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Recording the electrocardiogram from the squirrel monkey, Saimira sciureus
Physiology and Behavior. Vol. 5. pp. 819-821. Pergamon Press, 1970. Printed in Great Britain
BRIEF COMMUNICATION Recording the Electrocardiogram from the Squirrel Monkey, Saimira sciureus I WILLIAM
P. PARI~, K I L E E. I S O M A N D J A M E S F. R E U S
Veterans Administration Hospital, Perry Point, Maryland 21902, U.S.A. (Received 11 F e b r u a r y 1970) P.~t~, W. P., K. E. ISOMAND J. F. REUS. Recording the electrocardiogramfrom the squirrel monkey, Saimiri sciureus. PHYSIOL. BEHAV. 5 (7) 819-821, 1970.---A technique is described for recording the EKG from the squirrel monkey by utilizing surface electrodes placed on the animal's chest. The design of a commercially available restraining chair was modified to allow the monkey to operate a manipulandum and prevent the animal from disturbing the recording electrodes. Electrocardiogram
Heart rate
Squirrel monkey
Restraining chair
INVESTIGATORSinterested in studying autonomic processes in experimental animals have frequently elected to record the electrocardiogram (EKG) and measurements of heart rate (time between systoles). Interest in the E K G springs primarily from the practical reason that the E K G is easily obtained by the application of surface electrodes and does not necessitate complicated transducers and/or surgical procedures to prepare the experimental animal. This is especially true if the dog is the experimental animal. Not surprisingly, the majority of the early behavioral work concerned with heart rate conditioning was performed with the dog [7, 8]. However, it was not long before the pervasive laboratory rat was used in heart rate conditioning studies [2, 3, 12] and numerous reports appeared illustrating techniques for recording the E K G in the rat [4-6, 10, 11]. A need quickly developed for a more sophisticated animal model for behavioral heart rate investigations. The squirrel monkey (Saimiri sciureus) represented a good candidate since it possesses an advanced central nervous system with a large brain, and its small body size makes it accessible to small and large laboratories alike. In addition the squirrel monkey is readily available and inexpensive. This report deals with a technique developed for recording E K G in the squirrel monkey. Extensive clinical E K G records have already been reported by Wolf, Lehner, Miller and Clarkson [14], but their records were from anesthetized, supine animals. We were concerned with obtaining records from a conscious animal while the animal was performing in an operant testing situation.
The method selected utilized two surface electrodes and was a modification of the technique reported by Ramsay, Pomerleau and Snapper [13]. This consisted of an electrode belt with two floating-type electrodes. The belt and electrodes are illustrated in Fig. 1. The electrodes were small pure silver disks. These were sewed to round soft plastic wafers (i.d. = 5 ram; o.d. = 17 ram). The lead wire was soldered to the back of the silver disk and the electrode units were then sewed to a 120 m m long, 1-in. elastic strap. The latter is obtainable at any department store notions counter. The electrode units illustrated in Fig. 1 were sewed to the strap with black silk. The black stitches are obvious in the photograph. The electrode belt was wrapped around the monkey's chest and was secured by two pieces of Velcro fasteners, one at each end of the elastic strap. Electrode paste was placed in the center of the plastic wafers before applying the belt to the animal. The electrodes and skin contact areas were cleaned with alcohol before applying the electrodes. The soft plastic wafer moulded itself to the animal's chest contour and the elastic belt possessed sufficient flexibility to minimize movement-induced noise in the E K G record. The belt was placed on the monkey after it had been placed in its restraining chair. The chair used in our laboratory was described by Carmichael and MacLean [1] and obtained from Foringer and Co. (Model 110IS). The monkeys in our studies were to sit in this chair and operate a lever extending from a response panel which abutted the front of the chair. However, the design of the chair placed the monkey at the rear of the chair and the
x The authors wish to thank Luther R. Gilliam of the Medical Illustration Service, VA Hospital, Perry Point, for his photographic work. 819
820
PARE ISOM AND REUS
animal was unable to reach the lever. This was solved by making the animal sit facing the back of the chair and placing the rear of the chair up against the response panel. In this fashion the animal could easily reach the response lever. New holes were required on the side of the chair for the seat bars to accommodate the new seating orientation. The screw stops for the waist and neck yokes were also adjusted to allow an upright comfortable posture for the monkey. Seat restraints were also added to prevent the animal from turning around in the chair. These consisted simply of two plastic rectangular (132 mm × 76 ram) seat sides held in place by the seat bars. With the two pieces on the outside of the monkey's legs, the animal was not able to swivel within the yokes. The electrode belt was wrapped around the monkey's chest. The belt, however, could not be left in this exposed condition during test sessions because the animal would invariably move the belt with its hands. This was solved by fabricating a cylindrical electrode shield which was placed around the monkey's chest. The electrode shield is shown in Fig. 2. The shield extended from the waist.yoke to the monkey's shoulders. This upright cylinder was horizontally cut into two pieces. The chest half was bolted to the front section of the waist yoke; the back half was bolted to the rear section of the waist yoke. The bolt holes in the waist plates were slotted, thereby allowing for A-P adjustments of the electrode shield.
The electrode shield did not produce discomfort to the animal and completely prevented the animal from manipulating the electrode belt. Another technique which would have prevented the animal from handling the electrodes would have been the use of a chest yoke. This yoke would separate the animal's arms from the electrodes. Lilly [9] reported that this technique was first used by Dr. M. Hines with the Macaca mulatta. Using a chest yoke with our monkeys would have placed the animal's arms in a horizontal position thereby making it extremely difficult and awkward for the animal to reach the response lever and food trough. F o r this reason the chest yoke was abandoned in favor of the electrode shield described in this report. The monkey was first held in the chair and the neck yoke installed. The prepared electrode belt was then attached and the waist yoke, with the affixed shield, was put into place. The monkey and chair were subsequently placed into the operant chamber and the electrode leads connected to the oscillograph. Figure 3 is a sample of an oscillographic record of a squirrel monkey after two hours in'the operant chamber. This technique has proven very successful in our laboratory. The animal need not be surgically prepared and can be introduced to the experimental routine within a very short period of time. This technique has been used for over 18 months free of major recording problems.
4sol HEART
4ZO~-
B.otl/MIn. ~[00 240
EKG L
60 $e¢.
J
t
2 Sac.
J
FIG. 3. Oscillographic record of squirrel monkey EKG obtained with electrode belt and recorded via a Beckman Type RS Dynograph. Experimental interest was not in a clinical EKG but in heart rate. Therefore the form of the EKG was manipulated to emphasize the r-wave which served as the input to the cardiotechometer.
REFERENCES 1. Carmichael, J. and P. D. MacLean. Use of squirrel monkey for brain research, with description of restraining chair. Electroenceph, clin. Neurophysiol. 13: 128--129, 1961. 2. Caul, W. F. and R. E. Miller. Effects of shock probability on heart rate of rats during classical conditioning. Physiol. Behav. 3: 865--869, 1968. 3. deToledo, L. and A. H. Black. Heart rate: Changes during conditioned suppression in rats. Science 152: 14(H-1406, 1966. 4. Doerr, H. O. A method to ~tablish electrically good contacts with unrestrained rats. Psychophysiolagy 3: 3t6-317, 1967.
5. Eisman, E, Technique for monitoring cardiac function without haa_~_'ms or restraining the animal. Percept, Mot. Skills 20: I093==I09~) 1965. 6, Ferraro, D. P,, M, F, Silver and A. G. Snapper. A method for cardiac recording from surface electrodes in the rat during free-operant procedures. J. exp. Analysis Behav. 8: 17-18, 1965. 7. Figar, S. Conditional circulatory responses in men and animals. In: Handbook o f Physiology. Section 2: Circulation, Vot. 3, edited by W. F. Hamilton. Washington, D.C.: American Physiological Society, 1965, pp. 1191-2035.
FlG.
I. Photograph
of electrode
belt. The silver electrodes are sewed under the plastic wafers. These are stitched to the white elastic strap.
.
FIG. 2. Photograph of restraining chair for squirrel monkey. The chair has been modified and the monke) 15 facing what was originally the rear section of the chair. The cylindrical electrode shield is bolted to the waist yoke. The position of the electrode belt, on the animal’s chest, is indicated by the broken arrow. It is situated behind the electrode shield.
SQUIRREL MONKEY EKG 8. Gantt, W. H. Cardiovascular component of the conditional reflex to pain, food and other stimuli. Physiol. Rev. 40: 266291, 1960. 9. Lilly, J. C. Development of a double-table-chair method of restraining monkeys for physiological and psychological research. J. appl. Physiol. 12: 134-136, 1958. 10. Longo, N. and J. W. P¢llegrino. A simple telemetric method for monitoring cardiac function in small animals. Percept. Mot. Skills 24: 512-514, 1967. 11. Malcuit, G., J. A-Malouin and D. Belanger. A technique for monitoring cardiac activity in the rat. Psychophysiology 4: 493--495, 1968.
821 12. McDonald, G., J. A. Stem and W. W. Hahn. Classical heart rate conditioningin the rat. J. psychosom. Res. 7: 97-106, 1963. 13. Ramsay, D. A., O. F. Pomerleau and A. G. Snapper. Two methods for obtaining electrocardiograms of chair-restrained monkeys. Cond. Reflex. 3: 200-204, 1968. 14. Wolf, R. H., N. D. M. I.¢hner, E. C. Miller and T. B. Clarkson. Electrocardiogram of the squirrel monkey, Saimiri sciureus. J. appl. Physiol. 26: 346--351, 1969.
BRIEF COMMUNICATION Recording the Electrocardiogram from the Squirrel Monkey, Saimira sciureus I WILLIAM
P. PARI~, K I L E E. I S O M A N D J A M E S F. R E U S
Veterans Administration Hospital, Perry Point, Maryland 21902, U.S.A. (Received 11 F e b r u a r y 1970) P.~t~, W. P., K. E. ISOMAND J. F. REUS. Recording the electrocardiogramfrom the squirrel monkey, Saimiri sciureus. PHYSIOL. BEHAV. 5 (7) 819-821, 1970.---A technique is described for recording the EKG from the squirrel monkey by utilizing surface electrodes placed on the animal's chest. The design of a commercially available restraining chair was modified to allow the monkey to operate a manipulandum and prevent the animal from disturbing the recording electrodes. Electrocardiogram
Heart rate
Squirrel monkey
Restraining chair
INVESTIGATORSinterested in studying autonomic processes in experimental animals have frequently elected to record the electrocardiogram (EKG) and measurements of heart rate (time between systoles). Interest in the E K G springs primarily from the practical reason that the E K G is easily obtained by the application of surface electrodes and does not necessitate complicated transducers and/or surgical procedures to prepare the experimental animal. This is especially true if the dog is the experimental animal. Not surprisingly, the majority of the early behavioral work concerned with heart rate conditioning was performed with the dog [7, 8]. However, it was not long before the pervasive laboratory rat was used in heart rate conditioning studies [2, 3, 12] and numerous reports appeared illustrating techniques for recording the E K G in the rat [4-6, 10, 11]. A need quickly developed for a more sophisticated animal model for behavioral heart rate investigations. The squirrel monkey (Saimiri sciureus) represented a good candidate since it possesses an advanced central nervous system with a large brain, and its small body size makes it accessible to small and large laboratories alike. In addition the squirrel monkey is readily available and inexpensive. This report deals with a technique developed for recording E K G in the squirrel monkey. Extensive clinical E K G records have already been reported by Wolf, Lehner, Miller and Clarkson [14], but their records were from anesthetized, supine animals. We were concerned with obtaining records from a conscious animal while the animal was performing in an operant testing situation.
The method selected utilized two surface electrodes and was a modification of the technique reported by Ramsay, Pomerleau and Snapper [13]. This consisted of an electrode belt with two floating-type electrodes. The belt and electrodes are illustrated in Fig. 1. The electrodes were small pure silver disks. These were sewed to round soft plastic wafers (i.d. = 5 ram; o.d. = 17 ram). The lead wire was soldered to the back of the silver disk and the electrode units were then sewed to a 120 m m long, 1-in. elastic strap. The latter is obtainable at any department store notions counter. The electrode units illustrated in Fig. 1 were sewed to the strap with black silk. The black stitches are obvious in the photograph. The electrode belt was wrapped around the monkey's chest and was secured by two pieces of Velcro fasteners, one at each end of the elastic strap. Electrode paste was placed in the center of the plastic wafers before applying the belt to the animal. The electrodes and skin contact areas were cleaned with alcohol before applying the electrodes. The soft plastic wafer moulded itself to the animal's chest contour and the elastic belt possessed sufficient flexibility to minimize movement-induced noise in the E K G record. The belt was placed on the monkey after it had been placed in its restraining chair. The chair used in our laboratory was described by Carmichael and MacLean [1] and obtained from Foringer and Co. (Model 110IS). The monkeys in our studies were to sit in this chair and operate a lever extending from a response panel which abutted the front of the chair. However, the design of the chair placed the monkey at the rear of the chair and the
x The authors wish to thank Luther R. Gilliam of the Medical Illustration Service, VA Hospital, Perry Point, for his photographic work. 819
820
PARE ISOM AND REUS
animal was unable to reach the lever. This was solved by making the animal sit facing the back of the chair and placing the rear of the chair up against the response panel. In this fashion the animal could easily reach the response lever. New holes were required on the side of the chair for the seat bars to accommodate the new seating orientation. The screw stops for the waist and neck yokes were also adjusted to allow an upright comfortable posture for the monkey. Seat restraints were also added to prevent the animal from turning around in the chair. These consisted simply of two plastic rectangular (132 mm × 76 ram) seat sides held in place by the seat bars. With the two pieces on the outside of the monkey's legs, the animal was not able to swivel within the yokes. The electrode belt was wrapped around the monkey's chest. The belt, however, could not be left in this exposed condition during test sessions because the animal would invariably move the belt with its hands. This was solved by fabricating a cylindrical electrode shield which was placed around the monkey's chest. The electrode shield is shown in Fig. 2. The shield extended from the waist.yoke to the monkey's shoulders. This upright cylinder was horizontally cut into two pieces. The chest half was bolted to the front section of the waist yoke; the back half was bolted to the rear section of the waist yoke. The bolt holes in the waist plates were slotted, thereby allowing for A-P adjustments of the electrode shield.
The electrode shield did not produce discomfort to the animal and completely prevented the animal from manipulating the electrode belt. Another technique which would have prevented the animal from handling the electrodes would have been the use of a chest yoke. This yoke would separate the animal's arms from the electrodes. Lilly [9] reported that this technique was first used by Dr. M. Hines with the Macaca mulatta. Using a chest yoke with our monkeys would have placed the animal's arms in a horizontal position thereby making it extremely difficult and awkward for the animal to reach the response lever and food trough. F o r this reason the chest yoke was abandoned in favor of the electrode shield described in this report. The monkey was first held in the chair and the neck yoke installed. The prepared electrode belt was then attached and the waist yoke, with the affixed shield, was put into place. The monkey and chair were subsequently placed into the operant chamber and the electrode leads connected to the oscillograph. Figure 3 is a sample of an oscillographic record of a squirrel monkey after two hours in'the operant chamber. This technique has proven very successful in our laboratory. The animal need not be surgically prepared and can be introduced to the experimental routine within a very short period of time. This technique has been used for over 18 months free of major recording problems.
4sol HEART
4ZO~-
B.otl/MIn. ~[00 240
EKG L
60 $e¢.
J
t
2 Sac.
J
FIG. 3. Oscillographic record of squirrel monkey EKG obtained with electrode belt and recorded via a Beckman Type RS Dynograph. Experimental interest was not in a clinical EKG but in heart rate. Therefore the form of the EKG was manipulated to emphasize the r-wave which served as the input to the cardiotechometer.
REFERENCES 1. Carmichael, J. and P. D. MacLean. Use of squirrel monkey for brain research, with description of restraining chair. Electroenceph, clin. Neurophysiol. 13: 128--129, 1961. 2. Caul, W. F. and R. E. Miller. Effects of shock probability on heart rate of rats during classical conditioning. Physiol. Behav. 3: 865--869, 1968. 3. deToledo, L. and A. H. Black. Heart rate: Changes during conditioned suppression in rats. Science 152: 14(H-1406, 1966. 4. Doerr, H. O. A method to ~tablish electrically good contacts with unrestrained rats. Psychophysiolagy 3: 3t6-317, 1967.
5. Eisman, E, Technique for monitoring cardiac function without haa_~_'ms or restraining the animal. Percept, Mot. Skills 20: I093==I09~) 1965. 6, Ferraro, D. P,, M, F, Silver and A. G. Snapper. A method for cardiac recording from surface electrodes in the rat during free-operant procedures. J. exp. Analysis Behav. 8: 17-18, 1965. 7. Figar, S. Conditional circulatory responses in men and animals. In: Handbook o f Physiology. Section 2: Circulation, Vot. 3, edited by W. F. Hamilton. Washington, D.C.: American Physiological Society, 1965, pp. 1191-2035.
FlG.
I. Photograph
of electrode
belt. The silver electrodes are sewed under the plastic wafers. These are stitched to the white elastic strap.
.
FIG. 2. Photograph of restraining chair for squirrel monkey. The chair has been modified and the monke) 15 facing what was originally the rear section of the chair. The cylindrical electrode shield is bolted to the waist yoke. The position of the electrode belt, on the animal’s chest, is indicated by the broken arrow. It is situated behind the electrode shield.
SQUIRREL MONKEY EKG 8. Gantt, W. H. Cardiovascular component of the conditional reflex to pain, food and other stimuli. Physiol. Rev. 40: 266291, 1960. 9. Lilly, J. C. Development of a double-table-chair method of restraining monkeys for physiological and psychological research. J. appl. Physiol. 12: 134-136, 1958. 10. Longo, N. and J. W. P¢llegrino. A simple telemetric method for monitoring cardiac function in small animals. Percept. Mot. Skills 24: 512-514, 1967. 11. Malcuit, G., J. A-Malouin and D. Belanger. A technique for monitoring cardiac activity in the rat. Psychophysiology 4: 493--495, 1968.
821 12. McDonald, G., J. A. Stem and W. W. Hahn. Classical heart rate conditioningin the rat. J. psychosom. Res. 7: 97-106, 1963. 13. Ramsay, D. A., O. F. Pomerleau and A. G. Snapper. Two methods for obtaining electrocardiograms of chair-restrained monkeys. Cond. Reflex. 3: 200-204, 1968. 14. Wolf, R. H., N. D. M. I.¢hner, E. C. Miller and T. B. Clarkson. Electrocardiogram of the squirrel monkey, Saimiri sciureus. J. appl. Physiol. 26: 346--351, 1969.