Retinorecipient areas in the common marmoset (Callithrix jacchus): An image-forming and non-image forming circuitry.

The mammalian retina captures a multitude of diverse features from the external environment and conveys them via the optic nerve to a myriad of retinorecipient nuclei. Understanding how retinal signals act in distinct brain functions is one of the most central and established goals of neuroscience. Using the common marmoset (Callithrix jacchus), a monkey from Northeastern Brazil, as an animal model for parsing how retinal innervation works in the brain, started decades ago due to their marmoset's small bodies, rapid reproduction rate, and brain features. In the course of that research, a large amount of new and sophisticated neuroanatomical techniques was developed and employed to explain retinal connectivity. As a consequence, image and non-image-forming regions, functions, and pathways, as well as retinal cell types were described. Image-forming circuits give rise directly to vision, while the non-image-forming territories support circadian physiological processes, although part of their functional significance is uncertain. Here, we reviewed the current state of knowledge concerning retinal circuitry in marmosets from neuroanatomical investigations. We have also highlighted the aspects of marmoset retinal circuitry that remain obscure, in addition, to identify what further research is needed to better understand the connections and functions of retinorecipient structures.

Cytoarchitecture and myeloarchitecture of the entorhinal cortex of the common marmoset monkey (Callithrix jacchus).

The entorhinal cortex (EC) is associated with impaired cognitive function such as in the case of Alzheimer's disease, Parkinson's disease and Huntington's disease. The present study provides a detailed analysis of the cytoarchitectural and myeloarchitectural organization of the EC in the common marmoset Callithrix jacchus. Data were collected using Nissl and fiber stained preparations, supplemented with acetylcholinesterase and parvalbumin immunohistochemistry. The EC layers and subfields in the marmoset seem to be architectonically similar to those that have been proposed in nonhuman primates and humans to date; however, slight differences could be revealed using the present techniques. Throughout its rostrocaudal length, the entorhinal cortex presents a clear six-layered pattern. The entorhinal cortex is divided into six fields, named mainly in accordance to their rostrocaudal and mediolateral positions. At rostral levels, the neurons tend to be organized in patches that are surrounded by large, thick, radially oriented bundles of fibers, and the deep layers are poorly developed. At caudal levels, the divisions are more laminated in appearance. AChE staining at the borders of adjacent fields are consistent with the changes in layering revealed in Nissl-stained sections, of which the lateral regions of the EC display denser AChE staining than that of the medial banks. PV immunoreactivity was found in the labeled somata, dendrites, and axons in all layers and subdivisions. Additionally, we distinguished three subtypes of PV-immunoreactive neurons: multipolar, bipolar and spherical-shaped neurons, based on the shape of the somata and the disposition of the dendrites.

Region-specific glial hyperplasia and neuronal stability of rat lateral geniculate nucleus during aging.

The normal aging process is accompanied by functional declines in image-forming and non-image forming visual systems. Among the components of these systems, the thalamic lateral geniculate nucleus (LGN) offers a good model for aging studies since its three anatomical subdivisions, namely dorsal lateral geniculate nucleus (dLGN), intergeniculate leaflet (IGL) and ventral lateral geniculate nucleus (vLGN), receives light information from retina and projects to different brain areas involved in visual-related functions. Nevertheless, there is very little data available about quantitative morphological aspects in LGN across lifespan. In this study, we used design-based stereology to estimate the number of neurons, glial cells, the glia/neuron ratio and the volume of the LGN of Wistar rats from 3, 13 or 23months of age. We examined each LGN subdivision processed by immunohistochemistry for NeuN and Nissl counterstain. We observed no significant age-related neuronal loss in any nuclei and a 21% and 33% significant increase in dLGN and IGL glial cells of 23month-old rats. We also observed the glia/neuron relation increases in dLGN of 13month-old rats and in dLGN, IGL and vLGN internal portion of 23month-old ones. Moreover, we report an age-related increase in IGL volume. These results show region-specific glial hyperplasia during aging within LGN nuclei, perhaps due to compensatory responses to inflammation. In addition, we observed the glia/neuron ratio as a more sensitive parameter to quantify age-related alterations. Hence, we provide an updated and expanded quantitative characterization of these visual-related thalamic nuclei and its variability across lifespan.

Nuclear organization of the substantia nigra, ventral tegmental area and retrorubral field of the common marmoset (Callithrix jacchus): A cytoarchitectonic and TH-immunohistochemistry study.

It is widely known that the catecholamine group is formed by dopamine, noradrenaline and adrenaline. Its synthesis is regulated by the enzyme called tyrosine hydroxylase. 3-hydroxytyramine/dopamine (DA) is a precursor of noradrenaline and adrenaline synthesis and acts as a neurotransmitter in the central nervous system. The three main nuclei, being the retrorubral field (A8 group), the substantia nigra pars compacta (A9 group) and the ventral tegmental area (A10 group), are arranged in the die-mesencephalic portion and are involved in three complex circuitries - the mesostriatal, mesolimbic and mesocortical pathways. These pathways are involved in behavioral manifestations, motricity, learning, reward and also in pathological conditions such as Parkinson's disease and schizophrenia. The aim of this study was to perform a morphological analysis of the A8, A9 and A10 groups in the common marmoset (Callithrix jacchus - a neotropical primate), whose morphological and functional characteristics support its suitability for use in biomedical research. Coronal sections of the marmoset brain were submitted to Nissl staining and TH-immunohistochemistry. The morphology of the neurons made it possible to subdivide the A10 group into seven distinct regions: interfascicular nucleus, raphe rostral linear nucleus and raphe caudal linear nucleus in the middle line; paranigral and parainterfascicular nucleus in the middle zone; the rostral portion of the ventral tegmental area nucleus and parabrachial pigmented nucleus located in the dorsolateral portion of the mesencephalic tegmentum. The A9 group was divided into four regions: substantia nigra compacta dorsal and ventral tiers; substantia nigra compacta lateral and medial clusters. No subdivisions were made for the A8 group. These results reveal that A8, A9 and A10 are phylogenetically stable across species. As such, further studies concerning such divisions are necessary in order to evaluate the occurrence of subdivisions that express DA in other primate species, with the aim of characterizing its functional relevance.

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.

Morphological changes in the suprachiasmatic nucleus of aging female marmosets (Callithrix jacchus).

The suprachiasmatic nuclei (SCN) are pointed to as the mammals central circadian pacemaker. Aged animals show internal time disruption possibly caused by morphological and neurochemical changes in SCN components. Some studies reported changes of neuronal cells and neuroglia in the SCN of rats and nonhuman primates during aging. The effects of senescence on morphological aspects in SCN are important for understanding some alterations in biological rhythms expression. Therefore, our aim was to perform a comparative study of the morphological aspects of SCN in adult and aged female marmoset. Morphometric analysis of SCN was performed using Nissl staining, NeuN-IR, GFAP-IR, and CB-IR. A significant decrease in the SCN cells staining with Nissl, NeuN, and CB were observed in aged female marmosets compared to adults, while a significant increase in glial cells was found in aged marmosets, thus suggesting compensatory process due to neuronal loss evoked by aging.

Changes in the suprachiasmatic nucleus during aging: implications for biological rhythms

Animals have neural structures that allow them to anticipate environmental changes and then regulate physiological and behavioral functions in response to these alterations. The suprachiasmatic nucleus of the hypothalamus (SCN) is the main circadian pacemaker in many mammalian species. This structure synchronizes the biological rhythm based on photic information that is transmitted to the SCN through the retinohypothalamic tract. The aging process changes the structural complexity of the nervous system, from individual nerve cells to global changes, including the atrophy of total gray matter. Aged animals show internal time disruptions caused by morphological and neurochemical changes in SCN components. The effects of aging on circadian rhythm range from effects on simple physiological functions to effects on complex cognitive performance, including many psychiatric disorders that influence the well-being of the elderly. In this review, we summarize the effects of aging on morphological, neurochemical, and circadian rhythmic functions coordinated by the main circadian pacemaker, the SCN...