A cytoarchitectonic and TH-immunohistochemistry characterization of the dopamine cell groups in the substantia nigra, ventral tegmental area and retrorubral field in the rock cavy (Kerodon rupestris).

The 3-hydroxytyramine/dopamine is a monoamine of the catecholamine group and it is a precursor of the noradrenaline and adrenaline synthesis, in which the enzyme tyrosine hydroxylase acts as a rate-limiting enzyme. The dopaminergic nuclei retrorubral field (A8 group), substantia nigra pars compacta (A9 group) and ventral tegmental area (A10 group) are involved in three complex circuitries named mesostriatal, mesocortical and mesolimbic, which are directly related to various behavioral manifestations such as motor control, reward signaling in behavioral learning, motivation and pathological manifestations of Parkinson's disease and schizophrenia. The aim of this study was to describe the delimitation of A8, A9 and A10 groups and the morphology of their neurons in the brain of the rock cavy (Kerodon rupestris), a typical Brazilian Northeast rodent belonging to the suborder Hystricomorpha, family Caviidae. Coronal and sagittal sections of the rock cavy brains were submitted to Nissl staining and TH immunohistochemistry. The organization of these dopaminergic nuclei in the rock cavy brain is very similar to that found in other animals of the Rodentia order, except for the presence of the tail of the substantia nigra, which is found only in the species under study. The results revealed that, apart some morphological variations, A8, A9 and A10 groups are phylogenetically stable brain structures.

Nuclear organization of the serotonergic system in the brain of the rock cavy (Kerodon rupestris).

Serotonin, or 5-hydroxytryptamine (5-HT), is a substance found in many tissues of the body, including as a neurotransmitter in the nervous system, where it can exert different post-synaptic actions. Inside the neuro-axis, 5-HT neurons are almost entirely restricted to the raphe nuclei of the brainstem. As such, 5-HT-immunoreactivity has been considered a marker of the raphe nuclei, which are located in the brainstem, at or near the midline. The present study investigated distribution of serotonergic neurons in the brain of the rock cavy (Kerodon rupestris), a rodent species inhabiting the Brazilian Northeast. The cytoarchitectonic location of serotonergic neurons was established through a series of 5-HT immunostained sections, compared with diagrams obtained from adjacent coronal and sagittal sections stained by the Nissl method. The following nuclei were defined: the rostral group, consisting of rostral linear raphe, caudal linear raphe, median and paramedian raphe, dorsal raphe, and pontine raphe nuclei, and the caudal group composed of raphe magnus, raphe pallidus and raphe obscurus nuclei. Other serotonergic neuronal clusters, such as the supralemniscal group and the rostral and caudal ventrolateral medulla oblongata clusters, were found outside the midline. Rare 5-HT-producing neurons were identified in the lateral parabrachial nucleus and in the pontine reticular formation, mostly along fibers of the lateral lemniscus. Despite exhibiting some specializations, the picture outlined for serotonergic groups in the rock cavy brain is comparable to that described for other mammalian species.

Expression of the immediate-early gene egr-1 and substance P in the spinal cord following locomotor training in adult rats.

The immediate-early gene egr-1 has been shown to have an increased expression during long-term potentiation (LTP). High frequency electrical stimulation induces an increase in such expression in the dorsal horn of the spinal cord. However, evidence demonstrating the activation of this gene in the spinal cord and its relationship with LTP is still scarce. The substance P (SP) has also been associated with LTP in the dorsal horn of the spinal cord following high frequency stimulation. Here we evaluated the expression of both Egr-1 and SP in the sacrolumbar area of the spinal cord after locomotor training in adult rats. Increased neuronal Egr-1 expression was found in the spinal cord sections in rats that underwent locomotor training, especially in laminae IV and X across L3-S4 levels (p<0.05). Conversely, SP expression in synaptic terminals was not altered in the abovementioned regions. Our results suggest that locomotor training activates mechanisms in a similar way to LTP, and is involved in the synaptic plasticity in the spinal cord. The results also indicate that variations in the training protocol influence Egr-1 expression. Such events appear not to be directly influenced by SP, which suggests a plastic process that differs from those triggered by nociceptive stimuli.