Amino acid neurotransmitters in the central control of blood pressure and in experimental hypertension
There is now considerable evidence that afferent information from the arterial baroreceptor reflex is processed at three main integrative sites in the brainstem, before reaching the sympathetic efferent neurons arising from the intermediolateral cell column (IML) of the spinal cord (Fig. 1). These sites are the nucleus tractus solitarius (NTS), the caudal ventrolateral medulla and the rostral ventral medulla. However, the study of the brainstem and bulbospinal neurons and neurotransmitters that regulate blood pressure has been handicapped by a major difficulty inherent in studies of the central nervous system. The main problem is that the autonomic nervous system subserves many functions, such as respiration, digestion and micturition, and that neurons involved in those processes are intermingled with those innervating the cardiovascular system. To complicate matters further, there is a large range of neurotransmitters in the neurons traversing these pathways, often colocalized within a single neuron. Thus it becomes difficult to identify the particular neurons and the particular neurotransmitters that are specifically involved in the control of sympathetic activity and blood pressure. Indeed, even amongst the cardiovascular neurons there is a variety of neurotransmitters.