Degenerated boutons in the fundus striati (nucleus accumbens septi) after lesion of the parafascicular nucleus in the cat.

An attempt has been made to reveal which of the nine different types of synapses in the fundus striati, discriminated in a previous study, degenerate following experimental lesions in the parafasciculo-center median complex of the cat. Two types of synaptic contacts were found to be degenerated two days after the lesion was performed: (1) the axo-spinous type IV, characterized by densely-packed, small, round vesicles and a strong asymmetric thickening, and (2) the axo-dendritic or axo-somatic type VII, again characterized by small, round vesicles in a dense accumulation and an asymmetric thickening. After two days of survival the original characteristics of the boutons could still be recognized in both types of synapses. A positive correlation exists between the location and extent of the coagulation foci in the parafascicular nucleus and the appearance of degenerated boutons in the fundus striati. Therefore, the conclusion that the parafasciculofundus neurons terminate as type IV or type VII boutons is entirely justified. Additionally, the role of the special types of boutons in the synaptic organization of the fundus striati has been discussed.