| Popis: |
The magnocellular neurons of the hypothalamus which synthesize and release the peptide hormones vasopressin and oxytocin present a fascinating and attractive target for the electrophysiologist. These neurons are relatively large and are clustered together in dense aggregates, mostly in the paraventricular nuclei (PVN) and supraoptic nuclei (SON), which can be easily located. They have relatively simple neuronal profiles and send the vast majority of their axons to the neural lobe of the pituitary, which itself is remote from the rest of the brain and consists predominantly of the terminals of the magnocellular neurons. These features allow the neurons to be recorded and identified electrophysiologically. The ultra- structural and biochemical characteristics of these neurons also allow them to be readily visualized histologically. The neurosecretory product of the magnocellular neurons can be detected and measured in the plasma, and several physiological reflexes cause a selective activation of the neurons, resulting in the release of detectable quantities of hormone. During the past 25 years considerable insight has been gained into the functions of these neurons and the significance of their electrical activity; yet, though information regarding them continues to accumulate, there are many fundamental aspects which remain unclear. Our understanding of their organization and regulation, rather than being enhanced, has actually become more uncertain. |
