Parabrachial Area As Mediator Of Bradycardia In Rabbits

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


The purposes of the present study were to examine the role of the parabrachial nucleus (PBN) of the rabbit in the reception of barosensory information and in the mediation of bradycardia. This was accomplished by exploring the parabrachial region using (a) microinjection of horseradish peroxidase (HRP) into PBN as a neuroanatomical tracing procedure, (b) train microstimulation of PBN in conjunction with the recording of heart rate, blood pressure and respiration, and (c) single-pulse micro-stimulation of PBN and barosensory stimulation in conjunction with extracellular recording from single neurons in nucleus tractus solitarius (NTS), and (d) extracellular recording from single neurons in PBN following stimulation of the aortic nerve (AN).Single-pulse electrical stimulation of AN activated neurons in the lateral and medial PBN at a mean latency of 12.1 msec, thereby demonstrating that PBN receives barosensory information at a short latency. Injection of HRP into PBN revealed ascending monosynaptic projections to PBN from regions of NTS previously shown to receive primary barosensory input. Of 9 neurons found to project from this region of NTS to PBN monosynaptically during extracellular neuronal recording, only 1 of these neurons was found to be activated by barosensory stimulation.Train stimulation of medial or lateral PBN produced a large primary bradycardia associated with a small pressor response having a longer latency. Section of the cervical vagus nerves indicated that the bradycardia was mediated primarily by the parasympathetic nervous system. Injection of HRP into PBN revealed descending projections from areas of forebrain previously implicated in the mediation of bradycardia. These included central nucleus of amygdala, lateral preoptic area, medial forebrain bundle, bed nucleus of stria terminalis, anterior hypothalamic area, lateral hypothalamic area and zona incerta. Finally, in response to single-pulse stimulation of PBN, extracellularly recorded neurons were found in dorsal medulla primarily in regions of NTS previously implicated in cardiovascular regulation.The results of the present study indicate that PBN receives barosensory information at a short latency, and suggest that some barosensory projections from NTS to PBN may be monosynaptic. The results also are consistent with the view that PBN is part of a descending pathway involved in the mediation of bradycardia.


Biology, Animal Physiology

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