British Poultry Science
ISSN: 0007-1668 (Print) 1466-1799 (Online) Journal homepage: http://www.tandfonline.com/loi/cbps20
Ontogeny of brain temperature regulation in chicks (Gallus gallus domesticus) Z. Arad To cite this article: Z. Arad (1991) Ontogeny of brain temperature regulation in chicks (Gallus gallus domesticus), British Poultry Science, 32:1, 203-210, DOI: 10.1080/00071669108417341 To link to this article: http://dx.doi.org/10.1080/00071669108417341
Published online: 08 Nov 2007.
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=cbps20 Download by: [Universite Laval]
Date: 07 November 2015, At: 10:38
British Poultry Science (1991) 32: 203-210
ONTOGENY OF BRAIN TEMPERATURE REGULATION IN CHICKS (GALLUS GALLUS DOMESTICUS) Z. ARAD Department of Biology, Technion—Israel Institute of Technology, Haifa 32000, Israel
Downloaded by [Universite Laval] at 10:38 07 November 2015
Received for publication 4th July 1989
Abstract 1. Development of brain temperature regulation was studied in the domestic fowl (Gallus gallus domesticus) from hatching to 21 d of age. 2. Body and brain temperature at hatching were relatively low compared with adult levels. However, both were effectively regulated at ambient temperatures of 30 and 35°C, with only a minor difference between the 2 temperatures. 3. Body and brain temperature increased as a power function of age at significantly different rates, approaching adult levels at around 10 d of age and resulting in a linear increase in body-to-brain temperature difference with age. 4. The results indicated the existence of different patterns of posthatching development of brain temperature regulation in relation to the degree of precocity of a species. INTRODUCTION
It is well known that precocial birds develop thermoregulatory capacities earlier than altricial species. Most studies have focussed on the development of cold defence mechanisms such as maximal metabolic responses, increased insulation and decreasing surface:volume ratio (Koskimies and Lahti, 1964; Untergasser and Hayward, 1972; Bernstein, 1973). However, several studies have suggested that heat defence mechanisms might develop earlier than cold defence mechanisms. Some species exhibit panting and/or gular flutter immediately after hatching (Ricklefs and Hainsworth, 1968; Bernstein, 1971, 1973; Dawson et al., 1972; Hudson et al., 1974; O'Connor, 1975; Freeman, 1978; Dawson and Bennett, 1981; Chapman et al., 1981; Kirkham and Montevecchi, 1982; Mishaga and Whitford, 1983). Increased respiratory movements during heat exposure have been revealed even in the late (pipping) embryo of the domestic fowl (Dawes, 1979). Ricklefs and Hainsworth (1968) have suggested that the earlier development of heat loss capacities is of adaptive significance as parents cannot cool their offspring as effectively as they can warm them. This problem is aggravated when the parents themselves are heat-stressed as has 203
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been shown in the Western gull (Larus occidentalis livens), breeding under extremely hot and dry conditions (Hand et al., 1981). Coordinated thermoregulatory responses to environmental conditions should parallel the development of central control mechanisms. Arad et al. (19846) have addressed this problem indirectly by studying the development of brain cooling capacity in the developing, extremely precocial mallard duck hatchling (Anas platyrhynchos) and found that ducklings were able to maintain stable brain and body temperatures and to defend a large body-to-brain temperature difference on heat exposure from the day of hatching. On the other hand, altricial pigeon hatchlings (Arad, 1989) were found to be poikilothermic at hatching. Their body and brain temperatures increased thereafter as power functions of age. Bird species differ in their degree of precocity, depending on their morphology and general biology (Nice, 1962). I decided therefore, to examine the developmental pattern of brain cooling in the domestic fowl chick (Gallus gallus domesticus), which is considered less precocial than the duck. This was done by measuring brain and body temperatures in chicks from the day of hatching to 3 weeks of age, both at thermoneutrality (30°C) and during moderate heat exposure (35°C). MATERIALS AND METHODS
A total of 23 chicks were used in the study. Of these, 17 chicks were measured on 2 to 4 d and 6 were measured on 7 to 12 d during 21 d posthatching. Fertile eggs were obtained from a commercial supplier and artificially incubated at 37-5°C. Immediately after hatching, the chicks were weighed and prepared for experimentation. Between experiments, they were kept in individual cages in an environmental room (ambient temperature 25±2°C, 12L:12D lighting cycle) with growing-chick food and water available ad libitum. Within 2 h of hatching a guide tube, 7 mm long, was implanted in the brain under local anaesthesia (Lidocaine HC1, 2%). The guide tube was constructed from polyethylene tubing (PE 50) glued to the tip of a 1 ml plasticsyringe barrel, used as a flange. Head feathers were removed and the skin incised. The skull was punctured with a 23-gauge needle, 2 mm to the left of the midline, on the axis connecting the external ear openings. The guide tube was introduced so that its end rested close to the hypothalamus and the syringe tip was secured to the skull with tissue cement. The guide tube was then flushed with saline and capped, and the skin sutured. The guide tubes remained patent during the entire experimental period. A second guide tube (15 mm long, PE 90) was introduced through a small incision above the cloacal opening so that it rested parallel with the vent and was sutured to the skin. Postmortem examinations verified the correct location of the guide tubes. Brain and body temperatures were measured simultaneously every 2 to 3 d until the age of 21 d. Chicks measured within 8 to 12 h after hatching were assigned the age of 0-5 d. All experiments were conducted between 06.00 and 18.00. Before an experiment, the chicks were weighed to the nearest 0-01 g,
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then lightly held on a small board in a manner permitting normal respiration. One copper-constantan thermocouple (diameter 0-7 mm) was introduced into the brain guide tube and another into the rectal guide tube. Both thermocouples were connected to a digital thermometer (Sensortek, TH-6D) which was connected to a potentiometer chart recorder (Sensortek, BRZ-2PL). Ambient temperature was measured with a telethermometer probe (YSI, Type 402). All temperatures were measured to ±0-l°C after calibration of the instruments against a mercury-in-glass thermometer having an accuracy (±0-l°C) traceable to the U.S. National Bureau of Standards. Postmortem examination of histological brain sections revealed that the brain thermocouple was positioned in the posterior portion of the left cerebral hemisphere, within 3 to 5 mm of the hypothalamus, at all ages. Every chick was exposed in the dark for 2 to 3 h to each of the two ambient temperatures (Ta), 30 and 35±0-3°C, in an environmental chamber (Forma Scientific). Brain (Tbr) and body (Tc) temperatures were recorded every 1 min. A period of stable temperatures, approximately 30 min long, was selected from the data at each Ta for calculating mean values of Tbn Tc and body-to-brain temperature difference (AT=Tc—Tbr). Equations describing the data were calculated by least-squares linear regressions of raw (simple and multiple) or of logarithmically (base e) transformed data. Statistical significance was inferred if the probability (P) of the null hypothesis was 0-05 or less.
RESULTS
Body mass increased from about 40 g at hatching to about 180 g at 21 d of age (Fig. 1) with a typical acceleration at around day 10. Body and brain temperatures were lower than adult levels in the first few days, but increased as a power function of age at both 30 and 35°C Ta (Fig. 2). At both ambient temperatures the exponents for Tc were significantly (P
ISSN: 0007-1668 (Print) 1466-1799 (Online) Journal homepage: http://www.tandfonline.com/loi/cbps20
Ontogeny of brain temperature regulation in chicks (Gallus gallus domesticus) Z. Arad To cite this article: Z. Arad (1991) Ontogeny of brain temperature regulation in chicks (Gallus gallus domesticus), British Poultry Science, 32:1, 203-210, DOI: 10.1080/00071669108417341 To link to this article: http://dx.doi.org/10.1080/00071669108417341
Published online: 08 Nov 2007.
Submit your article to this journal
Article views: 10
View related articles
Citing articles: 5 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=cbps20 Download by: [Universite Laval]
Date: 07 November 2015, At: 10:38
British Poultry Science (1991) 32: 203-210
ONTOGENY OF BRAIN TEMPERATURE REGULATION IN CHICKS (GALLUS GALLUS DOMESTICUS) Z. ARAD Department of Biology, Technion—Israel Institute of Technology, Haifa 32000, Israel
Downloaded by [Universite Laval] at 10:38 07 November 2015
Received for publication 4th July 1989
Abstract 1. Development of brain temperature regulation was studied in the domestic fowl (Gallus gallus domesticus) from hatching to 21 d of age. 2. Body and brain temperature at hatching were relatively low compared with adult levels. However, both were effectively regulated at ambient temperatures of 30 and 35°C, with only a minor difference between the 2 temperatures. 3. Body and brain temperature increased as a power function of age at significantly different rates, approaching adult levels at around 10 d of age and resulting in a linear increase in body-to-brain temperature difference with age. 4. The results indicated the existence of different patterns of posthatching development of brain temperature regulation in relation to the degree of precocity of a species. INTRODUCTION
It is well known that precocial birds develop thermoregulatory capacities earlier than altricial species. Most studies have focussed on the development of cold defence mechanisms such as maximal metabolic responses, increased insulation and decreasing surface:volume ratio (Koskimies and Lahti, 1964; Untergasser and Hayward, 1972; Bernstein, 1973). However, several studies have suggested that heat defence mechanisms might develop earlier than cold defence mechanisms. Some species exhibit panting and/or gular flutter immediately after hatching (Ricklefs and Hainsworth, 1968; Bernstein, 1971, 1973; Dawson et al., 1972; Hudson et al., 1974; O'Connor, 1975; Freeman, 1978; Dawson and Bennett, 1981; Chapman et al., 1981; Kirkham and Montevecchi, 1982; Mishaga and Whitford, 1983). Increased respiratory movements during heat exposure have been revealed even in the late (pipping) embryo of the domestic fowl (Dawes, 1979). Ricklefs and Hainsworth (1968) have suggested that the earlier development of heat loss capacities is of adaptive significance as parents cannot cool their offspring as effectively as they can warm them. This problem is aggravated when the parents themselves are heat-stressed as has 203
Downloaded by [Universite Laval] at 10:38 07 November 2015
204
Z. ARAD
been shown in the Western gull (Larus occidentalis livens), breeding under extremely hot and dry conditions (Hand et al., 1981). Coordinated thermoregulatory responses to environmental conditions should parallel the development of central control mechanisms. Arad et al. (19846) have addressed this problem indirectly by studying the development of brain cooling capacity in the developing, extremely precocial mallard duck hatchling (Anas platyrhynchos) and found that ducklings were able to maintain stable brain and body temperatures and to defend a large body-to-brain temperature difference on heat exposure from the day of hatching. On the other hand, altricial pigeon hatchlings (Arad, 1989) were found to be poikilothermic at hatching. Their body and brain temperatures increased thereafter as power functions of age. Bird species differ in their degree of precocity, depending on their morphology and general biology (Nice, 1962). I decided therefore, to examine the developmental pattern of brain cooling in the domestic fowl chick (Gallus gallus domesticus), which is considered less precocial than the duck. This was done by measuring brain and body temperatures in chicks from the day of hatching to 3 weeks of age, both at thermoneutrality (30°C) and during moderate heat exposure (35°C). MATERIALS AND METHODS
A total of 23 chicks were used in the study. Of these, 17 chicks were measured on 2 to 4 d and 6 were measured on 7 to 12 d during 21 d posthatching. Fertile eggs were obtained from a commercial supplier and artificially incubated at 37-5°C. Immediately after hatching, the chicks were weighed and prepared for experimentation. Between experiments, they were kept in individual cages in an environmental room (ambient temperature 25±2°C, 12L:12D lighting cycle) with growing-chick food and water available ad libitum. Within 2 h of hatching a guide tube, 7 mm long, was implanted in the brain under local anaesthesia (Lidocaine HC1, 2%). The guide tube was constructed from polyethylene tubing (PE 50) glued to the tip of a 1 ml plasticsyringe barrel, used as a flange. Head feathers were removed and the skin incised. The skull was punctured with a 23-gauge needle, 2 mm to the left of the midline, on the axis connecting the external ear openings. The guide tube was introduced so that its end rested close to the hypothalamus and the syringe tip was secured to the skull with tissue cement. The guide tube was then flushed with saline and capped, and the skin sutured. The guide tubes remained patent during the entire experimental period. A second guide tube (15 mm long, PE 90) was introduced through a small incision above the cloacal opening so that it rested parallel with the vent and was sutured to the skin. Postmortem examinations verified the correct location of the guide tubes. Brain and body temperatures were measured simultaneously every 2 to 3 d until the age of 21 d. Chicks measured within 8 to 12 h after hatching were assigned the age of 0-5 d. All experiments were conducted between 06.00 and 18.00. Before an experiment, the chicks were weighed to the nearest 0-01 g,
Downloaded by [Universite Laval] at 10:38 07 November 2015
BRAIN TEMPERATURE REGULATION
205
then lightly held on a small board in a manner permitting normal respiration. One copper-constantan thermocouple (diameter 0-7 mm) was introduced into the brain guide tube and another into the rectal guide tube. Both thermocouples were connected to a digital thermometer (Sensortek, TH-6D) which was connected to a potentiometer chart recorder (Sensortek, BRZ-2PL). Ambient temperature was measured with a telethermometer probe (YSI, Type 402). All temperatures were measured to ±0-l°C after calibration of the instruments against a mercury-in-glass thermometer having an accuracy (±0-l°C) traceable to the U.S. National Bureau of Standards. Postmortem examination of histological brain sections revealed that the brain thermocouple was positioned in the posterior portion of the left cerebral hemisphere, within 3 to 5 mm of the hypothalamus, at all ages. Every chick was exposed in the dark for 2 to 3 h to each of the two ambient temperatures (Ta), 30 and 35±0-3°C, in an environmental chamber (Forma Scientific). Brain (Tbr) and body (Tc) temperatures were recorded every 1 min. A period of stable temperatures, approximately 30 min long, was selected from the data at each Ta for calculating mean values of Tbn Tc and body-to-brain temperature difference (AT=Tc—Tbr). Equations describing the data were calculated by least-squares linear regressions of raw (simple and multiple) or of logarithmically (base e) transformed data. Statistical significance was inferred if the probability (P) of the null hypothesis was 0-05 or less.
RESULTS
Body mass increased from about 40 g at hatching to about 180 g at 21 d of age (Fig. 1) with a typical acceleration at around day 10. Body and brain temperatures were lower than adult levels in the first few days, but increased as a power function of age at both 30 and 35°C Ta (Fig. 2). At both ambient temperatures the exponents for Tc were significantly (P
