Brain Advance Access originally published online on April 29, 2009
Brain 2009 132(7):1847-1857; doi:10.1093/brain/awp090
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Anterior thalamic lesions stop synaptic plasticity in retrosplenial cortex slices: expanding the pathology of diencephalic amnesia
1 MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, Bristol BS8 1TD, UK 2 Department of Psychology, University of Cardiff, CF10 3AT, UK
Correspondence to: Zafar I. Bashir, MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, Bristol BS8 1TD, UK E-mail: z.i.bashir{at}bristol.ac.uk
Recent, convergent evidence places the anterior thalamic nuclei at the heart of diencephalic amnesia. However, the reasons for the severe memory loss in diencephalic amnesia remain unknown. A potential clue comes from the dense, reciprocal connections between the anterior thalamic nuclei and retrosplenial cortex, another region vital for memory. We now report a loss of synaptic plasticity [long-term depression (LTD)] in rat retrosplenial cortex slices months following an anterior thalamic lesion. The loss of LTD was lamina-specific, occurring only in superficial layers of the cortex and was associated with a decrease in GABAA-mediated inhibitory transmission. As retrosplenial cortex is itself vital for memory, this distal lesion effect will amplify the impact of anterior thalamic lesions. These findings not only provide novel insights into the functional pathology of diencephalic amnesia and have implications for the aetiology of the posterior cingulate hypoactivity in Alzheimer's disease, but also show how distal changes in plasticity could contribute to diaschisis.
Key Words: diencephalic amnesia; long-term depression; diaschisis; retrosplenial cortex; anterior thalamus; Alzheimer's disease
Abbreviations: EPSCs, excitatory postsynaptic currents; IPSCs, inhibitory postsynaptic currents; LFS, low frequency stimulation; LTD, long-term depression; LTP, long-term potentiation; PPR, paired pulse ratio
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Received July 4, 2008. Revised February 4, 2009. Accepted March 6, 2009.
*Present address: Centre for Integrative Psychology, Hugh Robson Building, George Square, Edinburgh EH8 9XD, UK
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