THE PRODUCTION OF CARBON DIOXIDE BY NERVE

1. A modified Osterhout respiratory apparatus for the detection of CO₂ from nerve is described. 2. The lateral-line nerve from the dogfish discharges CO₂ at first with a gush for half an hour or so and then steadily at a lower rate for several hours. 3. Simple handling of the nerve does not increase the output of CO₂; cutting it revives gush. 4. The CO₂ produced by nerve is not escaping simply from a reservoir but is a true nervous metabolite. 5. The rate of discharge of CO₂ from a quiescent nerve varied from 0.0071 to 0.0128 mg. per gram of nerve per minute and averaged 0.0095 mg. 6. Stimulated nerve showed an increased rate of CO₂ production of 15.8 percent over that of quiescent nerve. 7. The results of these studies indicate that chemical change is a factor in nerve transmission.     

THE EXCRETION OF CARBON DIOXIDE BY RELAXED AND CONTRACTED SEA ANEMONES

1. The metabolism of the sea anemone Metridium marginatum Edw. was measured in four states, relaxed, relaxing, contracted, and contracting, by means of an Osterhout respiratory apparatus. The basis of measurement was the number of hundred-thousandths of a milligram of carbon dioxide excreted per second by a gram of living sea anemone. 2. In the relaxed state this varied from 6.1 to 4.4+ and averaged 5.43–. 3. In a comparison of the relaxed and contracted states the amount of carbon dioxide excreted was found to beabout the same; in one instance in relaxation 4.2 and in contraction 4.1+; in another in relaxation 7.8+ and 7.9– and in contraction 8.1–. 4. In a comparison of the three states relaxed, relaxing, and contracting, the first two were found to average about the same, 4.8+ and 4.6– respectively and the last proved to be appreciably higher 7.1–. 5. It is, therefore, concluded that the process of relaxing and the states of relaxation and of contraction are accompanied by no unusual metabolism, but that in the operation of contracting the metabolism becomes about half again as intense as that characteristic of the other states. 6. The maintenance of the contracted state in Metridium for days at a time without an increase of metabolism indicates that its musculature is of the type known as tonus muscle. 7. In tonus muscle, contraction is accomplished by an active shortening of the myofibrils, extension by a passive drawing out of these fibrils through the distension of the adjacent cavities, etc., and the continued maintenance of any particular state of shortening by some form of catch mechanism in the muscle, such, possibly, as the gelation of its sarcoplasm.     

CARBON DIOXIDE FROM THE NERVE CORD OF THE LOBSTER

1. The nerve cord of the lobster (Homarus americanus Milne-Edwards) is very delicate and can be used as a living preparation for only a few hours after its removal from the animal. 2. During the first hour or so after removal it discharges CO₂ at a steadily decreasing rate beginning at about 0.20 mg. CO₂ per gram of cord per minute and ending at about 0.07 mg. 3. This discharge exhibits a steady decrease in rate and is not divisible into a period of gush and a period of uniform outflow as with the lateral-line nerve of the dogfish. It terminates in a very few hours with the complete death of the cord. 4. Both handling and cutting the cord temporarily increase the rate of CO₂ output. 5. The stimulated cord discharges CO₂ at a rate about 26 per cent higher than that of the quiescent cord, an increase of about 1.6 times that of the increase observed in the lateral-line nerve of the dogfish under similar circumstances.     

CARBON DIOXIDE FROM THE UNSEVERED VAGUS NERVE OF THE SNAKE

1. The vagus nerve of the gopher-snake, Drymarchon corais couperi (Holbrook), discharges carbon dioxide at an average rate of 0.00234 mgm. of gas per gram of nerve per minute. The extremes were 0.0032 mgm. and 0.0017 mgm. 2. These rates were maintained as well when the nerve was separated from its central and its peripheral connections as when these connections were intact showing that the resting metabolism of nerve is a local operation and is not immediately dependent upon distant connections. 3. These observations also point to the conclusion that the passage of normal impulses over a nerve call for an increase of activity that is unobservable by the method employed and that must be small in amount compared with that produced by artificial stimulation.     

DYNAMICS OF NERVE CELLS : II. THE TEMPERATURE COEFFICIENTS OF CARBON DIOXIDE PRODUCTION BY THE HEART GANGLION OF LIMULUS POLYPHEMUS.

1. It is possible to determine by the colorimetric method the rate of production of carbon dioxide by the cardiac ganglion of Limulus. 2. Carbon dioxide formation in the cardiac ganglion was found to run parallel to the rate of heart beat for different temperatures. 3. The conclusion seems justified that the rate of cardiac rhythm of Limulus depends upon a chemical reaction in the nerve cells of the cardiac ganglion and that this reaction is associated with the production of carbon dioxide since the rate of beat and the rate of CO₂ production are similarly affected by changes in temperature.     

THE RESPIRATORY QUOTIENT OF FROG NERVE DURING STIMULATION

1. By means of a differential volumeter the increased oxygen consumption and the increased carbon dioxide output of frog nerve during and after stimulation have been observed. 2. Measurements of the R.Q. of nerve by this method are complicated by the retention of carbon dioxide. Attempts were made to avoid this (a) by studying the nerves at high CO₂ tensions to make the retention small and (b) by calculating the amount of CO₂ retained from the carbon dioxide dissociation curve of nerve and applying this value as a correction. 3. The results of both those methods when averaged together give an R.Q. of the excess metabolism of 1.19 and an R.Q. of the resting nerve of 0.97. 4. Observations on the time course of the gas exchange during stimulation indicate a delay in the appearance of the extra carbon dioxide output relative to the oxygen intake. 5. Very similar time curves can be calculated from the diffusion coefficients and the solubilities of the oxygen and the carbon dioxide.     

THE OXYGEN CONSUMPTION OF FROG NERVE DURING STIMULATION

1. The resting rate of oxygen consumption of the excised sciatic nerve of the frog is 1.23 c.mm. of oxygen per gm. of nerve per minute. 2. During stimulation with an induction coil with 100 make and 100 break shocks per second there is an excess oxygen consumption amounting on the average to 0.32 c.mm. of oxygen per gm. of nerve per minute of stimulation, or a 26 per cent increase over the resting rate. 3. The magnitude of the excess oxygen consumption in stimulation, in agreement with the all-or-none law, is not markedly influenced by considerable variations in the intensity of stimulation. 4. Increasing the frequency of stimulation from 100 to 200 shocks per second increases the extra oxygen used only 1.12–1.18 times. The same change in frequency of stimulation increases the negative variation 1.15 times and the heat production about 1.25 times (Hill). 5. This parallelism between the excess oxygen and the negative variation argues definitely for some causal connection between the excess oxygen and the nerve impulse itself. 6. Calculation shows that the oxygen tension inside these nerves was not zero.     

ON THE EFFECT OF COCAINE UPON SODIUM-DEFICIENT FROG NERVE

Cocaine diffuses through the epineurium with remarkable rapidity. The coefficient of diffusion of cocaine in the epineurium cannot be less than 0.44 x 10^–4 cm.²/min.; it probably is not less than 1.22 x 10^–4 cm.²/min. Lack of sodium markedly sensitizes the nerve fibers to the anesthetic action of cocaine. With sodium-deficient A fibers the action of cocaine develops in two phases. During the first phase cocaine substitutes for sodium and restores to A fibers the ability to conduct impulses; during the second phase cocaine produces anesthesia. It is suggested that cocaine anesthetizes the nerve fibers through the sodium mechanism; i.e., by interfering with some of those chemical reactions in which, directly or indirectly, the internal sodium takes part.     

PYRUVATE METABOLISM IN THE LOBSTER NERVE AS AFFECTED BY THE PARTIAL PRESSURE OF CARBON DIOXIDE: OBSERVATIONS ON THE SYNTHESIS OF ACETYLCHOLINE AND ON METABOLIC COMPARTMENTATION

Abstract— In the lobster nerve the fixation of CO, at various levels of _pCO2 was studied by the incorporation of [l-¹⁴C]pyruvate. Incorporation of ¹⁴C was solely dependent on CO₂ fixation since the C-1 was decarboxylated in the formation of acetyl-CoA. Paired-nerve studies with [2-¹⁴C]pyruvate afforded a study of pyruvate metabolism in the lobster nerve. [I¹⁴C]Pyruvate was incorporated to nearly the same extent at all levels of pCO₂ including zero pCO₂, a finding that suggested metabolic recycling of CO₂. The magnitude of the metabolic recycling of C-1 of pyruvate or pyruvate dismutation was estimated to be nearly 20 per cent of total CO₂ fixation. Re-evaluation of the relative contributions of the CO₂ fixation. and acetyl-CoA pathways on the basis of more extensive data gave a ratio of 2:3.
The pCO₂ affected synthesis of ACh and the level of citrate. With increasing pCO₂, the specific radioactivity of ACh decreased much more than the content of ACh. The decrease in the specific radioactivity of ACh but not that of citrate further suggested metabolic compartmentation. The implication of these findings is discussed.
Alanine functioned as a metabolic sink for the incorporated pyruvate. Pyruvate levels were estimated to be approximately 0.1 nmol/mg of protein.     

THE CARBON DIOXIDE EXCRETED IN ONE MINUTE BY ONE CENTIMETER OF NERVE-FIBER

One centimeter of nerve-fiber from the lateral-line nerve of the dogfish is estimated to excrete on the average 4.2 x 10^–8 mg. CO₂ per minute.