Neuroscience
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The role of transient receptor potential channel A1 (TRPA1) in noxious cold sensation remains unclear. Some data support the hypothesis that TRPA1 is a transducer of noxious cold whilst other data contest it. In this study we investigated the role of TRPA1 in cold detection in cutaneous nociceptors in vivo using complementary experimental approaches. ⋯ In addition, block of the TRPA1 channel with Ruthenium Red did not inhibit cold evoked activity in either cinnamaldehyde sensitive or insensitive cold responsive nociceptors. In cinnamaldehyde-sensitive-cold-sensitive afferents, although TRPA1 agonist-evoked activity was totally abolished by Ruthenium Red, cold evoked activity was unaffected by channel blockade. We conclude that these results do not support the hypothesis that TRPA1-expressing cutaneous afferents play an important role in noxious cold responses.
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A role of neuropeptides in neuropathic pain development has been implicated; however, the neuroimmune interactions that are involved in the underlying mechanisms may be more important than previously thought. To examine a potential role of relations between glia cells and neuropeptides in neuropathic pain, we performed competitive reverse-transcription polymerase chain reaction (RT-PCR) from the dorsal lumbar spinal cord and the dorsal root ganglion (DRG) after chronic constriction injury (CCI) in the rat sciatic nerve. The RT-PCR results indicated that complement component 1, q subcomponent (C1q) mRNA expression was higher than glial fibrillary acidic protein (GFAP) in the spinal cord 3 and 7 days post-CCI, suggesting that spinal microglia and perivascular macrophages are more activated than astrocytes. ⋯ We thus provide novel findings that inhibition of C1q-positive cells by minocycline can diminish injury-induced neuropeptide changes in the DRG. This suggests that immune cells-derived pronociceptive factors may influence opioid peptide expression. Therefore, the injury-induced activation of microglia and leukocytes and the subsequent activation of neuropeptides involved in nociception processes are potential targets for the attenuation of neuropathic pain.
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Stress responses are elicited by a variety of stimuli and are aimed at counteracting direct or perceived threats to the well-being of an organism. In the mammalian central and peripheral nervous systems, specific cell groups constitute signaling circuits that indicate the presence of a stressor and elaborate an adequate response. Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed in central and peripheral parts of these circuits and has recently been identified as a candidate for regulation of the stress axis. ⋯ Here, abundance of transcripts encoding enzymes required for adrenomedullary catecholamine biosynthesis, namely TH (tyrosine hydroxylase) and PNMT (phenylethanolamine N-methyltransferase), was higher in PACAP+/+ mice after 6 h of unrelieved restraint. Our results suggest that sustained corticosterone secretion, synthesis of the hypophysiotropic hormone CRH in the hypothalamus, and synthesis of the enzymes producing the hormone adrenaline in the adrenal medulla, are controlled by PACAP signaling in the mouse. These findings identify PACAP as a major contributor to the stimulus-secretion-synthesis coupling that supports stress responses in vivo.
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The suprachiasmatic nucleus (SCN) is a circadian oscillator and biological clock. Cell-to-cell communication is important for synchronization among SCN neuronal oscillators and the great majority of SCN neurons use GABA as a neurotransmitter, the principal inhibitory neurotransmitter in the adult CNS. Acting via the ionotropic GABA(A) receptor, a chloride ion channel, GABA typically evokes inhibitory responses in neurons via Cl(-) influx. ⋯ NKCC1 is expressed in VIP, GRP and VP neurons in the SCN as is WNK3, a chloride-sensitive neuron-specific with no serine-threonine kinase which modulates intracellular chloride concentration via opposing actions on NKCC and KCC cotransporters. The heterogeneous distribution of cation-chloride cotransporters in the SCN suggests that Cl(-) levels are differentially regulated within VIP/GRP and VP neurons. We suggest that GABA's excitatory action is more likely to be evoked in VP neurons that express KCC4.
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Dopamine (DA) neurons in the ventral tegmental area (VTA) constitute the origin of major dopaminergic neural pathways associated with essential functions including reward, motivation and cognition. Hence, regulation of VTA DA neurons' excitability is of important significance. Like other neurons, the activity level of VTA DA neurons is considerably determined by excitatory and inhibitory synaptic inputs. ⋯ Taken together, we propose that activation of D2-like receptors and GABA(B)R in the VTA enhances presynaptic GIRK channels activity, which in turn leads to reduced GABA release. The consequence of reduced GABA release on VTA DA neurons may contribute to their increased activity. Accordingly, a novel potential regulatory form of VTA DA neurons' excitability, which involves presynaptic potassium channels, is proposed.