RESUMEN
Dorsal medullary brain slices containing primarily the nucleus tractus solitarius (NTS) were obtained from normal or 40- to 50-day streptozotocin-diabetic rats and employed for superfusion studies of evoked transmitter release. Electrically stimulated (25 mA, 2-ms pulses, 3 Hz, 1 min) release of [3H]norepinephrine ([3H]NE) or [3H]5-hydroxytryptamine ([3H]5-HT) from 400-microns NTS slices stimulated at 75 min (S1) and 130 min (S2) resulted in S2/S1 release ratios that were not different between normal controls or diabetic control groups. Perfusion of normal [3H]NE-loaded slices with 0.1 mumol/l clonidine reduced the S2/S1 ratio by 23% (p < 0.05) which was uniform in the caudal, subpostremal, and intermediate segment levels of the NTS. In diabetic NTS slices, the S2/S1 ratio was significantly less reduced by clonidine in both the subpostremal (-3%) and intermediate (-11%) slice regions. Blockade of alpha 2-adrenoceptors with yohimbine (0.1 mumol/l) enhanced (p < 0.05) [3H]NE release (S2/S1 ratios) in slices from both normal and diabetic rats. Perfusion of [3H]NE-loaded slices with 5 mU/ml insulin did not affect S2 release. Evoked S2/S1 release ratios from NTS slices loaded with [3H]5-HT did not differ between normal control and diabetic control groups. Clonidine (0.1 mumol/l) reduced S2-evoked release in both normal (-30%) and diabetic (-44%) slices, but the groups were not different from each other. Superfusion with 5 mU/ml insulin did not alter S2/S1 ratios in normal [3H]5-HT loaded slices, but did increase the diabetic NTS slice S2/S1 ratio to 1.40 +/- 0.06 (p < 0.01). In summary, it appears that alpha 2-adrenoceptor-mediated inhibition of [3H]NE release in the NTS was selectively attenuated in a regionally specific manner in diabetic animals. Release inhibition may be associated with receptor downregulation in NTS regions associated with cardiovascular reflex transmission. Insulin superfusion augmented [3H]5-HT release in the diabetic NTS slices, possibly through increased transmitter synthesis or improved synaptic release.
Asunto(s)
Agonistas alfa-Adrenérgicos/farmacología , Clonidina/farmacología , Diabetes Mellitus Experimental/metabolismo , Insulina/farmacología , Núcleo Solitario/efectos de los fármacos , Animales , Diabetes Mellitus Experimental/fisiopatología , Modelos Animales de Enfermedad , Regulación hacia Abajo , Estimulación Eléctrica , Masculino , Norepinefrina/metabolismo , Ratas , Ratas Wistar , Serotonina/metabolismo , Núcleo Solitario/metabolismo , Estreptozocina/administración & dosificación , Estreptozocina/toxicidadRESUMEN
Rat medullary brain segments containing primarily nucleus tractus solitarius (NTS) were used for superfusion studies of evoked transmitter release and for isotherm receptor binding assays. Isotherm binding assays with [3H]CGS-21680 on membranes prepared from NTS tissue blocks indicated a single high-affinity binding site with a KD of 5.1 +/- 1.4 nM and a Bmax of 20.6 +/- 2.4 fmol/mg of protein. The binding density for [3H]CGS-21680 on NTS membranes was 23 times less than comparable binding on membranes from striatal tissue. Electrically stimulated (1 min at 25 mA, 2 ms, 3 Hz) release of [3H]norepinephrine ([3H]NE) from 400-microns-thick NTS tissue slices resulted in an S2/S1 ratio of 0.96 +/- 0.02. Superfusion of single tissue slices with 0.1-100 nM CGS-21680, a selective adenosine A2a receptor agonist, for 5 min before the S2 stimulus produced a significant concentration-dependent increase in the S2/S1 fractional release ratio that was maximal (31.3% increase) at 1.0 nM. However, superfusion of tissue slices with CGS-21680 over the same concentration range for 20 min before the S2 stimulus did not alter the S2/S1 ratio significantly from control release ratios. The augmented release of [3H]NE mediated by 1.0 nM CGS-21680 with a 5-min tissue exposure was abolished by 1.0 and 10 nM CGS-15943 as well as by 100 nM 8-(3-chlorostyryl)caffeine, both A2a receptor antagonists, but not by 1.0 nM 8-cyclopentyl-1,3-dipropylxanthine, the A1 receptor antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Bulbo Raquídeo/metabolismo , Norepinefrina/metabolismo , Terminales Presinápticos/metabolismo , Receptores Purinérgicos P1/metabolismo , Adenosina/análogos & derivados , Adenosina/farmacología , Animales , Técnicas In Vitro , Masculino , Fenetilaminas/farmacología , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
Rat brain slices from the dorsomedial medulla containing the nucleus tractus solitarius were loaded with [3H]norepinephrine ([3H]NE) for superfusion. Electrical stimulation (3 Hz, 25 mA, 1 min) resulted in fractional release ratios S2/S1 of 0.97 +/- 0.02 in normal Krebs-Henseleit (KH) and 0.93 +/- 0.06 in the presence of 30 microM cocaine. With cocaine in the KH medium, L-alpha-methylnorepinephrine (alpha-MeNE) significantly reduced the [3H]NE release S2/S1 without affecting the basal release ratios. Without cocaine in the KH medium both 0.1 and 1.0 microM alpha-MeNE increased the basal release B2/B1 that was not affected by yohimbine. Prazosin had no effect on the S2/S1 ratio but did attenuate the basal release effects of alpha-MeNE. In low Ca2+ studies where the S2 stimulus was abolished, 1.0 microM alpha-MeNE induced a sharply elevated increase in the B2/B1 ratio. It appears that alpha-MeNE in the presence of the uptake inhibitors reduces presynaptic neurotransmitter release through alpha 2-adrenoceptors, whereas when uptake of the monoamines was not blocked alpha-MeNE was considerably more efficacious as a displacing agent of neurotransmitter.
Asunto(s)
Nordefrin/metabolismo , Norepinefrina/metabolismo , Núcleo Solitario/metabolismo , Animales , Calcio/metabolismo , Cocaína/farmacología , Masculino , Ratas , Núcleo Solitario/efectos de los fármacos , Tiramina/farmacología , Yohimbina/farmacologíaRESUMEN
Several studies have suggested that oxygen-derived free radicals play an important role in the genesis of ischaemia-induced neuronal damage. We report here that the spin trap agent, N-tert.-butyl-alpha-phenylnitrone (PBN) reduced neuronal damage in gerbils subjected to forebrain ischaemia. PBN (100 mg/kg) administered either 30 min. prior to, or 30 min. after a 5 min. period of bilateral carotid occlusion prevented the increase in locomotor activity observed in saline-injected ischaemic animals and significantly reduced the damage to the hippocampal CAI pyramidal cell layer observed 5 days post-ischaemia. Telemetry measurements of body temperature revealed that administration of PBN and the induction of cerebral ischaemia were associated with small reductions in body temperature, but these changes were not significant. PBN (100 mg/kg) administered 2 hr post-ischaemia failed to protect against cerebral ischaemia. These findings support the hypothesis of an involvement of free radicals in ischaemia-reperfusion induced cerebral damage and suggest that spin trap agents may be useful for the prevention of cerebral ischaemic damage.
Asunto(s)
Isquemia Encefálica/tratamiento farmacológico , Óxidos de Nitrógeno/administración & dosificación , Daño por Reperfusión/prevención & control , Animales , Óxidos N-Cíclicos , Radicales Libres , Gerbillinae , Actividad Motora/efectos de los fármacos , Marcadores de Spin , TemperaturaRESUMEN
N-Tert-butyl-alpha-phenylnitrone (PBN), a spin trap agent, reduced ischemic hippocampal damage and the associated locomotor hyperactivity in Mongolian gerbils. Cerebral ischemia was induced in unanesthetized gerbils by a bilateral 5 min occlusion of the carotid arteries. PBN (100 mg/kg, i.p.) administered 30 min prior to carotid occlusion, prevented the increase in locomotor activity observed in saline-injected ischemic animals and significantly reduced damage to the hippocampal CAI pyramidal cell layer observed 5 days post-ischemia. These findings support the hypothesis of an involvement of reactive free radicals as a significant cause of ischemia-reperfusion-induced cerebral injury and suggest that PBN may be a useful agent for the prevention of cerebral ischemic damage.
Asunto(s)
Isquemia Encefálica/prevención & control , Óxidos de Nitrógeno/farmacología , Daño por Reperfusión/prevención & control , Animales , Isquemia Encefálica/patología , Óxidos N-Cíclicos , Gerbillinae , Hipocampo/patología , Masculino , Actividad Motora/efectos de los fármacos , Daño por Reperfusión/patología , Marcadores de SpinRESUMEN
Cerebral ischemic damage in gerbils was assessed by locomotor activity studies and histopathological examination of the hippocampal CA1 pyramidal cell layer. Pretreatment with AICAr (50 and 500 mg/kg) 30 min prior to a 5-min ischemic episode in unanesthetized gerbils, significantly attenuated the degree of ischemic neuronal damage as measured by either technique with the 500 mg/kg dose; the 50 mg/kg dose, although showing a trend, was not significant. A potential mechanism for AICAr-induced cerebroprotection may be that it is metabolized to uric acid, a free radical scavenger.