The Effects of Light on the Activity Levels of Mice

 

Lindsay Wielichowski

3-26-02

 

 

Abstract

 

            Light is a very important factor in the lives and activity levels of rodents.  I tested whether light affected mice activity levels over darkness.  I found that the mice did do more rotations at night when the lights were off, but the difference was not significant. 

Keywords:  light, activity level, rodents, nocturnal, dark, mice

 

 

Introduction

 

            Many rodents such as mice, Mus musculus, are nocturnal.  They depend on the light and dark to let them know when it is time to sleep, search for food, or look for mates.  Even the rodents that are caught and placed in laboratories keep their sleeping patterns.  They receive cues from windows and artificial light.  Their biological clocks are synchronized with the light and dark times of day (Brookline, 2001). 

Nocturnal animals came into existence after the appearance of vertebrates almost 300 million years ago.  The land that the animals lived on changed and became very crowed with herbivores and predators.  To adapt to the changes, many animals found to avoid predators and competition of food, they would only come out at night.   Sleeping was done during the day when all the other animals were out.  To survive at night many animals developed extremely advanced senses.  One of the characterists of nocturnal animals is large eyes.  With the large eyes food is easier to see.  The eyes have wider pupils, larger lens and bigger retinal surfaces to gather more ambient light (Denning, 2001). 

 

            Circadian rhythms are very important when talking about sleep.  It is also referred to as time keeping or our biological clock.  Humans and animals don’t run on an exact 24-hour rhythm.  We are dependant on day and night rhythms of light (Bootsma, 1999).  There are two brain structures that control the way light affects rodent sleep activity.  They are part of the visual system, which is connected then to the central nervous system.  Major changes in lighting can dominate normal sleep patterns.  Just by changing light schedules around, you can almost immediately change patterns (Benca, 1998).

 

            Wheel running is a common practice in the lab to test activity level of rodents.  It is also said that wheel running is an independent trait that is a redirected form of exploratory behavior (Carter et al. 1999).  Wheel running is not just a tool used with rodents, but it has also been used on domestic hens, red foxes, bobcat, domestic cats, pigtail macaque, rabbit, ferrets, and flying squirrels (Sherwin 1998).  It is found to be a successful tool in activity and learning studies.   

Hypothesis

            The activity levels of the mice will increase when tested at night, when the lights are off, when compared to during the day when the lights are on.  Activity level is defined by number of rotations the mice do in a 10-minute period. 

 

Materials and Methods

MOUSE SELECTION

            Six male mice approximately the same age were taken from the animal room at Alverno College.  They were housed in 3 separate cages.  The three white mice were housed together (Red-Eye, Black Eye 1, and Black Eye 2).  In the second cage two dark colored mice were housed together (Spots and Dark Belly).  In the last cage another dark mouse was housed (Tan Belly).  Each cage was treated the exact same way.  All received water, food, a paper towel ball, and 2 toilet paper rolls.  The cages were cleaned, water was changed and fresh shavings were laid once a week.

CONTROLED ROOM

            The mice were all kept in an environmental camber.  The temperature of the room was set at 25.0 degrees Celsius, with a humidity of 23.0.  A light source approximately 4ft in length with five Sylvania brand 120V 40 watt (soft white) bulbs, were hung from the ceiling approximately 182.87 cm off the floor.  The light source was on from 12:01am to 12:00pm.  It then turned off and was dark from 12:01pm to 12:00am.  This gave the mice equal intervals of 12 hours of light and 12 hours of dark.  Note:  Mice were placed in environmental chamber for 1 week before experiment started to allow them to adjust to new conditions.  

 

MEASURING ACTIVITY LEVELS

            Activity levels were measured by how many rotations each mouse made on a metal rodent counting wheel in ten minutes.  The metal exercise wheel was about 15 cm tall with a radius of 17 cm.  There was also a metal cage attached to the side of the wheel for the mice to go in and out of.  The cage was about 15x23 cm.  A company called Wahmann manufactured the counting wheel.  Mice were run twice in a day, once in light and once in dark, two times a week.  I ran trials any time between 9am-11am in the morning and 1pm-4pm at night.  The experiment was done over a 3-week period.

 

Results

            My major finding in this experiment was that I didn’t see a significant difference in morning and night number of rotations.  I found that in all the trials but one, (table 4) the mice on average ran more rotations at night then morning.  The number of rotations was consistent within the range of previous trials.  All the mice expect for #6 (Red Eye) ran over 60 rotations in the morning and night.  Red Eye, although consistent never ran over 55 rotations.  None of the trials I ran had a significant difference.  The T-test value for all the trials was:  Trial 1=0.09, Trial 2=0.25, Trial 3= 0.06, Trial 4=0.46, Trial 5=0.09, and Trial 6=0.21.  Refer to tables 1-6 below.        

 

 

Tables 1-6

 

Morning 1

Night 1

 

1

83

108

rotations

2

83

146

rotations

3

67

42

rotations

4

92

111

rotations

5

85

90

rotations

6

28

54

rotations

Average 1

73

91.8

rotations

 

 

 

Morning 2

Night 2

 

1

139

125

rotations

2

145

145

rotations

3

97

105

rotations

4

113

106

rotations

5

68

117

rotations

6

39

42

rotations

Average 2

100.1

106.6

rotations

 

 

 

Morning 3

Night 3

 

1

133

122

rotations

2

101

141

rotations

3

78

94

rotations

4

89

109

rotations

5

119

124

rotations

6

26

35

rotations

Average 3

91

104.1

rotations

 

 

 

 

Morning 4

Night 4

 

1

124

126

rotations

2

163

117

rotations

3

92

106

rotations

4

111

101

rotations

5

62

86

rotations

6

13

22

rotations

Average 4

94.1

93

rotations

 

 

 

 

Morning 5

 

Night 5

 

1

96

128

rotations

2

116

176

rotations

3

74

85

rotations

4

93

94

rotations

5

124

115

rotations

6

19

21

rotations

Average 5

87

103.1

rotations

 

 

 

Morning 6

Night 6

 

1

131

137

rotations

2

162

159

rotations

3

98

114

rotations

4

91

118

rotations

5

110

96

rotations

6

40

39

rotations

Average 6

105.3

110.5

rotations

 

 

Tables 1-6  The above tables show the day and number of rotations the mice did in a 10-mintue period.  It also shows the average number of rotations done. 

 

Note:  The numbers above stand for these mice.

#1-Tan Belly

#2-Spots

#3-Dark Belly

#4-Black Eye 1

#5-Black Eye 2

#6-Red Eye