Locus coeruleus neurons show reduced alpha2-receptor responsiveness and decreased basal activity in spontaneously hypertensive rats

Previous studies have indicated that brain noradrenaline (NA) neurons in spontaneously (genetically) hypertensive rats (SHR) are implicated in the development of hypertension. Thus, a number of biochemical aberrations in the metabolism of NA in the SHR brain have been detected although the data are not in total agreement. We report here experiments utilizing single cell recording techniques which show directly a reduction in neuronal activity of brain NA neurons in the locus coeruleus (LC) of SHR. This reduction develops gradually with age and in parellel with the increased blood pressure (BP), but is not altered by acute alterations in BP. The SHR were found to display an increased intraneuronal monoamine oxidase (MAO) activity as well as a specifically reduced sensitivity of inhibitory alpha2-receptors within the LC. It is suggested that in SHR the LC system, in spite of a reduced basal activity, displays increased responsiveness to sensory stimuli, a phenomenon that may contribute to the development of hypertension.