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Serotonergic axonal contacts on identified cat trigeminal motoneurons and their correlation with medullary raphe nucleus stimulation
Author(s) -
Nagase Yoshitaka,
Moritani Masayuki,
Nakagawa Shinji,
Yoshida Atsushi,
Takemura Motohide,
Zhang LiFeng,
Kida Hideki,
Shigenaga Yoshio
Publication year - 1997
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/(sici)1096-9861(19970804)384:3<443::aid-cne9>3.0.co;2-3
Subject(s) - excitatory postsynaptic potential , raphe , biology , raphe nuclei , serotonergic cell groups , serotonergic , neuroscience , stimulation , postsynaptic potential , nucleus , anatomy , serotonin , inhibitory postsynaptic potential , biochemistry , receptor
The innervation of the trigeminal motor nucleus by serotonergic fibers with cell bodies in the raphe nuclei pallidus and obscurus suggests that activation of this pathway may alter the excitability of trigeminal motoneurons. Thus, we recorded intracellular responses from cat jaw‐closing (JC) and jaw‐opening (JO) α‐motoneurons evoked by raphe stimulation and used a combination of intracellular staining of horseradish peroxidase (HRP) and immunohistochemistry at the light and electron microscopic levels to examine the distribution of contacts made by serotonin (5‐HT)‐immunoreactive boutons on the two motoneurons types. Electrical stimulation applied to the nucleus raphe pallidus‐obscurus complex induced a monosynaptic excitatory postsynaptic potential (EPSP) in JC (masseter) α‐motoneurons and an EPSP with an action potential in JO (mylohyoid) α‐motoneurons. The EPSP rise‐times (time to peak) and half widths were significantly longer in the JC than in the JO motoneurons. The EPSPs were suppressed by systemic administration of methysergide (2 mg/kg). Six JC and seven JO α‐motoneurons were well stained with HRP. Contacts were seen between 5‐HT‐immunoreactive boutons and the motoneurons. The JC motoneurons received a significantly larger number of the contacts than did the JO motoneurons. The contacts were distributed widely in the proximal three‐fourths of the dendritic tree of JC motoneurons but were distributed on more proximal dendrites in the JO motoneurons. At the electron microscopic level, synaptic contacts made by 5‐HT‐immunoreactive boutons on motoneurons were identified. The present study demonstrated that JC motoneurons receive stronger 5‐HT innervation, and this correlates with the fact that raphe stimulation caused larger EPSPs among these neurons than among JO motoneurons. J. Comp. Neurol. 384:443–455, 1997. © 1997 Wiley‐Liss, Inc.