Temporary inactivation of the dorsal entorhinal cortex impairs acquisition and retrieval of spatial information

We tested the effects of temporary inactivation of the dorsal entorhinal cortex on spatial discrimination using a conditioned cue preference (CCP) paradigm. The three phases of the procedure were: pre-exposure: unreinforced exploration of the center platform and two adjacent arms of an eight-arm radial maze; training: rats were confined to the ends of the two arms on alternate days - one arm always contained food and the other never contained food; testing: unreinforced exploration of the center platform and the two arms. Rats that received bilateral infusions of saline into the dorsal entorhinal cortex before the training trials or before the test trial spent significantly more time in the arm that previously contained food than in the arm that never contained food, demonstrating that they had acquired and were able to express information that discriminated between the two adjacent maze arms. In contrast, rats that received bilateral, intra-entorhinal infusions of muscimol, a gamma-aminobutyric acid(a) (GABA(a)) agonist, before either training or testing spent equal amounts of time in the two arms, indicating that they failed to acquire and were unable to express this information. Interactions between the entorhinal cortex and hippocampus in the acquisition and expression of the information required for this discrimination are discussed.