Daily expression of genes coding for neurotransmitters in central and peripheral tissues of redheaded bunting: Implication for circadian regulation of physiology in songbirds

ABSTRACT

In birds, circadian control of tissue level communication is not well understood. The present study investigated this, by monitoring daily oscillation of genes coding for peptides (neuropeptide Y, NPY; vasoactive intestinal peptide, VIP; somatostatis, SST) and intermediary enzymes of amine and amino acid neurotransmitters (dopamine [tyrosine hydroxylase, TH]; glutamate [glutaminase, GLS; glutamate oxaloacetate transaminase 2, GOT2]; gamma amino butyric actid, GABA [glutamic acid decarboxylase 65, GAD65]) biosynthetic pathway, along with c-FOS as an activation marker, in different tissues of migratory redheaded buntings, Emberiza bruniceps. We cloned a partial sequence of these genes, and measured their mRNA expression in the ‘central’ clock (retina, hypothalamus) and peripheral (heart, stomach, gut, liver) tissues, collected at six times (ZT 2, 6, 11, 13, 18 and 23; ZT 0 = lights on) from birds (n = 4/ ZT) in the 12 h:12 h light-dark cycle. There were daily mRNA oscillations of all genes, although with a tissue-specific expression pattern as well as with the differential phase relationships in genes within and between tissues. These results support a conserved tissue level circadian regulation of genes coding for peptide, amine and amino acid neurotransmitters, and substantiate the expression and plausible role of neurotransmitters in the peripheral tissues. We suggest a tissue-specific contribution of neurotransmitters in the circadian regulation of physiology and behaviour in a seasonal migratory species, the redheaded bunting.

KEYWORDS:

• Bird
• bunting
• circadian
• neuropeptide
• neurotransmitter

Acknowledgements

The animal experiment was carried out and tissue samples obtained when DS and VK worked at the University of Lucknow, Lucknow, India, using the facility developed through the DST-IRHPA grant and (IR/SO/LU-02/2005)..

Declaration of interest

Authors have no conflict of interest. Funding from Science and Engineering Research Board, New Delhi, through DU-DST PURSE and University of Delhi R&D grants is acknowledged. IM receives a CSIR SRF.

Supplemental material

Supplemental data for this article can be accessed at www.tandfonline.com/icbi.