Sensory Functions

Abstract

Learning-related changes in synaptic organization occur in the intermediate and medial part of hyperstriatum ventrale (IMHV) after imprinting (Horn, 1990). NCAMs are implicated in synaptic plasticity (Edelman & Crossin, 1991). Are they implicated in imprinting?Dark-reared chicks (n = 132) were exposed for 1 h to an imprinting stimulus (a rotating red box) and their preferences for it determined to provide a measure of learning (preference score). Chicks with low preference scores were classed as poor learners (PL), those with high preference scores as good learners (GL). A further 66 chicks remained in darkness throughout as dark controls (DC). Chicks were killed by decapitation 9-5 or 24 h after training and tissue removed from IMHV, hyperstriatum accessorium (HA) and posterior neostriatum (PNS), separately from each hemisphere. Tissue from three chicks in each group was pooled. The amounts of three major NCAM isoforms (180, 140 and 120 kDa) in the P2 fraction were measured using SDS electrophoresis-immunoblotting (antibodies from K. Crossin) and '25I-labelled secondary antibodies. For IMHV, differences occurred only 24 h after traininga. There were more NCAMs (for each isoform) in GLs than PLsb or DCsb; PLs did not differ significantly from DCs. Effects reached significance only in left IMHVC. In HA, there was more NCAM 180 kDa in GLs than in DCs 9 5 h after trainingd, but no significant difference between the two trained groups. There were no training-or learning-related effects in PNS.The change in HA could be a consequence of non-specific effects of training. The effects in the left IMHV cannot be accounted for in this way: GLs and PLs were matched for locomotor activity, and both groups had similar training experience, yet PLs differed significantly from GLs, but did not differ significantly from DCs. The results show that in the left IMHV learning is associated with increased expression of NCAMs, implicating enhanced cell-to-cell adhesion in long-term memory. One eye was removed on the day of birth (P0) under ether anaesthesia. Paired injections of red and green fluorescent latex microspheres, spaced mediolaterally, were made into area 17 on both sides (Saffan 2 ml kg-1 I.M.). After injections at P2, a discrete cortical injection labelled cells throughout the dLGN. Using two different tracers, the overlap of the two populations was complete and the percentage of doublelabelled cells low. The pattern of labelling was similar on both sides of the brain. At P6, the geniculo-cortical topography contralateral to the remaining eye was adultlike. Ipsilaterally, although a single injection labelled neurons in a confined area of the dLGN, the double injections revealed greater scatter than contralaterally. Although not apparent at P6, a double focus of geniculate labelling from a single cortical injection ipsilateral to the remaining eye was seen at P12. Recordings were made in area 17 of adults enucleated at birth. The hamsters were paralysed with gallamine triethiodide (35 mg kg-' h-1 i.v.) and anaesthetized wit...