PHARMACOLOGICAL MODULATIONS OF ADRENERGIC PHENOTYPE IN MEDULLARY C2 AND C3 CELL GROUPS OF ADULT-RAT

The adrenergic phenotype was analysed in the rat's rostral dorsomedial medulla under normal conditions and 3 days after a single intraperito neal injection of an eburnamine derivative, RU 24722, which increases tyrosine hydroxylase protein expression in the rostral portion of the nucleus tractus solitarius. This approach was investigated by a double immunofluorescence labelling of tyrosine hydroxylase and phenylethano lamine N-methyltransferase proteins. Under normal conditions, most adr energic cell bodies are anatomically distributed in the dorsal and ros tral medulla oblongata between the rostral part of the dorsal motor nu cleus of the vagus nerve and the medial longitudinal fasciculus. Adren ergic neurons detected in this medullar region were distributed betwee n both cell groups. Three days after the pharmacological RU 24722 trea tment, an upregulation in tyrosine hydroxylase and phenylethanolamine N-methyltransferase protein expression was detected in both cell group s characterized by a highly increased number of tyrosine hydroxylase- and phenylethanolamine N-methyltransferase-containing cell bodies. The number of TH-mRNA containing neurons was also increased, indicating t he transcriptional level of this regulation. These results demonstrate d a particular neuronal plasticity of adrenergic phenotype in the medu llary cell groups of adult rat.