Steroid-induced transmitter plasticity in insect peptidergic neurons

1. Transmitter plasticity, the ability to alter transmitter expression, has been demonstrated in a wide range of neurons in the vertebrates and invertebrates.

2. One preparation where this issue has been investigated in detail is a set of four neurosecretory neurons in the tobacco hawkmoth Manduca sexta.

3. These neurons undergo a transmitter switch during the transition from caterpillar to moth.

4. In larvae these neurons, known as the lateral neurosecretory cells (LNCs), express CAP₂, a myomodulatory neuropeptide involved in the neuroregulation of the activity of visceral muscles.

5. By the adult moth stage, however, the LNCs are no longer producing CAP₂ and instead are expressing a different peptide, bursicon, which is involved in tanning of the cuticle at adult emergence.

6. Here I review the evidence for this transmitter switch and discuss its regulation by steroids.