Increased expression of peripheral benzodiazepine receptors in the facial nucleus following motor neuron axotomy

Peripheral benzodiazepine receptors (PBRs) are expressed in a variety of tissues but are normally found at low levels in the brain. Following various types of nerve injury, a reactive gliosis results that exhibits a high expression of this receptor. To further characterize the expression of PBRs following neuronal injury, we evaluated PBR expression in the facial nucleus following facial nerve axotomy (FNA). Injury to a peripheral nerve results in a complex series of metabolic and morphological changes around the injured neuron. Transections of the facial nerve results in a rapid activation of both astrocytes and microglia around axotomized motor neurons. FNA resulted in an increase in the staining for both astrocytes (glial fibrillary acidic protein) and activated microglia (OX42). There was also a reduction in synaptic contacts with the motor nucleus as evidenced by reduced staining for the synaptic marker, synaptophysin. In sections labeled with [3H]-PK11195, the subsequent autoradiograms displayed marked increases in the labeling for PBRs. This increase was observed at 5, 7 and 10 days after nerve transection. The increase was primarily in the level of expression (Bmax), with no change in the affinity of the ligand (Kd). The increase in PBR expression after FNA supports the hypothesis that PBRs can be used as a sensitive marker for CNS injury.     

Aesthetic outcome of breast implant removal in 85 consecutive patients

As we began to see increasing numbers of women concerned about their gel-filled breast implants, we became aware that we could not advise them with any degree of confidence what they might expect in terms of aesthetic result after implant removal. We decided to review the records and outcomes over a 2-year period of a number of patients who underwent implant removal. Eighty-five consecutive patients were reviewed, 69 of whom had undergone cosmetic augmentation and 16 of whom had breast reconstruction with silicone gel implant(s). Thirty-nine of the 69 cosmetic augmentation patients had removal of implants alone, and 27 had removal accompanied by mastopexy. Three had reaugmentation with saline-filled implants; one had replacement with saline-filled implants. Fifteen of the 16 reconstruction patients underwent autogenous tissue transfer. Preoperative and postoperative photographs of all patients were mixed randomly and rated by two independent raters in four aesthetic categories on a five-point scoring system. Repeatability was measured several weeks later, when each rater scored randomly selected photographs from this patient pool. The patients also performed their own outcome evaluations by means of questionnaire. We discovered that cosmetic augmentation patients who undergo implant removal only often suffer adverse aesthetic results. The postremoval appearance of many cosmetic augmentation patients actually will be improved over their preoperative appearance when mastopexy is performed in conjunction with implant removal. The study demonstrated that patients with certain body types could expect a particular outcome; i.e., women with asthenic builds and older patients with lax, striated breast skin generally had unsatisfactory aesthetic outcomes with implant removal only. Patients selected for autogenous breast reconstruction had favorable results, with extended latissimus dorsi and TRAM flaps yielding equally good outcomes. The study allows us to offer patients an optimistic view of postoperative results following breast implant removal. We have begun to advise selected patients that implant removal accompanied by mastopexy provides a more pleasing aesthetic outcome than implant removal alone.     

Experimental and theoretical comparison of NIR spectroscopy measurements of cerebral hemoglobin changes

Two near-infrared spectroscopy (NIRS) methods are available for measuring changes (Delta) in total cerebral hemoglobin concentration (CHC): 1) a continuous measurement of the changes in total hemoglobin concentration (Delta[Hb]tot) and 2) the difference between two absolute measurements of CHC, each derived from a small, controlled change in inspired O2 fraction. This paper investigates the internal consistency of these two methods by using an experimental and theoretical comparison. NIRS was used to measure [Hb]tot in five newborn piglets before and after a change in arterial PCO2. Delta[Hb]tot demonstrated a low coefficient of variation of 2.8 +/- 2.8 (SD) % which allowed changes in CO2-cerebral blood volume reactivity to be clearly discriminated. However, a high coefficient of variation of 22.8 +/- 3.5% on the DeltaCHC measurements obscured any CO2 reactivity changes. A theoretical analysis demonstrates the effects of optical pathlength, background absorption, scatter, and blood vessel diameter on both methods. For more accurate monitoring of CHC, individual measurements of optical pathlength and more accurate pulse oximetry are required.     

Muscle-ligament interactions at the knee during walking.

A two-dimensional mathematical model of the knee is used with gait analysis to calculate muscle, cruciate ligament and tibio-femoral contact forces developed at the knee during normal level walking. Ten normal adult subjects--four females and six males--participated. The knee model is based upon a four-bar linkage comprising the femur, tibia and two cruciate ligaments. It takes account of the rolling and sliding of the femur on the tibia during flexion/extension and the changes in direction of the ligaments and muscle tendons. We considered forces transmitted by six elements: quadriceps, hamstrings, gastrocnemius, anterior and posterior cruciate ligaments, and tibio-femoral contact. The equations of mechanics can be used to determine the absolute values of only three of the knee forces simultaneously, so that twenty limiting solutions of three of the six forces were considered. A limiting solution was rejected if any of the three forces were negative, corresponding to compressive muscle or ligament forces, or tensile contact forces. These constraints always reduced and at times removed the redundancy of the knee structures. The high incidence of predicted single muscle activity, supported by electromyography, suggested that the ligaments play a significant role in load transmission during gait. The temporal patterns of muscle and ligament activity and ligament force magnitudes were sensitive to the choice of model parameters. The analysis showed that each of four possible minimum principles of muscle selection--minimal muscle force, muscle stress, ligament force and contact force--was unlikely to be valid throughout the walking cycle.