DISTINCT MECHANISMS FOR EXPRESSION OF FOS-LIKE IMMUNOREACTIVITY AND SYNAPTIC POTENTIATION IN TELENCEPHALIC HYPERSTRIATUM OF THE QUAIL-CHICK

In the intermediate and medial hyperstriatum ventrale (IMHV), a telenc ephalic region essentially involved in the initial processes of early learning tasks in poultry chicks, induction of an immediate early gene c-fos correlates significantly with the degree of learning (K.V. Anok hin, R. Mileusnic, I.Y. Shamakina, S.P.R. Rose, Effects of early exper ience on c-fos gene expression in the chick forebrain, Brain Res. 544 (1991) 101-107; B.J. McCabe, G. Hem, Learning-related changes in Fos-l ike immunoreactivity in the chick forebrain after imprinting, Proc. Na tl. Acad. Sci. USA 91 (1994) 11417-11421). In slices of IMHV in vitro, on the other hand, tetanic stimulation at a low frequency induces a p otentiation of synaptic responses (P.M. Bradley, B.D. Bums, A.C. Webb, Potentiation of synaptic responses in slices from the chick forebrain , Proc. R. Sec. Lend. B. 243 (1991) 19-24; T. Matsushima, K. Aoki, Pot entiation and depotentiation of DNQX-sensitive fast excitatory synapti c transmission in telencephalon of the quail chick, Neurosci. Lett. 18 5 (1995) 179-182). In this study, we have examined a possible causal l ink between these two forms of activity-dependent processes, c-fos exp ression and synaptic potentiation. C-fos was visualized immunohistoche mically using antibody raised against the Fos-protein, and potentiatio n was evaluated on the basis of field potential responses to local ele ctrical stimulation. Tetanic stimulation (5 Hz x 300 pulses) was requi red for potentiation, but not for c-Sos expression. Conversely, a nega tive correlation appeared between them, and slices with relatively hig h density of Fos-like immunoreactive cells around the stimulation site failed to show potentiation. Furthermore, drugs similarly effective i n blocking potentiation (such as AP5 (NMDA receptor antagonist) and bi cuculline (GABA(A) receptor antagonist)) had different effects On the c-fos induction. While AP5 had minor, if any, effects on c-fos express ion, bicuculline enhanced it selectively around the site of stimulatio n. Our results suggest that these two processes are basically distinct , and could represent different aspects in the formation of memory tra ces in IMHV. (C) 1998 Elsevier Science B.V.