Inner Structure of the Lateral Geniculate Complex of Adult and Newborn Acomys cahirinus.

Acomys cahirinus is a unique Rodentia species with several distinctive physiological traits, such as precocial development and remarkable regenerative abilities. These characteristics render A. cahirinus increasingly valuable for regenerative and developmental physiology studies. Despite this, the structure and postnatal development of the central nervous system in A. cahirinus have been inadequately explored, with only sporadic data available. This study is the first in a series of papers addressing these gaps. Our first objective was to characterize the structure of the main visual thalamic region, the lateral geniculate complex, using several neuronal markers (including Ca2+-binding proteins, glutamic acid decarboxylase enzyme, and non-phosphorylated domains of heavy-chain neurofilaments) to label populations of principal neurons and interneurons in adult and newborn A. cahirinus. As typically found in other rodents, we identified three subdivisions in the geniculate complex: the dorsal and ventral lateral geniculate nuclei (LGNd and LGNv) and the intergeniculate leaflet (IGL). Additionally, we characterized internal diversity in the LGN nuclei. The "shell" and "core" regions of the LGNd were identified using calretinin in adults and newborns. In adults, the inner and outer parts of the LGNv were identified using calbindin, calretinin, parvalbumin, GAD67, and SMI-32, whereas in newborns, calretinin and SMI-32 were employed for this purpose. Our findings revealed more pronounced developmental changes in LGNd compared to LGNv and IGL, suggesting that LGNd is less mature at birth and more influenced by visual experience.

Early Postnatal Development of the Lamination in the Lateral Geniculate Nucleus A-Layers in Cats.

The early postnatal development of the A-layers of the dorsal lateral geniculate nucleus (LGNd) was investigated in kittens aged 0-34 days by immunohistochemistry for the selective marker for neuronal differentiation (NeuN protein) and parvalbumin. We report two new facts about the LGNd development. First, there is a transient stratification of NeuN labelling in layer A, and to a lesser extent in layer A1, in kittens aged 0 and 4 days. Second, a transient population of large cells that are located between the LGNd A-layers (interlaminar cells) showed high expression levels of both NeuN and parvalbumin. These neurons possessed both the morphological and immunohistochemical features, similar to cells in the neighbouring perigeniculate nucleus. Both NeuN-stratification and double-stained interlaminar cells gradually disappeared during the second postnatal week, and almost completely vanished by the opening of the critical period. We discuss a possible linkage between these observed transitory networks and the ON-/OFF- and X-/Y-cells development and propose that the data obtained reflect the functioning of the early environmentally independent geniculate networks.

Transient expression of heavy-chain neurofilaments in the perigeniculate nucleus of cats.

The perigeniculate nucleus (PGN) is a visual part of the thalamic reticular nucleus modulating the information transfer between the lateral geniculate nucleus and the visual cortex. This study focused on the postnatal development of the PGN in cats, using the SMI-32 antibody, which recognizes non-phosphorylated heavy-chain neurofilaments responsible for neuronal structural maturation and is also used as a marker for motion processing, or Y, stream. We questioned whether transient neuronal populations exist in the PGN and can they possibly be related to the Y processing stream. We uncovered a transient, robust SMI-32 staining in the PGN of kittens aged 0-34 days with the significant decline in the cellular density of labeled cells in older animals. According to the double-labeling, in all examined age groups, perigeniculate SMI-32-immunopositive cells are part of the main parvalbumin-positive population. The maximal cellular density of the double-stained cells appeared in animals aged 10-28 days. We also revealed that the most significant growth of perigeniculate cells's soma occurred at three postnatal weeks. The possible link of our data to the development of the Y visual processing stream and to the heterogeneity of the perigeniculate neuronal population is also discussed.

Activation of the spinal and brainstem locomotor networks during free treadmill stepping in rats lacking dopamine transporter.

Dopamine is extremely important for the multiple functions of the brain and spinal cord including locomotor behavior. Extracellular dopamine levels are controlled by the membrane dopamine transporter (DAT), and animals lacking DAT (DAT-KO) are characterized by hyperdopaminergia and several alterations of locomotion including hyperactivity. Neuronal mechanisms of such altered locomotor behavior are still not fully understood. We believe that in hyperdopaminergic animals both the spinal and brain neuronal networks involved in locomotion are modified. Using the c-fos technique, we studied activated neuronal networks of the spinal cord and two brainstem structures related to locomotor control and being under the strong dopaminergic influence, the cuneiform nucleus (CnF) and ventrolateral periaqueductal gray (VLPAG), in wild-type (DAT-WT) and DAT-KO rats. In the spinal cord, most c-fos-positive cells were located in the dorsal laminae II-IV and in the central gray matter (laminae V-VI). No differences were revealed for the central areas. As for the dorsal areas, in the DAT-WT group, labeled cells mostly occupied the lateral region, whereas, in the DAT-KO group, c-fos-positive cells were observed in both medial and lateral regions in some animals or in the medial regions in some animals. In the brainstem of the DAT-WT group, approximately the same number of labeled cells were found in the CnF and VLPAG, but in the DAT-KO group, the VLPAG contained a significantly smaller number of c-fos-positive cells compared to the CnF. Thereby, our work indicates an imbalance in the sensorimotor networks located within the dorsal horns of the spinal cord as well as a disbalance in the activity of brainstem networks in the DAT-deficient animals.

Impaired visceral pain-related functions of the midbrain periaqueductal gray in rats with colitis.

The midbrain periaqueductal gray (PAG) is a key structure involved in the supraspinal modulation of pain. Previous studies have reported the association of gut inflammation-triggered chronic abdominal pain with structural and neuronal alterations within the PAG. However, whether PAG-executed visceral nociception processing and descending modulation are altered in gut pathology is not known. We used c-Fos immunohistochemistry and extracellular microelectrode recording in urethane-anesthetized male Wistar rats to evaluate the colitis-induced changes in visceral pain-related neuronal properties of the PAG and its descending outflow to visceral nociceptive neurons of the caudal ventrolateral medulla (CVLM). Analysis of c-Fos protein expression in inflamed animals has shown diminished activation of the lateral and ventrolateral PAG columns by noxious colorectal distension (CRD), although the nonstimulated c-Fos labeling in these PAG subdivisions was enhanced compared with that in controls. Microelectrode recording in the ventrolateral PAG revealed a colitis-elicited decrease in the proportion of CRD-excited neurons accompanied by an increase in the number of unresponsive cells and weakened reactions to the stimulation of CRD-inhibited PAG units. Colonic inflammation has also been found to cause a shift in the effects of ventrolateral PAG electrostimulation on CRD-excited CVLM neurons from being mostly inhibitory under normal conditions to excitatory in colitis. These findings identify impaired PAG functioning in ascending and descending visceral nociception control that may contribute to gut injury-associated visceral hyperalgesia. The data obtained can benefit a better understanding of the supraspinal mechanisms involved in the pathogenesis of postinflammatory chronic abdominal pain.

SMI-32 labeling in Cajal-Retzius cells of feline primary visual cortex.

Cajal-Retzius cells are one of the transient elements of the developing cerebral cortex. These cells express some characteristic molecules. One of them, heavy-chain neurofilaments, participating in the construction of the mature cerebral networks, are believed to be a specific feature of the human's Cajal-Retzius cells. Using histochemical stain for SMI-32 antibody to the non-phosphorylated heavy-chain neurofilaments, large neurons having horizontally oriented soma and bipolar processes were labeled in the molecular layer of the primary visual cortex of cats aged 0-2 postnatal days. Using DiI technique, similar neurons having a well-developed system of parallel vertical branches coming from the two horizontal processes were visualized in these areas. The location and general morphology of these neurons were similar to the Cajal-Retzius cells allowing to suppose for the carnivores to share similar with primates developmental mechanisms of the corticogenesis.

Heterochrony of postnatal accumulation of nonphosphorylated heavy-chain neurofilament by neurons of the cat dorsal lateral geniculate nucleus.

Accumulation of the heavy-chain neurofilaments reflects the maturation status of neuronal structures. The spatial distribution and postnatal developmental dynamic of neurons expressing nonphosphorylated heavy-chain neurofilaments (labeled by SMI-32 antibody) were analyzed in the dorsal lateral geniculate nucleus (LGNd) of the cat. Both interlaminar and intralaminar differences in the dynamic of SMI-32 staining were observed. The following results were obtained: (a) Ascending dorsoventral gradient in the density of SMI-32 immunopositive (SMI-32(+)) neurons (the greatest neuronal density in layer Cm, the minor in the top sublayer of layer A). This gradient was most prominent at the earliest stages of postnatal development (1st-2nd weeks) and slowly flattened up to adulthood; (b) Layer A1 exhibits increases in SMI-32-positive cells earlier than layer A; (c) The general transient increment in the number and density of SMI-32(+) neurons around 2-5 postnatal weeks. Since SMI-32 antibody is considered to be a putative marker for Y cells forming a motion processing stream, we suggest that peculiarities of SMI-32 staining at geniculate level could reflect the heterogeneity of Y cell subpopulations and the heterochrony of their postnatal maturation.

CAS: Cell Annotation Software - Research on Neuronal Tissue Has Never Been so Transparent.

CAS (Cell Annotation Software) is a novel tool for analysis of microscopic images and selection of the cell soma or nucleus, depending on the research objectives in medicine, biology, bioinformatics, etc. It replaces time-consuming and tiresome manual analysis of single images not only with automatic methods for object segmentation based on the Statistical Dominance Algorithm, but also semi-automatic tools for object selection within a marked region of interest. For each image, a broad set of object parameters is computed, including shape features and optical and topographic characteristics, thus giving additional insight into data. Our solution for cell detection and analysis has been verified by microscopic data and its application in the annotation of the lateral geniculate nucleus has been examined in a case study.