The morphological changes of pyramidal and spiny stellate cells in the primary visual cortex of chronic morphine treated cats

Morphine exposure may have a negative effect on the receptive field properties of neurons in primary visual cortex of cats. The present experiment used morphological methods in order to investigate whether chronic morphine treatment also affects dendritic characters of these neurons. According to the Sholl analysis and dendritic branch order analysis, we obtained the dendritic length and calculated the spine density on dendrites of the pyramidal neurons in layer III and the spiny stellate neurons in layer IV. The results showed that morphine exposure induced significant decreases in the total dendritic length and spine density on both pyramidal and spiny stellate neurons. The further branch order analysis revealed that spine density was decreased at every (first to fourth) branch order of dendrites of pyramidal and spiny stellate neurons. Decrease in dendritic length of the pyramidal neurons was observed only at the fourth branch order, while the spiny stellate neurons had shorter dendrite at the second and third branch order. These findings may underlie the degradation of receptive field properties of the primary visual cortex neurons following chronic morphine exposure.