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A stereotaxic frame assembly for investigating the cat auditory system
614
Electroencephalography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
A STEREOTAXIC F R A M E ASSEMBLY F O R I N V E S T I G A T I N G T H E CAT A U D I T O R Y SYSTEM I C. W. DUNLOP
Brain Research Unit, Department of Physiology, University of Sydney, N.S.W. 2006 ( A ustralia) (Accepted for publication: March 24, 1969)
A survey of stereotaxis for the cat has been made by Blum and Feldman (1964). Fixation of the head to the instrument is generally achieved by inserting bars into the external auditory meati and clamping bars over each inferior orbital ridge and behind the incisor teeth upward against the upper jaw. Jasper and Ajmone Marsan (1960) described a commonly used stereotaxic instrument and the principles of the method. However, this type of instrument is not satisfactory for the study of various regions of the auditory system. The use of ear bars causes variable damage to the tympanic membrane and associated structures and prevents ready access to the bullae and other peripheral auditory structures. The ear bars are hollow for the transmission of sound and the nearest the acoustic transducers can be placed is approximately 8 cm from the tympanic membrane (the length of the ear bars), thus creating resonance problems when delivering the acoustic stimulus. The nearness of the calibrated side bars of the conventional frame assembly (approximately 15 cm) on which the electrode holders ride restricts the movement of the electrodes for penetration of laterally situated brain structures such as the auditory and associated cortices; therefore a tangential penetration of the cortex is often prevented. A stereotaxic frame assembly is described here which permits fixation of the cat's head without ear bars, and more flexibility of electrode movement is achieved than in the conventional apparatus by further spacing of the side bar assembly to a distance of 25 cm (Fig. 1).
vertical rod. This platform has a cross-member (CM) which can be moved in an antero-posterior direction and tilted to any angle by the manipulation of two screws (S1, 2). This cross-member is attached to the cat's skull by another two screws ($3, 4) which are screwed into two 2 cm threaded brass tubes (T) situated on the cat's skull and embedded in dental acrylic (see below). The side bars of the frame assembly were constructed to carry the base block of a Trent Wells probe drive electrode carrier (Trent Wells, Mechanical Development. Southgate, California).
Fixation of cross-member to the cat's skull The skin overlying the cat's cranium is incised in the midline from the supra-orbital ridge to the external occipital protuberance. The skin flaps are retracted, underlying fascia removed, and the temporal muscles reflected as far laterally as possible. The exposed skull is cleaned of blood and muscle. Two stainless steel screws ($5), size 6/32, length 3/16 in. are firmly screwed into and through the bone (Fig. 2, b), 1 cm each of the sagitta[ suture, in the region rostral to the coronal suture. The two internally threaded brass tubes are now firmly attached to the cross-member (CM) by way of the two brass screws ($3, 4). The area around the two screws in the skull is now thoroughly dried, the cross-member assembly is held in position (approximately 1.5 cm
Construction and operation of the apparatus Fixation of the cat's head in the apparatus requires more time than in the conventional apparatus; however, the procedure is a simple one. The head holder (Fig. 2) can be considered to consist of three parts: I. A lower platform (LP) consisting of a cross-bar on which the upper jaw immediately behind the incisors rests. 2. A vertical rod (R) capable of being moved up and down and fixed in position by a screw clamp ((2). 3. An upper platform (UP) which is attached to this 1 Supported by grants from the National Health and Medical Research Council of Australia and the University of Sydney.
Fig. I A side-view photograph of the stereotaxic frame assembly consisting of a base plate, frame assembly and head holder.
Electroenceph. clin. Neurophysiol., 1969, 27:614-616
A CAT STEREOTAXIC APPARATUS
615
Fig. 2 a: Head holder removed from stereotaxic frame assembly, b: Arrangement of cross-member (CM), threaded brass tubes (T), screw ($5) and dental acrylic on surface of skull anterior to bregma, c: Skull positioned in head holder in the basal horizontal plane by manipulation of clamp (C) and screws (S1, 2) so that electrode at Y was at same height at X. d: Establishment of inter-aural line parallel to side bars of frame assembly by having electrodes at Y and Z at same height.
anterior to the bregma and at an angle of approximately 50 ° to the horizontal), and a dental acrylic preparation (Texton) is poured around the screws and brass tubes. During hardening of the dental acrylic care must be exercised in preventing movement of the preparation so that a rigid and strong cross-member fixation is obtained.
Orientation of cat's headfor stereotaxic electrode placement In all experiments the pinna are removed. For stereotaxic electrode placement, the inter-aural basal plane (XY, Fig. 2, c) is obtained by rotating the head holder by loosening clamp ((2) so that the inter-aural line (YZ, the line connecting the center of each external auditory meatus, Fig. 2, d) is in a plane horizontal to the side bars of the stereotaxic frame. Having established this plane, the basal horizontal plane of the instrument (a plane through the inter-aural line and the centers of the inferior orbital ridges) is obtained by manipulation of the cross-member and the vertical rod of the head
assembly, thus altering the degree of tilt of the head in an antero-caudal direction. The zero frontal plane and the zero horizontal plane (1 cm above the inter-aural basal plane) are measured at the inter-aural line. These measurements are then referred to the bregma so that future electrode coordinates can be easily assessed. The midline of the brain serves as the zero plane for designating locations left and right in the brain. Different planes of electrode penetrations of a given auditory region can be achieved by the combination of trigonometry and the use of the stereotaxic coordinates. Here the electrode holder may be tilted to an angle or kept in a vertical position with the horizontal plane of the cat's head set to a certain angle by loosening the clamp (C) attached to the head holder and rotating the assembly to that angle. This apparatus has been successful in electrode penetrations of the auditory cortex, medial geniculate body, and inferior colliculus of the cat.
Electroenceph. clin. Neurophysiol., 1969~ 27:614--616
616
c.w. SUMMARY
A stereotaxic frame assembly for investigating the cat auditory system is described. Ear bars are not used. This allows the acoustic transducers to be placed adjacent to the tympanic membrane, and avoids damage to this membrane by conventional ear bars. The apparatus also allows for a much greater flexibility of electrode movement, especially in regard to different angular penetrations of laterally located central nervous regions.
DUNLOP placer les capteurs contre la membrane du tympan et 6vite les 16sions de cette membrane par les barres d'oreille conventionnelles. L'appareil permet 6galement une beaucoup plus grande libert6 de mouvement des 61ectrodes, sp6cialement en raison des diff6rentes p6n6trations angulaires des r6gions nerveuses centrales situ6es lat6ralement. Acknowledgement is made to Mr. R. Munns for technical assistance.
R.ESUMI~
REFEKEN CES
CADRE STI~RI~OTAXIQUE POUR L'INVESTIGATION DU SYSTEME AUDITIF DU CHAT
BLUM, B. and FELOMAN, B. A mountable stereotaxic apparatus for the cat. Electroenceph. clin. Neurophysiol., 1964, 16: 403-408. JASPER, H. H. and AJMONE MARSAN, C. A stereotaxic atlas of the diencephalon of the cat. Nat. Res. Council of Canada, Ottawa, 1960.
L'auteur d6crit un cadre st6r6otaxique destin6 "h Finvestigation du syst~me auditif du chat et dans lequel les barres d'oreille ne sont pas n6cessaires. Ceci permet de
Reference: DUNLOP, C. W. A stereotaxic frame assembly for investigating the cat auditory system. Electroenceph. clin. Neurophysiol., 1969, 27: 614-616.
Electroencephalography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
A STEREOTAXIC F R A M E ASSEMBLY F O R I N V E S T I G A T I N G T H E CAT A U D I T O R Y SYSTEM I C. W. DUNLOP
Brain Research Unit, Department of Physiology, University of Sydney, N.S.W. 2006 ( A ustralia) (Accepted for publication: March 24, 1969)
A survey of stereotaxis for the cat has been made by Blum and Feldman (1964). Fixation of the head to the instrument is generally achieved by inserting bars into the external auditory meati and clamping bars over each inferior orbital ridge and behind the incisor teeth upward against the upper jaw. Jasper and Ajmone Marsan (1960) described a commonly used stereotaxic instrument and the principles of the method. However, this type of instrument is not satisfactory for the study of various regions of the auditory system. The use of ear bars causes variable damage to the tympanic membrane and associated structures and prevents ready access to the bullae and other peripheral auditory structures. The ear bars are hollow for the transmission of sound and the nearest the acoustic transducers can be placed is approximately 8 cm from the tympanic membrane (the length of the ear bars), thus creating resonance problems when delivering the acoustic stimulus. The nearness of the calibrated side bars of the conventional frame assembly (approximately 15 cm) on which the electrode holders ride restricts the movement of the electrodes for penetration of laterally situated brain structures such as the auditory and associated cortices; therefore a tangential penetration of the cortex is often prevented. A stereotaxic frame assembly is described here which permits fixation of the cat's head without ear bars, and more flexibility of electrode movement is achieved than in the conventional apparatus by further spacing of the side bar assembly to a distance of 25 cm (Fig. 1).
vertical rod. This platform has a cross-member (CM) which can be moved in an antero-posterior direction and tilted to any angle by the manipulation of two screws (S1, 2). This cross-member is attached to the cat's skull by another two screws ($3, 4) which are screwed into two 2 cm threaded brass tubes (T) situated on the cat's skull and embedded in dental acrylic (see below). The side bars of the frame assembly were constructed to carry the base block of a Trent Wells probe drive electrode carrier (Trent Wells, Mechanical Development. Southgate, California).
Fixation of cross-member to the cat's skull The skin overlying the cat's cranium is incised in the midline from the supra-orbital ridge to the external occipital protuberance. The skin flaps are retracted, underlying fascia removed, and the temporal muscles reflected as far laterally as possible. The exposed skull is cleaned of blood and muscle. Two stainless steel screws ($5), size 6/32, length 3/16 in. are firmly screwed into and through the bone (Fig. 2, b), 1 cm each of the sagitta[ suture, in the region rostral to the coronal suture. The two internally threaded brass tubes are now firmly attached to the cross-member (CM) by way of the two brass screws ($3, 4). The area around the two screws in the skull is now thoroughly dried, the cross-member assembly is held in position (approximately 1.5 cm
Construction and operation of the apparatus Fixation of the cat's head in the apparatus requires more time than in the conventional apparatus; however, the procedure is a simple one. The head holder (Fig. 2) can be considered to consist of three parts: I. A lower platform (LP) consisting of a cross-bar on which the upper jaw immediately behind the incisors rests. 2. A vertical rod (R) capable of being moved up and down and fixed in position by a screw clamp ((2). 3. An upper platform (UP) which is attached to this 1 Supported by grants from the National Health and Medical Research Council of Australia and the University of Sydney.
Fig. I A side-view photograph of the stereotaxic frame assembly consisting of a base plate, frame assembly and head holder.
Electroenceph. clin. Neurophysiol., 1969, 27:614-616
A CAT STEREOTAXIC APPARATUS
615
Fig. 2 a: Head holder removed from stereotaxic frame assembly, b: Arrangement of cross-member (CM), threaded brass tubes (T), screw ($5) and dental acrylic on surface of skull anterior to bregma, c: Skull positioned in head holder in the basal horizontal plane by manipulation of clamp (C) and screws (S1, 2) so that electrode at Y was at same height at X. d: Establishment of inter-aural line parallel to side bars of frame assembly by having electrodes at Y and Z at same height.
anterior to the bregma and at an angle of approximately 50 ° to the horizontal), and a dental acrylic preparation (Texton) is poured around the screws and brass tubes. During hardening of the dental acrylic care must be exercised in preventing movement of the preparation so that a rigid and strong cross-member fixation is obtained.
Orientation of cat's headfor stereotaxic electrode placement In all experiments the pinna are removed. For stereotaxic electrode placement, the inter-aural basal plane (XY, Fig. 2, c) is obtained by rotating the head holder by loosening clamp ((2) so that the inter-aural line (YZ, the line connecting the center of each external auditory meatus, Fig. 2, d) is in a plane horizontal to the side bars of the stereotaxic frame. Having established this plane, the basal horizontal plane of the instrument (a plane through the inter-aural line and the centers of the inferior orbital ridges) is obtained by manipulation of the cross-member and the vertical rod of the head
assembly, thus altering the degree of tilt of the head in an antero-caudal direction. The zero frontal plane and the zero horizontal plane (1 cm above the inter-aural basal plane) are measured at the inter-aural line. These measurements are then referred to the bregma so that future electrode coordinates can be easily assessed. The midline of the brain serves as the zero plane for designating locations left and right in the brain. Different planes of electrode penetrations of a given auditory region can be achieved by the combination of trigonometry and the use of the stereotaxic coordinates. Here the electrode holder may be tilted to an angle or kept in a vertical position with the horizontal plane of the cat's head set to a certain angle by loosening the clamp (C) attached to the head holder and rotating the assembly to that angle. This apparatus has been successful in electrode penetrations of the auditory cortex, medial geniculate body, and inferior colliculus of the cat.
Electroenceph. clin. Neurophysiol., 1969~ 27:614--616
616
c.w. SUMMARY
A stereotaxic frame assembly for investigating the cat auditory system is described. Ear bars are not used. This allows the acoustic transducers to be placed adjacent to the tympanic membrane, and avoids damage to this membrane by conventional ear bars. The apparatus also allows for a much greater flexibility of electrode movement, especially in regard to different angular penetrations of laterally located central nervous regions.
DUNLOP placer les capteurs contre la membrane du tympan et 6vite les 16sions de cette membrane par les barres d'oreille conventionnelles. L'appareil permet 6galement une beaucoup plus grande libert6 de mouvement des 61ectrodes, sp6cialement en raison des diff6rentes p6n6trations angulaires des r6gions nerveuses centrales situ6es lat6ralement. Acknowledgement is made to Mr. R. Munns for technical assistance.
R.ESUMI~
REFEKEN CES
CADRE STI~RI~OTAXIQUE POUR L'INVESTIGATION DU SYSTEME AUDITIF DU CHAT
BLUM, B. and FELOMAN, B. A mountable stereotaxic apparatus for the cat. Electroenceph. clin. Neurophysiol., 1964, 16: 403-408. JASPER, H. H. and AJMONE MARSAN, C. A stereotaxic atlas of the diencephalon of the cat. Nat. Res. Council of Canada, Ottawa, 1960.
L'auteur d6crit un cadre st6r6otaxique destin6 "h Finvestigation du syst~me auditif du chat et dans lequel les barres d'oreille ne sont pas n6cessaires. Ceci permet de
Reference: DUNLOP, C. W. A stereotaxic frame assembly for investigating the cat auditory system. Electroenceph. clin. Neurophysiol., 1969, 27: 614-616.