Neurotensin in the rat median eminence: the possible sources of neurotensin-like fibers and varicosities in the external layer.

The possible sources of neurotensin-like immunoreactive axons in the median eminence were studied after several experimental surgical approaches including unilateral lateral retrochiasmatic area transection, midsagittal knife cut through the median eminence, complete surgical isolation of the medial basal hypothalamus and bilateral paraventricular nucleus lesions. Both immunohistochemical and radioimmunoassay data demonstrate that neurotensin-containing neuronal somata located in the hypothalamic arcuate nuclei represent the main source of neurotensin occurring in the external zone of the median eminence of the rat: neither the complete isolation of the medial basal hypothalamus nor the transection of the major neuronal input channel to the median eminence in the lateral retrochiasmatic area altered neurotensin-like immunoreactivity in the median eminence; bilateral lesioning of the paraventricular nucleus resulted in insignificant changes of neurotensin level in the median eminence; and two days after lesioning the median eminence an increased amount of retrogradely accumulated neurotensin-like immunoreactivity was found in several perikarya of the arcuate nuclei due to the blockage of axonal transport in the transected fibers. Retrograde accumulation of neurotensin-like material in other cells scattered in the anterior hypothalamus (in the paraventricular, periventricular and anterior hypothalamic nuclei) indicates that in addition to the arcuate neurons these neurons may also participate in the neurotensin innervation of the median eminence.