A monosynaptic pathway from an identified vasomotor centre in the medial prefrontal cortex to an autonomic area in the thoracic spinal cord.

Chemical microstimulation (1 mM L-glutamate or 25 mM KCl) of the medial prefrontal cortex of anaesthetized rats produced falls in systolic and diastolic blood pressure of similar magnitude, without a change in heart rate. Application of the lectin Phaseolus vulgaris leucoagglutinin by iontophoresis from an adjacent barrel of the same micropipette revealed a direct projection to the central autonomic area of the thoracic spinal cord from this vasomotor area, which is equivalent to the region called prelimbic cortex by Krettek and Price [J. comp. Neurol. (1977) 171, 157-192] or Cg3 by Paxinos and Watson [The Rat Brain in Stereotaxic Coordinates (1986)]. Labelled axons descended in the dorsal corticospinal tract in the cervical spinal cord, where they displayed a few varicosities. In the thoracic spinal cord, labelled fibres occurred bilaterally in the gray matter, predominantly in the central autonomic area, where they displayed many varicosities. Electron microscope studies revealed that the anterogradely labelled varicosities in the central autonomic area were vesicle-filled boutons that formed asymmetric synaptic contacts. The synaptic targets were small dendrites or dendritic protrusions that were characterized by a high incidence of multivesicular bodies and coated vesicles. We conclude that a monosynaptic pathway that originates from a physiologically-defined vasomotor area in the medial prefrontal cortex terminates on a characteristic type of neuron in the central autonomic area of the thoracic spinal cord.