Distribution of CGRP-like immunoreactivity in the chick and quail brain

Calcitonin gene-related peptide (CGRP)-containing neurones have been implic ated in the transmission of visceral sensory information to the cortex and in the control of arterial blood pressure in mammals. However, little is kn own about its function in other vertebrates. As a first step toward investi gating the function of CGRP in birds, its distribution was studied in the d omestic chick and quail brain by means of immunocytochemistry, by using ant ibodies against rat CGRP. The distribution of CGRP immunoreactivity in the chick and quail central nervous system was found to be similar. CGRP-immuno reactive (CGRPi) perikarya were not present in the telencephalon. In the di encephalon, CGRPi perikarya were present mainly in the shell of the thalami c nucleus ovoidalis, the nucleus semilunaris paraovoidalis, the nucleus dor solateralis posterior thalami, and in the hypothalamic nucleus of the ansa lenticularis. In the brainstem, CGRPi perikarya were present in the nucleus mesencephalicus nervi trigemini, the nucleus tegmenti ventralis, the locus coeruleus, the nucleus linearis caudalis and in the parabrachial region. I n addition CGRPi perikarya were found in the motor nuclei of the III, IV, V , VI, VII, IX, X, and XII cranial nerves. The telencephalon contained CGRPi fibres within the paleostriatal complex (mainly in the ventral paleostriat um), parts of the neostriatum and ventral hyperstriatum, parts of the archi striatum, and the septum. In the diencephalon, the densest plexus of CGRPi fibres was observed in the dorsal reticular thalamus. A less dense CGRPi in nervation was present in some dorsal thalamic nuclei and in the medial and periventricular hypothalamus. The pretectum and midbrain tegmentum also con tained CGRPi fibres, whereas the optic tectum was virtually devoid of immun olabelling. Scattered CGRPi fibres were observed in the central grey and ne ighbouring pontine areas. Some of the sensory fibres of the trigeminal, vag al, glossopharyngeal, and spinal nerves were also CGRPi. The results of com parative studies indicate that the presence of CGRP in some thalamo-telence phalic projections is a primitive feature of the forebrain of amniotes. The refore, the brain areas giving rise to and receiving such a projection in d ifferent vertebrates, are likely to be homologous. J. Comp. Neurol. 421:515 -532, 2000. (C) 2000 Wiley-Liss, Inc.