Synaptic Connections of the Neurokinin 1 Receptor-Like Immunoreactive Neurons in the Rat Medullary Dorsal Horn

Abstract

The synaptic connections between neurokinin 1 (NK1) receptor-like immunoreactive (LI) neurons and γ-aminobutyric acid (GABA)-, glycine (Gly)-, serotonin (5-HT)- or dopamine-β-hydroxylase (DBH, a specific marker for norepinephrinergic neuronal structures)-LI axon terminals in the rat medullary dorsal horn (MDH) were examined under electron microscope by using a pre-embedding immunohistochemical double-staining technique. NK1 receptor-LI neurons were observed principally in laminae I and III, only a few of them were found in lamina II of the MDH. GABA-, Gly-, 5-HT-, or DBH-LI axon terminals were densely encountered in laminae I and II, and sparsely in lamina III of the MDH. Some of these GABA-, Gly-, 5-HT-, or DBH-LI axon terminals were observed to make principally symmetric synapses with NK1 receptor-LI neuronal cell bodies and dendritic processes in laminae I, II and III of the MDH. The present results suggest that neurons expressing NK1 receptor within the MDH might be modulated by GABAergic and glycinergic inhibitory intrinsic neurons located in the MDH and 5-HT- or norepinephrine (NE)-containing descending fibers originated from structures in the brainstem.

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

“…Two CfDBH immunopositive fibers appeared firstly in the early D-hinged stage, and then other two fibers developed in the late D-hinged stage, which extended to the pedal ganglia in the veliger larvae. Because DBH was only expressed in norepinephrinergic/epinephrinergic neurons in the catecholaminergic nervous system [37,38], the immunoreactivity of CfDBH could be indicator of the norepinephrinergic/epinephrinergic neurons in scallop larvae. While DDC could be expressed both in dopaminergic and norepinephrinergic/epinephrinergic neurons [31], its immunoreactivity could be considered as the indicator of the dopaminergic neurons when there was no CfDBH immunoreactivity.…”

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

“… 6 , 21 , 49 , 63 Lamina II, the substantia gelatinosa, is another layer that consistently responds to nociceptive stimuli 2 and involves GABA/glycinergic neurons projecting to lamina I. 5 , 47 , 62 Therefore, lamina II neurons are considered to regulate outputs from the Sp5C. Interestingly, neurons in laminae I and II receive dense modulatory projections such as adrenergic and serotonergic inputs 10 , 12 , 47 , 59 in addition to nociceptive inputs from the peripheral nervous system.…”

“… 5 , 47 , 62 Therefore, lamina II neurons are considered to regulate outputs from the Sp5C. Interestingly, neurons in laminae I and II receive dense modulatory projections such as adrenergic and serotonergic inputs 10 , 12 , 47 , 59 in addition to nociceptive inputs from the peripheral nervous system. Therefore, the Sp5C is considered to play a critical role in nociception regulation in the trigeminal nervous system.…”