Regional Characterization of Brain Neurotensin Receptor Subtypes in LS and SS Mice

Abstract

Neurotensin (NT) receptor subtypes were investigated in nine brain regions from long sleep (LS) and short sleep (SS) mice that were selectively bred for differences in sensitivity to ethanol. Differences in NT receptor densities may mediate, in part, genetically selected differences in ethanol sensitivity between the two lines of mice. The use of [3H] NT at concentrations from 0.02 to 20 nM yielded biphasic binding isotherms as revealed by Scatchard analysis. Membranes from LS ventral midbrain yielded dissociation constants (KD values) of 0.34 and 3.85 nM for the high (NTH) and low (NTL) affinity components, respectively. SS membranes displayed similar KD values, however the maximum number of binding sites (Bmax) for both receptor subtypes were significantly greater in SS than in LS membranes (46.7 vs. 71.5 fmol/mg protein for NTH and 170.2 vs. 208.2 fmol/mg protein for NTL). Using levocabastine, and H1 antagonist with selectivity for NTL, characterization of NTH and NTL binding in nine brain regions was performed. In general, membranes from each brain region of SS mice had higher densities than LS for both receptor subtypes. Significant differences for the total density of receptors and NTL were found in entorhinal cortex, nucleus accumbens, hippocampus, and ventral midbrain. The only region to differ in NTH was the ventral midbrain. Competition experiments using various NT fragments to compete for NTH binding showed the C-terminal amino acids to be essential for binding. The order of potency was NT1-13 = NT8-13 greater than Neuromedin N greater than NT1-8 = NT1-11.

Confirmation of Correlations and Common Quantitative Trait Loci Between Neurotensin Receptor Density and Hypnotic Sensitivity to Ethanol

“…We previously reported that NTS1 receptor densities were higher in several brain regions of SS mice selectively bred for low sensitivity to ethanol-induced LORR, compared with LS mice that were selectively bred for high sensitivity to LORR; that is, densities of NTS1 were higher in the ventral midbrain and frontal cortex of SS mice but were not different in striatum (Campbell et al, 1991). This observation is not consistent with a model in which NTS1 density was coselected with LORR, as suggested by the positive correlations between striatal NTS1 density and hypnotic sensitivity to ethanol (positive with LORR and QTLs were mapped with the use of the MAPMAKER/QTL software package.…”

“…Studies of neurotensin receptors from rat and mouse brain revealed biphasic binding isotherms best described by two independent binding sites: high-affinity (NTS1) and low-affinity (nts2; Campbell et al, 1991;Mazella et al, 1989). The H 1 histamine antagonist, levocabastine, has been shown to selectively inhibit binding of NT to nts2 (Campbell et al, 1991;Mazella et al, 1989), which provides a valuable tool to distinguish between NTS1 and nts2.…”

“…The H 1 histamine antagonist, levocabastine, has been shown to selectively inhibit binding of NT to nts2 (Campbell et al, 1991;Mazella et al, 1989), which provides a valuable tool to distinguish between NTS1 and nts2. Levocabastine has been used to demonstrate differences in densities of NTS1 in brain regions from mice and rats that were selectively bred for differential sensitivity to ethanol-induced LORR (LS and SS mice and HAS and LAS rats; Campbell et al, 1991;.…”

“…The H 1 histamine antagonist, levocabastine, has been shown to selectively inhibit binding of NT to nts2 (Campbell et al, 1991;Mazella et al, 1989), which provides a valuable tool to distinguish between NTS1 and nts2. Levocabastine has been used to demonstrate differences in densities of NTS1 in brain regions from mice and rats that were selectively bred for differential sensitivity to ethanol-induced LORR (LS and SS mice and HAS and LAS rats; Campbell et al, 1991;. Studies using LSXSS recombinant inbred (RI) strains indicated that differences in NTS1 densities were mediated by multiple genes with additive effect , and significant genetic correlations (positive for NTS1 density versus LORR and negative for NTS1 versus BECRR) were observed between hypnotic sensitivity to ethanol and NTS1 density in the striatum.…”

Neurotensin and Neurotensin Receptors in Stress-related Disorders: Pathophysiology & Novel Drug Targets

“…NT markedly enhanced ethanol sensitivity, assessed by ethanol-induced anesthesia and increased sleep duration, two-fold in rats [159], and up to three-fold in mice, in a dose-dependent manner [160]. The role of the neurotensinergic system in ethanol consumption was launched and consolidated by Gene Erwin and his colleagues [161][162][163][164][165][166][167][168][169][170][171][172]. Firstly, they showed that this NT-induced enhancement of ethanol sensitivity was different in SS compared to LS mice.…”