Thomas Smyth

NEUROMUSCULAR PHYSIOLOGY OF GIANT MUSCLE FIBERS OF A BARNACLE, BALANUS NUBILUS DARWIN.

Abstract 1. 1. The large barnacle, Balanus nubilis , contains several large muscles, all of which contain cross striated muscle fibers of great thickness. In large specimens single fibers over 2 mm thick have been found. 2. 2. The fibers receive innervation from two or three motor axons. 3. 3. The axons give post-synaptic potentials of small or larger size. The small post-synaptic potentials do not reach the threshold for eliciting a graded response; the larger ones do. The corresponding mechanical responses which are elicited are very small or moderate-sized twitches. 4. 4. The giant fibers give large resting potentials which are stable over long periods. The fibers contract strongly when stimulated. It is considered that this will be a valuable preparation for the study of fundamental aspects of nerve-muscle physiology.

Lipid metabolism of Periplaneta americana L. during embryogenesis.

Abstract 1. 1. During development the weight of oothecae of the American cockroach decreased by 25 per cent, 17 per cent being due to water loss, the remainder largely to lipid catabolism. 2. 2. The major lipid fractions were separated by silicic acid column chromatography and their constituents identified and quantitated by thin layer chromatography. 3. 3. Total extractable lipid decreased from 39·5 to 23·2 per cent of the dry weight of the oothecae. Of the major lipid classes, only the triglyceride fraction decreased, this by 75 per cent. 4. 4. Mono- and diglycerides remained constant until the time of nymphal emergence when they increased sharply, indicating intense triglyceride hydrolysis.

Visual reflex control of indirect flight muscles in the sheep blowfly

Abstract 1. When the visual field under the fly was moved from front to back the frequency of potentials in the longitudinal and dorsoventral flight muscles was reduced. 2. Movement from back to front caused a transient increase in the frequency of potentials. 3. Air currents did not produce any such large changes in the frequency of potentials.

Isolation of a neurotoxin with a presynaptic action from the venom of the black widow spider (Latrodectus mactans, Fabr.)

Abstract Whole venom gland homogenates from the black widow spider were fractionated by discontinuous polyacrylamide gel electrophoresis. Eleven fractions were extracted from gel sections and assayed for toxicity by injection into cockroach nymphs and by application to cockroach neuromuscular preparation. One of the fractions, a slowly migrating protein with a molecular weight of 125,000, produced a slow permanent paralysis and accounted for the major action of crude venom by inducing a large transient rise in the miniature endplate potential frequency and eventual synaptic failure. A possible second neurotoxin with a different action has also been isolated.

Electrical measurements on cuticles excised from adult male Periplaneta americana (L.).

Abstract 1. 1. Electrical potential differences were recorded as a function of time and electric current across pronotum cuticles excised from adult male Periplaneta americana 2. 2. These measurements were interpreted in terms of ion mobility ratios, d.c. resistance and capacitance for the cuticles. 3. 3. Changes in electrical properties were noted both as a function of time after excision and time after molt. 4. 4. No evidence was found for a natural electric polarization in the cuticle. 5. 5. Ducts of the dermal glands were believed to provide the major pathway for ions moving across the cuticle, and cuticular grease was assumed to constitute the major dielectric barrier.

Action of black widow spider venom at insect neuromuscular junctions

Abstract The most striking action of black widow spider venom on both excitatory and inhibitory neuromuscular junctions of the American cockroach is presynaptic, like the action previously reported for vertebrate neuromuscular junctions. As indicated by post-junctional miniature excitatory and inhibitory endplate potentials, the rate of spontaneous transmitter release increases greatly after venom application and then decreases to zero, at which time the junctions are permanently blocked. The resting potentials of the muscle fibers and the sizes of the last miniatures that occur are essentially unchanged. That the venom also has a post-synaptic action is indicated by 1–2 mV fluctuations of the muscle membrane potential that occur almost immediately after venom application and before there has been any massive release of transmitter.

The electrical resistance of intact integument of Periplaneta americana (L.)

Abstract 1. 1. Electrical d.c. resistance across live, intact integument of adult Periplaneta americana was measured using electrolyte contacts on the external surface. 2. 2. This technique involved little apparent injury and numerous measurements over a period of months could be performed on the same animals. 3. 3. Large changes in integument resistance were found during the first day after molting and after the animals had been kept in separate containers for several months. 4. 4. No evidence was found for a specific layer near the outer surface being responsible for the measured resistance. 5. 5. Interpretation based on specific channel rather tha a layer of grease as being more important in regulating ion permeability across this integument is discussed.