Critical Time-Window for NO–cGMP-Dependent Long-Term Memory Formation after One-Trial Appetitive Conditioning

Abstract

The nitric oxide (NO)-cGMP signaling pathway is implicated in an increasing number of experimental models of plasticity. Here, in a behavioral analysis using one-trial appetitive associative conditioning, we show that there is an obligatory requirement for this pathway in the formation of long-term memory (LTM). Moreover, we demonstrate that this requirement lasts for a critical period of approximately 5 hr after training. Specifically, we trained intact specimens of the snail Lymnaea stagnalis in a single conditioning trial using a conditioned stimulus, amyl-acetate, paired with a salient unconditioned stimulus, sucrose, for feeding. Long-term associative memory induced by a single associative trial was demonstrated at 24 hr and shown to last at least 14 d after training. Tests for LTM and its dependence on NO were performed routinely 24 hr after training. The critical period when NO was needed for memory formation was established by transiently depleting it from the animals at a series of time points after training by the injection of the NO-scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide (PTIO). By blocking the activity of NO synthase and soluble guanylyl cyclase enzymes after training, we provided further evidence that LTM formation depends on an intact NO-cGMP pathway. An electrophysiological correlate of LTM was also blocked by PTIO, showing that the dependence of LTM on NO is amenable to analysis at the cellular level in vitro. This represents the first demonstration that associative memory formation after single-trial appetitive classical conditioning is dependent on an intact NO-cGMP signaling pathway.

Critical role of nitric oxide-cGMP cascade in the formation of cAMP-dependent long-term memory

“…Previous studies on the roles of the NO-cGMP pathway in long-term neural plasticity in the rat hippocampus (Lu et al 1999;Lu and Hawkins 2002) and in nociceptive sensory receptors in Aplysia (Lewin and Walters 1999) suggested that the NO-cGMP pathway acts in parallel with the cAMP-PKA pathway to activate CREB, via PKG, for the formation of long-term neural plasticity. The NO-cGMP pathway plays an essential role in many systems of long-term neural and behavioral plasticity (Kendrick et al 1997;Hawkins et al 1998;Wong et al 1999;Katzoff et al 2002;Kemenes et al 2002;Lev-Ram et al 2002). It would be interesting to determine the extent by which our finding that the NO-cGMP pathway triggers LTM formation by stimulating the cAMP pathway is applicable to other systems.…”

Stimulation of the cAMP system by the nitric oxide-cGMP system underlying the formation of long-term memory in an insect

“…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).…”

“…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).…”

Nitric oxide-coupled signaling in odor elicited molecular events in the olfactory center of the terrestrial snail, Helix pomatia

“…and Lymnaea stagnalis sGC isoforms and subunits were cloned and shown to be associated with NO signaling in the olfactory system, and in an identified modulatory neuron regulating the feeding program [42,56,57]. In the appetitive behavior of Lymnaea stagnalis the NO-cGMP step was required in the course of early events of memory acquisition [58]. However, both in Aplysia sp.…”