AI Article Synopsis

  • Researchers explored how sensory signals from the urinary bladder connect in the spinal cord, focusing on synapses and neurotransmitters, primarily using advanced microscopy techniques.
  • They found that bladder afferent boutons in the spinal parasympathetic nucleus (SPN) form more connections with postsynaptic dendrites than those in the dorsal horn (DH), indicating a greater potential for synaptic plasticity in the SPN.
  • The study also revealed that in the DH, these boutons receive more inhibitory signals, suggesting that the processing of signals from the urinary bladder differs significantly between these two spinal regions compared to somatosensory information.

Article Abstract

That visceral sensory afferents are functionally distinct from their somatic analogues has been known for a long time but the detailed knowledge of their synaptic connections and neurotransmitters at the first relay nucleus in the spinal cord has been limited. To provide information on these topics, we investigated the synapses and neurotransmitters of identified afferents from the urinary bladder to the superficial laminae of the rat spinal dorsal horn (DH) and the spinal parasympathetic nucleus (SPN) by tracing with horseradish peroxidase, quantitative electron microscopical analysis, and immunogold staining for GABA and glycine. In the DH, most bladder afferent boutons formed synapses with 1-2 postsynaptic dendrites, whereas in the SPN, close to a half of them formed synapses with 3-8 postsynaptic dendrites. The number of postsynaptic dendrites and dendritic spines per bladder afferent bouton, both measures of synaptic divergence and of potential for synaptic plasticity at a single bouton level, were significantly higher in the SPN than in the DH. Bladder afferent boutons frequently received inhibitory axoaxonic synapses from presynaptic endings in the DH but rarely in the SPN. The presynaptic endings were GABA- and/or glycine-immunopositive. The bouton volume, mitochondrial volume, and active zone area, all determinants of synaptic strength, of the bladder afferent boutons were positively correlated with the number of postsynaptic dendrites. These findings suggest that visceral sensory information conveyed via the urinary bladder afferents is processed differently in the DH than in the SPN, and differently from the way somatosensory information is processed in the spinal cord.

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Source
http://dx.doi.org/10.1002/cne.24725DOI Listing

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