Bj. Yates et al., Transneuronal tracing of neural pathways controlling activity of diaphragmmotoneurons in the ferret, NEUROSCIENC, 90(4), 1999, pp. 1501-1513
Previous studies have shown that neurons in addition to those in the medull
ary respiratory groups are involved in activating phrenic motoneurons durin
g a number of behaviors, including vomiting and reaction to vestibular stim
ulation. However, the location of premotor inspiratory neurons outside of t
he main medullary respiratory groups is largely unknown, particularly in em
etic species. In the present study, the transneuronal tracer pseudorabies v
irus was injected into the diaphragm of the ferret, and the locations of re
trogradely-labeled motoneurons and transneuronally-labeled pre-motoneurons
in the brainstem and cervical and thoracic spinal cord were mapped. Injecti
ons of a monosynaptic tracer, cholera toxin, were also made in order to ver
ify the location of motoneurons innervating the diaphragm. Phrenic motoneur
ons identified with pseudorabies virus and cholera toxin were confined larg
ely to the C-5-C-7 levels of spinal cord, and often gave rise to prominent
polarized dendritic arbors that extended across the midline. At post-inocul
ation survival times greater than or equal to three days, transneuronally-l
abeled interneurons were located in the cervical and thoracic spinal cord a
nd portions of the brainstem, including the midline pontomedullary reticula
r formation and the lateral medullary reticular formation. Double-labeling
studies revealed that although the infected midline neurons were located in
the proximity of serotonergic neurons, only a small number of the virus-co
ntaining cells were positive for serotonin.
These findings suggest that neurons in the midline of the medulla and pens
influence the activity of phrenic motoneurons, perhaps during inspiratory b
ehaviors unique to emetic animals (such as vomiting). (C) 1999 IBRO. Publis
hed by Elsevier Science Ltd.