Characterization of the Expression and Function of a2C Adrenoceptor in Adra2c Knockout /lacZ Knock-in Mice

• Main Authors: Cheng-Chiu Huang, 黃正球
• Other Authors: Alice Chien Chang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/12971911276729965639

碩士 === 國立陽明大學 === 神經科學研究所 === 91 === a2 adrenoceptors mediate many physiological responses of norepinephrine (NE) and epinephrine (Epi). They belong to the superfamily of G-protein coupled receptors and are divided into a2A, a2B and a2C adrenoceptors by pharmacological parameters. Molecular cloning evidence indicates each is encoded by a unique gene in mice: Adra2a, Adra2b, and Adra2c respectively. Despite inconclusive, differential expression of the 3 receptor subtypes indicate each subtype may have unique physiological functions. However, assigning unique functions to a particular subtype in vivo is difficult because subtype-specific agonists and antagonists are lacking. We have adopted a gene-targeting approach to study the expression and functions of a2C adrenoceptor subtype in mice. After homologous recombination between wild-type allele and targeting vector in embryonic stem cells, the coding sequence of Adra2c is disrupted and replaced by a reporter gene lacZ (encoding b-galactosidase), whose expression is under the control of the regulatory sequence of Adra2c in its entirety.  The expression of a2C adrenoceptor in brain as indexed by in situ X-gal staining was clearly detected in frontal cortex, temporal cortex, endopiriform cortex, anterior olfactory nucleus, olfactory tubercle, claustrum, ventral pallidum, caudal caudate-putamen, hippocampus, bed nucleus of the stria terminalis and amygdala etc., in the CNS of adult homozygous mutant mice. Weak staining was found in cerebellum and brainstem region but no staining may be detected in thalamus except the anterodorsal nucleus. Co-localization with dopamine b-hydroxylase (DBH)-positive varicosities by immunocytochemistry (ICC) suggests a2C adrenoceptors in these areas are at the NE projection terminals. Hetero- and homozygous a2C knockout mice are viable and fertile. Juvenile fights between male siblings were frequently observed in our breeding colonies (12 out of 15 litters). Therefore, standard behavioral paradigm of isolation-induced aggression was employed to examine whether deficiency of a2C adrenoceptor is involved in this phenotypic trait of Adra2c-KO mutants. Preliminary data suggest, in a typical 15 min (900 sec) session, both hetero- (n=9) and homozygous (n=11) KO for a2C in contrast to wild-type control (n=11) exhibit decreased latency (sec) for attack (333.7±167.6, 282.3±115.3 vs. 898.6±4.5) and increased number of attack (9±4, 15±14, vs. 0.1±0.3) In lieu of the fact that dysfunction of the serotonin system has been implicated in mood disorders including depression and aggression. Co-localization of serotonin projections (5HT-ICC) and a2C adrenoceptor (X-gal) noted in areas including prefrontal cortex, olfactory system, basal ganglia, amygdala, bed nucleus of the stria terminalis and hippocampus provide support for the notion that aggressive behavior observed in mutant mice deficient in a2C adrenoceptor may be attributed to imbalanced interaction between 5-HT and NE systems. The serotonin receptor subtypes mediating the cross talk between the transmitter systems will be further identified and validated by receptor-ICC. In addition, serial homecage intrusion by BALB/c male elicited a differential c-fos expression in many brain areas, including olfactory system, prefrontal cortex, rhinal cortex, claustrum, caudal caudate-putamen, amygdalar complex, hippocampal CA1 region and subiculum in Adra2c-/- mice than wild-type control mice. Current data suggest the expression pattern and putative functions of a2C adrenoceptor in the mouse model. Furthermore, these brain structures consisted interconnected and coordinately functional units for sensory integration, social recognition and emotional regulation, thus may raise a psycho-therapeutical interest of a2C adrenoceptor.