Pituitary hormones and amnesia

Pituitary hormones profoundly influence behavior through direct actions on the brain. One of these behavioral effects is the attenuation of experimental amnesia. Traditionally, amnesia is considered as a "loss of memory." Memory comprises at least 2 stages: input (memory consolidation) and output (memory retrieval). Theoretically, disturbance of either aspect of memory may be the cause of amnesia. Also, it is possible that amnesia is based on a factor or factors not related to memory. Data and theories on amnesia in man were reviewed. Some salient features were mentioned: (1) amnesia can be induced by a variety of agents; (2) amnesia covers periods ranging from seconds to years; (3) amnesia gradients can be established; (4) amnesia is to a large extent reversible. From this survey, it seems possible that amnesia is not a homogeneous phenomenon and that even in one person a disturbance of both memory consolidation and memory retrieval may be produced by one and the same event. Animal studies in general have confirmed these conclusions. We have developed an animal model in order to study the effects of pituitary peptides on amnesia. This model is based on CO2-induced amnesia for a one-trial passive avoidance response in rats. This amnesia could be attenuated by treatment with ACTH-analogs 1 hour before the retrieval test. This anti-amnesic effect of ACTH-analogs was not dependent on the nature of the behavioral response or the amnesic treatment. The vasopressin-analog DGLVP similarly exerted an anti-amnesic effect when injected before the retrieval trial. In contrast to ACTH-analogs, however, it also reduced the amnesia when injected before acquisition. These results suggest that amnesia may comprise a "faulty-consolidation" and a "faulty-retrieval" component, which may be amended by different pituitary hormones. The study of the anti-amnesic activity of peptides therefore not only serves to characterize the nature of the behavioral effect of these peptides but may also prove to be helpful of the unraveling of processes involved in amnesia.