Prolactin-releasing peptide enhances synaptic transmission in rat thalamus

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a nonselective β-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABAA-ergic, α- and β-adrenergic transmissions are all involved in this action, whereas 5-HT1 and 5-HT2 serotonergic, muscarinic cholinergic and D2, D3, D4 dopaminergic mechanisms may not be implicated.

The role of GluA1 in central nervous system disorders

In the brain, the four subunits of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, glutamate A1 (GluA1), GluA2, GluA3, and GluA4 form functionally different tetramers. Of these, GluA1 is very important. It forms calcium-permeable (without GluA2) AMPA receptors and induces the trafficking and integration of AMPA receptors within synaptic membranes. Increased GluA1 expression and their phosphorylation are common mechanisms for the treatment of Alzheimer's disease, schizophrenia, depression, and chronic drug addiction. Moreover, GluA1 is also involved in pain and epilepsy. Increased phosphorylation of serine831 in the GluA1 receptor is a mechanism necessary to alleviate Alzheimer's disease and depression. GluA1-/- knockout mice are used as a model of schizophrenia. A decrease in the total cell AMPA receptor currents and phosphorylation of serine845 of GluA1 is observed in chronic drug addiction. Increased expression of GluA1 causes pain and is involved in epilepsy. GluA1-promoting AMPA receptor potentiators could be used to treat Alzheimer's disease and memory loss. In conclusion, GluA1 agonists or antagonists might be effective in various disorders and conditions of the central nervous system that are based on GluA1 status at the synaptic region.