Tohru Yazawa

Intrinsic and extrinsic neural and neurohumoral control of the decapod heart

The intra-cardiac nervous system of the decapod heart is composed of large and small ganglionic cells (LGCs and SGCs) and axons of extrinsic cardio-acceleratory and-inhibitory neurons (CAs and CIs). Candidate neurotransmitters for the neurons have been determined by pharmacological, cytochemical and immunocytochemical tests. SGCs may be cholinergic, LGCs and CAs are probably dopaminergic, and CIs are GABAergic. Serotonin and octopamine were cardio-excitatory neuromodulators of the heart. Proctolin, crustacean cardio-active peptide (CCAP), red pigment concentrating hormone (RPCH), and FMRFamide also had modulatory actions on the heart. Proctolin was the most potent peptide, which acted primary on the cardiac ganglion. Insect adipokinetic hormones had little effect on the heart.

Monoamines, amino acids and acetylcholine in the preoptic area and anterior hypothalamus of rats: measurements of tissue extracts and in vivo microdialysates

A microbore column high-performance liquid chromatography (HPLC) system was used to measure neurotransmitters in tissue extracts and in vivo microdialysates obtained from the preoptic area (PO) and anterior hypothalamus (AH) of rats. The extracts contained norepinephrine, epinephrine, 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine, 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), aspartate, glutamate, GABA, acetylcholine (ACh) and choline. The microdialysates obtained from the PO and AH of freely moving rats contained all of these substances except for norepinephrine, epinephrine, dopamine, and 5-HT. During collection of microdialysate from the PO and AH, core body temperature and locomotor activity were simultaneously measured by means of telemetry. The locomotor activity and body temperature increased during the night. This was accompanied by increased levels of 5-HIAA. The results suggest that serotonergic neuronal mechanisms in the PO and AH may be involved in hypothalamic regulation of spontaneous behaviors and body temperature.

Neural control of the cardio-arterial valves in an isopod crustacean, Bathynomus doederleini: excitatory and inhibitory junctional potentials

Summary1.InBathynomus doederleini, there are cardio-arterial valves at the junctions between the heart and the arteries. These comprise: one anterior median artery, a pair of anterior lateral arteries and five pairs of lateral arteries.2.The valves at the cardiac junctions of the three anterior arteries receive innervation from a pair of anterior cardiac nerves. The anterior cardiac nerve on each side contains one excitatory and one inhibitory motor axon for the valves.3.Excitatory junctional potentials (EJPs) were recorded from all three valves of the anterior arteries. Inhibitory junctional potentials (IJPs) were recorded from the valves of the pair of anterior lateral arteries, but not from the valve of the anterior median artery.4.A whole-mount preparation treated with glyoxylic acid developed fluorophore processes on all three valves of the anterior median and lateral arteries, suggesting that the processes are due to a pair of aminergic excitatory valve nerves.5.The lateral arterial valves receive innervation from the valve nerves running alongside the arteries. Each of the valves of the lateral arteries are innervated by inhibitory motor nerves producing IJPs in the valves, and probably only by these nerves.6.It is suggested that the flow of haemolymph to individual arteries is regulated by three types of innervation of the cardio-arterial valves. These are: dual innervation by excitatory and inhibitory axons, and single innervation which may be either excitatory or inhibitory.

The cardio-regulator nerves of the hermit crabs: anatomical and electrophysiological identification of their distribution inside the heart

Summary1.The cardiac ganglion and the routes of the cardio-regulator nerves inside the heart were investigated anatomically and electrophysiologically in the hermit crabs (Aniculus aniculus andDardanus crassimanus). It was proved that the dorsal cardiac nerve containing three regulator axons on each side, one inhibitor and two accelerators, pierced the heart wall and connected with the cardiac ganglion.2.The cardiac ganglion consisted of five large neurons and four small neurons. Configuration of the cardiac ganglion was analogous to the crab (Cancer orPortunus) cardiac ganglion in having a pair of circular trunks. However, arrangement of the large cells and the small cells was analogous to the lobster (Homarus, Panulirus orPalinurus) cardiac ganglion in alignment of the ganglionic cells.3.The two acceleratory nerves had almost identical innervating routes. The route of the inhibitory nerve was significantly different from the routes of the acceleratory nerves inside the heart.4.The inhibitory axon had the route only along the main trunk of the cardiac ganglion. IPSPs were recorded from large ganglionic cell bodies, one-toone to inhibitory impulses.5.The acceleratory axons were carried not only in the main trunk but also in the circular trunk. There were acceleratory branches extending toward the periphery away from both the trunks.6.EPSPs were recorded from large cell bodies in a one-to-one relationship to acceleratory stimuli. This provided direct evidence for ordinary synapses of the accelerator on the large ganglionic cells.

A physiological saline for Lepidopterous insects: Effects of ionic composition on heart beat and neuromuscular transmission

Abstract Three species of Lepidoptera, Bombyx mori, Agrius convolvuli and Antheraea yamamai were used to prepare a suitable physiological saline for maintaining heart beat and junctional potentials of somatic muscle cells. A variety of salines designed for Lepidoptera were reexamined. Heart beat in the three species could not be maintained in salines used previously as physiological or culture solutions for Lepidoptera. Ionic compositions were determined for physiological salines that were suitable for maintaining the normal heart beat and normal neuromuscular transmission in body muscle cells. It was found that salines should contain 12–28 mM NaCl, 32-16 mM KCl ([Na+] + [K+ ] = 44) and at least 9 mM CaCl2. In the salines, stimuli to motor nerves evoke action potentials of more than 40 mV in amplitude in ventral muscle cells. The ionic composition of a new physiological saline for Lepidoptera is as follows: NaCl, 12–28; KCl, 32-16([Na+] + [K+] = 44); CaCl2, 9; NaH2PO4, 1.5; Na2HPO4, 1.5; MgCl2, 18; sucrose, 175 (mM), pH 6.5.

Dopaminergic acceleration and GABAergic inhibition in extrinsic neural control of the hermit crab heart

The acceleratory and inhibitory cardio-regulatory nerves of hermit crabs (Aniculus aniculus, Dardanus crassimanus) were studied using histochemical, immunocytochemical and pharmacological tests. Glyoxylic acid-induced fluorescence was observed in two of three axons of the dorsal cardiac nerve. One axon of the nerve showed gamma-aminobutyric acid-like immunoreactivity. Effects of stimulation of cardio-acceleratory axons were blocked by the dopaminergic antagonists, haloperidol and chlorpromazine, but not by cholinergic, adrenergic or serotonergic blockers, suggesting that dopamine is the primary potential candidate for the neurotransmitter of cardio-accelerator neurons. Picrotoxin antagonized inhibition of the cardiac ganglion induced by gammaam-inobutyric acid and by cardio-inhibitory axons. Both small and large ganglionic cells may receive dopaminergic and GABAergic extrinsic neural control.

The cardio-regulator nerves of hermit crabs: Multimodal activation of the heart by the accelerator axons

Summary1.Some branches of the cardio-accelerator axons run directly to peripheral ganglionic tissue in the hermit crabs (Aniculus aniculus andDardanus crassimanus). Effects of the branches on cardiac tissues were studied electrophysiologically in a preparation in which the main trunk had been severed.2.The branches of the cardio-accelerator axons exerted their acceleratory effects directly on two different tissues, peripheral motor processes of the ganglion and the myocardium.3.Stimuli applied to the cardio-accelerator axons elicited impulses in ganglionic motor axons at terminal processes, but not in a one-to-one manner. For each ganglionic axon impulse an EJP was recorded from the myocardium. Therefore, the EJPs were identified as intrinsic EJPs due to activation of ganglionic axons by cardio-accelerator axons.4.Small depolarizing potentials recorded from the myocardium corresponded one-to-one to stimuli applied to the cardio-accelerator axons. The following results show that the small potentials were EJPs: (i) The potentials showed summation and facilitation. (ii) Amplitude of the potentials varied depending on the level of the membrane potential. (iii) Amplitude of the potentials increased in a high Ca2+, low Mg2+ saline and decreased in a Ca2+-free, high Mg2+ saline. The EJPs were identified as extrinsic EJPs evoked directly in a muscle cell innervated by the accelerator axons.5.The cardio-accelerator nerves excite the heart by multimodal activation, i.e. directly on the main trunk of the cardiac ganglion, on peripheral motor processes of the ganglion, and on the myocardium.

Inhibitory neural control of the myocardium in opisthobranch molluscs

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Cholinergic Inhibitory Innervation of the Cardioarterial Valves in the Isopod Bathynomus doederleini

Abstract In the isopod Bathynomus doederleini, the cardioarterial valves of all five pairs of lateral arteries and the pair of anterior lateral arteries are innervated by inhibitory (dilator) nerves which consist of one or two axons arising from the central nervous system. Stimulation of the valve dilator nerves produced inhibitory junctional potentials (IJPs) in valve muscle cells which arose one-to-one in response to stimulus pulses. Acetylcholine (ACh) hyperpolarized muscle cells of the valves. Both the IJPs and ACh-induced hyperpolarization brought about an increase of haemolymph pressure in the arteries, through relaxation of valve muscles. The muscarinic agonists, muscarine, carbamylcholine and arecoline, mimicked ACh-induced hyperpolarizing responses of the valve muscle cells. Atropine and methylxylocholine antagonized both the IJPs and ACh-induced hyperpolarizing potentials, while d-tubocurarine did not antagonize IJPs. These results indicate that ACh may be the transmitter for the valve dilator nerves. IJPs did not invert in Cl−-free saline. Amplitude of IJPs increased in low K+ salines, and decreased in high K+ salines. It is likely that IJPs are mediated predominantly by K+ ions. This could be the first case of cholinergic inhibitory transmission at neuromuscular junctions in crustaceans.

Cholinergic, Catecholaminergic and Gabaergic Mechanisms of Synaptic Transmission in the Heart of the Hermit Crab

Monoaminergic and cholinergic drugs accelerated bursting activity of the cardiac ganglion (CG). Dopaminergic antagonists suppressed accelerated CG activity by stimulation of extrinsic acceleratory nerves and also suppressed myocardial excitatory junctional potentials (EJPs) evoked by large ganglionic neurons (LGNs). Muscarinic antagonists suppressed excitatory postsynaptic potentials (EPSPs) of LGNs induced by small ganglionic neurons (SGNs), but nicotinic ones did not. γ-Aminobutylic acid (GABA) mimicked inhibitory effects on CG evoked by stimulation of extrinsic inhibitory nerves. The effects were suppressed by Picrotoxin and bicuculline. LGNs and two of three regulatory axons in the dorsal cardiac nerve showed green fluorescence induced by glyoxylic acid. No neuronal processes in the heart showed immunoreactivity to anti-serotonin antibody. Our results suggest the following; SGNs are cholinergic, LGNs and the two acceleratory axons are catecholaminergic, and the single inhibitory axon is GABAergic.