Parabrachial Nucleus Activity in Nociception and Pain in Awake Mice

Abstract

The parabrachial nuclear complex (PBN) is a nexus for aversion, and for the sensory and affective components of pain perception. We have previously shown that, during chronic pain, PBN neurons in anesthetized rodents have amplified activity. We report a method to record from PBN neurons of behaving, head-restrained mice, while applying reproducible noxious stimuli. We find that both spontaneous and evoked activity are higher in awake animals, compared to urethane anesthetized mice. Fiber photometry of calcium responses from CGRP-expressing PBN neurons demonstrates that these neurons respond to noxious stimuli. In both males and females with neuropathic or inflammatory pain, responses of PBN neurons remain amplified for at least 5 weeks, in parallel with increased pain metrics. We also show that PBN neurons can be rapidly conditioned to respond to innocuous stimuli, after pairing with noxious stimuli. Finally, we demonstrate that changes in PBN neuronal activity are correlated with changes in arousal, measured as changes in pupil area.Significance Statement:The parabrachial complex is a nexus of aversion, including pain. We report a method to record from parabrachial nucleus neurons of behaving mice, while applying reproducible noxious stimuli. This allowed us to track parabrachial activity over time in animals with neuropathic or inflammatory pain. It also allowed us to show that the activity of these neurons correlates with arousal states, and that these neurons can be conditioned to respond to innocuous stimuli.

Combined Experiments with <i>in Vivo</i> Fiber Photometry and Behavior Tests Can Facilitate the Measurement of Neuronal Activity in the Primary Somatosensory Cortex and Hyperalgesia in an Inflammatory Pain Mice Model

“…Previous studies have reported that the in vivo fiber photometry system could monitor the deep brain regions such as the ACC and prefrontal cortex, which comprise the pain matrix. [12][13][14][15][16] The results of these studies suggested that combination experiments of in vivo fiber photometry and behavior tests enable us to understand the interaction between changes of neuronal activities in pain matrix which contribute to affective component of pain and pain modulation, pain induced anxiety, or cognition of pain. On the other hand, we also monitored changes of calcium responses in the S1 cortex before and after administration of CFA, resulting that averaged amplitude of calcium responses in S1 were significantly increased 3 or 7 d after injection of CFA, in present study.…”

“…Recently, to identify the involvement of neuronal activities in the pain matrix in the development of chronic pain symptoms such as the sensory and affective components of pain, combined experiment with the behavior tests and in vivo calcium imaging using fiber photometry was applied. [12][13][14][15][16] The effects of drugs such as dexmedetomidine and duloxetine into ACC in chronic or inflammatory pain model mice with expressed GCaMP were measured using this combined experiment. As the results, administration of abovementioned drugs reduced the calcium responses of glutamatergic neurons in ACC and showed the anti-anxiety like behaviors.…”

“…12,14) Moreover, other previous studies also reported that the change of neuronal responses in parabrachial nucleus, ACC, or basolateral amygdala could be monitored using in vivo fiber photometry system in several pain model mice. 13,15,16) Thus, these combined experiment of this optical system and behavior tests seemed to be useful to understand the mechanism of causing chronic pain or to examine the effects of analgesics or pain treatments.…”