Hemispheric asymmetry, modular variability and age-related changes in the human entorhinal cortex.

The verrucae areae entorhinalis (VAE) are a characteristic feature of the human brain that occupy the anterior and posterolateral parts of the parahippocampal gyri and correspond to the islands of layer II neurons. We analyzed VAE in 60 neurologically normal subjects ranging from 23 to 85 years of age using a casting method. In 10 of these subjects the total number of neurons in the entorhinal islands was estimated stereologically using the optical fractionator. The number and surface area of VAE were higher in the left hemisphere compared with the right, and this leftward asymmetry was highly significant. Regression analysis showed a negative correlation between average VAE area and age in both hemispheres, representing a rate loss of about 800 microm2 per year. The estimated number of neurons obtained with the optical fractionator showed no significant difference between the left and the right hemisphere (468,000+/-144,000 vs. 405,000+/-117,000). There was a highly significant negative correlation between neuron numbers and age in both sides. In addition, clusters of small, undifferentiated layer II neurons ('heterotopias') were frequently observed in the rostral part of the entorhinal cortex in young and elderly adults. Layer II entorhinal neurons are among the first to show neurofibrillary changes during normal aging. The present data confirm the occurrence of age-related neuron loss in the entorhinal cortex. Considering the consistent projections from ipsilateral auditory association areas that, together with Broca's motor-speech area (Brodmann areas 44 and 45), show leftward asymmetry from early infancy (such as Brodmann area 22, planum temporale, and area 52 in the long insular gyrus), we speculate that functional lateralization of the human entorhinal cortex may be associated with specialization for memory processing related to language. Due to the dependence of hippocampal formation on entorhinal projections, this finding is also consistent with the greater capacity of the left hippocampus for verbal episodic memory.

Ossicula Bertini in human adults.

Remnants of ossicula Bertini in their embryological position, i.e., joined to the ethmoid, were found in three out of 20 adult individuals aged 17-23 years. The ossicles closed the inferior and/or a part of the anterior wall of the sphenoidal sinus, being joined to the wall of the sinus by sutures. The existence of these formations might be of importance in inflammation of the sphenoid sinus, or disease in or around the nasopharynx.

The effects of aluminium on brain gangliosides in uraemic rats treated with 24R,25-dihydroxyvitamin D3.

The administration of aluminium to uraemic rats leads to aluminium accumulation in different brain regions. Aluminium intoxication significantly alters brain gangliosides, the content of which is increased in uraemic animals. This phenomenon can be prevented by administration of 24R,25-dihydroxyvitamin D3 (24,25(OH)2D3). Our results could possibly find an application in the prevention of aluminium-induced encephalopathy in patients on haemodialysis.

Development of the human fetal auditory cortex: growth of afferent fibres.

The sequential development and growth of the subcortico-cortical fibres have been studied by means of acetylcholinesterase (AChE; acetylcholine acetylhydrolase; EC 3.1.1.7) histochemistry on the serial sections obtained from brains of human fetuses ranging from 10 to 28 weeks of gestation. It was found that thalamic and basal telencephalic fibres approaching the fetal auditory cortex have very strong AChE reactivity during a prolonged period of growth. In the youngest fetuses (10.5 weeks) a prominent fibre system was seen emerging from the ventroposterior thalamic territory while the auditory neopallium was free of AChE staining. In older fetuses (16-18 weeks) AChE-positive fibres originating in the ventroposterior thalamus and basal telencephalon penetrate the 'subplate layer' of the auditory cortex. On the basis of AChE reactivity of the 'subplate layer' the auditory cortex can be delineated from the surrounding neocortical areas. In the oldest fetuses (22-28 weeks) AChE-positive fibres of thalamic origin penetrate the developing cortical plate of the auditory cortex.

Development of acetylcholinesterase (AChE) staining in human fetal auditory cortex.

In this study acetylcholinesterase (AChE) staining methods have been used to demonstrate the development of the prospective afferent fibres of auditory cortex in human fetuses ranging between 8 and 28 weeks of gestation. Earliest AChE positive staining was found in fetuses at 20--24 weeks in the neuropil of the marginal zone and throughout subplate layer of the auditory cortex. On the basis of this characteristic AChE staining pattern, the auditory cortex may be delineated from surrounding cortical areas. At 24--26 weeks, during intensive lamination of the cortical plate, AchE-positive reaction appears in the deep part of the cortical plate. In the oldest fetuses (28 weeks) a columnar pattern of vertical, darkly stained zones was seen in the middle third of the cortical plate. We conclude that AChE staining is characteristically distributed within cytoarchitectonic compartments and 'synaptic' layers of the developing auditory cortex. The AChE-positive layers coincide with the laminar pattern of synpatogeneis. Thus, AChE-positive reaction during development may serve as a parameter of cortical afferent (thalamic?) innervation of the auditory cortex. In addition, AChE reactivity may indicate the specific transmitter nature of the afferent fibres in the auditory cortex.

The laminar organization of the prospective auditory cortex in the human fetus (11--13.5 weeks of gestation).

The prospective auditory cortex was analysed in human fetuses at 11--13,5 post-ovulatory weeks with Nissl, Golgi and E.M. techniques. At 11--12 weeks, marginal, cortical plate, intermediate, subventricular and ventricular layers were recognized. Post-migratory neurons with developing dendrites were seen in marginal layer, cortical plate and superficial part of the intermediate zone only. At 12--13,5 weeks the superficial part of the intermediate zone is transformed into the true cortical layer--"subplate layer"--characterized by maturing neurons with growing dendrites, fine axonal arborization and low cell density. The neuronal circuitry elements are thus present very early in the prospective auditory cortex and distributed throughout the deep cortical plate of the "subplate layer" corresponding to the synaptic territory of other areas of the human fetal cortex.