Intracellular study of direct entorhinal inputs to field CA1 in the isolated guinea pig brain in vitro

✍ Scribed by Denis Paré; Rodolfo Llinás

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 444 KB
• Volume: 5
• Category: Article
• ISSN: 1050-9631
• DOI: 10.1002/hipo.450050205

✦ Synopsis

While tri-synaptic entorhinal inputs have been shown repeatedly to exert potent effects on CAI pyramidal neurons, the role of the monosynaptic entorhinal input has remained something of a mystery as physiological studies dealing with this issue have yielded contradictory results. Indeed, some in vivo and in vitro studies reported that perforant path stimulation elicits robust monosynaptic excitatory responses in CAI (Doller and Weight, 1982; Yeckel and Berger, 1990), whereas others described that the monosynaptic component of the perforant path evoked only small field potentials that could not elicit population spikes in field CA1 (hdersen et al., 1966b; Colbert and Levy, 1992; Park and Llinis, 1994).

In the present study, we re-investigated this issue in the isolated, arterially perfused whole brain preparation at the intracelldar level. This approach is well suited for this problem because it preserves the hippocampal network and permits visualization of the entorhinal cortex. Direct entorhinal stimulation is preferable to perforant path stimulation because it circumvents the problems of interpretation related to the artificial activation of entorhinal axons ending at a particular level of field CAI but originating in distributed sices of the entorhinal cortex. In addition, because of the complete sensory de-afferentation and low temperature at which whole brain experiments are conducted, this preparation eliminates the need for anesthetics that could interfere with some components of PP-evoked responses.

Barbiturate-anesthetized (Somnotol, 35 mg/kg) Hartley guinea pigs (1 50-200 g) were perfused intracardially with a cold (lO"C), oxygenated