Mitochondrial protein synthesis may be involved in long-term memory formation.

The hypothesis that two qualitatively different stages of cerebral protein synthesis (PS) are required for the formation of long-term memory (LTM) for an active-avoidance task was investigated in rats. Cytoplasmic PS was inhibited with anisomycin (ANI-5.0 mg subcutaneously). When ANI was injected at 15 min pre- and 30 min posttraining, so that cerebral PS was inhibited by 90% for 2 hours starting just before training. LTM formation was prevented. When ANI was given after training, it was not effective. Mitochondrial PS was inhibited with chloramphenicol (CAP-1.5 mg intracisternally). Inhibition occurred 40 min after the injection. CAP interfered with LTM formation only when injected between 15 and 55 min after training. From these data it was concluded that two stages of PS are required for the formation of LTM. The first one takes place in the cytoplasm, starts with the commencement of training and is independent of newly synthesized mRNA. The second stage takes place in mitochondria starting approximately 25 min after training and is dependent upon newly formed mRNA.

Exponential data-analysis of passive-avoidance behavior in rats and mice.

Data obtained with the passive-avoidance task are usually presented as the median values of the latencies to respond. In an earlier publication we described a better way of presenting such data based on the observation that the complement of the cumulative distribution of step-through latencies can be closely fitted by a simple exponential function. Thus the "step-through rate constant" (STRC) is concise and accurate quantitative description of population behavior in this test. In this paper we present two examples of the application of this procedure. In the first, variation in the interval between training and testing in rats changes the STRCs of the different groups. In the second (based on data published by Flood et al.) administration of cycloheximide is seen to partition the experimental population of mice into two subgroups with different STRCs.

Proposal for APS-IUPS convention for diagraming physiological mechanisms.

As physiological research reveals the existence of systems of increasing complexity and the existence of important interactions between them, the diagrammatic depiction of those systems and their interactions becomes an essential step in clarifying our own concepts in scientist-to-scientist communication and in teaching. Although control engineers, electronic engineers, and computer programmers long ago established their own diagrammatic conventions, physiologists are only now beginning to feel the need for a uniform convention suited to their own special needs in place of the numerous (and mostly ad hoc) diagram types that have recently proliferated in the literature. The convention proposed here is based on a formal theory of mechanism developed by W. Ross Ashby (An Introduction to Cybernetics, 1956). Its purely mechanistic structure transcends traditional interdisciplinary barriers to communication. Wide acceptance of the convention proposed here would therefore enhance the ability of physiology to encompass mechanisms from molecular and cell biology and integrate them with general and systems physiology in a metadisciplinary effort to comprehend "the wisdom of the body." Among its many advantages is its simplicity; diagrams may be drawn at various levels of detail and complexity by use of a few basic rules, and they can be readily understood without knowledge of the theory.

A novel method for quantifying passive-avoidance behavior based on the exponential distribution of step-through latencies.

In the extensive literature dealing with the one-trial passive-avoidance task the data are usually represented by the median latency to respond. We propose here a novel representation and analysis of passive-avoidance data which is based on the observation that the complement of the cumulative distribution of step-through latencies (i.e., the fraction of animals remaining in the safe compartment) decays exponentially with time from the onset of the trial. A remarkably close fit of this complementary distribution is seen when the best-fitting straight line is drawn through the data points plotted on semilog coordinates. The slope of this line k, which we call "the step-through rate constant," (or alternatively, the T1/2 which is equal to 0.69/k) provides an accurate description of the population behavior as a whole in most cases. In view of the exponential distribution of passive-avoidance data this treatment appears to be more appropriate than the widely-used measures of central tendency, the median and mean. It is applicable to research on the effects of drugs on passive-avoidance memory, and probably appropriate to other behavioral paradigms and species.

Effects of hypoxia on memory consolidation: implications for a multistage model of memory.

Anoxia treatment given 2.5 or 5 min after a single trial passive avoidance task in day-old chicks yielded a temporary retention loss between 20 and 50 min after learning. No effect was obtained when the treatment was administered immediately or 10 min after learning. The temporary retention deficit was not due to a generalized retrieval loss since anoxia given at various times after 10 min following learning with retention tested 30 or 60 min after anoxia treatment, did not yield a retention deficit. Similar findings were obtained with hypoxia. The implications of the results for a multistage model of memory were examined. In particular, it was suggested that the temporary retention deficit may be due to the breakdown of retrieval mechanisms associated with the second stage in a 3-stage model of memory processing.

Delayed post hypoxic transient amnesia is not associated with electrical brain seizures.

Rats rendered hypoxic by brief exposure to N2 after learning an avoidance response go into convulsions and subsequently become amnestic. Overt convulsions can be avoided whilst yet producing delayed post-hypoxic transient amnesia (DPHTA) by using 2% O2 in N2 in place of pure N2. The experiments reported here show that with this gas mixture, the ECoG shows hardly any of the electrical activity associated with seizures which occurs with N2. It is concluded that electrical seizures are not associated with the mechanism responsible for DPHTA.

Retrograde amnesia production by the intracisternal injection of 20 micronl of saline in rats.

The intracisternal injection of 20 micronl of saline into a rat within an hour after training it in an active avoidance response was found to induce retrograde amnesia. The results obtained by combining this procedure with the intracisternal injection of 2,6 Diaminopurine (DAP), which inhibits RNA synthesis and prevents long-term memory formation when administered at the proper time and in the correct dosage, suggest the existence of a medium term memory (MTM) mechanism. MTM was normally evident up to 75 min after training but was demonstrable up to 210 min when LTM formation was prevented by DAP.

Transport of plasma FFA in cats; effect of hypothalamic stimulation.

Two tracer methods, repetitive single injection of [3-H]palmitate and continuous infusion of [1 minus 14-C]palmitate, were applied simultaneously to study tracer kinetics of the free fatty acid (FFA) miscible pool in anesthetized cats before, during, and after electrical stimulation of the hypothalamus. The results indicated that the FFA pool of the cat behaved as though it consisted of two compartments which exchange FFA with each other. The data were analyzed according to a two-compartmental mammillary system model. The space of the central compartment which represents the plasma was found to be 74 ml/kg body wt. No anatomical significance could be unequivocally ascribed to the peripheral compartment. The variables of the model system were determined for each cat, and a highly significant positive linear relationship between the net FFA transport (mumol/min) and the total quantity of FFA (mumol) in both compartments was established by a regression analysis of the control data. No significant changes were observed in this relationship during or following hypothalamic stimulation which had a significant effect on the plasma FFA level. This result suggests that hypothalamic stimulation affects FFA mobilization by modifying the rate of FFA inflow into the circulation, while the mechanisms for clearing FFA from the plasma are not altered.

Effect of electrical stimulation of the hypothalamus on plasma free fatty acid concentration in cats.

The effect of electrical stimulation of various hypothalamic regions on levels of plasma free fatty acids, glucose, triglycerides, and cholesterol was studied in fasted cats. Appreciable changes were observed in plasma free fatty acids and glucose but not in plasma triglycerides or cholesterol. These changes appeared to be dependent upon small differences in the placement of electrodes and could not be related to a distinct hypothalamic locus. The results indicate that there is a dissociation between hypothalamic neurons that may affect plasma glucose concentration and those that may affect the plasma free fatty acids. It is suggested that the hypothalamus of the cat contains neurons that may influence autonomic discharge to adipose tissue and thus affect the plasma free fatty acid level and other neurons that may influence autonomic discharge to the liver and thus affect glucose output into the circulation. The distribution of both types of neurons is not limited to a distinct region of the hypothalamus in cats.