Visual attention and neuronal firing patterns in the feline pulvinar nucleus of thalamus

In behaving cats, temporal patterns of neuronal firing were studied during slow wave sleep (SWS), motionless quiet wakefulness (QW) coupled with specific direction of the animal's attention, and during bar pressing performance (BP) for milk reward. The analysis was based on relative relations between sequential spike intervals. The strength of the method is based on the fact that the probabilities of occurrence of patterns are determined by the history of a spike train. During SWS, the neuronal firing modes closely followed the theoretical model of independent distribution of intervals, whereas during QW and BP specific for each neuron departures from the model, i.e., patterning was observed. Most importantly, in seven chronically studied neurons idiosyncratic patterns were related to direction of the animal's attention, and, very likely, to the visual forms the animals gazed at, because the patterns disappeared in the dark and during SWS without major changes in the mean firing rate. The replications of patterns upon recurrence of a particular direction of attention was proven statistically. The constancy and idiosyncrasy of these patterns were apparent even though the comparable episodes occurred several hours apart, and the animals slept and/or ate in between, and the distance, i.e., the retinal size of visual forms varied from one episode to another. On the basis of correlative evidence, it was argued that, compared to more abstract modes of information processing, the identification and quantification of patterns based on relative relations between intervals require the least amount of storage of intermediate results. Hence, these patterns are likely to represent a simple and phylogenetically old principle of communication between neurons. It was postulated that the idiosyncrasy and invariance of patterns may play a role in constancy of feature extraction and Gestalt perception.

Different pattern of codon recognition by mammalian mitochondrial tRNAs

Analysis of an almost complete mammalian mitochondrial DNA sequence has identified 23 possible tRNA genes and we speculate here that these are sufficient to translate all the codons of the mitochondrial genetic code. This number is much smaller than the minimum of 31 required by the wobble hypothesis. For each of the eight genetic code boxes with four codons for one amino acid we find a single specific tRNA gene with T in the first (wobble) position of the anticodon. We suggest that these tRNAs with U in the wobble position can recognize all four codons in these genetic code boxes either by a "two out of three" base interaction or by U.N wobble.

Acute calcium nephrotoxicity. An electron microscopical and semiquantitative light microscopical study

Rats were infused for three hours with doses of calcium gluconate to elevate serum calcium level and were killed either immediately after infusion or after 24 hours. Necrosis of proximal tubular cells was observed when serum calcium level was 16.0 mg/dl or higher. Above 16.0 mg/dl, an additional 5% of renal tubular profiles contained damaged cells for each 1 mg/dl in serum calcium. No difference in extent of damage was found in rats killed immediately or after 24 hours. Initial changes were formation of granular dense bodies in mitochondria, cell swelling, rupture, and extensive mitochondrial calcification. Renal tubular basement membrane changes appeared to be initiated by protrusion of cytoplasmic buds, forming ovoid bodies, which became embedded in the basement membrane. These ovoid bodies then appeared to serve as a nidus for further extensive basement membrane calcification.