Central neural regulation of heart and blood vessels in mammals.

The study of the central regulation of the circulation in the past has been directed primarily at observing reflex responses to stimulation of peripheral receptors and at producing changes in cardiovascular parameters during electrical stimulation of central sites. These studies have demonstrated that the nervous system can regulate the circulation to different vascular beds with a high degree of specificity and that it has the ability to provide a range of coordinated responses which are appropriate to the metabolic needs of a particular behavioural pattern. In addition, it has become firmly established that the nervous system is capable of coupling cardiovascular changes with other autonomic and somatic activities to produce an integrated response. In the last decade it has become apparent that although the mode of operation of central cardiovascular regulation has been described in general terms, very little is known about the accurate anatomical localization of neuronal circuits and pathways and of impulse traffic corresponding to the changes in cardiovascular parameters that have been observed. This essay reviews recent information on discrete neuronal circuits and pathways and their mode of operation in electrophysiological terms. One of the most serious difficulties in this endeavour is the problem of demonstrating specificity of pathways and circuits because patterns of firing of afferent and efferent peripheral nerves can be usually identified, but the demonstration of specificity of central structures is a conceptual and technical challenge to the most skilled investigator. Several studies have been made in the last decade in an attempt to trace anatomically and functionally pathways involved in central cardiovascular regulation. Progress has been made especially with regard to the precise sites of termination of cardiovascular afferent fibres and the pattern of discharge of efferent cardiovascular neurons; some work has also been done to trace discrete pathways between the hypothalamus and the medulla and the medulla and the spinal cord. However, in view of the difficulties of establishing the specificity of cardiovascular pathways, progress will depend on the acquisition of a wiring diagram of simple cardiovascular reflex arcs before attempts are made to study the functional interactions of regions in the brain that have been traditionally associated with central regulation of the circulation. Future experiments should concentrate less on the demonstration of cardiovascular responses to stimulation or lesions in the central nervous system and more on the connections of discrete regions.(ABSTRACT TRUNCATED AT 400 WORDS)