Characterization of the influence of unsaturated free fatty acids on brain GABA/benzodiazepine receptor binding in vitro

A New Hypothesis for Alzheimer's Disease: The Lipid Invasion Model

This paper proposes a new hypothesis for Alzheimer's disease (AD)-the lipid invasion model. It argues that AD results from external influx of free fatty acids (FFAs) and lipid-rich lipoproteins into the brain, following disruption of the blood-brain barrier (BBB). The lipid invasion model explains how the influx of albumin-bound FFAs via a disrupted BBB induces bioenergetic changes and oxidative stress, stimulates microglia-driven neuroinflammation, and causes anterograde amnesia. It also explains how the influx of external lipoproteins, which are much larger and more lipid-rich, especially more cholesterol-rich, than those normally present in the brain, causes endosomal-lysosomal abnormalities and overproduction of the peptide amyloid-β (Aβ). This leads to the formation of amyloid plaques and neurofibrillary tangles, the most well-known hallmarks of AD. The lipid invasion model argues that a key role of the BBB is protecting the brain from external lipid access. It shows how the BBB can be damaged by excess Aβ, as well as by most other known risk factors for AD, including aging, apolipoprotein E4 (APOE4), and lifestyle factors such as hypertension, smoking, obesity, diabetes, chronic sleep deprivation, stress, and head injury. The lipid invasion model gives a new rationale for what we already know about AD, explaining its many associated risk factors and neuropathologies, including some that are less well-accounted for in other explanations of AD. It offers new insights and suggests new ways to prevent, detect, and treat this destructive disease and potentially other neurodegenerative diseases.

Neuroprotective activity of new Δ3-N-acylethanolamines in a focal ischemia stroke model

N-acylethanolamines (NAE, also called ethanolamides) are significant lipid signaling molecules with anti-inflammatory, pain-relieving, cell-protective, and anticancer properties. Here, we present the use of a hitherto unreported group of Δ3-NAE and also some Δ4- and Δ5-NAE, in in vitro and in vivo assays to gain a better understanding of their structure-bioactivity relationships. We have developed an efficient synthetic method to rapidly produce novel unlabeled and ¹³ C-labeled Δ3-NAE (NAE-18:5n-3, NAE-18:4n-6) and Δ4-NAE (NAE-22:5n-6). The new NAE with shorter carbon backbone structures confers greater neuroprotection than their longer carbon backbone counterparts, including anandamide (Δ5-NAE-20:4n-6) in a focal ischemia mouse model of stroke. This study highlights structure-dependent protective effects of new NAE following focal ischemia, in which some of the new NAE, administered intranasally, lead to significantly reduced infarct volume and improved recovery of limb use. The relative affinity of the new NAE toward cannabinoid receptors was assessed against anandamide, NAE-22:6n-3 and NAE-20:5n-3, which are known cannabinoid receptor ligands with high-binding constants. Among the newly synthesized NAE, Δ4-NAE-22:5n-6 shows the greatest relative affinity to cannabinoid receptors hCB₁ and hCB₂ , and inhibition of cyclic adenosine monophosphate activity through hCB₂ compared to anandamide.

N-3 (Omega-3) Fatty Acids: Effects on Brain Dopamine Systems and Potential Role in the Etiology and Treatment of Neuropsychiatric Disorders

BACKGROUND & OBJECTIVE

A number of neuropsychiatric disorders, including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and, to some extent, depression, involve dysregulation of the brain dopamine systems. The etiology of these diseases is multifactorial, involving genetic and environmental factors. Evidence suggests that inadequate levels of n-3 (omega- 3) polyunsaturated fatty acids (PUFA) in the brain may represent a risk factor for these disorders. These fatty acids, which are derived from the diet, are a major component of neuronal membranes and are of particular importance in brain development and function. Low levels of n-3 PUFAs in the brain affect the brain dopamine systems and, when combined with appropriate genetic and other factors, increase the risk of developing these disorders and/or the severity of the disease. This article reviews the neurobiology of n-3 PUFAs and their effects on dopaminergic function.

CONCLUSION

Clinical studies supporting their role in the etiologies of diseases involving the brain dopamine systems and the potential of n-3 PUFAs in the treatment of these disorders are discussed.

Fatty Acid Regulation of Voltage- and Ligand-Gated Ion Channel Function

Free fatty acids (FFA) are essential components of the cell, where they play a key role in lipid and carbohydrate metabolism, and most particularly in cell membranes, where they are central actors in shaping the physicochemical properties of the lipid bilayer and the cellular adaptation to the environment. FFA are continuously being produced and degraded, and a feedback regulatory function has been attributed to their turnover. The massive increase observed under some pathological conditions, especially in brain, has been interpreted as a protective mechanism possibly operative on ion channels, which in some cases is of stimulatory nature and in other cases inhibitory. Here we discuss the correlation between the structure of FFA and their ability to modulate protein function, evaluating the influence of saturation/unsaturation, number of double bonds, and cis vs. trans isomerism. We further focus on the mechanisms of FFA modulation operating on voltage-gated and ligand-gated ion channel function, contrasting the still conflicting evidence on direct vs. indirect mechanisms of action.

GABAergic pharmacological activity of propofol related compounds as possible enhancers of general anesthetics and interaction with membranes

Phenol compounds, such as propofol and thymol, have been shown to act on the GABAA receptor through interaction with specific sites of this receptor. In addition, considering the high lipophilicity of phenols, it is possible that their pharmacological activity may also be the result of the interaction of phenol molecules with the surrounding lipid molecules, modulating the supramolecular organization of the receptor environment. Thus, in the present study, we study the pharmacological activity of some propofol- and thymol-related phenols on the native GABAA receptor using primary cultures of cortical neurons and investigate the effects of these compounds on the micro viscosity of artificial membranes by means of fluorescence anisotropy. The phenol compounds analyzed in this article are carvacrol, chlorothymol, and eugenol. All compounds were able to enhance the binding of [(3)H]flunitrazepam with EC50 values in the micromolar range and to increase the GABA-evoked Cl(-) influx in a concentration-dependent manner, both effects being inhibited by the competitive GABAA antagonist bicuculline. These results strongly suggest that the phenols studied are positive allosteric modulators of this receptor. Chlorothymol showed a bell-type effect, reducing its positive effect at concentrations >100 μM. The concentrations necessary to induce positive allosteric modulation of GABAA receptor were not cytotoxic. Although all compounds were able to decrease the micro viscosity of artificial membranes, chlorothymol displayed a larger effect which could explain its effects on [(3)H]flunitrazepam binding and on cell viability at high concentrations. Finally, it is suggested that these compounds may exert depressant activity on the central nervous system and potentiate the effects of general anesthetics.

Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors

The biology underlying excessive daytime sleepiness (hypersomnolence) is incompletely understood. After excluding known causes of sleepiness in 32 hypersomnolent patients, we showed that, in the presence of 10 μM γ-aminobutyric acid (GABA), cerebrospinal fluid (CSF) from these subjects stimulated GABA(A) receptor function in vitro by 84.0 ± 40.7% (SD) relative to the 35.8 ± 7.5% (SD) stimulation obtained with CSF from control subjects (Student's t test, t = 6.47, P < 0.0001); CSF alone had no effect on GABA(A) signaling. The bioactive CSF component had a mass of 500 to 3000 daltons and was neutralized by trypsin. Enhancement was greater for α2 subunit- versus α1 subunit-containing GABA(A) receptors and negligible for α4 subunit-containing ones. CSF samples from hypersomnolent patients also modestly enhanced benzodiazepine (BZD)-insensitive GABA(A) receptors and did not competitively displace BZDs from human brain tissue. Flumazenil--a drug that is generally believed to antagonize the sedative-hypnotic actions of BZDs only at the classical BZD-binding domain in GABA(A) receptors and to lack intrinsic activity--nevertheless reversed enhancement of GABA(A) signaling by hypersomnolent CSF in vitro. Furthermore, flumazenil normalized vigilance in seven hypersomnolent patients. We conclude that a naturally occurring substance in CSF augments inhibitory GABA signaling, thus revealing a new pathophysiology associated with excessive daytime sleepiness.

Effects of propofol and other GABAergic phenols on membrane molecular organization

GABA(A) receptor is the main inhibitory receptor of the central nervous system. The phenols propofol and thymol have been shown to act on this receptor. GABA(A) is an intrinsic protein, the activity of which may be affected by physical changes in the membrane. Taking into account the lipophilicity of phenols, their interaction with the membrane and a consequent non-specific receptor modulation cannot be discarded. By using Langmuir films, we analyze the comparative effects on the molecular properties of the membrane exerted by propofol, thymol and other related compounds, the activities of which on the GABA(A) are under investigation in our laboratory. All the compounds were able to expand phospholipid films, by their incorporation into the monolayer being favored by less-packed structures. Nonetheless, they were able to be incorporated at lateral pressures above the equilibrium pressure estimated for a natural membrane. Epifluorescence images revealed their presence between phospholipid molecules, probably at the head-group region. Hence, all results indicated that the phenols studied were clearly able to interact with membranes, suggesting that their anesthetic activity could be the combined result of their interaction with specific receptor proteins and with their surrounding lipid molecules modulating the supramolecular organization of the receptor environment.

On the protective effect of omega-3 against propionic acid-induced neurotoxicity in rat pups

BACKGROUNDS

The investigation of the environmental contribution for developmental neurotoxicity is very important. Many environmental chemical exposures are now thought to contribute to the development of neurological disorders, especially in children. Results from animal studies may guide investigations of human populations toward identifying environmental contaminants and drugs that produce or protect from neurotoxicity and may help in the treatment of neurodevelopmental disorders.

OBJECTIVE

To study the protective effects of omega-3 polyunsaturated fatty acid on brain intoxication induced by propionic acid (PPA) in rats.

METHODS

24 young male Western Albino rats were enrolled in the present study. They were grouped into three equal groups; oral buffered PPA-treated group given a nuerotoxic dose of 250 mg/Kg body weight/day for 3 days; omega-3 - protected group given a dose of 100 mg/kg body weight/day omega-3 orally daily for 5 days followed by PPA for 3 days, and a third group as control given only phosphate buffered saline. Tumor necrosis factor-α, caspase-3, interlukin-6, gamma amino-buteric acid (GABA), serotonin, dopamine and phospholipids were then assayed in the rats brain's tissue of different groups.

RESULTS

The obtained data showed that PPA caused multiple signs of brain toxicity as measured by depletion of gamaaminobyteric acid (GABA), serotonin (5HT) and dopamine (DA) as three important neurotransmitters that reflect brain function. A high significant increase of interlukin-6 (Il-6), tumor necrosis factor-α (TNF-α) as excellent markers of proinflammation and caspase-3 as a proapotic marker were remarkably elevated in the intoxicated group of rats. Moreover, brain phospholipid profile was impaired in PPA-treated young rats recording lower levels of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylcholine (PC).

CONCLUSIONS

Omega-3 fatty acids showed a protective effects on PPA - induced changes in rats as there was a remarkable amelioration of most of the measured parameters (i.e. higher GABA, 5HT, DA, PE, PS and PC) and lower Il-6, TNF-α and caspase-3.

Sensing the fuels: glucose and lipid signaling in the CNS controlling energy homeostasis

The central nervous system (CNS) is capable of gathering information on the body's nutritional state and it implements appropriate behavioral and metabolic responses to changes in fuel availability. This feedback signaling of peripheral tissues ensures the maintenance of energy homeostasis. The hypothalamus is a primary site of convergence and integration for these nutrient-related feedback signals, which include central and peripheral neuronal inputs as well as hormonal signals. Increasing evidence indicates that glucose and lipids are detected by specialized fuel-sensing neurons that are integrated in these hypothalamic neuronal circuits. The purpose of this review is to outline the current understanding of fuel-sensing mechanisms in the hypothalamus, to integrate the recent findings in this field, and to address the potential role of dysregulation in these pathways in the development of obesity and type 2 diabetes mellitus.

Central but not systemic lipid infusion augments the counterregulatory response to hypoglycemia

This study tests the hypothesis that lipids could act as an alternative fuel source in the brain during insulin-induced hypoglycemia. Male Sprague-Dawley rats were subjected to hyperinsulinemic (5 mU.kg(-1).min(-1)) hypoglycemic (approximately 50 mg/dl) clamps. In protocol 1, intralipid (IL), a fat emulsion, was infused intravenously to prevent the fall in free fatty acid levels that occurs in response to hyperinsulinemic hypoglycemia. Intravenous lipid infusion did not alter the counterregulatory responses to hypoglycemia. To test whether IL could have central effects in mediating the counterregulatory response to hypoglycemia, in protocol 2 the brains of precannulated rats were intracerebroventricularly (icv) infused with IL or artificial cerebrospinal fluid (aCSF) as control. Unexpectedly, the epinephrine and glucagon response to hypoglycemia was significantly augmented with icv IL infusion. To determine whether central IL infusion could restore defective counterregulation, in protocol 3 rats were made recurrently hypoglycemic (RH) for 3 days and on the 4th day underwent hyperinsulinemic hypoglycemic clamps with icv IL or aCSF infusion. RH rats had the expected impaired epinephrine response to hypoglycemia, and icv IL infusion again significantly augmented the epinephrine response in RH rats to normal. With regard to our experimental model of hypoglycemic counterregulation, we conclude that 1) systemic lipid infusion did not alter the counterregulatory response to hypoglycemia, 2) the icv infusion of lipids markedly increased CSF FFA levels and paradoxically augmented the epinephrine and glucagon responses, and 3) the blunted sympathoadrenal response in recurrently hypoglycemic rats was completely normalized with the icv lipid infusion. It is concluded that, in the setting of insulin-induced hypoglycemia, increased brain lipids can enhance the sympathoadrenal response.

Function of oleic acid on epidermal barrier and calcium influx into keratinocytes is associated with N-methyl D-aspartate-type glutamate receptors

BACKGROUND

Unsaturated fatty acids from sebum affect calcium dynamics in epidermal keratinocytes, disrupt the barrier function and induce abnormal keratinization. However, the mechanisms of these effects have not been clarified.

OBJECTIVES

To investigate the function of unsaturated fatty acids in epidermis.

METHODS

Antagonists of calcium channel receptors were applied to mouse skin together with oleic acid. Measurements were made of transepidermal water loss (TEWL), and hyperproliferation was assessed. The effects of the antagonists on calcium influx into cultured normal human keratinocytes and on cytokine production were also evaluated.

RESULTS

N-methyl-d-aspartate (NMDA) receptor antagonists such as MK801 and D-AP5 specifically inhibited the increase in TEWL caused by oleic acid, and suppressed keratinocyte hyperproliferation. These compounds also inhibited the increase in the intracellular concentration of calcium ions induced by oleic acid. MK801 suppressed the production of interleukin-1alpha by keratinocytes induced by oleic acid.

CONCLUSIONS

Unsaturated fatty acids such as oleic acid might function via NMDA receptors.

Reduced numbers of dopamine neurons in the substantia nigra pars compacta and ventral tegmental area of rats fed an n-3 polyunsaturated fatty acid-deficient diet: a stereological study

Inadequate dietary n-3 polyunsaturated fatty acid (PUFA) content is associated with altered function of the CNS dopamine systems. In this study, the effects of dietary n-3 PUFA content were determined on dopamine cell number and morphology. Adult (postnatal day 70), male, Long-Evans rats were raised from conception on diets containing adequate (control) or negligible n-3 PUFAs. The number and morphology of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta and ventral tegmental area were determined stereologically. The number of tyrosine hydroxylase-positive cells in rats fed the n-3 PUFA-deficient diet was 33.9% lower in the substantia nigra pars compacta and 33.7% lower in the ventral tegmental area than in those fed the control diet (P<0.05); however, the volume of tyrosine hydroxylase-positive cell bodies was not different between diet groups in either brain region. Rats fed the n-3 PUFA-deficient diet also exhibited dendritic depletion and isolation of tyrosine hydroxylase-positive cells compared to rats fed the control diet, which had clustering of tyrosine hydroxylase-positive cells and extensive dendritic arborization. These findings support a role for n-3 PUFAs in the survival of dopamine neurons and suggest that altered dopamine cell number, as well as function, contributes to the behavioral effects observed in rats raised on n-3 PUFA-deficient diets.

Fatty acid sensing and nervous control of energy homeostasis

Nutrient sensitive neurons (glucose and fatty acids, FA) are present in both the hypothalamus and the brainstem and play a key role in nervous control of energy homeostasis. Through neuronal output, especially the autonomic nervous system, it is now evidenced that FA may modulate food behaviour and both insulin secretion and action. For example, central administration of oleate inhibits both food intake and hepatic glucose production in rats. This suggests that a slight increase in plasma FA concentrations in the postprandial state might be detected by the central nervous system as a satiety signal. At cellular levels, subpopulations of FA-sensitive neurons (either excited or inhibited by FA) are now identified within the hypothalamus. However molecular effectors of FA effects remain unclear. They probably include ionic channels such as chloride or potassium. FA metabolism seems also required to induce neuronal response. Thus, FA per se or their metabolites modulate neuronal activity, as a mean of directly monitoring ongoing fuel availability by CNS nutrient-sensing neurons involved in the regulation of insulin secretion. Beside these physiological effects, FA overload or dysfunction of their metabolism could impair nervous control of energy homeostasis and contribute to development of obesity and/or type 2 diabetes in predisposed subjects.

Long-chain polyunsaturated fatty acids and the pathophysiology of myalgic encephalomyelitis (chronic fatigue syndrome)

Evidence is put forward to suggest that myalgic encephalomyelitis, also known as chronic fatigue syndrome, may be associated with persistent viral infection. In turn, such infections are likely to impair the ability of the body to biosynthesise n-3 and n-6 long-chain polyunsaturated fatty acids by inhibiting the delta-6 desaturation of the precursor essential fatty acids--namely, alpha-linolenic acid and linoleic acid. This would, in turn, impair the proper functioning of cell membranes, including cell signalling, and have an adverse effect on the biosynthesis of eicosanoids from the long-chain polyunsaturated fatty acids dihomo-gamma-linolenic acid, arachidonic acid and eicosapentaenoic acid. These actions might offer an explanation for some of the symptoms and signs of myalgic encephalomyelitis. A potential therapeutic avenue could be offered by bypassing the inhibition of the enzyme delta-6-desaturase by treatment with virgin cold-pressed non-raffinated evening primrose oil, which would supply gamma-linolenic acid and lipophilic pentacyclic triterpenes, and with eicosapentaenoic acid. The gamma-linolenic acid can readily be converted into dihomo-gamma-linolenic acid and thence arachidonic acid, while triterpenes have important free radical scavenging, cyclo-oxygenase and neutrophil elastase inhibitory activities. Furthermore, both arachidonic acid and eicosapentaenoic acid are, at relatively low concentrations, directly virucidal.

Effects of Oleic Acid on Distinct Populations of Neurons in the Hypothalamic Arcuate Nucleus Are Dependent on Extracellular Glucose Levels

Pharmacological manipulation of fatty acid metabolism in the hypothalamic arcuate nucleus (ARC) alters energy balance and glucose homeostasis. Thus, we tested the hypotheses that distinctive populations of ARC neurons are oleic acid (OA) sensors that exhibit a glucose dependency, independent of whether some of these OA sensors are also glucose-sensing neurons. We used patch-clamp recordings to investigate the effects of OA on ARC neurons in brain slices from 14- to 21-day-old Sprague–Dawley (SD) rats. Additionally, we recorded spontaneous discharge rate in ARC neurons in 8-wk-old fed and fasted SD rats in vivo. Patch-clamp studies showed that in 2.5 mM glucose 12 of 94 (13%) ARC neurons were excited by 2 μM OA (OA-excited or OAE neurons), whereas six of 94 (6%) were inhibited (OA-inhibited2.5or OAI2.5neurons). In contrast, in 0.1 mM glucose, OA inhibited six of 20 (30%) ARC neurons (OAI0.1neurons); none was excited. None of the OAI0.1neurons responded to OA in 2.5 mM glucose. Thus OAI2.5and OAI0.1neurons are distinct. Similarly, in seven of 20 fed rats (35%) the overall response was OAE-like, whereas in three of 20 (15%) it was OAI-like. In contrast, in fasted rats only OAI-like response were observed (three of 15; 20%). There was minimal overlap between OA-sensing neurons and glucose-sensing neurons. In conclusion, OA regulated three distinct subpopulations of ARC neurons in a glucose-dependent fashion. These data suggest that an interaction between glucose and fatty acids regulates OA sensing in ARC neurons.

Surface activity of thymol: implications for an eventual pharmacological activity

In the present work, we studied the ability of thymol to affect the organization of model membranes and the activity of an intrinsic membrane protein, the GABA(A) receptor (GABA(A)-R). In this last aspect, we tried to elucidate if the action mechanism of this terpene at the molecular level, involves its binding to the receptor protein, changes in the organization of the receptor molecular environment, or both. The self-aggregation of thymol in water with a critical micellar concentration approximately = 4 microM and its ability to penetrate in monomolecular layers of soybean phosphatidylcholine (sPC) at the air-water interface, even at surface pressures above the equilibrium, lateral pressure of natural bilayers were demonstrated. Thymol affected the self-aggregation of Triton X-100 and the topology of sPC vesicles. It also increased the polarity of the membrane environment sensed by the electrochromic dye merocyanine. A dipolar moment of 1.341 Debye was calculated from its energy-minimized structure. Its effect on the binding of [3H]-flunitrazepam ([3H]-FNZ) to chick brain synaptosomal membranes changed qualitatively from a tendency to the inhibition to a clear activatory regime, up on changing the phase state of the terpene (from a monomeric to a self-aggregated state). Above its CMC, thymol increased the affinity of the binding of [3H]-FNZ (K(d-control)= 2.9, K(d-thymol)= 1.7 nM) without changing the receptor density (B(max-control)= 910, B(max-thymol)= 895 fmol/mg protein). The activatory effect of thymol on the binding of [ [3H]-FNZ was observed even in the presence of the allosteric activator gamma-aminobutyric acid (GABA) at a concentration of maximal activity, and was blocked by the GABA antagonist bicuculline. Changes in the dipolar arrangement and in the molecular packing of GABA(A)-R environment are discussed as possible mediators of the action mechanism of thymol.

Eicosapentaenoic acid in the treatment of schizophrenia and depression: rationale and preliminary double-blind clinical trial results

It has been hypothesised that polyunsaturated fatty acids (PUFA) play an important role in the aetiology of schizophrenia and depression. Evidence supporting this hypothesis for schizophrenia includes abnormal brain phospholipid turnover shown by 31P Magnetic Resonance Spectroscopy, increased levels of phospholipase A2, reduced niacin skin flush response, abnormal electroretinogram, and reduced cell membrane levels of n-3 and n-6 PUFA. In depression, there is strong epidemiological evidence that fish consumption reduces risk of becoming depressed and evidence that cell membrane levels of n-3 PUFA are reduced. Four out of five placebo-controlled double- blind trials of eicosapentaenoic acid (EPA) in the treatment of schizophrenia have given positive findings. In depression, two placebo-controlled trials have shown a strong therapeutic effect of ethyl-EPA added to existing medication. The mode of action of EPA is currently not known, but recent evidence suggests that arachidonic acid (AA) if of particular importance in schizophrenia and that clinical improvement in schizophrenic patients using EPA treatment correlates with changes in AA.

Relationship between protein phosphatase type-2C activity and induction of apoptosis in cultured neuronal cells

The cellular composition and concentration of fatty acids are crucial for proliferation and survival. We recently showed stimulation of protein phosphatase type-2C (PP2C) by unsaturated fatty acids. Here, we describe that treatment of cultured chick neurons with 100 microM oleic acid for 24h increased the percentage of damaged neurons to 61+/-9% compared with 25+/-4% in controls. Oleic acid-induced cell death showed features of apoptosis such as chromatin condensation, shrinkage of the nucleus, DNA fragmentation and caspase-3 activation. Extensive studies with a variety of fatty acids revealed a striking correlation between activation of PP2C and induction of apoptosis. Lipophilicity, oxidizability, and an acidic group were required for both effects. In addition, activation of PP2C and induction of apoptosis could discriminate between cis- and trans-conformation of the fatty acids. The results are in favor of PP2C playing an important, yet unidentified role in apoptosis.

A new category of psychotropic drugs: neuroactive lipids as exemplified by ethyl eicosapentaenoate (E-E)

New treatments for psychiatric disorders are urgently required. Recent reviews show that there have been no improvements in efficacy of drugs for either affective disorders or schizophrenia since the first compounds were introduced over 40 years ago. Neuroactive lipids represent an entirely novel class of psychotropic compounds. Ethyl eicosapentaenoate is the first example of this group. Placebo-controlled studies have found it to be effective in depression, in treatment-unresponsive schizophrenia and in tardive dyskinesia. It is extremely well tolerated with none of the usual side-effects of either antidepressants or neuroleptics. It probably works by modulating postreceptor signal transduction processes.

Neurochemical investigation of the schizophrenic brain by in vivo phosphorus magnetic resonance spectroscopy

Abnormal phospholipid metabolisms may play important roles in the pathophysiology of schizophrenia. Phosphorus magnetic resonance spectroscopy (31P-MRS) offers a new method for studying phosphorus-related metabolism in vivo. A decrease in the level of phosphomonoesters (PME) and an increase in the level of phosphodiesters (PDE) has been demonstrated in the prefrontal lobe of neuroleptic-naive schizophrenic patients. Most of the studies in medicated schizophrenic patients have shown decreased PME and/or increased PDE. The decreased PME in the frontal lobe appears to be associated with negative symptoms and poor working memory performance. 1H-decoupled 31P-MRS revealed a reduction in the phosphocholine element of PME and an elevation in the mobile phospholipids of PDE in the prefrontal region of medicated schizophrenic patients. PDE were elevated in the temporal lobes of neuroleptic-naive schizophrenic patients, and this increase was partially normalized by haloperidol administration. Data about the temporal lobes of medicated schizophrenic patients have not been consistent. Except for the reduction in the adenosine triphosphate (ATP) in the basal ganglia and the correlation between the increase in the frontal lobe phosphocreatine (PCr) and negative symptomatology, data related to changes in high-energy phosphates are contradictory. No consensus on the effect of neuroleptics on phosphorus metabolites has been achieved. Methodological problems inherent in 31P-MRS may have contributed to the confusion in understanding available data. Future directions of MRS studies are suggested in the last section of the paper.

Additivities of compounds that increase the numbers of high affinity [3H]muscimol binding sites by different amounts define more than 9 GABA(A) receptor complexes in rat forebrain: implications for schizophrenia and clozapine research

BACKGROUND

The numbers of [3H]MUS binding sites were reported to be elevated in layers II and III, but not V or VI, in cingulate cortex of schizophrenic brains post mortem. These increases in [3H]MUS binding sites are probably due to compensatory up-regulation of GABA(A) receptors on pyramidal cells as a consequence of a selective loss of GABAergic interneurons in layer II of cingulate cortex. The number of [3H]flunitrazepam binding sites was reported to be reduced in schizophrenic cingulate cortex, and this may directly reflect the loss of GABAergic interneurons. Chronic administration of clozapine to rats was reported to significantly reduce the numbers of [3H]MUS binding sites in temporal cortex and hippocampus which may be due to selective blockade of GABA(A) receptors on GABAergic interneurons that make synaptic contact with pyramidal cells. Basket cells are GABAergic interneurons that make synaptic contact with pyramidal cells as well as other interneurons. Basket cells can also generate both theta and gamma oscillations. Clozapine increases the power of theta and gamma EEG. Schizophrenic patients show reduced EEG power at 40 Hz (gamma frequency) but not at lower frequencies during auditory stimulation. The GABA(A) receptor blocker bicuculline at 10 nM, but not 10 microM, was reported to increase the amplitude of slow oscillations (< or =1 Hz) in rat hippocampal slices. It therefore seems possible that clozapine, by selectively blocking another GABA(A) receptor, could increase the amplitude of gamma oscillations.

FINDINGS

Twenty-six compounds that inhibit [35S]TBPS binding in ways that are reversible by 10 nM R-5135 were found to increase [3H]MUS binding to membranes prepared from rat whole forebrain. In almost all cases the increases in binding were due to increases in the number of binding sites with little effect on affinity (Kd) for [3H]MUS. Concentration-response curves for the compounds revealed maximum increases in [3H]MUS (Esat) binding ranging from 140% (for meclizine) to 313% of control for honokiol. Additivity experiments showed that propofol (44% above control) and diflunisal (50% above control) were almost entirely additive, but there was also a small, but significant overlap, suggesting the existence of three groups of [3H]MUS binding sites defined by propofol and diflunisal. Meclizine was entirely additive with both propofol and diflunisal, indicating the existence of a fourth [3H]MUS binding site. Alphaxalone is also completely additive with meclizine, and has an Esat value significantly larger than that for propofol + diflunisal suggesting a fifth [3H]MUS binding site. The Esat for mefenamate is significantly greater than the Esat for alphaxalone, and mefenamate is also completely additive with meclizine, suggesting the existence of a sixth [3H]MUS binding site. The Esat for magnolol is significantly greater then the Esat, for mefenamate, and the Esat for honokiol is greater than that for magnolol, suggesting, but not proving, the existence of a seventh and an eighth group of [3H]MUS binding sites. The binding of [3H]MUS alone, without enhancers may represent a ninth group of binding sites which is probably heterogeneous as indicated by the very low pseudo Hill coefficients for bicuculline and strychnine in displacing [3H]MUS without enhancer. Altogether, our results suggest the existence of more than 9 different [3H]MUS binding sites. Clozapine was a very weak overall displacer of [3H]MUS (IC50 = 280 microM). However, 5 microM clozapine reduced [3H]MUS binding 6% (P < 0.0001, n = 10) and significantly reduced [3H]MUS binding enhanced by propofol (approximately 14%) or clotrimazole (approximately 17%) but not 17 other compounds tested.

TENTATIVE CONCLUSIONS

In the absence of enhancers [3H]MUS may bind preferentially to GABA(A) receptors on pyramidal cells and less to interneurons in cerebral cortex. Conversely, [3H]flunitrazepam may bind preferentially to GABA(A) receptors (allosterically) on interneurons and less to pyramidal cells. Clozapine appears to selectively block a small fraction (10-20%) of [3H]MUS binding sites with an IC50 value in the low micromolar range. This fraction may be preferentially located on certain GABAergic interneurons (basket cells?) that make synaptic contact with pyramidal cells. The blockade of these GABA(A) receptors by clozapine would be expected to increase the firing rate of the interneurons and the release of GABA onto pyramidal cells. Such blockade would also increase the generation of gamma oscillations by the basket cells. Some of these interneurons appear to be destroyed selectively, probably during the second trimester of gestation by a non-paralytic polio virus, in individuals who wil

The potential role of fatty acids in attention-deficit/hyperactivity disorder

As currently defined, attention-deficit/hyperactivity disorder (ADHD) encompasses a broad constellation of behavioural and learning problems and its definition and diagnosis remain controversial. The aetiology of ADHD is acknowledged to be both complex and multifactorial. The proposal considered here is that at least some features of ADHD may reflect an underlying abnormality of fatty acid metabolism. Clinical and biochemical evidence is discussed which suggests that a functional deficiency of certain long-chain polyunsaturated fatty acids could contribute to many of the features associated with this condition. The implications in terms of fatty acid treatment proposals are also discussed; such a form of treatment is relatively safe compared to existing pharmacological interventions, although further studies are still needed in order to evaluate its potential efficacy in the management of ADHD symptoms.

Essential fatty acids, lipid membrane abnormalities, and the diagnosis and treatment of schizophrenia

Recent research suggests that deficient uptake or excessive breakdown of membrane phospholipids may be associated with schizophrenia. We review available clinical research on abnormalities in membrane fatty acid composition and metabolism in schizophrenia, and therapeutic trials of fatty acid in this disorder. All potentially relevant English-language articles were identified from the medical and psychiatric literature with the aid of computer searches using key words such as lipids, phospholipids, prostaglandins and schizophrenia. All studies which include human subjects are reviewed. Empirical studies related to membrane hypotheses of schizophrenia focus on: 1) assessment of prostaglandins (PG) and their essential fatty acid (EFA) precursors in the tissues of patients with schizophrenia; 2) evaluation of the niacin flush test as a possible diagnostic marker; 3) evaluation of phospholipase enzyme activity; 4) NMR spectroscopy studies of brain phospholipid metabolism; and 5) therapeutic trials of PG precursors for the treatment of schizophrenia. The most consistent clinical findings include red blood cell fatty acid membrane abnormalities, NMR spectroscopy evidence of increased phospholipid turnover and a therapeutic effect of omega-3 fatty acid supplementation of neuroleptic treatment in some schizophrenia patients. Studies of EFA metabolism have proved fruitful for generating and testing novel etiologic hypotheses and new therapeutic agents for schizophrenia. Greater attention to factors that influence tissue EFA levels such as diet, tobacco and alcohol are required to reconcile inconsistent findings. Treatment studies, although promising, require independent replication.

A gas chromatographic-mass spectral assay for the quantitative determination of oleamide in biological fluids

Oleamide is a putative endogenous sleep-inducing lipid which potently enhances currents mediated by GABAA and serotonin receptors. While a quantitative assay would aid in determining the role of oleamide in physiological processes, most of the available assays are lacking in sensitivity. We now describe a quantitative assay for measuring low nanogram amounts of oleamide in biological fluids using GC/MS in the selective ion-monitoring mode. The internal standard (13C18 oleamide) was added to known concentrations of oleamide, which were converted to the N-trimethylsilyl or N-tert-butyldimethylsilyl derivatives before analysis by GC/MS, yielding linear calibration curves over the range of 1-25 ng of oleamide when monitoring the m/z 338/356 fragments. Using this technique, oleamide levels were determined following solvent extraction of normal rat cerebrospinal fluid and plasma to be 44 and 9.9 ng/ml, respectively. This technique constitutes a sensitive and reliable method for determining low nanogram quantities of oleamide in biological fluids.

Tagetone modulates the coupling of flunitrazepam and GABA binding sites at GABAA receptor from chick brain membranes

The effects of tagetone on flunitrazepam (FNTZ) binding to synaptosomal membranes from chick brains in the presence and absence of allosteric modulations induced by gamma-aminobutyric acid (GABA) were investigated. Tagetone, at 50 micrograms/ml (final concentration), decreased the binding affinity of [3H]FNTZ to synaptosomal membranes form chick brain (Kd = 3.34 +/- 0.36 nM without tagetone and Kd,t = 5.86 +/- 0.86 nM with tagetone; p < 0.05, two tailed Student's t-test) without affecting maximal binding (Bmax = 488 +/- 24 fmoles/mg protein, and Bmax,t = 500 +/- 25 fmoles/mg protein in the absence and in the presence of tagetone respectively). The potency of GABA to stimulate [3H]FNTZ binding increased in the presence of tagetone (EC50 values were 2.78 and 1.12 microM with and without tagetone respectively). GABA was able to decrease merocyanine delta A570-610 values in a concentration dependent manner; half maximal effect was attained at a GABA concentration of 34 +/- 13 microM. Tagetone, at a concentration of 50 micrograms/ml and in the presence of GABA 30 microM or 60 microM, enhanced the ability of GABA alone on decreasing delta A570-610. Tagetone alone did not change delta A570-610 values. FNTZ, a well known GABA modulator, could also potentiate the effect of GABA. Theoretical calculations indicate that the effects on merocyanine delta A570-610 value are mainly exerted at the membrane potential level (delta psi m). The present results strongly suggest that tagetone affected the function of GABAA receptor in a complex way: on the one hand it impaired FNTZ binding: on the other hand tagetone improved both the coupling between FNTZ and GABA binding sites and it enhanced GABA-induced chloride permeability. Changes in the geometrical and electrostatic properties of the self-organized membrane structure may account for these effects of tagetone.

Dietary fish oil affects monoaminergic neurotransmission and behavior in rats

We studied the effects of a fish oil enriched diet on fatty acid composition of cerebral membranes and on several neurochemical and behavioral variables of monoaminergic function in rats. The frontal cortex, striatum, hippocampus and cerebellum were studied in rats fed fish oil (FPO, 50% salmon oil + 50% palm oil), which provided an (n-6)/(n-3) polyunsaturated fatty acid (PUFA) ratio of 0.14 versus 6. 19 in controls fed a diet containing a mixture of African peanut oil and rapeseed oil. In the FPO group compared to the control group, the major modifications in fatty acid composition of cerebral membranes included the following: higher levels in 22:6(n-3), lower levels in 20:4(n-6) and a significantly greater proportion of phosphatidylserine. Dopamine levels were 40% greater in the frontal cortex of rats fed FPO than from those fed the control diet. In this cerebral region there was also a reduction in monoamine oxidase B (MAO-B) activity and greater binding to dopamine D2 receptors. By contrast, a lower binding to dopamine D2 receptors (-7%) was observed in the striatum. Ambulatory activity was also reduced in FPO-fed rats, possibly related to observed changes in striatal dopaminergic receptors. This suggested that the level of (n-6) PUFA, which was considerably lower in the FPO diet than in the control diet, could act on locomotion through an effect on striatal dopaminergic function, whereas the high level of (n-3) PUFA could act on cortical dopaminergic function.

Anxiogenic-like effects of Tagetes minuta L essential oil on T-maze and tonic immobility behaviour in domestic chicks

In a first experiment, four doses (ranging between 0.04 and 0.45 mg/kg of body weight) of the essential oil from Tagetes minuta L. were subcutaneously injected in two-day-old chicks and a dose-response curve assessed for escape performance in a T-maze test. The 0.1, 0.25 and 0.45 mg/kg doses impaired the first escape performance suggesting an anxiogenic-like effect of the essential oil. After 3 h the same chicks were tested for a second escape performance, without being injected again, and no differences were observed compared to controls, suggesting that the essential oil did not affect retention. Furthermore, the effects of the essential oil were observed in the three sections of the T-maze apparatus. So, the performance was impaired in the isolation chamber section, suggesting the induction of increased anxiogenic behaviour, and also in the mirror section, suggesting that the social reinstatement behaviour was modified by an increased anxiety level. Changes in the principal corridor section were not observed, suggesting that the locomotor activity was not affected by these oil doses. The second escape performance was not affected in any of the T-maze sections, confirming that these doses did not affect learning ability. In a second experiment, a middle dose of the essential oil (0.25 mg/kg) increased the tonic immobility reaction in 15 days old chicks similarly to an anxiogenic dose of FG 7142 (1 mg/kg), while an anxiolytic dose of diazepam (0.08 mg/kg) did not affect this behaviour. Taken together, the present results suggest that the essential oil from Tagetes minuta L. may exert a negative modulation on the GABAergic function without affecting the learning ability.

Oleamide potentiates benzodiazepine-sensitive gamma-aminobutyric acid receptor activity but does not alter minimum alveolar anesthetic concentration

A naturally occurring brain lipid, cis-9,10-octadeceamide--oleamide (OA), is found in increased concentrations in the cerebrospinal fluid of sleep-deprived cats, which suggests that it may be an endogenous sleep-inducing substance. We studied the effects of this fatty-acid derivative on the function of cloned gamma-aminobutyric acid (GABA(A)) receptors expressed in Xenopus oocytes. Oocytes were injected with cRNA synthesized in vitro to express simple GABA(A) receptors (alpha1beta1, alpha3beta1, alpha5beta1, and alpha1beta2 subunit combinations) and receptors in which the GABA-induced chloride currents were potentiated in the presence of benzodiazepines (alpha1beta1gamma2s and alpha1beta2gamma2s subunit combinations). OA only produced significant potentiation of the peak Cl- current when applied with GABA to benzodiazepine-sensitive GABA(A) receptors. The peak currents of the simple GABA(A) receptors in the presence of OA were either unaffected or slightly inhibited by OA, but the overall mean currents were not significantly altered. Oleic acid was also capable of potentiating benzodiazepine-sensitive GABA(A) receptor function. The function of other ligand-gated ion channels, such as the N-methyl-D-aspartate receptor (NR1 + NR2A or 2C) and the 5-HT3 receptor expressed in Xenopus oocytes, were unaffected by OA. Sprague-Dawley rats receiving intraperitoneal injections of oleamide (10, 20, or 100 mg/kg) showed no change in the minimum alveolar anesthetic concentration (MAC) of desflurane required to abolish movement in response to noxious (tail clamp) stimulation (control MAC 6.48% +/- 1.28% atm; 100 mg/kg OA MAC 7.05% +/- 0.42% atm). These results reinforce the view that oleyl compounds may be natural modulators of inhibitory ion channel function, but that these effects contribute little to the central nervous system depression produced by volatile anesthetics as measured by MAC.

IMPLICATIONS

The putative sleep-inducing substance, oleamide, potentiates benzodiazepine-sensitive gamma-aminobutyric acid receptor function but does not alter desflurane minimum alveolar anesthetic concentration in rats.

A search for the metabolic signal that sensitizes lateral hypothalamic self-stimulation in food-restricted rats

Food deprivation and restriction increase the rewarding potency of food, drugs of abuse, and electrical brain stimulation. Based on evidence that the rewarding effects of these stimuli are mediated by the same neuronal circuitry, lateral hypothalamic self-stimulation (LHSS) was used to investigate the involvement of various metabolic signals in the sensitization of reward. In Experiment 1, glucoprivation with 2-deoxy-d-glucose (150 mg/kg, intraperitoneally (i.p.)) and lipoprivation with nicotinic acid (150 mg/kg, subcutaneously (s.c.)), individually and in combination, failed to affect the LHSS threshold in ad lib.-fed rats. These results suggest that signals associated with acute shortage of metabolic substrate do not sensitize reward. Because numerous responses to more prolonged negative energy balance are mediated by neuropeptide Y (NPY), the effect of exogenous neuropeptide Y upon LHSS was investigated in Experiment 2. Intraventricular infusion of orexigenic neuropeptide Y doses (2.0, 5.0, and 12.5 g), in ad lib.-fed rats, had no effect on LHSS threshold. In Experiment 3, other concomitants of prolonged negative energy balance--high circulating levels of free fatty acids (FFA) and beta-hydroxybutyrate (HDB)-were investigated. Nicotinic acid (250 mg/kg, s.c.), which suppressed serum HDB and FFA levels, had no effect on LHSS in food-restricted or ad lib.-fed rats. Mercaptoacetate (68.4 mg/kg, i.p.), which suppressed serum HDB levels and exacerbated the elevation of FFA levels, also had no effect. Thus, the brain reward system, if modulated by these substances, is not affected by transient, though marked, changes in their levels. To investigate the effect of a sustained increase in levels of FFA and HDB, a "ketogenic" diet was employed. Although this diet produced a fourfold increase in serum HDB levels, it had no effect on LHSS thresholds. Moreover, the failure of mercaptoacetate (68.4 mg/kg, i.p.) to decrease LHSS thresholds in these rats supports the conclusion that acute shortage of metabolic substrate does not sensitize reward. Other possible mechanisms of reward sensitization, including sustained decreases in circulating insulin and leptin and increases in corticosterone, are discussed.

Functional modulation of human recombinant gamma-aminobutyric acid type A receptor by docosahexaenoic acid

Human gamma-aminobutyric acid type A (GABAA) receptors were expressed in the baculovirus/Sf-9 insect cell expression system using recombinant cDNA of alpha1beta2gamma2s subunits. The effect of unsaturated fatty acids on GABAA receptor complexes was investigated electrophysiologically using conventional whole cell recording under voltage clamp. Three distinct effects of docosahexaenoic acid (DHA) on the GABA responses were observed. First, DHA, at a concentration of 10(-7) M or greater, accelerated the desensitization after the peak of the GABA-induced current. Second, DHA (10(-6) M) potentiated the peak amplitude of GABA response. This potentiation by DHA was inhibited in the presence of Zn2+ (10(-5) M); Cu2+ and Ni2+ mimicked the action of Zn2+. Zn2+ (10(-5) M) did not block the GABA response on alpha1beta2gamma2s receptor complexes. Third, DHA, at a concentration of 3 x 10(-6) M or higher, gradually suppressed the peak amplitude of GABA response. A protein kinase A inhibitor, a protein kinase C inhibitor, and a Ca2+ chelator did not modify the effects of DHA on GABA-induced chloride ion current. Six unsaturated fatty acids other than DHA were examined. Arachidonic acid mimicked the effect of DHA while e.g. oleic acid had no effect. The inhibition of the GABA response in the presence of DHA was also observed in cells expressing GABAA receptors of alpha1 and beta2 subunit combinations. The data show that the gamma subunit is essential for DHA and arachidonic acid to potentiate the GABA-induced Cl- channel activity and to affect the desensitization kinetics of the GABAA receptor.

The membrane phospholipid hypothesis as a biochemical basis for the neurodevelopmental concept of schizophrenia

The neurodevelopmental hypothesis of schizophrenia is becoming an important feature of research in the field. However, its major drawback is that it lacks any biochemical basis which might draw the diverse observations together. It is suggested that the membrane phospholipid hypothesis can provide such a biochemical basis and that the neurodevelopmental phospholipid concept offers a powerful paradigm to guide future research.

Cis-unsaturated free fatty acids block VIP-mediated GH and PRL secretion by perturbing the cAMP/protein kinase A pathway

Cis-unsaturated free fatty acids (FFA) like oleic acid are strong blockers of both basal and stimulated GH secretion in vivo by acting directly on the somatotroph cell. Several lines of evidence suggest that this inhibitory action is the result of a perturbation of the function of several plasma membrane integral proteins. It has been reported recently that cis-FFA are able to block several steps in the inositolphosphates/phospholipase C/Ca2+ (InsPs/PLC/Ca2+) signal transduction pathway triggered by the activation of the TRH receptor. In this paper we present evidence showing that the inhibition of growth hormone (GH) and prolactin (PRL) secretion by cis-FFA in vitro is also exerted at several different levels on the cAMP-protein kinase A (cAMP/PKA) pathway triggered by the stimulation of the vasoactive intestinal peptide (VIP) receptor in pituitary clonal cells. By means of a sequential analysis of signal transduction events, we observed that cis-unsaturated FFA; (1) reduce the activity of adenylate cyclase; (2) perturb the activity of protein kinase A; (3) suppress the VIP-triggered Ca2+ influx, and (4) do not perturb VIP binding or the homologous desensitization of the VIP receptor.

Calcium metabolism, osteoporosis and essential fatty acids: a review

Essential fatty acid (EFA)-deficient animals develop severe osteoporosis coupled with increased renal and arterial calcification. This picture is similar to that seen in osteoporosis in the elderly, where the loss of bone calcium is associated with ectopic calcification of other tissues, particularly the arteries and the kidneys. Recent mortality studies indicate that the ectopic calcification may be considerably more dangerous than the osteoporosis itself, since the great majority of excess deaths in women with osteoporosis are vascular and unrelated to fractures or other bone abnormalities. EFAs have now been shown to increase calcium absorption from the gut, in part by enhancing the effects of vitamin D, to reduce urinary excretion of calcium, to increase calcium deposition in bone and improve bone strength and to enhance the synthesis of bone collagen. These desirable actions are associated with reduced ectopic calcification. The interaction between EFA and calcium metabolism deserves further investigation since it may offer novel approaches to osteoporosis and also to the ectopic calcification associated with osteoporosis which seems to be responsible for so many deaths.

Endogenous synthesis cannot compensate for absence of dietary oleic acid in rats

It is important to know whether an organism is able to synthesize all the oleic acid it needs. To determine this, it is sufficient to feed animals a diet containing essential fatty acids but totally lacking oleic acid, and then determine whether tissue concentrations of fatty acids of the (n-9) series are altered due to insufficient endogenous synthesis of oleic acid from stearic acid. In fact, the effects of a total oleic acid deficiency have not previously been studied because all the vegetable oils used in human and animal nutrition contain this fatty acid in variable amounts. Thus, we fed rats semipurified diets whose lipids (triglycerides) were synthesized chemically. Female rats were fed the diets for 3 wk before mating, and their pups (fed the same diets) were killed when 21 and 60 d old. Generally speaking, oleic acid deficiency resulted in a lower level of this acid in the various organs examined (liver, kidney, testes, heart, muscle and sciatic nerve in 21-d-old rats and liver, kidney, heart, muscle and sciatic nerve in 60-d-old rats). Brain, myelin and nerve endings were not affected at either age. This lower level was accompanied by a higher level of 16:1(n-7) and, to a lesser extent, 18:1(n-7). Dietary supplementation with oleic acid (1666 mg/100 g diet) for up to 21 d resulted in normal levels of this fatty acid in some organs (liver, heart, sciatic nerve) but not in others (kidney, muscle, testes) and a decrease in 16:1(n-7), which returned to about the same levels as in the control group in all organs except liver. Adding small or large amounts of stearic acid to the oleic acid-deficient diet had little or no effect on oleic acid levels in the tissues. We conclude that rats (particularly in liver) do not have sufficient synthesizing potential to guarantee the normal fatty acid composition of certain organs if oleic acid is totally absent in the diet.

Characterisation of the furanocoumarin phellopterin as a rat brain benzodiazepine receptor partial agonist in vitro

Phellopterin, a naturally occurring furanocoumarin found in the roots of Angelica dahurica, inhibits [3H]diazepam and ethyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4] benzodiazepine-3-carboxylate ([3H]Ro 15-1788) binding to the benzodiazepine site of the rat brain gamma-aminobutyric acidA (GABAA) receptor in vitro with IC50 values of 400 and 680 nM, respectively. Two other naturally occurring furanocoumarins, byakangelicol and imperatorin were significantly less potent, with IC50 values for inhibition of [3H]diazepam binding of 8.0 and 12.3 microM, respectively. Scatchard plot analysis showed that the inhibitory activity of phellopterin was due to competitive inhibition of the benzodiazepine ligand binding. The results of GABA- and t-butylbicyclophosphorothionate (TBPS)-shift assays suggest that phellopterin is a partial agonist of the central benzodiazepine receptors in vitro.

Muscarinic, N-methyl-D-aspartate (NMDA) and benzodiazepine receptor binding sites in cortical membranes from amyotrophic lateral sclerosis patients

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder causing marked pathology in the motoneuron system. The pathophysiology of the selective degeneration of motor neurons in the disease is as yet unknown, but evidence suggests that excitotoxic mechanisms might be involved. The present study was undertaken to determine whether defects in neurotransmitter receptors are involved in the disease, analyzing uniformly sampled specimens from neocortex and motorcortex. The binding to benzodiazepine, muscarinic cholinergic, and NMDA receptors in ALS brains was compared to that in control brains, using a single radioligand concentration of [3H]Ro 15-1788, [3H]QNB and [3H]MK-801. The benzodiazepine and the muscarinic cholinergic receptor binding was unaffected in any cortical region from the ALS subjects compared to controls. NMDA receptor binding labeled by [3H]MK-801 was significantly increased in several neocortical regions in the ALS group compared to the control group. Scatchard analysis of [3H]MK-801 binding in frontal cortex revealed a single binding site with an unaltered maximal binding capacity but an increased binding affinity of the site in the ALS group compared to the controls. The generalized alteration in the affinity of the binding site for [3H]MK-801 in the ALS cortex may indicate a modification of the NMDA receptor due to different sensitivity for endogenous modulators or to a different subunit composition of the NMDA receptor in ALS with altered functional properties. These findings may reflect a pathophysiological phenomenon in ALS.

Schizophrenia as a membrane lipid disorder which is expressed throughout the body

Clinical, biochemical and genetic evidence now indicates that schizophrenia is a disorder of membrane phospholipid metabolism associated with increased loss of highly polyunsaturated fatty acids from membranes owing to enhanced activity of a phospholipase A2. This changes the properties of membranes throughout the body and is responsible for such physical abnormalities as reduced vasodilator responses to niacin and histamine and altered immunological functions. A modest membrane abnormality is likely to produce its most serious consequences in the brain, which requires the co-ordinated sequential and parallel activities of millions of neurons. The concept leads to testable proposals for relatively simple and safe treatment modalities.