Biomedical subjects

R G Chiang

Publications and source records attributed to R G Chiang.

10 recordsLinked to original sources

PubMed1990

Morphology of the dorsal vessel in the abdomen of the blood-feeding insect Rhodnius prolixus.

The dorsal vessel (DV) in the abdomen of the blood-feeding insect Rhodnius prolixus was divided functionally into two regions, the heart, into which haemolymph entered the DV through four pairs of ostia located in abdominal segment VII, and the aorta, along which the haemolymph was propelled from abdominal segment VI to the thorax. Osmium-fixed whole mounts revealed the DV to consist of spirally arranged striated muscle fibers and to possess two rows of ventrally attached longitudinal fibers extending the length of the abdomen. Seven pairs of alary muscles were found attached to the DV in the posterior abdominal segments. Contractions of the alary muscles attached to the ventral surface of abdominal segments VII and VIII served to expand the heart. Electron microscopy revealed the DV to consist of a thin layer of contractile elements surrounded by an inner (intima) and outer (adventitia) connective tissue layer. Embedded in the intima along each lateral side of the DV were two large groups of endocardial cells extending the length of the DV. A small group of pericardial cells was embedded in the adventitia along the mid-ventral side of the DV, and clusters of pericardial cells were found attached to the alary muscles. Nerve terminals were found only on the heart: they contained agranular synaptic vesicles approximately 30 nm in diameter and densely stained granules approximately 100-120 nm in diameter. These structural components are discussed in relation to the role of the DV in circulation.

Abdomen↗

PubMed1988

Extracellular application of cobalt: a fast and simple method for delineating invertebrate neurosecretory pathways.

The extracellular cobalt backfilling technique was shown to be an excellent method to obtain cobalt backfills of invertebrate neurosecretory cells (NSCs). Aqueous cobalt was placed in an extracellular suction electrode into which a portion of a neurohaemal (NH) region containing the axons and/or terminals of NSCs was drawn. Spontaneously discharging extracellular action potentials were recorded as the cobalt was applied to the NH region, and the greater the electrical activity, the more extensive the cobalt backfilling. The greatest success occurred with 0.5 M cobalt chloride dissolved in physiological saline. No backfills were obtained in the absence of electrical activity. This technique was shown to backfill NSCs terminating in NH regions of the insect, Rhodnius prolixus, the isopod crustacean, Oniscus asellus, and the freshwater pulmonate snail, Helisoma. Combined with a light insensitive silver intensification method, this paper describes a relatively fast and simple method for delineating invertebrate neurosecretory pathways.

Action Potentials↗

PubMed1987

Changes during the moult cycle in the bursting firing pattern of the electrical activity recorded extracellularly from the sinus gland of the terrestrial isopod, Oniscus asellus.

Ongoing electrical activity of the sinus gland (SG) of the terrestrial isopod, Oniscus asellus, was recorded extracellularly from almost intact breeding or non-breeding females to delineate the major times of neurohormone release during the moult cycle. In intermoult, SGs discharged in long bursts (10-50 s) at high frequency (10-45 Hz), and their activity ratios (total burst duration divided by total time the SG was monitored) ranged from 0.22 to 0.73. At premoult initiation when release of moult-inhibiting hormone is expected to decline, a decrease in SG activity occurred. It rose again in early premoult in parallel with increases in ecdysteroid titre; declined again in late premoult during peak ecdysteroid titres; increased again just prior to posterior ecdysis, and was very low during posterior ecdysis itself. Activity increased immediately after posterior and anterior ecdysis suggesting the release of neurohormones involved in calcification of the new cuticle. Burst duration was ca. two-fold longer in breeding compared to non-breeding females during early premoult suggesting the release of neurohormones involved in vitellogenesis, and before anterior ecdysis suggesting release of neurohormones involved in egg deposition. Thus, the release of neurohormones occurred during 4 major periods in each moult cycle, clearly demonstrating a relationship between SG activity in situ, and the physiological events dependent on SG hormones.

Animals↗

PubMed1986

Electrical activity of the sinus gland of the terrestrial isopod, Oniscus asellus: characteristics of identified potentials recorded extracellularly from neurosecretory terminals.

Spontaneously occurring neurosecretory action potentials recorded extracellularly from the sinus gland (SG) of the terrestrial isopod. Oniscus asellus, are of 5 types (A through E) identified by their amplitudes and patterns of discharge. Type A have the largest (200-450 microV) and type E the smallest (25-50 microV) amplitude. Types A, B and C originate from the bulb of the SG, and discharge at high frequencies (30-60 Hz) in coordinated bursts ranging from seconds to several minutes in duration. Coordination of their discharges suggests a mechanism for synchronizing bursting activity among different cell types. Types D and E originate from the lateral extension of the SG, and discharge at low frequencies (0.5-1.0 Hz) for prolonged periods (5-10 min). Their activity is not synchronized with discharges of other potentials. Following transection of the brain through the lateral part of the central protocerebral neuropile, A, B and C potentials are eliminated whereas D and E potentials remain active. This result suggests A, B and C potentials arise from neurosecretory cells (NSCs) whose cell bodies are located in the medial protocerebrum, and D and E potentials arise from NSCs identified in the optic lobe. Alterations in the appearance of action potentials following exposure to salines deficient in Na+ or Ca2+, or containing tetrodotoxin or cobalt, reveal that A and B potentials are primarily Ca2+ dependent whereas C potentials are both Ca2+ and Na+ dependent.

Action Potentials↗

PubMed1986

Reorganization of synaptic ultrastructure at facilitated lobster neuromuscular terminals.

Prolonged stimulation of the single excitor axon to the lobster distal accessory flexor muscle in the presence of ouabain caused long-term facilitation at its neuromuscular synapses. Hence the extracellularly recorded synaptic potentials failed less frequently and increased their mean amplitude, compared to the non-facilitated (control) potentials from homologous sites in the contralateral muscle. The fine structure of synaptic terminals between matched pairs of facilitated and control preparations was compared with the aid of serial section electron microscopy. Differences between facilitated and control preparations were similar both when the latter were bathed in normal saline or ouabain-containing saline, suggesting that the changes were related to the electrical stimulation rather than to the presence of ouabain. First, the facilitated terminals were smaller in surface area than the control. Second, the number and size of synaptic contacts in the facilitated terminals resembled those in the control. Third, presynaptic dense bodies or active sites increased in number although their sizes remained unaltered in the facilitated terminal. This increase is attributed to the addition of dense bodies at existing synaptic contacts since synaptic contacts remained constant in number between facilitated and control preparations. Fourth, the number and size of synaptic vesicles were unaffected by prolonged stimulation although there was a redistribution of vesicles such that they appeared to be channelled in distinct streams to synaptic contacts. Fifth, mitochondria increased in number and were situated closer to the dense bodies at facilitated nerve terminals than at control terminals. Overall, these changes denote considerable reorganization of the synaptic terminals associated with elevated transmitter release.

Animals↗

PubMed1985

Coupling of electrical activity from contralateral sinus glands.

Bursts of electrical activity recorded extracellularly from the sinus gland (SG) of the isopod, Oniscus asellus, occur synchronously in right and left SGs. Synchronization results from the electrical activity of two physiologically identifiable neurosecretory cell (NSC) types in one SG being coupled to the electrical activity of their respective contralateral counterparts. Furthermore, the coupling mechanism which serves to coordinate hormone release from contralateral SGs appears to differ for each of the two NSC types.

Animals↗

PubMed1985

Ultrastructure and distribution of identified neurosecretory terminals in the sinus gland of the terrestrial isopod Oniscus asellus.

An ultrastructural study of the sinus gland of the terrestrial isopod, Oniscus asellus, reveals that this structure consists of two regions: the bulb, which is attached by a narrow stalk to the optic lobe, and the lateral extension, which extends from the bulb along the optic tract to the compound eye. The bulb has a distal region containing only neurosecretory terminals, and a proximal region containing terminals, glial cells, and axons that give rise to the distally located terminals. In total, the sinus gland contains five types of terminals which can be distinguished by their location and the appearance of their neurosecretory granules. Three terminal types are located in the bulb and two in the lateral extension. The size of the terminals in the bulb varies among the three types, but the number of terminals is approximately the same for each type. Conversely, the two terminal types in the lateral extension are similar in size, but differ in number. Axons of two terminal types in the bulb can be traced to the central region of the protocerebrum; axons of one terminal type in the bulb and of terminals in the lateral extension can be traced to the optic lobe.

Animals↗

PubMed1985

Recording electrophysiological data on video tape: a superior and less costly alternative to conventional tape recorders.

Electrical potentials recorded extracellularly from the sinus gland of the isopod, Oniscus asellus, were stored on video tape with the aid of a digital-audio (DA) processor and a video cassette recorder (VCR). The DA processor transforms the analog signal to digital pulses of equal amplitude and converts these pulses into a television signal for recording on video tape. In playback, the DA processor reconverts the pulses to an analog signal with negligible distortion. When viewed on the oscilloscope screen, electrical potentials reproduced by this method were indistinguishable from electrical potentials recorded 'live' from the sinus gland. However, electrical potentials recorded from the same sinus gland and reproduced by a conventional FM tape recorder were easily differentiated from the 'live' recording. The special effects inherent in the VCR (e.g. stop action, frame advance) also permitted detailed analysis of spontaneously occurring electrical potentials. Special effects were not possible with the FM tape recorder. The price, ease of operation and ability to produce extremely high quality recordings, makes the DA processor and VCR an exceptional system for storing electrophysiological data.

Animals↗

PubMed1984

Decrease in transmitter output and synaptic ultrastructure at lobster neuromuscular terminals with decentralization.

The effects of decentralization on the physiology and ultrastructure of neuromuscular terminals were examined by transecting the single excitor axon to the distal accessory flexor muscle in the walking legs of lobsters (Homarus americanus). Decentralization caused a reduction in the amplitude of the excitatory junctional potential without altering the resting potential or input resistance of the muscle fiber thereby suggesting a reduction in transmitter release. Confirmation was obtained by recording of synaptic currents at focal sites which showed failure of transmission and a reduced amplitude on decentralized fibers compared to their intact counterparts on the contralateral leg. The mean quantal content of synaptic transmission decreased approximately 2-7-fold at these decentralized sites compared to their intact counterparts. The ultrastructure of these identified sites was examined with serial section electron microscopy. There are few if any qualitative changes in synaptic ultrastructure between decentralized and control terminals. However, quantitatively there were changes in synaptic ultrastructure which were progressive in nature depending on the severity of the reaction to decentralization. Thus terminals showing a moderate decline in quantal content were characterized by a reduction in the number of presynaptic dense bars and synapses. Terminals showing a severe drop in transmitter release showed in addition to the above changes, a reduction in the size of synapses and terminals. These results show a progression in the loss of the structural parameters controlling transmitter release. Finally synaptic vesicles and mitochondria did not reveal any consistent or marked change with decentralization.

Animals↗

PubMed1979

Correlation between presynaptic dense bodies and transmitter output at lobster neuromuscular terminals by serial section electron microscopy.

Lobster neuromuscular terminals releasing comparatively small (low-output type) and large (high-output type) amounts of transmitter but arising from the single excitatory motor axon to the proximal accessory flexor muscle were serially sectioned for electron microscopy. The three-dimensional reconstruction showed the two types of terminals to have a complex branching pattern in which thin branches of the motor axon often enlarged into synapse bearing terminal regions. Quantitative comparison showed that the mean surface area of a synapse is similar in the two types of terminals. However, the low-output terminal has a higher synaptic density and devotes a greater part of its surface area to synapses compared to its high-output counterpart suggesting that transmitter output is not directly related to synaptic area. The mean surface area of a presynaptic dense body is not significantly different between low- and high-output synapses, but there is a significantly greater density of these active zones in the high-output terminal. This results in the ratio of mean dense body area to mean synaptic area being approximately 3 X greater in the high-output synapses than the low-output ones. This significant difference in the surface area of presynaptic dense bodies between low- and high-output synapses correlates with the difference in transmitter output at these two synapses, and implicates the dense bodies in the mechanism of transmitter release at lobster neuromuscular synapses.

Animals↗