A VIBRATION-SENSITIVE DESCENDING STATOCYST INTERNEURONE IN THE CRAYEISH PROCAMBARUS CLARKII

1. An interneurone specifically sensitive to substratum vibration was identified in the crayfish circumoesophageal connective. The interneurone, called B1 in this paper, received excitatory input from the statocysts on both sides. Electrical stimulation of the statocyst nerve elicited several spikes in the interneurone with latencies that depended on which side was stimulated. 2. B1 responded phasically to artificial bending of the statocyst sensory hairs. The response was similar to that of the phasic-type receptor in the statocyst 3. The morphology of B1 was studied by an intracellular staining technique using nickel chloride and subsequent silver intensification. The interneurone projects its neurite arborization to the dorsal part of the deutocerebrum and parolfactory lobe on both sides, where the statocyst primary afferents also project. The overlapping of central projections, together with the properties of the response of B1 suggests that the interneurone receives excitatory input from the phasic-type receptors and transmits information about phasic body movement, but not static positional information, to the posterior ganglia 4. Branches of B1 also project to the antennal and tegumentary lobes ipsilateral to the axon. B1 may receive additional mechanosensory information from the cuticular sensory hairs on the antennae and the cephalic body surface

Observations on the number of nuclei within the fibres of some red and white muscles

Nuclei have been enumerated in muscle fibres of different physiological properties within adult rats and rabbits. Almost invariably, and regardless of muscle type, there is a direct relationship between the cross-sectional area (or fibre breadth) of muscle fibres and the number of nuclei within them. The one exception occurred in muscles of older rats where increased nuclear numbers do not always appear to result in broader muscle fibres. The greater complement of nuclei in broader fibres is accompanied by larger amounts of cell substance per nucleus. Confirming early observations in the literature, red fibres of the slow-phasic type have more nuclei than have white, fast-phasic fibres of similar breadth. These conclusions are not vitiated by differences in the number of nuclei within capillaries or in satellite cells, by differences in nuclear length or by variation in the degree to which fibres are contracted. In respect of their complement of nuclei, and the average amount of cell substance formed per nucleus the small red fibres that occur within muscles of predominantly fast-phasic character appear to be fast-rather than slow-phasic in type. When the number of nuclei observed per fibre is plotted against fibre cross-sectional area, the shapes of the resulting distributions suggest that estimates of muscle nuclei may be valuable not only as an index of growth potential, but of the extent to which that potential is expressed. In one muscle, the above distribution was of a form which indicated that some fibres may have formed abnormally large amounts of protein per nucleus. However, this was not adequately confirmed. Various factors have been investigated that are relevant to the accuracy of enumerating nuclei and measuring fibre breadths.

The neurophysiology of respiration in decapod crustacea. I. The motor system

The pump responsible for gill ventilation in the crayfish is operated by 11 muscles of the second maxillae. These muscles arc described and named and their action analyzed by the recording of nerve and muscle potentials. During quiet breathing, the normal motor command to each muscle is a short, high-frequency burst of evenly spaced action potentials (7–25 spikes at average frequencies of 60–140/sec). Histological and physiological evidence shows that the muscles represent mixed populations of fiber types. Most fibers are of the "gradedly responding" phasic type. Although methylene blue staining reveals two axons to each muscle, the normal motor command arrives via one axon only. The second may be a "fast" axon operating only in exceptional circumstances. No evidence has been found of a peripheral inhibitory system.