Quantitative autoradiographic distribution of [ 125i]bolton-hunter neuropeptide y receptor binding sites in rat brain. comparison with [ 125i]peptide yy receptor sites

Abstract

The autoradiographic distribution of [ 125I]Bolton-Hunter neuropeptide Y receptor binding sites was quantified in rat brain. The highest level of [ 125I]Bolton-Hunter neuropeptide Y binding sites was seen in the hippocampus (ventral stratum radiatum, CA3 subfield: 6029 ± 250 fmol/g tissue). The distribution of these sites was clearly laminated, being particularly concentrated in the oriens layer (dorsal CA3 subfield: 2562 ± 147fmol/g tissue) and stratum radiatum (dorsal CA3 subfield: 2577 ± 95fmol/g tissue). Lower levels of sites were seen in the pyramidal cell layer (1708 ±105 fmol/g tissue) and the molecular layer (1155 ± 116fmol/g tissue). The cortical distribution of [ 125I]Bolton-Hunter neuropeptide Y receptor sites was also laminated, being particularly enriched in superficial laminae (occipital cortex, layers I–II, 4038 ± 148fmol/g tissue; layers III–IV, 1392 ± 97 fmol/g tissue and layers V–VI, 1522 ± 138fmol/g tissue). Other areas containing high amounts of sites included the anterior olfactory nuclei (ventral part, 4935 ± 119fmol/g tissue; lateral part, 4530 ± 149fmol/g tissue; dorsal part, 3378 ± 140fmol/g tissue and medial part, 2601 ± 150fmol/g tissue); anteromedial (5168 ± 211fmol/g tissue), medial (4611 ± 107fmol/g tissue) and lateral posterior thalamic nuclei (4465 ± 189fmol/g tissue); medial mammillary nucleus (5555 ± 241 fmol/g tissue); medial geniculate nucleus (4747 ± 56 fmol/g tissue); claustrum (4123 ± 235fmol/g tissue); posteromedial cortical amygdaloid nucleus (3524± 138 fmol/g tissue), tenia tecta (2540 ± 195 fmol/g tissue); lateral septum (1785 ± 90fmol/g tissue); suprachiasmatic hypothalamic nucleus (1604 ± 115fmol/g tissue), and substantia nigra, pars compacta (1846 ± 142fmol/g tissue) and pars lateralis (1750 ± 165fmol/g tissue). Areas moderately enriched with [ 125I]Bolton-Hunter neuropeptide Y binding sites included the zonal layer of the superior colliculus (1347 ± 71fmol/g tissue); anterior pretectal nucleus (1172 ± 113fmol/g tissue); ventral tegmental area (1090 ± 97fmol/g tissue); periventricular fibre system (1026 ± 48fmol/g tissue); core of nucleus accumbens (948 ± 29fmol/g tissue) and area postrema (799 ± 87fmol/g tissue). These results are discussed with regard to some of the suggested biological effects of neuropeptide Y in the central nervous system such as effects on learning, locomotion and circadian rhythms. Moreover, we also compared the distribution of [ 125I]Bolton-Hunter neuropeptide Y receptor sites with that of [ 125I]peptide YY sites in rat brain. The resolution of the autoradiographic image is better with [ 125I]peptide YY most likely because of higher affinity and percentage of specific labelling. This is especially true in hypothalamic and brainstem nuclei, and in the cerebellum. It is also possible that [ 125I]peptide YY may bind to a different population of sites in these areas. This latter possibility is currently under investigation.