Substance P-containing primary afferent receives inhibitory modulation directly from enkephalin- and GABA-containing interneurons in the dorsal horn of the chicken

The role of spinal orexin-1 receptors in posterior hypothalamic modulation of neuropathic pain

“…OX 1 R are probably not on primary afferent terminals, excitatory interneuron, or projection neurons, which would increase nociceptive transmission when excited, a finding not in line with our observations (Figure 4). Based on our findings, OX 1 R are more likely to activate GABA, glycine or enkephalin containing neurons in the dorsal horn which are inhibitory in nature (Tsuruhara and Takahashi, 1987, Atsumi et al, 1993, Fleming and Todd, 1994, Jonas et al, 1998, Kerchner et al, 2001, Kodama and Kimura, 2002, Liu et al, 2002, Moore et al, 2002, Baba et al, 2003, Peever et al, 2003, Dergacheva et al, 2005, Ataka and Gu, 2006). Although there is no evidence for colocalization of OX 1 R on GABA, glycine, or enkephalin neurons to date, based on the antinociceptive role demonstrated in the present study, and the excitatory nature of orexin-A, it is likely that orexin-A neurons in the PH have an indirect inhibitory role on nociception in the dorsal horn by activating inhibitory interneurons, which then inhibit primary afferent terminals or projection neurons.…”

Neurokinin-1 Receptor Immunoreactive Neuronal Elements in the Superficial Dorsal Horn of the Chicken Spinal Cord: With Special Reference to Their Relationship with the Tachykinin-containing Central Axon Terminals in Synaptic Glomeruli

“…The other subclass was conventional dendrites, which seemed to originate from projection neurons from lamina I and/or deeper laminae, or stalked cells of lamina II origin [31]. As we previously reported, a proportion of both subclasses of dendrites in the chicken spinal cord may contain GABA and/or enkephalin [2, 27]. …”

“…Lamina II of the adult rat dorsal horn has been reported to display only weak NK-1R-like immunoreactivity, although the greatest concentration of substance P-immunoreactive, i.e. tachykinin-immunoreactive, primary afferent axons has been observed in this region [2, 3, 7, 18, 21, 34]. In the present study, a certain number of lamina II neurons expressed NK-1R immunoreactivities as well as lamina I and lamina IV neurons (Fig.…”

“…We reported that substance P-immunoreactive primary afferents often formed synaptic glomeruli as central terminals through lamina II of the chicken spinal cord [26]. We also reported that the substance P-immunoreactive central terminals were not only pre-synaptic, but also post-synaptic to glycine-, gamma amino-butyric acid (GABA)- and enkephalin-immunoreactive neuronal elements in the chicken dorsal horn [2, 27]. Therefore, we speculated that nociceptive sensation is likely to be modified through the exchange of information among neuronal elements in the synaptic glomeruli.…”

“…The previous NK-1R immunohistochemical studies, however, indicated that NK-1Rs are preferentially contained in excitatory neuronal elements in the rat spinal dorsal horn [14]. If this is true for the chicken, the peripheral elements in the synaptic glomeruli that appear to contain inhibitory neurotransmitter [2, 27] may not show NK-1R immunoreactivities. In the above case, substance P in the central axon terminals does not play any role in the activation of peripheral elements, although the peripheral elements and the central axon terminals apparently have a close inter-relationship in the synaptic glomeruli.…”