INCREASED IMMUNOGOLD LABELING OF NEURAL CELL-ADHESION MOLECULE ISOFORMS IN SYNAPTIC ACTIVE ZONES OF THE CHICK STRIATUM 5-6 HOURS AFTER ONE-TRIAL PASSIVE-AVOIDANCE TRAINING

An area of the chick striatum, the lobus parolfactorius plays an impor tant role in one-trial passive avoidance learning tasks.(16,19,20) In the present study we report evidence that 5-6 h post-training, a signi ficantly higher proportion of synaptic active zones in this area conta in labelled epitopes of the neural cell adhesion molecule, with the gr eatest occurrence of labels at the edges of active zone profiles (in b oth control and trained groups). This suggests that there is a period after training when expression of the neural cell adhesion molecule in synaptic membranes almost doubles, and that events at active zone edg es may play a specific role in mechanisms of synaptic adhesion. Cellul ar mechanisms of long-term memory formation are believed to include al terations in neural circuitry at the synaptic level. The involvement o f the neural cell adhesion molecule (NCAM) in functional synaptic modi fications has been demonstrated using a number of physiological models .(6,9,13) Performance of rats in the Morris mater maze, a spatial lear ning paradigm which requires the hippocampus, is impaired by either in traventricular injection of NCAM antibodies,(1) or injection into the hippocampus of an enzyme which increases hemophilic adhesion of the mo lecule, due to the removal of polysialic acid residuals from extracell ular NCAM domains.(3) In addition, intraventricular injections of anti -NCAM antibodies 6-8 h post-training mere shown to impair memory for a one-trial passive avoidance task in the rat.(7) An avoidance training model in the one-day-old chick indicates a similar time window, 5-6 h post-training during which memory for the task can be impaired by int raventricular injection of NCAM antibodies.(14,17) In the hyperstriatu m ventrale, a chick forebrain area involved in the passive avoidance t ask, subtle changes in the distribution pattern, but not density of NC AM molecules in synaptic membranes were revealed 5-6 h post-training.( 15) However, on the basis of studies of synaptic morphometry, a region of striatum, the lobus parolfactorius (LPO), appears to play a more i mportant role in longer term memory storage for the task.(14,16,20) (C ) 1997 IBRO. Published by Elsevier Science Ltd.