WITHDRAWN: How to Increase and Decrease the Strength of Memory Traces: The Effects of Drugs and Hormones

Clonidine Blocks Acquisition But not Expression of Conditioned Opiate Withdrawal in Rats

“…When clonidine was administered prior to the test session, after conditioning had already taken place, it was found to be ineffective in altering the conditioned withdrawal response. It is well known that manipulation of noradrenergic systems by a variety of agents, including clonidine, can modulate learning and memory storage processes to produce either enhancement or impairment of memory, depending upon strength of training, dose of drug administered, and their interaction (for example, see Martinez et al 1991;McGaugh 1992). Thus, it is unclear whether the efficacy of clonidine in blocking acquisition of the conditioned responses was as a result of its ability to attenuate withdrawal symptomatology directly, or attributable to the modulation of associative learning processes by the drug.…”

“…A nonspecific motoric deficit would not be expected to reduce activity selectively in a single compartment in the absence of some motivational impetus to avoid that compartment. An alternative explanation for the enhanced aversion seen when clonidine was administered prior to the test for expression may be a facili-tated retrieval of the conditioned association produced by clonidine through action on noradrenergic systems that modulate memory storage processes (e.g., Martinez et al 1991;McGaugh 1992).…”

[Leu]Enkephalin Enhances Active Avoidance Conditioning in Rats and Mice

“…10, NO.1 and memory. In the studies of Gold andvan Buskirk (1975, 1976) (Schulteis and Martinez 1992a;Martinez et al 1991aMartinez et al , 1991bMcCarty and Gold 1981;Gold 1989;McGaugh 1989).…”

“…As with LE, the most frequently observed effect of exogenous administration of other opioid peptides is learning and memory impairment (see Martinez et al 1991a for review), although a few cases of enhancement were observed. For example, al though ME is reported to impair acquisition (Rigter et al 1980a) and retention (Introini et al 1985;Izquierdo and Dias 1981) of avoidance conditioning in rats and mice, other reports indicate that ME enhances acquisi tion of Y-maze (Martinez et al 1984) and complex maze (Kastin et al 1976) learning and delays extinction of a pole-jump response (de Wied et al 1978) in rats.…”

“…Thus, LE can either enhance or impair learning within the same species and the same task; these findings are in agreement with recent theoretical proposals regarding the nature of compounds, such as LE, that modulate learning and memory. [Neuropsychopharmacology 10:53-60, 19941 improve or worsen learning and memory (Martinez et al 1991a;Schulteis and Martinez 1992a;Gold 1989). These characteristics are derived from discovering commonalities among the consider able list of endogenous hormones that influence learned performance in experimental animals.…”