Subnucleus-Specific Loss of Neurons in Medial Thalamus of Schizophrenics

The hypoactivity of dorsolateral prefrontal cortex in schizophrenics is well known. One cause of this hypoactivity may be defective corticocortical or thalamocortical connections. Recent imaging studies of the thalamus suggest reductions in volume of the whole thalamus and reduced activity in the medial group of thalamic nuclei, which may indicate loss of functional input to the cortex. Using stereological techniques in six pairs of individually matched brains from schizophrenics and controls, we measured the volumes and obtained estimates of the number of neurons in the three subnuclei (parvocellular, pc; densocellular, dc; magnocellular, mc) of the mediodorsal nucleus (MD) and from the ventral posterior medial nucleus. There was a significant reduction in total neuron number in MD as a whole but this neuron loss was largely restricted to MDpc and MDdc [-30.9 and -24.5%, respectively (P ≤ 0.01)]. MDmc and the control ventral posterior medial nucleus showed no significant changes in cell number. Because the subnuclei of MD have different connections and project to different areas of the frontal cortex, the specific loss of neurons in MDpc and MDdc has implications for the functional defects observed in schizophrenia.