Acute modulation of somatostatin receptor function by melatonin in the rat frontoparietal cortex

Since melatonin (N‐acetyl‐5‐methoxytryptamine) decreases locomotor activity and rearing and increases grooming behavior in a similar manner as somatostatin (SRIF), we examined if melatonin could induce these changes through somatostatinergic neurotransmission in the rat frontoparietal cortex. Male W...

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Published in:Journal of pineal research 2001-08, Vol.31 (1), p.46-56
Main Authors: Izquierdo-Claros, Rosa María, Del Carmen Boyano-Adánez, María, Torrecillas, Guadalupe, Rodríguez-Puyol, Manuel, Arilla-Ferreiro, Eduardo
Format: Article
Language:English
Subjects:
adenylyl cyclase
Adenylyl Cyclases - metabolism
Animals
Biological and medical sciences
Central nervous system
Central neurotransmission. Neuromudulation. Pathways and receptors
Frontal Lobe - drug effects
Frontal Lobe - metabolism
frontoparietal cortex
Fundamental and applied biological sciences. Psychology
G proteins
GTP-Binding Protein alpha Subunits, Gi-Go - metabolism
GTP-Binding Protein alpha Subunits, Gs - metabolism
Kinetics
Male
melatonin
Melatonin - pharmacology
Parietal Lobe - drug effects
Parietal Lobe - metabolism
Rats
Rats, Wistar
Receptors, Somatostatin - drug effects
Receptors, Somatostatin - metabolism
RNA, Messenger - genetics
RNA, Messenger - metabolism
Somatostatin - genetics
Somatostatin - metabolism
somatostatin receptors
Vertebrates: nervous system and sense organs
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Summary:Since melatonin (N‐acetyl‐5‐methoxytryptamine) decreases locomotor activity and rearing and increases grooming behavior in a similar manner as somatostatin (SRIF), we examined if melatonin could induce these changes through somatostatinergic neurotransmission in the rat frontoparietal cortex. Male Wistar rats (200–250 g) received a single injection of melatonin (25 μg/kg per day) subcutaneously (s.c.) and were sacrificed 5 hr later. Melatonin treatment increased the number of 125I‐Tyr11‐SRIF receptors in frontoparietal cortical membranes without any changes in the dissociation constant (Kd). The capacity of SRIF to inhibit basal and forskolin (FK)‐stimulated adenylyl cyclase (AC) activity was increased in melatonin‐treated rats as compared to the control animals. Melatonin administration also induced a lower AC activity, both under basal conditions and after stimulation of the enzyme via stimulatory guanine nucleotide‐binding proteins (Gs), or directly with FK. Functional inhibitory guanine nucleotide‐binding protein (Gi) activity was increased in frontoparietal cortical membranes from melatonin‐treated rats when compared to controls. Western blot analyzes showed that melatonin administration did not alter the amount of the Giα1 or Giα3 subunits, but reduced Giα2 levels in frontoparietal cortical membranes. No significant changes in SRIF‐like immunoreactivity content and SRIF mRNA levels were detected in this brain area after melatonin treatment. Administration of the melatonin receptor antagonist luzindole (10 mg/kg, s.c.) 30 min before melatonin injection did not change the melatonin‐induced effects on the SRIF receptor–effector system. In conclusion, the present results show that acute melatonin administration increases the activity of the SRIF receptor–effector system and decreases Giα2 levels in the rat frontoparietal cortex. In addition, the coupling of Gs to AC is disturbed by melatonin.
ISSN:0742-3098
1600-079X
DOI:10.1034/j.1600-079X.2001.310107.x