A universal approach to estimate biomass and carbon stock in tropical forests using generic allometric models.

Allometric equations allow aboveground tree biomass and carbon stock to be estimated from tree size. The allometric scaling theory suggests the existence of a universal power-law relationship between tree biomass and tree diameter with a fixed scaling exponent close to 8/3. In addition, generic empirical models, like Chave's or Brown's models, have been proposed for tropical forests in America and Asia. These generic models have been used to estimate forest biomass and carbon worldwide. However, tree allometry depends on environmental and genetic factors that vary from region to region. Consequently, theoretical models that include too few ecological explicative variables or empirical generic models that have been calibrated at particular sites are unlikely to yield accurate tree biomass estimates at other sites. In this study, we based our analysis on a destructive sample of 481 trees in Madagascar spiny dry and moist forests characterized by a high rate of endemism (> 95%). We show that, among the available generic allometric models, Chave's model including diameter, height, and wood specific gravity as explicative variables for a particular forest type (dry, moist, or wet tropical forest) was the only one that gave accurate tree biomass estimates for Madagascar (R2 > 83%, bias < 6%), with estimates comparable to those obtained with regional allometric models. When biomass allometric models are not available for a given forest site, this result shows that a simple height-diameter allometry is needed to accurately estimate biomass and carbon stock from plot inventories.

Dissociation of somatosensory and motor evoked potentials in a patient with an intramedullary spinal tumor.

We describe a patient with an intramedullary spinal tumor who demonstrated postoperative improvement of motor and sensory function despite the lack of somatosensory evoked potentials (SSEPs) before and after intraoperative monitoring. The motor system was evaluated by direct spinal cord stimulation across the tumor bed. The resultant evoked compound muscle action potentials and compound nerve activities were normal. Although there is sufficient clinical evidence that SSEPs are sensitive to posterior and posterolateral ischemic insults of the spinal cord, the technique should be employed with an awareness of its limitations in monitoring the descending tracts which have a different blood supply and occupy more anterior locations in the spinal cord.

Thrombosed arteriovenous malformations: a type of occult vascular malformation. Magnetic resonance imaging and histopathological correlations.

Thrombosed arteriovenous malformations (AVMs) are the predominant type of occult vascular malformation and do not seem to differ significantly in clinical or radiographic presentation from other types of occult vascular malformations. Thrombosed AVMs and occult vascular malformations occasionally present with symptoms secondary to subacute or occult hemorrhage that requires operation. The histopathology of thrombosed AVMs and occult vascular malformations does not seem to have prognostic significance. Five patients with histologically verified thrombosed AVMs are reported. Two patients had previous incomplete resection of histologically proven thrombosed AVMs and presented with recurrence and bleeding. Two patients presented with seizures and headaches, and one patient presented with hemiparesis and headache. All histology specimens had evidence of hemorrhage. The pathological findings of these lesions seem variable; two specimens contained a mixture of cavernous angioma and AVM. Two previously resected lesions had been defined histologically as thrombosed AVMs. Successful excision of the lesions was accomplished in four patients, and one patient had stereotactic biopsy. The magnetic resonance imaging characteristics of lesions seem to add a degree of specificity over computed tomography and angiography. We have found that the literature poorly describes the natural history and histology of these lesions. Conservative management for seizures and headaches due to thrombosed AVMs may not be warranted because of a propensity for hemorrhage and recurrence.

Diacylglycerols mimic phorbol diester induction of leukemic cell differentiation.

Activation of cellular protein kinase C appears to be involved in the mechanism by which phorbol diesters induce differentiation of human myeloid leukemia cells (HL-60). Protein kinase C is thought to be physiologically activated by diacylglycerol derived from receptor-mediated phosphatidylinositol hydrolysis. sn-1,2-diacylglycerols with short saturated acyl side chains (C4-C10) were synthesized and found to be potent activators of protein kinase C partially purified from HL-60 cells. These diacylglycerols were also competitive inhibitors of [3H]phorbol dibutyrate binding to the soluble phorbol diester receptor. The most potent diacylglycerol, sn-1,2-dioctanoylglycerol, displaced greater than 90% of [3H]phorbol dibutyrate from the phorbol diester receptor of intact HL-60 cells. Because of probable cellular metabolism of sn-1,2-dioctanoylglycerol, hourly doses were required to maintain persistent occupancy of the phorbol diester binding site. Treatment of HL-60 cells with either phorbol 12-myristate 13-acetate or sn-1,2-dioctanoylglycerol produced identical phosphoprotein changes. Finally, sn-1,2-dioctanoylglycerol induced differentiation of the HL-60 cells into cells with morphologic characteristics of macrophages. Substitution of the hydroxyl group at position 3 with a hydrogen, chloro, or sulfhydryl moiety inactivated sn-1,2-dioctanoylglycerol. These data strengthen the hypothesis that protein kinase C activation plays a role in macrophage differentiation.

Diacylglycerols release LH: structure-activity relations reveal a role for protein kinase C.

A series of diacylglycerols were synthesized with varying lengths and substituents in order to establish the structure-activity relationship between each with activation of protein kinase C and stimulation of a biological response system (pituitary luteinizing hormone release). This approach enables distinction between actions mediated by direct activation of protein kinase C and those due to other, presumably nonspecific, actions. The ability of diacylglycerols to function as regulators of a biological response system (pituitary luteinizing hormone release) and of protein kinase C was investigated with a series of sn-1,2 diacylglycerols containing fatty acids 4-10 carbons in length and with analogs in which the 3' hydroxyl was replaced with a chloro, hydrogen, or sulfhydryl moiety. Several diacylglycerols stimulated LH release in a saturable, time and dose dependent manner that was independent of extra-cellular calcium. Dioctanoylglycerol (diC8) was the most effective of the diacylglycerols tested; 3' analogs lacking the hydroxyl were inactive. The diacylglycerols activated protein kinase C in vitro whereas the 3' analogs did not. These data implicate protein kinase C in the mechanism of LH release, demonstrate that unsaturated fatty acyl moieties within the diacylglycerol are not required for protein kinase C activation, and establish diacylglycerol-protein kinase C structure-function relationships that should prove useful for investigations in other systems.

Headaches after childbirth.

71 women were examined daily for the presence of headache in their first post partum week. Post natal headache (PNH) occurred in 27, (39%) of the women and was most frequent on days 4-6 post partum. PNH was significantly associated with a previous or family history of migraine and pre-menstrual migraine. Although 83% of those with PNH had a migraine diathesis, they did not describe their headache as one of their usual migraines as it was considerably milder. Headaches were more frequent among multigravida but as rather more multigravida had a previous migraine diathesis this may reflect a sampling bias. PNH subjects had significantly more tension and depression suggesting that at least some PNH may be tension headache. Around 3 or 4 days post partum, women began to lose weight and the onset of headache often coincided with the start of this weight loss. 12 women with, and 12 without PNH took part in a metabolic study, and collected sequential 24 h urine samples from days 2-7 post partum. Potassium and oestrogen excretion were increased on day 3, and progesterone on days 3, 4 and 5. Differences in the excretion pattern of these hormones might reflect small changes in renal function and further work measuring plasma hormone levels could help to clarify this. PNH, like pre-menstrual headache and pill withdrawal headache may represent a further example of the triggering effect that a fall in sex hormone level has on the migraine diathesis.