Chronic administration of phencyclidine produces decreased sensitivity to mechanical stimulation in the absence of altered affective behavior: Implications for pain processing in schizophrenia

Evaluation of acute and chronic nociception in subchronically administered MK-801-induced rat model of schizophrenia

Patients diagnosed with schizophrenia have been reported to exhibit atypically low pain sensitivity and to vary in their experience of chronic pain. To the best of our knowledge, there has yet to be an animal study that provides information concerning the relationship between models of schizophrenia and pain. In the present study, we investigated several distinct nociceptive behaviors in a translational rat model of schizophrenia (0. 5 mg/kg MK-801, twice a day for 7 days followed by a 7-day washout period). The presence of the expected cognitive deficit was confirmed with novel object recognition (NOR) paradigm prior to nociception testing. MK-801-treated rats with lack of novelty interest in NOR testing showed: hyposensitivity to thermal and mechanical stimuli; short-term hypoalgesia followed by augmented hyperalgesia in response to formalin-induced spontaneous nociception and increased thermal and mechanical hyperalgesia in the complete Freund's adjuvant (CFA) induced chronic pain model. In conclusion, MK-801 induced antinociception effects for thermal stimuli in rats that were consistent with the decreased pain sensitivity observed in schizophrenia patients. Additionally, the amplified biphasic response exhibited by the MK-801 group in the formalin-induced spontaneous nociception test affirms the suitability of the test as a model of acute to delayed pain transition.

Reduced pain perception in patients with schizophrenia; A missed case of hand fracture

Altered pain perception among patients with schizophrenia is often underrecognized in the medical community. The cause is not known, and medical professionals are not sure whether these patients experience less pain or are simply unable to express it. There are documented cases of patients with schizophrenia presenting to hospital settings with serious injuries without obvious (expected) pain. Research into the underlying cause(s) is underway; meanwhile, ensuring awareness of this issue among medical providers is of upmost importance. We report a case of a patient with schizophrenia who presented voluntarily to the emergency department (ED) with a hand fracture that went unrecognized in the ED and further discuss the implications of reduced pain perception. Additionally, we summarize existing hypotheses regarding the source of this reduced pain perception in this population.