R.J. Walker

Iontophoretic application of acetylcholine and gaba onto insect central neurones

Abstract 1. 1. Electrical activity showing action potentials, EPSP and IPSP can be recorded with micro-electrodes from the nerve cell bodies in the ganglia of the cockroach. 2. 2. The sensitivity of the nerve cell to iontophoretically applied acetylcholine is 1·31×10 −13 mole. It is of the same order of sensitivity to acetylcholine as shown by mollusc nerve cells. 3. 3. The sensitivity of the nerve cell to iontophoretically applied GABA is 1·05 ×10 −13 mole. 4. 4. A full summary is given on page 630.

The effect of dopa, α-methyldopa and reserpine on the dopamine content of the brain of the snail, Helix aspersa

Abstract 1. 1. Paper chromatographic analysis using five different solvent systems and spectrophotofluorimetry reveal the presence of 5·5 μg/g dopamine in teh circumoesophageal ganglionic mass of Helix aspersa, and 0·18 μg/ml DOPA in the blood. 2. 2. Injection of reserpine decreased the brain dopamine content. 3. 3. Injection of DOPA increased the brain dopamine content. 4. 4. Amine oxidase inhibitors and o-methyl transferase inhibitors have no effect on brain dopamine content. 5. 5. Dopamine was the only catecholamine found in the nervous system of the crab Carcinus maenas and the clam mercenaria mercenaria. No catecholamine was found in the ventral nerve cord of the leech Hirudo medicinalis.

The effects of drugs on the neurones of the snail Helix aspersa

Abstract 1. (1) The effect of adding various chemicals to the isolated brain of the snail Helix aspersa is described. The reactions were followed by measuring the effect of the chemicals on the resting potential and the spontaneous action potentials of the nerve cells. 2. (2) All the following chemicals were effective at dilutions between 10−7 and 10−11 g/ml. The sign indicates their overall acceleratory (+) or inhibitory (−) effect on the spontaneous activity. Acetylcholine (+) Glutamic acid (±) Adrenaline (+) Histamine (±) Cocarboxylase (±) Nor-adrenaline (±) Dimethyl-amino-ethanol (−) 5-HT (+) Dopamine (−) Phenylalanine (−) γ-Aminobutyric acid (+) Thiamine hydrochloride (±) 3. (3) Dopamine and phenylalanine caused a hyperpolarization of the resting potential. 4. (4) Phenylalanine, glutamic acid and cocarboxylase could protect the cell against the action of high concentrations of acetylcholine. 5. (5) It is thought that most of the above chemicals may occur naturally in the snail and that acetylcholine and dopamine are the most likely transmitter substances. 6. (6) Most of the drugs had a dual action; inhibiting some cells and accelerating others. It is suggested that there is a marked chemical heterogeneity in the CNS with cells reacting specifically but different to a given chemical.

The presence of glutamate in nerve-muscle perfusates of Helix, Carcinus and Periplaneta

Abstract 1. 1. The perfusion of nerve-muscle preparations in the snail Helix aspersa, the crab Carcinus maenas and the cockroach Periplaneta americana is described. 2. 2. When the nervous system in these preparations is stimulated, a ninhydrin positive substance (NPS) appears in the perfusate. 3. 3. The amount of NPS produced is proportional to the number of stimuli. 4. 4. The NPS is identified by thin-layer chromatography as glutamate. 5. 5. The Helix muscle will contract to the addition of 2 × 10−8 g/ml of glutamate; Periplaneta muscle contracts to the addition of 5 × 10−8 g/ml glutamate. 6. 6. The role of glutamate as a nerve-muscle transmitter is discussed.

The pharmacology of helix dopamine receptor of specific neurones in the snail, helix aspersa

Abstract 1. 1. Dopamine was found to hyperpolarize and inhibit the spontaneous activity of certain Helix neurones. 2. 2. The inhibitory effect of dopamine was antagonized by ergometrine, ergotamine, ergotoxine, dibenyline, rogitine and yohimbine. 3. 3. The inhibitory effect of dopamine was not antagonized by inderal, N-isopropyl methoxamine, oubain, atropine or methysergide. 4. 4. It was suggested that the dopamine receptor of Helix neurones resembled the α adrenergic receptor of vertebrates.

The specific chemical sensitivity of Helix nerve cells

Abstract 1. 1. The connexions between some cell bodies and the peripheral nerves in the ganglia of Helix aspersa are described. 2. 2. The responses of the nerve cells to chemicals (acetylcholine, histamine, 5HT, 5HTP, dopamine, glutamic acid, GABA, phenylalanine and β-alanine) were tested. 3. 3. Eighteen identified cells gave consistent selective responses to the chemicals. Some were sensitive to acetylcholine, others to 5HT, or histamine, or dopamine. 4. 4. Helix brain contains material which when chromatogrammed can excite or inhibit nerve action.

Uptake of DOPA and 5-hydroxytryptophan by monoamine-forming neurones in the brain of Helix aspersa

Abstract 1. 1. The brain of Helix aspersa after fluorescence microscopy shows many fluorescent structures. Usually these emit either a green or yellow light. However, the cells at the junction of the visceral and right parietal ganglia are green in colour with yellow areas. 2. 2. After injection of l -DOPA the fluorescence of these cells is distinctly green in colour. 3. 3. After injection of 5-HTP the fluorescence of these cells is distinctly yellow in colour. 4. 4. Pretreatment of the DOPA-injected snails with a DOPA decarboxylase inhibitor prevented the appearance of the green fluorescence. 5. 5. It is suggested that the cells at the junction of the visceral and right parietal ganglia contain both dopamine and 5-HT.

Long-lasting synaptic inhibition and its transmitter in the snail Helix aspersa

1. 1. Inhibition of Long Duration (ILD) was produced in a known cell in Helix aspersa by stimulation of the left pallial nerve. 2. 2. The ILD was found to be caused by an increase in permeability to potassium ions, with a reversal potential in the region of −80 mV. 3. 3. The ILD was blocked by treatment with ergometrine. 4. 4. The inhibitory action of dopamine on this cell was found to be due to a specific increase in potassium permeability, with an equilibrium potential close to −80 mV. 5. 5. The inhibitory action of glutamate on this cell was found to be caused by an increase in permeability to both potassium and chloride ions, in the ratio of 1:1, and with a reversal potential of −54 mV. The response to glutamate was not antagonized by ergometrine. 6. 6. Dopamine is the most probable transmitter responsible for ILD in the cell studied.

The effect of acetylcholine, glutamic acid and GABA on the contractions of the perfused cockroach leg

Abstract 1. 1. The perfused cockroach leg preparation is described. 2. 2. The leg gives an increased contraction to the addition of acetylcholine (5 × 10 −6 ); l -glutamic acid (10 −7 ); d -glutamic acid (10 −6 ); l -aspartic acid (10 −3 ). The figures in brackets are the threshold values in g/ml. 3. 3. Increased amounts of acetylcholine, glutamic acid or aspartic acid bring about greater and longer lasting contractions. 4. 4. Addition of 5-HT has little effect, though higher concentrations (10 −3 g/ml) can cause a slight inhibition of the contraction. 5. 5. GABA has a marked inhibition on the contraction; the threshold concentration being 5×10 −6 g/ml. Higher concentrations bring about more marked and longer lasting inhibition. The effect is quickly reversible. 6. 6. GABA has little inhibitory effect on contractions induced by acetyklcholine but it will easily inhibit contractions caused by glutamic acid.

Cellular localization of monoamines by fluorescence microscopy in Hirudo medicinalis and Lumbricus terrestris

Abstract 1. 1. The cellular localization of 5-hydroxytryptamine and primary monoamines in the ventral nerve cord of Hirudo medicinalis and Lumbricus terrestris is described. 2. 2. The ganglia of Hirudo medicinalis only contain 5-hydroxytryptamine. 3. 3. This is confined to the soma of six cells, two of which are the giant cells of Retzius. 4. 4. The ventral nerve cord of Lumbricus terrestris contains both 5-hdyroxytryptamine (or 5-hydroxytryptophan) and a primary catecholamine. 5. 5. Many cells show the 5-hdyroxytryptamine fluorescence and are scattered throughout the nerve cord. Only a few cells contain primary catecholamine.