Effect of cryoprotective agents on rat cutaneous nerves.

Desheathed rat cutaneous nerves were exposed to various concentrations of ethylene glycol (EG), glycerol and dimethyl sulfoxide (DMSO) at temperatures of 1, 24, and 38 °C for periods of time ranging from 5 to 60 min. Measurements of the percent recovery of the original action potential (AP) were determined after removal of the cryoprotective agent (CPA) under various conditions, i.e., temperature, time and sequence of rinsing. A comparison of the results obtained after the nerves were exposed directly to a 15% concentration of the three CPAs at 1 °C for a 15-min period showed that the percentage of recovery of the AP was 90, 69, and 36% of the original values when treated with DMSO, EG, or glycerol, respectively. In all three groups, the nerves were rinsed at 1 °C for 15 min. If the exposure to glycerol at 1 °C was carried out in a gradual stepwise manner, the recovery of the AP in 10 and 15% solutions ranged from 58 to 64%. If the temperatures of the exposure and rinse were increased to 24 and 38 °C, glycerol produced some toxicity within 10 min and after 25 min no recovery of AP was obtained. The results of a 10-min direct exposure to EG at 1 °C showed a moderate decrease in recovery of the AP as the concentration was increased from 10 to 15–20%. Increasing the exposure time to 15 and 30 min at 1 °C also contributed to further reduction in recovery. DMSO, however, in concentrations of 10, 15, and 20% produced only a slight decline of AP after a 5–15 min exposure at 1 °C. Recovery ranged from 96% after 10 min in a 10% solution to 88% after 15 min in a 20% solution. Toxicity became more apparent with DMSO when nerves were exposed to 30% concentrations for 5–10 min; the latter time resulted in a 49% recovery of the AP. Exposure of nerves to a CPA solution containing isotonic concentrations of electrolytes resulted in a 10–30% improvement in recovery when compared with specimens treated with lower levels of salt. The effect of raising the temperature of the rinse to 38 °C and increasing the wash time to 20 min was studied in a few selected experiments. After a direct 15-min exposure to a 15% solution of a CPA at 1 °C the recovery in the case of glycerol was significantly increased with such treatment whereas with EG and DMSO it remained unchanged. There was no evidence of thermal or cold shock in this work.     

Effect of electrical stimulation of the vagus nerves on bile secretion in Anaesthetized sheep.

Bile was collected before and during electrical stimulation of the vagus nerves in acute experiments on sheep with ligated cystic ducts. Most stimuli caused no change in bile formation, but a 10-V, 10-Hz stimulus caused a slight increase in bicarbonate output. Neither the response to infused secretin nor the maximum rate of bile salt transport by liver cells changed during vagal stimulation. It was concluded that the vagal innervation of the liver is not likely to play a major role in the regulation of bile formation in sheep.     

Effect of neuropeptides released from sensory nerves on blood flow in the rat airway microcirculation.

Stimulation of sensory nerves in the airway mucosa causes local release of the neuropeptides substance P and calcitonin gene-related peptide (CGRP). In this study we used a modification of the reference-sample microsphere technique to measure changes in regional blood flow and cardiac output distribution produced in the rat by substance P, CGRP, and capsaicin (a drug that releases endogenous neuropeptides from sensory nerves). Three sets of microspheres labeled with different radionuclides were injected into the left ventricle of anesthetized F344 rats before, immediately after, and 5 min after left ventricular injections of capsaicin, substance P, or CGRP. The reference blood sample was withdrawn from the abdominal aorta and was simultaneously replaced with 0.9% NaCl at 37 degrees C. We found that stimulation of sensory nerves with a low dose of capsaicin causes a large and selective increase in microvascular blood flow in the extrapulmonary airways. The effect of capsaicin is mimicked by systemic injection of substance P but not by CGRP, suggesting that substance P is the main agent of neurogenic vasodilation in rat airways.     

Effect on the heart muscle of experimental carbon monoxide poisoning.

The electron microscopic technique failed to reveal ultrastructural alterations specific for carbon monoxide poisoning. In this contract, the specificity of the lead salt detection method of calcium determination is discussed.     

Partial degeneration of autonomic nerves of the heart of methotrexate-treated guinea pigs

In the present investigation partial degeneration of adrenergic and cholinergic nerves of the heart of guinea pigs following methotrexate treatment has been reported. No appreciable change was observed in the autonomic nerve fibres after 3 days of treatment. However, after prolonged treatment some nerve fibres showed signs of degeneration and a few adrenergic and cholinergic nerve fibres had disappeared.