Neuronal nitric oxide synthase immunopositive neurons in cat vestibular complex: a light and electron microscopic study

Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless, there are little data about the neuronal nitric oxide synthase immunoreactivity (nNOS-ir) in the vestibular complex of a cat. In this respect, the aims of this study were to: (1) demonstrate nNOS-ir in the neurons and fibers, from all major and accessory vestibular nuclei; (2) describe their light microscopic morphology and distribution; (3) investigate and analyze the ultrastructure of the NOS I-immunopositive neurons, fibers, and synaptic boutons. For demonstration of the nNOS-ir, the peroxidase–antiperoxidase–diaminobenzidin method was applied. Immunopositive for nNOS neurons and fibers were present in all major and accessory vestibular nuclei. On the light microscope level, the immunopositive neurons were different in shape and size. According to the latter, they were divided into four groups—small (with diameter less than 15 μm), medium-sized (with diameter from 15 to 30 μm), large type I (with diameter from 30 to 40 μm), and large type II (with diameter greater than 40 μm). On the electron microscope level, the immunoproduct was observed in neurons, dendrites, and terminal boutons. According to the ultrastructural features, the neurons were divided into three groups—small (with diameter less than 15 μm), medium-sized (with diameter from 15 to 30 μm), and large (with diameter greater than 30 μm). At least two types of nNOS-ir synaptic boutons were easily distinguished. As a conclusion, we hope that this study will contribute to a better understanding of the functioning of the vestibular complex in cat and that some of the data presented could be extrapolated to other mammals, including human.