Caudolateral areas of medulla-mediating release of ACTH in cats

The effect of electrical stimulation of the caudolateral brain stem on plasma adrenocorticotropin (ACTH) was assessed in cats anesthetized with α-chloralose-urethan. To examine the influence of stimulus pattern on ACTH release, an equal number of pulses was presented in a continuous pattern and in a burst pattern at each electrode site. Stimulation of the magnocellular portion (layers 4-6) of trigeminal nucleus caudalis evoked a significant (P < 0.01) and equal peak change in plasma ACTH after continuous pattern (+121 ± 32 pg/ml) and after burst pattern stimuli (+126 ± 30 pg/ml, n = 21). In contrast, stimulation of more ventromedial portions (layers 7-8) of nucleus caudalis had no significant effect on plasma ACTH. Stimulation of the trigeminal lateral cervical region the caudal extent of the A₁ noradrenergic cell group, or the lateral reticular nucleus evoked significant peak increases in plasma ACTH regardless of stimulus pattern. Transient changes in arterial pressure accompanied brain stem stimulation and were not correlated with the changes in ACTH. The results indicate that stimulation of trigeminal subnucleus caudalis, a brain stem region that processes nociceptor afferent information, evokes a prompt increase in plasma ACTH. Stimulation of brain stem regions that process autonomic and cardiovascular afferent information (A₁ region, lateral reticular nucleus) also facilitate ACTH release. No significant influence of stimulus pattern on brain stem-evoked ACTH release was seen. The results support the hypothesis that the influence of the central nervous system on ACTH release may be processed by parallel pathways at the caudal brain stem level.