Diurnal Heart R a t e and Body Temperature in Marmosets JOHN K. HAMPTON, JR. T h e University of T e x a s Dental Science Institute at Houston a n d T h e University of T e x a s Graduate School of Biomedical Sciences at Houston, T e x a s 77004 ABSTRACT Marmosets, Saguinus oedipus oedipus and S . fuscicollis, have been shown to have a diurnal heart rate pattern that has a marked difference between high and low values (about 5 5 beats/minute) and shows a low point during daylight hours around 1300-1400 hours. A similar pattern for body temperature was seen. A species difference existed; the larger S. 0. oedipus has a higher heart rate during both light and dark periods. All measurements were made on undisturbed animals at hourly intervals using radiotelemetry. They were kept in a controlled environment with a light cycle of 12L: 12D and a tem1°C. perature of 27 * Basic metabolic criteria, such as body temperature and heart rate, are badly needed if meaningful studies on marmosets are to be done. Diurnal variations, responses to ambient conditions, and species differences may be critical to experimental observations. Morrison and Sim6es ('63) have studied the diurnal body temperature of Callithrix jacchus and its metabolic responses to variations in ambient temperature and activity. The pigmy marmoset, Cebuella pygmea, was more recently studied by Morrison and Middleton ('67). Similarly, Scholander et al. ('50) examined the metabolic heat regulation of Leontocebus geoffroyi ( = Saguinus oedipus geoffroyi). A limited zone of thermoneutrality and marked diurnal variations were revealed for these species. Not only does its metabolic heat production change considerably as ambient temperature vanes, the marmoset has also been shown to be unable to maintain body temperature very well whenever its environmental temperature varies relatively little beyond or below its zone of thermoneutrality. New World primates such as Saimiri sciurea, as well as the larger Lagothrix lagotricha, seem to share with marmosets this thermal lability when compared with Old World primates such as Macaca mulatta and M . speciosa (Chaffee et al., AM. J. PHYS.ANTHROP.,38: 339-342. '69). Chaffee et al. ('66) have made it clear that S. sciurea can undergo adaptation to hot or cold environments. However, they showed that changes in some tissue enzymes do not occur as would have been expected by extrapolation of data from studies on rodents. Thus, the studies reported here extend some of these data to two additional marmoset species. By the use of radiotelemetry it has been possible to obtain body temperature and heart rate around the clock in animals undisturbed by capture or restraint and maintained in a rigidly controlled environment. METHODS The marmosets used in this study were adults; two males of S. fuscicollis and a male and a female of Saguinus oedipus oedipus. They were kept in a n isolation chamber 4' x 4' x 4' made of three-quarter in. plywood lined with acoustical tile. Its door was fitted with a small one-way glass port, and the animal was restricted by a cage placed inside this unit. Good ventilation was provided by forced, tempered air maintained at a temperature of 27" 2 1"C. Food and water was ad libitum. A timed light cycle of 12L: 12D was used. Telemetry units for heart rate were manufactured by the E&M Instrument Co., Inc., Houston, Texas. The transmitters were FM units, model 1100-E2 (18 gm) or 339 340 JOHN K. HAMPTON, JR. 1100-El ( 8 gm). They were carried on the dorsum of the animals supported by a harness made of insulated copper hook-up wire. The transmitters were wrapped in plastic for moisture protection and taped to the harness. Batteries were changed once each week. Silver ring electrodes were implanted subcutaneously on the dorsum of the animal in a straight line lateral to the vertebral column and four to five centimeters apart. Teflon insulated leads emerged from the skin in the neck region and were undisturbed by the subjects. The biotelemetry receiver (E&M Instrument Co., Inc., Model FM-1100-7) was connected to a physiograph (E&M Instrument Co., Inc., Model PMP-4A). This unit was modified so that a timer activated a switch to the paper-drive motor and to a solenoid, which threw levers on the amplifiers from the “idle” position to the “record” position. The timer was set to provide a record for three minutes at each hour. Heart rate was measured by counting two apparently typical 30 second intervals from each three minute record. We constructed our temperature transmitters after modification of the design reported by Stong (’68). The modification reduced the number of turns in each portion of the coil by one-half. The thermistor used was a 1 Megohm YSI 44015 (Yellow Springs Instrument Co.) powered by a 1.4 volt mercury battery (Mallory 675), and the transister used was an RCA SK3020. This unit functions as a so-called “blocking” oscillator and transmits pulses with a frequency that is varied by the effect of temperature on the thermistor. The receiver was an ordinary, portable AM radio. The pulsed out-put at the earphone jack was carried to the signal input of a n ACDC preamplifier of the physiograph recorder and filtered there through a 0.2 microfarad capacitor. The thermistor of the modified transmitter was placed at the tympanic membrane, and the transmitter encased in a head bandage encircling the head. An impression of the auditory canals was made with rubber-base dental impression material. A working cast was then prepared and the final unit constructed of dental acrylic. It consisted of a skullcap portion carrying the transmitter and ear plugs, one of which contained the thermistor; the other ear plug was drilled to permit hearing. Body temperature at the tympanic membrane was measured in one S. 0 . oedip u s . After a few days, the earplugs caused irritation of the ear canals. This probably could be avoided by using softer plastics for the plugs or as a coating for the hard acrylic. RESULTS AND DISCUSSION Measuring body temperature with a sensor at the tympanic membrane seems justified (Cooper, Cranston and Snell, ’64; Benzinger and Taylor, ’63), especially since ambient temperature was controlled (Nadel and Horvath, ’70). Our findings for the diurnal temperature pattern in this single S. 0.oedipus was altogether similar to that reported by Morrison and Simdes (’63) for Callithrix jacchus. A change of about 4°C was characteristic and showed the distinct biphasic form during daytime with a low point near noon. Figure 1 presents the extensive data we collected on heart rates from S. 0. oedipus and S. fuscicollis. Diurnal variations were clearly seen. Both species showed a n abrupt rise from the nighttime low at 0600 hours to a daytime high at 0800 hours. A depression corresponding to the afternoon “siesta” occurred in both heart rate and body temperature. The second heart-rate peak was reached at 1700-1800 hours; the rate fell within 4-5 hours to the first of two nighttime lows. It was surprising to find that the larger (by about 100 gm) S. 0. oedipus had a faster heart rate than the smaller S. fuscicollis. This difference averaged 35 beats per minute at all hours. The female S. 0 . oedipus did not differ notably from the male. CONCLUSIONS Marmosets, and perhaps New World primates generally, have a narrow zone of thermal neutrality. They are thermally labile when ambient temperature exceeds these limits despite marked changes in oxygen consumption. We have shown that diurnal heart-rate, as well as body temperature, varies characteristically and substantially. Thus, any temporal studies using these animals must take into careful account the time of day for sampling and 34 1 MARMOSET DIURNAL HEART RATE S a g u i n u s oedipus TWO ANIMALS ( C O T T O N TO PI (*I657 & "1764) STANDARD ERROR OF THE M E A N A N D SIZE OF SAMPLE INDICATED 260. w 2 [Y IQ! 6 W I a 180 . r . - 1 2 3 4 . - 5 . 6 . 7 . 8 9 . . . . 14- . .17 .18 . . . -22 23. 2.4 . 10 I I 12 13 I5 16 19 2 0 21 HOUR OF DAY ( T A M A R I N1 Saguinus fuscico//is TWO A N I M A L S (*1514 &I - 1 5 1 6 ) S T A N D A R D ERROR OF T H E M E A N A N D S I Z E OF S A M P L E I N D I C A T E D 22 0 210 200 ul 2 190 cz 180 Q w I 170 I60 30 45 I50 b 140 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 HOUR OF DAY Fig. 1 Heart rates (beats/minute) taken at hourly intervals for two Saguinus oedipus oedipus ( l a ) and two S. fuscicollis ( l b ) by radiotelemetry. Each datum represents the mean ( 2 S.E.) of the number of observations successfully made (noted below each bar) on both animals for each species. 342 JOHN K. HAMPTON, JR. observations. Furthermore, a constant and optimal environment is necessary to avoid great changes in baseline or experimental values. Since a substantial species difference was observed, it, too, must be noted in the design and report of studies. Finally, these experiments make i t clear that the comparative biology of primates warrants a great deal more attention that it has received. ACKNOWLEDGMENTS We wish to acknowledge the assistance of Dr. Ronald Anderson and partial support from USPHS grant DE-02232. LITERATURE CITED Benzinger, T. H., and G. W. Taylor 1963 Cranial measurements of internal temperature in man. In: Temperature - Its Measurement and Control in Science and Industry. Vol. 3, part 3. Reinhold, New York, pp. 111-120. Chaffee, R. R. J., S. M. Horvath, R. E. Smith and R. S. 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