Subfornical organ and supraoptic nucleus connections with septal neurons in rats

Extracellular single unit recordings obtained in pentobarbital-anesthetized male Sprague Dawley rats were utilized to examine the electrophysiology of connections of medial septum-diagonal band of Broca (MS-DBB) neurons with the subfornical organ (SFO), hippocampal commissure (HC), and supraoptic nucleus (SON). Of the 119/216 cells tested that demonstrated antidromic activation from SON, many (60%) were orthodromically excited by SFO stimulation, whereas most (68%) were unresponsive to stimulation in the adjacent HC. Separate populations of MS-DBB neurons that displayed antidromic activation from the SFO (11/140 cells tested) or HC (24/78 tested) were orthodromically excited by SON stimulation. Three cells were activated antidromically from both the SFO and SON. These observations reveal some possible interconnections between these three brain regions and point to the existence of an indirect pathway whereby the SFO can influence SON neurons through an influence on MS-DBB neurons.