An ultrastructural study of cat petrosal ganglia: a search for autonomic ganglion cells.

It is not known whether cranial and spinal ganglia contain autonomic (motor) neurons in addition to sensory cells. Early light microscopic studies indicate the possibility of synaptic input to some nerve cells via perisomatic axon terminals and dendrites. It has also been suggested that visceromotor relay-type cells in the petrosal ganglion might be involved in the efferent control of the carotid body. The present ultrastructural analysis of 902 neurons in 17 levels from two cat petrosal ganglia provides no evidence for synapses on the cell somata or on their axonal extensions. Processes resembling dendrites were lacking although small surface projections typical of sensory cells were common. The petrosal ganglion thus appears to consist entirely of afferent unipolar neurons.