Functional and anatomical analyses of active spinal circuits in a mouse model of chronic pain.

ABSTRACT: Decades of efforts in elucidating pain mechanisms, including pharmacological, neuroanatomical, and physiological studies have provided insights into how nociceptive information transmits from the periphery to the brain and the locations receiving nociceptive signals. However, little is known about which specific stimulus-dependent activated neurons, amongst heterogeneous neural environments, discriminatively evoke the cognate pain behavior. We here shed light on the population of neurons in the spinal cord activated by a painful stimulus to identify chronic pain-dependent activated neuronal subsets using Fos2A-iCreER (TRAP2) mice. We have found a large number of neurons activated by a normally nonpainful stimulus in the spinal cord of spinal nerve-ligated mice, compared with sham. Neuronal activation was observed in laminae I and II outer under heat hyperalgesia. A large number of neurons in laminae II inner were activated in both mechanical allodynia and heat hyperalgesia conditions, while mechanical allodynia tends to be the only stimulus that activates cells at lamina II inner dorsal region. Neuroanatomical analyses using spinal cell markers identified a large number of spinal inhibitory neurons that are recruited by both mechanical allodynia and heat hyperalgesia. Of interest, spinal neurons expressing calretinin, calbindin, and parvalbumin were activated differently with distinct pain modalities (ie, mechanical allodynia vs heat hyperalgesia). Chemogenetic inhibition of those activated neurons significantly and specifically reduced the response to the pain stimulus associated with the stimulus modality originally given to the animals. These findings support the idea that spinal neuronal ensembles underlying nociceptive transmission undergo dynamic changes to regulate selective pain responses.

Fearing Pain at the End of Life: A Review of Advance Directives.

BACKGROUND: Patients, caregivers, and healthcare professionals often describe a "good death" as a pain-free process. However, many patients experience pain during their last weeks of life. Advance directives (ADs) are legally binding documents that allow individuals to express their wishes for end-of-life care which should include management of their pain. METHODS: An interprofessional team conducted a comprehensive analysis of ADs from all 50 states and the District of Columbia to assess the inclusion of language that reflects patients' wishes for pain relief at the end of life. RESULTS: Thirty-seven (73%) of the 51 entities examined reflected the prototypical directive, containing explicit instructions for withholding or withdrawing interventions that may prolong suffering rather than options for treating pain. Of these, 12 (24%) did not include the word "pain". Only 14 states (27%) provided clear guidance for managing pain. Unexpectantly, researchers found that 13 (25%) addressed the common fears of patients, caregivers, and healthcare teams when using opioids to relieve suffering, such as addiction, sedation, appetite, or respiratory suppression, and hastening death. CONCLUSION: The majority of ADs reviewed lacked clear and comprehensive measures for addressing pain relief. This deficiency may contribute to the undertreatment of pain and amplify the anxiety felt by patients, families, and healthcare providers when making end-of-life decisions. The results highlight the need for improvements in ADs to help ensure that patients' wishes regarding pain management are adequately addressed, documented and respected.