Electroencephalography and Clinical Neurophysiology , 1979, 4 7 : 6 2 7 - - 6 2 8
627
© Elsevier/North-Holland Scientific Publishers, Ltd.
Technical contribution HISTOLOGICAL MARKING WITH MULTIPLE THIN-FILM ELECTRODE PROBE FOR INTRACORTICAL RECORDING I.B. MULLER-PASCHINGER, O. PROHASKA, R. VOLLMER 1 and H. PETSCHE
Brain Research Institute, Austrian Academy o f Sciences, and Institut fiir Allgemeine Elektrotechnik, Technical University, Vienna (Austria) (Accepted for publication: May 29, 1979)
Intracortical multielectrodes produced by thinfilm technology (Prohaska et al. 1977) have small multiple contact surfaces (50 × 50 sq. pm and 10 × 10 sq. pro) at small distances (300 and 150 pm, respectively). In order to relate the electrophysiological findings to morphological peculiarities, marking the positions of the single contacts is indispensable. Difficulties in achieving good results arise not only from the smallness of the contact areas but even more from the different degrees of shrinking of the various cortical layers. Therefore, every contact has to be marked individually and every mark must be located under the microscope;otherwise histological interpretation of the electrophysiological findings is not feasible. Since the contact layers of the multiple electrodes are of silver, an attempt was made to find a method whereby electrolytic deposits of silver might best be made visible.
useful: (~1) the sections are placed in 0.5% perhydrol for 2 min; (2) the staining reaction itself takes place in a solution of 5% sodium acetate (100 ml) mixed with rubeanic acid (2 ml of a 0.1% alcoholic solution) (Romeis 1968). During this procedure, dark brown silver sulphide is formed. The best results are obtained if the slides are left in this solution at 37°C for 12--14 h. (3) As counterstain, either nuclear fast red or cresyl violet is used. Both methods give sufficient colour contrast to find the dark brown silver marks under the microscope. (4) After dehydration, the sections are protected with a synthetic mounting medium and a coverslip. Since the size of the silver contacts of the 8-fold electrode is 50 × 50 sq. pm and the brown staining extends maximally over 70 pm, the marking o.f one electrode contact is easily found when looking through 5---6 sections. If a 16-fold electrode with 10 × 10 sq. pm contact surfaces is used, the marking of each electrode can be found in 2--3 adjacent sections.
Method and results Summary At the end of the experiment, before killing the rabbit, roughly half of the 1 p m thick silver layer of each contact is deposited into the brain tissue by passing a Current through each electrode contact against a c o m m o n reference (20---40 mA/sq, cm for 20---40 sec). Immediately after marking the animal is killed by an overdose of Nembutal. Then the small part of the cortex from which the records were made (a cortical disk of about 3 m m in diameter), is cut out and fixed by immersion in formalin. After fixation and dehydration the area of interest is embedded in paraffin. Afterwards the tissue is cut in the sagittal direction (since the electrode was introduced into the brain with the electrode contacts showing rostrally) in sections of 12 pro. For the silver reaction the following steps prove 1 Present address: Neurological Department, Krankenhaus Lainz, Vienna.
A histological method, based on electrolytically deposited silver,is described to verify the positions of the contacts of intracortical multielectrodes.
R~sum~
Marquage histologique ~ partir d'une dlectrode multiple d film mince permettant des enregistrements intracorticaux Une m~thode histologique basle sur un d4pSt ~lectrolytique d'argent, est d~crite pour localiser les contacts successifs d'une micro~lectrode intracorticale. The authors gratefully acknowledge the support of this work by the Fonds zur FSrderung der wissenschaftlichen Forschung, project nrs. 1729 and 2784.
628 References
Prohaska, O., Olcaytuc, F., Womastek, K. and Petsche, H. A multielectrode for intracortical recordings
I.B. MULLER-PASCHINGER ET AL. produced by thin-film technology. Electroenceph. clin. Neurophysiol., 1977, 42: 421--422. Romeis, B. Mikroskopische Technik. R. Oldenbourg Verlag, Miinchen, Wien, 1968.
627
© Elsevier/North-Holland Scientific Publishers, Ltd.
Technical contribution HISTOLOGICAL MARKING WITH MULTIPLE THIN-FILM ELECTRODE PROBE FOR INTRACORTICAL RECORDING I.B. MULLER-PASCHINGER, O. PROHASKA, R. VOLLMER 1 and H. PETSCHE
Brain Research Institute, Austrian Academy o f Sciences, and Institut fiir Allgemeine Elektrotechnik, Technical University, Vienna (Austria) (Accepted for publication: May 29, 1979)
Intracortical multielectrodes produced by thinfilm technology (Prohaska et al. 1977) have small multiple contact surfaces (50 × 50 sq. pm and 10 × 10 sq. pro) at small distances (300 and 150 pm, respectively). In order to relate the electrophysiological findings to morphological peculiarities, marking the positions of the single contacts is indispensable. Difficulties in achieving good results arise not only from the smallness of the contact areas but even more from the different degrees of shrinking of the various cortical layers. Therefore, every contact has to be marked individually and every mark must be located under the microscope;otherwise histological interpretation of the electrophysiological findings is not feasible. Since the contact layers of the multiple electrodes are of silver, an attempt was made to find a method whereby electrolytic deposits of silver might best be made visible.
useful: (~1) the sections are placed in 0.5% perhydrol for 2 min; (2) the staining reaction itself takes place in a solution of 5% sodium acetate (100 ml) mixed with rubeanic acid (2 ml of a 0.1% alcoholic solution) (Romeis 1968). During this procedure, dark brown silver sulphide is formed. The best results are obtained if the slides are left in this solution at 37°C for 12--14 h. (3) As counterstain, either nuclear fast red or cresyl violet is used. Both methods give sufficient colour contrast to find the dark brown silver marks under the microscope. (4) After dehydration, the sections are protected with a synthetic mounting medium and a coverslip. Since the size of the silver contacts of the 8-fold electrode is 50 × 50 sq. pm and the brown staining extends maximally over 70 pm, the marking o.f one electrode contact is easily found when looking through 5---6 sections. If a 16-fold electrode with 10 × 10 sq. pm contact surfaces is used, the marking of each electrode can be found in 2--3 adjacent sections.
Method and results Summary At the end of the experiment, before killing the rabbit, roughly half of the 1 p m thick silver layer of each contact is deposited into the brain tissue by passing a Current through each electrode contact against a c o m m o n reference (20---40 mA/sq, cm for 20---40 sec). Immediately after marking the animal is killed by an overdose of Nembutal. Then the small part of the cortex from which the records were made (a cortical disk of about 3 m m in diameter), is cut out and fixed by immersion in formalin. After fixation and dehydration the area of interest is embedded in paraffin. Afterwards the tissue is cut in the sagittal direction (since the electrode was introduced into the brain with the electrode contacts showing rostrally) in sections of 12 pro. For the silver reaction the following steps prove 1 Present address: Neurological Department, Krankenhaus Lainz, Vienna.
A histological method, based on electrolytically deposited silver,is described to verify the positions of the contacts of intracortical multielectrodes.
R~sum~
Marquage histologique ~ partir d'une dlectrode multiple d film mince permettant des enregistrements intracorticaux Une m~thode histologique basle sur un d4pSt ~lectrolytique d'argent, est d~crite pour localiser les contacts successifs d'une micro~lectrode intracorticale. The authors gratefully acknowledge the support of this work by the Fonds zur FSrderung der wissenschaftlichen Forschung, project nrs. 1729 and 2784.
628 References
Prohaska, O., Olcaytuc, F., Womastek, K. and Petsche, H. A multielectrode for intracortical recordings
I.B. MULLER-PASCHINGER ET AL. produced by thin-film technology. Electroenceph. clin. Neurophysiol., 1977, 42: 421--422. Romeis, B. Mikroskopische Technik. R. Oldenbourg Verlag, Miinchen, Wien, 1968.
