Post-occlusive reactive hyperemia in patients with peripheral vascular disease

We measured tissue oxygen saturation (StO2) changes during a post-occlusive reactive hyperemia (PORH) test on lower extremities of peripheral vascular disease (PVD) patients and healthy controls. The StO2 changes were measured by the near-infrared tissue oximeter prototyped by ViOptix Inc. We found that PVD indicators may include the post-occlusive StO2 reperfusion rate, the time duration of the reperfusion phase in a PORH test, and the StO2 dispersion rate in reactive hyperemia. We suggest critical values of these indicators for PVD assessments.

The activity of neurons in the rostral medulla of the rat during withdrawal from noxious heat

Neurons of the rostral ventromedial medulla (RVM) have been implicated in the modulation of nociceptive transmission. In order to further analyze their role in pain behavior, we studied their activity while eliciting the tail flick reflex with noxious heat. Recording sites were regions in the RVM from which microstimulation (less than or equal to 10 microA, 400 mu sec, 50 Hz continuous pulse trains) inhibited the tail flick reflex. Extracellular unit activity and tail temperature were recorded, stored, and plotted with reference to either the time of tail flick or the time when the stimulating temperature reached 45 degrees C. Neuronal discharges were found to be either increased (on-cells), decreased (off-cells), or unchanged around the time of the tail flick. The decreases in discharge were more closely correlated with the tail flick behavior than with the temperature of the stimulus. These off-cells were located at sites of lowest threshold for tail flick inhibition and tended to be ventral to on-cells. We propose that off-cells must pause if the tail flick is to occur, and that this pausing allows the transmission of nociceptive input through spinal reflex loops.

The vestibulothalamic pathway: contribution of the ascending tract of Deiters

Axoplasmic transport techniques were used to determine the contribution of the ascending tract of Deiters (ATD) to the vestibulothalamic projection in cats. Large injections of HRP into the thalamus centered on the border region between the ventrobasal complex and the caudal ventrolateral nucleus resulted in bilateral retrograde labeling of cells in the vestibular nuclear complex and the nucleus prepositus hypoglossi (PH). Similar thalamic injections were also made in animals with extensive bilateral lesions of the medial longitudinal fasciculus (MLF) and the brachium conjunctivum (BC). HRP-positive neurons in these cases were localized principally to the ventral lateral vestibular nucleus and adjacent superior vestibular nucleus ipsilateral to the thalamic injection, evidence that vestibulothalamic neurons in these nuclei may project to the thalamus over the unlesioned ATD. Injections of [35S]methionine into the rostral vestibular nuclear complex in animals with MLF and BC lesions confirmed these findings, demonstrating orthograde transport of radiolabel in the ATD with termination in thalamus. These experiments document a contribution of the ATD to the ipsilateral vestibulothalamic projection; other sources of the vestibulothalamic pathway (PH, Y group) likely travel through projection systems destroyed in the lesions made in the present study.

Excitatory projection from the interpeduncular nucleus to central superior raphe neurons

The projection from the interpeduncular nucleus (IP) to the central superior raphe nucleus (CS) was studied using electrophysiologic methods. IP stimulation generates monosynaptic EPSPs in a large number of CS neurons studied with latency of 1-2 ms. Intracellular peroxidase injections into CS neurons responding to IP shock confirmed the location and somatic origin of intracellular potentials. These findings document the existence of a direct excitatory projection from IP onto CS neurons.