Identification of serotonin receptors on someHelix pomatia neurons

Four types of responses to iontophoretic application of serotonin were found in neurons of the ventral aspect of the visceral ganglion ofHelix pomatia. The responses differed in size, duration, latent periods, habituation to serotonin, and response to the action of serotonin antagonists (D-tubocurarine, tryptamine, neostigmine). Each type of response was evidently connected with a particular type of serotonin receptor. A scheme of distribution of the different types of serotonin receptors in the neurons of this region is drawn up.Institute of Psychiatry, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 300–305, May–June, 1978.     

Patterns of serotonin-immunoreactive neurons in the central nervous system of the earthworm Lumbricus terrestris L.

Summary The distribution patterns of serotonin-immunoreactive somata in the cerebral and subpharyngeal ganglion, and in the head and tail ganglia of the nerve cord of Lumbricus terrestris are described from whole-mount preparations. A small number of serotonin-immunoreactive neurons occurs in the cerebral ganglion, in contrast to the large population of serotonin-immunoreactive neurons that exists in all parts of the ventral nerve cord. From the arrangement of serotonin-immunoreactive somata in the subpharyngeal ganglion, we suggest that this ganglion arises from the fusion of two primordial ganglia. In head and tail ganglia, the distribution of serotonin-immunoreactive somata resembles that in midbody segments. Segmental variations in the pattern and number of serotonin-immunoreactive somata in the different body regions are discussed on the background of known developmental mechanisms that result in metameric neuronal populations in annelids and arthropods.Abbreviations CG1, CG2 cerebral soma group 1, 2 - CNS central nervous system - GINs giant interneurons - 5-HT 5-hydroxytryptamine, serotonin - 5-HTi 5-HT-immunoreactive - N side nerve - SG19 subpharyngeal soma group 1–9 - SN segmental nerve     

Disulfide bonds in acetylcholine receptors of frog sympathetic ganglion neurons

Changes in responses of frog sympathetic ganglion neurons to perfusion with cholinomimetics were studied during modification of acetylcholine receptors by dithiothreitol and ferricyanide. Perfusion with dithiothreitol suppressed responses to carbachol, suberyldicholine, and 5-methylfurmethide, whereas subsequent perfusion with ferricyanide partly restored responses to suberyldicholine but suppressed responses to 5-methylfurmethide. Acetylcholine and tetramethylammonium, used as protectors, protected nicotinic and muscarinic receptors against the action of dithiothreitol, but acetylcholine was more effective than tetramethylammonium for nicotinic acetylcholine receptors. It is suggested that disulfide bonds, some of them located in the anionic centers of the receptors, are present in the recognition sites of acetylcholine receptors of the frog sympathetic ganglion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 593–600, November–December, 1979.     

Metabolic and ionic dependence of serotonin-induced neuronal response in rat sensory ganglia

Intracellular recording techniques were used to investigate the effects of neuronal serotonin application, either by micropipet under pressure or by addition to the superfusing fluid, on membrane potential and conductance during experiments on spinal ganglia cells from adult rats. Serotonin action on spinal ganglia neurons induced depolarization with reduced conductance, hyperpolarization, and increased membrane conductance, as well as mixed response. Only one response pattern was examined. Depolarization response in spinal ganglia neurons sensitive to methysergide were potentiated by activating type 2 serotonin receptors (5HT₂): e- and hyperpolarizing response insensitive to methysergide, propranolol, and cocaine action was produced via type 1 serotonin receptor (5HT_1A). Neuronal response produced by serotonin (5HT₂ mediation) did not depend on change in intraneuronal concentration of cAMP and the action of pertussis toxin. The second pattern of response was inhibited in the presence of pertussis toxin and modulated considerably by change in intraneuronal cAMP concentration and tryptazine action. Findings from research on ionic dependence showed that response mediated by 5HT₂ resulted from blockade of M-current potassium channels and that brought about by 5HT_1A is associated with disturbed function of cAMP-dependent potassium ionic channels.A. M. Gorkii Medical Institute, Donetsk. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 86–93, January–February, 1989.     

Responses of rat spinal ganglion neurons mediated by activation of serotonin receptors of the third type

Application of serotonin (5-hydroxytryptamine; 5-HT) to rat dorsal root ganglion neurons under conditions in which potassium conductance was blocked by cesium ions elicited depolarizing responses followed by an increase in membrane conductance. The responses did not exhibit desensitization and were due to activation of 5-HT receptors of the third type (5-HT₃Rs), since they were insensitive to methysergide, the 5-HT₂R antagonist, but were inhibited by tropicetrone (ISC 205–930) and metoclopramide, the 5-HT₃R antagonists. The reversal potential of the 5-HT-induced depolarizing responses was –11.9 mV; their amplitude decreased following a decrease in extracellular Na⁺ concentration but remained constant after intracellular injection of GTP. The amplitude of the responses increased following elevation of intracellular cAMP concentration caused by theophylline or sodium fluoride whose potentiating effect was reduced by butamide, a protein kinase A inhibitor. Potentiation of the 5-HT-induced responses was also produced by increased intracellular Ca²⁺ concentration following either direct intracellular injections or a burst of action potentials. The potentiation could be prevented by trifluoroperazine, the calmodulin inhibitor. The 5-HT effects were also potentiated by methylfurmetide, an activator of muscarinic acetylcholine receptors. The effect of methylfurmetide was slightly decreased by trifluoroperazine and was markedly decreased by polymixin B, a protein kinase C inhibitor. The effects of 5-HT were also enhanced by ethanol.Neirofiziologiya/Neurophysiology, Vol. 25, pp. 258–263, July–August, 1993.     

Mutual modulating effects of serotonin and dopamine on neurons of rat spinal ganglia

It was established in experiments on isolated rat spinal ganglia that the introduction of dopoamine (0.01–1.0 µM) into a superfusate potentiates the depolarizing responses of the neurons evoked by the action of serotonin, which is delivered from a micropipette under pressure, while the addition of serotonin in the same concentrations potentiates the depolarizing responses of the neurons evoked by the action of dopamine. The mutual potentiation of the effects of dopamine and serotonin depends on the concentration of the monoamines and is eliminated by blockers of the D₁- (but not D₂-dopamine) and type 2 serotonin (but not IA) receptors. The mutual potentiation of the effects of monoamines is of a postsynaptic nature and is associated with a change in the intracellular concentration of second messengers (Ca²⁺ and cAMP).A. M. Gor'kii Donetsk Medical Institute, Ministry of Health of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 168–173, March–April, 1991.     

Physiological and morphological properties of the metathoracic common inhibitory neuron of the locust

Summary Intracellular recordings were made from the soma of the metathoracic common inhibitory neuron of the locustsSchistocerca andChortoicetes. The soma is passively invaded by a spike of 2–5 mV in amplitude. The response of the common inhibitor to a variety of different inputs was studied. Tests for coupling between the common inhibitory and excitatory motoneurons to the same or antagonistic muscles were made by simultaneous recordings from pairs of neuron somata. No low resistance or synaptically mediated coupling was found. The somata of the two common inhibitory neurons which supply muscles on opposite sides of the body lie together on the ventral surface of the ganglion on the mid-line (Fig. 6). They are not coupled in any way. Cobalt chloride injected into the common inhibitor has shown it to have an extensive and complex dendritic tree confined to the ipsilateral half of the ganglion (Fig. 8). A single branch extends into the mesothoracic ganglion. There are differences in the branching patterns of the dendrites in different animals (Fig. 10).Beit Memorial Research Fellow.     

Ionic mechanisms of excitatory action of transmitter,exogenous acetylcholine,and serotonin on superior cervical ganglion neurons in rabbits

Ionic mechanisms of EPSP generation and depolarization induced by iontophoretic application of acetylcholine (ACh) and serotonin (5-hydroxytryptamine, 5-HT) — acetylcholine and serotonin potentials — were investigated in neurons of the isolated rabbit superior cervical ganglion by means of intracellular microelectrodes. The reversal potentials (E_r) for EPSP and the ACh-potential were –14.4±1.6 and –16.5±1.2 mV respectively, and they were about the same for the 5-HT potential. In some neurons (about one-third) much more negative values for E_r were obtained for EPSP and the ACh-potential by extrapolation, probably due to an increase in the resistance of their membrane during hyperpolarization. A decrease in the external sodium and potassium concentrations was shown to make E_r for EPSP and the ACh-potential more negative, whereas an increase in the external potassium concentration made it more positive than in normal solution; a change in the external chloride concentration did not alter E_r. It is suggested that the excitatory transmitter and exogenous ACh (and also, probably, 5-HT) share the same ionic mechanism of action of the membrane, which includes an increase in the permeability of the membrane to two ions — sodium and potassium — simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 637–644, November–December, 1978.     

Physiological properties of nicotinic acetylcholine receptors of sympathetic ganglionic neurons

The basic properties of nicotinic acetylcholine receptors of the neurons of a sympathetic ganglion responsible for the performance by these receptors of their main function — initiation of an electric current through the postsynaptic membrane — and determining the particular features of the acetylcholine receptors of these neurons by contrast with receptors of other objects, are described. Stoichiometric relations of the recognition center of the acetylcholine receptors with the transmitter, the relative strength of various agonists, and the method of action of -bungarotoxin on this center are indicated; the "life-time" and conductance of the ion channel are described. On the basis of "life-time" two groups of acetylcholine receptors are distinguished: synaptic (long-living) and extrasynaptic (short-living). Selective blockers of acetylcholine receptors of ganglionic neurons, namely bis-ammonium compounds, have two types of effect (competitive and channel-blocking), caused by the action of the blocker on two different regions of the receptor molecule, respectively. Since the channel-blocking action develops at lower concentrations than the competitive, and since it correlates closely with the ganglion-blocking effect, it is concluded that it is the first of these which determines the properties of selective blockers of acetylcholine receptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 319–326, May–June, 1984.     

Modification to the Hodgkin-Huxley equation as applied to the somatic membrane of mollusk giant neurons

A modified system of Hodgkin-Huxley equations was used to describe transmembrane ionic currents during fixed changes of membrane potential and generation of action potentials in the soma of mollusk giant neurons. The effect of the axon was disregarded. The results of theoretical calculations are in satisfactory agreement with experimental results.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 315–322, May–June, 1973.     

Ionic mechanisms underlying modulating effects of serotonin on acetylcholine-induced responses in Helix pomatia neurons

The ionic mechanisms underlying modulatory effects of serotonin on acetylcholine-response in identified and nonidentifiedHelix pomatia neurons were investigated using voltage-clamping techniques at the neuronal membrane. External application of 10^–5–10^–4 M serotonin to the membrane of neurons responding to application of acetylcholine depending on Na⁺ depolarization (D_Na response) reduced membrane conductivity during response to acetylcholine without changing reversal potential of acetylcholine-induced current. Acetylcholine (10^–6–10^–4 M) administration took place 1–3 min later. Neurons with response to acetylcholine application dependent on Cl⁺ depolarization (D_Cl response) or hyperpolarization (H_Cl response) behaved similarly. Analogous effects could be produced by external application of theophylline which, together with the latency and residual effect characteristic of serotonin action points to the participation of intracellular processes associated with the cellular cyclase system in the changes produced by serotonin in acetylcholineinduced response. Serotonin brought about a shift in reversal potential and an increase in the acetylcholine-induced current in those neurons where this response was associated with changed permeability at the membrane to certain types of ions. During two-stage acetylcholine-induced response of the D_Na-H_K type, serotonin inhibited the inward current stage. Mechanisms underlying modulatory serotonin action on acetylcholine-induced response in test neurons are discussed in the light of our findings.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 57–64, January–February, 1988.     

Contribution of a humoral factor to postsynaptic sensitization in heterosynaptic facilitation

It was shown that heterosynaptic facilitation develops in the cerebral ganglia giant neurons of the freshwater gastropod molluskPlanorbis corn eus due to diffuse neurohumoral influences on pre- and postsynaptic structures and not local synaptic action on presynaptic mechanisms. It was also found that n-cholinergic synaptic mechanisms come under this facilitatory influence. Serotonin is the source of facilitation in neurons of bothPlanorbis corneus cerebral ganglion and those of the aplysia abdominal ganglion. Seeing that: a) conditioning stimuli facilitate the effects produced by iontophoretic acetylcholine application, as well as n-cholinergic synaptic transmission and b) the amplitude of EPSP and acetylcholine potential increase 4–6 times during facilitation when the input impedance of the post-synaptic membrane is increased by just 20%, it was deduced that the postsynaptic membrane of the giant neuron makes a significant contribution to heterosynaptic facilitation of the sensitization of n-cholinergic receptors. The part played by n-cholinergic receptors of the postsynaptic membrane in heterosynaptic facilitation and conditioned reflex habituation is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 250–259, March–April, 1986.     

Modulation of electrical activity of neuron RPal ofHelix pomatia

Changes in the types of electrical activity of bursting neuron RPal ofHelix pomatia were studied. Neuron RPal may either be "silent" or may exhibit bursting activity with waves of membrane potential of low and high amplitude. Changes in activity of this neuron took place spontaneously over a period of tens or hundreds of seconds. Changes in electrical activity in neuron RPal were synchronized with changes in membrane potential in other neurons. Similar changes in electrical activity of neuron RPal can be produced by application of the water-soluble fraction from snail ganglion homogenate, containing "modulating factor," to the soma. It is suggested that the prolonged changes in electrical activity of neuron RPal described above are connected with the action of compounds resembling neurotransmitters or neurohormones, and secreted by other neurons, on it. These compounds reach the neuron continuously or they are bound with the receptors of the neuron for a long enough period of time to produce stationary changes in its membrane conductance.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 398–405, July–August, 1981.     

Serotonin-induced changes in the responses of the electroexcitable membrane of snail neurons

The effects of serotonin (5-HT) added to the washing solution on the plastic properties of the electroexcitable membrane of nonidentified neurons of the parietal ganglion and identified neurons RPa2 are studied on the isolated nervous system of the snail. The neurons of the first group, which became rapidly habituated to the intracellular stimulation, are shown to manifest the ability to restore action potential generation in the presence of 5-HT. In contrast, the neurons possessing endogenous rhythmic activity (RPa2) in the presence of 5-HT generate burst activity against the background of the development of slow waves of the membrane potential. A comparative analysis of the effect of 5-HT and compounds with a known effect on Ca²⁺ and the calcium-dependent potassium channels (quinine, CoCl₂ and CdCl₂) points to the existence of various mechanisms providing for the serotoninergic regulation of the plasticity of the electroexcitable neuron membrane. This difference stems from the processes of activation and blockade of the Ca-dependent mechanisms.A. I. Karaev Institute of Physiology Azerbaizhan Academy of Sciences, Baku. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 286–290, May–June, 1992.     

Naloxone-dependent depression by morphine of responses of snail neurons to serotonin

Morphine, added to the extracellular solution in a concentration of 1·10^–5 M, quickly and reversibly weakens the depolarizing and hyperpolarizing responses of neurons of the snailHelix lucorum evoked by 1·10^–6 M serotonin. The inhibitory effect of morphine is completely abolished by the addition of naloxone (1·10^–5 M), suggesting that opiate receptors are involved in the process. Interaction between morphine and serotonin is noncompetitive in type, as is shown by the character of the dose-effect curves recorded during the action of serotonin before and after morphine application.Institute of Psychiatry, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 589–593, November–December, 1981.     

Electrophysiological investigation of the cat ciliary ganglion

Electrical responses of some nerves of the ciliary ganglion to stimulation of its other nerves were recorded, and intracellular recordings were also made from neurons of the ganglion (in situ). The overwhelming majority of preganglionic fibers terminate synaptically on neurons of the ganglion. Postganglionic fibers leave in the lateral and medial ciliary nerves, in which the velocity of conduction of excitation ranges from 1.9 to 9.0 m/sec. A few preganglionic fibers pass through the ciliary ganglion into the lateral ciliary nerve, giving off collaterals to neurons of the ganglion, so that stimulation of the lateral ciliary nerve evokes a response in the medial ciliary nerve (preganglionic axon reflex). The resting potential of neurons of the ciliary ganglion is 57±2.8 mV, and their action potential 68±3.6 mV. Single orthodromic stimulation usually evokes a single action potential in a neuron. The amplitude of the EPSP is increased during hyperpolarization of the postsynaptic membrane, confirming the chemical nature of synaptic transmission in the ganglion. The antidromic response consists of an IS-component and spike. The spike is followed by after-hyperpolarization, with a mean amplitude equal to 31% of the spike amplitude, and the time taken for it to fall to one–third of its initial amplitude is 75–135 msec.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 101–108, July–August, 1969.     

Subsynaptic modulation of excitatory chemical transmission produced by metacerebral neurons in the mollusk buccal ganglion

The effects of stimulating neuron LMcl (which secretes serotonin from the axonal endings) on the response of buccal cells LBc2 and LBc3 to stimulation of synaptic (predominantly cholinergic) inputs from iron peripheral neurons were investigated inHelix pomatia. Stimulation of neuron LMc1 was found to modulate such response LBc2 and LBc3 producing an increase in the former and decrease in the latter. Results of pharmacological action show the modulation of excitatory chemical transmission produced by LMc1 in the buccal ganglion to be subsynaptic.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 539–546, July–August, 1989.     

Effect of body orientation in the gravitational field on directional sensitivity of the cercal system of neurons in crickets

Changes in the spatial orientation of three-dimensional directional sensitivity diagrams of neurons of the terminal abdominal ganglion of the cricket during body tilting were studied. Spike responses were recorded from neurons of the ganglion to acoustic stimuli in different directions, with the cricket's body tilted at different angles to the horizontal plane. During tilting of the cricket's body the orientation of the directional sensitivity diagrams was found to change parallel with the orientation of the body. Neurons of the abdominal ganglion are excited by cercal sensillae, among which there are receptors which respond to changes in the position of the cricket's body in the gravitational field (gravity receptors). The results suggest that cercal gravity receptors have no specific influence on the directional sensitivity of neurons of the first central division of the cercal system.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 604–611, November–December, 1980.     

Electrophysiological investigation of the conduction of excitation in the pterygopalatine ganglion of the cat

When responses in some nerves of the pterygopalatine ganglion of the cat in situ to stimulation of its other nerves were recorded it was found that most fibers passing through the ganglion are continuous sympathetic postganglionic fibers (at least three groups). Most of the parasympathetic preganglionic fibers forming synapses on neurons of the ganglion constitute a group of fibers with the same threshold of excitation. Intracellular recording from single neurons of the pterygopalatine ganglion showed that stimulation of the Vidian nerve evokes orthodromic spike potentials in some neurons of the ganglion with a short latent period, and in others with a long latent period (2.5–6.0 and 10–44 msec, respectively). Evidently only fast-conducting fibers terminate synaptically on most neurons of the ganglion and only slow-conducting fibers on some of them. Recording from intact nerves of the pterygopalatine ganglion revealed no tonic activity in them. Microelectrode recording from single neurons of the ganglion showed that either the frequency of generation of spike potentials is relatively low (1–3/sec) or such potentials are absent altogether.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 514–520, September–October, 1976.     

Electrophysiological investigation of pathways in the middle cervical sympathetic ganglion of the turtle

Single unit responses in the middle cervical sympathetic ganglion ofEmys orbicularis to stimulation of other nerves and changes in these responses during the action of sympathetic blocking agents on the ganglion were investigated. The results showed that some fibers of the cervical sympathetic trunk of the turtle are interrupted in this ganglion. Postganglionic fibers pass out of the ganglion and enter the lateral branch and the sympathetic trunk. Other fibers pass through the ganglion without interruption and, together with postganglionic fibers, leave the ganglion in the cervical sympathetic trunk in a cranial direction. The velocity of conduction of excitation along the preganglionic fibers is between 4–3 and 2–1.5 m/sec and along the postganglionic fibers between 4–2.6 and 0.7–0.5 m/sec (fibers of types B₂ and C). Synaptic delay in the fast-conducting fibers averages 6.6 msec. Preganglionic fast-conducting fibers form synaptic contacts on neurons with type B₂ axons, while preganglionic slow-conducting fibers form contacts on neurons with type C axons. Terminals of two preganglionic fibers differing very slightly in their threshold of excitability, and probably constituting the same group, converge on some neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 83–89, January–February, 1972.