Brain Research, 142 (1978) 357-362 357 © Elsevier/North-Holland BiomedicalPress A method to detect and record from striatal cells of low spontaneous activity by stimulating the corticostriatal pathway WOLFRAM SCHULTZ* and URBAN UNGERSTEDT** Department of Histology, Karolinska Institutet, S-104 O1 Stockholm (Sweden) (Accepted September 14th, 1977) The striatum of rats, the terminal area of the nigrostriatal dopamine system 1,e4, is one of the most neuropharmacologically investigated areas of the mammalian brain. Biochemical, histochemical, behavioral and electrophysiological studies have provided a wealth of knowledge concerning this structure. Of these, electrophysiological single cell recordings are often hampered by a number of technical problems already at the extracellular level. Primarily due to the small size of striatal neurons and the virtual absence of spontaneous activity it has been difficult to isolate impulses from individual cells and maintain recordings for any extended period of time, particularly with large- tipped iontophoresis electrodes5. It would thus be advantageous to improve the techniques for finding and recording striatal cellular activity. Such a technique is described in the present study whereby cells were activated through the excitatory homolateral corticostriatal projection3,11,22, 2s. The results obtained with this method are evaluated in comparison to data obtained from other commonly used recording techniques. The present method has been developed and applied 19 after a series of experiments had been conducted in this laboratory in which striatum cellular activity was recorded with glutamate-filled electrodesis. Male Sprague-Dawley rats (150-550 g) were anesthetized by injecting 350 mg/kg chloral hydrate i.p., using supplementary doses of 50-70 mg/kg whenever necessary. Body temperature was controlled at 37-38 °C. Animals were mounted in a stereotaxic frame. In order to permit vertical insertion of the recording microelectrode, a hole of 1.5 mm diameter was drilled through the skull 2,5 mm lateral to the midline and 1.0 mm anterior to the bregma. Recordings were obtained in the striatum between 3.0 and 6.0 mm below the cortical surface by employing standard amplification and display techniques. The use of a storage oscilloscope was essential for monitoring striatum cellular activity of extremely low frequencies. Neuronal impulses were converted into standard pulses by a Schmitt-trigger and counted with an electronic counter (Ortec) for time periods ranging from 2 to 5 rain. Details of the other common techniques used for evaluating the present method will be described during the presentation of the data. * Present address for correspondence:Institut de Physiolog]e de l'Umverslt6,Fribourg, Switzerland. ** To whomreprint requests should be addressed.