Activation of two different but complementary biochemical pathways stimulates release of hypothalamic luteinizing hormone-releasing hormone.

Evidence exists that a norepinephrine/prostaglandin E2 (PGE2)/cAMP pathway is involved in the regulation of luteinizing hormone-releasing hormone (LHRH) secretion. The aim of the present experiments was to determine if release of LHRH from the immature rat hypothalamus could also be stimulated by activation of protein kinase C. Median eminences from 28-day-old female rats were incubated in vitro with either dioctanoylglycerol (a synthetic diacylglycerol that selectively activates protein kinase C in intact cells) or 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (another protein kinase C activator). Both agents increased LHRH release, the response to dioctanoylglycerol being more pronounced than that to the phorbol ester. This direct activation of protein kinase C was not accompanied by changes in PGE2 formation. Activation of the PGE2/cAMP pathway by either norepinephrine, PGE2, or forskolin (a stimulator of adenylate cyclase) increased LHRH release. Dioctanoylglycerol or phorbol ester in conjunction with either norepinephrine, PGE2 or forskolin resulted in an additive effect on LHRH release suggesting coexistence of both pathways. Phospholipase C, which activates protein kinase C via formation of diacylglycerol, increased the release of both LHRH and PGE2. This suggests that an increase in endogenous phospholipase C activity caused by neurotransmitter inputs may lead to both activation of protein kinase C and PGE2 formation. Blockade of cyclooxygenase activity by indomethacin obliterated phospholipase C-induced PGE2 release. The same treatment reduced the LHRH response by only 50% indicating that protein kinase C activation can cause LHRH release in the absence of PGE2 synthesis. It is suggested that the median eminence of the rat possesses a protein kinase C-dependent pathway that is coupled positively to LHRH release and complements PGE2/cAMP-dependent mechanisms. Norepinephrine, however, does not appear to be the neurotransmitter responsible for activating the protein kinase C pathway. Simultaneous activation of both pathways may provide a mechanism by which a large increase in LHRH secretion occurs, such as in the afternoon of first proestrus.     

Venous skin flaps: an experimental study and report of two clinical distal island flaps

An experimental study of saphenous flaps in 26 dogs is reported, which confirmed the work of Baek et al. (1985) that venous flaps can survive. In addition, it showed that venous island flaps could survive after division of the venous pedicle proximally or distally, or as free flaps, providing through flow was re-established by venous anastomoses. In this study no flaps survived on a single venous pedicle without through flow. Two successful clinical cases of venous flaps are also reported, in which through flow was re-established by a simple venous anastomosis. One of these flaps threatened to become necrotic until the thrombosed anastomosis was successfully redone.     

Genetic ablation of the t-SNARE SNAP-25 distinguishes mechanisms of neuroexocytosis.

Axon outgrowth during development and neurotransmitter release depends on exocytotic mechanisms, although what protein machinery is common to or differentiates these processes remains unclear. Here we show that the neural t-SNARE (target-membrane-associated-soluble N-ethylmaleimide fusion protein attachment protein (SNAP) receptor) SNAP-25 is not required for nerve growth or stimulus-independent neurotransmitter release, but is essential for evoked synaptic transmission at neuromuscular junctions and central synapses. These results demonstrate that the development of neurotransmission requires the recruitment of a specialized SNARE core complex to meet the demands of regulated exocytosis.     

L-Dopa-responsive Parkinson's syndrome in association with phenylketonuria: In vivo dopamine transporter and D2 receptor findings.

Reports of parkinsonism in phenylketonuria are exceedingly rare. We report on a patient who had received a delayed diagnosis of phenylketonuria as an infant and subsequently developed levodopa-responsive parkinsonism at the age of 33. Single-photon emission computed tomography (SPECT) using (123)I-FP-CIT ([(123))I]-2 beta-carbomethoxy-3beta-(-4-iodophenyl)-N-(3-fluoropropyl)-nortropane) used to measure dopamine transporter levels on two occasions, 7 and 9 years after the onset of neurological symptoms, were normal. Iodine-123-iodo-lisuride SPECT (IBZM) imaging, however, showed reduced caudate over putamen binding. This combination of imaging findings indicates a possible upregulation of postsynaptic D2 receptors in the context of intact presynaptic dopamine nerve terminal density.