The Phenomenon of Compensatory Cell Proliferation in Olfactory Epithelium in Fish Caused by Prolonged Exposure to Natural Odorants.

It was previously shown that activation of the processes of neurogenesis in the olfactory epithelium (OE) can be caused after intranasal administration of toxic or neurotrophic factors, after axon transection, or as a result of bulbectomy. Our study showed for the first time that a significant increase in olfactory cell renewal can also occur in animals due to periodic chemostimulation with natural odorants (amino acids and peptides) for 15 days. Using electron and laser confocal microscopy in fish (Paracottus knerii (Cottidae), Dybowski, 1874) from Lake Baikal, we showed that periodic stimulation of aquatic organisms with a water-soluble mixture of amino acids and peptides causes stress in OE, which leads to programmed death cells and compensatory intensification of their renewal. We estimated the level of reactive oxygen species, number of functionally active mitochondria, intensity of apoptosis processes, and mitosis activity of cells in the OE of fish in the control group and after periodic natural odorants exposure. This study showed that new stem cells are activated during enhanced odor stimulation and subsequent degenerative changes in the cells of the sensory apparatus. Those new activated stem cells are located in previously proliferatively inactive regions of OE that become involved in compensatory processes for the formation of new cells.

Rearrangement of Actin Microfilaments in the Development of Olfactory Receptor Cells in Fish.

At present, it remains poorly understood how the olfactory neuron migrates through the thick neuroepithelium during its maturation from a stem cell and how it develops a specific sensitivity to environmental odorants after maturation. We investigated the cytochemical features associated with the development of olfactory cells before and after the incorporation of dendrites into the surface of the olfactory epithelium. Using cytochemical staining for the actin cytoskeleton and other cell components, we found that immature neurons acquire a streamlined shape that resembles a «hot-dog¼ during their migration: a dense layer of actin microfilaments forms beneath the surface membrane of the growing dendrite, and the bulk of the nuclear material moves inside this layer. We have found that when the cell makes contact with its environment, the dendritic terminal develops a wide actin layer, inside which a pore is formed. It is assumed that the functional receptors of odorants generate across this pore the first intracellular signal from environmental water-soluble odorants. These data illustrate the important role of the cytoskeleton in the differentiation of olfactory cells.

The effects of agonists of ionotropic GABA(A) and metabotropic GABA(B) receptors on learning.

The research described here investigates the role played by inhibitory processes in the discriminations made by the nervous system of humans and animals between familiar and unfamiliar and significant and nonsignificant events. This research compared the effects of two inhibitory mediators of gamma-aminobutyric acid (GABA): 1) phenibut, a nonselective agonist of ionotropic GABA(A) and metabotropic GABA(B) receptors and 2) gaboxadol a selective agonist of ionotropic GABA(A) receptors on the process of developing active defensive and inhibitory conditioned reflexes in alert non-immobilized rabbits. It was found that phenibut, but not gaboxadol, accelerates the development of defensive reflexes at an early stage of conditioning. Both phenibut and gaboxadol facilitate the development of conditioned inhibition, but the effect of gaboxadol occurs at later stages of conditioning and is less stable than that of phenibut. The earlier and more stable effects of phenibut, as compared to gaboxadol, on storage in memory of the inhibitory significance of a stimulus may occur because GABA(B) receptors play the dominant role in the development of internal inhibition during an early stage of conditioning. On the other hand this may occur because the participation of both GABA(A) and GABA(B) receptors are essential to the process. We discuss the polyfunctionality of GABA receptors as a function of their structure and the positions of the relevant neurons in the brain as this factor can affect regulation of various types of psychological processes.