Memory short-term, animal studies

The technique also lends itself readily to the study of memory function, in particular by use of delayed responding procedures. In delayed responding, the animal is required to retain information over a short period (usually seconds) and then to show, by pressing an appropriate lever, whether it has correctly remembered the information (Dunnett et al. 1988). In the procedure described below, a rat in a Skinner Box is presented with a lever, either on the left or the right side of the food dispenser. The rat presses the lever and the lever is withdrawn. Five seconds later, two levers are presented and the rat has to press the lever which was not presented previously to obtain a food reward (delayed alternation or delayed non-matching to sample). If the rat presses the same lever as that previously presented, the lever is withdrawn but no food is given. In this fashion, the animal can be trained to retain a piece of information (position of a lever), and thereby demonstrate its short-term memory capacity. 

The radial maze consists of eight dead-end arms arranged like spokes around a central chamber (Fig. 6a). The spatial memory and foraging behavior of the animal can be studied after it has been released in the maze. In one variant, hungry rats are presented with one food pellet at the end of each arm and given a limited time to feed. Parameters typically recorded include number of arms repeatedly visited, or omitted, and time to complete the maze. Rats with impaired short-term memory function will do poorly in this maze. 

The focus of this paper was on the effects in rats of dietary supplementation with LC-PUFA on the fatty acid composition of brain phospholipids and on behavioral function involving short-term memory, as measured by the DMP task on the Morris water maze. Dose-response studies suggest a threshold effect on the incorporation of DHA into brain phospholipids. Furthermore, to maintain optimal n-6 fatty acid status, dietary DHA supplementation, particularly at high levels, is best accompanied by a source of long-chain n-6 fatty acids, either AA or GLA. With respect to functional outcomes, dietary n-3 deficiency, but not supplementation, impairs short-term memory in Long Evans rats. This suggests that once optimum levels of DHA have been attained in the brain, any further increase is not reflected in functional improvements. Increasing DHA in the diet did not improve mnemonic capability in SHR rats, an animal model of... 

ACh is metabolised extraneuronally by the enzyme acetylcholinesterase, to reform precursor choline and acetate. Blocking its activity with various anticholinesterases has been widely investigated and some improvement in memory noted. Such studies have invariably used reversible inhibition because of the toxicity associated with long-term irreversible inhibition of the enzyme. Physostigmine was the pilot drug. It is known to improve memory in animals and some small effects have been seen in humans (reduces number of mistakes in word-recall tests rather than number of words recalled), but it really needs to be given intravenously and has a very short half-life (30 min). 

---