Pre-test epinephrine injections reverse DDC-induced retrograde amnesia

Neuromodulatory signaling in hippocampus-dependent memory retrieval

Considerable advances have been made toward understanding the molecular signaling events that underlie memory acquisition and consolidation. In contrast, less is known about memory retrieval, despite its necessity for utilizing learned information. This review focuses on neuromodulatory and intracellular signaling events that underlie memory retrieval mediated by the hippocampus, for which the most information is currently available. Among neuromodulators, adrenergic signaling is required for the retrieval of various types of hippocampus-dependent memory. Although they contribute to acquisition and/or consolidation, cholinergic and dopaminergic signaling are generally not required for retrieval. Interestingly, while not required for retrieval, serotonergic and opioid signaling may actually constrain memory retrieval. Roles for histamine and non-opioid neuropeptides are currently unclear but possible. A critical effector of adrenergic signaling in retrieval is reduction of the slow afterhyperpolarization mediated by β1 receptors, cyclic AMP, protein kinase A, Epac, and possibly ERK. In contrast, stress and glucocorticoids impair retrieval by decreasing cyclic AMP, mediated in part by the activation of β2 -adrenergic receptors. Clinically, alterations in neuromodulatory signaling and in memory retrieval occur in Alzheimer's disease, Down syndrome, depression, and post-traumatic stress disorder, and recent evidence has begun to link changes in neuromodulatory signaling with effects on memory retrieval.

Epinephrine-induced enhancement of memory retrieval for inhibitory avoidance conditioning in preweanling Sprague-Dawley rats

Developmental research on memory is commonly conducted using preweanling rats, but the extent to which these animals are susceptible to hormone-induced memory retrieval is unclear. This study examined the effects of epinephrine (.001, .01, or .1 mg/kg) on retrieval of IA conditioning in 17-day-old infants. Animals tested 24 hr following training performed significantly worse than infants tested 5 min after training and adults tested 24 hr later, indicating that infantile amnesia had occurred. Epinephrine attenuated this deficit in a dose-dependent manner, with a significant improvement in performance at doses of .01 mg/kg for latency and at .01 and .1 mg/kg for safe side-dependent measures. The role of epinephrine as a memory modulator is discussed in terms of its neurobiological and internal contextual effects.

Forgetting, reminding, and remembering: the retrieval of lost spatial memory

Retrograde amnesia can occur after brain damage because this disrupts sites of storage, interrupts memory consolidation, or interferes with memory retrieval. While the retrieval failure account has been considered in several animal studies, recent work has focused mainly on memory consolidation, and the neural mechanisms responsible for reactivating memory from stored traces remain poorly understood. We now describe a new retrieval phenomenon in which rats' memory for a spatial location in a watermaze was first weakened by partial lesions of the hippocampus to a level at which it could not be detected. The animals were then reminded by the provision of incomplete and potentially misleading information-an escape platform in a novel location. Paradoxically, both incorrect and correct place information reactivated dormant memory traces equally, such that the previously trained spatial memory was now expressed. It was also established that the reminding procedure could not itself generate new learning in either the original environment, or in a new training situation. The key finding is the development of a protocol that definitively distinguishes reminding from new place learning and thereby reveals that a failure of memory during watermaze testing can arise, at least in part, from a disruption of memory retrieval.