The action of acetylcholine, dopamine and 5-hydroxytryptamine on the spontaneous activity of the cells of Retzius of the leech, Hirudo medicinalis

A Rare Cause of Epistaxis: Nasopharyngeal Leech Infestation

Leeches are rare cause of foreign body in airways. A 23-year-old male, experiencing epistaxis and difficulty in swallowing is presented. During nasopharyngoscopy, a moving leech was observed on the nasopharynx posterior wall in midline location, and removal of the leech was decided under general anaesthesia. The flexible nasopharyngoscopy was inserted, but removal was unsuccessful due to the leech's movements. Leeches are blood-sucking parasites, so neuromuscular blocking agent was given to prevent the movement. After administration, motion of the leech was lost and easily removed undamaged. In patients presenting with unexplained epistaxis, hemoptysis, dyspnea, and foreign body sensation in the airway, leech infestation should be included as the differential diagnosis and history of contact with stream water should be questioned. We concluded that use of low dose neuromuscular blocking agents facilitates the gentle removal, and could be necessary for successful management of removal of leech under general anaesthesia.

Spatial-specific action of serotonin within the leech midbody ganglion

Serotonin is a conspicuous neuromodulator in the nervous system of many vertebrates and invertebrates. In previous experiments performed in the leech nervous system, we compared the effect of the amine released from endogenous sources [using selective serotonin reuptake inhibitors (SSRIs), e.g. fluoxetine] with that of bath-applied serotonin. The results suggested that the amine does not reach all its targets in a uniform way, but produces the activation of an interneuronal pathway that generated specific synaptic responses on different neurons. Taking into account that the release of the amine is often regulated at the presynaptic level, we have investigated whether autoreceptor antagonists mimic the SSRIs effect. We found that methiothepin (100 microM) produced similar effects than fluoxetine. To further test the hypothesis that endogenous serotonin produce its effect by acting locally at specific sites, we analyzed the effect of iontophoretic applications of serotonin. We found a site in the neuropil of the leech ganglia where serotonin application mimicked the effect of the SSRIs and the 5-HT antagonist. The results further support the view that the effect of serotonin exhibits a spatial specificity that can be relevant to understand its modulatory actions.

Diversity and modulation of ionic conductances in leech neurons

A complete understanding of animal behavior at the cellular level requires detailed information on the intrinsic biophysical properties of neurons, muscles, and the synaptic connections they make. In the past 10 to 15 years, electrophysiological studies of leech neurons have revealed a diverse array of voltage-gated ionic conductances distinguished by their pharmacological sensitivity to classic ion channel blockers. Voltage-clamp studies have provided new information about the kinetics and voltage-dependence of Na+ conductances, several K+ currents, including IA, IK and IK(Ca.), and high- and low-voltage-gated Ca2+ conductances. These studies showed that the action potentials of most leech neurons result from the usual sequence of permeability changes to Na+, K+, and Ca2+ ions. They also added insight as to the role played by particular combinations of conductances in providing individual neurons with electrical properties appropriate for the particular information they encode. Evidence is accumulating on the modulatory actions fo endogenous neurotransmitters such as FMRFamide, serotonin, and octopamine on motor behaviors in the animal. Parallel studies suggest that changes in behavior can be explained, at least in part, by the alteration of firing patterns of selected neurons and muscles resulting from modulation of multiple ion conductances. This makes the leech exceptionally attractive for neuroethological studies because it is one of the simplest organisms in which the methods of psychology and neurobiology can be combined. Information gathered from this animal will therefore increase our understanding regarding general principles underlying the cellular basis of behavior.

Neuromodulatory effects of acetylcholine and serotonin on the sensitivity of leech mechanoreceptors

1. Each segmental ganglion of the leech Hirudo medicinalis contains 6 touch (T) cells, 4 pressure (P) cells and 4 nociceptive (N) cells. The receptive terminals of these cells innervate the skin in discrete areas. These cells are known to have extrasynaptic receptors. 2. We tested the effect of transmitter substances present in leech CNS on the sensitivity of T and P cells to mechanical stimuli. Substances tested included octopamine, FMRFamide, proctolin, substance P, glutamate, GABA, acetylcholine and serotonin. 3. Only acetylcholine and serotonin had consistent effects. Serotonin (1 x 10(-3) M) increased the number of action potentials of T cells elicited by a standard stimulus. Serotonin (1 x 10(-4) M) and acetylcholine (1 x 10(-3) M) increased the number and frequency of action potentials in P cells.

Studying the isolated central nervous system; a report on 35 years: more inquisitive than acquisitive

1. The CNS from invertebrate animals such as slugs, snails, leeches, and cockroaches, can be isolated and kept alive for many hours. 2. The electrical and pharmacological properties of invertebrate CNS neurons have many similarities and it is probable that the basic rules governing the CNS evolved more than 600 million years ago. 3. The nerve cells can show sodium action potentials, calcium action potentials, EPSP, IPSP, biphasic potentials, electrogenic sodium pump potentials, and a variety of potassium, sodium, calcium and chloride currents. 4. Invertebrate CNS ganglia contain identifiable individual nerve cells whose properties and responses to neurotransmitters and drugs are constant and repeatable from preparation to preparation. 5. It was possible to set up an isolated CNS-nerve trunk-muscle preparation and study the transport of radioactive material from the CNS to the muscle and from muscle to CNS. This has provided information about axoplasmic transport in both invertebrate and vertebrate preparations. 6. The methods developed from studies of invertebrate isolated CNS preparations have been applied to vertebrate isolated CNS preparations. 7. In addition to thin slices of the mammalian brain, it is possible to keep 5 cm lengths of the whole mammalian spinal cord and brain stem alive for many hours. 8. The isolated mammalian spinal cord has functional ipsilateral and contralateral reflexes, ascending and descending pathways, extensive sensory integrative local area networks, and inhibitory interneuron circuits. Much of the in vivo circuitry is functional in vitro. 9. The isolated mammalian spinal cord and brain stem can be developed to include functional higher brain circuits that will provide increased understanding of the control and integrative action of the mammalian central nervous system.

The Retzius cells in the leech: a review of their properties and synaptic connections

1. The Retzius cells (RCs) project an axonal branch in each anterior, posterior and dorsal segmental root. 2. RCs are the only serotonin-containing neurons projecting to the periphery. 3. RCs are activated by mechano-sensory neurons, by serotonin-containing neurons and by two pairs of subesophageal neurons, Tr 1 and Tr 2. 4. RCs also receive an excitatory and an inhibitory input from sensilla. 5. These inputs could form two systems, one converging onto RCs of each ganglion and one distributing to other ganglia after processing by RCs. 6. RCs play a role in muscle tension, in mucous release and in swimming activity.

Action potential prolongation: an effect of physostigmine (eserine) upon Retzius cells in the leech C.N.S

Physostigmine (PHY; eserine) prolongs the action potentials in the Retzius cells within leech ganglia to about 800 ms. The effect was reversible and occurred at concentrations of 1-10 mM which are several orders of magnitude greater than those required to inhibit cholinesterase. The prolonged action potentials showed an early, spike-like depolarization followed by a plateau. The initial depolarization exhibited a strong dependence on external Na+ while the amplitude of the plateau had somewhat less Na+ dependence: 52 and 24 mV/decade, respectively. The duration of the plateau was increased by elevating Na+ and decreased by elevating Ca2+. Increasing the action potential frequency, by intracellular stimulation, decreased both the duration and amplitude of the plateau. Neostigmine, di-isopropylphosphofluoridate, and acetylcholine did not prolong RZ action potentials. Thus, the membrane effects of physostigmine appear to be independent of any inhibition of cholinesterase or accumulation of acetylcholine.

The action of 5-hydroxthryptamine and related compounds on the activity of Retzius cells of the leech Hirudo medicinalis

1 The equipotent molar ratios of a range of tryptamine analogues, as compared with 5-hydroxytryptamine (5-HT), have been determined on the basis of their ability to hyperpolarize the membrane potential of the Retzius cell of the leech, Hirudo medicinalis.2 The substitution of methyl, fluoro, chloro, methoxy or acetyl groups onto the 5-HT molecule progressively reduced the potency.3 5-Methoxylation or terminal N-methylation of tryptamine considerably increased the potency of tryptamine but these compounds tended to depolarize cells rather than cause hyperpolarization. In some experiments they were ineffective on preparations pretreated with 5-HT.4 It is suggested that these compounds may act by a different mechanism from the 5-hydroxylated indoles, perhaps involving a different receptor.

Simple behavioural tests for defective vision in cats (film)

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