Arterial baroreceptor signal processing in the nucleus tractus solitarius
Abstract
This dissertation presents original work in the field of neurophysiology. The results of the thesis work are of direct importance in understanding the neurophysiological mechanisms underlying short-term negative feedback control of cardiovascular function. It has long been known that primary sensory afferents, known as the arterial baroreceptors, provide the central nervous system (CNS) with information that includes an encoding of (relative) mean arterial pressure. When these mechanoreceptors are activated, there is a resulting reflex reduction in cardiac output and peripheral resistance, and therefore blood pressure. The baroreceptors, sensitive to arterial wall distension, provide direct synaptic drive to a specific group of neurons in the nucleus tractus solitarius (NTS), located in the caudal medulla. Unlike the baroreceptors, whose arterial pressure-response functions have been well defined, we know precious little regarding the encoding properties of second order neurons in the NTS. Therefore, in vivo recordings were undertaken to define these properties. In the first series of experiments, the activity of physiologically identified second order NTS neurons was recorded while the baroreceptors were stimulated by natural arterial pressure waveforms originating from the heart. During these recordings, arterial pressure was manipulated using pharmacological and physical means. The responses of the second order cells to these stimuli were recorded, providing the first qualitative description of the initial afferent signal processing that takes place in the baroreflexes. In order to quantify the encoding of two particular arterial pressure variables, mean arterial pressure (P) and its rate of change (dP/dt), a special preparation was developed that allowed for direct control of the baroreceptor stimulus at one specific location, the carotid sinus ipsilateral to the recording site in the NTS. Using this method, the encoding of these variables was shown to be non-linear, a result that is in qualitative agreement with the previous study using naturalistic stimulation. Together, these results indicate that second order neurons receiving myelinated baroreceptor inputs are capable of providing the direction and magnitude of dP/dt, but are unlikely to provide a reliable encoding of P. This result implies that the CNS uses the myelinated afferent input for dynamic rather than steady-state blood pressure control. More importantly, this work may force a different view on the processing of the baroreceptor signal, namely that the CNS extracts and separates different pieces of information provided within it and employs them for different functions.
Subject Area
Neurosciences|Physiology
Recommended Citation
Rogers, Robert Francis, "Arterial baroreceptor signal processing in the nucleus tractus solitarius" (1995). Dissertations available from ProQuest. AAI9543138.
https://repository.upenn.edu/dissertations/AAI9543138