EFFECTS OF SELECTIVE CHOLINERGIC AND GABAERGIC LESIONS OF THE NUCLEUS BASALIS MAGNOCELLULARIS ON PLACE OR RESPONCE LEARNING IN PLUS-SHAPED MAZE.

In the present study we evaluated effects of selective cholinergic or GABAergic lesions of the nucleus basalis magnocellularis (NBM) using immunotxins 192 IgG-saporin and GAT1-SAP on place and response learning in plus-shaped maze. In current behavioral paradigm rats learned food-rewarded mazes that were efficiently learned using either place or turning strategies. A histological evaluation indicated that 192 IgG-saporin lesions specifically depleted cholinergic neurons but did not result in noticeable damage to the GABAergic cells within NBM. GAT1-SAP lesions resulted extensive damage of GABAergic and a mild reduction of cholinergic NBM neurons. The results of present behavioral experiments showed, that selective lesions of cholinergic or GABAergic neurons in the NBM impair, but do not abolish, the animal's ability to learn location of rewarded arm of maze (place learning) or a skilled motor behavior (response learning). Our findings suggest the role of NBM cholinergic and GABAergic cortical projection neurons in processing of cognitive information. We suggested that lesions of NBM projections to the cortex modulate learning-mediated plasticity and impair both place and response learning.

EFFECTS OF MEDIAL SEPTAL LESION ON HIPPOCAMPAL EXTRACELLULAR GLUTAMATE AND GABA LEVELS DURING SPATIAL ALTERNATION TESTING.

The present study investigated spatial working memory assessed in spontaneous alternation (SA) task and hippocampal glutamate and GABA release prior to, during, and after SA test in sham-operated and electrolytic medial septal (MS) lesioned rats. Also, have been investigated the effects of MS lesion on KCl-stimulated release of glutamate and GABA in the hippocampus. Behavioral study showed that electrolytic lesion of MS significantly impaired SA performance. Although both groups of animals had an insignificant rise in their respective hippocampal glutamate efflux during the SA, the rise of MS lesioned animals was blunted when compared with control animals. Hippocampal GABA levels did not change during behavioral testing in both groups. Most of control animals showed increase in KCl-stimulated glutamate release. By contrast, only one MS lesioned rat showed increase in glutamate release in response to KCl stimulation. Most of control and MS lesioned rats were non-responders in GABA release in response to KCl stimulation. Decreased glutamate release (upon stimulation) in the MS lesioned rats may contribute to spatial working memory impairment in these animals. We propose that SA testing coupled with in vivo microdialysis sampling represents a suitable approach to revealing the neurochemical correlates of hippocampal-dependent memory function, and thus could be a useful tool for better understanding of the neurochemical basis of cognitive decline associated with various disorders and neurodegenerative diseases.

MEMANTINE ATTENUATES THE OKADAIC ACID INDUCED SHORT-TERM SPATIAL MEMORY IMPAIRMENT AND HIPPOCAMPAL CELL LOSS IN RATS.

In the present study, the possible beneficial effect of memantine on the Okadaic Acid (OA) induced spatial short-term memory impairment was examined in spatial alternation task, and the neuroprotective potential of memantine on OA-induced structural changes in the hippocampus was evaluated by Nissl staining. OA was dissolved in artificial cerebrospinal fluid (aCSF) and injected intracerebroventriculary (ICV) 200 ng in a volume of 10 µl bilaterally. Vehicle control received aCSF ICV bilaterally. Control and OA injected rats were divided into 2 subgroups injected i.p. with saline or memantine (5 mg/kg). Memantine or saline were given daily for 13 days starting from the day of OA injection. Behavioral study showed that bilateral ICV microinjection of OA induced impairment in spatial short-term memory. Nissl staining in the present study showed that the ICV microinjection of OA significantly decreased the number of surviving pyramidal neurons in the CA1 region of the hippocampus. Chronic administration of memantine effectively attenuated OA induced spatial short-term memory impairment and the OA-induced neuropathological changes in the hippocampus. Therefore, ICV injection of OA can be used as an experimental model to study mechanisms of neurodegeneration and define novel therapeutics targets for AD pathology.

SPATIAL MEMORY IMPAIRMENT AND HIPPOCAMPAL CELL LOSS INDUCED BY OKADAIC ACID (EXPERIMENTAL STUDY).

In the present study, we evaluated and compared effect of intracerebroventricular (ICV) and intrahippocampal bilateral microinjection of okadaic acid (OA) on spatial memory function assessed in one day water maze paradigm and hippocampal structure in rats. Rats were divided in following groups: Control(icv) - rats injected with ICV and aCSF; Control(hipp) - rats injected intrahippocampally with aCSF; OAicv - rats injected with ICV and OA; OAhipp - rats injected intrahippocampally with OA. Nissl staining of hippocampal sections showed that the pyramidal cell loss in OAhipp group is significantly higher than that in the OAicv. The results of behavioral experiments showed that ICV or intrahippocampal bilateral microinjection of OA did not affect learning process and short-term spatial memory but induced impairment in spatial long-term memory assessed in probe test performance 24 h after training. OA-induced spatial memory impairment may be attributed to the hippocampal cell death. Based on these results OA induced memory deficit and hippocampal cell loss in rat may be considered as a potential animal model for preclinical evaluation of antidementic drug activity.

Selective lesion of GABA-ergic neurons in the medial septum by GAT1-saporin impairs spatial learning in a water-maze.

The aim of this study was to investigate the role of the medial septal (MS) GABAergic cells in hippocampal dependent spatial learning using the immunotoxin GAT1-SAP to produce selective lesions of GABAergic MS neurons. In current study rats were trained in a visible platform version of the Morris water maze in which either a place or cue strategy could be used to escape successfully. Immunohistochemical studies showed that intraseptal injection of GAT1-SAP extensively damaged GABAergic MS neurons and spared most cholinergic neurons. The rats' responses on the competition test were classified as either cue or place, based on the swim path for those trials. An overview of the data from both competition trials for each group show that the control rats in 14 trials out of 16 competition test trial used place strategy, while MS-lesioned ones used this strategy in 2 trials only. Decreased place-bias in MS-lesioned rats compared to the control rats was significant (P<0.01). The data obtained in the control and GAT1-SAP lesioned animals in the present study, demonstrate that lesioned rats were impaired in hidden platform trials during training, and displayed a pronounced cue-bias in competition tests. Therefore, above data suggest involvement of the MS GABAergic neurons in organization of the spatial map-driven behavior and this structure, along with the hippocampus, should be viewed as a constituent of the functional system responsible for the cognitive types of spatial memory.

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.

Effects of chronic memantine treatment on hippocampal extracellular glutamate and GABA levels during spatial alternation testing.

These experiments examined the release of glutamate (Glu) and GABA in the hippocampus of memantine (2,5mg/kg, i.p. for four weeks) or saline treated rats prior to, during, and after spontaneous alternation test. Glu and GABA release during the 10 min samples taken at the time of the behavioral testing of memantine or saline treated animals were not different from those seen immediately before and after testing. Similarly, the alternation scores were not significantly different between groups. We found increase in KCl-stimulated glutamate and GABA release in the hippocampus of memantine treated rat compared to the saline treated rat. This difference in KCl response between memantine treated and control rat was statistically significant (p<0,05). Our evaluation of memantine reveals that changes in KCl-stimulated Glu and GABA release after chronic memantine treatment did not affect working memory in adult rats assessed in spontaneous alternation task.

Effects of the uncompetitive NMDA receptor antagonist memantine on spatial memory in medial septal lesioned rats.

These experiments examined the effects of acute administration of memantine (2.5 or 5 mg/kg) or saline on spatial memory and learning process within single sessions, on place versions of food-rewarded maze in MS electrolytic lesioned and sham-lesioned rats. Sham-lesioned rats trained in the place task learned more rapidly than did MS electrolytic lesioned rats. This fact certifies for obvious deficit of the place learning performance strategy in the MS-lesioned rats. The results indicate that the drug-treated (5 mg/kg memantine) sham-lesioned rats exhibited significantly impaired performance relative to the saline controls in terms of trials-to-criterion (P<0.05). 2.5 mg/kg memantine administered 30 min before behavioral testing, did not affect performance in place learning task. 2.5 mg/kg and 5 mg/kg memantine administered before behavioral testing, did not improve performance in place learning task in MS electrolytic lesioned rats. Our experimental data support the interpretation that memantine does not produce intolerable side effects in human AD patients because it is being used at doses that are below the threshold for interacting with NMDA receptors.

Effects of the uncompetitive nmda receptor antagonist memantine on recognition memory in rats.

Memantine is an NMDA receptor antagonist that has been recently approved in EU for the treatment of moderate to severe Alzheimer's disease. The previous studies have not allowed for the evaluation of the possible effects of this drug at therapeutic doses on different forms of memory. To address this question, we administered memantine to adult rats, using doses 2.5 or 5 mg/kg and evaluated the effects of these doses on open field activity and recognition memory. Memantine or saline was administered daily by intraperitoneal injection beginning on the day of behavioral testing and continuing 5 days. The main results of experiments are as follows: the memantine treatment produced a dose-related suppression of total ambulations. There was no significant impairment in detecting spatial and object novelty in the 2.5 mg/kg memantine treated rats. However, the 5 mg/kg intraperitoneal dose of memantine disrupted both recognition memory and locomotor behaviors. Our evaluation of memantine reveals that at doses lower than are required for neuroprotection disrupt memory. This raises the possibility that the beneficial effects seen in AD patients may be attributable to the interaction of memantine with other transmitter systems.

Effects of excitotoxic lesions of the CA1 region of the hippocampus on acquisition of a place and cue water maze task.

The aim of the present study was to investigate the effects of excitotoxic lesions of the dorsal CA1 region of the hippocampus on acquisition of a place and cue water maze task. The ibotenic acid injections into CA1 produced removal of the pyramidal cells in CA1, while saving most of the pyramidal cells in CA3 and granule cells in DG intact. In conditions of visible platform training trials, differences in the platform reaching latency between the animals of different groups, were not found. When testing was performed in conditions of submerged platform, the latency of the platform finding was significantly increased (P<0.05). This fact certifies for deficit of the place learning strategy in the CA1-lesioned rats. Decreased place-bias in CA1-lesioned rats in hidden platform training trials compared to the sham-operated rats was significant, but in testing trials when required to choose between the spatial location they had learned and the visible platform in a new location majority of them swam first to the old spatial location. Decreased place-bias in CA1-lesioned rats compared to the sham-operated rats was not significant. We suggest that spatial learning deficits observed after dorsal hippocampal lesions cannot be accounted solely to the loss of dorsal hippocampal CA1 region cells.

Object exploration and reactions to spatial and nonspatial changes in dentate gyrus lesioned rats.

In order to investigate the possible involvement the DG in spatial and object recognition memory, we have opted for a non-associative task where no explicit reward was present. Colchicine was used for bilateral DG lesions for its well-known specificity for DG lesion. Colchicine-induced lesions produce severe damage in the granule cells of DG, while minimally affecting pyramidal cells in CA1 and CA3. The main results are as follows: The overall habituation to the familiar environment in DG lesioned rats was decreased than in sham operated rats. There was no significant impairment in detecting spatial novelty. Lesions of the DG did not affect the detection of a novel object placed in a familiar location. Considering both the impaired habituation and the generally intact detection of spatial changes, we suggest that exploratory activity in relation to the entire environment and to the particular objects is thought to be subserved by diverse nervous substrate, and testing in the given conditions allows for their differential estimation.

[Regularities of the egocentric spatial memory development in children aged 24-60 months].

In order to assess development of the egocentric system of the spatial short-term memory in children (n=66) of different ages (24-60 months) the Inverted Delayed Reaction test has been used. It was found that in the children aged 24-36 months regularities of performance of the Inverted Delayed Reaction test significantly differ in conditions of different loads onto the mechanisms of dead reckoning; the children aged 36-60 months do not show sensitivity to different loads. In children aged 42+/-4 months functional elimination of any of the sensory system (visual, kinesthetic, vestibular) during rotation significantly deteriorated results of the Inverted Delayed Reaction test performance, while in children aged 60+/-4 months number of correct responses decreased if two or three sensory systems were eliminated simultaneously. The data obtained permit to conclude that the Inverted Delayed Reaction test is sufficiently sensitive for evaluation development of the egocentric spatial memory system in children and that formation of the dead reckoning mechanisms starts in an age of 24 months and in the period of 24-60 months its further upgrading does occur.

Spatial memory following selective cholinergic lesion of the nucleus basalis magnocellularis.

The aim of this study was to investigate the modulation of the cognitive function by the cholinergic cells of the nucleus basalis magnocellularis (NBM) and was designed to investigate the role of the NBM cholinergic cells in learning and memory using the immunotoxin 192 IgG-saporin to produce selective lesions of cholinergic NBM neurons. A total of 16 male outbred albino rats were used in the present study to investigate the ability of sham-operated and NBM immunotoxin lesioned rats to learn the location of a visible, as well as submerged platform in a water maze. Examination of the AChE stained sections showed that after injections of 192 IgG saporin into the NBM, animals exhibited significantly less AChE staining in PFC as compared to sections obtained from sham-operated animals. An overview of the data from both competition trials for each group show that the sham-operated rats in 13 trials out of 16 competition test trial used place strategy and NBM-lesioned ones used this strategy in 6 trials. Decreased place-bias in NBM-lesioned rats compared to the sham-operated rats was significant (t(d )= 2,42, P<0.02).The data obtained in the sham-operated and NBM-lesioned animals in the present study, demonstrate that the choice of strategy in the competition trial is related to performance during training: the rats exhibiting cue strategy (NBM-lesioned) on the competition trial had significantly worse performance during hidden platform training than those (sham-operated) exhibiting a place strategy. These findings suggest that the NBM is essential for accurate spatial learning and suggest its role in processing information about the spatial environment, but also we can propose, that the behavioral deficits described in the present study is nonmnemonic, possibly caused by deficit in attentional function.

Effects of the selective lesions of cholinergic septohippocampal neurons on different forms of memory and learning process.

The aim of this study was to investigate the modulation of the hippocampal function by the cholinergic cells of the septum and the role of the septo-hippocampal cholinergic system in learning and memory. Immunotoxin 192 IgG-saporin was used to produce selective lesions of cholinergic septohippocampal neurons. Hippocampal AChE was used as a quantitative measure of lesion extent. A total of 16 male outbred albino rats were used in the present study to investigate the ability of sham-operated and medial septal (MS) immunotoxin lesioned rats to learn the location of a visible, as well as submerged platform in a water maze. The rats' responses on the competition test were classified as either cue or place, based on the swim path for those trials. Examination of the AChE stained sections showed that after injections of 192 IgG saporin into the MS, animals exhibited significantly less AChE staining in hippocampus as compared to sections obtained from sham-operated animals. Differences in the platform reaching latency between the animals of different groups for the training trials were not found. Data from both competition trials for each group show that the sham-operated rats in 13 trials out of 16 competition test trial used place strategy and MS-lesioned ones used this strategy in 11 trials. Decreased place-bias in MS-lesioned rats compared to the sham-operated rats was not significant. These findings suggest that the septo-hippocampal cholinergic system is not essential for all types of hippocampal-dependent memory and deficits observed after septal electrolytic lesions cannot be accounted solely to the loss of hippocampal ACh.

Effects of electrolytic lesion of medial septal nucleus on learning strategy selection in a visible platform version of the water maze.

This experiment investigated the ability of sham-operated and medial septal (MS) damaged rats to learn the location of a visible, as well as submerged platform in a water maze. The rats' responses on the competition test were classified as either cue or place, based on the swim path for those trials. Sham-operated rats acquired both the visible and hidden platform versions of the task, but when required to choose between the spatial location they had learned and the visible platform in a new location majority of them swam first to the old spatial location. The MS damaged rats acquired the visible platform version of the water maze task but failed to learn the platform's location in space. When the visible platform was moved to a new location they often swam directly to it. Sham-operated rats identified as place responders had significantly more accurate searches during hidden platform training, providing additional evidence of their effective use of a place learning strategy than MS is damaged. These findings suggest that in the absence of a septohippocampal functional system behaviour was not affected by spatial information and responding to local reinforced cues was enhanced. These data add to a growing literature demonstrating that the septo-hippocampal system is essential for accurate spatial learning and suggest its role in processing information about the spatial environment.

[Concerning a conflict nature of the "spatial delayed response" test]. / O konfliktnoi prirode testa "prostranstvennaia otsrochennaia reaktsiia".

Neuropsychological analysis of rats' performance of the spatial delayed response (SDR) in different testing conditions revealed a conflict nature of the indirect variation of the SDR task. It was found that the execution of the response based on the image short-term memory interferes with the response differentiation acquired during learning the rule of indirect SDR performance, i.e., during acquisition of the spatial discrimination. It is evident that the maximization of conditions, which promote the acquisition of response differentiation (additional training of animals for spatial discrimination), makes it difficult to perform the indirect variation of the SDR task, while the minimization of these conditions facilitates the correct task performance.

[Formation of spatial short-term memory in 18-54-month old children]. / Formirovanie mekhanizmov prostranstvennoi kratkosrochnoi pamiati u detei v vozraste 18-54 mesiatsev.

The development of the spatial short-term memory (SSTM) in children aged 18-54-months was assessed by performance of the inverted delayed-response task (IDR). A child perceived the localization of a target object in one of the two containers (left or right) situated on a table in front of the child. The distance between the containers was 30 cm. Then the child was escorted to the opposite side of the table so that the target object that was earlier in the left container seemed to be in the right one. After the rotation, in 74% of cases children at the age of 18-24-months failed to localize the object correctly despite the presence of various reference objects in the room. Percent of correct responses increased with age. Children aged 24-54-months performed the IDR better in the presence of reference objects than in their absence. The preschool children at the age of 48-54-months correctly localized the object in 70% of cases even in the absence of the experimental reference objects. The results of this experiment demonstrate the stages of the SSTM development in children.

Characteristics of neuronal activity in prefrontal cortex during performance of spatial delayed reactions in monkeys.

Several types of neurons were differentiated on the basis of a study of neuronal activity in various parts of the cortex near the sulcus principalis during the execution of spatial delayed reactions by monkeys. It was established that the different types of neurons are represented in different numbers in different parts of the cortex near the sulcus principalis. The determination of several factors influencing the activity of these neurons and the comparison of data on their quantitative representation in the anterior, middle, and posterior parts of the cortex near the sulcus principalis with the existing behavioral data obtained after local ablations of identical regions of the brain made it possible to postulate that neurons belonging to the different types are involved in the analysis of different processes and represent different functional units.

Significance of emotional excitation in the mechanisms of spatial short-term memory in lower apes.

Correlates of variation in the level of emotional tension are studied in long-term experiments on adult monkeys. The simultaneous appearance of the electrodermal response and of a change in the heart rate is shown to reflect more accurately a rise in the level of emotional tension. Continuous recording of autonomic indexes reveals an increase in tension level during the presentation of conditioned signals and the performance of the motor response in the spatial delayed response test program. The emotiogenic structures are thought to influence the specific mechanisms of short-term memory during the presentation of conditioned signals and the performance of food-procuring instrumental behavior.