J Comp Physiol A (2008) 194:1063–1075 DOI 10.1007/s00359-008-0377-4 123 ORIGINAL PAPER Receptive Weld properties of neurons in the electrosensory lateral line lobe of the weakly electric Wsh, Gnathonemus petersii Michael G. Metzen · Jacob Engelmann · João Bacelo · Kirsty Grant · Gerhard von der Emde Received: 21 December 2007 / Revised: 9 September 2008 / Accepted: 23 September 2008 / Published online: 15 October 2008  Springer-Verlag 2008 Abstract The receptive Weld of a sensory neuron is known as that region in sensory space where a stimulus will alter the response of the neuron. We determined the spatial dimensions and the shape of receptive Welds of electrosen- sitive neurons in the medial zone of the electrosensory lat- eral line lobe of the African weakly electric Wsh, Gnathonemus petersii, by using single cell recordings. The medial zone receives input from sensory cells which encode the stimulus amplitude. We analysed the receptive Welds of 71 neurons. The size and shape of the receptive Welds were determined as a function of spike rate and Wrst spike latency and showed diVerences for the two analysis methods used. Spatial diameters ranged from 2 to 36 mm (spike rate) and from 2.45 to 14.12 mm (Wrst spike latency). Some of the receptive Welds were simple consisting only of one uniform centre, whereas most receptive Welds showed a complex and antagonistic centre-surround organisation. Several units had a very complex structure with multiple centres and surrounding-areas. While receptive Weld size did not correlate with peripheral receptor location, the com- plexity of the receptive Welds increased from rostral to cau- dal along the Wsh’s body. Keywords Centre-surround organisation · Receptive Weld size · Spike rate · First spike latency · Fovea Abbreviations CN Command nucleus CS Command signal EOCD Electric organ corollary discharge EOD Electric organ discharge ELL Electrosensory lateral line lobe lat First spike latency PS Point stimulus PSTH Peri-stimulus time histogram RF Receptive Weld SR Spike rate Introduction The weakly electric Wsh Gnathonemus petersii is one of the best studied model systems concerning active electroloca- tion. In these Wsh, active electrolocation is based on the generation of brief electrical pulses of about 400 s dura- tion that are generated by an electric organ in the tail (Liss- mann and Machin 1958). The resulting 3D electric Weld is perceived by specialised cutaneous electroreceptor organs. In the context of active electrolocation, these electrorecep- tors are the mormyromasts which contain diVerent sensory cells (A- and B-cells). Whereas A-cells respond in propor- tion to amplitude-modulations of the EOD, B-cells are additionally sensitive to the shape of the EOD (Szabo and Wersäll 1970; Bell 1990a; von der Emde and Bleckmann 1992). Nearby objects alter the local transepidermal volt- age, which is the adequate stimulus for the A-cells of the mormyromasts, and are thus detected by the Wsh. The aVer- ent Wbres of A-cells terminate exclusively in the medial zone of the ELL (Bell et al. 1989). Even though higher amplitudes increase the number of spikes, it is thought that these Wbres code the EOD-amplitude in form of a latency- M. G. Metzen (&) · J. Engelmann · G. von der Emde Department of Neuroethology/Sensory Ecology, Institute of Zoology, University of Bonn, Endenicher Allee 11-13, 53115 Bonn, Germany e-mail: michael.metzen@uni-bonn.de J. Engelmann · J. Bacelo · K. Grant Unité de Neurosciences Intégratives et Computationnelles, C.N.R.S., 1 Avenue de la Terrasse, 91198 Gif sur Yvette, France