Effects of benzodiazepines on central serotonergic mechanisms.

If the rat conflict test were a valid animal model of anxiety neurosis, evidence which implicates serotonin systems in the anxiety-reducing actions of benzodiazepine tranquilizers could be summarized as follows: (1) The punishment-lessening effects of benzodiazepines in the conflict test are mimicked by serotonin antagonists (methysergide, cinanserin, bromolysergic acid), serotonin synthesis inhibition (PCPA), and serotonin nerve terminal damage (5,6-dihydroxytryptamine). (2) Punishment effects may be intensified by the serotonin precursor, 5-hydroxytryptophan (in combination with a monoamine oxidase inhibitor), serotonin agonists (alpha-methyltryptamine), or intraventricular injections of serotonin itself. Intraventricularly administered serotonin also antagonizes the punishment-lessening effects of benzodiazepines. (3) Stimulation of the serotonergic cell bodies in the dorsal raphe nucleus by local application of crystalline carbachol causes intense suppression of behavior. The suppressive effects of raphe stimulation are antagonized by systemic administration of benzodiazepines. (4) In biochemical experiments, the decrease in norepinephrine turnover induced by oxazepam rapidly undergoes tolerance, whereas the decrease induced in serotonin turnover is maintained over repeated doses. These results parallel findings in the conflict test which indicate that the depressant action of oxazepam rapidly undergoes tolerance, whereas the anxiety-reducing action is maintained over repeated doses. Although central serotonin neurons are thus implicated in the therapeutic actions of benzodiazepine tranquilizers, it is quite possible that the drugs actually act indirectly to reduce serotonin activity. The concept that benzodiazepines may exert a primary action on GABA-containing neurons, which in turn regulate serotonergic transmission, was supported by preliminary psychopharmacological evidence. The GABA-antagonist picrotoxin, at doses that do not disrupt unpunished behavior, fully antagonizes the punishment-lessening effects of benzodiazepines in the conflict test.     

豚鼠腹腔神经节迟慢兴奋性突触后电位与5－HT和P物质的关系

应用细胞内记录,研究了豚鼠腹腔神经节（ＣＧ）细胞非胆碱能迟慢兴奋性突触后电位（ＬＳ－ＥＰＳＰ）与５－羟色胺（５－ＨＴ）及Ｐ物质（ＳＰ）的相互关系。当重复电刺激内脏大神经（ＳＮ）时,有７８．２％的细胞（１６１／２０６）在动作电位发放后出现ＬＳ－ＥＰＳＰ,灌注或压力注射５－ＨＴ或ＳＰ,分别在６８．５％的细胞（１０２／１４９）及５２．１％的细胞（９８／１８８）上引起５－ＨＴ或ＳＰ去极化反应,两者差异非常显著（Ｐ＜０．０１）;大部分具有ＬＳ－ＥＰＳＰ的细胞对５－ＨＴ（７３／８８,８３．０％）或ＳＰ（６８／１１４５９．６％）敏感,而不出现ＬＳ－ＥＰＳＰ的细胞仅有少数对５－ＨＴ（１０／２６,３８．５％）或ＳＰ（１１／３６,３０．６％）敏感,两类细胞的差异非常显著（５－ＨＴ：Ｐ＜０．０００１,ＳＰ：Ｐ＜０．０１）。上述结果支持５－ＨＴ与ＳＰ均作为递质参与ＬＳ－ＥＰＳＰ形成的观点。此外,在１３３个细胞上同时检测了５－ＨＴ与ＳＰ的作用,其中有６６个细胞（４９．６％）对５－ＨＴ及ＳＰ均敏感,提示在ＣＧ细胞,５－ＨＴ与ＳＰ之间可能存在某种机能联系。     

Effect of damage of the nigro-neostriatal dopaminergic system by MPTP on the transmission of corticofugal impulses to the neurons of the caudate nucleus

It is shown in acute experiments on cats (males) that the induced responses as action potentials (AP) by the latent period (LP) less than 8.0 ms in the caudate nucleus neurons (CN) to a single stimulation of the motor zone of the cortex (MI) are more frequently inhibited than facilitated after specifying single stimulation of the compact part of the black substance (BS) in the intervals between stimuli 10-100 ms. As a result of system multiple injection of MPTP neurotoxin during 5 days per 5 mg/kg the number of CN neurons responding to stimulation of MI, AP, LP less than 8.0 Usec and to stimulation of BS-LP less than 10.0 ms reliably decreases. A conclusion is made that dopaminergic nigro-striatum system exerts a protective action on the impulse transfer on monosynaptic connections from the cortex to striatum.     

Long-term potentiation in the neurons of the edible snail

A brief high-frequency stimulation of the anal nerve of the isolated nerve ring of snail Helix induced a pronounced increase in the amplitude of EPSPs, evoked in identified neurons of left parietal and visceral ganglions by low frequency (once in 5 min) stimulation of the same nerve. The amplitude of EPSP returned to the control level 30-120 min after tetanization. We called this effect long-term potentiation. A brief application of serotonin (10 microM) in the majority of neurons also induced lasting either 15-30 min or more than 2 hours facilitation of EPSP, evoked by anal nerve stimulation. Intracellular cAMP injections, being without effect on EPSP amplitude in many neurons, in certain neurons caused an increase in EPSP amplitude, lasting up to 30 min. It is suggested that the 3 factors shown to increase synaptic efficiency in molluscan neurons may have common mechanisms of action.     

Effects on sleep of microdialysis of adenosine A1 and A2a receptor analogs into the lateral preoptic area of rats

Evidence suggests that adenosine (AD) is an endogenous sleep factor. The hypnogenic action of AD is mediated through its inhibitory A1 and excitatory A2A receptors. Although AD is thought to be predominantly active in the wake-active region of the basal forebrain (BF), a hypnogenic action of AD has been demonstrated in several other brain areas, including the preoptic area. We hypothesized that in lateral preoptic area (LPOA), a region with an abundance of sleep-active neurons, AD acting via A1 receptors would induce waking by inhibition of sleep-active neurons and that AD acting via A2A receptors would promote sleep by stimulating the sleep-active neurons. To this end, we studied the effects on sleep of an AD transport inhibitor, nitrobenzyl-thio-inosine (NBTI) and A1 and A2A receptor agonists/antagonists by microdialyzing them into the LPOA. The results showed that, in the sleep-promoting area of LPOA: 1) A1 receptor stimulation or inhibition of AD transport by NBTI induced waking and 2) A2A receptor stimulation induced sleep. We also confirmed that NBTI administration in the wake promoting area of the BF increased sleep. The effects of AD could be mediated either directly or indirectly via interaction with other neurotransmitter systems. These observations support a hypothesis that AD mediated effects on sleep-wake cycles are site and receptor dependent.     

Actions of Excitatory Amino Acids on Somatostatin Release from Cortical Neurons in Primary Cultures

L-Glutamate, N-methyl-D-aspartic acid (NMDA), quisqualate, and kainate were found to increase endogenous somatostatin release from primary cultures of rat cortical neurons in a dose-dependent manner. The rank order of potency calculated from the dose-response curves was quisqualate greater than glutamate = NMDA greater than kainate, with EC50 values of 0.4, 20, and 40 microM, respectively. Alanine, glutamine, and glycine did not modify the release of somatostatin. The stimulation of somatostatin release elicited by L-glutamate was Ca2+ dependent, was decreased by Mg2+, and was blocked by DL-amino-5-phosphonovaleric acid (APV) and thienylphencyclidine (TCP), two specific antagonists of NMDA receptors. The NMDA stimulatory effect was strongly inhibited by APV in a competitive manner (IC50 = 50 microM) and by TCP in a noncompetitive manner (IC50 = 90 nM). The release of somatostatin induced by the excitatory amino acid agonists was not blocked by tetrodotoxin (1 microM), a result suggesting that tetrodotoxin-sensitive, sodium-dependent action potentials are not involved in the effect. Somatostatin release in response to NMDA was potentiated by glycine, but the inhibitory strychnine-sensitive glycine receptor did not appear to be involved. Our data suggest that glutamate exerts its stimulatory action on somatostatin release essentially through an NMDA receptor subtype.     

Comparative research on synaptic transmission in the sympathetic ganglia of rabbits and frogs during acetylcholinesterase inhibition

Organophosphorus inhibitor of acetylcholinesterase (AChE) armin (1 x 10(-6) M) induced a variety of pre- and postsynaptic effects resulting from the AChE inhibition and subsequent accumulation of acetylcholine (ACh) in the synaptic cleft. The intensity of postsynaptic effects (level of neuron depolarization, degree of action potential depression) was shown to be different in the ganglia of frog and rabbit. This could be explained by differences in the total amount of ACh released in response to nerve stimulation as well as at rest. Both muscarinic and nicotinic cholinoreceptors were involved in the process of sustained depolarization of the neurons in the rabbit superior cervical ganglion after AChE inhibition. In frog ganglion neurons the nicotinic receptors did not participate in depolarization evidently due to their fast desensitization. The activation of presynaptic muscarinic receptors resulted in decrease of ACh released by nerve stimulation seems to weaken depolarization and blockade of synaptic transmission in sympathetic ganglia treated by AChE inhibitors.     

Subthreshold aortic nerve inputs to neurons in nucleus of the solitary tract

Subthreshold aortic nerve (AN) inputs to neurons receiving a monosynaptic AN-evoked input (MSNs: respond to each of two AN stimuli separated by 5 ms) and neurons receiving a polysynaptic AN input (PSNs) in the nucleus of the solitary tract (NTS) were identified in anesthetized rats. In extracellular recordings from 24 MSNs and 49 PSNs, 12% of MSNs and 29% of PSNs only responded to AN stimulation during the application of excitatory amino acids. In intracellular recordings from 24 MSNs and 22 PSNs, 12% of MSNs and 14% of PSNs responded to AN stimulation with excitatory postsynaptic potentials that did not evoke action potential discharge. Reductions in arterial pressure produced minimal changes in the spontaneous discharge of suprathreshold AN-evoked neurons, suggesting that these neurons receive excitatory inputs from nonbaroreceptor sources. The results suggest that some baroreflex-related NTS neurons exist in a "reserve state and can be changed to an active state or vice versa. This will change the number of neurons involved in baroreflex circuits and provides a novel mechanism for regulating baroreflex function independently of alterations in peripheral afferent input.     

Acceleratory nervous regulation of juvenile myogenic hearts in the isopod crustacean Ligia exotica

We examined regulation of the myogenic heart by two identified cardioacceleratory neurons (CA1, CA2) in early juveniles of the isopod Ligia exotica. Repetitive stimulation of either the CA1 or CA2 axon increased the frequency and plateau amplitude of the action potential and decreased the maximum hyperpolarization of the cardiac muscle. These effects were larger with increasing stimulus frequency. The rate of increase in the frequency caused by CA1 stimulation was significantly larger than that by CA2. No impulse activity of the cardiac ganglion was induced by acceleratory nerve stimulation. The frequency of the muscle activity was decreased by injection of a hyperpolarizing current into the muscle during stimulation of the acceleratory nerve. In a quiescent heart, acceleratory nerve stimulation caused an overall depolarization in the muscle membrane and the amplitude of the depolarization induced by CA1 stimulation was significantly larger than that by CA2. These results suggest that CA1 and CA2 neurons regulate the myogenic heart affecting directly the cardiac muscle; the CA1 neuron produces more potent effects than does the CA2 neuron.     

5-Hydroxytryptamine involvement in the intrinsic control of oesophageal EMG activity

The effects and the sites of action of 5-Hydroxytryptamine (5HT) were examined in transverse muscular strips of pigeon oesophagus. 5-Hydroxytryptamine (0.001 to 30 microM) induced a concentration-dependent excitatory effect on the EMG activity. This response was mainly characterized by an increase in burst frequency. The maximum 5-HT-induced excitatory effect was not altered by methysergide (10 microM), but was abolished by tetrodotoxin (3 microM). Excitatory response to 5-HT was partly opposed by atropine (1 microM), potentiated by 5-methoxy-N, N-dimethyltryptamine (1 microM) and was not altered by guanethidine (10 microM). These results indicate that 5-HT activates the pigeon oesophagus indirectly via neural elements and has no direct action on the smooth muscle cells. 5-HT is thought to stimulate three different intramural neuron types: excitatory cholinergic neurons, excitatory non-cholinergic neurons and inhibitory non-cholinergic non-adrenergic neurons. The action on these different neurons seems to be mediated via different receptors.     

Convergence of mechanosensory inputs onto neuromodulatory serotonergic neurons in the leech

By the frequency-dependent release of serotonin, Retzius neurons in the leech modulate diverse behavioral responses of the animal. However, little is known about how their firing pattern is produced. Here we have analyzed the effects of mechanical stimulation of the skin and intracellular stimulation of mechanosensory neurons on the electrical activity of Retzius neurons. We recorded the electrical activity of neurons in ganglia attached to their corresponding skin segment by segmental nerve roots, or in isolated ganglia. Mechanosensory stimulation of the skin induced excitatory synaptic potentials (EPSPs) and action potentials in both Retzius neurons in a ganglion. The frequency and duration of responses depended on the strength and duration of the skin stimulation. Retzius cells responded after T and P cells, but before N cells, and their sustained responses correlated with the activity of P cells. Trains of five impulses at 10 Hz in every individual T, P, or N cell in isolated ganglia produced EPSPs and action potentials in Retzius neurons. Responses to T cell stimulation appeared after the first impulse. In contrast, the responses to P or N cell stimulation appeared after two or more presynaptic impulses and facilitated afterward. The polysynaptic nature of all the synaptic inputs was shown by blocking them with a high calcium/magnesium external solution. The rise time distribution of EPSPs produced by the different mechanosensory neurons suggested that several interneurons participate in this pathway. Our results suggest that sensory stimulation provides a mechanism for regulating serotonin-mediated modulation in the leech.     

The action of the neurotoxins 5,6-dihydroxytryptamine and p-chlorophenylalanine on the electrical activity parameters of the command neurons during long-term sensitization and learning in the snail]

The influence of 5,6-dihydroxytryptamine (5,6-DHT), which selectively destroyed serotonin terminals, and p-chlorphenylalanine, which inhibited serotonin synthesis, was studied on the long-term sensitization (LTS) in a snail. The membrane mechanisms were analyzed by measuring electrical characteristics of command neurons of defensive behavior LPa3, RPa3, LPa2, and RPa2. Snails injected with saline served as an active control. It was shown that the injected drugs inhibited the LTS in certain concentrations. A significant increase was observed in the membrane potential and the threshold of the action potential generation in the command neurons after 5,6-DHT injection in the doses of 20 and 30 mg/kg (in comparison with the active control). Sensitization of snails injected with saline solution led to the LTS and decrease in the membrane and threshold potentials of the command neurons. After the LTS, changes in membrane and threshold potentials in snails injected with 5,6-DHT were negligible in comparison with those injected with 5,6-DHT but without the LTS. Neither the LTS nor subsequent learning resulted in a further decrease in membrane and threshold potentials. Thus, the neurotoxin injection led to an increase in excitability of command neurons and their depolarization, and the LDS did not elicit further excitability increase. Since the shifts of the threshold and membrane potentials were the same, it was concluded that the increase in membrane excitability was induced by the depolarizing shift of the membrane potential.     

Action of cholecystokinin on the dog sphincter of Oddi: influence of anti-cholinergic agents.

Effects of cholecystokinin (CCK) on bile flow through the sphincter of Oddi (SO) were studied in anaesthetized dogs. Intravenous injection of CCK (0.25, 0.5, 1 and 2 IDU/Kg) elicited a dose-dependent reduction in flow through the SO in the first minutes after CCK administration. Pirenzepine and atropine decreased significantly (P less than 0.05) by 29% and a 40% respectively the inhibitory effect induced by 1 IDU/Kg of CCK, whereas hexamethonium elicited an increase in the inhibitory effect induced by 0.5 IDU/Kg of CCK (P less than 0.05). Intravenous infusion of cummulative doses of CCK had different effects according to the dose infused. Lower doses (0.025 and 0.05 IDU/Kg/min) increased transphincteric flow, however, high doses (0.1, 0.2 and 0.4 IDU/Kg/min) were inhibitory. These finding indicated that CCK had two effects on the SO : firstly, a contractile effect, probably mediated through a direct myogenic action and neuronal release of ACh, and secondly a relaxant effect, probably mediated by stimulation of inhibitory postganglionic neurons.     

Human motor cortex excitability during the perception of others' action

Neuroscience research during the past ten years has fundamentally changed the traditional view of the motor system. In monkeys, the finding that premotor neurons also discharge during visual stimulation (visuomotor neurons) raises new hypotheses about the putative role played by motor representations in perceptual functions. Among visuomotor neurons, mirror neurons might be involved in understanding the actions of others and might, therefore, be crucial in interindividual communication. Functional brain imaging studies enabled us to localize the human mirror system, but the demonstration that the motor cortex dynamically replicates the observed actions, as if they were executed by the observer, can only be given by fast and focal measurements of cortical activity. Transcranial magnetic stimulation enables us to instantaneously estimate corticospinal excitability, and has been used to study the human mirror system at work during the perception of actions performed by other individuals. In the past ten years several TMS experiments have been performed investigating the involvement of motor system during others' action observation. Results suggest that when we observe another individual acting we strongly 'resonate' with his or her action. In other words, our motor system simulates underthreshold the observed action in a strictly congruent fashion. The involved muscles are the same as those used in the observed action and their activation is temporally strictly coupled with the dynamics of the observed action.     

The effects of morphine on sympathetic transmission in the stellate ganglion of the cat

The aim of this study was to investigate which of the processes involved in synaptic transmission are affected by morphine in concentrations comparable to those used during surgical procedures. The effects of morphine sulfate on ganglionic transmission were studied in the stellate ganglion of the cat using intracellular and extracellular recordings in vitro. The neurons of the stellate ganglion were depolarized using preganglionic nerve stimulation, postganglionic nerve stimulation, and intracellular stimulation before and after introduction of morphine sulfate (up to 20 micrograms/mL). Tissue concentrations of morphine were estimated using radiolabeled morphine. Axonal transmission and the excitability of the postganglionic neurons to direct intracellular stimulation was not affected at the concentrations of morphine studied. In addition, morphine had a dose-dependent depolarizing effect on the resting membrane potential of most of the neurons in the stellate ganglion. Such neuronal depolarizations alone could initially produce excitation in some cell populations, followed by inhibition, secondary to the membrane depolarization, leading to depression of sympathetic nerve activity. The overall ganglionic transmission as recorded using an evoked potential was biphasic. At low doses morphine facilitated transmission, while at larger doses morphine attenuated evoked potentials. These effects do not appear to be mediated through classical opiate receptors since they are not blocked by naloxone.     

Regulation of cyclic GMP elevation in the developing antennal lobe of the Sphinx moth, Manduca sexta.

In the moth, Manduca sexta, 3',5'-guanosine monophosphate (cGMP) is transiently elevated during adult development in about 100 neurons of the antennal lobe. We demonstrate that nearly all of these neurons are local interneurons of the lateral cluster I, that their capacity to show a strong cGMP response during development is regulated by the steroid hormone 20-hydroxyecdysone, and that in a subpopulation of these neurons cGMP elevation seems to be controlled directly by the gaseous messenger molecule nitric oxide (NO). Treatment with the acetylcholine esterase inhibitor eserine, antennal nerve transection, and electrical stimulation of the antennae suggest that NO/cGMP signaling during development is an activity-dependent process. Besides input from the antennae, input from the central brain and the ventral ganglia is involved in upregulating cGMP in the antennal-lobe neurons. Possible sources are centrifugal aminergic neurons, since application of serotonin and histamine enhances the GMP signal in local interneurons. Comparing the time course of cGMP elevation with events occurring during development leads us to the hypothesis that the NO/cGMP signaling pathway might be involved in synapse formation of a subset of antennal-lobe neurons.     

GABA参与兔杏仁体抑制内膝体神经元电活动

本文采用多管微电极胞外记录技术观察了短纯音引起兔内膝神经元的声反应及刺激杏仁体对声反应的影响,并在此基础上观察电泳ＧＡＢＡ及其拮抗剂Ｂｉｃｕｃｕｌｌｉｎｅ的效应。实验结果表明：ＧＡＢＡ可以抑制ＭＧＢ神经元的声反应及自发放电活动,而ＧＡＢＡＡ拮抗剂Ｂｉｃｕｃｕｌｌｉｎｅ的作用则相反;电泳ＧＡＢＡ对ＭＧＢ神经元产生同刺激杏仁体一样的抑制产应,并且这种影响可被Ｂｉｃｕｃｕｌｌｉｎｅ翻转;嗅鼻沟后缘听区农     

Role of extracellular calcium in the metabolic and hemodynamic actions of sympathetic nerve stimulation, noradrenaline and prostaglandin F2 alpha in perfused rat liver. Differential inhibition by nifedipine and verapamil

In perfused rat liver hepatic nerve stimulation (10 Hz, 2 ms) caused an increase in glucose and lactate output, a decrease in flow and an overflow of noradrenaline into the hepatic vein. Noradrenaline (1 microM) (NA) and prostaglandin F2 alpha (5 microM) (PGF2 alpha), which are implicated as mediators of nerve action, elicited similar effects. 1) All actions of nerve stimulation and the hemodynamic but not the metabolic effects of noradrenaline and PGF2 alpha were largely dependent on extracellular calcium. 2) The dihydropyridine type calcium antagonist nifedipine (5 microM) inhibited the hemodynamic but not the metabolic actions of nerve stimulation, NA and PGF2 alpha, while the phenylalkylamine type calcium antagonist verapamil (5 microM) had no effect. These findings allow the following conclusions: Calcium influx into I nerve endings, necessary for the release of neurotransmitter, II parenchymal cells, for the display of metabolic effects induced by nerve stimulation, and III the actions of NA and PGF2 alpha, do not appear to be mediated by the normal affinity nifedipine- or the verapamil-sensitive channels. Calcium influx into vascular smooth muscle and/or endothelial cells for the display of hemodynamic action induced by nerve stimulation and the NA and PGF2 alpha effects, appear to occur through nifedipine-sensitive but verapamil-insensitive channels.     

Propofol suppresses synaptic responsiveness of somatosensory relay neurons to excitatory input by potentiating GABAA receptor chloride channels

Propofol is a widely used intravenous general anesthetic. Propofol-induced unconsciousness in humans is associated with inhibition of thalamic activity evoked by somatosensory stimuli. However, the cellular mechanisms underlying the effects of propofol in thalamic circuits are largely unknown. We investigated the influence of propofol on synaptic responsiveness of thalamocortical relay neurons in the ventrobasal complex (VB) to excitatory input in mouse brain slices, using both current- and voltage-clamp recording techniques. Excitatory responses including EPSP temporal summation and action potential firing were evoked in VB neurons by electrical stimulation of corticothalamic fibers or pharmacological activation of glutamate receptors. Propofol (0.6 – 3 μM) suppressed temporal summation and spike firing in a concentration-dependent manner. The thalamocortical suppression was accompanied by a marked decrease in both EPSP amplitude and input resistance, indicating that a shunting mechanism was involved. The propofol-mediated thalamocortical suppression could be blocked by a GABA_A receptor antagonist or chloride channel blocker, suggesting that postsynaptic GABA_A receptors in VB neurons were involved in the shunting inhibition. GABA_A receptor-mediated inhibitory postsynaptic currents (IPSCs) were evoked in VB neurons by electrical stimulation of the reticular thalamic nucleus. Propofol markedly increased amplitude, decay time, and charge transfer of GABA_A IPSCs. The results demonstrated that shunting inhibition of thalamic somatosensory relay neurons by propofol at clinically relevant concentrations is primarily mediated through the potentiation of the GABA_A receptor chloride channel-mediated conductance, and such inhibition may contribute to the impaired thalamic responses to sensory stimuli seen during propofol-induced anesthesia.