Morphological identification of nitric oxide sources and targets in the cat oculomotor system

Abstract

Nitric oxide (NO) production by specific neurons in the prepositus hypoglossi (PH) nucleus is necessary for the correct performance of eye movements in alert cats. In an attempt to characterize the morphological substrate of this NO function, the distribution of nitrergic neurons and NO-responding neurons has been investigated in different brainstem structures related to eye movements. Nitrergic neurons were stained by either immunohistochemistry for NO synthase I or histochemistry for reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase. The NO targets were identified by cyclic guanosine monophosphate (cGMP) immunohistochemistry in animals treated with a NO donor immediately before fixation of the brain. Connectivity between cells of the NO-cGMP pathway was analyzed by injections of the retrograde tracers horseradish peroxidase or fast blue in different structures. The motor nuclei commanding extraocular muscles did not contain elements of the NO-cGMP pathway, except for some scattered nitrergic neurons in the most caudal part of the abducens nucleus. The PH nucleus contained the largest number of nitrergic cell bodies and a rich neuropil, distributed in two groups in medial and lateral positions in the caudal part, and one central group in the rostral part of the nucleus. An abundant cGMP positive neuropil was the only NO-sensitive element in the PH nucleus, where no cGMP-producing neuronal cell bodies were observed. The opposite disposition was found in the marginal zone between the PH and the medial vestibular nuclei, with a large number of NO-sensitive cGMP-producing neurons and almost no nitrergic cells. Both nitrergic and NO-sensitive cell bodies were found in the medial and inferior vestibular nuclei and in the superior colliculus, whereas the lateral geniculate nucleus contained nitrergic neuropil and a large number of NO-sensitive cell bodies. Some of the cGMP-positive neurons in the marginal zone and medial vestibular nucleus projected to the PH nucleus, predominantly to the ipsilateral side. These morphological findings may help to explain the mechanism of action of NO in the oculomotor system.

Anatomical and pharmacological relationship between acetylcholine and nitric oxide in the prepositus hypoglossi nucleus of the cat: Functional implications for eye‐movement control

“…The presence in the PH nucleus of a dense population of neurons containing NOS I has previously been extensively reported in the rat (Rodrigo et al, 1994;Saxon and Beitz, 2000), cat (Maqbool et al, 1995;Moreno-López et al, 2001), and monkey (Satoh et al, 1995), and their physiological role in the processing of oculomotor signals has been studied in recent years (Moreno-López et al, 1996, 2001. The present results agree with previous studies and contribute new data.…”

“…The present results agree with previous studies and contribute new data. We corroborate the existence of a homogeneous cluster of nitrergic neurons in the rostral part of the nucleus and two separate groups from the middle to the caudal end of the PH nucleus (Moreno-López et al, 2001). Moreover, we now demonstrate that neurons in the latter two clusters differ not only in their situation in the nucleus but also in their mean diameters, confirming the existence of a compartmentalization of the PH nucleus (McCrea and Horn, 2006).…”

“…The mean number of nitrergic neurons in the PH nucleus was 5372 Ϯ 1379.6 (Table 1). As reported previously (Moreno-López et al, 2001), NOS I-positive neurons tended to group in one cluster in the rostralmost part of the PH nucleus (Fig. 2D), and in two clusters at the caudalmost level of the nucleus (Fig.…”

“…The PH nucleus contains a dense population of nitrergic neurons (Rodrigo et al, 1994;Maqbool et al, 1995;MorenoLópez et al, 1996MorenoLópez et al, , 2001, and microinjections of NO synthase inhibitors or NO donors in this nucleus induced a nystagmus with slow phases directed toward the side where the NO concentration was higher (Moreno-López et al, 1996. Retrograde labeling combined with immunohistological studies have demonstrated that GABAergic afferents from the ipsilateral medial vestibular nucleus to the PH nucleus are the main target of NO (Moreno-López et al, 2001. These studies suggest that NO controls the background activity in the PH nucleus by facilitating GABA release from vestibular afferents.…”

Immunoreactivity for calcium-binding proteins defines subregions of the vestibular nuclear complex of the cat

“…In other regions of the central nervous system, neurochemical techniques, including enzyme histochemistry and immunohistochemistry, have shown anatomical subdivisions not apparent in cell or fiber stains. Examples include staining for cytochrome oxidase in visual cortex (Horton and Hubel 1981), and acetylcholinesterase in the superior colliculus and striatum (Graybiel and Ragsdale 1978;Graybiel 1983;Chevalier and Mana 2000), immunoreactivity to nitric oxide synthase in the nucleus prepositus hypoglossi (Moreno-Lopez et al 2001), immunoreactivity to zebrin in the cerebellum (Sillitoe et al 2003), and immunoreactivity to calcium-binding proteins in thalamus and cortex Jones 1991a, 1991b;Rausell et al 1992;Cusick et al 1993;de Venecia et al 1995;Jones et al 1995).…”