Presence and functional significance of neuropeptide and neurotransmitter receptors in subcommissural organ cells.

The subcommissural organ (SCO) of mammals is innervated by several neuropeptide and neurotransmitter systems. So far, substance P (SP), oxytocin (OXT), vasopressin (VP), somatostatin (SOM), thyrotropin-releasing factor (TRF), and angiotensin II (ANGII) were identified in neuropeptidergic input systems, and serotonin (5HT), gamma-amino butyric acid (GABA), noradrenaline (NA), dopamine (DA), and acetylcholine (Ach) were neurotransmitters observed in systems afferent to the SCO. In the present report, based on literature data and our own investigations, we describe the occurrence of peptide and transmitter receptors in the SCO by means of autoradiographic and biochemical studies. Further, we summarize aspects of the signal transduction cascades possibly linked to different receptor types of the SCO; these studies included the use of calcium imaging (FURA-2 technique), ELISA technique, and immunocytochemistry. Receptors were identified for adenosine, angiotensin II, imidazoline, glucocorticoids, mineralocorticoids, NA, and embryonic brain kinase. The studies on intracellular signal-transduction indicated receptors for tachykinins and for ATP. In SCO cells, Ca(++) and c-AMP were identified to act as second messengers. As important transcription factor, cAMP-/Ca(++)-response element binding protein (CREB) was observed. Ach and NA did not show a significant effect on the subcommissural signal transduction.