Brain Research, 416(1987) 129-135 129 Elsevier BRE 12712 Neurotensin in the rat median eminence: the possible sources of neurotensin-like fibers and varicosities in the external layer • 1" Alexander K~ss ', Miklos Palkovits 2, Ferenc A. Antoni 3, Robert L. Eskay 4 and Lana R. Skirboll 1 1Clinical Neuroscience Branch, NIMH, Bethesda, MD (U.S.A.), 2FirstDepartment of Anatomy, Semmelweiss University Medical School, Budapest (Hungary), 3Department of Human Anatomy, Oxford (U.K.) and 4Laboratory of Clinical Studies, Bethesda, MD (U.S.A.) (Accepted 9 December 1986) Key words: Neurotensin; Immunohistochemistry; Median eminence; Arcuate nucleus; Hypothalamic lesion 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 immunohistochemi- cal 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: (1) neither the complete isolation of the medial basal hypothalamus nor the transection of the major neuronal input channel to the median eminence in the lat- eral retrochiasmatic area altered neurotensin-like immunoreactivity in the median eminence; (2) bilateral lesioning of the paraventric- ular nucleus resulted in insignificant changes of neurotensin level in the median eminence; and (3) 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) indi- cates that in addition to the arcuate neurons these neurons may also participate in the neurotensin innervation of the median emi- nence. INTRODUCTION Distribution of neurotensin in the central nervous system of rats has been mapped by both immunohis- tochemical radioimmunoassay techniques5'8'12a5'29 and maps obtained from these two methods show a strong correlation with each other. Neurotensin-im- munolabelled processes and terminals are widely dis- tributed throughout the central nervous system. The presence of neurotensin-containing cell bodies has been reported in several brain areas along the entire neuraxis from the forebrain to the spinal cord6,8,10,13,26. The median eminence has been shown in radioim- munoassay studies to have the highest level of neuro- tensin in the central nervous system. It has also been demonstrated that neurotensin may be secreted from nerve endings in the external layer into the hypotha- lamo-hypophyseal portal system 4. On the basis of precise retrograde axonal transport studies, the arcuate, the paraventricular and the peri- ventricular nuclei represent the most likely sources of fibers projecting to the external layer of the rat medi- an eminence 16,3°. Among these, the arcuate and the parvicellular part of the paraventricular nuclei con- tain neurotensin-like immunopositive perikarya in high number. A few immunopositive cells are also lo- cated periventricularly. In the present study, various types of surgical approaches including a unilateral transection of the retrochiasmatic area (RCAL), *Present address: Institute of Experimental Endocrinology, Centre of Pysiological Sciences, Slovak Academy of Sciences, Kramare, Vlarska u. c 3,809 36 Bratislava, Czechoslovakia. Correspondence: R.L. Eskay, Lab. Clinical Studies, NIAAA, NIH Bldg. 10, Rm 3C216, Bethesda, MD 20892, U.S.A. 0006-8993/87/$03.50© 1987Elsevier Science Publishers B.V. (Biomedical Division)