381 Gen. Physiol. Biophys. (2013), 32, 381–388 doi: 10.4149/gpb_2013032 A miniature microdrive for recording auditory evoked potentials from awake anurans Haitham S. Mohammed 1 , Nasr M. Radwan 2 , Wolfgang Walkowiak 3 and Anwar A. Elsayed 1 1 Biophysics Department, Faculty of Science, Cairo University, Giza, Egypt 2 Zoology Department, Faculty of Science, Cairo University, Giza, Egypt 3 Zoological Institute, University of Cologne, Cologne, Germany Abstract. Electrical activity recording from the brains of awake animals is a corner stone in the study of the neurophysiological basis of behavior. To meet this need, a microelectrode driver suitable for the animal of interest has to be developed. In the present study a miniature microdrive was developed specifically for the leopard toad, Bufo regularis, however, it can be used for other small animals. he microdrive was designed to meet the following requirements: small size, light weight, simple and easy way of attaching and removing, advancing and withdrawing of microelectrode in the animal brain without rotation, can be reused and made from inexpensive materials. To assess the performance of the developed microdrive, we recorded auditory evoked potentials from different auditory centers in the toad’s brain. he potentials were obtained from mesencephalic, diencephalic and telencephalic auditory sensitive areas in response to simple and complex acoustic stimuli. he synthetic acoustical tones introduced to the toad were carrying the dominant frequencies of their mating calls. Key words: Anuran — Brain — Microdrive — Auditory — Acoustic stimulus Correspondence to: Haitham S. Mohammed, Biophysics Depart- ment, Faculty of Science, Cairo University, Giza, Egypt E-mail: haitham_sharaf@yahoo.com Introduction A major aim of neuroscience is to understand the relationship between brain activity and behaviour. Investigators have devel- oped techniques to record activity within the brain of behaving animals (Korshunov 1995; Kralik et al. 2001; Battaglia et al. 2009; Galashan et al. 2011). hese techniques usually involve electrodes attached to a device, in a manner that allows for their gradual advancement into the brain structure of interest. Such a device (microdrive) should meet several requirements; small size and weight, precise advancement and withdrawal, stability over time, simple installation and low cost. Sensory evoked potentials can be used to test the suitabil- ity of a microdrive, because they occur in a defined period of time (shortly ater a stimulus) and can therefore be averaged easily. Moreover, their general waveform patterns are usually well documented (Carey and Zelick 1993; Feng et al. 2006). A sensory evoked response may be defined as a local signal generated by integration of membrane currents in response to the stimulation of a peripheral sense organ or sensory nerve. Evoked potentials appear at certain time interval ater the stimulus (i.e. latency) and usually in a particular wave shape pattern. Depending on the type of electrode used the evoked response represents the combined activity of some to many neurons. Because of the longer time constants, afferent activity processed in the dendrites contributes more strongly to local field potentials than spike activity. Auditory evoked potentials (AEP) in animals have been of interest to gain insight into the auditory pathway and auditory neurophysiology. For example, Feng et al. (2006) have used AEP from the midbrain auditory center in the frog central nervous system to validate the ultrasonic sensitivity of a certain anurans species (A. tormotus). Several researchers have adopted different strategies for developing microdrives that are suitable to their work (McHughet al. 1996; Yu and Margoliash 1996; Yamamoto and Wilson 2008). Experiments are oten carried out with small animals such as rats, mice, or birds. Some of the developed microdrives are relatively heavy, oten exceeding 10% of the animal’s body weight (e.g. 3.5 g for the device described by McHugh et al. (1996), or about 8 g for the device used by Yamamoto and Wilson (2008)). he weight of the electrode