Jean-Claude Beaujouan

Differential localization of3H-[Pro9]SP binding sites in the guinea pig and rat brain

Abstract Due to the existence of differences in the pharmacological properties of tachykinin NK-1 receptors in the rat and the guinea pig, the autoradiographic distribution of NK-1 binding sites was compared in the brain of the two species using the selective NK-1 ligand3H-[Pro9]SP. If a good similarity in the distribution of NK-1 binding sites could be seen in basal ganglia, a relative absence of correlation was observed between the estimated optical densities in other brain structures of the two species. For instance, the interpeduncular nucleus, the lateral habenular nucleus and the deep layers of the cerebral cortex were labeled in the guinea pig but not in the rat while the reverse was observed for the columns of the vermis lobules 9–10, the dorsal raphe nucleus, the medial habenular nucleus, the superficial cortical layers and the dorsal hippocampus. Furthermore, the high similarity found in the localization of125I-BHSP (a non selective ligand) and3H-[Pro9]SP binding sites, does not suggest the existence of NK-1 binding site subtypes in the guinea pig brain.

17 - Tachykinin Receptors: Binding and Cellular Activity Assays

Publisher Summary This chapter discusses the technical aspects of the methods related to treatment of tachykinin (TK) receptors. TKs represent a family of structurally related peptides that share a common C-terminal amino acid sequence, exhibit different rank order of potency according to the tissue investigated, and show some analogy in their biological effects. Mammalian TK are derived from large precursors encoded by two genes, namely, the preprotachykinins A (PPTA) and preprotachykinins B (PPTB) genes. The PPTA large precursors generate substance P (SP) alone or both SP and neurokinin A (NKA), SP and neuropeptide K (NPK), or SP and NPγ through alternative splicing, whereas the PPTB precursors give rise to neurokinin B (NKB) alone. NK1 receptors are characterized by their preferential affinity for SP. NK2 receptors are characterized by their preferential affinity for NKA. NK3 receptors are characterized by their preferential affinity for NKB. Binding studies have demonstrated that TK analogs recognize TK receptors, but the agonist or antagonist properties of these compounds have been demonstrated using biological assays on peripheral isolated organs. It is reported that dog carotid artery, rabbit pulmonary artery, and rat portal vein distinguish responses are mediated by NK1, NK2, and NK3 receptors. However, there is not always a perfect correlation between the relative potencies of TK or analogs in binding studies and those in assays made on these peripheral organs.

Pharmacological characterization of tachykinin septide-sensitive binding sites in the rat submaxillary gland

Binding studies have shown that [125I]NKA is a selective ligand of tachykinin septide-sensitive binding sites from membranes of the rat submaxillary gland. Indeed, this ligand bound with high affinity to a single population of sites. In addition, competition studies indicated that natural tachykinins and tachykinin-related compounds had a similar affinity for these sites than for those labeled with [3H]ALIE-124, a selective ligand of septide-sensitive binding sites. Moreover, selective tachykinin NK2, or NK3 agonists or antagonists exhibited weak or no affinity for [125I]NKA binding sites. As indicated by Ki values of several compounds, the pharmacological characteristics of the septide-sensitive binding sites (labeled with [125I]NKA) largely differ from those of classic NK1 binding sites, as determined on crude synaptosomes from the rat brain using [125I]Bolton-Hunter substance P (SP) as ligand. Indeed, several tachykinins including neurokinin A (NKA), neuropeptide K (NPK), neuropeptide gamma (NKgamma), and neurokinin B, as well as some SP and NKA analogues or C-terminal fragments such as septide, ALIE-124, SP(6-11), NKA(4-10), which have a weak affinity for classic tachykinin NK1 binding sites exhibited a high affinity for the septide-sensitive binding sites. In contrast, SP, classic selective NK1 agonists, and antagonists had a high affinity for both types of binding sites. The presence of a large population of tachykinin septide-sensitive binding sites in the rat submaxillary gland may thus explain why NPK and NPgamma induce salivary secretion and may potentiate the SP-evoked response in spite of the absence of tachykinin NK2 receptors in this tissue.

Tachykinin binding sites in the interpeduncular nucleus of the rat: normal distribution, postnatal development and the effects of lesions

Tachykinin binding sites in the basal midbrain were labeled in adult and neonatal rats using 125I-Bolton Hunter (BH) substance P (SP) and 125I-BH eledoisin as ligands. In the adult, binding was very low in the tegmentum and raphe adjacent to the interpeduncular nucleus (IPN). Within the IPN, no binding with either ligand was seen in the target subnuclei of the habenular SP and substance K projections, the lateral subnuclei and the cap of the rostral subnucleus. Labeling with 125I-BH-SP was very light and was restricted primarily to the central subnucleus of the IPN while 125I-BH-eledoisin labeling was very dense over the dorsal, the ventral sector of the rostral, the intermediate and the central subnuclei. Lesions of major afferents to the IPN, the fasciculus retroflexus or the locus coeruleus, had no effect on the distribution or density of the binding of either ligand. In rats 0, 4 or 7 days or age, 125I-BH-SP binding was very dense in the ventral tegmental region, the raphe and in the dorsal, rostral and central subnuclei. 125I-BH-eledoisin binding was extremely dense in the raphe and in the dorsal, rostral, intermediate and central subnuclei but was less dense in the ventral tegmentum. Adult levels of binding in the midbrain were established by 11 days of age. Neonatal lesions restricted to the fasciculus retroflexus had no effect on the density of labeling with either ligand in animals allowed to reach adulthood.