Engineering of efficient panchromatic sensitizers for nanocrystalline TiO(2)-based solar cells

A new series of panchromatic ruthenium(II) sensitizers derived from carboxylated terpyridyl complexes of tris-thiocyanato Ru(II) have been developed. Black dye containing different degrees of protonation [(C(2)H(5))(3)NH][Ru(H(3)tcterpy)(NCS)(3)] 1, [(C(4)H(9))(4)N](2)[Ru(H(2)tcterpy)(NCS)(3)] 2, [(C(4)H(9))(4)N](3)[Ru(Htcterpy)(NCS)(3)] 3, and [(C(4)H(9))(4)N](4)[Ru(tcterpy)(NCS)(3)] 4 (tcterpy = 4,4',4' '-tricarboxy-2,2':6',2' '-terpyridine) have been synthesized and fully characterized by UV-vis, emission, IR, Raman, NMR, cyclic voltammetry, and X-ray diffraction studies. The crystal structure of complex 2 confirms the presence of a Ru(II)N6 central core derived from the terpyridine ligand and three N-bonded thiocyanates. Intermolecular H-bonding between carboxylates on neighboring terpyridines gives rise to 2-D H-bonded arrays. The absorption and emission maxima of the black dye show a bathochromic shift with decreasing pH and exhibit pH-dependent excited-state lifetimes. The red-shift of the emission maxima is due to better pi-acceptor properties of the acid form that lowers the energy of the CT excited state. The low-energy metal-to-ligand charge-transfer absorption band showed marked solvatochromism due to the presence of thiocyanate ligands. The Ru(II)/(III) oxidation potential of the black dye and the ligand-based reduction potential shifted cathodically with decreasing number of protons and showed more reversible character. The adsorption of complex 3 from methoxyacetonitrile solution onto transparent TiO(2) films was interpreted by a Langmuir isotherm yielding an adsorption equilibrium constant, K(ads), of (1.0 +/- 0.3) x 10(5) M(-1). The amount of dye adsorbed at monolayer saturation was (n(alpha) = 6.9 +/- 0.3) x 10(-)(8) mol/mg of TiO(2), which is around 30% less than that of the cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) complex. The black dye, when anchored to nanocrystalline TiO(2) films achieves very efficient sensitization over the whole visible range extending into the near-IR region up to 920 nm, yielding over 80% incident photon-to-current efficiencies (IPCE). Solar cells containing the black dye were subjected to analysis by a photovoltaic calibration laboratory (NREL, U.S.A.) to determine their solar-to-electric conversion efficiency under standard AM 1.5 sunlight. A short circuit photocurrent density obtained was 20.5 mA/cm(2), and the open circuit voltage was 0.72 V corresponding to an overall conversion efficiency of 10.4%.

Decrease in reelin and glutamic acid decarboxylase67 (GAD67) expression in schizophrenia and bipolar disorder: a postmortem brain study

BACKGROUND

Reelin (RELN) is a glycoprotein secreted preferentially by cortical gamma-aminobutyric acid-ergic (GABAergic) interneurons (layers I and II) that binds to integrin receptors located on dendritic spines of pyramidal neurons or on GABAergic interneurons of layers III through V expressing the disabled-1 gene product (DAB1), a cytosolic adaptor protein that mediates RELN action. To replicate earlier findings that RELN and glutamic acid decarboxylase (GAD)(67), but not DAB1 expression, are down-regulated in schizophrenic brains, and to verify whether other psychiatric disorders express similar deficits, we analyzed, blind, an entirely new cohort of 60 postmortem brains, including equal numbers of patients matched for schizophrenia, unipolar depression, and bipolar disorder with nonpsychiatric subjects.

METHODS

Reelin, GAD(65), GAD(67), DAB1, and neuron-specific-enolase messenger RNAs (mRNAs) and respective proteins were measured with quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) or Western blot analyses. Reelin-positive neurons were identified by immunohistochemistry using a monoclonal antibody.

RESULTS

Prefrontal cortex and cerebellar expression of RELN mRNA, GAD(67) protein and mRNA, and prefrontal cortex RELN-positive cells was significantly decreased by 30% to 50% in patients with schizophrenia or bipolar disorder with psychosis, but not in those with unipolar depression without psychosis when compared with nonpsychiatric subjects. Group differences were absent for DAB1,GAD(65) and neuron-specific-enolase expression implying that RELN and GAD(67) down-regulations were unrelated to neuronal damage. Reelin and GAD(67) were also unrelated to postmortem intervals, dose, duration, or presence of antipsychotic medication.

CONCLUSIONS

The selective down-regulation of RELN and GAD(67) in prefrontal cortex of patients with schizophrenia and bipolar disorder who have psychosis is consistent with the hypothesis that these parameters are vulnerability factors in psychosis; this plus the loss of the correlation between these 2 parameters that exists in nonpsychotic subjects support the hypothesis that these changes may be liability factors underlying psychosis.

Pharmacokinetics and pharmacodynamics of subcutaneous injection of long-acting human insulin analog glargine, NPH insulin, and ultralente human insulin and continuous subcutaneous infusion of insulin lispro

To compare the pharmacokinetics/dynamics of the long-acting insulin analog glargine with NPH, ultralente, and continuous subcutaneous (SC) infusion of insulin lispro (continuous subcutaneous insulin infusion [CSII]), 20 C-peptide-negative type 1 diabetic patients were studied on four occasions during an isoglycemic 24-h clamp. Patients received SC injection of either 0.3 U/kg glargine or NPH insulin (random sequence, crossover design). On two subsequent occasions, they received either an SC injection of ultralente (0.3 U/kg) or CSII (0.3 U x kg(-1) x 24 h(-1)) (random sequence, crossover design). After SC insulin injection or CSII, intravenous (IV) insulin was tapered, and glucose was infused to clamp plasma glucose at 130 mg/dl for 24 h. Onset of action (defined as reduction of IV insulin >50%) was earlier with NPH (0.8 +/- 0.2 h), CSII (0.5 +/- 0.1 h), and ultralente (1 +/- 0.2 h) versus glargine (1.5 +/- 0.3 h) (P < 0.05) (mean +/- SE). End of action (defined as an increase in plasma glucose >150 mg/dl) occurred later with glargine (22 +/- 4 h) than with NPH (14 +/- 3 h) (P < 0.05) but was similar with ultralente (20 +/- 6 h). NPH and ultralente exhibited a peak concentration and action (at 4.5 +/- 0.5 and 10.1 +/- 1 h, respectively) followed by waning, whereas glargine had no peak but had a flat concentration/action profile mimicking CSII. Interindividual variability (calculated as differences in SD of plasma insulin concentrations and glucose infusion rates in different treatments) was lower with glargine than with NPH and ultralente (P < 0.05) but was similar with glargine and CSII (NS). In conclusion, NPH and ultralente are both peak insulins. Duration of action of ultralente is greater, but intersubject variability is also greater than that of NPH. Glargine is a peakless insulin, it lasts nearly 24 h, it has lower intersubject variability than NPH and ultralente, and it closely mimics CSII, the gold standard of basal insulin replacement.

Increase in the cerebrospinal fluid content of neurosteroids in patients with unipolar major depression who are receiving fluoxetine or fluvoxamine

We recently reported that fluoxetine or paroxetine, two selective serotonin reuptake inhibitors (SSRIs), when administered to rats, increase the brain content of the neurosteroid 3alpha-hydroxy-5alpha-pregnane-20-one (3alpha5alpha-ALLO) without altering the brain content of other neurosteroids. ALLO (3alpha5alpha and 3alpha5beta isomers) binds with high affinity to various gamma-aminobutyric acid (GABA) receptor A subtypes and facilitates the action of GABA at these receptors. We hypothesized that the increase of ALLO brain content induced by treatment with SSRIs could contribute to alleviating the anxiety and dysphoria associated with the symptomatology of major unipolar depression. We measured ALLO content in four cisternal-lumbar fractions of cerebrospinal fluid (CSF) before and 8-10 weeks after treatment with fluoxetine or fluvoxamine in 15 patients with unipolar major depression. The concentration of ALLO ( approximately 40 fmol/ml in each CSF fraction of three control subjects) was about 60% lower in patients with major unipolar depression. However, in the same patients, fluoxetine or fluvoxamine treatment normalized the CSF ALLO content. Moreover, a statistically significant correlation (r = 0.58; P < 0.023; n = 15) existed between symptomatology improvement (Hamilton Rating Scale for Depression scores) and the increase in CSF ALLO after fluoxetine or fluvoxamine treatment. The CSF content of PREG and PROG remained unaltered after treatment and failed to correlate with the SSRI-induced increase of CSF ALLO. The normalization of CSF ALLO content in depressed patients appears to be sufficient to mediate the anxiolytic and antidysphoric actions of fluoxetine or fluvoxamine via its positive allosteric modulation of GABA type A receptors.

A decrease of reelin expression as a putative vulnerability factor in schizophrenia

Postmortem prefrontal cortices (PFC) (Brodmann's areas 10 and 46), temporal cortices (Brodmann's area 22), hippocampi, caudate nuclei, and cerebella of schizophrenia patients and their matched nonpsychiatric subjects were compared for reelin (RELN) mRNA and reelin (RELN) protein content. In all of the brain areas studied, RELN and its mRNA were significantly reduced (approximately 50%) in patients with schizophrenia; this decrease was similar in patients affected by undifferentiated or paranoid schizophrenia. To exclude possible artifacts caused by postmortem mRNA degradation, we measured the mRNAs in the same PFC extracts from gamma-aminobutyric acid (GABA)A receptors alpha1 and alpha5 and nicotinic acetylcholine receptor alpha7 subunits. Whereas the expression of the alpha7 nicotinic acetylcholine receptor subunit was normal, that of the alpha1 and alpha5 receptor subunits of GABAA was increased when schizophrenia was present. RELN mRNA was preferentially expressed in GABAergic interneurons of PFC, temporal cortex, hippocampus, and glutamatergic granule cells of cerebellum. A protein putatively functioning as an intracellular target for the signal-transduction cascade triggered by RELN protein released into the extracellular matrix is termed mouse disabled-1 (DAB1) and is expressed at comparable levels in the neuroplasm of the PFC and hippocampal pyramidal neurons, cerebellar Purkinje neurons of schizophrenia patients, and nonpsychiatric subjects; these three types of neurons do not express RELN protein. In the same samples of temporal cortex, we found a decrease in RELN protein of approximately 50% but no changes in DAB1 protein expression. We also observed a large (up to 70%) decrease of GAD67 but only a small decrease of GAD65 protein content. These findings are interpreted within a neurodevelopmental/vulnerability "two-hit" model for the etiology of schizophrenia.

Histamine-containing neurons in the rat hypothalamus

A specific antiserum against histamine was produced in rabbits, and an immunohistochemical study of histamine-containing cells was carried out in rat brain. The antiserum bound histamine in a standard radioimmunoassay and stained mast cells located in various rat and guinea pig tissues. Enterochromaffin-like cells in the stomach and neurons in the posterior hypothalamic area could be detected with this antiserum. The staining was highly specific and was not abolished by preabsorption with histidine, histidine-containing peptides, serotonin, or catecholamines, whereas preabsorption with histamine completely abolished the staining. Immunoglobulins of this antiserum purified by affinity chromatography stained the same cells as did the crude antiserum, whereas the serum fraction, which was not absorbed by histamine-affinity ligand, failed to stain any neuron. Histamine-immunoreactive neuronal cell bodies were found only in the hypothalamic and premammillary areas of colchicine-treated rats. The largest group of cells was seen in the caudal magnocellular nucleus and medially on the dorsal and ventral aspects of the ventral premammillary nucleus. Immunoreactive nerve fibers, but no cell bodies, were detected in other parts of the brain. Histamine-immunoreactive mast cells were found in the median eminence and pituitary gland. The results suggest that histamine-containing neurons are located only in a small area of the posterior hypothalamus, and these cells are probably the source of ascending and descending fibers detected in other brain areas.

Neurosteroids act on recombinant human GABAA receptors

The endogenous steroid metabolites 3 alpha,21dihydroxy-5 alpha-pregnan-20-one and 3 alpha-hydroxy-5 alpha-pregnan-20-one potentiate GABA-activated Cl- currents recorded from a human cell line transfected with the beta 1, alpha 1 beta 1, and alpha 1 beta 1 gamma 2 combinations of human GABAA receptor subunits. These steroids are active at nanomolar concentrations in potentiating GABA-activated Cl- currents and directly elicit bicuculline-sensitive Cl- currents when applied at micromolar concentrations. The potentiating and direct actions of both steroids were expressed with every combination of subunits tested. However, an examination of single-channel currents recorded from outside-out patches excised from these transfected cells suggests that despite the common minimal structural requirements for expressing steroid and barbiturate actions, the mechanism of GABAA receptor modulation by these pregnane steroids may differ from that of barbiturates.

Isolation, sequencing, synthesis, and pharmacological characterization of two brain neuropeptides that modulate the action of morphine

Two peptides that crossreact with an antiserum raised against Phe-Met-Arg-Phe-NH2 were purified from bovine brain extract. Their structures were determined to be Ala-Gly-Glu-Gly-Leu-Ser-Ser-Pro-Phe-Trp-Ser-Leu-Ala-Ala-Pro-Gln-Arg-Phe- NH2 and Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2. The sequences were determined by gas-phase sequencing, except for the COOH-terminal phenylalaninamides. These were assigned on the basis of the reactivity of the peptides with the anti-Phe-Met-Arg-Phe-NH2 antiserum, which appears to recognize the determinant -Arg-Phe-NH2. Both peptides were synthesized, and the synthetic peptides were found to have the same HPLC retention times as the endogenous Phe-Met-Arg-Phe-NH2-immunoreactive peptides, thus confirming the assignment of phenylalaninamide to the COOH-terminal positions. Both of the synthetic peptides were found to decrease tail-flick latency in rats, and the octapeptide was more active than the octadecapeptide. The octapeptide was found also to attenuate the prolongation of the tail-flick latency induced by morphine.

Isolation, characterization, and purification to homogeneity of an endogenous polypeptide with agonistic action on benzodiazepine receptors

A brain polypeptide termed diazepam-binding inhibitor (DBI) and thought to be chemically and functionally related to the endogenous effector of the benzodiazepine recognition site was purified to homogeneity. This peptide gives a single band of protein on NaDodSO4 and acidic urea gel electrophoresis. A single UV-absorbing peak was obtained by HPLC using three different columns and solvent systems. DBI has a molecular mass of approximately equal to 11,000 daltons. Carboxyl-terminus analysis shows that tyrosine is the only residue while the amino-terminus was blocked. Cyanogen bromide treatment of DBI yields three polypeptide fragments, and the sequences of two of them have been determined for a total of 45 amino acids. DBI is a competitive inhibitor for the binding of [3H]diazepam, [3H]flunitrazepam, beta-[3H]carboline propyl esters, and 3H-labeled Ro 15-1788. The Ki for [3H]-diazepam and beta-[3H]carboline binding were 4 and 1 microM, respectively. Doses of DBI that inhibited [3H]diazepam binding by greater than 50% fail to change [3H]etorphine, gamma-amino[3H]butyric acid, [3H]-quinuclidinyl benzilate, [3H]dihydroalprenolol, [3H]adenosine, and [3H]imipramine binding tested at their respective Kd values. DBI injected intraventricularly at doses of 5-10 nmol completely reversed the anticonflict action of diazepam on unpunished drinking and, similar to the anxiety-inducing beta-carboline derivative FG 7142 (beta-carboline-3-carboxylic acid methyl ester), facilitated the shock-induced suppression of drinking by lowering the threshold for this response.

Coupling of inositol phospholipid metabolism with excitatory amino acid recognition sites in rat hippocampus

Ibotenate, a rigid structural analogue of glutamate, markedly enhances the hydrolysis of membrane inositol phospholipids, as reflected by the stimulation of [3H]inositol monophosphate formation in rat hippocampal slices prelabeled with [3H]inositol and treated with Li+. Quisqualate, homocysteate, L-glutamate, and L-aspartate also induce a significant (albeit weaker) increase in [3H]inositol monophosphate formation, whereas N-methyl-D-aspartate, kainate, quinolinate, and N-acetylaspartylglutamate are inactive. The increase in [3H]inositol monophosphate formation elicited by the above-mentioned excitatory amino acids is potently and selectively antagonized by DL-2-amino-4-phosphonobutyric acid, a dicarboxylic amino acid receptor antagonist. These results suggest that, in the hippocampus, a class of dicarboxylic amino acid recognition sites is coupled with phospholipase C, the enzyme that catalyzes the hydrolysis of membrane inositol phospholipids.

Lesions of central norepinephrine terminals with 6-OH-dopamine: biochemistry and fine structure

Intracisternal injections of 6-hydroxydopamine produce rapid and long-lasting depletion of brain catecholamines without effects on serotonin concentrations. Depletion of norepinephrine is greatest in areas containing only nerve terminals and axons and least in areas containing monoamine cell bodies. The norepinephrine loss is accompanied by electron microscopic evidence of nerve terminal degeneration and decreased turnover. Dopamine loss is less marked and is not accompanied by degeneration or alteration of turnover rate.

Reelin is preferentially expressed in neurons synthesizing gamma-aminobutyric acid in cortex and hippocampus of adult rats

During embryonic development of brain laminated structures, the protein Reelin, secreted into the extracellular matrix of the cortex and hippocampus by Cajal-Retzius (CR) cells located in the marginal zone, contributes to the regulation of migration and positioning of cortical and hippocampal neurons that do not synthesize Reelin. Soon after birth, the CR cells decrease, and they virtually disappear during the following 3 weeks. Despite their disappearance, we can quantify Reelin mRNA (approximately 200 amol/ g of total RNA) and visualize it by in situ hybridization, and we detect the translated product of this mRNA by immunocytochemistry preferentially in gamma-aminobutyric acid (GABA)ergic neurons of adult rat cortex and hippocampus. In adult rat cerebellum, Reelin is expressed in glutamatergic neurons (granule cells). The translated product of this mRNA is readily exported from the granule cell somata to the parallel fibers, where it has been detected by electron microscopy in axon terminals located presynaptically to Purkinje cell dendrites.

An epigenetic mouse model for molecular and behavioral neuropathologies related to schizophrenia vulnerability

Reelin and glutamic acid decarboxylase (GAD)67 expressed by cortical gamma-aminobutyric acid-ergic interneurons are down-regulated in schizophrenia. Because epidemiological studies of schizophrenia fail to support candidate gene haploinsufficiency of Mendelian origin, we hypothesize that epigenetic mechanisms (i.e., cytosine hypermethylation of CpG islands present in the promoter of these genes) may be responsible for this down-regulation. Protracted l-methionine (6.6 mmolkg for 15 days, twice a day) treatment in mice elicited in brain an increase of S-adenosyl-homocysteine, the processing product of the methyl donor S-adenosyl-methionine, and a marked decrease of reelin and GAD67 mRNAs in both WT and heterozygous reeler mice. This effect of l-methionine was associated with an increase in the number of methylated cytosines in the CpG island of the reelin promoter region. This effect was not observed for GAD65 or neuronal-specific enolase and was not replicated by glycine doses 2-fold greater than those of l-methionine. Prepulse inhibition of startle declined at a faster rate as the prepulsestartle interval increased in mice receiving l-methionine. Valproic acid (2 mmolkg for 15 days, twice a day) reverted l-methionine-induced down-regulation of reelin and GAD67 in both WT and heterozygous reeler mice, suggesting an epigenetic action through the inhibition of histone deacetylases. The same dose of valproate increased acetylation of histone H3 in mouse brain nearly 4-fold. This epigenetic mouse model may be useful in evaluating drug efficacy on schizophrenia vulnerability. Hence the inhibition of histone deacetylases could represent a pharmacological intervention mitigating epigenetically induced vulnerability to schizophrenia in individuals at risk.

Fluoxetine-elicited changes in brain neurosteroid content measured by negative ion mass fragmentography

Fluoxetine administered intraperitoneally to sham-operated or adrenalectomized/castrated (ADX/CX) male rats dose-dependently (2.9-58 mumol/kg i.p.) increased the brain content of the neurosteroid 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone, 3 alpha, 5 alpha-TH PROG). The increase of brain 3 alpha, 5 alpha-TH PROG content elicited by 58 mumol/kg fluoxetine lasted more than 2 hr and the range of its extent was comparable in sham-operated (approximately 3-10 pmol/g) and ADX/CX rats (2-9 pmol/g) and was associated with a decrease (from 2.8 to 1.1 pmol/g) in the 5 alpha-pregnan-3,20-dione (5 alpha-dihydroprogesterone, 5 alpha-DH PROG) content. The pregnenolone, progesterone, and dehydroepiandrosterone content failed to change in rats receiving fluoxetine. The extent of 3 alpha, 5 alpha-TH PROG accumulation elicited by fluoxetine treatment differed in various brain regions, with the highest increase occurring in the olfactory bulb. Importantly, fluoxetine failed to change the 3 alpha, 5 alpha-TH PROG levels in plasma, which in ADX/CX rats were at least two orders of magnitude lower than in the brain. Two other serotonin re-uptake inhibitors, paroxetine and imipramine, in doses equipotent to those of fluoxetine in inhibiting brain serotonin uptake, were either significantly less potent than fluoxetine (paroxetine) or failed to increase (imipramine) 3 alpha, 5 alpha-TH PROG brain content. The addition of 10 microM of 5 alpha-DH PROG to brain slices of ADX/CX rats preincubated with fluoxetine (10 microM, 15 min) elicited an accumulation of 3 alpha, 5 alpha-TH PROG greater than in slices preincubated with vehicle. A fluoxetine stimulation of brain 3 alpha, 5 alpha-TH PROG biosynthesis might be operative in the anxiolytic and antidysphoric actions of this drug.

Gangliosides prevent glutamate and kainate neurotoxicity in primary neuronal cultures of neonatal rat cerebellum and cortex

Using a sensitive histofluorescence staining method that allows for a quantitation of neuronal death, we compared the protective effects of gangliosides (a group of naturally occurring glycosphingolipids), phencyclidine (PCP), and MK-801 (dibenzocyclohepteneimine) on glutamate- and kainate-induced neuronal death in primary cultures of cortical and cerebellar neurons prepared from neonatal rats. PCP and MK-801 block neurotoxicity induced by glutamate doses 50 times higher than the LD50 (LD50 in Mg2+-free medium, 10 microM) but only partially block the kainate neurotoxicity (LD50 in presence of Mg2+, 100 microM). In contrast, pretreatment with gangliosides (GT1b greater than GD1b greater than GM1) results in complete and insurmountable protection against the neurotoxicity elicited by glutamate or kainate. In primary cultures of cerebellar granule cells gangliosides, unlike PCP and MK-801, fail to block glutamate-gated cationic currents and the glutamate-evoked increase of (i) inositol phospholipid hydrolysis (ii) c-fos mRNA content, and (iii) nuclear accumulation of c-fos protein. Protection of glutamate neurotoxicity by gangliosides does not require their presence in the incubation medium; however, it is proportional to the amount of glycosphingolipid accumulated in the neuronal membranes. The ganglioside concentration (30-60 microM) that blocks glutamate-elicited neuronal death also prevents glutamate- and kainate-induced protein kinase C translocation from cytosol to neuronal membranes.

Diazepam binding inhibitor (DBI): a peptide with multiple biological actions

Diazepam binding inhibitor (DBI) is a 9-kD polypeptide that was first isolated in 1983 from rat brain by monitoring its ability to displace diazepam from the benzodiazepine (BZD) recognition site located on the extracellular domain of the type A receptor for gamma-aminobutyric acid (GABAA receptor) and from the mitochondrial BZD receptor (MBR) located on the outer mitochondrial membrane. In brain, DBI and its two major processing products [DBI 33-50, or octadecaneuropeptide (ODN) and DBI 17-50, or triakontatetraneuropeptide (TTN)] are unevenly distributed in neurons, with the highest concentrations of DBI (10 to 50 microMs) being present in the hypothalamus, amygdala, cerebellum, and discrete areas of the thalamus, hippocampus, and cortex. DBI is also present in specialized glial cells (astroglia and Bergmann glia) and in peripheral tissues. In the periphery, the highest concentration of DBI occurs in cells of the zona glomerulosa and fasciculata of the adrenal cortex and in Leydig cells of the testis; interestingly, these are the same cell types in which MBRs are highly concentrated. Stimulation of MBRs by appropriate ligands (including DBI and TTN) facilitates cholesterol influx into mitochondria and the subsequent formation of pregnenolone, the parent molecule for endogenous steroid production; this facilitation occurs not only in peripheral steroidogenic tissues, but also in glial cells, the steroidogenic cells of the brain. Some of the steroids (pregnenolone sulfate, dehydroepiandrosterone sulfate, 3 alpha-hydroxy-5 alpha-pregnan-20-one, and 3 alpha, 21-dihydroxy-5 alpha-pregnan-20-one) produced in brain (neurosteroids) function as potent (with effects in the nanomolar concentration range) positive or negative allosteric modulators of GABAA receptor function. Thus, accumulating evidence suggests that the various neurobiological actions of DBI and its processing products may be attributable to the ability of these peptides either to bind to BZD recognition sites associated with GABAA receptors or to bind to glial cell MBRs and modulate the rate and quality of neurosteroidogenesis. The neurobiological effects of DBI and its processing products in physiological and pathological conditions (hepatic encephlopaty, depression, panic) concentrations may therefore be explained by interactions with different types of BZD recognition site. In addition, recent reports that DBI and some of its fragments inhibit (in nanomolar concentrations) glucose-induced insulin release from pancreatic islets and bind acyl-coenzyme A with high affinity support the hypothesis that DBI isa precursor of biologically active peptides with multiple actions in the brain and in peripheral tissues.

An efficient photoelectric X-ray polarimeter for the study of black holes and neutron stars

The study of astronomical objects using electromagnetic radiation involves four basic observational approaches: imaging, spectroscopy, photometry (accurate counting of the photons received) and polarimetry (measurement of the polarizations of the observed photons). In contrast to observations at other wavelengths, a lack of sensitivity has prevented X-ray astronomy from making use of polarimetry. Yet such a technique could provide a direct picture of the state of matter in extreme magnetic and gravitational fields, and has the potential to resolve the internal structures of compact sources that would otherwise remain inaccessible, even to X-ray interferometry. In binary pulsars, for example, we could directly 'see' the rotation of the magnetic field and determine if the emission is in the form of a 'fan' or a 'pencil' beam. Also, observation of the characteristic twisting of the polarization angle in other compact sources would reveal the presence of a black hole. Here we report the development of an instrument that makes X-ray polarimetry possible. The factor of 100 improvement in sensitivity that we have achieved will allow direct exploration of the most dramatic objects of the X-ray sky.

Brain 5alpha-dihydroprogesterone and allopregnanolone synthesis in a mouse model of protracted social isolation

Allopregnanolone (ALLO), is a brain endogenous neurosteroid that binds with high affinity to gamma-aminobutyric acid type A (GABA(A)) receptors and positively modulates the action of GABA at these receptors. Unlike ALLO, 5alpha-dihydroprogesterone (5alpha-DHP) binds with high affinity to intracellular progesterone receptors that regulate DNA transcription. To investigate the physiological roles of ALLO and 5alpha-DHP synthesized in brain, we have adopted a mouse model involving protracted social isolation. In the frontal cortex of mice, socially isolated for 6 weeks, both neurosteroids were decreased by approximately 50%. After administration of (17beta)-17-(bis-1-methyl amino carbonyl) androstane-3,5-diene-3-carboxylic acid (SKF105,111), an inhibitor of the enzyme (5alpha-reductase Type I and II) that converts progesterone into 5alpha-DHP, the ALLO and 5alpha-DHP content of frontal cortex of both group-housed and socially isolated mice decreased exponentially to 10%-20% of control values in about 30 min. The fractional rate constants (k h(-1)) of ALLO and 5alpha-DHP decline multiplied by the ALLO and 5alpha-DHP concentrations at any given steady-state estimate the rate of synthesis required to maintain that steady state. After 6 weeks of social isolation, ALLO and 5alpha-DHP biosynthesis rates were decreased to 30% of the values calculated in group-housed mice. Moreover, in socially isolated mice, the expression of 5alpha-reductase Type I mRNA and protein was approximately 50% lower than in group-housed mice whereas 3alpha-hydroxysteroid oxidoreductase mRNA expression was equal in the two groups. Protracted social isolation in mice may provide a model to investigate whether 5alpha-DHP by a genomic action, and ALLO by a nongenomic mechanism down-regulate the action of drugs acting as agonists, partial agonists, or positive allosteric modulators of the benzodiazepine recognition sites expressed by GABA(A) receptors.

Dopamine-sensitive adenylate cyclase: location in substantia nigra

A dopamine-sensitive adenylate cyclase with characteristics similar to those measured in the striatum is present in the rat substantia nigra. Destruction of dopamine cell bodies by intranigral 6-hydroxydopamine application failed to abolish the response of nigral adenylate cyclase to dopamine. In contrast, brain hemitransection between the striatum and substantia nigra, or a more circumscribed lesion of striatonigral pathways, abolished the dopamine stimulation of adenylate cyclase in the substantia nigra. These results suggest that dopamine receptors within the substantia nigra are not located on dopamine cell bodies but are associated with a pathway, containing gamma-aminobutyric acid or substance P, which projects from forebrain structures to the substantia nigra.