FINE ARCHITECTURE OF THE HIPPOCAMPUS IN ADOLESCENT, ADULT AND AGED RATS. ELECTRON MICROSCOPIC STUDY.

The study included adolescents (P30-36), adult (P125-130) and aged (P330-340) male Wistar rats - 4 animals in each age group. The rats were housed individually, in wire-top polypropylene cages (30-cm width x 30 cm length x 25 cm height) and maintained on a 12-h light/dark cycle. Standard food pellets and tap water were ad libitum. The animal maintenance and electron microscopic procedures were conducted in accordance with European Union Directive on the protection of animals used for scientific research. The Ultrastructure of adult and adolescent rats are almost same. However, remarkable changes are expressed between adult and senescent rats. Precisely, in the last one there are following ultrastructural modifications - lipofuscin concentrations, small destructive cytoplasmic organelles, changes in presynaptic vesicular and mitochondrial quantity. Rare apoptotic signs in neurons. Analysis of all this means that aging in rat's hippocampus causes selective changes, also it underlines changes in neurotransmission and neuronal developmental pathways.

THE EFFECT OF HIGH INTENSITY WHITE NOISE ON THE ULTRASTRUCTURE OF AXO-DENDRITIC SYNAPSES IN COLLICULUS INFERIOR OF ADULT MALE CATS. QUANTITATIVE ELECTRON MICROSCOPIC STUDY.

Environmental noise is a serious problem for the society and medicine. Chronic loud noise is known to produce numerous adverse effects on different levels of the organism. In addition to behavioral changes, the involvement of different regions of the brain was documented. The analysis of structural modifications provoked by noise in brain give the possibility to suggest that one of the effects of noise may be the alterations in neurotransmission. Therefore, of special interest should be the elucidation of the effects of chronic noise on the fine structure of synapses of brain areas participating in the processing of auditory information. In the present study, using transmission electron microscope. We elucidate the effects of high intensity chronic white noise on the morphology of axo-dendritic synapses, and size and diameter of synaptic vesicles in auditory region, inferior colliculus of adult male cats. Experimental animals were exposed to 100 dB (5-20 kHz) white noise for one hour per day, for 10 consecutive days. On 11th day, after special procedures, the area of interest was examined under electron microscope. In ~ 15% large synaptic terminals the clustering of synaptic vesicles, as well as swelling, partial vacuolization or degeneration of presynaptic mitochondria were detected. Morphometric analysis of docked (with presynaptic membrane) and undocked synaptic vesicle size revealed that docked vesicles are smaller than undocked vesicles. It was observed in both control and experimental animals, however, in experimental animals, such difference was more significant. Such results suggest that due to continuous transmission, the majority of vesicles are unable to replenish their cargo via transporters. Evaluation of synaptic vesicles size undertaken in the current electron microscopic study has advanced the understanding of the pathophysiology of white noise exposure on auditory brain processing regions, in addition to our understanding of fractional neurotransmitter release at the nerve terminal and on overall brain function.

EFFECT OF ARSENIC EXPOSURE ON BEHAVIOR OF RATS OF VARIOUS AGE GROUPS.

Arsenic is ranked first among toxicants posing a significant potential threat to human health based on known or suspected toxicity. Recent animal studies suggest that the brain is the major target of arsenic exposure. The present study demonstrates the effect of Arsenic compounds on behavior changes in different age (young and adult) groups of rats. In order to study anxiety behavior, learning and memory processes we used open field, elevated plus maze, spontaneous alteration behavior and multi-branched maze tests. Our experiments revealed that 68 mg/L (35 ppm) Sodium (meta) arsenite (when animals got arsenic from drinking water for three months) induces more significant effect on body weight gain in adult rats rather than in young ones. Arsenic exposure may result in rat's emotional instability despite the animals' age. According to the spontaneous alteration test, obtained data revealed that behavior is changed only in adult rats compared to control ones. Also it was found that Arsenic consumption at the same concentration induces considerable difficulties in learning process (multi-branched maze test results) in the adult arsenic exposed group. We have found differences in maze test performance, during fulfilling memory tasks by arsenic exposed animals in comparison to control ones. This distinction was mostly notable in young groups. These data show that Arsenic exposure affects short-term memory more dramatically in adult animals rather than of young ones, whereas difficulties in long-term memory were detected among young animals.

Exploratory behavior and recognition memory in medial septal electrolytic, neuro- and immunotoxic lesioned rats.

In the present study, the effect of the medial septal (MS) lesions on exploratory activity in the open field and the spatial and object recognition memory has been investigated. This experiment compares three types of MS lesions: electrolytic lesions that destroy cells and fibers of passage, neurotoxic - ibotenic acid lesions that spare fibers of passage but predominantly affect the septal noncholinergic neurons, and immunotoxin - 192 IgG-saporin infusions that only eliminate cholinergic neurons. The main results are: the MS electrolytic lesioned rats were impaired in habituating to the environment in the repeated spatial environment, but rats with immuno- or neurotoxic lesions of the MS did not differ from control ones; the MS electrolytic and ibotenic acid lesioned rats showed an increase in their exploratory activity to the objects and were impaired in habituating to the objects in the repeated spatial environment; rats with immunolesions of the MS did not differ from control rats; electrolytic lesions of the MS disrupt spatial recognition memory; rats with immuno- or neurotoxic lesions of the MS were normal in detecting spatial novelty; all of the MS-lesioned and control rats clearly reacted to the object novelty by exploring the new object more than familiar ones. Results observed across lesion techniques indicate that: (i) the deficits after nonselective damage of MS are limited to a subset of cognitive processes dependent on the hippocampus, (ii) MS is substantial for spatial, but not for object recognition memory - the object recognition memory can be supported outside the septohippocampal system; (iii) the selective loss of septohippocampal cholinergic or noncholinergic projections does not disrupt the function of the hippocampus to a sufficient extent to impair spatial recognition memory; (iv) there is dissociation between the two major components (cholinergic and noncholinergic) of the septohippocampal pathway in exploratory behavior assessed in the open field - the memory exhibited by decrements in exploration of repeated object presentations is affected by either electrolytic or ibotenic lesions, but not saporin.