TRH: immunocytochemical distribution in vagal nuclei of the cat and physiological effects of microinjection.

In the present study, we have applied antiserum to thyrotropin-releasing hormone (TRH) and avidin-biotin immunocytochemistry to determine the distribution of TRH-like immunoreactivity in the vagal nuclei of the cat. A dense network of TRH-immunoreactive (TRH-IR) fibers and terminals is noted in the dorsal motor nucleus of the vagus (DMV) from 0 to 2.5 mm rostral to the obex. Horseradish peroxidase conjugated wheat germ agglutinin (HRP-WGA)-labeled neurons are noted in this region of the DMV after application of the tracer to the musculature of the pylorus. In dual-stained sections, TRH-IR fibers and terminals appear to terminate in close proximity to HRP-WGA-labeled neurons in the DMV. In contrast, a moderate to low density of TRH-IR fibers and terminals is noted in the nucleus ambiguus (NA), and no HRP-WGA-labeled neurons are noted in this nucleus. To determine the physiological significance of TRH fibers in these vagal nuclei, TRH was microinjected into the DMV and NA while monitoring gastric (antrum and pylorus) and duodenal motility as well as mean blood pressure (MBP) and heart rate. Microinjections of TRH (16-500 ng) into the DMV resulted in increases in pyloric and antral motility (minute motility index increased from 1.28 to 8.70 in the pylorus, P less than 0.05, and from 2.29 to 4.25 in the antrum, P less than 0.05). TRH microinjection also increased the intraluminar pressure in the stomach by 6.1 +/- 1.3 mmHg. No significant changes in duodenal motility, MBP, or heart rate were noted.(ABSTRACT TRUNCATED AT 250 WORDS)