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Biomedical subjects

J Bruner

Publications and source records attributed to J Bruner.

52 records · Page 3Linked to original sources
PubMed1979

Maintained contraction of the crayfish claw opener muscle in the absence of motor neuron activity.

In the whole crayfish (Astacus sp.), contraction of the dactyl opener muscle may persist for many minutes in the complete absence of action potentials in the excitor nerve or muscle. Such maintained contraction has not been observed in isolated claw preparations. Generally, maintained contraction resembles catch in that the muscle holds its previous position and does not recontract if stretched. In one animal, however, the muscle continued to slowly open in the absence of nerve activity. Maintained contraction occurred in 5 of 6 whole animal preparations; in those 5 animals it occurred on 49% of trials. We could find no difference in nerve activity or muscle potentials on trials when such contraction occurred and on those when it did not. It is proposed that in the whole animal maintained contraction may be controlled by a factor which is released into the blood supply when the animal is aroused.

Animals↗
PubMed1979

The presynaptic action of L-glutamate at the crayfish neuromuscular junction. Results obtained by intra-axonal recordings and nerve terminal damage.

The presynaptic action of glutamate was investigated in crayfish neuromuscular preparations. The excitability of locally stimulated nerve terminals increased during the perfusion of glutamate. Electrotonically propagated depolarizations were recorded in the excitatory axons when glutamate was ionophoretically applied to sensitive spots on the muscle membrane. Depolarizations of the axon were also obtained when glutamate, GABA and aspartate were added to the bath. In order to evaluate the part of the presynaptic effect in the depolarization induced in muscle fibres, nerve terminals were damaged either by treatment with high-Ca solutions or by denervation. In both cases, a decreased sensitivity to glutamate was found. Possible relationships between the nerve terminal damage and the change in the response to glutamate are proposed.

Animals↗
PubMed1977

Tuberculin-specific transfer factor in dogs.

Five mongrel dogs were sensitized to tuberculoprotein with Freund adjuvant, as determined by responses to tuberculin skin tests and by in vitro lymphocyte cultures. These animals served as blood donors for production of transfer factor. Nine mongrel dogs received single doses of transfer factor that was tuberculin specific. Successful transfer of tuberculin sensitivity as measured by lymphocyte transformations was achieved in five of nine animals. Canine lymphocyte cultures frequently showed relatively low transformations to mitogens as compared with responses noted in other animals. Dissociation between skin test reactivity and in vitro lymphocyte transformation to tuberculoprotein was noted in two of nine animals. Increases in lymphocyte transformations to phytochemagglutinin were seen in three of nine recipient animals after transfer factor administration. Successful transfer from an animal sensitized by prior transfer factor administration was achieved in one instance. These data indicate that transfer factor-like substances are present in dogs. The reasons why successful transfer was achieved in only half of the recipient animals needs further explanation.

Animals↗
PubMed1975

[Short and long term depression of neuromuscular transmission in crayfish].

Following single excitation of the abdominal giant motoneuron of crayfish, an important depression of neuro-muscular transmission is observed for about 15 mn. The time course of recovery is not modified even after low frequency (1/30 Hz) repetitive stimulation. Recovery curves obtained for different Mg++ concentration in physiological solutions show two phases of depression: short-term depression which is largely reduced in high Mg++ concentrations - thus probably depending on transmitter depletion in motoneuron terminals - long-term depression which is not modified by changing Mg++ concentration and seems to be independent of depletion.

Abdomen↗
PubMed1970

Habituation: occurrence at a neuromuscular junction.

At the neuromuscular junctions between the motor giant axon and fast flexor muscle fibers in crayfish, stimulation at frequencies of one per minute produces a large decline in the amplitude of excitatory junctional potentials. Recovery (dishabituation) can be brought about by increases in stimulus frequency, which trigger a potentiation process; at still higher frequencies, a second form of depression intervenes. The last process appears to be due to depletion of transmitter; the first probably depends instead upon electrical changes in presynaptic terminals. Because of the interactions between the three processes, the junctions display the properties of habituation and dishabituation usually associated with complex central nervous networks.

Animals↗
PubMedDate not supplied

[Effects of the monosaccharide derivative 8RN-DAGal on the putative P-type calcium channel expressed in Xenopus oocytes].

P-type calcium channels are expressed in Xenopus oocytes after injection of rat cerebellar mRNA. The FTX and omega-Aga-IVa toxins extracted from Agelenopsis aperta venom are known to inhibit the activity of this channel. The present results demonstrate that 8RN-DAGal is also a antagonist of P-type calcium channels. The inhibition of the current, obtained with Ba2+, as charge carrier, is voltage dependent.

Animals↗