GABA‐, glycine‐, and glutamate‐immunoreactive bouton profiles in apposition to neurons of the central cervical nucleus in the rat

Abstract

The neurons of the central cervical nucleus (CCN) convey information about the position and movements of the head, and receive excitatory input from dorsal neck muscles and the labyrinth. Both of these afferent sources form glutamatergic synaptic contacts with CCN neurons. However, these sensory afferent sources can also inhibit CCN neurons. To further elucidate the synaptic organization, we made an electron microscopic investigation, identifying and evaluating the relative frequency of bouton profiles containing the inhibitory transmitters GABA and glycine in apposition to identified CCN neurons. In addition, labeling for glutamate was performed. The identification of the CCN neurons was made possible by injections of retrograde tracer substances into the cerebellum. These substances were made visible by preembedding immunocytochemistry or postembedding immunogold staining. Such staining was also used to detect the three amino acids that were found in boutons apposed to the identified neurons (cf. Ö rnung et al., J. Comp. Neurol. 1996;365:413-426; Lindå et al., J. Comp. Neurol. 2000;425:10-23). Due to the relatively poor transport of the tracer substances into dendrites of the CCN neurons, the analysis was restricted to the cell body and included bouton profiles in direct apposition to the soma membrane. Data from 10 CCN neurons revealed that about 50% of the apposing bouton profiles were immunoreactive for GABA, and about 34% for glycine. In four neurons, the degree of colocalization of GABA and glycine was determined to be close to 30%. Thus, the vast majority of glycine-labeled profiles also contained GABA, while a considerable fraction of the profiles were immunoreactive for only GABA. The values for glycine immunoreactive bouton profiles presented here may represent somewhat low estimates, depending on the method used. Data from four neurons showed that about 18% of the profiles were labeled for glutamate. The large fraction of purely GABA immunoreactive profiles, or at least a substantial group of them, is suggestive of their derivation from axons descending from the brainstem. Anat Key words: amino acid transmitters; electron microscopy; choleragenoid; horseradish peroxidase; postembedding immunocytochemistryThe central cervical nucleus (CCN) is a spinocerebellarspinovestibular cell group in the upper cervical segments of the spinal cord. It has been studied extensively in the rat and cat (Matsushita and Ikeda, 1975;Wiksten, 1975;Petras, 1977;Cummings and Petras, 1977;Hirai et al., 1978;Wiksten, 1979a, b;Carleton and Carpenter, 1983;Wiksten and Grant, 1983; Hirai et al., 1984a, b;Matsushita and Tanami, 1987;Wiksten, 1987;McKelvey-Briggs et al., 1989;Donevan et al., 1990;Neuhuber et al., 1990;Matsushita, 1991;Matsushita et al., 1991;Popova et al., 1995;Sato et al., 1997). Physiological studies have shown that the CCN transmits information about position and movement of the head, both in space (vestibular input) and in relation to the trunk (neck proprioceptive input) (Hirai et al., 1984b;Popova e...

Cytoarchitecture of the Spinal Cord

“…Projections from upper cervical segments to lateral, medial and descending vestibular nuclei also originate from the CeCv (Carleton and Carpenter, 1983;Bankoul and Neuhuber 1992;Matsushita et al, 1995;Xiong and Matsushita, 2001). Calretinin and calmodulin (Ren andRuda, 1994), enkephalin (Ikeda et al, 1995), GABA and glycine (Ragnarson et al, 2002), glutamate (Ornung et al, 1995;Ragnarson et al, 2002;Persson et al, 2006) and parvalbumin (Ren and Ruda, 1994) are found within neurons of the CeCv. Calretinin and calmodulin (Ren andRuda, 1994), enkephalin (Ikeda et al, 1995), GABA and glycine (Ragnarson et al, 2002), glutamate (Ornung et al, 1995;Ragnarson et al, 2002;Persson et al, 2006) and parvalbumin (Ren and Ruda, 1994) are found within neurons of the CeCv.…”