Functional and anatomical organization of cardiovascular pressor and depressor sites in the lateral hypothalamic area: I. descending projections

Abstract

The present study describes the anatomical organization of projections from functionally defined cell groups of the lateral hypothalamic area. Cardiovascular pressor and depressor sites were identified following microinjection (5-50 nl) of 0.01-1.0 M L-glutamate or D,L-homocysteate into the anesthetized rat. Subsequent injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) or wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were made into pressor or depressor sites and their connections with the brainstem and spinal cord were traced. Decreases in blood pressure (10-45 mmHg) and heart rate (20-70 bpm) were elicited from tuberal (LHAt) and posterior (LHAp) regions of the lateral hypothalamic area (LHA). Depressor neurons in the LHAt have descending projections to the central gray, dorsal and median raphe nuclei, pedunculopontine tegmental nucleus, pontine reticular formation, medial and lateral parabrachial nuclei, laterodorsal tegmental region, and medullary reticular formation including the region of the lateral tegmental field, nucleus ambigous, and rostrocaudal ventral lateral medulla. In contrast, descending projections from depressor neurons in the LHAp have dense terminal fields in the rostral, middle, and commissural portions of the nucleus of the solitary tract and the lateral tegmental field as well as the ventrolateral central gray, pedunculopontine tegmental nucleus, and medial and lateral parabrachial nuclei. Both the LHAt and LHAp have light projections to the intermediate region of the cervical and thoracic spinal cord. Increases in blood pressure (10-40 mmHg) and heart rate (20-70 bpm) were elicited almost exclusively from neurons located medial to the LHAt and LHAp in a region surrounding the fornix, termed the perifornical area (PFA). Pressor cells in the PFA have descending projections to the central gray, dorsal and median raphe nuclei, laterodorsal tegmental nucleus, and Barrington's nucleus as well as a light projection to the commissural portion of the nucleus of the solitary tract and the intermediate region of the cervical and thoracic spinal cord. The retrograde labeling observed in the WGA-HRP studies indicates that cells in most terminal fields have reciprocal projections to the pressor and depressor regions of the LHA. The results demonstrate that groups of neurons in the lateral hypothalamus with specific cardiovascular function have differential projections to the brain stem.

Divergent projections of catecholaminergic neurons in the nucleus of the solitary tract to limbic forebrain and medullary autonomic brain regions

“…The NTS has long been known to be involved in autonomic functions (Ross et al, 1981;Sessle and Henry, 1985;Altschuler et al, 1989;Allen and Cechetto, 1992;Ciriello et al, 1994). Neurons in the NTS serve as the principal relay of afferent inputs from various information including baroreceptor, chemoreceptor, cardiopulmonary, cardiovascular and visceral afferents (Palkovits and Zaborszky, 1977;Hancock, 1988;Ciriello et al, 1994;Grigson et al, 1997b;Shimura et al, 1997).…”

“…The nucleus of the solitary tract (NTS), located in the dorsomedial medulla, is a critical structure involved in many autonomic functions including cardiovascular-and respiratory-related activities (Ross et al, 1981;Sessle and Henry, 1985;Allen and Cechetto, 1992). Afferent synaptic input to the NTS arises from primary afferent fibers that innervate the tongue (Hamilton and Norgren, 1984) and visceral fibers of the glossopharyngeal and vagus nerves that serve various modalities including baroreceptor and chemoreceptor functions (Altschuler et al, 1989;Ciriello et al, 1994).…”

Interaction of medullary P2 and glutamate receptors mediates the vasodilation in the hindlimb of rat

“…Thirdly, HDA stimulation elicits rapid adenosine release in the NTS derived from extracellular ATP [20], presumably eliciting a β-adrenergic iliac vasodilation that is overridden by a vasopressinergic vasoconstriction [41,42]. Nonetheless, subunits of P2 receptors are expressed in NTS neurons of rat [14,15]; and the reductions in HVC responses seen here can be explained by blockade of input signals from the HDA to the NTS [7,8], independent of the pathways in control of AP and HR increases. averaged curve after combined blockade; in light gray, standard error of the mean.…”

“…Previous anatomical studies [7,8] showed bilateral projections, predominantly ipsilateral, from the perifornical hypothalamus to the NTS and ventrolateral medulla.…”

“…The increase in vascular conductance is mediated by withdrawal of sympathetic tone and release of epinephrine by the adrenal medulla [5,6]. Identified projections from HDA neurons to the rostral ventrolateral medulla (RVLM) and nucleus tractus solitarius (NTS) suggest that cardiovascular responses elicited by hypothalamic stimulation are mediated in the medulla [7][8][9]. Stimulation of the HDA produces excitatory post-synaptic potentials in neurons at the intermediate NTS of cat [10,11]; suggesting that the resulting rise in peripheral HVC can derive from activation of sympathoinhibitory pathways involved in the baroreflex.…”