Ontogeny of bombesin/gastrin-releasing peptide binding sites in rat brain
R Getz1, C Merchant, J Rosenstein
1Departments of Anatomy and Biochemistry and Molecular Biology, George Washington University School of Medicine and Health Sciences, Washington, D.C. 20037, USA.
Insights
Bombesin/gastrin-releasing peptide (BN/GRP) binding sites in rat brains develop significantly after birth. These binding sites redistribute across brain regions during development, with changes noted in olfactory, limbic, and cortical areas.
Area of Science:
- Neuroscience
- Developmental Biology
- Pharmacology
Background:
- Bombesin/gastrin-releasing peptide (BN/GRP) receptors are implicated in various physiological processes.
- Understanding the developmental trajectory of BN/GRP binding sites is crucial for comprehending their role in brain maturation.
Purpose of the Study:
- To characterize the developmental changes in bombesin/gastrin-releasing peptide (BN/GRP) binding sites in the rat brain.
- To identify specific brain regions exhibiting developmental alterations in BN/GRP binding site density and distribution.
Main Methods:
- Utilized radioligand binding assays with radio-labeled ((125)I-Tyr(4))BN on rat brain homogenates from different postnatal ages.
- Employed in vitro autoradiography to visualize and quantify the distribution of BN/GRP binding sites across various brain regions.
- Assessed the binding affinity and specificity using BN, GRP, and their analogs.
Main Results:
- BN/GRP binding site density increased significantly around birth and between postnatal days 7 and 10, reaching adult levels by P10.
- High-affinity binding was observed, with the C-terminal portion of BN or GRP being essential for activity.
- Autoradiography revealed a developmental redistribution of binding sites, with increases in the parietal cortex and decreases in areas like the central gray and inferior colliculus in adult rats compared to early postnatal stages.
Conclusions:
- The rat brain exhibits significant developmental changes in the density and regional distribution of BN/GRP binding sites.
- These findings highlight a dynamic maturation process of BN/GRP neurotransmission in the developing rat brain.
- The C-terminal region of BN/GRP is critical for high-affinity binding during brain development.
Abstract:
The development of bombesin/gastrin-releasing peptide (BN/GRP) binding sites was determined in the rat brain. Using rat brain homogenate, the density of radio-labeled peptide binding sites increased dramatically around birth, remained constant during the first post-natal week, and then increased again between Postnatal (P) Days 7 and 10; the density of binding sites was similar in P10 and adult animals. Rat brain homogenates derived from P1, P7, or P10 animals bound ((125)I-Tyr(4))BN with high affinity (K(d) = 2-4 nM) to a single class of sites (B(max) = 11, 17, and 51 pmol/mg protein, respectively). BN, GRP, and GRP(18-27) inhibited specific radiolabeled peptide binding to rat brain homogenate with high affinity using P1, P3, P7, or P14 animals, whereas GRP(1-16) was inactive. These data indicate that the C-terminal of BN or GRP is essential for high-affinity binding activity in the rat brain during development. In vitro autoradiography revealed high ((125)I-Tyr(4))BN grain densities in the anterior olfactory nucleus, olfactory tubercle, nucleus accumbens, central medial thalamic nucleus, and hippocampus. Moderate grain densities were observed in the parietal cortex, periventricular hypothalamic nucleus, central gray, inferior colliculus, pontine reticular, and gigantocellular reticular nuclei in P1, P3, and P7 rat brains. In P14 and adult animals, relative to P1, P3, or P7 rat brains, the density of binding sites increased significantly in the parietal cortex. The ((125)I-Tyr(4))BN grain density was not significantly changed in the anterior olfactory nucleus, periventricular nucleus of the hypothalamus, olfactory tubercle, hippocampus, dentate gyrus, central medial thalamic nucleus, and nucleus accumbens but decreased significantly in the central grey, inferior colliculus, and pontine reticular nucleus. These data indicate that there is a redistribution of BN/GRP binding sites in the rat brain during development.
