Med. & Biol. Eng. & Comput., 1979, 17, 131-132
Technical note New technique for E.E.G. recording and drug infusion in the free-moving mouse Keyword--E.E. G. recording
Introduction THE short life span of a mouse is favourable for chronic experiments, enabling one to record the electrical activities of the animal for the whole life (about a year). In chronic experiments, animals must be attached to wires and catheters leading to recording and perfusion apparatus with a slip-ring connector. The slip-ring connectors available commercially or usually made in laboratories seem to prevent free movement of small animals like mice. When such a device is used, wires and catheters are likely to be bitten off and tend to twist because of the circular movement of the mouse. In the present report, we will introduce a slip-ring arrangement equipped with double springs and a microinfusion pump, which hardly prevents a mouse from moving freely. A stable recording of the e.e.g, and the body movement of the animal by our apparatus will be also described.
head down, the small tension of the springs avoids keeping the head afloat in the air. Since the weight of the microconnector (D in Fig. 1), the body movement transducer (E) and the support (K) adhered to the skull of the mouse is almost balanced by the tension of the springs, the mouse can move and sleep freely without any apparent restrictions. The wires from the implanted electrodes are connected to the slip-ring connector via the microconnector (D in Fig. 1) installed on the top of the support. When the animal is just below the slip-ring connector, the wires loosen, and when away from the connector, they are nearly on the plane involving the stretched springs. The wires leading from the implanted
2 Electrode-wire protection with double springs In chronic experiments, i t is most important to develop a way of inducing signals correctly and with stability from animals moving freely. Protecting the conductive wires with one steel spring, which has been usually applied to rats or larger animals, is not suitable for such small animals as mice. Owing to the restrictive effect of the spring on the movement of mice, observation of their normal behaviour is almost impossible. The authors used two stainless-steel springs (wire diameter 0.2 mm; coil diameter 8 ram, C in Fig. 1) instead of one spring. At the lower end of the central axis of the mercury slipring connector (A in Fig. 1), a rod 18 cm long is fixed vertically. An epoxy-resin rod (3 cm long, K in Fig. 1, the details will be described elsewhere) is attached to the skull of the mouse and on the top of it a stainless-steel tube 6 cm long and 0.6 mm in outer diameter is attached at the right angle to the midline of the mouse, then both ends of the stainless-steel tube are connected to the corresponding ends of the rod at the lower part of the mercury slip-ring connector with two springs (C in Fig. 1). When a mouse is attached to this arrangement, the central axis of the slip-ring connector can easily follow the movement of the mouse, even if the mouse moves around vigorously on the plane of area 40• cm 2. When the mouse is asleep, curling up the body with the Received 7th April 1978
Fig. 1 Experimental arrangement for measuring the e.e.g, and body movement of the free-moving mouse
A slip-ring connector B infusion pump C spring, D micro-connector E body movement transducer F disc G bearing H mercury I platinum J silicone rubber tube K support (epoxy-resin rod)
0140-0118/79[010131 -/- 02 $01,50/0 9 IFMBE : 1979
Medical & Biological Engineering & Computing
January 1979
131
electrodes stably conduct information from the animal for a period of up to a year without restricting delicate movements of the mouse and without being bitten off. While the experiment is suspended, the mouse can be removed from the slip-ring connector system by disconnecting the lower end of the springs and the microconnector at the lower end of the wires. 3 Micro-infusion pump While infusing liquid medication into the ventricles of a mouse, if catheters are connected through the central axis of the slip-ring connector, rotation of the central axis of the slip-ring connector becomes slower on the account of abrasion of the tube walls at the connected parts, and the axis cannot follow the nimble movements of the mouse. As an improvement, a small d.c. motor (Escap R-16C11-207; gear box, Escap E16) is suspended directly at the lower end of the central axis of the slipring connector, and infusion is performed at the flow rate of 2/zl/h, according to the principle of the peristaltic pump (BEVAN et al., 1969; LITTLER et al., 1972). A silicone rubber tube of a fixed length filled with liquid medication is inserted to be connected near the skull of the mouse. l lO0~v
timel=~ EEG
Acknowledgments--The authors would like to thank Prof. S. Yoshimura for his courtesy in reading the manuscript.
time ~
--• ~
EEl3=
BM
.
beam interruption is employed (FENCL et al., 1971). For the purpose of quantifying movement of a mouse more precisely, the authors adopted a vibration transducer (a b.m. transducer) on the support attached to the skull of a mouse (K in Fig. 1). This b.m. transducer, weighing about 1 g, is a semiconductor strain gauge embedded in silicone oil. Fig. 2 shows the simultaneous recording of the electroencephalogram (e.e.g.) and the signals from the b.m. transducer. The record gives nearly the same pattern as that of the electromyogram (e.m.g.) according to the sleep-awaking rhythm and the paradoxical sleep (r.e.m. sleep). For the measurement of the e.e.g, during sleep, the e.m.g, of the neck muscle is generally examined and the stage of sleep is determined from a correlation between the e.e.g, and the e.m.g, of the neck muscle. The output of the b.m. transducer installed on the head of the mouse is basically reflecting activity of the neck muscle. It can be utilised as a substitute for the e.m.g, of the neck muscle. The support attached to the skull of the mouse is fixed permanently, and rarely becomes detached during the whole lifespan of the animal. In the replacement of general electrodes for e.m.g, measurement, the b.m. transducer provides a more stable and easier measurement of the neck muscle movement over a long period of time.
-
~
~
. . . . .
::~: ::~:_~:==.7 ~t-
-*
A. HIGASHI K. UCHIZONO M. HOSHINO Y. TANI
time
time EEG=:- -_-. ":-i: BM
:S_~:~_._._~= sz:'~
.
National Institute for Physiological Sciences Myodaiji, Okazaki Japan
L~S.7 IlL
Fig. 2 Correlation between the e.e g. and body movement e.e.g. : The original e.e.g, recorded with bipolar electrodes from the occipital cortex of the mouse at a slow paper speed. The larger amplitude corresponds with shorter sleep periods of the mouse, while the smaller amplitude corresponds with wakefulness or r.e.m, sleep b.m. : body movement as the deflection of a vibrating transducer installed on the head of a mouse, recorded in parallel with the e.e.g., which differs very little from the e.m.g, of the neck muscle except the part during the r.e.m. sleep
4 Measurement of body movement For the measurement of a small animal's movement, some highly precise apparatus equipped with a pressure transducer or an accelerometer as a sensor is available commercially, and in some cases the method of light
132
Medical
T. YANO K. YAZAWA
Department of Physiology, Faculty of Medicine University of Tokyo, Hongo Tokyo, Japan
References BEVAN, A. T., HONOUR, A. J. and STOTT, F. D. (1969) Direct arterial pressure recording in unrestricted man. Clinical Sci. 36, 329-344. FENCL, V., LOSKY, G. and PAPPENHEIMER, J. R. (1971) Factors in cerebrospinal fluid from goats that affect sleep and activity in rats. J. Physiol. 216, 565-589. LrrrLER, W. A., HONOUR, A. J., SLEIGHT, P. and STOTT, F. D. (1972) Continuous recording of direct arterial pressure and electrocardiogram unrestricted man. Brit. Med. J. 3, 76-78.
& Biological Engineering & Computing
January 1979
Technical note New technique for E.E.G. recording and drug infusion in the free-moving mouse Keyword--E.E. G. recording
Introduction THE short life span of a mouse is favourable for chronic experiments, enabling one to record the electrical activities of the animal for the whole life (about a year). In chronic experiments, animals must be attached to wires and catheters leading to recording and perfusion apparatus with a slip-ring connector. The slip-ring connectors available commercially or usually made in laboratories seem to prevent free movement of small animals like mice. When such a device is used, wires and catheters are likely to be bitten off and tend to twist because of the circular movement of the mouse. In the present report, we will introduce a slip-ring arrangement equipped with double springs and a microinfusion pump, which hardly prevents a mouse from moving freely. A stable recording of the e.e.g, and the body movement of the animal by our apparatus will be also described.
head down, the small tension of the springs avoids keeping the head afloat in the air. Since the weight of the microconnector (D in Fig. 1), the body movement transducer (E) and the support (K) adhered to the skull of the mouse is almost balanced by the tension of the springs, the mouse can move and sleep freely without any apparent restrictions. The wires from the implanted electrodes are connected to the slip-ring connector via the microconnector (D in Fig. 1) installed on the top of the support. When the animal is just below the slip-ring connector, the wires loosen, and when away from the connector, they are nearly on the plane involving the stretched springs. The wires leading from the implanted
2 Electrode-wire protection with double springs In chronic experiments, i t is most important to develop a way of inducing signals correctly and with stability from animals moving freely. Protecting the conductive wires with one steel spring, which has been usually applied to rats or larger animals, is not suitable for such small animals as mice. Owing to the restrictive effect of the spring on the movement of mice, observation of their normal behaviour is almost impossible. The authors used two stainless-steel springs (wire diameter 0.2 mm; coil diameter 8 ram, C in Fig. 1) instead of one spring. At the lower end of the central axis of the mercury slipring connector (A in Fig. 1), a rod 18 cm long is fixed vertically. An epoxy-resin rod (3 cm long, K in Fig. 1, the details will be described elsewhere) is attached to the skull of the mouse and on the top of it a stainless-steel tube 6 cm long and 0.6 mm in outer diameter is attached at the right angle to the midline of the mouse, then both ends of the stainless-steel tube are connected to the corresponding ends of the rod at the lower part of the mercury slip-ring connector with two springs (C in Fig. 1). When a mouse is attached to this arrangement, the central axis of the slip-ring connector can easily follow the movement of the mouse, even if the mouse moves around vigorously on the plane of area 40• cm 2. When the mouse is asleep, curling up the body with the Received 7th April 1978
Fig. 1 Experimental arrangement for measuring the e.e.g, and body movement of the free-moving mouse
A slip-ring connector B infusion pump C spring, D micro-connector E body movement transducer F disc G bearing H mercury I platinum J silicone rubber tube K support (epoxy-resin rod)
0140-0118/79[010131 -/- 02 $01,50/0 9 IFMBE : 1979
Medical & Biological Engineering & Computing
January 1979
131
electrodes stably conduct information from the animal for a period of up to a year without restricting delicate movements of the mouse and without being bitten off. While the experiment is suspended, the mouse can be removed from the slip-ring connector system by disconnecting the lower end of the springs and the microconnector at the lower end of the wires. 3 Micro-infusion pump While infusing liquid medication into the ventricles of a mouse, if catheters are connected through the central axis of the slip-ring connector, rotation of the central axis of the slip-ring connector becomes slower on the account of abrasion of the tube walls at the connected parts, and the axis cannot follow the nimble movements of the mouse. As an improvement, a small d.c. motor (Escap R-16C11-207; gear box, Escap E16) is suspended directly at the lower end of the central axis of the slipring connector, and infusion is performed at the flow rate of 2/zl/h, according to the principle of the peristaltic pump (BEVAN et al., 1969; LITTLER et al., 1972). A silicone rubber tube of a fixed length filled with liquid medication is inserted to be connected near the skull of the mouse. l lO0~v
timel=~ EEG
Acknowledgments--The authors would like to thank Prof. S. Yoshimura for his courtesy in reading the manuscript.
time ~
--• ~
EEl3=
BM
.
beam interruption is employed (FENCL et al., 1971). For the purpose of quantifying movement of a mouse more precisely, the authors adopted a vibration transducer (a b.m. transducer) on the support attached to the skull of a mouse (K in Fig. 1). This b.m. transducer, weighing about 1 g, is a semiconductor strain gauge embedded in silicone oil. Fig. 2 shows the simultaneous recording of the electroencephalogram (e.e.g.) and the signals from the b.m. transducer. The record gives nearly the same pattern as that of the electromyogram (e.m.g.) according to the sleep-awaking rhythm and the paradoxical sleep (r.e.m. sleep). For the measurement of the e.e.g, during sleep, the e.m.g, of the neck muscle is generally examined and the stage of sleep is determined from a correlation between the e.e.g, and the e.m.g, of the neck muscle. The output of the b.m. transducer installed on the head of the mouse is basically reflecting activity of the neck muscle. It can be utilised as a substitute for the e.m.g, of the neck muscle. The support attached to the skull of the mouse is fixed permanently, and rarely becomes detached during the whole lifespan of the animal. In the replacement of general electrodes for e.m.g, measurement, the b.m. transducer provides a more stable and easier measurement of the neck muscle movement over a long period of time.
-
~
~
. . . . .
::~: ::~:_~:==.7 ~t-
-*
A. HIGASHI K. UCHIZONO M. HOSHINO Y. TANI
time
time EEG=:- -_-. ":-i: BM
:S_~:~_._._~= sz:'~
.
National Institute for Physiological Sciences Myodaiji, Okazaki Japan
L~S.7 IlL
Fig. 2 Correlation between the e.e g. and body movement e.e.g. : The original e.e.g, recorded with bipolar electrodes from the occipital cortex of the mouse at a slow paper speed. The larger amplitude corresponds with shorter sleep periods of the mouse, while the smaller amplitude corresponds with wakefulness or r.e.m, sleep b.m. : body movement as the deflection of a vibrating transducer installed on the head of a mouse, recorded in parallel with the e.e.g., which differs very little from the e.m.g, of the neck muscle except the part during the r.e.m. sleep
4 Measurement of body movement For the measurement of a small animal's movement, some highly precise apparatus equipped with a pressure transducer or an accelerometer as a sensor is available commercially, and in some cases the method of light
132
Medical
T. YANO K. YAZAWA
Department of Physiology, Faculty of Medicine University of Tokyo, Hongo Tokyo, Japan
References BEVAN, A. T., HONOUR, A. J. and STOTT, F. D. (1969) Direct arterial pressure recording in unrestricted man. Clinical Sci. 36, 329-344. FENCL, V., LOSKY, G. and PAPPENHEIMER, J. R. (1971) Factors in cerebrospinal fluid from goats that affect sleep and activity in rats. J. Physiol. 216, 565-589. LrrrLER, W. A., HONOUR, A. J., SLEIGHT, P. and STOTT, F. D. (1972) Continuous recording of direct arterial pressure and electrocardiogram unrestricted man. Brit. Med. J. 3, 76-78.
& Biological Engineering & Computing
January 1979
