Cooperation and competition during development: neonatal lesioning of the superior cervical ganglion induces cell death of trigeminal neurons innervating the cerebral blood vessels but prevents the loss of axon collaterals from the neurons that survive

Abstract

In the adult rodent trigeminal ganglion there is a period of postnatal cell death in the population of cells with axons innervating the middle cerebral artery (O'Connor and van der Kooy, 1986b). The superior cervical ganglion (SCG) also has a projection to the middle cerebral artery (MCA; Mayberg et al., 1984; Cowen et al., 1986, 1987; present report). We hypothesized that the trigeminal ganglion cells innervating the MCA may be competing with the superior cervical projection for target area or for a target factor for survival, and thus the removal of the superior cervical projection at birth (sympathectomy) may promote the survival of some of the trigeminal-artery innervating cells that normally would die. Multiple fluorescent retrograde tracing was employed to analyze the postnatal development of the trigeminal projection to the MCA in sympathectomized and sibling control rats. We found that the SCG projection to the MCA exhibits a period of postnatal cell death. The trigeminal ganglion projection exhibits axon degeneration as well as postnatal cell death. Postnatal day 0 (P0) lesioning of the SCG did not prevent cell death or axon loss in the trigeminal projection to the cerebral artery. In fact, increased cell death of the trigeminal-artery projecting neurons was observed in the lesioned animals when compared to nonlesioned sibling controls. By P55, we found that 80% of these trigeminal neurons had died in lesioned animals, compared with 50% in controls. In both control and sympathectomized rats, close to 90% of the trigeminal neurons innervating the artery in the neonate can no longer be retrogradely labeled from the MCA by tracer applications at P25-90. Thus, although the presence of an intact SCG may protect some trigeminal-artery projecting neurons from cell death, it does not prevent axon retraction and does not permit a larger absolute number of trigeminal axons to innervate the arteries in the adult. Thus, separate mechanisms are responsible for the survival of perikarya versus the retraction of their axons from the MCA. Surprisingly, in the neonatally sympathectomized rats almost 20% of those trigeminal cells that maintained a projection to the MCA at P90 also had a projection to the forehead. In contrast, less than 3% of the artery innervating trigeminal cells in the P90 control rats had an axon collateral to the forehead.(ABSTRACT TRUNCATED AT 400 WORDS)