Serotonin 5‐HT1B receptor‐mediated calcium influx‐independent presynaptic inhibition of GABA release onto rat basal forebrain cholinergic neurons

Modulatory roles of serotonin (5‐HT) in GABAergic transmission onto basal forebrain cholinergic neurons were investigated, using whole‐cell patch‐clamp technique in the rat brain slices. GABA_A receptor‐mediated inhibitory postsynaptic currents (IPSCs) were evoked by focal stimulation. Bath application of 5‐HT (0.1–300 μm ) reversibly suppressed the amplitude of evoked IPSCs in a concentration‐dependent manner. Application of a 5‐HT_1B receptor agonist, CP93129, also suppressed the evoked IPSCs, whereas a 5‐HT_1A receptor agonist, 8‐OH‐DPAT had little effect on the evoked IPSCs amplitude. In the presence of NAS‐181, a 5‐HT_1B receptor antagonist, 5‐HT‐induced suppression of evoked IPSCs was antagonised, whereas NAN‐190, a 5‐HT_1A receptor antagonist did not antagonise the 5‐HT‐induced suppression of evoked IPSCs. Bath application of 5‐HT reduced the frequency of spontaneous miniature IPSCs without changing their amplitude distribution. The effect of 5‐HT on miniature IPSCs remained unchanged when extracellular Ca²⁺ was replaced by Mg²⁺. The paired‐pulse ratio was increased by CP93129. In the presence of ω‐CgTX, the N‐type Ca²⁺ channel blocker, ω‐Aga‐TK, the P/Q‐type Ca²⁺ channel blocker, or SNX‐482, the R‐type Ca²⁺ channel blocker, 5‐HT could still inhibit the evoked IPSCs. 4‐AP, a K⁺ channel blocker, enhanced the evoked IPSCs, and CP93129 had no longer inhibitory effect in the presence of 4‐AP. CP93129 increased the number of action potentials elicited by depolarising current pulses. These results suggest that activation of presynaptic 5‐HT_1B receptors on the terminals of GABAergic afferents to basal forebrain cholinergic neurons inhibits GABA release in Ca²⁺ influx‐independent manner by modulation of K⁺ channels, leading to enhancement of neuronal activities.     

Transcriptome response to infraorbital nerve transection in the gonadally intact male rat barrel cortex: RNA‐seq

The effects of infraorbital nerve (ION) transection on gene expression in the adult male rat barrel cortex were investigated using RNA sequencing. After a 24‐hour survival duration, 98 genes were differentially regulated by ION transection. Differentially expressed genes suggest changes in neuronal activity, excitability, and morphology. The production of mRNA for neurotrophins, including brain‐derived neurotrophin factor (BNDF), was decreased following ION transection. Several potassium channels showed decreased mRNA production, whereas a sodium channel (Na_Vβ4) associated with burst firing showed increased mRNA production. The results may have important implications for phantom‐limb pain and complex regional pain syndrome. Future experiments should determine the extent to which changes in RNA result in changes in protein expression, in addition to utilizing laser capture microdissection techniques to differentiate between neuronal and glial cells. J. Comp. Neurol. 524:152–159, 2016. © 2015 Wiley Periodicals, Inc.     

Vagal Intramuscular Arrays: The Specialized Mechanoreceptor Arbors That Innervate the Smooth Muscle Layers of the Stomach Examined in the Rat

The fundamental roles that the stomach plays in ingestion and digestion notwithstanding, little morphological information is available on vagal intramuscular arrays (IMAs), the afferents that innervate gastric smooth muscle. To characterize IMAs better, rats were given injections of dextran biotin in the nodose ganglia, and, after tracer transport, stomach whole mounts were collected. Specimens were processed for avidin–biotin permanent labeling, and subsets of the whole mounts were immunohistochemically processed for c‐Kit or stained with cuprolinic blue. IMAs (n = 184) were digitized for morphometry and mapping. Throughout the gastric muscle wall, IMAs possessed common phenotypic features. Each IMA was generated by a parent neurite arborizing extensively, forming an array of multiple (mean = 212) branches averaging 193 µm in length. These branches paralleled, and coursed in apposition with, bundles of muscle fibers and interstitial cells of Cajal. Individual arrays averaged 4.3 mm in length and innervated volumes of muscle sheet, presumptive receptive fields, averaging 0.1 mm³. Evaluated by region and by muscle sheet, IMAs displayed architectural adaptations to the different loci. A subset (32%) of circular muscle IMAs issued specialized polymorphic collaterals to myenteric ganglia, and a subset (41%) of antral longitudinal muscle IMAs formed specialized net endings associated with the serosal boundary. IMAs were concentrated in regional patterns that correlated with the unique biomechanical adaptations of the stomach, specifically proximal stomach reservoir functions and antral emptying operations. Overall, the structural adaptations and distributions of the IMAs were consonant with the hypothesized stretch receptor roles of the afferents. J. Comp. Neurol. 524:713–737, 2016. © 2015 Wiley Periodicals, Inc.