A Comparative Study of α₂‐ and β‐Adrenoceptor Distribution in Pigeon and Chick Brain

Abstract

The pharmacological properties and anatomical distribution of alpha2-, beta1- and beta2-adrenoceptors in pigeon and chick brains were studied by both homogenate binding and tissue section autoradiography. [3H]Bromoxidine (alpha2-adrenoceptor-), [3H]CGP 12177 (beta-adrenoceptor) and [125I]cyanopindolol (beta-adrenoceptor) were used as radioligands. In both species, [3H]bromoxidine binding to avian brain tissue showed a pharmacological profile similar to that previously reported for alpha2-adrenoceptors in mammals. Regarding the anatomical distribution, the areas with the highest densities of alpha2-adrenoceptors in the pigeon brain included the hyperstriatum, nuclei septalis, tectum opticum and some brainstem nuclei. Most beta-adrenoceptors found in tissue membranes and sections from chick and pigeon brain were of the beta2 subtype, in contrast to what has been reported in the mammalian brain, where the beta1 subtype is predominant. A striking difference was found between the two species regarding the densities of these receptors: while pigeon brain was extremely rich in [125I]cyanopindolol binding throughout the brain (mainly cerebellum) in the pigeon, the levels of labelling in the chick brain were much lower; the exception was the cerebellum, which displayed a higher density than other parts of the brain in both species. Overall, our results support the proposed anatomical equivalences between a number of structures in the avian and mammalian encephalon.

Neuronal and glial localization of α2A‐adrenoceptors in the adult zebrafish (Danio rerio) brain

“…Sensory integration centers, the optic tectum (mostly visual input; superior colliculus in mammals; Butler and Hodos, 1996) and the semicircular torus (mostly acoustic and lateral line input; inferior colliculus in mammals; Butler and Hodos, 1996), exhibited moderate levels of ␣ 2A -AR labeling; that is, superficial tectal layers contained higher numbers of medium-sized ␣ 2A -AR-ir neurons and fibers than deeper periventricular layer (SGP), in agreement with previous study (Ruuskanen et al, 2005b). This pattern is similar to that described for birds (Ball et al, 1989;Dermon and Kouvelas, 1989;Fernandez-Lopez et al, 1997) andmammals (Palacios andKuhar, 1980;Unnerstall et al, 1984), highlighting a possibly similar role of the noradrenergic system in sensory modulation and integration among vertebrates. The fact that the dorsomedial tectal portion, the origin of the tectal projections to the nucleus rostrolateralis that is involved in feeding Saidel and Butler, 1997), included a high density of ␣ 2A -AR supports the idea that ␣ 2A -ARs play a role in the visual and motor control of feeding.…”

“…The ␣ 2A -AR distribution pattern in most of the zebrafish diencephalic areas is comparable to that obtained in other studies of teleost fish (Zikopoulos and Dermon, 2005), including the zebrafish (Ruuskanen et al, 2005b), as well as in studies of avian (Ball et al, 1989;Dermon and Kouvelas, 1989;Fernandez-Lopez et al, 1997) and mammalian (Unnerstall et al, 1984) brain. Specifically, the presence of high density of ␣ 2A -AR in the zebrafish hypothalamic areas is in agreement with mammalian (Unnerstall et al, 1984), avian (Ball et al, 1989;Dermon and Kouvelas, 1989;Fernandez-Lopez et al, 1997), and teleost (Ruuskanen et al, 2005b;Zikopoulos and Dermon, 2005) studies. In particular the dorsal zone of periventricular hypothalamus, suggested to be involved in the sex change in hermaphrodite fish (Zikopoulos et al, 2001), contained fibers expressing a high density of ␣ 2A -ARs.…”

Noradrenergic Inputs Mediate State Dependence of Auditory Responses in the Avian Song System

“…Although there is very little ␤ 1 adrenergic receptor expression, ␤ 2 receptors are prevalent throughout the avian telencephalon (Dermon and Kouvelas, 1988;Fernandez-Lopez et al, 1997;Revilla et al, 1998). We therefore tested the effects of the ␤ 2 agonist isoproterenol in NIf (n ϭ 3 sites in three birds).…”

“…The major subtypes expressed in the avian telencephalon are the ␣ 1 , ␣ 2 , and ␤ 2 adrenergic receptors Fernandez-Lopez et al, 1997). We first tested the effects of infusing ␣ 1 and ␣ 2 agonists into NIf.…”

Local action of exogenous nitric oxide (NO) on the skin blood flow of rock pigeons (Columba livia) is affected by acclimation and skin site

“…Passive vasodilatation, which is mediated by α2-ARs in mammals, seems also to be mediated by the β-adrenergic pathway in birds, at least in the pigeon (Marder and Raber, 1989;Ophir et al, 2000). Even though the β2 subtype predominates in the central nervous system (CNS) of the pigeon (Fernandez-Lopez et al, 1997), the β1 subtype seems to be more responsive to changes in acclimation state, thus contributing to the fine-tuning of responses to thermal stimuli (Ophir et al, 2000). Recent results suggest that the fundamental difference between birds and mammals in the haemodynamic control exercised by the sympathetic nervous system could be partly explained by differences in the distribution, number and affinity of α-and β-ARs (Arieli, 1998) and, furthermore, by the hierarchical relationship between the receptor subtypes in the CNS and periphery (Ophir et al, 2000).…”