Age-related changes in neurochemical components and retinal projections of rat intergeniculate leaflet.

Aging leads to several anatomical and functional deficits in circadian timing system. In previous works, we observed morphological alterations with age in hypothalamic suprachiasmatic nuclei, one central component of this system. However, there are few data regarding aging effects on other central components of this system, such as thalamic intergeniculate leaflet (IGL). In this context, we studied possible age-related alterations in neurochemical components and retinal projections of rat IGL. For this goal, young (3 months), adult (13 months), and aged (23 months) Wistar rats were submitted to an intraocular injection of neural tracer, cholera toxin subunit b (CTb), 5 days before a tissue fixation process by paraformaldehyde perfusion. Optical density measurements and cell count were performed at digital pictures of brain tissue slices processed by immunostaining for glutamic acid decarboxylase (GAD), enkephalin (ENK), neuropeptide Y (NPY) and CTb, characteristic markers of IGL and its retinal terminals. We found a significant age-related loss in NPY immunoreactive neurons, but not in immunoreactivity to GAD and ENK. We also found a decline of retinal projections to IGL with age. We conclude aging impairs both a photic environmental clue afferent to IGL and a neurochemical expression which has an important modulatory circadian function, providing strong anatomical correlates to functional deficits of the aged biological clock.

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.