Comparative study of the three dimensional distributions of sleep and feeding related hypothalamic transcripts in the rat, Rhesus monkey and human.
A. MEDINA; D. M. KROLEWSKI; I. A. KERMAN; R. BERNARD; S. BURKE; E. G. JONES; W. BUNNEY, Jr; S. J. WATSON; H. AKIL
Society for Neuroscience. 2008.
The hypothalamus is a complex integrative diencephalic structure that regulates critical survival functions, including feeding and sleep. Multiple hypothalamic transmitter systems regulate these functions via extensive local and long-distance projections. Most of the anatomical and functional characteristics of these circuits have been derived primarily from rodent studies, with comparatively less data from primates. In this study we set out to compare the distribution and proportional 3D sizes of three hypothalamic transmitter systems, including orexinergic, histaminergic and melanin-concentrating hormone systems, in rodent and primate brains.
Three-dimensional reconstructions of mRNA distributions of prepro-orexin (PPO), pro-melanin-concentrating hormone (PMCH) and histidine decarboxylase (HDC; a key enzyme in histamine synthesis) were examined in rat, Rhesus monkey and human. Brains were cut at 10µm, and radioactive in situ hybridizations (ISHs) were performed in regularly-spaced sections: 100µm for rat, 200µm for monkey, and 500µm for human. Digitized images of ISH autoradiograms were overlaid using AdobeÂ® PhotoshopÂ® CS 8.0, and then processed to create a 3D reconstruction of the mRNA signals distribution using Volocity 2.6 software (Improvision Inc, Lexington, MA). Measurements in each subject were made establishing the total voxel count for each signal, and then comparing it to the counts for the other two transcripts to establish a percentage to illustrate the proportional size of each system. When comparing the distribution and abundance of HDC, PMCH and PPO, significant differences can be appreciated between species, especially when comparing the rat with the primates; of the total number of voxels occupied by each signal in rat, 6.1 % correspond to HDC, 77.7 % to PMCH and 16.2 % to PPO. In the Rhesus monkey the distribution is 46.6% for HDC, 43.4% for PMCH and 9.8 % for PPO, whereas in humans the percentages are 43.73% for HDC, 40.3% for PMCH and 15.9 % for PPO. According to this preliminary data, there seem to be important differences in the anatomical distribution and abundance of the transcripts studied between rodents and primates. Since the distribution of these functional systems does not match the classical histology described for the hypothalamus and functional cells are found beyond the limits of traditional anatomical nuclei, three dimensional mapping of in situ signals constitutes a valuable tool to establish the relative proportions of the systems on each species.