Background: In insect classical conditioning, octopamine (the invertebrate counterpart of noradrenaline) or dopamine has been suggested to mediate reinforcing properties of appetitive or aversive unconditioned stimulus, respectively. However, the roles of octopaminergic and dopaminergic neurons in memory recall have remained unclear.

The nitric oxide (NO)-cGMP signaling system and cAMP system play critical roles in formation of multiple-trial induced, protein synthesis-dependent long-term memory (LTM) in many vertebrates and invertebrates. The relationship between the NO-cGMP system and cAMP system, however, remains controversial. In honey bees, the two systems have been suggested to converge on protein kinase A (PKA), based on the finding in vitro that cGMP activates PKA when sub-optimal dose of cAMP is present. In crickets, however, we have suggested that NO-cGMP pathway operates on PKA via activation of adenylyl cyclase and production of cAMP for LTM formation. To resolve this issue, we compared the effect of multiple-trial conditioning against the effect of an externally applied cGMP analog for LTM formation in crickets, in the presence of sub-optimal dose of cAMP analog and in condition in which adenylyl cyclase was inhibited. The obtained results suggest that an externally applied cGMP analog activates PKA when sub-optimal dose of cAMP analog is present, as is suggested in honey bees, but cGMP produced by multiple-trial conditioning cannot activate PKA even when sub-optimal dose of cAMP analog is present, thus indicating that cGMP produced by multiple-trial conditioning is not accessible to PKA. We conclude that the NO-cGMP system stimulates the cAMP system for LTM formation. We propose that LTM is formed by an interplay of two classes of neurons, namely, NO-producing neurons regulating LTM formation and NO-receptive neurons that are more directly involved in formation of long-term synaptic plasticity underlying LTM formation.3 Main textRecent studies have suggested that many of the molecular mechanisms underlying learning and memory are conserved among vertebrates and invertebrates, the most convincing evidence for which has been obtained by the study of the mechanisms of the formation of LTM [7]. LTM is defined as a protein synthesis-dependent phase of memory lasting for day to a lifetime. It is usually formed by multiple pairing trials but not by a single trial. It has been demonstrated that the cAMP signaling system plays critical roles in producing LTM, or long-term synaptic plasticity considered to underlie LTM formation, in mammals [1], insects [6,19] and mollusks [2]. In all of these animals, production of cAMP stimulates PKA, and this activates the transcription factor CREB (cAMP element-binding protein). Activation of CREB leads to a protein synthesis-dependent long-term synaptic plasticity that underlies LTM formation [7,20].The NO-cGMP system also plays critical roles in the formation of LTM in mammals [9], honey bees [15,16], crickets [14] and mollusks [8]. NO is a membrane-permeable intercellular signaling molecule produced by NO synthase (NOS).NO diffuses into neighboring cells and stimulates soluble guanylyl cyclase, and produced cGMP plays various physiological roles [5], including induction of LTM in many animals.In crickets, we have reported that the NO-cGMP system and cAMP system play major roles in formatio...

Reactive oxygen species (ROS), including superoxide anions, hydrogen peroxide and hydroxyl radicals, can be produced in vivo by mechanisms related to mitochondrial respiration, xanthine oxidase (XOD), nitric oxide synthase (NOS), NADPH oxidase, and arachidonic acid metabolism.1,2) Disruption to one or more of these mechanisms is thought to be responsible for the pathogenesis of various diseases. [3][4][5][6] Of these mechanisms, XOD may be involved in the generation of ROS in the endothelium during ischemia and/or reperfusion. 7,8) Roy and McCord demonstrated that xanthine dehydrogenase is proteolytically converted to XOD in tissues within seconds or minutes of an ischemic episode, depending on the tissue involved. 9) Although both enzymes are involved in the catabolism of purine compounds, the latter transfers electrons to molecular oxygen to yield the ROS, superoxide anions and hydrogen peroxide. 10,11) Thus, the deleterious effects of reoxygenation or reperfusion in ischemic tissues can therefore be explained on the basis of the ROS produced by the xanthine-XOD (XϩXOD) system. For a better understanding of the pathogenesis of tissue damage by ROS, it is important to clarify which species of oxygen intermediates are involved in these events, and whether or not there are differences in sensitivity to ROS among various tissues.The direct effects of ROS on cultured vascular endothelial cells or isolated, perfused tissues have been extensively investigated, either by using ROS directly, or using a ROS-generating system, such as the XϩXOD system. [12][13][14][15][16][17] In these studies, ROS scavengers are used to clarify the species of ROS involved in these effects. Among the various biological effects attributed to ROS, vascular endothelial dysfunction has consistently been noted, irrespective of the preparations used. 2,18) In addition, ROS generated by the XϩXOD system caused contraction of rat pulmonary artery 19) and canine basilar artery, 20) whereas it relaxed canine coronary artery, 21) implying the existence of species or tissue differences in response to ROS. Furthermore, the responses of arteries to ROS are well-known to be influenced by the presence of endothelium. 12,13,16) Thus, the responses of the vasculature, including the endothelium, to ROS are complex, and the sensitivity to ROS probably varies depending on the tissue involved. Disruption to the functional integrity of blood vessels will inevitably alter the function of the organ supplied by these vessels. Thus, in the present study, we directed our attention to the effects of ROS on porcine coronary artery, in terms of muscular and endothelial functions, and attempted to determine characteristics of the responses of each vascular element, and to clarify the specific ROS involved. MATERIALS AND METHODS Preparation of Coronary Arterial RingsPorcine hearts, immersed in ice-cooled saline, were transported to the laboratory from an abattoir, usually within 1 h of death. The left anterior descending coronary artery was isolated 2-3 cm from its orig...

No abstract