Insensitivity To Pain In Schizophrenia: An Examination Of Sensory And Affective Pain Processing In An Animal Model

Abstract

Patients with schizophrenia have been shown to display decreased sensitivity to pain, which can severely compound the impact of injuries and illnesses. Currently, the reasons for pain insensitivity in this population are unclear. Alterations in both the sensory and affective systems of pain processing have been observed, but the unique contribution of each of these systems has not been elucidated. The aim of this study was to systematically investigate these two components of pain in an animal model of schizophrenia. Animals first underwent L5 spinal nerve ligation surgery in order to provoke a condition of ongoing pain responding. Following recovery from surgery, animals were treated with a combination of 2.58 mg/kg of phencyclidine (PCP), or saline, to induce a condition that parallels human schizophrenia, and 20 mg/kg of the atypical antipsychotic clozapine, or vehicle, in a block design. Responses to mechanical and thermal stimuli were assessed to determine changes in sensory processing, and affective pain processing was examined with the place escape avoidance paradigm. The results showed that animals receiving PCP exhibited decreased sensitivity to mechanical stimulation, and unaltered behavior in the place escape avoidance paradigm. These findings corroborate and strengthen the human literature investigating schizophrenia and alterations in pain perception. Future directions and implications are discussed.