5‐HT_1A receptor localization on the axon hillock of cervical spinal motoneurons in primates

Abstract

Serotonin (5-HT) has direct and specific effects on the activity of spinal cord motoneurons. The 5-HT1A receptor has been shown to mediate motoneuron responses in spinal reflex pathways using the highly selective 5-HT1A receptor agonist 8-OH-DPAT. We have developed an antipeptide antibody that recognizes a specific region (the second external loop) of the 5-HT1A receptor. This 5-HT1A receptor antibody labels populations of neurons and glia in the primate cervical spinal cord. The highest receptor density is present in the superficial lamina of the dorsal horn, around the central canal, and on the axon hillock of large ventral horn motoneurons. The cellular labeling pattern on motoneurons shows a single, densely stained, tapering process emanating from the perikaryon. A more diffuse label is also present throughout the soma. Dendritic labeling was not apparent. These results suggest that post-synaptic 5-HT1A receptors may be involved in modulating spinal motoneuron activity at the key site of action potential initiation, the axon hillock.

Cellular localization of the 5-HT receptor in primate brain neurons and glial cells

“…It has previously been suggested that cortical py ramidal neurons contain a significant number of 5-HTIA receptors (Francis et al 1992). The 5-HT 1A receptor-IR of the axon hillock has also been reported in the monkey s pinal cord (Kheck et al 1995). The reason for the locali zed concentration of 5-HT 1A rcceptor-IR with the 51A-170 anti peptide antibody is certainly due to the s pecific cpitope selected (aa 170-186).…”

“…'Ci fic pattern of immunoreactivity observed in brain and s pin"l cord sections. The antigen peptide was serially diluted from 750 mg/ mlto 0.075 mg/ ml with affinity pu rified SIA -\ 70 antibody (1/6OCXJ) and mixed for 4 to 6 hours under constant agitation prior to incubation of tissue slices (Kheck et al 1995). No specific sltlining in tissue slices above background labeling was detected with the preimmune serum and a gradual blockade was secn with the serially diluted p reabsorbcd serum (total blocking occurrt""-d at 7.5 mg/ ml).…”

Respiratory Abnormalities Resulting from Midcervical Spinal Cord Injury and their Reversal by Serotonin 1A Agonists in Conscious Rats

“…function experimentally (Lalley et al, 1994;Sahibzada et al, 2000;Teng et al, 2003) and clinically (Mendelsohn et al, 1991). Although the precise mechanisms are not clear, antibody studies have demonstrated the presence of 5-HT 1A on the axon hillocks of ventral horn motoneurons in the cervical spinal cord of primates (Kheck et al, 1995), possibly indicating a direct stimulatory pathway (Takahashi and Berger, 1990;Richmonds and Hudgel, 1996). Because the greatest density of 5-HT 1A receptors is found in the superficial layers of the dorsal horns of the spinal cord (Thor et al, 1993;Kheck et al, 1995), we also reasoned that 5-HT 1A agonists may, alternatively, act on a pathway involving the afferents from respiratory muscles to supraspinal respiratory centers (Teng et al, 1999).…”

Arthropod 5-HT2Receptors: A Neurohormonal Receptor in Decapod Crustaceans That Displays Agonist Independent Activity Resulting from an Evolutionary Alteration to the DRY Motif

“…For example, 5-HT receptors could be located near the siz in all but the PD and PY motoneurons. This has been shown for primate motoneurons, for example, in which 5-HT 1A receptors are concentrated at the axon hillock (Kheck et al, 1995). The sizs for stomatogastric neurons are thought to reside in the large diameter processes in the coarse neuropil (Raper, 1979;Miller, 1980).…”