Developmental cell death in vivo: rescue of neurons independently of changes at target tissues
1Neuroscience Graduate Program, Oregon Health and Science University, Portland, Oregon 97201, USA.
Abstract:
Programmed cell death is a prominent feature of neural development that is regulated by a variety of cell-cell interactions. We used the avian ciliary ganglion to dissect the relative contributions of target tissues vs. ganglionic inputs in regulating cell death. The two populations of the ciliary ganglion innervate different targets: choroid neurons innervate vasculature, whereas ciliary neurons innervate the iris and ciliary body. By counting after labeling all neurons with Islet-1 and choroid neurons with anti-somatostatin, we determined that alpha-bungarotoxin (alpha-btx) at 12.5 microg/day rescued only ciliary neurons, whereas 75 microg/day rescued both ciliary and choroid neurons. It is unlikely that alpha-btx acted by blocking nerve transmission at both targets because the choroid vasculature lacked transcripts for alpha-btx binding molecules. In addition, no inherent trophic activity could be ascribed to alpha-btx, and survival could not be attributed to differences in total trophic activity of eyes from saline vs. alpha-btx-treated embryos. In contrast, the alpha7 antagonist alpha-methyllycaconitine (MLA) rescued ciliary neurons at 2.6 microg/day, whereas 26 microg/day rescued choroid neurons. Nerve terminals of ciliary neurons rescued with alpha-btx were significantly larger; however, differences in nerve terminal size or branching of axons were not observed in ciliary neurons rescued with MLA or choroid neurons rescued by either MLA or alpha-btx. Our results suggest that neuronal survival can be promoted independently of changes at the target tissues when orthograde signals acting by means of neuronal alpha7 nicotinic receptors are blocked.
Insights
Neuronal survival during development is regulated by cell-cell interactions. Blocking alpha7 nicotinic receptors with alpha-methyllycaconitine (MLA) independently promotes survival of ciliary and choroid neurons.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Programmed cell death is crucial for neural development.
- Cell-cell interactions regulate neuronal survival.
- The avian ciliary ganglion model system allows study of neuronal development.
Purpose of the Study:
- To investigate the roles of target tissues and ganglionic inputs in regulating programmed cell death.
- To determine the specific contributions of alpha-bungarotoxin (alpha-btx) and alpha-methyllycaconitine (MLA) in neuronal survival.
- To elucidate the mechanisms by which neuronal survival is promoted during development.
Main Methods:
- Utilized the avian ciliary ganglion model.
- Employed neuron labeling techniques (Islet-1, anti-somatostatin).
- Administered alpha-btx and MLA at varying concentrations to assess neuronal rescue and survival.
Main Results:
- Alpha-btx rescued ciliary neurons at lower doses and both ciliary and choroid neurons at higher doses.
- Alpha-methyllycaconitine (MLA) selectively rescued ciliary and choroid neurons at different concentrations.
- Neuronal survival promotion was observed independently of target tissue changes when alpha7 nicotinic receptors were blocked.
Conclusions:
- Neuronal survival can be modulated by blocking alpha7 nicotinic receptors.
- Orthograde signals acting through neuronal alpha7 nicotinic receptors play a role in regulating cell death.
- Target tissue interactions are not the sole regulators of neuronal survival in the ciliary ganglion.
