Somatostatin-Expressing Neurons in the Tuberal Region of Rat Hypothalamus during Aging

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The location and neurochemical composition of somatostatin (SOM)-immunoreactive (ir) neurons in the tuberal region of the rat hypothalamus were studied using immunohistochemical method in young (2–3-month-old), adult (1-year-old), and aged (2–2.5-year-old) male and female rats. The highest percentage of SOM-ir neurons was found in the arcuate nucleus (AN) and ventrolateral part of the ventromedial nucleus (VMNvl). A smaller part of them was observed in the dorsomedial (DMN) and medial tuberal (MTu) nuclei, as well as in the VMN shell. Single SOM-ir neurons occurred in the dorsomedial part of the ventromedial nucleus (VMNdm), periventricular (PeV) and perifornical (PeF) nuclei. No age-related changes were found in the number of SOM-ir neurons. The percentage of SOM-ir neurons colocalizing calbindin (CB), neuronal nitric oxide synthase (nNOS) and neuropeptide Y (NPY) increased in the AN during aging. In the VMNvl, from one third to one half of SOM-ir neurons in all rats colocalized nNOS, and only from 7.9 to 18.6% of them colocalized CB and NPY. In the DMN of males, a significantly higher percentage of SOM-ir neurons colocalizing NPY was observed in all age groups when compared with females. Thus, aging is accompanied by neurochemical changes in the SOM-ergic system of the tuberal hypothalamic nuclei, mainly in the arcuate nuclei.