Stimulation of pelvic visceral organs can markedly alter the activity of neurons In the hypothalamus. These changes in firing may be importantly involved In the control of several autonomic and neuroendocrine functions including the regulation of labor and parturition. It is unclear how information from pelvic visceral structures reaches the hypothalamus. However, using several anatomical and physiological techniques, we found that a large number (as many as 9000) spinal cord neurons project directly to the hypothalamus. Several hundred neurons that project to the hypothalamus are In areas of the lumbosacral gray manner in which processing of visceral information occurs. The working hypothesis of the proposed studies is that at least some pelvic visceral information is transmitted directly to the hypothalamus via the spinohypothalamic tract (SHT). This hypothesis will be tested using several techniques. Retrograde and anterograde tract tracing studies are proposed to determine which hypothalamic regions receive a direct projection from regions of the spinal cord (i.e. lumbosacral segments) that are involved in processing much of the information that originates In pelvic visceral organs. Double labeling experiments are proposed to determine whether the axons of spinal cord neurons project directly to (appose) oxytocin-immunoreactive neurons In the paraventricular nucleus (PVN) and supraoptic nucleus (SON). We will also determine whether oxytocinergic neurons receive an Input from SHT axonal varicosities on their distal dendrites. In these experiments, neurons In the PVN and SON will be filled with Lucifer Yellow In thick, fixed sections. The axonal varicosities of SHT neurons and oxytocin- containing neurons will be immunocytochemically Identified. Appositions between SHT varicosities and filled neurons will be counted and reconstructed. In additional anatomical experiments, we will determine whether fibers of SHT neurons appose oxytocin-immunoreactive neuroendocrine neurons In the PVN and SON. Electrophysiological studies are proposed to determine the response characteristics of neurons that project to the hypothalamus from the lumbosacral spinal cord. In these studies, we will use quantified stimulation of pelvic visceral organs (including the colon/rectum, bladder and female reproductive organs) and lumbosacral cutaneous receptive fields.
