Expanding the horizons of melatonin use: An immunohistochemical neuroanatomic distribution of MT1 and MT2 receptors in human brain and retina

Introduction

There is increasing evidence implicating the active role of melatonin beyond regulation of the human biological clock and reproduction. Its therapeutic use has been extended to neurodegenerative disorders, psychiatric disturbances, memory as well as a host of other neurological manifestations. This study was thus designed to identify regions of brain and retina for the expression of different types of melatonin receptors.

Method

Six unfixed brains and 10 retinae were studied. Tissue samples were taken from 14 sites in the brain. Immuno-histochemical staining was done using antibody against Melatonin 1and Melatonin 2 receptors.

Result

In the cerebral cortex, MT 1 receptor presence was mostly detected in layers 4 and 5 while MT2 receptors were mapped in all the layers. The frontal and occipital poles were devoid of both the receptors. The suprachiasmatic nuclei of the hypothalamus had immunoreactivity for both MT1 and MT2 while the larger cells of the supraoptic nuclei showed positivity for MT1 receptors. The pyramidal and granule cells of the cerebellar cortex showed the presence of MT2 receptors while the pons and the medullary reticular formation stained positive for MT1 and MT2.

Discussion

Differential and comparative characterization of MT1 and MT 2 receptors in different regions of brain and retina has led to virtual creation of a neuroanatomical map localizing potential areas susceptible to interventions specifically targeting melatonergic pathways.