinea pig caudate nucleus slices.

The influence of chronic chlorimipramine (10 mg/kg daily s.c. for 14 days) treatment (CCT) on 5-HT modulation of basal 3H-choline overflow from guinea pig caudate nucleus slices was studied. The increase in basal tritium overflow induced by 5-HT (3-100 mumol/l) or by DOI (30-100 mumol/l) in normal slices was significantly lower in CCT slices. When tetrodotoxin 0.5 mumol/l was added, the facilitatory effect by 5-HT was cancelled, its late inhibitory effect became more evident and to the same extent in normal and CCT slices. This inhibition was cancelled by ICS 205-930 30 mumol/l. These results indicate that the 5-HT2-mediated facilitatory response of intrastriatal cholinergic neurones to 5-HT is reduced by CCT, while the inhibitory response is unaffected.

The modulation of cortical acetylcholine release by GABA, GABA-like drugs and benzodiazepines in freely moving guinea-pigs.

In order to define the modulatory role played by gamma-aminobutyric acid (GABA) in corticopetal cholinergic projections, the effect of this amino acid and related drugs on gross behaviour, the EEG and the release of acetylcholine (ACh) from the cerebral cortex in freely moving guinea-pigs was studied. gamma Aminobutyric acid, injected intracerebroventricularly (20-50 mumol) induced a three-phase picture: first (5-15 min) behavioural activation and increased release of ACh, then (30-90 min) depression, EEG synchronization and reduced release of ACh, and finally "rebound" stimulation. Ethanolamine-O-sulphate (EOS) injected intraventricularly (28 mumol/kg) or intraperitoneally (14 mmol/kg) reproduced the first two phases of the effects of GABA (i.e. stimulation followed by inhibition), while diazepam (0.7 and 3.5 mumol/kg, i.p.) and flurazepam (32 mumol/kg, i.p.) caused, at first, only depression. Muscimol and 4,5,6,7-tetrahydroisoxazolo(4,5-c)pyridine-3-ol (THIP) injected intraventricularly (in the nmol range) or intraperitoneally (in the mumol range) produced behavioural activation and increased release of ACh; the depressant signs appeared only after very large, toxic doses. Picrotoxin and bicuculline, at sub-convulsive doses, reduced the symptomatology caused by GABA and antagonized the sedation produced by diazepam. Methysergide (8-16 mumol/kg, i.p.) prevented the behavioural activation and the increased release of ACh by GABA, unmasked the depression due to subthreshold doses of diazepam (i.c.v., 7-70 nmol) and reversed the stimulation induced by muscimol into sedation and reduced the outflow of ACh. Pretreatment with 5,7-HT also dampened and shortened the stimulation by muscimol.(ABSTRACT TRUNCATED AT 250 WORDS)

The nicotinic modulation of [(3)H]D-aspartate outflow in primary cultures of rat neocortical neurons: effect of acute and long term nicotine treatment.

The effect of nicotine 1 nM-10 microM on the efflux of [(3)H]D-aspartate was tested in primary cultures of rat cortical neurons kept at rest and subjected to electrical field stimulation. Two trains of pulses at 20 Hz for 20 s were applied at the 60th (St(1)) and 90th (St(2)) min of perfusion. The drug slightly and transiently increased the efflux of resting cells while, when given during St(2), it greatly enhanced the electrically evoked efflux estimated as St(2)/St(1) ratio, EC(50) being 107 nM. The nicotinic receptors (nAChR) giving rise to this positive modulation were partly mecamylamine- and partly alpha-bungarotoxin-sensitive. They appeared to be located at the nerve endings since nicotine facilitation was only slightly prevented by tetrodotoxin during depolarisation with 15 mM KCl. Pretreatment with glutamate antagonists did not reveal any interaction between nAChR and ionotropic glutamate receptors. Membrane glutamate carrier involvement in the nicotine effect was ruled out. Long-term treatment with nicotine 1 microM (from the 3rd-4th to the 8th-9th day in vitro) reduced the maximal response to the drug but shifted its threshold concentration to the left (from 10 nM to 1 nM), leaving the contribution of the two receptor subtypes unchanged. Reduced responsiveness to nicotine was also evident in long-term treated cerebellar granule cells. In conclusion, presynaptic nAChR's, both containing and lacking alpha(7) subunits, can contribute to enhance the glutamatergic secretion in primary cultures of rat cortical neurons, chiefly during electrical stimulation.

Effect of adenosine, adenosine triphosphate, adenosine deaminase, dipyridamole and aminophylline on acetylcholine release from electrically-stimulated brain slices.

The effect of adenosine on release of acetylcholine (ACh) was investigated in slices of rat cortex perfused with Krebs solution, at rest and during electrical stimulation at frequencies between 0.2 and 20 Hz. Electrical stimulation brought about a linear increase in release of ACh. Adenosine, in concentrations ranging from 1 to 100 microM, reduced in a dose-dependent manner the release of ACh and was more active on the stimulated than on the resting release. However, the fractional reduction by adenosine of stimulated release of ACh did not vary with increasing stimulation rate. Adenosine triphosphate was less active than adenosine in reducing release of ACh. The inhibitory effect of adenosine was antagonized by aminophylline (0.5 mM) and did not occur when the stimulated release of ACh was enhanced by blocking muscarinic autoreceptors with atropine (15 nM). Aminophylline (0.1 and 0.5 mM) itself exerted a biphasic effect on release of ACh, increasing it at rest and during stimulation at low frequencies, and decreasing it at higher stimulation rates. The manipulation of endogenous adenosine concentrations by adding adenosine deaminase or diphyridamole, an inhibitor of adenosine uptake, had little effect on release of ACh. Dipyridamole, (4 microM), only significantly decreased release of ACh at the 20 Hz stimulation rate.

Effects of nociceptin/orphanin FQ and endomorphin-1 on glutamate and GABA release, intracellular [Ca2+] and cell excitability in primary cultures of rat cortical neurons.

The effects of nociceptin/orphanin FQ (N/OFQ) and endomorphin-1 (EM-1) on glutamate and GABA release, intracellular calcium, neuronal excitability and glutamate current were investigated in rat primary cortical neuronal cultures. Through their specific receptors N/OFQ and EM-1 (0.02-1 microM) inhibited the electrically evoked outflow of [3H]D-aspartate at most to -50% and that of [3H]GABA to -30%. In addition, at 1 microM, both peptides induced a decrease of the firing rate caused by electrical depolarization. N/OFQ 1-10 microM did not influence either the electrically evoked calcium influx or the glutamate-evoked currents, whereas EM-1 1 microM significantly inhibited them. Thus, in cortical neurons in culture, both N/OFQ and EM-1 inhibited the secretory process and neuronal excitability but EM-1 also affected calcium influx and cell body responsiveness to glutamate. Consequently, EM-1 appeared to dampen this excitatory signal more then N/OFQ did.

Nociceptin/orphanin FQ receptors modulate glutamate extracellular levels in the substantia nigra pars reticulata. A microdialysis study in the awake freely moving rat.

Intracerebral microdialysis was employed in awake freely moving rats to investigate the effects of nociceptin/orphanin FQ receptor ligands on glutamate extracellular levels in the substantia nigra pars reticulata. Nociceptin/orphanin FQ, ineffective at 0.1 microM, induced a prolonged stimulation of nigral glutamate levels at 1 and 10 microM (mean effect of 137+/-9 and 167+/-13%, respectively, of basal values). These effects were prevented by the novel nociceptin/orphanin FQ receptor antagonist [Nphe(1)]nociceptin/orphanin FQ(1-13)NH(2) (100 and 300 microM, respectively) but not by the non-selective opioid receptor antagonist naloxone (10 microM). [Nphe(1)]nociceptin/orphanin FQ(1-13)NH(2) (100 microM) inhibited by itself glutamate outflow (maximal reduction to 71+/-4%) while naloxone was ineffective. The nociceptin/orphanin FQ receptor ligand [Phe(1)psi(CH(2)-NH)Gly(2)]nociceptin/orphanin FQ(1-13)NH(2) also facilitated glutamate outflow at 10 microM (mean effect of 145+/-10%). Intranigral perfusion with tetrodotoxin (1 microM) or with the dopamine D(2) receptor antagonist raclopride (1 microM), failed to affect basal glutamate output and prevented the facilitatory effect of nociceptin/orphanin FQ (10 microM). However, perfusion with the GABA(A) receptor antagonist bicuculline (10 microM) increased local glutamate extracellular levels by itself and attenuated the effect of the peptide. Our data suggest that nociceptin/orphanin FQ increases glutamate extracellular levels in the substantia nigra pars reticulata via activation of nociceptin/orphanin FQ receptors located on non-glutamatergic, possibly dopaminergic and GABAergic, neuronal elements.

Facilitation of GABA release by neurotensin is associated with a reduction of dopamine release in rat nucleus accumbens.

The main aim of the present study was to investigate the effects of local perfusion with the tridecapeptide neurotensin on extracellular GABA and dopamine levels in the nucleus accumbens of the halothane-anaesthetized rat, using in vivo microdialysis. In an initial set of characterization studies we examined the Na+ dependence of neurotransmitter release by local perfusion with ouabain, veratridine and tetrodotoxin. Local perfusion with the Na+ ATPase inhibitor ouabain (10 microM) or the Na+ channel agonist veratridine (20 microM) perfused into the nucleus accumbens increased both extracellular GABA and dopamine levels. The Na+ channel antagonist tetrodotoxin (1 microM) consistently decreased (24% of basal) dopamine levels, while even at 10 microM it did not affect GABA. However, tetrodotoxin (10 microM) abolished the veratridine-induced increase in both GABA and dopamine, demonstrating that Na(+)-dependent neuronal activity is involved in this release mechanism. In a second set of experiments a hypothesis for a functional link between neurotensin, dopamine and GABA in the medial nucleus accumbens was tested. Towards this aim, the effects of local perfusion with a high 1 microM concentration of neurotensin into the nucleus accumbens increased both GABA (210% of basal value) and dopamine (145% of basal) release. However, a low (10 nM) concentration of neurotensin again increased GABA release (160% of basal), but decreased that of dopamine (75% of basal value). Furthermore, the local perfusion with the GABAA receptor antagonist bicuculline abolished the neurotensin (10 nM) induced inhibition of dopamine release without affecting the increase in GABA release. These findings suggest that neurotensin modulates both GABA and dopamine neurotransmission in the nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a differential cholecystokinin-B and -A receptor regulation of GABA release in the rat nucleus accumbens mediated via dopaminergic and cholinergic mechanisms.

In the present study we characterized the cholecystokinin receptor regulation of (i) the dopamine D2 agonist binding sites in striatal sections including the nucleus accumbens and (ii) GABA and dopamine release in the central part of the rat nucleus accumbens, by combining the in vitro filter wipe-off and the in vivo microdialysis techniques. In the binding study we demonstrate that sulphated cholecystokinin octapeptide (1 nM) increased (219 +/- 30%) the KD value of the D2 agonist [3H]N-propylnorapomorphine binding sites in sections from the striatum including the accumbens. This effect was counteracted by the cholecystokinin-B antagonist PD134308 (50 nM). In a parallel study using microdialysis in the central nucleus accumbens, we found that local perfusion with sulphated cholecystokinin octapeptide (1 microM) induced an increase in GABA (135 +/- 7%) and dopamine (146 +/- 8%) release which was unaffected by the cholecystokinin-A antagonist L-364,718 (10 nM). In contrast, when the cholecystokinin-B antagonist PD134308 (10 nM) was co-perfused with the peptide it prevented the increase in dopamine and decreased GABA release (-24 +/- 2%). This reduction was counteracted by the addition to the perfusate medium of the cholecystokinin-A antagonist or the cholinergic muscarinic M2 receptor antagonist AF-DX 116 (0.1 microM). Taken together, these data demonstrate that the facilitation by sulphated cholecystokinin octapeptide of GABA and dopamine release in the central accumbens probably reflects an inhibitory effect of the peptide on both pre- and postsynaptic D2 receptors, mediated via cholecystokinin-B receptor activation. In addition, for the first time we provide evidence for a differential cholecystokinin-A and -B receptor-mediated regulation of GABA transmission in the central accumbens, where the cholecystokinin-B receptor exerts a dominant excitatory influence while the cholecystokinin-A receptor mediates an inhibition of GABA release via a local muscarinic M2 receptor.

Changes in hippocampal and cortical B1 bradykinin receptor biological activity in two experimental models of epilepsy.

An increased response to the activation of receptors mediating excitatory effects may be involved in some forms of epilepsy. In this study, it has been tested whether B1 bradykinin receptors (which mediate excitatory effects in the peripheral nervous system and have little constitutional expression in the central nervous system) may be proposed in this role. Two experimental models of epilepsy (kindling and kainate) have been employed, and glutamate outflow experiments have been performed in hippocampal and cortical slices taken from control, kindled and kainate-treated rats. The endogenous B1 receptor agonist Lys-des-Arg9-bradykinin (10(-7) M) did not affect electrically-evoked glutamate overflow in control animals, but concentration-dependently increased it in kindled rats (maximal effect +40 to + 50%) and, to a lesser extent (+20%), in kainate-treated rats. These effects were fully prevented by the selective B1 receptor antagonist R-715 (10(-6) M), but not by the selective B2 receptor antagonist Hoe 140 (10(-6) M). The observed changes in B1 bradykinin receptor biological activity may play a role in epileptic hyperexcitability.

5-HT1A agonists increase and 5-HT3 agonists decrease acetylcholine efflux from the cerebral cortex of freely-moving guinea-pigs.

1. The influence of 5-hydroxytryptamine1A (5-HT1A), 5-HT2 and 5-HT3 agonists and antagonists on acetylcholine (ACh) release from the cerebral cortex was studied in freely moving guinea-pigs. 2. 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 0.01-1 mg kg-1, s.c.) caused the 5-HT syndrome and dose-dependently increased ACh release. Ru 24969 (1-10 mg kg-1, s.c.) shared the same effects, but it was less potent. (-)-Propranolol (5 mg kg-1) and metitepine (2 mg kg-1) prevented these behavioural and neurochemical responses. 3. (+/-)-1(4-Iodo-2,5-dimethoxyphenyl)2-aminopropane (DOI) up to 2 mg kg-1 did not modify ACh release and ketanserin (0.5 mg kg-1) was ineffective on 5-HT-induced changes of ACh outflow. 4. 2-Methyl-5-HT (500 micrograms, i.c.v.) and 5-HT (500 micrograms, i.c.v.) plus metitepine (2 mg kg-1, s.c.) inhibited the gross behaviour and ACh release. ICS 205-930 (0.5 mg kg-1) prevented these responses. 5. 2-Methyl-5-HT, up to 10 mumols 1(-1), and 8-OH-DPAT, up to 0.1 mumols 1(-1), (like 5-HT) did not change [3H]-choline efflux from cerebral cortex slices. 6. These results suggest that exogenous 5-HT and related selective agonists modulate guinea-pig cortical cholinergic structures through 5-HT1A and 5-HT3 receptors. The stimulation of 5-HT1A autoreceptors may lead to disinhibition of the cholinergic cells, tonically inhibited by the tryptaminergic control. Conversely, the stimulation of 5-HT3 receptors inhibits ACh release, possibly through an interneurone. No direct 5-HT modulation of the cholinergic nerve endings was found.

Effect of 5-hydroxytryptamine on [3H]-acetylcholine release from guinea-pig striatal slices.

1. The effect of 5-hydroxytryptamine (5-HT) on spontaneous and electrically-evoked tritium efflux was studied in guinea-pig caudate nucleus slices preloaded with [3H]-choline. 2. 5-HT, 10-300 mumol l-1, temporarily increased the spontaneous tritium efflux (as well as the endogenous acetylcholine (ACh) release) and, after 15 min perfusion, inhibited it. The facilitatory effect of 5-HT on spontaneous efflux was increased while the inhibitory effect did not occur in slices taken from dopamine-depleted guinea-pigs. 3. The increase in spontaneous tritium efflux by 5-HT was blocked by methiothepin, methysergide (pA2 8.7) and by the selective 5-HT2 antagonist, ritanserin (pA2 6.7). 4. The inhibition of spontaneous tritium efflux by 5-HT was prevented by methysergide and methiothepin but not by ritanserin and (-)-propranolol. 5. 5-HT, 100 mumol l-1, inhibited the electrically-evoked tritium efflux and this effect was unchanged in dopamine-depleted slices. 6. The inhibition of electrically-evoked tritium efflux by 5-HT was blocked by methiothepin and methysergide but not by (-)-propranolol or ritanserin. 7. These results suggest that 5-HT may exert a rapid and transient (excitatory) and a more prolonged (inhibitory) control over striatal cholinergic neurones.

Influence of acute and chronic chlorimipramine treatment on the 5-HT receptor-mediated modulation of acetylcholine release from the cerebral cortex of freely moving guinea-pigs.

1. Acetylcholine (ACh) release from the cerebral cortex of freely moving guinea-pigs, implanted with epidural cups, was studied. 2. A single dose of chlorimipramine (Cl-Imip, 10 mg kg-1, s.c.), reduced the cortical ACh release both in normal and in chronically (10 mg kg-1 daily, s.c., for 14 days) Cl-Imip-treated guinea-pigs; the 5-HT3 antagonist MDL 72222 (1 mg kg-1, s.c.) antagonized this effect. 3. A single dose of Cl-Imip significantly reduced the effect of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylaminotetralin) (8-OH-DPAT, 0.1 mg kg-1, s.c.), which nearly doubled the cortical ACh release in control animals. MDL 72222 restored to normal the response to 8-OH-DPAT reduced by the anti-depressant. 4. A single dose of Cl-Imip did not change the inhibitory, MDL 72222-sensitive, effect induced by the 5-HT3 agonist 2-methyl-5-hydroxytryptamine (2-methyl-5-HT, 500 micrograms, i.c.v.). 5. In chronically Cl-Imip-treated guinea-pigs, the facilitatory effect of 8-OH-DPAT was no longer present, while the inhibitory, MDL 72222-sensitive, effect of 2-methyl-5-HT was maintained. 6. These results indicate that the 5-HT1A receptor-mediated increase in ACh release is reduced by prolonged Cl-Imip treatment, while the 5-HT3 receptor-mediated inhibition of ACh release is unaffected. The relevance of these findings to the antidepressant mechanism of Cl-Imip is discussed.

The effect of catecholamines and sympathetic stimulation on the release of acetylcholine from the guinea-pig colon.

1. In isolated guinea-pig terminal colon, the effect of sympathetic stimulation on contraction and acetylcholine release elicited by pelvic and transmural stimulation was investigated.2. Sympathetic stimulation reduced the nerve-mediated contractile responses more than those produced by added acetylcholine.3. Sympathetic stimulation also reduced the acetylcholine released during pelvic and transmural stimulation at low frequency. The inhibitory effect on acetylcholine released from resting colons is concealed by the simultaneous release of acetylcholine in considerable amounts from stimulated periarterial nerves which probably contain parasympathetic fibres.4. The inhibitory effect of endogenous and exogenous catecholamines prevails when cholinergic neurones fire at low rates. It was confirmed that adrenaline is more active than noradrenaline.5. The release of acetylcholine from unstimulated colons was for the most part maintained by nerve-conducted activity, because tetrodotoxin was able to reduce it to about one-tenth.6. It is suggested that the sympathetic control of gastrointestinal tone and motility is exerted through two different routes: inhibition of intramural cholinergic plexuses and direct relaxation of smooth muscle cells.7. The possible site and mechanism of action of catecholamines on intramural cholinergic structures is briefly discussed.