A headholder for stereotaxic operations of small laboratory animals

Physiology and Behavior. Vol. 7, pp. 263-264. Pergamon Press, 1971, Printed in Great Britain

BRIEF COMMUNICATION A Headholder for Stereotaxic Operations of Small Laboratory Animals' LENNART

HEIMER,

VICTOR KUIKKA,

KNUT

LARSSON AND ERIK NORDSTROM

Department of Psychology, M.L T. Cambridge Massachusetts, U.S.A. and Departments of Psychology and Anatomy, University of G6teborg, G6teborg, Sweden (Received 8 M a r c h 1971) HEIMER, L., V. KUIKKA,K. LARSSONAND E. NORDSTROM. A headholderfor stereotaxic operations of small laboratory animals. PHYSXOL.BEnAV.7 (2) 263-264, 1971.--A he.adholder for small laboratory animals is described in which the head is kept in position by two needles tightened onto the posterior part of the occipital bone on both sides. The head is oriented in the horizontal plane with the help of a removable bridge fixed at three points. Consequently this apparatus offers the advantage of: (1) not damaging the eardrums with subsequent impairment of hearing: (2) easily placing the head in the correct position; and, (3) giving free access to the lateral aspect of the head. Stereotaxic instruments

Surgical techniques

Small laboratory animals

THE OREAT advances in many fields of brain science during recent decades have been made possible partly through the ever-increasing use of experimental methods, such as electrical stimulation-recording techniques and lesion experiments to mention a few. The accurate placement of electrodes in different brain structures is today a routine procedure in most neuroanatomic and neurophysiologic laboratories, and the instrument most often associated with this procedure is the Horsley-Clarke stereotaxic instrument. In all commercially available stereotaxic instruments for small laboratory animals, the head is fixed by insertion of plugs into the external auditory canals of the animal. This procedure, however, can easily damage the eardrums with subsequent impairment of hearing, which is especially detrimental in behavioral experiments. Furthermore, due to the soft tissue covering the auditory canals, it is sometimes difficult to place the ear plugs in correct position, a circumstance which introduces uncertainty about the exact orientation of the head. To avoid these shortcomings we constructed a headholder, in which the head is kept in position by two needles tightened onto the posterior part of the occipital bone on both sides. Before the head is fixed in position the skull roof is oriented in the horizontal plane with the help of a bridge containing three screws. The fixation technique used in this instrument offers an additional advantage, namely free access to the lateral side of the head. Needless to say, this is of special value in surgical procedures aimed at exposing the lateral or basal regions of the brain. With the help of the instrument it is, for instance, relatively easy to reach different regions of the olfactory cortex, including the olfactory tubercle, by using a

subtemporal approach. In such cases, the head can be conveniently tilted to one side, before it is fixed in position by the sharp needles.

Description of the Instrument The main features of the headholder are visualized in Fig. 1, while Fig. 2 presents a drawing for building of the apparatus. The instrument consists of two parts. A bridge orientates the head in the horizontal plane before the head is secured in position by a headholder. The headholder is mounted on two parallel plates which measure 4 × 125 x 375 mm, and are connected by transverse beams. Three guideways with slides are mounted on the upper plate. The slide (A) can be moved by a screw (B). Attached to this slide is a vertically oriented screw (C), which has a nut shaped as a fork. This fork supports a pin guided by slots in the block (D). The clamp (E) is movable by a srew (F) and fixed by a nut (G). The two other slides (H) are adjustable to one another by a right and left spiralled screw (I), which is mounted beneath the upper plate. These slides (H) carry vertical arms with pins made by tempered steel (J). The bridge is fastened to the guideways (K) by four screws (L). Three additional screws (M), forming a triangle, orient the position of the skull roof. Before the anesthetized rat is fixed in the headholder, the skin and the periosteum is removed from the upper position of the head. The head is thereafter oriented in horizontal position by gently pushing it toward the three screws (M) of the bridge. The two sharp steel pins (J) are thereafter tightened onto the occipital bone on the most posterior part of the skull.

aSupported in part by Grant HD 00344 from National Institute of Health and Human Development. Reprint orders to Lennart Heimer, Department of Psychology, M.I.T., Cambridge, Mass. 02139, U.S.A. 263

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FIG. 1. Negative image of a counterstained Golgi preparation produced by exposing Contrast Grade 2 Fotorite paper in Beseler enlarger with Componon f4/28 mm lens.

(.facing page 262)

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FIG. 2. Negative image of a Nauta preparation produced as in Fig, I. Degeneration, as seen in the microscope, has been drawn on the print.

FIG. 3. Negative image of Nissl preparation adjacent lo Ihat in Fig. 2, with the same procedulc

5 4 FIG. 4. Drawing of degeneration noted in Fig. 2 and in light of nuclear boundaries observed in Fig. 3.

FIG. 5. Positive image of Nissl preparation shown in Fig. 3 obtained with Kodalith Ortho negative and subsequent contact printing on Fotorite paper.