The effects of several protein modifying reagents, including phenoxybenzamine, N-ethylmaleimide (NEM), 5,5'-dithiobis (2-nitro)--benzoic acid (DTNB), p-chloromercuryphenyl sulfonic acid (PCMP) and p-bromophenacylbromide (PBPB), on the binding of 125I-Bolton Hunter substance P (125I-BHSP), 125I-Bolton Hunter eledoisin (125I-BHELE) and 3H-neurokinin B (3H-NKB)4 to cortical synaptosomes were examined. PCMP (10(-4) M), DTNB (10(-4) M) and NEM (10(-3) M) were without effect on the 125I-BHSP binding but reduced markedly the specific binding of 125I-BHELE or 3H-NKB. Although phenoxybenzamine and PBPB inhibited the 125I-BHSP binding when used in high concentrations (10(-4) M and 10(-3) M), they were more potent in inhibiting the 125I-BHELE or 3H-NKB binding. These results indicate that the NKB binding site is more sensitive to alkylating reagents than the SP binding sites and that these reagents can be used to distinguish SP and NKB receptors in the brain.

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PubMedDate not supplied

Localization of tachykinin binding sites (NK1, NK2, NK3 ligands) in the rat brain.

A comparative autoradiographic analysis of the distribution of tachykinin binding sites was made on brain serial sections using several ligands. (1) 3H-SP, 125I-BHSP and 3H-physalaemin labeled identical binding sites (NK1 type). (2) 3H-NKB, 125I-BHE and 3H-eledoisin also labeled identical sites (NK3 type). (3) 125I-BHNKA preferentially labeled NK3 binding sites, the distribution of 125I-BHNKA binding sites being identical to that of 3H-NKB or 125I-BHE binding sites. (4) The distributions of 3H-SP and 3H-NKB binding sites were markedly different. (5) A very low density of labeling was found with 3H-NKA or 125I-NKA, and these binding sites were distributed only in areas rich in either 3H-SP or 3H-NKB binding sites. (6) Particular efforts were made to look for the presence of tachykinin binding sites in the substantia nigra, since this structure is particularly rich in SP and NKA and contains functional tachykinin receptors of the NK1 and NK2 types as suggested by physiological studies. Confirming previous reports, low or very low labeling was observed in the substantia nigra with 3H-SP or 125I-BHSP and 3H-NKB or 125I-BHE. Similar results were found with 3H-NKA, 125I-NKA or 125I-BHNKA. In conclusion, our data do not provide evidence yet for the existence of NK2 binding sites in the rat brain.

Animals↗

PubMedDate not supplied

NK-1 receptors are the only class of tachykinin receptors found on mouse cortical astrocytes.

Extending our previous studies, our results indicate that cultured cortical astrocytes from the mouse possess only NK-1 receptors coupled to phospholipase C. An excellent correlation was found in the potency of tachykinins and selective analogs at inhibiting 125I-BHSP binding and at stimulating phospholipase C activity, their rank order being that of NK-1 receptors. No binding sites could be found with ligands of NK-2 or NK-3 receptors. No additive effect could be shown with NK-2 or NK-3 agonists when phospholipase C activity was estimated with high concentrations of NK-1 agonists. C- or N-terminal SP fragments did not modify SP- or [Pro9]SP-evoked responses.

Animals↗

PubMedDate not supplied

Possible existence of a new tachykinin receptor subtype in the guinea pig ileum.

The guinea pig ileum possesses NK-1 and NK-3 tachykinin receptors. As expected, [Pro9]SP and senktide, which are selective agonists of NK-1 and NK-3 receptors, respectively, were found to be highly potent in contracting the guinea pig ileum. Surprisingly, similar observations were made with septide, SP-O-CH3, [Apa9-10]SP, or [Pro9,10]SP although, in contrast to [Pro9]SP, these four peptides showed a low affinity for 3H-[Pro9]SP-specific NK-1 binding sites on membranes from the guinea pig ileum. They were also devoid of affinity for NK-2 and NK-3 binding sites. GR 71251, a compound which has been described as a NK-1 antagonist, was more potent in inhibiting the septide- than the [Pro9]SP-evoked contracting response. Altogether, these results suggest that septide, [Apa9-10]SP, and [Pro9,10]SP exert their high contracting activity in the guinea pig ileum by acting on a new subtype of tachykinin receptors.

Animals↗

PubMedDate not supplied

NK-1 tachykinin receptor in rat and guinea pig brains: pharmacological and autoradiographical evidence for a species difference.

The affinities of a large variety of peptide or nonpeptide tachykinin analogues were determined on membranes from rat and guinea pig brains using the selective NK-1 radioligand 3H-[Pro9]SP. Nonpeptide antagonists clearly revealed a species difference; (+/-)CP-96,345 was more potent in the guinea pig, while RP 67580 was found to be a better competitor of 3H-[Pro9]SP binding to rat brain membranes. This was confirmed on brain slices by autoradiography. Numerous brain structures were analyzed by optical densitometry. From these data, a heterogeneity of NK-1 binding sites among different structures can be excluded in both rat and guinea pig brains.

Animals↗

PubMedDate not supplied

The mapping of the central aminergic pathways.

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Biogenic Amines↗