Ultrastructural alterations of motor cortex synaptic junctions in Brown Swiss cattle with weaver syndrome.

An ultrastructural comparison was made between the motor cortex synapses of the brain of 4 adult Brown Swiss cattle with weaver syndrome and 2 healthy cattle (a Holstein steer and a Guernsey cow). Compared with the healthy cattle, the paramembranous densities at synaptic junctions of cattle with weaver syndrome had a decreased mean height of the presynaptic dense projections (P less than 0.001), had significantly smaller peak-to-peak distances (P less than 0.001), and had a significantly decreased mean thickness of the postsynaptic density (P less than 0.0001). These synaptic changes in cattle with weaver syndrome may be associated with clinical manifestations of the syndrome, such as impairment of transmitter release, instability of postsynaptic receptor sites, lesion-induced synaptic turnover from injury elsewhere in the CNS, or loss of a specific cell population of the motor cortex.