The problem of molecular coding of neural information. A critical review

An RNA-Based Theory of Natural Universal Computation

Life is confronted with computation problems in a variety of domains including animal behavior, single-cell behavior, and embryonic development. Yet we currently do not know of a naturally existing biological system that is capable of universal computation, i.e., Turing-equivalent in scope. Generic finite-dimensional dynamical systems (which encompass most models of neural networks, intracellular signaling cascades, and gene regulatory networks) fall short of universal computation, but are assumed to be capable of explaining cognition and development. I present a class of models that bridge two concepts from distant fields: combinatory logic (or, equivalently, lambda calculus) and RNA molecular biology. A set of basic RNA editing rules can make it possible to compute any computable function with identical algorithmic complexity to that of Turing machines. The models do not assume extraordinarily complex molecular machinery or any processes that radically differ from what we already know to occur in cells. Distinct independent enzymes can mediate each of the rules and RNA molecules solve the problem of parenthesis matching through their secondary structure. In the most plausible of these models all of the editing rules can be implemented with merely cleavage and ligation operations at fixed positions relative to predefined motifs. This demonstrates that universal computation is well within the reach of molecular biology. It is therefore reasonable to assume that life has evolved - or possibly began with - a universal computer that yet remains to be discovered. The variety of seemingly unrelated computational problems across many scales can potentially be solved using the same RNA-based computation system. Experimental validation of this theory may immensely impact our understanding of memory, cognition, development, disease, evolution, and the early stages of life.

The morphological basis of age-induced memory changes

The results are presented of a layer-by-layer electron microscopic study of the cortex (40th area) in persons aged 78, 79, and 83 years whose anamneses did not include any neuropsychic disorders and who had died during surgical intervention These findings are examined in the light of current hypotheses about the morphological substrate of the mechanisms of memory. Cortical changes are uncovered which, according to these hypotheses, lie at the basis of the memory mechanisms. These include changes of the cytoplasm, neurocytes, dendrites, spines, axons, and their terminals. The same types of changes are found in the auditory cortex of old cats used for the control of the degree of preservation of elements of the human cortex.

Interanimal transferability of taste aversion learning for 0.1% saccharin

Three experiments were performed to assess the interanimal transferability of conditioned taste aversion to 0.1% saccharin. Two experiments used an intracerebrospinal fluid (subdural) route for administering brain extracts and a third used an intraperitoneal (IP) route. As assessed by repeated measurements ANOVA, saccharin consumption was significantly lower during extinction of conditioned aversion for experimental recipients (ER) receiving extracts from aversively conditioned donors, than that of control recipients (CR), receiving extracts from unconditioned donors in one subdural experiment, F(21, 189) = 1.61, p less than 0.05. In the IP experiment the results were in the same direction, though not significant, F(34, 238) = 1.39, p less than 0.1. Results of the other subdural experiment are discussed. It is concluded that these experiments with the conditioned taste aversion paradigm have potential as a model for investigations of behavioral interanimal transfer (BIT) and for neuromolecular research aimed at identification of associated putative neurochemical(s) and the elaboration of their mechanism of action.

Scotophobin A causes dark avoidance in goldfish by elevating pineal N-acetylserotonin

We had shown that synthetic rat scotophobin A caused several effects upon goldfish, apparently mediated by the pineal gland. Here we report that norepinephrine decreased goldfish dark avoidance in a manner that was blocked by scotophobin or pinealectomy. Increased dark avoidance was caused by either propranolol or scotophobin alone. Certain components of the pineal melatonin pathway also affected goldfish light-dark preference: serotonin, and especially N-acetylserotonin, increased dark avoidance, as did the hydroxyindole-O-methyl-transferase (HIOMT) product inhibitor, S-adenosyl-homocysteine. Melatonin and S-adenosyl-methionine were without effect in this regard. Pinealectomy prevented the dark avoidance increase caused by serotonin and N-acetylserotonin. These data suggested that increased dark avoidance behavior in goldfish was correlated with N-acetylserotonin buildup in the pineal, and that scotophobin could cause this, if it were to inhibit pineal HIOMT. To test this hypothesis the effect of various agents upon pineal melatonin levels was determined. Scotophobin was found to both reduce pineal melatonin and to block the melatonin-increasing effect of N-acetylserotonin. This led to the discovery that, indeed, scotophobin was an effective inhibitor (KI50, 6 x 10(-7) M) of purified bovine HIOMT.

Scotophobin A causes several responses in goldfish if the pineal gland is present

Rat scotophobin A increased dark avoidance in goldfish in dark and light avoidance shuttlebox experiments, controlled for general and light cycling-induced swimming activity. A possible site of action for scotophobin was suggested by the reports that dark avoidance was also increased in goldfish by pinealectomy, a treatment which increased shock sensitivity as well. It was found that scotophobin alone decreased the voltage required to induce tail-flip contractures in goldfish. The pineal gland was further implicated in the mode of action of scotophobin when it was found that this peptide suppressed the norepinephrine-induced aggregation of goldfish chromatophores whose state is in part controlled by pineal melatonin. Pinealectomized goldfish became insensitive to the effects of scotophobin upon both light-dark preference and chromatophore aggregation state. There observations strongly suggest that the pineal gland is required for the action of scotophobin.

Isolation and identification of two learning-induced brain peptides

Goldfish were trained either to avoid the blue compartment of a tank and swim into the green compartment or, conversely, to avoid green and prefer blue. Preliminary experiments indicated that acquisition of the avoidance behavior was associated with the presence in the brain of two peptides, one found in blue avoiding (BA), another in green avoiding (GA) fish. With the help of behavioral bioassays, the peptides were isolated and purified, and their structure was determined by ultrasmicroanalytical techniques. The sequence of the BA peptide, pglu-ile-gly-ala-val-phe-pro-leu-lys-tyr-gly-ser-lys-OH was reproduced by synthesis. Sequential analysis of the GA peptide gave two alternative structures, NAc-lys-gly-gln-ile-ala-val-phe-pro-leu-lys-tyr-gly-ser-OH or NAc-lys-gly-ala-val-gln-ile-phe-pro-lys-tyr-gly-ser-OH, both of which are being synthetized to be compared with the natural compound. Overlapping sequences between the BA and GA peptides suggest the existence of a family of peptides associated with behavior based on color discrimination.

Stimulus specific effect of scotophobin on mouse plasma corticoids

Scotophobin is a peptide previously extracted from brains of rodents shocked in the dark compartment of a white/dark apparatus and identified as the behaviorally active dark avoidance-inducing factor. This study attempted to ascertain whether a stable synthetic analog of scotophobin induced no adrenocortical stress reaction, a generalized, unconditioned stress reaction, or a stress reaction selectively triggered by the dark compartment of the apparatus. Twenty eight mice were injected IP with the synthetic substance and 28 with placebo. A day later half of each group was placed in the dark compartment and the other half in the light compartment. Fifteen min afterward, the animals were bled, and serum samples were obtained. Plasma corticoid levels were determined by radioassay. Only the animals injected with scotophobin analog and exposed to the dark box had elevated levels. The interaction effect between drug treatment and light or dark environment was highly significant.