Suckling stimulus suppresses messenger RNA for tyrosine hydroxylase in arcuate neurons during lactation

Tyrosine hydroxylase (TH) mRNA in tuberoinfundibular dopamine (TIDA) neuron s is suppressed during lactation but rebounds upon pup removal. A time cour se of TH mRNA changes after pup removal revealed three phases: (1) a nuclea r phase (evident 1.5 hours after pup removal, maximal at 3 hours) with TH m RNA appearing in 1 or 2 nuclear loci with little or no change in cytoplasmi c mRNA; (2) a cytoplasmic phase (noted 6 hours after pup removal, peaked 12 -24 hours) with a significant increase in total TH mRNA levels mainly in th e cytoplasm; and (3) a stabilization phase (24-48 hours after pup removal) when nuclear signals were low and cytoplasmic RNA showed a slight decline w ith extension of RNA clusters into the cell dendrites. In rats whose pups c ould suckle only on one side, TH was up-regulated only on the side contrala teral to nipple blockade. These data indicate that after suckling terminate s, TH up-regulation is evident at 1.5 hours, but 6 hours is needed before t he cells transport sufficient mRNA into the cytoplasm. The rapid signaling of TH upregulation stems from the fact that the TIDA neurons respond to neu ral signals from termination of suckling. J. Comp. Neurol. 438:423-432, 200 1. (C) 2001 Wiley-Liss, Inc.