ABSTRACT
In recent years, the rabbit nictitating (NM) membrane preparation has been used extensively to examine cellular activity in different brain regions during classical conditioning (Berger, Alger, & Thompson, 1976; Berger & Thompson, 1977, 1978a,b; Berry & Thompson, 1978; Cegavske, Patterson, & Thompson, 1979; Thompson, Berger, Berry, & Hoehler, 1980). In the early phases of adopting this preparation for use with electrophysiological techniques, we focused our analysis on the neural activity of limbic system structures, most notably that of the hippocampus. Primarily two reasons led us to do so. First, a well-known literature has established an important role for the hippocampus and related structures in human and animal memory function (Berger &Orr, 1982; Milner, 1966; O'Keefe&Nadel, 1978; Olton, Becker, & Handelmann, 1979; Squire, 1982; Squire & Zola-Morgan, 1982). Second, an abundance of information exists concerning anatomical and electrophysiological characteristics of hippocampal neurons (Anderson, 1959; Andersen, 1960 a ,b; Andersen, Eccles, & Løyning, 1964a ,b; Blackstad, 1956; Lorentede No*, 1934; MacVicar & Dudek, 1980; Nicholl & Alger, 1981; Raisman, Cowan, & Powell, 1965; Ramon y Cajal, 1911; Schwartzkroin, 1975; Spencer &Kandel, 1968; Swanson, Sawchenko, & Cowan, 1980; Swanson, Wyss, & Cowan, 1978; Wong, Prince, & Basbaum, 1979). In particular, the connectional relations of the principal hippocampal cells to their major afferent and efferent brain structures have been well defined and well characterized (Hjorth-Simonsen & Jeune, 1972; Jacobs, Foote, & Bloom, 1978; Loy, Koziell, Lindsey, & Moore, 1980; Mosko, Lynch, & Cotman, 1973; Nauta, 1956; Raisman, Cowan, & Powell, 1966; Steward, 1976; Swanson & Cowan, 1977; Swanson, Wyss, & Cowan, 1980). Coupled with the organizational simplicity of the structure (Andersen, Bliss, & Skrede, 1971a), the latter information allows recording from identified anatomical cell types during conditioning with knowledge of the relative position of that cell type within the circuitry of the hippocampus as a whole. Because of these conditions, we felt there was a high probability: (1) that any changes in hippocampal cellular activity recorded during conditioning would be relevant to normal mnemonic processes; (2) that we would distinguish changes in cellular activity that are "local" to the hippocampus from those that are occurring in afferent regions and are merely reflected in hippocampal responsivity; (3) that if changes in cellular responses are occurring within the hippocampus, the antecedent neural activity necessary for the development of hippocampal cellular plasticity could be described accurately; and (4) that the effect of changes in hippocampal activity on efferent target neurons could be determined.
