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D Murchison

Publications and source records attributed to D Murchison.

6 recordsLinked to original sources
PubMed1992

Synaptic interactions among neurons that coordinate swimmeret and abdominal movements in the crayfish.

1. Many interneurons in the crayfish (Procambarus clarkii) abdominal nervous system influence two behaviors, abdominal positioning and swimmeret movements. Such neurons are referred to as dual output cells. Other neurons which influence either one behavior or the other are single output cells. 2. Extensive synaptic interactions were observed between both dual and single output neurons involved in the control of abdominal positioning and swimmeret movements. Over 60% of all neuron pairs examined displayed interactions. Pairs of agonist neurons displayed excitatory interactions, while pairs of antagonists had inhibitory interactions. This pattern of interaction was observed in about 75% of interactive neuron pairs whether abdominal positioning or swimmeret outputs were considered. 3. Evidence for both serial and parallel connectivity, as well as, reciprocal or looping connections was observed. Looping connections can be found both between the abdominal positioning and swimmeret systems and within each system. 4. Most (28/34) single output neurons were not presynaptic to dual output neurons. No single output neurons were found to excite dual output neurons to spiking, although inhibitory interactions and weak excitations were observed. 5. Abdominal positioning inhibitors displayed properties consistent with a role in mediating some of the coordination between the swimmeret and abdominal positioning systems. 6. None of the dual output neurons examined influenced the swimmeret motoneurons directly.

Abdomen↗
PubMed1990

Dual motor output interneurons in the abdominal ganglia of the crayfish Procambarus clarkii: synaptic activation of motor outputs in both the swimmeret and abdominal positioning systems by single interneurons.

Many behavior patterns of the crayfish involve the positioning of the abdomen by the tonic motor system. Movements and positionings of the swimmerets are coordinated with these abdominal movements. Evidence from extracellular analyses suggested that single interneurons of the abdominal nerve cord could produce motor outputs in both the swimmeret and the abdominal positioning systems. Our intracellular investigation has revealed that many single cells can evoke outputs in both motor systems. Interneurons which produced fictive extension or flexion of the abdomen or inhibition of abdominal movement were also able to modulate a variety of swimmeret behavior including cyclic beating and excitation or inhibition of episodic outputs. Although interneurons were discovered that evoked each of the possible classes of dual-output combinations, those that evoked combinations frequently observed in the freely behaving animal were more common than those that evoked infrequently observed combinations. Evidence also indicated that abdominal positioning inhibitors are present in greater numbers than previously suspected and that many are closely associated with the swimmeret circuitry. Interneurons with the ability to start and stop swimmeret cyclic outputs with current injections of opposite polarity are proposed to be higher-order cells, and some are shown to have the properties of trigger neurons. It is proposed that most dual-output cells are presynaptic to single-output cells and that groups of related dual-output cells may function together as command elements.

Animals↗
PubMed1975

Failure to confirm a vascular cause of muscular dystrophy.

The vascular hypothesis of the cause of muscular dystrophy suggests that ischemia is responsible for the muscle fiber necrosis. A xenon 133 clearance study of muscle blood flow in Duchenne and other muscular dystrophies showed no obvious difference between the response to exercise and arterial occlusion compared with control subjects. Radioautographic study of distribution of 4-125l-antipyrine in skeletal muscle of mice with muscular dystrophy showed no abnormal areas of ischemia. A statistical examination was also made of the grouping of damaged fibers, one of the observations on which the vascular hypothesis was based. Only 0.9% of fibers undergoing phagocytosis occurred in groups of four or more fibers in greater frequency than would have been expected by chance, and 70% of such fibers were isolated. These studies argue strongly against the vascular hypothesis of the cause of muscular dystrophy.

Adult↗