Disrupted visceral feedback reduces locomotor activity and influences background contextual fear conditioning in C57BL/6J0laHsd mice

The present experiments were designed to study fear conditioning as an emotional learning task with disrupted visceral feedback. For that purpose we used the peripherally acting beta 1-adrenoceptor blocker atenolol and studied its effects on the behavior of male C57BL/6JOlaHsd mice in an exploration-related test and during fear-conditioning. In the first experiment, we treated mice with saline or different doses of the beta 1-adrenergic blocker atenolol (5 mg/kg and 20 mg/kg body weight i.p.) 30 min before behavioral testing in a motility box. Only the high but not the low dose of atenolol led to a reduction of locomotor activity (p < 0.02). Factors known to be related to emotionality (rearing, area preference) were unaffected. In a second experiment, saline- and atenolol-treated mice (same dosages and mode of application) were trained for auditory fear conditioning, and 24h later they were retested in the same environment. We found differences between the effects of atenolol upon contextual- and cue-fear conditioning. Animals treated with 20 mg/kg BW doses of atenolol showed significantly decreased background contextual fear compared to saline-treated control animals. In contrast, no differences were found during CS presentation in the conditioning context between atenolol-treated animals and saline-treated controls, independent from a paired or an unpaired conditioning paradigm, Thus, the blockade of peripheral beta 1-adrenoceptors by atenolol may have disrupted the positive feedback to the central nervous system via visceral afferents resulting in a decreased locomotor activity and background contextual fear. (c) 2007 Elsevier B.V. All rights reserved.