Physiology & Behavior, Vol. 15, pp. 373-376. Pergamon Press and Brain Research Publ., 1975. Printed in the U.S.A.
Development of Olfactory-guided Behavior in the Golden Hamster ESTELLE H. G R E G O R Y 1 AND ALLEN BISHOP
California State University, Los Angeles
(Received 8 January 1975) GREGORY, E. H. AND A. BISHOP. Development of olfactory-guided behavior in the golden hamster. PHYSIOL. BEHAV. 15(4) 373-376, 1975. - Hamster pups were tested for an odor preference every day from 1-16 days of age with shavings from their home cage and with clean wood shavings. The hamster pups showed a clear preference for their home cage shavings by 8 days of age. They were then tested for preferences with other odor combinations. Tests for preference with other odor pairs indicate that this preference is due to a change in the hamsters rather than a change in the stimulus. In these tests the hamster pups did not demonstrate a preference for their home shavings over shavings in which a nonlactating female had lived. Further tests will have to be done to determine how specific the hamster pup's olfactory preferences are.
Olfactory development
Neonatal olfactory preference
Hamster olfaction
A great deal of interest has been demonstrated recently in olfactory interactions between mother and young. A maternal pheromone has been identified in the rat to which the pups respond between 14 and 27 days o f age [7]. Other investigations have demonstrated that rat pups respond to familiar odors at even earlier ages [5, 10, 11, 13]. The behavior of both rats [8] and hamsters [1,21 is modified by extraordinary olfactory influences at early ages. In addition, adult hamster social interactions are dependent on olfactory input [6,9]. It seems clear that we must examine the normal course of development of olfaction in order to evaluate the role of olfaction on subsequent social behaviors. Devor and Schneider [3] have demonstrated that hamster pups show a preference for home cage bedding over fresh bedding. The basis for this preference is not clear. Nor is it clear how specific is this preference. Do hamster pups specifically prefer their home odor to food odor? Is the home odor strong enough for the pups to recognize at ages when they do not demonstrate a preference or must it become stronger? The present study was undertaken in order to explore some details of the odor preferences of hamster pups.
from 1 to 16 days of age (day of birth = Day 0). The pregnant females were housed individually in plastic cages at least 2 days prior to term. Eleven litters, which contained 102 pups, were used in this study. Each mother and her young were kept in their own cage for the duration of the experiment. The wood shavings (pine) were maintained at a depth of 3 5 - 4 0 mm and were never changed; however, new wood shavings were added when the level decreased to about 25 mm.
Apparatus Testing was conducted in two alleyways constructed of Plexiglas. The first alleyway measured 31 X 10 X 8.2 cm and was used for testing animals 1 to 6 days of age. The larger alleyway measured 82 X 18 X 11.5 cm and was used for testing animals 7 to 16 days of age. Each alleyway was wiped clean with warm water (no soap was used for fear of odor contamination) after every two tests. Hamsters were tested as a litter group and also individually.
Procedure Group test. One litter was removed from the home cage and transported to the test room. The pups were tested by being placed as a group in the center of the alleyway, which was divided into halves by a line across the midpoint of the long axis. One half contained shavings from the floor of the pups' home cage and the other half contained clean wood shavings (or different combinations at older ages as ex-
METHOD
Animals Female golden hamsters were mated in our laboratory and their young were then observed in the test situation
1Send reprint requests to: Dr. E. Gregory, Department of Psychology, California State University, Los Angeles, CA 90032. 373
374 plained below). The shavings were approximately 6 mm deep. The home side was alternated daily, although the pups showed no consistent side preference. The pups were then scored individually as to their location (on home cage or flesh shavings) at the end of a predetermined time interval. If an animal did not move from its original location it was scored not home. The time interval was varied in order to allow the hamsters sufficient time to make a choice; the time necessary was lessened as the hamsters grew and their coordination increased (10 min for ages 1 - 5 days; 3 min for ages 6 - 1 6 days). In order to be scored as having chosen the home shavings the hamster had to move its head at least 12 mm toward the home cage side and had to be at that position when the final scoring was done at the end of the time interval. The hamsters were also scored at shorter time intervals during the test. These observations gave results which were not different from those obtained at the end of the time interval, so only the results for the end of the interval are presented. I n d i v i d u a l test. Following the group test individual hamsters were chosen at random to be tested individually. Three hamsters from each litter were tested individually for 3 rain at ages 2 - 6 days. Pups were not tested individually on Day 1 to minimize the danger of cannibalism by the mother. It was considered that minimal time away from the mother and minimal handling at that age would be desirable. All hamsters were tested individually for 1 min on Days 7 - 1 6 . The testing and scoring procedures were identical to those described for the group tests except that each pup was given only one preference task per day. Since the hamsters were being fed small seeds it was possible that the preference being demonstrated for the home rather than clean shavings was for food, not home odor. Another possibility was that the demonstrated preference was due to an increase in the odor of the stimulus, since the cages were not cleaned during the experiment, rather than to a change in the animals. To eliminate these possibilities the hamsters were tested on a number of different stimulus combinations once they had demonstrated a clear preference for the home shavings in the home vs. clean discrimination. The stimulus combinations were as follows: (1) dilute home (home shavings mixed 50:50 with clean shavings) vs. clean shavings; (2) old home (home shavings saved from days when the hamsters were not demonstrating a preference, frozen, then warmed t6 room temperature and used for testing at a later age) vs. clean shavings; (3) home vs. clean shavings + food (clean shavings in which about 2 oz. of food had been sprinkled); (4) home vs. female shavings (shavings from a cage in which a non-lactating female hamster had been living); (5) dilute home vs. clean shavings + food (this was thought to be a more difficult discrimination than No. 3). Once each fitter reached criterion on the home vs clean combination, i.e., no more than 1 hamster not choosing the home side for two consecutive days, its members were tested on different combinations of odors. Most litters reached this criterion by Day 11, so data for all litters were combined for Days 1 1 - 1 6 . Each litter was tested as a group on 2 different odor combinations each day from Day 11 to Day 16. In addition, each hamster was also tested individually on 1 of the odor pairs each day. The odor combinations for which each litter was tested were selected at random for the first two days of testing. For the remaining days efforts were made to test each litter on the odor combinations to which they had not yet been exposed so that
G REG O RY AND BISHOP all fitters would be tested on all odor combinations at least once on Days 11 - 16. The results o f all group tests were combined for each odor combination for all tests on Days 1 1 - 1 6 . The same procedure was followed for the individual tests at these ages. That is, the total number of pups choosing home side was compared to the total number of pups choosing home shavings mixed with food (home vs. clean + food), and so forth. These data were evaluated with the binomial test assuming the probability of choosing the home side on any trial to be 0.5. In this way a critical number was determined for each test. If the number of animals choosing the home side exceeded this number the preference was considered significant. RESULTS The number of hamsters choosing their home shavings over clean shavings is shown for the group tests (Fig. 1) and the individual tests (Fig. 2). The hamsters were showing a clear preference for their home shavings by at least 8 days of age when they were tested as litter groups, and seemed to show preferences a few days earlier when tested individually. During the time period of 1 1 - 1 6 days of age the hamsters tested as a group clearly preferred the home shavings to clean shavings as did the hamsters tested individually. Table 1 shows the results of the various comparison tests. A clear preference for dilute home shavings over clean shavings was also demonstrated by the hamsters tested both as a group and individually. The hamsters preferred their old home shavings when compared to clean shavings. When tested as a group, they preferred their home shavings to clean shavings mixed with food; however, the hamsters tested individually did not. When they were tested for a preference between dilute home shavings and clean shavings mixed with food both the hamsters tested as a group and the hamsters tested individually preferred the home shavings. The hamsters did not demonstrate a preference for their home shavings over shavings from another female's cage. DISCUSSION The hamster pups showed a clear preference for their home cage odor in preference to clean wood shavings at early ages. That this change was due to a change in the pups rather than in the stimulus was demonstrated by the pups showing a preference for old (weaker odor) wood shavings as well as diluted home shavings. It is possible that this preference was due to taste input as well as olfactory information; however, the pups were not observed to chew or lick the shavings during the testing. The hamster pups did not show a preference for their home shavings compared to shavings from the cage of a non-lactating female. This study demonstrates that as the hamster pups progress in age they show a clear preference for shavings from the home cage. Since the mother retrieves the pups less frequently as they get older, the ability of the pups to seek out the home cage odor, and thereby their mother, serves a useful function. In a previous study [5], rat pups also demonstrated a preference for their home cage odor as they progressed in age. In these rodents there is a synchronization between the behavior of the pups and that of the mother. When the pups are being retrieved by the mother almost constantly they show little behavior of their own to return to an odor
HAMSTER OLFACTORY-GUIDED BEHAVIOR
375 TABLE 1 RESPONSES OF HAMSTERS 11-16 DAYS OF AGE. IN EACH COMPARISON THE PREDICTED CHOICE IS LISTED FIRST.
Home Shavings vs. Clean Shavings I00 o
Group Test
90
Comparison
Percent choosing predicted direction Group Test Individual Test
¢--
~
70
E
60
~
50
Home vs. clean Dilute home vs. clean Old home vs. clean Home vs. clean + food Home vs. other female Dilute home vs. clean + food
f..
90* (n = 93* (n = 96* (n= 60"(n= 46 ( n = 60* (n =
198) 224) 51) 149) 243) 105)
87* 80* 92* 56 33 72*
(n = (n = (n--(n= (n= (n =
96) 85) 60) 78) 153) 67)
*p
Development of Olfactory-guided Behavior in the Golden Hamster ESTELLE H. G R E G O R Y 1 AND ALLEN BISHOP
California State University, Los Angeles
(Received 8 January 1975) GREGORY, E. H. AND A. BISHOP. Development of olfactory-guided behavior in the golden hamster. PHYSIOL. BEHAV. 15(4) 373-376, 1975. - Hamster pups were tested for an odor preference every day from 1-16 days of age with shavings from their home cage and with clean wood shavings. The hamster pups showed a clear preference for their home cage shavings by 8 days of age. They were then tested for preferences with other odor combinations. Tests for preference with other odor pairs indicate that this preference is due to a change in the hamsters rather than a change in the stimulus. In these tests the hamster pups did not demonstrate a preference for their home shavings over shavings in which a nonlactating female had lived. Further tests will have to be done to determine how specific the hamster pup's olfactory preferences are.
Olfactory development
Neonatal olfactory preference
Hamster olfaction
A great deal of interest has been demonstrated recently in olfactory interactions between mother and young. A maternal pheromone has been identified in the rat to which the pups respond between 14 and 27 days o f age [7]. Other investigations have demonstrated that rat pups respond to familiar odors at even earlier ages [5, 10, 11, 13]. The behavior of both rats [8] and hamsters [1,21 is modified by extraordinary olfactory influences at early ages. In addition, adult hamster social interactions are dependent on olfactory input [6,9]. It seems clear that we must examine the normal course of development of olfaction in order to evaluate the role of olfaction on subsequent social behaviors. Devor and Schneider [3] have demonstrated that hamster pups show a preference for home cage bedding over fresh bedding. The basis for this preference is not clear. Nor is it clear how specific is this preference. Do hamster pups specifically prefer their home odor to food odor? Is the home odor strong enough for the pups to recognize at ages when they do not demonstrate a preference or must it become stronger? The present study was undertaken in order to explore some details of the odor preferences of hamster pups.
from 1 to 16 days of age (day of birth = Day 0). The pregnant females were housed individually in plastic cages at least 2 days prior to term. Eleven litters, which contained 102 pups, were used in this study. Each mother and her young were kept in their own cage for the duration of the experiment. The wood shavings (pine) were maintained at a depth of 3 5 - 4 0 mm and were never changed; however, new wood shavings were added when the level decreased to about 25 mm.
Apparatus Testing was conducted in two alleyways constructed of Plexiglas. The first alleyway measured 31 X 10 X 8.2 cm and was used for testing animals 1 to 6 days of age. The larger alleyway measured 82 X 18 X 11.5 cm and was used for testing animals 7 to 16 days of age. Each alleyway was wiped clean with warm water (no soap was used for fear of odor contamination) after every two tests. Hamsters were tested as a litter group and also individually.
Procedure Group test. One litter was removed from the home cage and transported to the test room. The pups were tested by being placed as a group in the center of the alleyway, which was divided into halves by a line across the midpoint of the long axis. One half contained shavings from the floor of the pups' home cage and the other half contained clean wood shavings (or different combinations at older ages as ex-
METHOD
Animals Female golden hamsters were mated in our laboratory and their young were then observed in the test situation
1Send reprint requests to: Dr. E. Gregory, Department of Psychology, California State University, Los Angeles, CA 90032. 373
374 plained below). The shavings were approximately 6 mm deep. The home side was alternated daily, although the pups showed no consistent side preference. The pups were then scored individually as to their location (on home cage or flesh shavings) at the end of a predetermined time interval. If an animal did not move from its original location it was scored not home. The time interval was varied in order to allow the hamsters sufficient time to make a choice; the time necessary was lessened as the hamsters grew and their coordination increased (10 min for ages 1 - 5 days; 3 min for ages 6 - 1 6 days). In order to be scored as having chosen the home shavings the hamster had to move its head at least 12 mm toward the home cage side and had to be at that position when the final scoring was done at the end of the time interval. The hamsters were also scored at shorter time intervals during the test. These observations gave results which were not different from those obtained at the end of the time interval, so only the results for the end of the interval are presented. I n d i v i d u a l test. Following the group test individual hamsters were chosen at random to be tested individually. Three hamsters from each litter were tested individually for 3 rain at ages 2 - 6 days. Pups were not tested individually on Day 1 to minimize the danger of cannibalism by the mother. It was considered that minimal time away from the mother and minimal handling at that age would be desirable. All hamsters were tested individually for 1 min on Days 7 - 1 6 . The testing and scoring procedures were identical to those described for the group tests except that each pup was given only one preference task per day. Since the hamsters were being fed small seeds it was possible that the preference being demonstrated for the home rather than clean shavings was for food, not home odor. Another possibility was that the demonstrated preference was due to an increase in the odor of the stimulus, since the cages were not cleaned during the experiment, rather than to a change in the animals. To eliminate these possibilities the hamsters were tested on a number of different stimulus combinations once they had demonstrated a clear preference for the home shavings in the home vs. clean discrimination. The stimulus combinations were as follows: (1) dilute home (home shavings mixed 50:50 with clean shavings) vs. clean shavings; (2) old home (home shavings saved from days when the hamsters were not demonstrating a preference, frozen, then warmed t6 room temperature and used for testing at a later age) vs. clean shavings; (3) home vs. clean shavings + food (clean shavings in which about 2 oz. of food had been sprinkled); (4) home vs. female shavings (shavings from a cage in which a non-lactating female hamster had been living); (5) dilute home vs. clean shavings + food (this was thought to be a more difficult discrimination than No. 3). Once each fitter reached criterion on the home vs clean combination, i.e., no more than 1 hamster not choosing the home side for two consecutive days, its members were tested on different combinations of odors. Most litters reached this criterion by Day 11, so data for all litters were combined for Days 1 1 - 1 6 . Each litter was tested as a group on 2 different odor combinations each day from Day 11 to Day 16. In addition, each hamster was also tested individually on 1 of the odor pairs each day. The odor combinations for which each litter was tested were selected at random for the first two days of testing. For the remaining days efforts were made to test each litter on the odor combinations to which they had not yet been exposed so that
G REG O RY AND BISHOP all fitters would be tested on all odor combinations at least once on Days 11 - 16. The results o f all group tests were combined for each odor combination for all tests on Days 1 1 - 1 6 . The same procedure was followed for the individual tests at these ages. That is, the total number of pups choosing home side was compared to the total number of pups choosing home shavings mixed with food (home vs. clean + food), and so forth. These data were evaluated with the binomial test assuming the probability of choosing the home side on any trial to be 0.5. In this way a critical number was determined for each test. If the number of animals choosing the home side exceeded this number the preference was considered significant. RESULTS The number of hamsters choosing their home shavings over clean shavings is shown for the group tests (Fig. 1) and the individual tests (Fig. 2). The hamsters were showing a clear preference for their home shavings by at least 8 days of age when they were tested as litter groups, and seemed to show preferences a few days earlier when tested individually. During the time period of 1 1 - 1 6 days of age the hamsters tested as a group clearly preferred the home shavings to clean shavings as did the hamsters tested individually. Table 1 shows the results of the various comparison tests. A clear preference for dilute home shavings over clean shavings was also demonstrated by the hamsters tested both as a group and individually. The hamsters preferred their old home shavings when compared to clean shavings. When tested as a group, they preferred their home shavings to clean shavings mixed with food; however, the hamsters tested individually did not. When they were tested for a preference between dilute home shavings and clean shavings mixed with food both the hamsters tested as a group and the hamsters tested individually preferred the home shavings. The hamsters did not demonstrate a preference for their home shavings over shavings from another female's cage. DISCUSSION The hamster pups showed a clear preference for their home cage odor in preference to clean wood shavings at early ages. That this change was due to a change in the pups rather than in the stimulus was demonstrated by the pups showing a preference for old (weaker odor) wood shavings as well as diluted home shavings. It is possible that this preference was due to taste input as well as olfactory information; however, the pups were not observed to chew or lick the shavings during the testing. The hamster pups did not show a preference for their home shavings compared to shavings from the cage of a non-lactating female. This study demonstrates that as the hamster pups progress in age they show a clear preference for shavings from the home cage. Since the mother retrieves the pups less frequently as they get older, the ability of the pups to seek out the home cage odor, and thereby their mother, serves a useful function. In a previous study [5], rat pups also demonstrated a preference for their home cage odor as they progressed in age. In these rodents there is a synchronization between the behavior of the pups and that of the mother. When the pups are being retrieved by the mother almost constantly they show little behavior of their own to return to an odor
HAMSTER OLFACTORY-GUIDED BEHAVIOR
375 TABLE 1 RESPONSES OF HAMSTERS 11-16 DAYS OF AGE. IN EACH COMPARISON THE PREDICTED CHOICE IS LISTED FIRST.
Home Shavings vs. Clean Shavings I00 o
Group Test
90
Comparison
Percent choosing predicted direction Group Test Individual Test
¢--
~
70
E
60
~
50
Home vs. clean Dilute home vs. clean Old home vs. clean Home vs. clean + food Home vs. other female Dilute home vs. clean + food
f..
90* (n = 93* (n = 96* (n= 60"(n= 46 ( n = 60* (n =
198) 224) 51) 149) 243) 105)
87* 80* 92* 56 33 72*
(n = (n = (n--(n= (n= (n =
96) 85) 60) 78) 153) 67)
*p
