Tone-specific and nonspecific plasticity of the auditory cortex elicited by pseudo-conditioning: Role of acetylcholine receptors and the somatosensory cortex Running title: Cortical plasticity elicited by pseudo-conditioning

Experience-dependent plastic changes in the central sensory systems are due to activation of both the sensory and neuromodulatory systems. Nonspecific changes of cortical auditory neurons elicited by pseudo-conditioning are quite different from tone-specific changes of the neurons elicited by auditory fear conditioning. Therefore, the neural circuit evoking the nonspecific changes must also be different from that evoking the tone-specific changes. We first examined changes in the response properties of cortical auditory neurons of the big brown bat elicited by pseudo-conditioning with unpaired tonal (CSu) and electric leg (USu) stimuli and found that it elicited nonspecific changes to CSu (a heart-rate decrease, an auditory response increase, a broadening of frequency tuning and a decrease in threshold) and, in addition, a small tone-specific change to CSu (a small short-lasting best frequency shift) only when CSu frequency was 5 kHz lower than the best frequency of a recorded neuron. We then examined the effects of drugs on the cortical changes elicited by the pseudoconditioning. The development of the nonspecific changes was little affected by atropine (a muscarinic cholinergic receptor antagonist) and mecamylamine (a nicotinic cholinergic receptor antagonist) applied to the auditory cortex and by muscimol (a GABA-A receptor agonist) applied to the somatosensory cortex. However, these drugs abolished the small short-lasting tone-specific change as they abolished the large long-lasting tone-specific change elicited by auditory fear conditioning. Our current results indicate that, different from the tone-specific change, the nonspecific changes depend on neither the cholinergic neuromodulator nor the somatosensory cortex.