Subthalamic nucleus modulates burst firing of nigral dopamine neurones via NMDA receptors

International audienceThe role of the subthalamic nucleus in the burst firing of dopamine neurones of the substantia nigra was investigated using extracellular single unit recordings combined with pressure or iontophoretic micro-injections in anaesthetized rats. Inhibition of subthalamic neurones by pressure injection of gamma-aminobutyric acid (GABA) regularized the burst firing pattern in eight out of 17 dopamine neurones. Bicuculline injection near subthalamic neurones increased their firing rate and increased burst discharge in a subpopulation of dopamine neurones tested (34 out of 102). The increase was depressed by iontophoresis of the N-methyl-D-aspartate (NMDA) antagonist (+-)2-amino,5-phosphonopentanoic acid (AP-5), but not of the non-NMDA antagonist, 6-cyano,7-nitroquinoxaline-2,3-dione (CNQX). These data suggest that the subthalamic nucleus promotes burst discharge in a subpopulation of substantia nigra dopamine neurones via NMDA receptors

Activation of Brain Noradrenergic Neurons during Recovery from Halothane Anesthesia

International audiencealpha 2-Adrenoceptor agonists, known as antihypertensive agents, may be used during general anesthesia for their anesthetic sparing action and to reduce the occurrence of side effects. Previous studies have shown that the brain's noradrenergic nucleus, locus coeruleus, is an important target in mediating the hypnotic action of alpha 2 agonists. The authors studied the effects of recovery from halothane anesthesia on the electrical activity of locus coeruleus neurons to examine cellular substrates underlying the clinical effectiveness of alpha 2 agonists

Afferent regulation of locus coeruleus neurons: anatomy, physiology and pharmacology.

International audienceTract-tracing and electrophysiology studies have revealed that major inputs to the nucleus locus coeruleus (LC) are found in two structures, the nucleus paragigantocellularis (PGi) and the perifascicular area of the nucleus prepositus hypoglossi (PrH), both located in the rostral medulla. Minor afferents to LC were found in the dorsal cap of the paraventricular hypothalamus and spinal lamina X. Recent studies have also revealed limited inputs from two areas nearby the LC, the caudal midbrain periaqueductal gray (PAG) and the ventromedial pericoerulear region. The pericoeruleus may provide a local circuit interface to LC neurons. Recent electron microscopic analyses have revealed that LC dendrites extend preferentially into the rostromedial and caudal juxtaependymal pericoerulear regions. These extracoerulear LC dendrites may receive afferents in addition to those projecting to LC proper. However, single-pulse stimulation of inputs to such dendritic regions reveals little or no effect on LC neurons. Double-labeling studies have revealed that a variety of neurotransmitters impinging on LC neurons originate in its two major afferents, PGi and PrH. The LC is innervated by PGi neurons that stain for markers of adrenalin, enkephalin or corticotropin-releasing factor. Within PrH, large proportions of LC-projecting neurons stained for GABA or met-enkephalin. Finally, in contrast to previous conclusions, the dorsal raphe does not provide the robust 5-HT innervation found in the LC. We conclude that 5-HT inputs may derive from local 5-HT neurons in the pericoerulear area. Neuropharmacology experiments revealed that the PGi provides a potent excitatory amino acid (EAA) input to the LC, acting primarily at non-NMDA receptors in the LC. Other studies indicated that this pathway mediates certain sensory responses of LC neurons. NMDA-mediated sensory responses were also revealed during local infusion of magnesium-free solutions. Finally, adrenergic inhibition of LC from PGi could also be detected in nearly every LC neuron tested when the EAA-mediated excitation is first eliminated. In contrast to PGi, the PrH potently and consistently inhibited LC neurons via a GABAergic projection acting at GABAA receptors within LC. Such PrH stimulation also potently attenuated LC sensory responses. Finally, afferents to PGi areas that also contain LC-projecting neurons were identified. Major inputs were primarily autonomic in nature, and included the caudal medullary reticular formation, the parabrachial and Kölliker-Fuse nuclei, the PAG, NTS and certain hypothalamic areas.(ABSTRACT TRUNCATED AT 400 WORDS