5-6-dichloro-1-beta-d-ribofuranosylbenzimidazole-3--5--monophosphorothioate and 8-chloroadenosine-3--5--cyclic-monophosphorothioate

Activation of the cAMP pathway was found to be implicated in the memory process. In the context-signal learning paradigm of the crab Chasmagnathus, the protein kinase (PKA) activator Sp-5,6-DCl-cBIMPS facilitated long-term memory (LTM) induced by spaced training while the PKA inhibitor 8-chloroadenosine-3', 5'-monophosphorothioate, Rp-isomer (Rp-8-Cl-cAMPS) produced amnesia. In the present report the effect of the PKA inhibitor on long-term retention was assessed when administered (systemic injection of 2 microg/animal) at various times after training. According to previous results obtained with a lower dose, retention is impaired when the drug is administered immediately pretraining. An effect on acquisition was ruled out considering that the drug did not affect the performance during training. On the contrary, no effect of the PKA inhibitor was found with an immediately posttraining injection and amnesia was observed only when training was shortened from 15 to 12 trials (training duration from 45 to 36 min). At 2 and 12 h posttraining Rp-8-Cl-cAMPS injection failed to impair retention, but amnesia was found when the drug was injected at 4 and 8 h after training. In order to assess a possible effect of the drug in retrieval, the PKA inhibitor was administered 15 min before testing, and no amnestic effect was observed. These results suggest that two phases of PKA activity are required during consolidation of LTM, one during training and the other between 4 and 8 h after training. The link between these two periods of PKA activation and the two phases of the transcription factor NF-kappaB activation previously found in this model, as well as the similar time course found in rodents, is discussed. An amnestic effect of the drug was not found when administered immediately before a massed training protocol that yielded an intermediate-term memory, suggesting that in this type of memory PKA activation is not required.

Topics: Animals; Brachyura; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dichlororibofuranosylbenzimidazole; Enzyme Activation; Enzyme Inhibitors; Male; Memory; Thionucleotides; Time Factors

The effect of the stable prostacyclin analog iloprost and its mechanism of action were investigated with the use of pressurized rat tail small arteries with a spontaneous myogenic tone. Iloprost concentration dependently dilated these vessels with a half-maximal effective dose of 5.0 +/- 0.5 x 10(-8) M. Application of 10(-7)-10(-6) M glibenclamide, a blocker of ATP-sensitive potassium (K(ATP)) channels, inhibited the iloprost-induced dilation. Glibenclamide did not affect the basal vessel diameter. The application of 5 x 10(-5)-10(-3) M tetraethylammonium (TEA) and 5 x 10(-9)-10(-7) M iberiotoxin, blockers of calcium-activated potassium (K(Ca)) channels, decreased vessel diameter in the presence of iloprost. Both TEA and iberiotoxin reduced the basal vessel diameter. Glibenclamide at 10(-6) M inhibited the dilation produced by 5 x 10(-5) M Sp-5,6-DCl-cBIMPS, an activator of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. Iberiotoxin at 10(-7) M decreased vessel diameter in the presence of Sp-5,6-DCl-cBIMPS. H-89 and Rp-8-CPT-cAMPS, blockers of cAMP-dependent protein kinase A (PKA), inhibited the iloprost-induced dilation of these vessels. With use of the whole cell configuration of the patch-clamp technique, it was observed that 5 x 10(-7) M iloprost enhanced an outward current, determined largely by K(Ca) channels, 1.79 +/- 0.17-fold in freshly isolated smooth muscle cells from rat tail small artery. These data show that iloprost dilates rat tail small arteries with a spontaneous myogenic tone and suggest that K(ATP) as well as K(Ca) channels are involved in this effect, which is mediated, at least partly, by PKA.

Topics: Adenosine Triphosphate; Animals; Arteries; Calcium; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dichlororibofuranosylbenzimidazole; Enzyme Inhibitors; Glyburide; Iloprost; In Vitro Techniques; Kinetics; Male; Muscle, Smooth, Vascular; Peptides; Potassium Channels; Rats; Rats, Inbred WKY; Scorpion Venoms; Tail; Tetraethylammonium; Tetraethylammonium Compounds; Thionucleotides; Vasoconstriction; Vasodilation

On sudden presentation of a danger stimulus, the crab Chasmagnathus elicits an escape response that habituates promptly and for a long period. We have previously reported that administration of a cAMP-permeable analog (CPT-cAMP) along with a phosphodiesterase inhibitor (IBMX) improves long-term habituation (LTH). In present experiments we studied the effect of systemic administration of the protein kinase A (PKA) activator Sp-5,6-DCl-cBIMPS and that of the PKA inhibitor Rp-8-Cl-cAMPS on LTH tested 24 h after a weak training protocol (5 trials of danger stimulus presentation) or a strong training protocol (15-30 trials), respectively. A 50 microliters pre-training injection of 75 microM Sp-5,6-DCl-cBIMPS, and to a lesser degree of 25 microM, improved retention of the habituated response but not affect short-term habituation (STH). Like pre-training injection, post-training administration of Sp-5,6-DCl-cBIMPS proved to exert a facilitatory action on retention though with 75 microM dose only. Conversely, both pre- and post-training injection of 25 microM Rp-8-Cl-cAMPS impaired LTH without affecting STH. Thus, the PKA activator Sp-5,6-DCl-cBIMPS enables a weak training to produce LTH while the PKA inhibitor Rp-8-Cl-cAMPS impairs LTH when a strong training is given. Activation of crab PKA by Sp-5,6-DCl-cBIMPS and its inhibition by Rp-8-Cl-cAMPS were assessed using an in vitro PKA activity assay. These results provide independent evidences supporting the view that PKA plays a key role in long-term memory storage in this learning paradigm.

Topics: Amnesia; Animals; Antineoplastic Agents; Brachyura; Brain Chemistry; Conditioning, Psychological; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dichlororibofuranosylbenzimidazole; Ganglia, Invertebrate; Habituation, Psychophysiologic; Male; Memory; Thionucleotides