Central nucleus of the amygdala in descending control of pain-related behavior

The central nucleus of amygdala (CeA) is known to be involved in pain and nociception, but the mechanisms or its role in descending control of pain-related behavior is poorly understood. The aim of this study was to investigate the involvement of the neuropeptide corticotropin-releasing factor (CRF) and the glutamatergic system of the CeA in pain and nociception in healthy control animals and in an animal model of chronic neuropathic pain induced by spared-nerve injury (SNI). Two aspects of pain were studied: emotional-like pain behavior was assessed by using the aversive place-avoidance paradigm and sensory-discriminative was assessed by determining the mechanical limb-withdrawal threshold and the thermal (heat) limb-withdrawal latency. Moreover, the aims were to determine whether medullospinal serotoninergic pathways and the midbrain periaqueductal grey (PAG), respectively, were involved in relaying pain-modulation induced by the CeA in SNI and healthy control animals. Additionally, hemisphere of the CeA and submodality of pain stimulus were among studied parameters. Surgical procedures and electrophysiological recordings were performed under general anesthesia. The studies on the role of the CeA in the emotional-like aspect of pain in SNI rats revealed that activation and blocking of the group I metabotropic glutamate receptors (mGluRs) facilitates and inhibits, respectively, the aversive aspect of pain. Furthermore, increase of endogenous CRF as well as blocking glutamatergic N-methyl-D-aspartate (NMDA) receptors in the CeA reduced the aversive aspect of neuropathic pain. The studies on the sensory-discriminative aspect of pain revealed that an increase of endogenous CRF in the CeA is pronociceptive in both control and SNI rats. CeA injection of a high dose of glutamate had a mechanical antinociceptive effect that was mediated by NMDA receptors in healthy but not SNI rats. A low dose of glutamate had a pronociceptive effect mediated by NMDA receptors in SNI rats. Furthermore, tonic descending pronociception induced by NMDA receptors and the mGluR1 in the CeA contributes to the maintenance of neuropathic hypersensitivity. The investigation on the role of serotonergic neurons of the rostroventromedial medulla (RVM) in modulation of spinal nociception by amygdaloid glutamate in SNI rats indicated that the RVM is a relay for both descending pro- and antinociceptive effects from the CeA. The investigation on the role of the PAG in the descending control of nociception induced by glutamate in the CeA of healthy rats indicated that the PAG is a relay in the descending control of nociception induced by amygdaloid glutamate. Furthermore, the right-hemispheric lateralization of the pronociceptive effect by amygdaloid CRF in controls was lost in SNI rats. However, descending antinociception induced by the glutamatergic system of the CeA showed no hemispheric lateralization in healthy controls; a high dose of glutamate in both the left and right CeA induced equal attenuations of mechanical and thermal nociception, which effects were, respectively, NMDA-dependent and NDMA-independent.

Influence of amygdaloid glutamatergic receptors on sensory and emotional pain-related behavior in the neuropathic rat

The role of amygdaloid glutamatergic receptors (GluRs) in maintenance of the sensory versus emotional component of neuropathic pain was studied by assessing monofilament-induced limb withdrawal response (sensory pain) and aversive place-conditioning behavior (emotional pain) following amygdaloid administration of various glutamatergic compounds in nerve-injured animals. The results indicate that endogenous activation of amygdaloid group I metabotropic GluRs, mGluR(1) and mGluR(5), and the NMDA-R contributes to maintenance of sensory and emotional components of neuropathic pain. The predominant effect by amygdaloid group I mGluRs was facilitation of emotional-like pain behavior.This study was supported by the Academy of Finland, Helsinki, Finland, the Sigrid Juselius Foundation, Helsinki, Finland, the Center for International Mobility (CIMO), Helsinki, Finland, the Portuguese Foundation for Science and Technology, Lisbon, Portugal, and the Gulbenkian Foundation, Lisbon, Portugal

Polyethylene terephthalate (PET) micro- and nanoplastic particles affect the mitochondrial efficiency of human brain vascular pericytes without inducing oxidative stress

The objective of this investigation was to evaluate the influence of micro- and nanoplastic particles composed of polyethylene terephthalate (PET), a significant contributor to plastic pollution, on human brain vascular pericytes. Specifically, we delved into their impact on mitochondrial functionality, oxidative stress, and the expression of genes associated with oxidative stress and ferroptosis. Our findings demonstrate that the exposure of a monoculture of human brain vascular pericytes to PET particles in vitro at a concentration of 50 ppm for a duration of 6 days did not elicit oxidative stress. Notably, we observed an augmentation in various aspects of mitochondrial respiration, including extracellular acidification, proton pump leakage, maximal respiration, spare respiratory capacity, and ATP production in pericytes subjected to PET particles. Furthermore, there were no statistically significant alterations in mitochondrial DNA copy number, or the expression of genes linked to oxidative stress and ferroptosis. These outcomes suggest that, at a concentration of 50 parts per million (ppm) and for 6 days exposure, PET particles do not induce oxidative stress in human brain vascular pericytes. Instead, they seem to incite a potential mitochondrial hormesis, also named mitohormesis, response, which seemingly enhances mitochondrial function. Further investigations are warranted to explore the stages of mitohormesis and the potential consequences of plastics on the integrity of the blood-brain barrier and intercellular interactions. This research contributes to our comprehension of the potential repercussions of nanoplastic pollution on human health and underscores the imperative need for ongoing examinations into the exposure to plastic particles

Forward genetics identifies a novel sleep mutant with sleep state inertia and REM sleep deficits

Switches between global sleep and wakefulness states are believed to be dictated by top-down influences arising from subcortical nuclei. Using forward genetics and in vivo electrophysiology, we identified a recessive mouse mutant line characterized by a substantially reduced propensity to transition between wake and sleep states with an especially pronounced deficit in initiating rapid eye movement (REM) sleep episodes. The causative mutation, an lle102Asn substitution in the synaptic vesicular protein, VAMP2, was associated with morphological synaptic changes and specific behavioral deficits, while in vitro electrophysiological investigations with fluorescence imaging revealed a markedly diminished probability of vesicular release in mutants. Our data show that global shifts in the synaptic efficiency across brain-wide networks leads to an altered probability of vigilance state transitions, possibly as a result of an altered excitability balance within local circuits controlling sleep-wake architecture.ISSN:2375-254