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Effects of Anesthesia on Sensory Evoked Potentials in Chicken Brain
EFFECTS OF ANESTHESIA ON SENSORY EVOKED POTENTIALS IN CHICKEN BRAIN R. E. PHILLIPS Department of Animal Science, University of Minnesota, St. Paul, Minnesota 55101 (Received for publication November 6, 1968)
Paper No. 6714 Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul. This work was supported in part by NSF grant GB-2938 and by the Minnesota Agricultural Experiment Station.
tal, 45 to 50 milligrams of alpha chloralose, and approximately 1.5 to 2 grams of urethan. These anesthetics were chosen for the following reasons: pentobarbital sodium is a familiar anesthetic and is readily available, but it has a short period of action so that during long recording experiments repeated injections have to be given and the depth of anesthesia is apt to fluctuate rather markedly; urethan is an excellent anesthetic for holding the bird at a steady level of anesthesia over a very long period, but it is poorly metabolized so usually the birds do not recover from it and it was suspected of depressing responses more than the others might; chloralose has been frequently used because it seems to exaggerate any responsiveness that may exist and so show connections when other anesthetics do not. Chloralose has the drawback that it seems to be a convulsant as well as an anesthetic and some birds are difficult to sedate with it. Also, it is difficult to get into solution and must be combined with borax by heating 4.5 gm. sodium borate and 4.5 gm. chloralose in 100 cc. of distilled water. (Once this is in solution it will remain so, even at room temperature.) For stimulation the birds were immobilized in a towel with the head held in a fixed position with a bar arrangement so that the light of a Grass PS2 photostimulator could be flashed in the eye at a standard direction and distance. Responses were observed on the face of an oscilloscope and photographed with a polaroid camera. The amplitudes and numbers of peaks in responses were compared as measures
338
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 12, 2015
In the course of experiments tracing sensory pathways in the brain of chickens, several anesthetics were used at various times, and it became of interest to determine what effect different anesthetics might be having on the results. This information is also helpful in comparing results of authors using different anesthetics. The anesthetics we used were pentobarbital sodium, urethan, and alpha chloralose. Responses recorded from chronicallyimplanted electrodes to standard flash stimuli were compared in each bird using all three anesthetics and no anesthetic. The birds used for the experiments were a series of chickens with permanently implanted electrodes that were being used for studies of behavior evoked by intracranial electrical stimulation. Each of these birds had fifteen electrodes implanted stereotaxically in various parts of the brain. The electrodes were soldered to the contacts of an Amphenol cable connector cemented to the skull. After behavior testing was completed the birds were tested for evoked responses on each of the fifteen electrodes, first in the waking state and then on different days under different anesthetics so that the bird might recover between times. The anesthetics were given intravenously to effect, that is so that the bird would just respond slightly to pinching the comb. This meant about 45 milligrams per kilogram of sodium pentobarbi-
339
RESEARCH NOTES
were evoked under pentobarbital than in unanesthetized birds (again P<0.01). Differences in the number of peaks per response were less marked and more variable than the differences in maximum amplitude, but they showed the same trend; cholralose tended to give the most complex responses, the awake birds responded the least, and pentobarbital and urethan differed little from one another. We conclude that chloralose is the best anesthetic if the maximum extent of projections is being explored, but that either nembutal or urethan would be satisfactory for most purposes. It should be noted that some reversals of ranks occurred for all combinations, and occasionally chloralose failed to reveal a response that was clear under one of the other two drugs, so the choice is not absolute. ACKNOWLEDGMENT
Thanks are due Orlan Youngren, Alan Davenport, and Mrs. Aileen Nygard for technical assistance.
FUNGAL FLORA OF THE AVIAN RESPIRATORY TRACT D. N. GARG* AND M. S. SETHI Department of Pathology and Hygiene, U.P. Agricultural University, Pant Nagar (Nainital), India (Received for publication November 9, 1968)
The bibliography of Chute et al. (1962) has covered much of the published reports on avian mycosis. The fungal flora of the respiratory tract of fowls has not been fully determined. Jordan (1954) reported the isolation of Penicillium spp., Aspergillus spp., Mucor, Phycomycetes and * Present Address: Ph.D. scholar, Department of Bacteriology and Hygiene, College of Veterinary Medicine, Punjab Agricultural University, Hissar (India).
unidentified yeasts from the lungs of 25 normal fowls while Chute et al. (1956) reported that Aspergillus fumigatus is most often but not always associated with tissue invasion. These authors also found the members of the general Penicillum, Paecilomyces, Cephalosporium, Trichoderma, Scopulariopsis and Mucor in the respiratory tract. The isolation and identification of fungi as has been identified in the present study is expected to unfold
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 12, 2015
of the effect of the anesthetics. In two birds all four, in the other 16 birds only three conditions, including awake, were compared. Comparisons of nembutal- and urethan-anesthetized and the waking state in seven birds (105 electrodes) analyzed by means of sign tests of the amplitudes of the highest peaks, indicated that both pentobarbital sodium and urethan gave reliably larger responses than did recording in the unanesthetized state, but the two drugs did not differ from one another. Comparison of all four conditions in two birds (30 electrodes) showed that chloralose gave much the largest response; as before, pentobarbital and urethan gave similar responses which were, again, larger than the responses recorded in awake birds. All differences are significant at the 1% level. Finally, comparison of chloralose, pentobarbital and the awake state in five more birds (75 electrodes) showed that chloralose gave a greater response than either pentobarbital sodium-anesthetized or waking birds and that larger and more frequent responses
Paper No. 6714 Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul. This work was supported in part by NSF grant GB-2938 and by the Minnesota Agricultural Experiment Station.
tal, 45 to 50 milligrams of alpha chloralose, and approximately 1.5 to 2 grams of urethan. These anesthetics were chosen for the following reasons: pentobarbital sodium is a familiar anesthetic and is readily available, but it has a short period of action so that during long recording experiments repeated injections have to be given and the depth of anesthesia is apt to fluctuate rather markedly; urethan is an excellent anesthetic for holding the bird at a steady level of anesthesia over a very long period, but it is poorly metabolized so usually the birds do not recover from it and it was suspected of depressing responses more than the others might; chloralose has been frequently used because it seems to exaggerate any responsiveness that may exist and so show connections when other anesthetics do not. Chloralose has the drawback that it seems to be a convulsant as well as an anesthetic and some birds are difficult to sedate with it. Also, it is difficult to get into solution and must be combined with borax by heating 4.5 gm. sodium borate and 4.5 gm. chloralose in 100 cc. of distilled water. (Once this is in solution it will remain so, even at room temperature.) For stimulation the birds were immobilized in a towel with the head held in a fixed position with a bar arrangement so that the light of a Grass PS2 photostimulator could be flashed in the eye at a standard direction and distance. Responses were observed on the face of an oscilloscope and photographed with a polaroid camera. The amplitudes and numbers of peaks in responses were compared as measures
338
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 12, 2015
In the course of experiments tracing sensory pathways in the brain of chickens, several anesthetics were used at various times, and it became of interest to determine what effect different anesthetics might be having on the results. This information is also helpful in comparing results of authors using different anesthetics. The anesthetics we used were pentobarbital sodium, urethan, and alpha chloralose. Responses recorded from chronicallyimplanted electrodes to standard flash stimuli were compared in each bird using all three anesthetics and no anesthetic. The birds used for the experiments were a series of chickens with permanently implanted electrodes that were being used for studies of behavior evoked by intracranial electrical stimulation. Each of these birds had fifteen electrodes implanted stereotaxically in various parts of the brain. The electrodes were soldered to the contacts of an Amphenol cable connector cemented to the skull. After behavior testing was completed the birds were tested for evoked responses on each of the fifteen electrodes, first in the waking state and then on different days under different anesthetics so that the bird might recover between times. The anesthetics were given intravenously to effect, that is so that the bird would just respond slightly to pinching the comb. This meant about 45 milligrams per kilogram of sodium pentobarbi-
339
RESEARCH NOTES
were evoked under pentobarbital than in unanesthetized birds (again P<0.01). Differences in the number of peaks per response were less marked and more variable than the differences in maximum amplitude, but they showed the same trend; cholralose tended to give the most complex responses, the awake birds responded the least, and pentobarbital and urethan differed little from one another. We conclude that chloralose is the best anesthetic if the maximum extent of projections is being explored, but that either nembutal or urethan would be satisfactory for most purposes. It should be noted that some reversals of ranks occurred for all combinations, and occasionally chloralose failed to reveal a response that was clear under one of the other two drugs, so the choice is not absolute. ACKNOWLEDGMENT
Thanks are due Orlan Youngren, Alan Davenport, and Mrs. Aileen Nygard for technical assistance.
FUNGAL FLORA OF THE AVIAN RESPIRATORY TRACT D. N. GARG* AND M. S. SETHI Department of Pathology and Hygiene, U.P. Agricultural University, Pant Nagar (Nainital), India (Received for publication November 9, 1968)
The bibliography of Chute et al. (1962) has covered much of the published reports on avian mycosis. The fungal flora of the respiratory tract of fowls has not been fully determined. Jordan (1954) reported the isolation of Penicillium spp., Aspergillus spp., Mucor, Phycomycetes and * Present Address: Ph.D. scholar, Department of Bacteriology and Hygiene, College of Veterinary Medicine, Punjab Agricultural University, Hissar (India).
unidentified yeasts from the lungs of 25 normal fowls while Chute et al. (1956) reported that Aspergillus fumigatus is most often but not always associated with tissue invasion. These authors also found the members of the general Penicillum, Paecilomyces, Cephalosporium, Trichoderma, Scopulariopsis and Mucor in the respiratory tract. The isolation and identification of fungi as has been identified in the present study is expected to unfold
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 12, 2015
of the effect of the anesthetics. In two birds all four, in the other 16 birds only three conditions, including awake, were compared. Comparisons of nembutal- and urethan-anesthetized and the waking state in seven birds (105 electrodes) analyzed by means of sign tests of the amplitudes of the highest peaks, indicated that both pentobarbital sodium and urethan gave reliably larger responses than did recording in the unanesthetized state, but the two drugs did not differ from one another. Comparison of all four conditions in two birds (30 electrodes) showed that chloralose gave much the largest response; as before, pentobarbital and urethan gave similar responses which were, again, larger than the responses recorded in awake birds. All differences are significant at the 1% level. Finally, comparison of chloralose, pentobarbital and the awake state in five more birds (75 electrodes) showed that chloralose gave a greater response than either pentobarbital sodium-anesthetized or waking birds and that larger and more frequent responses