Chapter 35: Neurotransmitters and receptors in the subfornical organ. Immunohistochemical and electrophysiological evidence

Publisher Summary The circumventricular organs (CVO) of the mammalian brain comprise specific areas of heterogeneous structure. A great degree of similarity is found in a subgroup of the CVOs: subfornical organ (SFO), organum vasculosum of the lamina terminalis (OVLT) and area postrema. These three CVOs are characterized by capillary loops with permeable fenestrated endothelium and surrounding perivascular spaces. Neurons in these three CVOs may generally act as sensors for chemical or physical properties of the blood in processes of homeostatic regulation. Therefore, it appeared interesting to further characterize neuronal elements of the SFO using morphological and physiological techniques for the evaluation of specific transmitter- related nerve cell properties. For this purpose, a combined approach was chosen. Immunohistochemical techniques were applied on tissue sections of the rat SFO using markers for the classical neurotransmitters acetylcholine, γ-aminobutyric acid, glycine (Gly) or their receptors. The second approach was the utilization of the recently developed patch clamp technique on tissue slices of the rat brain containing the SFO. This in vitro technique allows electrical recording from viable tissue sections to identify cells as true neurons under conditions of applying certain currents and voltages as well as certain transmitters resulting in typical membrane- and ion channel-related electrical responses.