European Journal of Biomedical and Pharmaceutical Sciences

AGE RELATED CHANGES IN THE CIRCADIAN RHYTHM OF MELATONIN AND SOME NEUROTRANSMITTERS IN THE MALE RATS

Seham Abdel-Kader, Mona Abdel-Rahman, Heba ElMasry and *Rehab E. El-Hennamy

ABSTRACT

Ageing refers to a series of time-dependent anatomical and physical changes that reduce physiological reserve and functional capacity. Age leads to important circadian rhythm changes in some physiological parameters like hormonal secretion and neurotransmitters contents. The present work aimed to study the age-related changes in the circadian rhythm of melatonin, acetylcholine Ach, serotonin 5-HT, and norepinephrine NE. Rats were divided into two groups, adult and aged rats, that maintained under 12: 12 LD. Ach, 5-HT, and NE levels were measured in the cerebral cortex and hippocampus by enzyme-linked immunosorbent assay (ELISA) and the fluorimetric method respectively. Melatonin levels in the serum were assayed by radioimmunoassay. Acetylcholine levels in the cerebral cortex of adult rats were peaked at the dark phase of the light-dark cycle. On the contrary, its level in aged rats peaked at the light phase of the light-dark cycle. Moreover, cortical acetylcholine levels in aged rats were decreased nearly at all time intervals as compared to the adult group. Serotonin contents of both the cerebral cortex and the hippocampus of aged rats were also decreased. Its rhythm was phase delayed in the cerebral cortex and exhibit a biphasic pattern in the hippocampus with peaks at light and the dark phases. NE contents in the cortex and hippocampus of adult rats peaked during the light phase. While, its rhythm displayed a biphasic pattern in the aged rat cortex. Melatonin levels of aged rats were decreased at most time intervals and exhibit an advance in the beginning of increment and decrement but, the peak was demonstrated at the same time as adults. In conclusion, the neurotransmitters in the studied brain areas as well as the melatonin levels were declined during the aging process and exhibit a shift or disturbances in its circadian rhythm which may result from atrophy of the brain tissue and abnormalities of the circadian system respectively.

Keywords: Melatonin, Acetylcholine, Serotonin, Norepinephrine, Circadian Rhythm, Aging, Rats.