The lagena (the third otolith endorgan in vertebrates)

In this review, the structure and functions of the lagena (the third otolith organ) in an evolutionary lineage of the vertebrates are described and discussed. The lagenar macula appears first in the posterior part of the sacculus of elasmobranchs; in these animals, the lagena is considered to be involved in the balance support (orientation with respect to the gravitation force). The lagena as a separate endorgan has been described in teleost fishes; in some species, the lagena is connected with the sacculus, while in other species the interrelations of these structures can be dissimilar. The lagena supplements the functions of the sacculus; in fishes (animals with no special organ of hearing), it is involved in discrimination of sound oscillations, identification of the gravitation vector, and orientation in the course of movements within the vertical plane. In amphibians, the lagena is localized in the posterior part of the sacculus, near the auditory structures; it performs mostly vestibular and (to a much lesser extent) auditory functions. In amniotes, the lagena was first separated from the sacculus; it is localized in the cochlear canal, distally with respect to the hearing organ. Information on the functions of the lagena in amniotes is rather limited and contradictory. Central projections of this organ have been examined practically only in birds. Lagenar afferents project to the vestibular nuclei and cerebellum, while some fibers come to the auditory nuclei of the medulla. The lagena in birds can be related to their navigation abilities (birds are supposed to be capable of orienting within the magnetic field of the Earth due to the magnetic properties of the lagenar otoconia; this structure can also provide detection of movements along the vertical axis. The close proximity between the otolithic and auditory endorgans in the cochlear canal of amniotes can be indicative of the functional significance of these interrelations. This aspect, however, remains at present undiscovered. In mammals (except Monotremata), there is no lagena as an independent endorgan. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 160–178, March–April, 2008.     

Mechanisms of madness: evolutionary psychiatry without evolutionary psychology

Delusions are currently characterised as false beliefs produced by incorrect inference about external reality (DSM IV). This inferential conception has proved hard to link to explanations pitched at the level of neurobiology and neuroanatomy. This paper provides that link via a neurocomputational theory, based on evolutionary considerations, of the role of the prefrontal cortex in regulating offline cognition. When pathologically neuromodulated the prefrontal cortex produces hypersalient experiences which monopolise offline cognition. The result is characteristic psychotic experiences and patterns of thought. This bottom-up account uses neural network theory to integrate recent theories of the role of dopamine in delusion with the insights of inferential accounts. It also provides a general model for evolutionary psychiatry which avoids theoretical problems imported from evolutionary psychology.     

Characteristics of interhemispheric relationships in the absence or presence of a skill

A comparative analysis of the time and amplitude characteristics of the negative N200 and positive P300 components of visual evoked potentials recorded at symmetric points of the frontal, parietal, temporal, and occipital areas of the right and left hemispheres of the cerebral cortex has been performed in subjects with or without the skill of operating a computer. Subjects inexperienced in an operator’s work exhibited an interhemispheric difference in the time and amplitude characteristics of the studied components. In subjects that had the skill of operating a computer, the interhemispheric difference was little, which suggests that the cortex plays only a small role in the cerebral control of this activity.     

Effects of two-vessel forebrain ischemia and of administration of indomethacin and quinacrine on Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase activity in various rat brain areas

The effect of a two-vessel forebrain ischemia (induced by occlusion of carotid arteries and hypotension), subsequent reperfusion, and administration of indomethacin and quinacrine on the Na⁺,K⁺-ATPase activity and diene conjugate content was studied in various rat forebrain fields. The most pronounced metabolic alterations were observed during ischemia and reperfusion. Under these effects, there was a statistically significant reduction of the Na⁺,K⁺-ATPase activity in the brain cortex and striatum and an increase of the diene conjugate content in the rat brain cortex in comparison with sham-operated animals. Injection of indomethacin, a cyclooxygenase inhibitor, to rats subjected to ischemia and reperfusion, resulted to a statistically significant increase of the Na⁺,K⁺-ATPase activity in the brain cortex, hippocampus, and striatum (p < 0.02) as compared with control animals. The diene conjugate content in the rat brain cortex during brain ischemia and reperfusion was statistically significantly lower in the rats injected with indomethacin. The effect of quinacrine (a blocker of phospholipase A₂) was similar to that of indomethacin in the rat cortex, whereas in the rat striatum and hippocampus, the quinacrine effect during ischemia and reperfusion was less marked than that of indomethacin. The obtained data indicate the ability of inhibitors of the arachidonic pathway of free radical formation to normalize the Na⁺, K⁺-ATPase activity during brain ischemia. There also revealed local peculiarities of metabolic disturbances in different regions of the rat forebrain during ischemia and reperfusion.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 41, No. 1, 2005, pp. 33–38.Original Russian Text Copyright © 2005 by Molchanova, Moskvin, Zakharova, Yurlova, Nosova, Avrova.     

Comparison of different methods of census of juvenile salmonids (Salmonidae) in the small river Mikocheva (Western Kamchatka)

Seinings of the lowland bed of a typical small river of Western Kamchatka demonstrated that of several methods for the census of juveniles of salmonids (Salmonidae) the most accurate result in comparison with complete removal is obtained by three-fold seining with calculation of abundance by the Zippin method. In comparison with a seine, a drive-in trap and electrofishing possess a lower average catching efficiency and a higher selectivity. The average density of fish estimated by the results of seining at the investigated stretch was 0.55–0.57 specimens/m².