Leucine-rich repeat-containing G-protein-coupled receptor 8 in the rat brain: Enrichment in thalamic neurons and their efferent projections.

Leucine-rich repeat-containing G-protein-coupled receptor 8 (LGR8; also classified as relaxin family peptide 2 receptor; RXFP2) has been identified as a cognate receptor for the peptide hormone, insulin-like peptide 3 (INSL3) and INSL3-LGR8 signaling plays an essential role in testis descent and germ cell development in human and rodents. Lgr8 mRNA has been detected in human tissues including testis, kidney and brain, but its regional and cellular distribution in these tissues in human or other species is largely unknown. In an initial step to elucidate the physiological function of a putative INSL3-LGR8 system in rat brain, the localization of Lgr8 mRNA was investigated using in situ hybridization histochemistry, revealing a discrete distribution in forebrain, with expression highly enriched in the thalamus. High densities were detected in the parafascicular nucleus (Pf), the dorsolateral, ventrolateral and posterior thalamic nuclei, and in the medial habenula. Lgr8 transcripts were also detected in frontal and motor cortices. The comparative distribution of LGR8 (receptor protein) was examined by autoradiography of [125I]-human INSL3 binding sites, with high densities detected in the thalamus, especially in Pf, and in the entire striatum--the caudate putamen (CPmicro), islands of Calleja, olfactory tubercle, nucleus accumbens--with lower levels in distinct layers of cerebral cortex. Notably, these areas also receive dopaminergic projections. These findings demonstrate the existence of LGR8 in neuronal soma in the thalamus and axons/terminals in thalamic target areas such as the striatum and frontal cortex. LGR8 was also detected throughout the medial habenula-fasciculus retroflexus-interpeduncular nucleus pathway, further indicating that the receptor is transported from mRNA-expressing soma to remote axonal/terminal sites. These findings suggest the existence of a broadly distributed LGR8 signaling system in the rat involved in sensorimotor, limbic and cognitive functions. Further studies are now required to elucidate the precise function of LGR8, under normal and pathological conditions, as importantly, several of the equivalent receptor-positive areas in human brain are part of the pathology of neurodegenerative conditions including Parkinson's disease.

A 12-month prospective study of gasserian ganglion stimulation for trigeminal neuropathic pain.

AIMS: Trigeminal neuropathic pain is a broad diagnostic category that includes pain of several etiologies and excludes trigeminal neuralgia. The authors report a prospective series of percutaneous gasserian ganglion stimulation for trigeminal neuropathic pain. METHODS: Patients who experienced >50% reduction in pain from a 7- to 10-day trial period underwent permanent implantation and were prospectively followed. RESULTS: Eight of 10 trialed patients received a permanent implant. At the 12-month follow-up, 2 patients had been explanted and 1 was lost to follow-up. Three (all working at that the time) continued to experience >50% improvement in pain. DISCUSSION: The results in this series were variable but 3 patients showed long-term improvements. Patients who continued to work responded better to treatment.

Lesion of thalamic centromedian--parafascicular complex after chronic deep brain stimulation.

A patient with PD who exhibited disabling tremor and prominent dyskinesia underwent deep brain stimulation (DBS) of the left thalamic ventral intermediate nucleus. The electrode migrated and was replaced but with suboptimal clinical response. Two years later, postmortem analysis found the second electrode tip had entered the thalamic centromedian-parafascicular complex. There was a small thalamotomy and cell loss exceeding that found in PD. Thalamic damage may occur in association with DBS for PD.

Targeting the subthalamic nucleus in the treatment of Parkinson's disease.

As more is learnt about the functional implications of basal ganglia connectivity, the role of the subthalamic nucleus as a target site for stereotactic procedures in the amelioration of the symptoms of Parkinson's disease is becoming clearer. A comparison of various neurosurgical procedures in the disease is discussed in relation to current thinking about circuitry. Experimental investigations involving lesioning or stimulation of the subthalamic nucleus in nonhuman primate models and in clinical studies of Parkinson's disease are compared. Neurosurgical procedures that lesion structures bilaterally are more likely to induce side effects than is deep-brain stimulation, which has the added advantage of reversibility and which is more amenable to titration in relation to medication and dosage. A small but growing number of parkinsonian patients have received subthalamic stimulation either unilaterally or bilaterally. Stimulation of the subthalamic nucleus ameliorates tremor, rigidity and hypokinesia, as opposed to thalamic stimulation which is probably best reserved for tremor-dominant patients. Such procedures also do not involve the same complex technical and ethical issues that are associated with foetal mesencephalic grafting. Although subthalamic stimulation shows great promise, it has not been developed to the point where it can be used as more than an experimental treatment. Further experimental research is required before the new strategies can be used on a larger scale.

Combined stereotactic thalamotomy and posteroventral pallidotomy for Parkinson's disease.

Stereotactic thalamotomy has traditionally provided good relief of tremor for patients with intractable tremor-dominant Parkinson's disease. However, bradykinesia, dyskinesia, and rigidity are often less reliably treated with this technique. Although posteroventral pallidotomy (PVP) can alleviate dyskinesias, appendicular bradykinesia, and rigidity, tremor may not be completely ameliorated. We have combined Vim/VOp junction thalamotomy and PVP in 29 patients with severe tremor, rigidity, and bradykinesia. Patients underwent unilateral Vim thalamotomy followed at the same sitting by PVP. The distinct physiological consequences of each procedure were documented by intraoperative electromyography (EMG) and video recording, revealing the effects on both tremor and agonist/antagonist co-contraction. Lack of reciprocal inhibition of antagonistic muscle groups often remained following thalamotomy but was eliminated by subsequent PVP. The complementary therapeutic effects of PVP and Vim thalamotomy may be due to the interruption of different neuronal circuits by the two procedures. The effect of Vim thalamotomy has been attributed to the interruption of the rubrothalamocortical loop. PVP interrupts the outflow of the globus pallidus interna (GPi), which may cause disinhibition of locomotor centers in the mesencephalon and spinal cord. There is no direct interruption of the rubrothalamocortical loop by PVP, explaining why this procedure sometimes exacerbates tremor in certain patients. The combination of the two procedures appears to provide excellent relief of the majority of symptoms in patients suffering from tremor-dominant Parkinson's disease.

An NMR study of pyridine associated with DMPC liposomes and magnetically ordered DMPC-surfactant mixed micelles.

With molecular dynamics simulations of phospholipid membranes becoming a reality, there is a growing need for experiments that provide the molecular details necessary to test these computational results. Pyridine is used here to explore the interaction of planar aromatic groups with the water-lipid interface of membranes. It is shown by magic angle spinning 13C nuclear magnetic resonance (NMR) to bind between the glycerol and choline groups of dimyristoylphosphatidylcholine (DMPC) liposomes. The axial pattern for the 31P NMR spectrum of DMPC liposomes is preserved even with more than half of the interfacial sites occupied, indicating that pyridine does not disrupt the lamellar phase of this lipid. 2H NMR experiments of liposomes in deuterium oxide demonstrate that pyridine might promote greater penetration of water into restricted regions in the interface. Magnetically oriented DMPC/surfactant micelles were investigated as a means for improving resolution and sensitivity in NMR studies of species bound to bilayers. The quadrupolar splittings in the 2H NMR spectra of d5-pyridine in DMPC liposomes and magnetically oriented DMPC/Trixon X-100 micelles indicate a common bound state for the two bilayer systems. The well resolved quadrupolar splittings of d5-pyridine in oriented micelles were used to establish the tilt of the pyridine ring relative to the bilayer plane.

Pediatric liver transplantation in Georgia: a paradigm for the health care crisis in the United States?

The United States health care system, felt by many to be the most technologically advanced program in the world, has many critics. Two indisputable facts that drive such criticism are 1) inequitable access and 2) rising costs out of proportion to other countries. Although Georgia is a poor state and ranks nationally near the bottom in most measures of child and adolescent care, we decided to start a pediatric liver transplant program at Egleston Children's Hospital at Emory, Atlanta. Over the past 2 1/2 years, 18 transplants have been performed in 14 patients; 10 children are presently surviving. Looking carefully at the expenses of the first 10 patients, the average cost of orthotopic liver transplantation for the eight survivors was $206,375. The hospital costs for providing care to these 10 children were over $2 million. In a state that ranks 49th out of 50 states in infant mortality and with nearly one-third of its pre-school children not immunized against preventable diseases, is this a fair and equitable distribution of our resources?

Vitamin B6 metabolism by human liver.

The B6 vitamers (pyridoxine, pyridoxamine, and pyridoxal) are primarily metabolized in liver to pyridoxal 5'-phosphate (PLP) and the deadend catabolite 4-pyridoxic acid. We have built on the elegant early work of Snell and others to describe the activities of the human liver enzymes responsible for vitamin B6 metabolism and to develop a model of the relative rates of these interconversions in vivo. This model is consistent with changes in plasma B6 after a load, the clearance of different vitamers (e.g., pyridoxine versus pyridoxal), and with the low plasma PLP in patients with cirrhosis. Because cirrhotics were found to be capable of PLP synthesis, we have used oral supplementation with pyridoxine to restore plasma PLP to the normal range, and have evaluated the effects of this intervention on amino acid metabolism. No significant differences were observed in plasma or urinary clearance of methionine (or cystathionine) after an oral load, nor in amino acid clearance from circulation after a protein load for cirrhotic patients before and after restoration of normal plasma PLP. Hence, the abnormal metabolism of vitamin B6 does not appear to be an important factor in the deranged amino acid metabolism in this disease. Nonetheless, this approach may be generally useful in assessing the importance of PLP in other abnormalities.

Vitamin B6 repletion in cirrhosis with oral pyridoxine: failure to improve amino acid metabolism.

This study evaluated the effect of daily oral pyridoxine supplementation in patients with cirrhosis. Eight subjects were treated with 25 mg of pyridoxine for 28 days. Before and after the supplementation period, B6 status was assessed by measuring fasting plasma vitamer levels and response to a 25 mg oral pyridoxine load. In addition, a 24-hr urine collection was analyzed during each load study for B6 metabolites. The data indicated that supplementation achieved repletion of peripheral B6 stores, as evidenced by: (i) a significant (p less than 0.005) rise in fasting plasma pyridoxal phosphate after supplementation (mean +/- S.D. = 56.8 +/- 30.5 nmoles per liter) as compared to initial levels (17.0 +/- 17.8 nmoles per liter); (ii) a higher (p less than 0.05) percentage excretion of the pyridoxine load as urinary 4-pyridoxic acid (31.0 +/- 9.3%) compared to the initial load (19.6 +/- 5.8%), and (iii) a postsupplementation area under the plasma concentration vs. time curve for pyridoxal phosphate (377 +/- 529 nmoles.hr per liter), which was decreased (p less than 0.005) from the presupplementation value (934 +/- 756 nmoles.hr per liter). The postsupplementation fasting plasma pyridoxal phosphate concentrations were within the normal range. The consequences of B6 repletion on amino acid metabolism were measured by oral protein loads (n = 4) or oral methionine loads (n = 4). No significant changes were observed for methionine or any other amino acid in regard to plasma fasting concentration, peak concentration or AUC. Although the vitamin B6 deficiency of cirrhosis was corrected by daily oral pyridoxine supplementation, there was apparently no improvement in the deranged amino acid metabolism.

Comparison of the effects of Hepatic-Aid and a Casein modular diet on encephalopathy, plasma amino acids, and nitrogen balance in cirrhotic patients.

Hepatic-Aid is purported to ameliorate encephalopathy and promote positive nitrogen balance in protein-intolerant, cirrhotic patients by correcting their imbalanced amino acid profile. This study evaluated Hepatic-Acid by comparing a 50-g Casein diet with an identical diet with 20-g Casein/30-g Hepatic-Aid per day in a cross-over study. Four patients with biopsy-proven stable cirrhosis, encephalopathy, and under-nutrition were studied. Each study period included three days of equilibration and eight days of metabolic balance, with the following measured at baseline and on balance days 5 and 8: routine biochemistry, fasting ammonia, psychometric tests, EEG, and plasma amino acid profiles. There was no significant change in clinical status, routine biochemistry, fasting ammonia, psychometrics or EEG between the two study periods. Mean (+/-SD) nitrogen balance on the Casein diet at 1.5 +/- 1.5 g/day was not significantly different from that on the Hepatic-Aid diet at 1.5 +/- 1.2 g/day. Plasma amino acid profiles showed a significant fall (p less than 0.05) in fasting and intraprandial tyrosine (tyr) and phenylalanine (phe) on Hepatic-Aid, but only intraprandial leucine (leu), isoleucine (ile), and valine (val) were significantly increased (p less than 0.05) on Hepatic-Aid. The ratio leu + ile + val to tyr + phe was significantly increased (p less than 0.05) on Hepatic-Aid. It is concluded that Hepatic-Aid, as given in this study, maintains N balance similar to Casein, alters the amino acid profile towards normal, but does not ameliorate encephalopathy.

Total parenteral nutrition with F080 in cirrhotics with subclinical encephalopathy.

It has been proposed that hepatic encephalopathy and malnutrition in cirrhosis can be reversed by infusion of a protein formula (F080) enriched with branched-chain amino acids (valine, leucine, isoleucine) and containing decreased amounts of aromatic amino acids (phenylalanine, tyrosine, tryptophan). This hypothesis was tested by measuring changes in encephalopathy status, plasma ammonia, amino acid profile, and liver function during seven metabolic balance studies in three patients with cirrhosis and subclinical encephalopathy given increasing amounts (20-100 g/d) of F080. The results showed the following: 1) positive nitrogen balance was achieved only with 80 and 100 g F080/day; 2) plasma ammonia fell during negative, but increased during positive nitrogen balance; 3) plasma tyrosine and cystine fell significantly (p less than 0.05) with all intakes of F080; 4) the abnormal branched-chain to aromatic amino acid ratio was reversed; 5) extracellular volume was expanded in all patients; 6) albumin, bilirubin, prothrombin time became abnormal; and 7) encephalopathy did not significantly change from baseline. It is concluded that, in this population, F080 is an inadequate nutritional formula when given as the sole protein source because it produces hypotyrosinemia and hypocystinemia. The marked changes in the ratio of branched-chain to aromatic amino acids are not accompanied by improvement in encephalopathy.