This investigator is engaged in a long term effort to define the neurophysiological mechanisms and anatomical interconnections of central neurons subserving cardiovascular reflex control. The present studies will focus on both afferent and efferent limbs of the vagal innervation of the heart. Initial studies of afferent projections will use horseradish peroxidase (HRP) techniques to determine the general locations of cardiac vagal afferent cell bodies in the nodose gnaglion and to define the regions of the nucleus tractus solitarius (NTS) in which their central projections terminate. In subsequent electrophysiological studies, single unit recordings from the cell bodies of cardiac vagal afferents will be obtained, and antidromic central stimulation will be used to determine whether specific fiber types terminate on different cell populations in NTS. In addition, the hypothesis of a presynaptic interaction between afferent inputs to NTS neurons will be tested by observing the effect of electrically stimulating other peripheral cardiovascular afferent nerves (e.g., aortic or carotid sinus) on the threshold for antidromic activation of the central endings of single vagal afferent neurons. Studies of efferent vagal mechanisms will evaluate the significance of the recent observation that vagal neurons controlling heart rate reside in two specific brain stem areas--the nucleus ambiguus (NA) and the dorsal motor nucleus (DMN). The hypothesis that these neurons selectively process afferent input from different receptor groups will be tested by recording from units in each area during manipulation of afferent input from selected cardiovascular receptors. Emphasis in these studies will be on the manner in which neurons in both nuclei process physiologic input from carotid sinus and left ventricular baroreceptors alone and in combination. Intracellular iontophoresis of HRP will be used to fill the dendritic trees of some of these cells to determine the extent of their anatomical connections with other brain stem regions involved in cardiovascular reflexes. These studies will provide new insight into central mechanisms influencing vagal control of heart rate in normal animals.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL029302-03
Application #
3340412
Study Section
Cardiovascular Study Section (CVA)
Project Start
1984-03-01
Project End
1987-11-30
Budget Start
1986-03-01
Budget End
1987-11-30
Support Year
3
Fiscal Year
1986
Total Cost
Indirect Cost
Name
University of Iowa
Department
Type
Schools of Medicine
DUNS #
041294109
City
Iowa City
State
IA
Country
United States
Zip Code
52242
Hayward, Linda F; Riley, Alecia P; Felder, Robert B (2002) alpha(2)-Adrenergic receptors in NTS facilitate baroreflex function in adult spontaneously hypertensive rats. Am J Physiol Heart Circ Physiol 282:H2336-45
Hayward, L F; Johnson, A K; Felder, R B (1999) Arterial chemoreflex in conscious normotensive and hypertensive adult rats. Am J Physiol 276:H1215-22
Sundaram, K; Johnson, S M; Felder, R B (1997) Altered expression of delayed excitation in medial NTS neurons of spontaneously hypertensive rats. Neurosci Lett 225:205-9
Hegarty, A A; Felder, R B (1997) Vasopressin and V1-receptor antagonists modulate the activity of NTS neurons receiving baroreceptor input. Am J Physiol 273:R143-52
Ma, S; Abboud, F M; Felder, R B (1995) Effects of L-arginine-derived nitric oxide synthesis on neuronal activity in nucleus tractus solitarius. Am J Physiol 268:R487-91
Hegarty, A A; Hayward, L F; Felder, R B (1995) Sympathetic responses to stimulation of area postrema in decerebrate and anesthetized rats. Am J Physiol 268:H1086-95
Hayward, L F; Felder, R B (1995) Cardiac rhythmicity among NTS neurons and its relationship to sympathetic outflow in rabbits. Am J Physiol 269:H923-33
Hayward, L; Hay, M; Felder, R B (1993) Acute resetting of the carotid sinus baroreflex by aortic depressor nerve stimulation. Am J Physiol 264:H1215-22
Hajduczok, G; Hade, J S; Mark, A L et al. (1991) Central command increases sympathetic nerve activity during spontaneous locomotion in cats. Circ Res 69:66-75
Felder, R B; Mifflin, S W (1988) Modulation of carotid sinus afferent input to nucleus tractus solitarius by parabrachial nucleus stimulation. Circ Res 63:35-49

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