Parabrachial Neurons Research Articles

Stimulation of parabrachial neurons elicits a sympathetically mediated pressor response in cats.

We examined the role of the parabrachial neuronal mass in mediating the pressor response to electrical stimulation of parabrachial nucleus (PBN). In anesthetized cats, 100 mM L-glutamate (L-glu) was microinjected into PBN at sites from which low-intensity (25 microA) electrical stimulation evoked a pressor response. Arterial pressure, heart rate, and, in some animals, renal or phrenic nerve activity were monitored. Microinjection of L-glu caused an increase in arterial pressure that was comparable with that elicited by low-intensity electrical stimulation. Electrical stimulation, and to a lesser extent L-glu microinjection, caused an increase in renal sympathetic nerve activity but no significant change in heart rate. No consistent change in central respiratory drive accompanied the pressor response. These responses were preserved after baroreceptor denervation but were blocked by intravenous administration of the alpha-adrenergic receptor antagonist phentolamine. Microinjection into PBN of 2 mM kainic acid, which selectively depolarizes neurons but spares axons, reversibly blocked the arterial pressure and renal nerve responses to the 25-microA electrical stimulus. We conclude that the pressor response elicited by electrical stimulation of PBN in the anesthetized cat is mediated by cellular elements in PBN, not by fibers of passage. Because phentolamine completely blocked the pressor response, we suggest that it is subserved peripherally by sympathetic alpha-adrenergic rather than humoral (e.g., angiotensin, vasopressin) vasoconstrictor mechanisms. Finally, our data indirectly suggest that PBN stimulation may differentially engage efferent components of the sympathetic nervous system to elicit the pressor response.

Long dendrites of the parabrachial nucleus neurons projecting to the amygdala: A horseradish peroxidase and Golgi study in the cat

The parabrachial nucleus neurons were demonstrated to have long dendrites extending into the brachium conjunctivum after horseradish peroxidase was injected into the amygdala. This morphologic characteristic was confirmed using the Golgi impregnation technique.

Interactions between the basal ganglia, the pontine parabrachial region, and the trigeminal system in cat

Anatomical studies utilizing wheat germ lectin-bound horseradish peroxidase demonstrated direct connections between the pontine parabrachial region and the substantia nigra pars reticulata and to a lesser extent, the entopeduncular nucleus as well as a number of other forebrain regions including the amygdala, hypothalamus, thalamus, bed nucleus stria terminalis and substantia innominata. The pontine parabrachial region was also shown to receive direct inputs from the spinal trigeminal system and to send axons to areas surrounding trigeminal and hypoglossal motor areas. Once the anatomical connections were determined, electrophysiological studies were undertaken to investigate some of the functional aspects of these connections between the pontine parabrachial, basal ganglia and trigeminal systems. Extracellular single unit recordings were obtained from 228 cells in the dorsal pontine parabrachial region of the cat. These cells were tested for responsiveness to trigeminal sensory stimulation and activation of basal ganglia outputs (i.e. substantia nigra and entopeduncular nucleus). Twenty-two percent of pontine parabrachial cells responded to only trigeminal stimulation; 4% responded to entopeduncular nucleus only; 37% responded to substantia nigra only, and 28% responded to both substantia nigra and trigeminal stimulation. Furthermore, 43% of pontine parabrachial cells with both substantia nigra and sensory response had the sensory response altered by a preceding stimulus to the substantia nigra. Thus, the substantia nigra is shown to exert influences on both the spontaneous activities and afferent responses of pontine parabrachial neurons. The significance of these findings are discussed in relation to the importance of descending basal ganglia influences and ascending influences from the pontine parabrachial region on various sensorimotor activities.

Perseverative effects of parabrachial lesions: A mechanism of reduced activation?

The acquisition of a spatial reversal task and two reversals of it and the acquisition of an active two-way avoidance task were tested in three groups of male Sprague-Dawley rats: two experimental and one control group. The experimental group received chemical lesions of the parabrachial nuclei (group NPB) or of the dorsal hippocampus (group HC), using ibotenic acid. (Ibotenic acid is a compound which, contrary to kainic acid, fails to produce distant lesions, but, in conformity with kainic acid, spares the majority if not all fibers of passage.) The control group (group CG) received injections of the vehicle solution only. Animals of group NPB, in comparison to those of the other two groups, acquired the reversal task more quickly, but in the acquisition of its two reversals they needed considerably more time and made more perseverative errors. Likewise, only group NPB was significantly impaired in the acquisition of the avoidance task. From these results and from available evidence on connections of the parabrachial neurons with regions specifically involved in variables of the tested tasks (such as the prefrontal cortex), it is concluded that the parabrachial region exerts an activating influence on forebrain areas.

Widespread cortical projections of the ventral tegmental area and of other brain stem structures in the cat.

Thirty-three cat brains with injections of horseradish peroxidase in various regions of the cerebral cortex were screened for afferent projections from the ventral tegmental area, the locus ceruleus, and the parabrachial nuclei. All three structures were found to project to rather divergent parts of the cortex, including regions in the posterior half of the hemisphere. These results, especially for the ventral tegmental area and, to a lesser degree, for the parabrachial neurons, disagree with most of the target loci of established cortical afferents in the rat. Though our results might be attributed to species differences in the cortical innervation of brain stem structures, we prefer explanations which emphasize different densities in the distribution of brain stem afferents to the cortex, and/or which suggest different cortical targets of catecholaminergic and noncatecholaminergic neurons.

Convergence of sensory input from tooth pulp, optic chiasm and sciatic nerve onto locus coeruleus neurons in the rat

Electrophysiological studies using rats were performed to determine whether or not neurons in the locus coeruleus (LC), subcoeruleus and parabrachial areas receive convergence of sensory input from tooth pulp (TP), optic chiasm (OC) and sciatic nerve (SN). Convergence of input from these nerves was observed in 23% and 33% of LC and subcoeruleus neurons, respectively, and from two nerves in 31% and 20% of LC and subcoeruleus neurons, respectively, while convergence was rarely detected in parabrachial neurons. These results suggest that there is a convergence of peripheral sensory input onto more than half the noradrenergic coerulear neurons.