Pain-sensing sensory neurons of the dorsal root ganglion (DRG) can become sensitized or hyperexcitable in response to surgically induced peripheral tissue injury. We investigated the potential role and molecular mechanisms of nociceptive ion channel dysregulation in acute pain conditions such as those resulting from skin and soft tissue incision. We used selective pharmacology, electrophysiology, and mouse genetics to link increased current densities arising from the Ca3.2 isoform of T-type calcium channels (T-channels) to nociceptive sensitization using a clinically relevant rodent model of skin and deep tissue incision. Furthermore, knockdown of the Ca3.2-targeting deubiquitinating enzyme USP5 or disruption of USP5 binding to Ca3.2 channels in peripheral nociceptors resulted in a robust antihyperalgesic effect in vivo and substantial T-current reduction in vitro. Our study provides mechanistic insight into the role of plasticity in Ca3.2 channel activity after surgical incision and identifies potential targets for perioperative pain that may greatly decrease the need for narcotics and potential for drug abuse.
Several studies suggest that voltage-gated calcium currents are involved in generating high frequency burst firing in the subiculum, but the exact nature of these currents remains unknown. Here, we used selective pharmacology, molecular and genetic approaches to implicate Cav3.1-containing T-channels in subicular burst firing, in contrast to several previous reports discounting T-channels as major contributors to subicular neuron physiology. Furthermore, pharmacological antagonism of T-channels, as well as global deletion of CaV3.1 isoform, completely suppressed development of long-term potentiation (LTP) in the CA1-subiculum, but not in the CA3-CA1 pathway. Our results indicate that excitability and synaptic plasticity of subicular neurons relies heavily on T-channels. Hence, T-channels may be a promising new drug target for different cognitive deficits.
Neurotrophins are established molecular mediators of neuronal plasticity in the adult brain. We analyzed the impact of aging on brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) protein isoforms, their receptors, and on the expression patterns of multiple 5′ exon-specific BDNF transcripts in the rat cortex and hippocampus throughout the life span of the rat (6, 12, 18, and 24 months of age). ProNGF was increased during aging in both structures. Mature NGF gradually decreased in the cortex, and, in 24-month-old animals, it was 30 % lower than that in adult 6-month-old rats. The BDNF expression did not change during aging, while proBDNF accumulated in the hippocampus of aged rats. Hippocampal total BDNF mRNA was lower in 12-month-old animals, mostly as a result of a decrease of BDNF transcripts 1 and 2. In contrast to the regionspecific regulation of specific exon-containing BDNF mRNAs in adult animals, the same BDNF RNA isoforms (containing exons III, IV, or VI) were present in both brain structures of aged animals. Deficits in neurotrophin signaling were supported by the observed decrease in Trk receptor expression which was accompanied by lower levels of the two main downstream effector kinases, pAkt and protein kinase C. The proteolytic processing of p75NTR observed in 12-monthold rats points to an additional regulatory mechanism in early aging. The changes described herein could contribute to reduced brain plasticity underlying the age-dependent decline in cognitive function.
Background: The most currently used general anaesthetics are potent potentiators of g-aminobutyric acid A (GABA A ) receptors and are invariably neurotoxic during the early stages of brain development in preclinical animal models. As causality between GABA A potentiation and anaesthetic-induced developmental neurotoxicity has not been established, the question remains whether GABAergic activity is crucial for promoting/enhancing neurotoxicity. Using the neurosteroid analogue, (3a,5a)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), which potentiates recombinant GABA A receptors, we examined whether this potentiation is the driving force in inducing neurotoxicity during development. Methods: The neurotoxic potential of CDNC24 was examined vis-a-vis propofol (2,6-diisopropylphenol) and alphaxalone (5a-pregnan-3a-ol-11,20-dione) at the peak of rat synaptogenesis. In addition to the morphological neurotoxicity studies of the subiculum and medial prefrontal cortex (mPFC), we assessed the extra-, pre-, and postsynaptic effects of these agents on GABAergic neurotransmission in acute subicular slices from rat pups. Results: CDNC24, like alphaxalone and propofol, caused dose-dependent hypnosis in vivo, with a higher therapeutic index. CDNC24 and alphaxalone, unlike propofol, did not cause developmental neuroapoptosis in the subiculum and mPFC. Propofol potentiated post-and extrasynaptic GABA A currents as evidenced by increased spontaneous inhibitory postsynaptic current (sIPSC) decay time and prominent tonic currents, respectively. CDNC24 and alphaxalone had a similar postsynaptic effect, but also displayed a strong presynaptic effect as evidenced by decreased frequency of sIPSCs and induced moderate tonic currents. Conclusions: The lack of neurotoxicity of CDNC24 and alphaxalone may be at least partly related to suppression of presynaptic GABA release in the developing brain.
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