Different roles for M1 and M2 receptors within perirhinal cortex in object recognition and discrimination

• Pre-sample infusions of M1 and M2 antagonists into PRh impaired object recognition.
• M1 antagonists impaired oddity discrimination performance, but not a M2 antagonist.
• PRh M1 and M2 receptors have distinct functions in recognition and discrimination.

Recognition and discrimination of objects and individuals are critical cognitive faculties in both humans and non-human animals, and cholinergic transmission has been shown to be essential for both of these functions. In the present study we focused on the role of M1 and M2 muscarinic receptors in perirhinal cortex (PRh)-dependent object recognition and discrimination. The selective M1 antagonists pirenzepine and the snake toxin MT-7, and a selective M2 antagonist, AF-DX 116, were infused directly into PRh. Pre-sample infusions of both pirenzepine and AF-DX 116 significantly impaired object recognition memory in a delay-dependent manner. However, pirenzepine and MT-7, but not AF-DX 116, impaired oddity discrimination performance in a perceptual difficulty-dependent manner. The findings indicate distinct functions for M1 and M2 receptors in object recognition and discrimination.