Evidence for a molecular code for learned shock-avoidance in cockroaches

An exploration of how to define and measure the evolution of behavior, learning, memory and mind across the full phylogenetic tree of life

There are probably few terms in evolutionary studies regarding neuroscience issues that are used more frequently than ‘behavior', ‘learning', ‘memory', and ‘mind'. Yet there are probably as many different meanings of these terms as there are users of them. Further, investigators in such studies, while recognizing the full phylogenetic spectrum of life and the evolution of these phenomena, rarely go beyond mammals and other vertebrates in their investigations; invertebrates are sometimes included. What is rarely taken into consideration, though, is that to fully understand the evolution and significance for survival of these phenomena across phylogeny, it is essential that they be measured and compared in the same units of measurement across the full phylogenetic spectrum from aneural bacteria and protozoa to humans. This paper explores how these terms are generally used as well as how they might be operationally defined and measured to facilitate uniform examination and comparisons across the full phylogenetic spectrum of life. This paper has 2 goals: (1) to provide models for measuring the evolution of ‘behavior' and its changes across the full phylogenetic spectrum, and (2) to explain why ‘mind phenomena' cannot be measured scientifically at the present time.

A ganglionic model of "learned helplessness"

The phenomenon known as "learned helplessness" (LH) is seen broadly across the animal kingdom. Some of the basic characteristics of this behavior are: failure to escape shock when it is possible to do so following non-escapable shock; reversion to non-escape behavior even after successful escape; if the animal is given escape/avoidance training prior to being given inescapable shocks, the latter will not interfere with its ability to later show normal escape/avoidance behavior (generally described as an immunization effect); following inescapable shock training the animals often become "passive and still" when confronted with an inescapable shock. These behaviors are seen in intact mammals, lower vertebrates, and invertebrates. In fact, the basic characteristics are even seen in a spinal rat and, with the exception of one characteristic not yet examined, in an isolated thoracic ganglion of an insect. The brain is evidently not essential either in mammals or in invertebrates for demonstrating this behavior. Not only can an insect ganglion show the behavioral characteristics of LH, but the neural information underlying the phenomenon of LH can be shown to transfer from one ganglion innervating one pair of legs to another ganglion innervating a different pair of legs. Thus, how CNS information underlying LH is coded and transferred from one site to another within the CNS can be examined in such a system. The LH model has provided valuable insights into the physiology of depression. This model suggests that human depression is caused by one's lack of control over traumatic events. It is supported by a number of parallels between depression and LH behavior. Tricyclic antidepressants, MAO inhibitors, and ECT, which are effective in treating depression, also can prevent and reverse LH in mammals. It would be important to find out if they are also effective in invertebrate models. The fact that the characteristics of the behavior called LH are seen in invertebrates such as slugs, cockroaches, and locusts provokes other intriguing questions about the presence of cognition at these phylogenetic levels, as well as what animal or preparation constitutes an appropriate model for human depression.

Respiratory and enzymatic properties of squid heart mitochondria

Mitochondria isolated from systemic hearts of the squid Illex illecebrosus showed high respiratory control ratios, and, with appropriate substrates, the expected ADP/O ratios. Of amino acids tested, proline and ornithine were oxidized at highest rates; of carboxylates, malate, succinate and pyruvate gave the highest state-3 respiration rates. Pyruvate oxidation is enhanced with proline, ornithine, and 1-pyrroline-5-carboxylate (pyrroline carboxylate) all of which can serve to augment the Krebs cycle. However, proline, ornithine and pyrroline carboxylate oxidation is not similarly dependent upon pyruvate. Rotenone inhibited state-3 respiration of malate, proline, ornithine and pyrroline carboxylate. Neither intermediates of fatty acid oxidation nor glycerol 3-phosphate were utilized at significant rates. Key enzymes in proline and ornithine oxidation, i.e. proline dehydrogenase, pyrroline-carboxylate dehydrogenase, ornithine aminotransferase, and glutamate dehydrogenase were located in the mitochondria. The synthesis of proline is catalyzed by pyrroline-carboxylate reductase, which was found exclusively in the cytosol. The respiration, phosphorylation and enzyme data taken together suggest that the main carbon sources for heart mitochondria of Illex are pyruvate plus the proline and ornithine pool.