RESUMEN
RATIONALE AND OBJECTIVES: The ability to create short boluses in targeted arteries with rapid rise times is limited by the transport of bubbles from the venous to arterial portion of the circulation. Acoustic interruption of contrast agent in arteries may create the short boluses necessary for simple wash-in/wash-out measures of blood flow. METHODS: An ultrasound contrast agent was used with spectral Doppler ultrasound to observe contrast interruption in femoral arteries and VX2 carcinoma in a rabbit model. At an upstream location in the femoral artery, single, sinusoidal ultrasound tone bursts at 1.8 MHz with durations of 0.25 to 1 seconds were applied to interrupt the flow of contrast agent injected intravenously. RESULTS: In VX2 carcinoma, bursts as short as 40 cycles produced contrast interruption lasting only one cardiac cycle within the tumor periphery and I(SPPA) <3 W/cm2 produced measurable interruptions. CONCLUSIONS: Acoustic fields applied transcutaneously interrupted flow of contrast agents to form temporally short negative boluses.
Asunto(s)
Medios de Contraste , Arteria Femoral/diagnóstico por imagen , Fluorocarburos , Ultrasonografía Doppler en Color/métodos , Animales , Carcinoma/diagnóstico por imagen , Medios de Contraste/administración & dosificación , Portadores de Fármacos , Femenino , Arteria Femoral/fisiología , Fluorocarburos/administración & dosificación , Infusiones Intravenosas , Liposomas , Neoplasias Experimentales/diagnóstico por imagen , Conejos , Flujo Sanguíneo Regional , Programas Informáticos , Muslo , Factores de Tiempo , Ultrasonografía Doppler en Color/instrumentación , Ultrasonografía Doppler en Color/estadística & datos numéricosRESUMEN
Descending projections were studied in autoradiographically prepared material after injections of tritiated leucine in the pontine tegmentum of rats. Injections involving the medial pontine reticular formation resulted not only in labeling commissural fibers, the medial reticulospinal tract, and the dorsal cap of the inferior olive, but also, in two cases, in labeling a cerebellar projection that originated from a region near the midline and clearly dorsal to the nucleus reticularis tegmenti pontis. The labeled fibers passed ventral in the midline to the pontine gray, then laterally through the gray and into the middle cerebellar peduncle to terminate as mossy fibers primarily in the flocculus, lobulus simplex, and Crus I of the ansiform lobule. Injections involving the mesencephalic nucleus of the trigeminal nerve (Vmes), resulted in labeling of Probst's tract, which descends in the dorsolateral reticular formation. Probst's tract gave off extensive terminal branches to the lateral medullary reticular formation and weaker projections to restricted portions of the descending trigeminal nucleus, the solitary nucleus, and the hypoglossal nucleus. In one case, fibers could be traced into the dorsal horn of the upper cervical cord.
Asunto(s)
Mesencéfalo/anatomía & histología , Puente/anatomía & histología , Formación Reticular/anatomía & histología , Núcleos del Trigémino/anatomía & histología , Nervio Abducens/anatomía & histología , Animales , Cerebelo/anatomía & histología , Masculino , Vías Nerviosas/anatomía & histología , Núcleo Olivar/anatomía & histología , Ratas , Ratas Endogámicas , Médula Espinal/anatomía & histología , Núcleos Vestibulares/anatomía & histologíaRESUMEN
Two-second cathodal current pulses were applied at one-minute intervals at a point external to the round window in the ear of each albino rat subject. Responses were recorded in the vestibular nerve ganglion, the vestibular nuclei (single units), or in the eye movements (search coil recording method) of anaesthetized, decerebrated, or alert rats. The unit responses to the galvanic stimuli were characterized and compared with responses to galvanic and rotational stimuli reported in the literature. The main focus of the study, however, was effects of stimulus repetition. In both the vestibular nerve and vestibular nuclei recordings, the responses of many units were substantially larger or smaller at the end of a 13-pulse stimulus train than at the beginning. In the vestibular nuclei, but not in the nerve, there was a slight bias towards a decrease in response magnitude, with 10/88 units showing decreases great enough to be considered as reflecting an habituation process. In contrast, the eye movement responses showed more consistent response decrements, especially in the alert condition, but also in the other conditions (none of the unit recordings were done in alert rats). It is concluded that some of the modifications underlying habituation of the vestibuloocular reflex probably occur in portions of the neuronal reflex pathways that are downstream from the vestibular nuclei.
Asunto(s)
Oído Interno/fisiología , Movimientos Oculares , Nervio Vestibular/fisiología , Núcleos Vestibulares/fisiología , Animales , Estimulación Eléctrica , Ratas , Nervio Vestibular/citología , Núcleos Vestibulares/citologíaRESUMEN
A cataleptic animal clings in a vertical position, unmoving, for abnormally long periods by supporting some of its weight on its hindlegs, grasping with the forepaws, flexing its forelimbs, and holding the head horizontal. When the head is snugly wrapped with a bandage, the head slowly falls backward, the neck hyperextends, the forelimbs extend and the grasp is released, resulting in the animal falling backward to the ground. It was earlier suggested that in cataleptic animals, the bandage inhibits vestibular and kinesthetic mechanisms of head support, yielding the backfall sequence [35]. However, preliminary experiments showed that labyrinthectomized rats made cataleptic by haloperidol fall backwards when placed in a vertical clinging position, even without a bandage, suggesting that in the rat the bandage-backfall reaction depends only on the vestibular system. In the present paper, this result is verified but, by additional experiments, the latter conclusion is shown to be incorrect. In labyrinthectomized rats made cataleptic by other means (lateral hypothalamic damage, or bulbocapnine), backfall from clinging did not occur unless a bandage was applied. Therefore, the bandage does indeed appear to inhibit the kinesthetic mechanisms that maintain head support in labyrinthectomized cataleptic rats. Haloperidol, particularly in high doses, greatly weakens postural support in labyrinthectomized rats (causing the animal to sag down and fall back when clinging), although the effect is not detectable in rats with labyrinths intact. However, labyrinthectomy reveals that the bandage can trigger an active dorsiflexion of the neck which in itself appears to inhibit clinging and righting. Bandage-induced dorsiflexion is present to a much lesser degree in intact animals, indicating that labyrinthine mechanisms inhibit the dorsiflexion reflex. Therefore, in the intact, cataleptic rat the bandage backfall reaction appears to be produced by the combined effects of a passive component (inhibition of kinesthetic support mechanisms), and an active component (elicitation of dorsiflexion of the neck).
Asunto(s)
Catalepsia/fisiopatología , Oído Interno/fisiopatología , Cinestesia/fisiología , Músculos/fisiopatología , Músculos del Cuello/fisiopatología , Animales , Aporfinas/farmacología , Catalepsia/inducido químicamente , Haloperidol/farmacología , Masculino , Pimozida/farmacología , Postura , Ratas , Reflejo/fisiología , Nervio Trigémino/fisiopatologíaRESUMEN
Electrolytic lesions were produced in the pontine reticular formation (PRF) of adult hooded rats. Unilateral lesions abolished quick phases of optokinetic head nystagmus to the side of the lesion. Some lesions also had temporary effects on slow phases of optokinetic head nystagmus. Effects of bilateral lesions were similar, except that they affected head movements in both directions. A class of "fast" head movements abolished by PRF lesions thus emerges that is analogous to the class of rapid eye movements abolished by similar lesions in other species, a finding that can be related to the coupling which has been observed between "fast" head and eye movements.
Asunto(s)
Nistagmo Fisiológico , Formación Reticular/fisiopatología , Animales , Encéfalo/anatomía & histología , Electronistagmografía , Cabeza/fisiología , Puente/fisiología , Ratas , Ratas Endogámicas , Tiempo de Reacción/fisiologíaRESUMEN
Ocular responses to optokinetic stimulation were reexamined in adult albino rats of two different strains. Eye movements were measured in head-restrained animals using the search coil method. In contrast to some previous results, the albino rats showed optokinetic nystagmus, and some of them made responses comparable to those previously recorded from pigmented rats. However, the type of stimulus pattern used to elicit optokinetic nystagmus proved to be crucial for albino rats. The deficit is attributed to abnormalities in the albino rat's visual sensory apparatus. Inverted optokinetic nystagmus was elicited in albino rats by restricting the optokinetic stimulation to the anterior visual field of both eyes. The same phenomenon has been observed previously in albino rabbits and mice, and has been suggested to be due to the abnormally small number of uncrossed optic nerve fibers in albinos.
Asunto(s)
Nistagmo Fisiológico , Albinismo/fisiopatología , Animales , Ratas , Ratas Endogámicas , Especificidad de la EspecieRESUMEN
The behavioral effects of vestibular endorgan lesions were compared with those of vestibular ganglion lesions in the albino rat. No differences in head tilt angle or spontaneous eye nystagmus beat frequency were noted between the two groups during the first 36 h after the lesion was made. Of rats studied beyond 36 h, 2/7 with lesions restricted to the endorgans and 2/3 with ganglion lesions showed pronounced secondary increases in head tilt and tonic eye deviation, but not eye nystagmus. Single units were recorded in the ganglion acutely, as well as 1,2, and 14 days after an endorgan lesion was made. Practically no resting activity could be recorded in the ganglion acutely (2-7 h) after endorgan damage, and the resting activity at subsequent times was slight. It is concluded that an intact vestibular ganglion isolated from the sensory periphery is of no functional significance during the first 36 h, when the largest decreases in magnitude of the behavioral signs of unilateral labyrinthectomy occur in the rat. A slight significance at later times is not ruled out.
Asunto(s)
Dominancia Cerebral/fisiología , Regeneración Nerviosa , Equilibrio Postural , Nervio Vestibular/fisiología , Vestíbulo del Laberinto/inervación , Vías Aferentes/fisiología , Animales , Oído Interno/inervación , Femenino , Masculino , Degeneración Nerviosa , Nistagmo Fisiológico , Orientación/fisiología , Ratas , Ratas EndogámicasAsunto(s)
Encéfalo/ultraestructura , Técnicas Histológicas , Animales , Benzoxazinas , Colorantes , Oxazinas , Ratas , Coloración y EtiquetadoRESUMEN
Electrolytic lesions in the caudal part of the medial pontine reticular formation (PRF) in the rat abolished apomorphine- or amphetamine-induced stereotypic lateral head movements and turning to the damaged side. Rats with unilateral PRF lesions turned and circled only to the intact side, and rats with bilateral lesions did not turn at all. PRF lesions were also effective in abolishing or reducing amphetamine-induced circling in rats with unilateral nigrostriatal bundle damage. Thus, head movements induced by dopamine agonists are added to the class of head movements mediated by the PRF. It is proposed that the decussations of the motor pathways for drug-induced turning are located between the midbrain and caudal pons.