ON AND OFF FIELD POTENTIALS IN THE RAT SUPERIOR COLLICULUS DURING DEVELOPMENT

The present investigation is aimed at characterizing the development o f ON and OFF visually evoked responses in the rat superior colliculus from postnatal day 13 (P13) to postnatal day 25, Depth profiles of fie ld potentials reveal that ON and OFF long latency biphasic held potent ials are already present when collicular cells are first responsive to light (P13), There is an inversion in the polarity of these reponses as the electrode penetrates the collicular layers, suggesting a synapt ic organization similar to the one found in adult animals. At P15, OFF field potentials begin to exhibit oscillatory activity, Local cobalt injections within the superior colliculus abolishes these OFF oscillat ions, suggesting a postsynaptic origin. Fast Fourier transform (FFT) a nalysis of the OFF field potentials demonstrates that oscillatory acti vity increases in frequency during development, This increase is thoug ht to reflect the myelination and stabilization of synaptic connection s that occur during this period, To our knowledge, this is the first r eport of OFF oscillatory responses in the superior colliculus. (C) 199 7 Elsevier Science Ltd.