Electron microscope study of the association between hypothalamic blood vessels and oxytocin-like immunoreactive...

An association between oxytocin-like immunoreactive neurons and hypothalamic blood vessels has been observed with the light microscope. Recently, it has been demonstrated that oxytocin stimulates vascular smooth muscle contraction in vitro. A hypothesis has thus been proposed that oxytocin may play a role in modulating blood flow in certain brain regions. In a study on the golden-mantled ground squirrel (Spermophilus lateralis) we noted the association at the light microscope level between oxytocin-like immunoreactive neurons and blood vessels in preoptic and paraventricular nuclei of the hypothalamus. To determine if these neurons were associated with hypothalamic capillaries, transverse 30 micron immunostained hypothalamic sections were prepared for thin sectioning and observation by transmission electron microscopy. Oxytocin-like immunoreactive neurons were observed to lie within 77 nm of the edge of the lumen of capillary blood vessels. One neuronal cell body was observed approximately 380 nm from the edge of a capillary lumen and what appears to be an output region of a neuron was observed to terminate on the basement membrane of a capillary blood vessel.