Distribution of nitric oxide in the rock cavy (Kerodon rupestris) brain II: The brainstem.

In a recent paper, we described the distribution of Nitric oxide (NO) in the diencephalon of the rock cavy (Kerodon rupestris). This present paper follows this work, showing the distribution of NO synthesizing neurons in the rock cavy's brainstem. For this, we used immunohistochemistry against the neuronal form of nitric oxide synthase (NOS) and NADPH diaphorase histochemistry. In contrast to the diencephalon in the rock cavy, where the NOS neurons were seen to be limited to some nuclei in the thalamus and hypothalamus, the distribution of NOS in the brainstem is widespread. Neurons immunoreactive to NOS (NOS-ir) were seen as rostral as the precommissural nuclei and as caudal as the caudal and gelatinous parts of the spinal trigeminal nucleus. Places such as the raphe nuclei, trigeminal complex, superior and inferior colliculus, oculomotor complex, periaqueductal grey matter, solitary tract nucleus, laterodorsal tegmental nucleus, pedunculopontine tegmental, and other nuclei of the reticular formation are among the locations with the most NOS-ir neurons. This distribution is similar, but with some differences, to those described for other rodents, indicating that NO also has an important role in rock cavy's physiology.

Distribution of nitric oxide synthase in the rock cavy (Kerodon rupestris) brain I: The diencephalon.

Nitric oxide (NO) is a highly soluble and membrane-permeable neurotransmitter, so it does not need to be packed in vesicles or have a membrane receptor. In the nervous system, NO is synthesized by the neuronal form of the nitric oxide synthase (NOS) enzyme and has been considered as a local neurotransmitter. NOS distribution is widespread in the nervous system of various vertebrate species, which may explain its participation in many functions such as memory, blood pressure regulation and sexual behavior. Here we used immunohistochemistry against NOS and NADPH diaphorase histochemistry to map the distribution of NO in the diencephalon of the rock cavy (Kerodon rupestris), a rodent endemic to the Brazilian Northeast. Rock cavy has crepuscular habits and is adapted to ecological conditions such as heat and scarcity of water and food. This study found that NOS distribution was more concentrated in the hypothalamus of this animal. Among the hypothalamic nuclei, the median preoptic, supraoptic, paraventricular nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, ventral and dorsal premammillary nucleus, supramammillary nucleus, lateral mammillary nucleus and dorsal hypothalamic nucleus had the largest collections of NOS immunoreactive (NOS-ir) neurons. Some nuclei of the thalamus and epithalamus such as the paraventricular nucleus of the thalamus, the ventral lateral geniculate nucleus, the medial geniculate nucleus and the lateral habenula showed NOS-ir neurons. This distribution is similar to that described in other rodents, indicating that NO also has an important role in rock cavy's physiology.