New experimental model system to study central regulation of intraocular pressure

To elucidate the mechanisms of intraocular pressure (IOP) regulation by the central nervous system (CNS), the change in IOP following microiontophoretic application of oxytocin (OXT) onto the cat hypothalamus was investigated. Under sodium pentobarbital anesthesia, the experimental cat was fixed in a stereotaxic apparatus, immobilized and ventilated artificially through a tracheal cannula. The intraocular and blood pressures were continuously recorded using an electromanometer. A 3- to 5-barreled glass microelectrode was used; OXT and, as a control, saline were applied iontophoretically onto the hypothalamus according to the stereotaxic coordinates. On completion of the experiment, the animal was deeply anesthetized and perfused transcardially. Frozen sections of the brain were cut and stained with neutral red, and the tracks of the electrodes were reconstructed. The IOP was elevated gradually when OXT was applied onto the supraoptic nucleus. The latency and the amplitude of this response were 171 +/- 25 seconds and 0.99 +/- 0.46 mmHg (mean +/- SD; N = 4), respectively. The IOP showed no change after saline application to the same site. It was concluded that OXT-sensitive cells in the cat hypothalamus may play a role in regulating IOP. The combination of iontophoretic application of peptide and simultaneous IOP-monitoring as presented in this study provides a useful model system to study the mechanisms of IOP regulation by the CNS.