Independent regulation of neuropeptide mRNA level and poly(A) tail length.

Osmotic stimulation increases arginine-vasopressin (AVP) and oxytocin (OT) mRNA levels and poly(A) tail size concurrently. We now show that these changes are independently regulated. Whereas depletion of serotonin with p-chlorophenylalanine (PCPA) blocked the increase in hypothalamic levels of AVP and OT mRNA following osmotic stimuli in rats (2% saline drinking or dehydration), the increase in mRNA size was similar in PCPA and control animals. PCPA alone did not modify mRNA size. In addition to demonstrating an apparent obligatory role for serotonin in osmotically induced AVP and OT mRNA accumulation, the results provide evidence for different signaling pathways mediating transcript abundance and poly(A) tail length. Direct investigation of the regulatory mechanisms should be amenable to study in this system.