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Results for “Efferent Pathways”

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PubMed1979

The central origin of efferent pathways in the carotid sinus nerve of the cat.

The application of horseradish peroxidase to the central cut end of the carotid sinus nerve of the cat produced retrograde labeling of neurons in the ipsilateral medulla in the region of the nucleus ambiguus at anterior-posterior coordinates -8 to -10.5. These data coupled with previous electrophysiological observations suggest that the nucleus ambiguus may be the origin of an efferent inhibitory pathway to the carotid body.

Animals↗
PubMedDate not supplied

Metabolic and feeding patterns: role of sympathetic and parasympathetic efferent pathways.

The continuous transfer of fuel from the blood to tissues, and its adjustment to the rate of energy metabolism involve close relationships between the control of endogenous stores and that of the periodic intake of food. Neural and blood-borne signals to the brain and efferent sympathetic and parasympathetic pathways seem responsible for three different metabolic and feeding cycles. The matching of input and output of glucose to and from the blood, i.e. the regulation of the blood glucose level proper, is achieved by a short-term feedback mechanism which involves the action of insulin and glucagon on hepatic glucose production and peripheral glucose utilization. Oscillations in level of blood glucose, plasma insulin and glucagon in 8-11 min cycles, as observed in certain species, presumably reflect the play of this short-term regulation of the blood glucose level. The respective role of a pancreatic feedback and of a neural loop in this short-term regulation is discussed. Signals to brain targets and efferent pathways determine the periodic onset of meals after the energy ingested in the preceding meal has been exhausted in free-fed and briefly deprived rats. New evidence has been provided that the fall in blood glucose level exerts a decisive and direct action on the brain to determine meal onset and/or meal size. Superimposed on this prandial periodicity, a lipostatic mechanism modulates the feeding pattern in a dark-light periodicity by the alternation of fat synthesis and fat mobilization. The effects of VMH lesions and vagotomy, either combined or separately, on daily metabolic and feeding patterns suggest that the neural input to the pancreas and adipose tissues plays a primary role in this endogenous cycle and is also involved in the regulation of a constant fat body mass.

Animals↗
PubMed1981

Role of globus pallidus and substantia nigra efferent pathways in striatally evoked head turning in the rat.

These studies have examined the role of brain areas that receive efferent projections from the globus pallidus (GP) and substantia nigra (SN) in producing the contralateral head turning evoked by unilateral electrical stimulation of the neostriatum in the conscious rat. Two parameters were studied: the latency for a 90 degree head turn and changes in the normal latency evoked by administration of the GABA drugs picrotoxin and muscimol in GP. Electrolesions in the ipsilateral ventromedial and centromedian thalamic nuclei had no effect on the head turn parameters. Although small electrolesions in the SN slowed, but did not abolish the head turn, it prevented the changes in the response latency brought about by GABA drugs in GP. Treatment with 6-hydroxydopamine, which partly destroyed the nigro-striatal dopamine neurones, had no effect on the head turn. Areas of the brainstem that receive basal ganglia efferents were lesioned. An electrolesion of the nucleus tegmenti pedunculopontinus had no effect on the head turn latencies. The head turning was abolished by a lesion in the lateral periaqueductal grey (PAG); a more rostral PAG lesion, on the same level as SN, was ineffective. It is concluded that the head turning is mediated by basal ganglia efferents which pass close to the nigra without synapsing and project to the PAG. The GABA-sensitive GP efferents which modulate the response, probably project to SN.

Animals↗
PubMed1993

Specific enhancement by fentanyl of the effects of intrathecal bupivacaine on nociceptive afferent but not on sympathetic efferent pathways in dogs.

BACKGROUND: Bupivacaine alone, or in combination with opioids, has been shown to provide adequate pain relief without motor paralysis. This study examined the effects of bupivacaine administered intrathecally on sympathetic efferent and A delta- and C-fiber-mediated afferent pathways in dogs and the interactions with intrathecal fentanyl. METHODS: Spontaneous activity in renal sympathetic nerves was observed, as were reflex somatosympathetic responses mediated by A delta and C fibers evoked by supramaximal electrical stimulation of the tibial and radial nerve. Bupivacaine was administered intrathecally in doses of 0.5, 1, 2, and 3.5 mg, each in 0.5 ml, and 7 mg in 1 ml with or without pretreatment with 5.4 mg intrathecal fentanyl (ED25 for depression of C tibial reflexes) in each of five preparations. RESULTS: Bupivacaine caused a dose-dependent inhibition of both A delta- and C-fiber-mediated somatosympathetic responses evoked by tibial nerve stimulation. The depression of radial and tibial nerve reflexes and spontaneous renal sympathetic activity was similar. Pretreatment with fentanyl (5.4 micrograms, intrathecally) depressed tibial C-fiber reflexes by only 23.8% without any significant effect on either tibial A delta or radial A delta and C fiber responses. Fentanyl markedly enhanced the effect of subsequent doses of bupivacaine on tibial A delta and C reflexes without any additional effect on either spontaneous sympathetic activity or radial responses. CONCLUSIONS: Intrathecal bupivacaine has no selectivity for the afferent and efferent pathways, and intrathecal fentanyl acts synergistically to enhance the effect of bupivacaine on the afferent pathway without a measurable effect on sympathetic outflow.

Adrenergic Fibers↗