Age-related deficits on the radial maze and in fear conditioning: Hippocampal processing and consolidation

Abstract

Young adult, middle-aged, and old male F-344 rats were assessed for their hippocampal ability. This was accomplished by examining the animals on two different paradigms, each incorporating a simultaneous measure of hippocampal-dependent and -independent processing. The animals were fear conditioned and then tested for retention of the conditioning context and tone. This was followed by an 8-arm radial maze task which combined spatial working and cued reference memory elements. The two paradigms are compared in terms of task demands, potential confounds, and validity for aging studies. The results indicate that the performance of the animals on the two tasks is correlated. Age-related deficits limited to the hippocampal aspects of the above tasks were found, with no deficits found in the analogous but hippocampusindependent aspects of these tasks.The function of the hippocampus in incorporating new memories is time-related. Therefore, the possibility of age-related changes in consolidation was examined. It has previously been shown on the fear conditioning paradigm that the hippocampus is involved in retention of the aversive context for approximately 28 days. In the present study, an attempt was made to test the animals for retention of the conditioning context both early into the period of consolidation (10 days) and after consolidation should have been completed (52 days). The results indicate that, initially, the old animals show comparable retention to young rats. When examined later, young animals showed a stronger retention of the conditioning context than they had previously. The aged rats, however, did not seem to benefit from this additional period of time and in fact showed a decrease in retention of the conditioning context. The data are interpreted in terms of consolidation, alternative explanations of the data are presented, and suggestions are given for future research. Finally, the implications of such age-related changes in hippocampal consolidation on learning and memory are discussed.

Lifelong environmental enrichment in rats: impact on emotional behavior, spatial memory vividness, and cholinergic neurons over the lifespan

“…Our fear-conditioning data confirmed that the freezing response towards a context previously associated with a footshock was not altered by age and that contextual fear memory lasted for at least 24 h in aged rats (Houston et al 1999;Oler and Markus 1998;but Statistics: asterisk significantly different from standard rats at the same age; section sign, significantly different from young rats in the same housing condition; dollar sign, significantly different from middle-aged rats in the same housing condition; p <0.05 (NK) in each case. Group abbreviations are as in Fig.…”

Long-Term Potentiation Is Impaired in Middle-Aged Rats: Regional Specificity and Reversal by Adenosine Receptor Antagonists

“…One recent study found progressively greater impairments across subjects from 30 to 90 years of age (Davis et al, 2003), whereas another reported a steady decrease across multiple measures of memory in healthy adults from age 20 forward (Park et al, 2003). Declines in memory from young adulthood to middle age have also been described previously for rats (Deupree et al, 1993;Granger et al, 1996;Oler and Markus, 1998;Ward et al, 1999;Meneses et al, 2004) and monkeys (Herndon et al, 1997;Sloane et al, 1997), suggesting that this effect could be a general feature of mammalian brain. These observations raise the question of whether long-term potentiation (LTP), a form of synaptic plasticity widely regarded as a substrate of memory encoding, also begins to deteriorate relatively early in adult life.…”

Changes in parvalbumin immunoreactivity with aging in the central auditory system of the rat

“…The cognitive deficits were found mainly in spatial learning but also in fear conditioning and in odor discrimination tasks in this strain (Oler and Markus, 1998;Harker and Whishaw, 2002;Villarreal et al, 2004;LaSarge et al, 2007). In many tasks, a tone stimulus was used for fear conditioning (Oler and Markus, 1998;Villareal et al, 2004).…”

“…The cognitive deficits were found mainly in spatial learning but also in fear conditioning and in odor discrimination tasks in this strain (Oler and Markus, 1998;Harker and Whishaw, 2002;Villarreal et al, 2004;LaSarge et al, 2007). In many tasks, a tone stimulus was used for fear conditioning (Oler and Markus, 1998;Villareal et al, 2004). Since old Fischer 344 rats are hearing-impaired with large hearing losses (Popelar et al, 2003(Popelar et al, , 2006Buckiova 2007), the results of those experiments may also have been influenced by the limited hearing abilities of the aged animals.…”