5‐Hydroxytryptamine, substance P, and thyrotropin‐releasing hormone in the adult cat spinal cord segment L₇: Immunohistochemical and chemical studies

Abstract

The terminal projections of the descending 5-hydroxytryptamine (5-HT) bulbospinal pathway and the coexistence among 5-HT-, substance P (SP)-, and thyrotropin-releasing hormone (TRH)-like immunoreactivities (LI) in fibers innervating the L7 segment in the cat spinal cord were studied quantitatively and semiquantitatively by use of the indirect double-staining immunofluorescence technique. The content of 5-HT, SP, and TRH in different parts of the spinal cord was determined by use of radioimmunoassay (RIA) (SP and TRH) and high-performance liquid chromatography with electrochemical detection (HPLC-ECD) (5-HT). For all three substances studied, immunoreactive (IR) axon terminals were found in all parts of the gray matter, but with clear regional variation in the density of innervation. Thus, all three substances showed a dense innervation in the motor nucleus, particularly in the ventral part of the nucleus, while the superficial dorsal horn was very densely innervated by SP-IR fibers (laminae I and II) and TRH-IR fibers (laminae II and III). In the motor nucleus, the studied substances coexisted to a very high degree, but some 5-HT-IR fibers (about 10%) lacked peptide-LI and some SP-IR fibers (about 10%) lacked 5-HT-LI while virtually all TRH-IR fibers also contained 5-HT-LI. In the superficial dorsal horn (laminae I-III), no coexistence was detected, while other parts of the gray matter displayed various degrees of coexistence in between those found in the motor nucleus and laminae I-III. The quantitative analysis of IR varicosities in the motor nucleus suggested that the unilateral L7 motor nucleus is innervated by about 55-110 x 10(6) 5-HT-IR nerve terminals, which may indicate as many as 4,000 boutons per descending 5-HT cell body in the brain stem only with this restricted projection. When combing these results with the biochemical data, it could be calculated that the concentration of 5-HT in IR varicosities is about 3-6 x 10(-3) M, while the corresponding figures for SP and TRH was 0.3-0.5 x 10(-3) M and 0.1-0.2 x 10(-3) M, respectively. In cats subjected to spinal cord transection at the lower thoracic level, all 5-HT-IR fibers in the L7 segment had disappeared 44 days after the lesion, indicating a strict suprasegmental origin of 5-HT-IR fibers in this segment.(ABSTRACT TRUNCATED AT 400 WORDS)

The organization of the brainstem and spinal cord of the mouse: Relationships between monoaminergic, cholinergic, and spinal projection systems

“…Because the RPa and ROb preferentially innervate the ventral horn, whereas the RMg and adjacent tegmentum project predominantly to the dorsal horn in rat and cat (Basbaum and Fields, 1979;Skagerberg and Björklund, 1985), this finding suggests that relatively few 5HT-IR neurons project to the dorsal horn in the mouse. Indeed, using the same anitsera, the 5HT-IR fiber distribution in the spinal superficial dorsal horn was less prominent in our study in the mouse compared to the rat (Johnson et al, 1993) and cat (Arvidsson et al, 1990b).…”

“…In addition, there was a strong serotoninergic innervation of the mouse somatic motor nuclei throughout the spinal cord, similar to that described in the cat (Arvidsson et al, 1990b), primate (Arvidsson et al, 1990a), and rat (Jones and Light, 1990;Marlier et al, 1991). These 5HT-IR axons mainly originate from RPa/ROb neurons and modulate the excitability of somatic motoneurons (Hounsgaard et al, 1988).…”

Anatomical distribution of serotonin‐containing neurons and axons in the central nervous system of the cat

“…1d, L1, 8C) (Krukoff et al, 1985). 8D) Arvidsson et al, 1990;Ramirez-Leon et al, 1994). At all levels of the spinal cord, dense networks of immunolabeled fibers, a number of which were large varicose, were visualized in layer I (marginal zone; Fig.…”

Purines released from astrocytes inhibit excitatory synaptic transmission in the ventral horn of the spinal cord

“…In order to adapt to internal and external changes, the organism adjusts neuronal activity by different cellular mechanisms providing high degrees of flexibility on time scales ranging from milliseconds to hours. The activity of spinal networks is regulated by descending pathways releasing neuromodulators such as serotonin, noradrenaline, glutamate or GABA (Arvidsson et al, 1990; Jacobs and Azmitia, 1992; Ono and Fukuda, 1995; Schmidt and Jordan, 2000; Conn et al, 2005; Farrant and Nusser, 2005; Perrier and Delgado-Lezama, 2005; Cotel et al, 2013; Perrier et al, 2013). Flexibility is also ensured by intrinsic modulatory systems releasing transmitters such as endocannabinoids (Ameri, 1999; El Manira and Kyriakatos, 2010) or purines (Dale and Gilday, 1996).…”