Spine morphology of neurons in the avian forebrain is affected by rearing conditions

An area of the caudal forebrain of male zebra finches, the Archi-Neostriatum caudale (ANC), which is active during arousal (Bischof & Herrmann, 1986, 1988), shows rearing-dependent changes in neuron morphology (Rollenhagen & Bischof, 1991). We demonstrate here that rearing conditions also affect the shape of spines of one of the four ANC neuron types. This neuron type was examined in birds reared under five different conditions--in isolation (1), caged (2), in the aviary (3), and with social contact (4) or chasing (5) after an isolation period. Our results show that social experience determines the proportion of the three types of spines (thin, mushroom, and stubby) of the investigated neuron type. Rearing conditions and short social contact also affect the spine stem length of the thin spine type. Long-term isolation results in a reduction in number and elongation of shafts of thin spines, along with an increase of stubby-and mushroom-shaped spines. Short-term social contact or arousal enhances the number of mushroom-and thin-shaped spines and reduces the length of spine stems of thin spines. We suggest that isolation prevents the ANC neuron from reaching full development. The increase of mushroom and thin spine types due to social contact indicates that the stubby-shaped spines are replaced by, or transformed into, mushroom-shaped spines, and the mushroom-shaped spines are replaced by, or transformed into, thin spines. These results confirm and extend the experimental background for our hypothesis (Rollenhagen & Bischof, 1991) that social contact is necessary for development of normal morphology of ANC neurons.