Synaptic connections of the neurokinin 1 receptor-like immunoreactive neurons in the rat medullary dorsal horn

Descending projections from the insular cortex to the trigeminal spinal subnucleus caudalis facilitate excitatory outputs to the parabrachial nucleus in rats

ABSTRACT

Nociceptive information from the orofacial area projects to the trigeminal spinal subnucleus caudalis (Sp5C) and is then conveyed to several nuclei, including the parabrachial nucleus (PBN). The insular cortex (IC) receives orofacial nociceptive information and sends corticofugal projections to the Sp5C. The Sp5C consists of glutamatergic and GABAergic/glycinergic interneurons that induce excitatory postsynaptic currents and inhibitory postsynaptic currents, respectively, in projection neurons. Therefore, quantification of glutamatergic IC inputs in combination with identifying postsynaptic neuronal subtypes is critical to elucidate IC roles in the regulation of Sp5C activities. We investigated features of synaptic transmission from the IC to glutamatergic and GABAergic/glycinergic Sp5C neurons of laminae I/II using vesicular GABA transporter-Venus transgenic rats that received an injection of adeno-associated virus-channelrhodopsin-2-mCherry into the IC. Selective stimulation of IC axon terminals in Sp5C slice preparations induced monosynaptic excitatory postsynaptic currents in both excitatory glutamatergic and inhibitory GABAergic/glycinergic Sp5C neurons with a comparable amplitude. Paired whole-cell patch-clamp recordings showed that unitary inhibitory postsynaptic currents from inhibitory neurons influencing excitatory neurons, including neurons projecting to the PBN, exhibited a high failure rate and were suppressed by both bicuculline and strychnine, suggesting that excitatory neurons in the Sp5C receive both GABAergic and glycinergic inhibition with low impact. Moreover, selective stimulation of IC axons increased the firing rate at the threshold responses. Finally, we demonstrated that selective stimulation of IC axons in the Sp5C by a chemogenetic approach decreased the thresholds of both mechanical and thermal nociception. Thus, IC projection to the Sp5C is likely to facilitate rather than suppress excitatory outputs from the Sp5C.

Involvement of descending serotonergic and noradrenergic pathways in CB1 receptor-mediated antinociception

Cannabinoids produce antinociceptive and antihyperalgesic effects mainly through activation of the inhibitory CB1 receptors. The demonstration that antinociceptive effects of systemic cannabinoids are significantly diminished following surgical dorsolateral funiculus lesion provides evidence that supraspinal sites and descending pain modulatory pathways play crucial roles in systemic cannabinoid analgesia. In this review, we will firstly provide a background, brief overview of descending modulatory pathways followed by descending pathways implicated in cannabinoid analgesia. We will then describe the recent evidence of the involvement of descending serotonergic and noradrenergic pathways in CB1 receptor-mediated antinociception. This review will provide evidences that systemically administered cannabinoids reinforce the descending serotonergic and noradrenergic pathways to produce acute antinociceptive effects via spinal 5-HT7, 5-HT2A and alpha-2 adrenoceptors activation.

The expression of dopa decarboxylase and dopamine beta hydroxylase and their responding to bacterial challenge during the ontogenesis of scallop Chlamys farreri

Dopa decarboxylase (DDC) and dopamine beta hydroxylase (DBH) is responsible for the synthesis of dopamine and norepinephrine, respectively. In the present study, dopa decarboxylase (CfDDC) and dopamine beta hydroxylase (CfDBH) were selected as indicator to investigate the development of catecholaminergic nervous system in the larvae of scallop Chlamys farreri. The CfDDC and CfDBH transcripts were all detectable during the whole ontogenesis expect for the CfDDC transcripts in 2-cell embryos stage. The expression level of CfDDC and CfDBH mRNA increased significantly in the veliger stage, and reached the peak in late (35.64-fold, P < 0.05) and mid-veliger (400.21-fold, P < 0.05) larvae, respectively. By immunofluorescence, two CfDDC immunoreactive areas were observed in the trochophore and D-hinged larvae, and then three CfDDC immunoreactive areas and two immunopositive fibres formed in early and late veliger larvae, respectively. Two CfDBH immunopositive fibers appeared initially in the early D-hinged stage, and another two similar fibers developed in the late D-hinged stage. The bacteria Vibrio anguillarum challenge could induce the mRNA expression of CfDDC and CfDBH in different developmental stage. The significantly increase of CfDDC mRNA was observed in the trochophore larvae at 12 h (8.61-fold, P < 0.05) and in late D-hinged larvae at 24 h (1.56-fold, P < 0.05) post challenge. The expression level of CfDBH mRNA decreased significantly in late D-hinged larvae at 6 h (0.45-fold, P < 0.05), whereas it increased significantly in late veliger larvae at 12 h after bacterial challenge (14.52-fold, P < 0.05). These results concluded that the scallop catecholaminergic nervous system appeared firstly as the form of dopaminergic neurons in the trochophore larvae, and the developing catecholaminergic nervous system in the trochophore, D-hinged and veliger larvae of scallop could respond to the immune stimulation in different patterns.