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. 2007 Jun 5;14(6):385-9.
doi: 10.1101/lm.348307. Print 2007 Jun.

Eye-blink conditioning is associated with changes in synaptic ultrastructure in the rabbit interpositus nuclei

Andrew C W Weeks  1 , Steve Connor, Richard Hinchcliff, Janelle C LeBoutillier, Richard F Thompson, Ted L Petit
Affiliations

Eye-blink conditioning is associated with changes in synaptic ultrastructure in the rabbit interpositus nuclei

Andrew C W Weeks et al. Learn Mem. .

Abstract

Eye-blink conditioning involves the pairing of a conditioned stimulus (usually a tone) to an unconditioned stimulus (air puff), and it is well established that an intact cerebellum and interpositus nucleus, in particular, are required for this form of classical conditioning. Changes in synaptic number or structure have long been proposed as a mechanism that may underlie learning and memory, but localizing these changes has been difficult. Thus, the current experiment took advantage of the large amount of research conducted on the neural circuitry that supports eye-blink conditioning by examining synaptic changes in the rabbit interpositus nucleus. Synaptic quantifications included total number of synapses per neuron, numbers of excitatory versus inhibitory synapses, synaptic curvature, synaptic perforations, and the maximum length of the synapses. No overall changes in synaptic number, shape, or perforations were observed. There was, however, a significant increase in the length of excitatory synapses in the conditioned animals. This increase in synaptic length was particularly evident in the concave-shaped synapses. These results, together with previous findings, begin to describe a sequence of synaptic change in the interpositus nuclei following eye-blink conditioning that would appear to begin with structural change and end with an increase in synaptic number.

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Figures

Figure 1.
Figure 1.
The percentage of conditioned responses (mean ± SE) across daily sessions. Paired animals (n = 8) show a large increase in conditioned responses while unpaired animals (n = 7) do not.
Figure 2.
Figure 2.
The number of excitatory and inhibitory synapses per neuron (mean ± SE) and various curvature subtypes (excitatory only) between the three groups. (*) The paired group is significantly different from the other two groups (P < 0.05).
Figure 3.
Figure 3.
Electron micrograph (15,000×) illustrating curvature types. (A) A concave synaptic segment; (B) a flat segment.
Figure 4.
Figure 4.
Electron micrograph (25,000×) illustrating curvature type. Two convex synapses are evident.
See this image and copyright information in PMC

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