Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The functional organization of the PRN of the cat medulla was studied in light of its potential role as an integrator of postural and cardiovascular afferent information. Neurons in a large number of afferent sites including the cerebellar deep nuclei, vestibular, accessory oculomotor and solitary nuclei, superior colliculus, bulbar reticular formation, cerebral cortex and spinal cord were retrogradely labeled with HRP following injection of the dorsal and ventral PRN. Collateral axonal projections of PRN neurons were studied with fluorescence histochemistry focusing on their cerebello- and spinopetal connections. About 50% of PRN axons projecting to the ipsilateral anterior cerebellar lobe had collateral branches to the corresponding contralateral cortex. Similarly, 40% of PRN neurons projecting to the region of the intermediolateral nucleus (IML) at and caudal to the T2 level distributed collateral branches to the same region at and caudal to the T4 and T7 levels. The PRN was systematically explored for single units antidromically activated by electrical stimulation of the IML in chloralosed, paralyzed and artificially ventilated cats. Of 62 such PRN units, 40% were found to respond orthodromically to electrical stimulation of the carotid sinus nerve (CSN) and/or fastigial nucleus. Under similar anesthetic conditions, the region of the PRN was reexplored for single units orthodromically activated by electrical stimulation of the vestibular nuclear complex following chronic surgical ablation of the fastigioreticular input to the PRN. Of 47 such PRN units, 62% could be antidromically activated by electrical stimulation of the IML, however, none responded orthodromically to CSN stimulation. All units found responsive to IML stimulation in both preparations were located mainly in the ventral PRN. These experiments provide anatomical and electrophysiological evidence of direct pathways from the PRN to the IML region which mediate cardiovascular and vestibular afferent information. In addition to their obvious role in motor regulation, projections of the motor cortex, accessory oculomotor nuclei, superior colliculus and bulbar reticular formation to the PRN may influence sympathetic activity through its connections with the IML region. These extensive connections and functional autonomic relations of the PRN suggest a central role in mediating orthostatic reflex activity.



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