Encoding environmental information is a primary focus in neuroscience, as environmental context is crucial for the spatial orientation of animals. Place cells in the hippocampus play a key role in forming the spatial map of the surrounding space by mapping targets, environmental objects, various landmarks, and boundaries. However, it was previously unclear whether specific mapping properties exist for contrasting environmental elements that do not physically obstruct animal movement. In this study, we examined the calcium activity of CA1 hippocampal neurons in mice using miniscope imaging, alongside their behavior in an arena with contrasting colored elements on the floor. Our findings indicate that the place fields of CA1 hippocampal cells are concentrated in areas of environmental heterogeneity, rather than in the individual elements themselves or in areas preferred by the mice. This suggests that the contrasting surface signals of the environment are represented by CA1 hippocampal neurons within the overall spatial pattern.

The present study showed arena size-dependent effects on the impairment of locomotor activity and rearing after lesions of caudal hippocampus in C57BL/6 mice: intensive high-speed locomotion without intra- and intertrial habituation accompanied by a decreased number of rears and a reduced tortuosity of the route, suggesting significant impairments of exploratory behavior in an unfamiliar large environment. The lesions of the rostral hippocampus resulted in slight hyperactivity in the large arena without impairment of habituation or rearing. The caudal hippocampus is thus crucial for the environment-dependent modifications of exploratory behavior. Changes on exploratory behavior after its lesions are similar to ones following more extensive or complete lesions of the hippocampus.

In this brief review the role of the hippocampal formation in the processes of navigation, orientation and spatial memory in wild animals is discussed. Studies in bats revealed previously unknown types of spatial neurons associated with three-dimensional navigation and their new properties. The involvement of the hippocampal formation in the processes of long-distance flights of birds during migration and homing is considered. The available data on the difference in hippocampal morphology in relative species (or subspecies) of mammals and birds that differ in their food-caching ability, foraging types, and the size of the home range should be supplemented analysis brain functions with utilizing modern technologies. The results of research on wild species are significant for both zoologists and neuroscientists and should be developed into interdisciplinary frameworks.

Functional differentiation of the hippocampus along its longitudinal septotemporal axis is beyond doubt, though the factors determining this subregional specificity remain controversial. The spatial specificity gradient of hippocampal place cells decreases along its longitudinal axis from the septal pole to the temporal area. This difference in the scale of spatial representation suggests differences in the involvement of neurons in these subregions in the exploration and mapping of territories of different sizes. Using c-Fos as a marker for hippocampal neuron activation in novel environments, we studied the influences of exploration of arenas of different sizes on neuron activation in the septal and temporal subregions of fields CA1 and CA3 and the dentate fascia (DF) in C57BL/6 mice. The results of these studies showed that expression intensity was influenced by arena size, and a relationship between subregion activation factors and area size was found. Elevated c-Fos expression was seen only in the temporal part of the hippocampus, while significant changes in activation were noted in field CA3 and the DF in mice exploring the largest arena. c-Fos expression in the septal subregions showed no differences in arenas of different sizes. However, repeat testing of animals in an arena of a different size led to additional activation of expression in the temporal part of CA3 and the septal part of the DF. High neuron activity in the temporal subregion of the hippocampus may be due not only to the size of the arena explored, but also to the greater indeterminacy of a large space in terms of the biological significance of its different areas.

We studied the effects of whole body gamma-radiation (4 Gy, dose rate 0.6 Gy/min) and proton-beam head irradiation (with an energy of 150 meV, 4 Gy and a dose rate of 0.8 Gy/min) on the intensity and timing of audiogenic seizures in rats of the Krushinsky–Molodkina selected strain. In experiments using gamma rays the rat behavior was tested in the open field, elevated plus maze, and Morris water maze tests. No changes in audiogenic tonic–clonic seizures (originating in the brain stem) were found during the first exposure to sound after gamma-irradiation. Slower development of seizures and larger latency of the tonic seizure phase were found following serial daily exposure to sound in rats after proton irradiation. It was also noted that audiogenic myoclonic seizures (which developed in the forebrain) in irradiated rats that were exposed daily to sound had shorter durations, while the intensity of these seizures was at a maximum in all groups. The behavioral tests revealed a moderate increase in anxiety after radiation exposure.

Оценено влияние двустороннего цитотоксического удаления малоизученной каудальной части гиппокампа ( 30 его полного объема) на обучение рыжих полевок Clethrionomys (Myodes) glareolus в водном тесте Морриса. Использована версия теста, предназначенная для оценки долговременной пространственной памяти. Показано, что удаление влияет на динамику обучения, замедляя его, а также снижает на ранних этапах обучения точность запоминания местоположения платформы. Полученные данные свидетельствуют об участии этой области в контроле пространственного обучения грызунов.