An analytical model for nanoparticles concentration resulting from infusion into poroelastic brain tissue.

We consider the infusion of a diluted suspension of nanoparticles (NPs) into poroelastic brain tissue, in view of relevant biomedical applications such as intratumoral thermotherapy. Indeed, the high impact of the related pathologies motivates the development of advanced therapeutic approaches, whose design also benefits from theoretical models. This study provides an analytical expression for the time-dependent NPs concentration during the infusion into poroelastic brain tissue, which also accounts for particle binding onto cells (by recalling relevant results from the colloid filtration theory). Our model is computationally inexpensive and, compared to fully numerical approaches, permits to explicitly elucidate the role of the involved physical aspects (tissue poroelasticity, infusion parameters, NPs physico-chemical properties, NP-tissue interactions underlying binding). We also present illustrative results based on parameters taken from the literature, by considering clinically relevant ranges for the infusion parameters. Moreover, we thoroughly assess the model working assumptions besides discussing its limitations. While not laying any claims of generality, our model can be used to support the development of more ambitious numerical approaches, towards the preliminary design of novel therapies based on NPs infusion into brain tissue.

On the preliminary design of hyperthermia treatments based on infusion and heating of magnetic nanofluids.

We study a magnetic-nanoparticle-mediated hyperthermia treatment by considering both the nanofluid infusion and the subsequent thermal activation of the infused nanoparticles. Our study aims at providing a quantitative framework, which is currently missing, for the design of hyperthermia treatments. In more detail, we consider a heterogeneous spherical tumor, and we obtain a simplified analytical expression for the nanoparticles concentration profile during the infusion. We then exploit such an expression in order to compute the steady-state temperature profile achieved through the heating step. Despite the simplifications introduced to enable the analytical derivations, we account for many physically relevant aspects including tissue heterogeneity, poroelasticity, blood perfusion, and nanoparticles absorption onto tissue. Moreover, our approach permits to elucidate the effects on the final temperature profile of the following control parameters: infusion duration and flow rate, nanoparticles concentration in the nanofluid, magnetic field intensity and frequency. We present illustrative numerical results, based on parameters values taken from experimental studies, which are consistent with previous numerical investigations and current hyperthermia approaches. In particular, we obtain optimal working curves which could be effectively used for planning real procedures. While not laying any claims of generality, this work takes a preliminary yet quantitative step toward the design of hyperthermia treatments.

Osmotic actuation modelling for innovative biorobotic solutions inspired by the plant kingdom.

Osmotic-driven plant movements are widely recognized as impressive examples of energy efficiency and low power consumption. These aspects motivate the interest in developing an original biomimetic concept of new actuators based on the osmotic principle exploited by plants. This study takes a preliminary step in this direction, by modelling the dynamic behaviour of two exemplificative yet relevant implementations of an osmotic actuator concept. In more detail, the considered implementations differ from each other in the way actuation energy storage is achieved (through a piston displacement in the former case, through membrane bulging in the latter). The dynamic problem is analytically solved for both cases; scaling laws for the actuation figures of merit (namely characteristic time, maximum force, maximum power, power density, cumulated work and energy density) as a function of model parameters are obtained for the bulging implementation. Starting from such performance indicators, a preliminary dimensioning of the envisaged osmotic actuator is exemplified, based on design targets/constraints (such as characteristic time and/or maximum force). Moreover, model assumptions and limitations are discussed towards effective prototypical development and experimental testing. Nonetheless, this study takes the first step towards the design of new actuators based on the natural osmotic principle, which holds potential for disruptive innovation in many fields, including biorobotics and ICT solutions.

Neuroactive steroids as modulators of depression and anxiety.

Certain neuroactive steroids modulate ligand-gated ion channels via non-genomic mechanisms. Especially 3alpha-reduced pregnane steroids are potent positive allosteric modulators of the GABA type A-receptor. During major depression there is a dysequilibrium of 3alpha-reduced neuroactive steroids, which is corrected by clinically effective pharmacological treatment. To investigate whether these alterations are a general principle of successful antidepressant treatment we studied the impact of non-pharmacological treatment options on neuroactive steroid concentrations during major depression. Neither partial sleep deprivation, transcranial magnetic stimulation nor electroconvulsive therapy affected neuroactive steroid levels irrespectively of the response to these treatments. These studies suggest that the changes in neuroactive steroids observed after antidepressant pharmacotherapy more likely reflect distinct pharmacological properties of antidepressants rather than the clinical response. In patients with panic disorder changes in neuroactive steroid composition have been observed opposite of those seen in depression. These changes may represent counterregulatory mechanisms against the occurrence of spontaneous panic attacks. However, during experimental panic induction with either cholecystokinin-tetrapeptide or sodium lactate there was a pronounced decline in the concentrations of 3alpha-reduced neuroactive steroids in patients with panic disorder, which might result in a decreased GABAergic tone. In contrast, no changes in neuroactive steroid concentrations could be observed in healthy controls with the exception of 3alpha, 5alpha-tetrahydrodeoxycorticosterone, allotetrahydrodeoxycorticosterone. The modulation of GABA type A-receptors by neuroactive steroids might contribute to the pathophysiology of depression and anxiety disorders and might offer new targets for the development of novel anxiolytic compounds.

Influence of mirtazapine on plasma concentrations of neuroactive steroids in major depression and on 3alpha-hydroxysteroid dehydrogenase activity.

Concentrations of 3alpha-reduced neuroactive steroids are altered in depression and normalize after antidepressant pharmacotherapy with selective serotonin re-uptake inhibitors (SSRIs). We investigated the impact of mirtazapine on the activity of a key neurosteroidogenic enzyme, the 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD), and on the levels of neuroactive steroids in relation to clinical response. A total of 23 drug-free in-patients suffering from a major depressive episode (DSM-IV criteria) underwent 5-week treatment with mirtazapine (45 mg/day). Plasma samples were taken weekly at 0800 and quantified for neuroactive steroids by means of combined gas chromatography/mass spectrometry analysis. Enzyme activity was determined by assessment of steroid conversion rates. Irrespective of clinical outcome, there were significant increases in 3alpha,5alpha-tetrahydroprogesterone, 3alpha,5beta-tetrahydroprogesterone, 5alpha-dihydroprogesterone, and 5beta-dihydroprogesterone after mirtazapine treatment, whereas 3beta,5alpha-tetrahydroprogesterone levels were significantly decreased. In vitro investigations demonstrated a dose-dependent inhibitory effect of mirtazapine on the activity of the microsomal 3alpha-HSD in the oxidative direction (conversion of 3alpha,5alpha-tetrahydroprogesterone to 5alpha-dihydroprogesterone). Mirtazapine affects neuroactive steroid composition similarly as do SSRIs. The inhibition of the oxidative pathway catalyzed by the microsomal 3alpha-HSD is compatible with an enhanced formation of 3alpha-reduced neuroactive steroids. However, the changes in neuroactive steroid concentrations more likely reflect direct pharmacological effects of this antidepressant rather than clinical improvement in general.

Decreased plasma and cerebrospinal fluid content of neuroactive steroids in Parkinson's disease.

The levels of the neuroactive steroids allopregnanolone (THP) and 5alpha-dihydroprogesterone (DHP) were quantified in the plasma of 11 (group 1) and in the liquor of 12 (group 2) Parkinson's disease (PD) patients using a gas-chromatographic/mass-spectrometric method. When compared with controls, both groups showed a significant decrease in DHP and THP concentrations. These decreases could be a useful marker of PD. Moreover, in view of the importance of GABA-ergic transmission to substantia nigra (SN) neurons and GABA-ergic modulation exerted by the two neuroactive steroids, our data indicate a global dysregulation of the SN GABA-ergic system in PD patients. Moreover, a lack of neuroprotective factors (i. e., GDNF, BDNF), promoted by DHP, may contribute to dopaminergic cell death.

GABA(A) receptor active steroids are altered in epilepsy patients with tuberous sclerosis.

BACKGROUND: The neuroactive steroid 3alpha, 5alpha-tetrahydroprogesterone is the most potent endogenous positive modulator of gamma-amino-butyric acid (GABA)(A) receptors. There is evidence for a relation between neuroactive steroids and seizure susceptibility. OBJECTIVE: To evaluate the putative role of counteregulator neuroactive steroids in the occurrence of seizures in patients with tuberous sclerosis. METHODS: Plasma concentrations of the enantiomers 3alpha, 5alpha- and 3alpha, 5beta-tetrahydroprogesterone (3alpha(s)-THP), which are positive modulators of GABA(A) receptors, were measured in 18 patients, along with their endogenous functional antagonists 3beta, 5alpha- and 3beta, 5beta-THP (3beta(s)-THP), to assess their possible modification compared with control subjects. Neuroactive steroids were assayed using a highly sensitive and specific gas chromatographic/mass spectrometric method. RESULTS: In the tuberous sclerosis patients with poorly controlled seizures, there was a significantly lower 3alpha(s)/3beta(s)-THP ratio than in seizure-free patients or control subjects. CONCLUSIONS: The reduced 3alpha(s)/3beta(s)-THP ratio may decrease GABAergic tone, contributing to the appearance of seizures in tuberous sclerosis patients with epilepsy.

Neuroactive steroids: molecular mechanisms of action and implications for neuropsychopharmacology.

Besides their binding to cognate intracellular receptors gonadal steroids may also act as functional antagonists at the 5-HT3 receptor. A structure-activity relationship for the actions of a variety of steroids at the 5-HT3 receptor was elaborated that differed considerably from that known for GABA(A) receptors. Steroids appear to interact allosterically with ligand-gated ion channels at the receptor membrane interface. The functional antagonism of gonadal steroids at the 5-HT3 receptor may play a role for the development and course of nausea during pregnancy and of psychiatric disorders. Moreover, we could demonstrate that 3alpha-reduced neuroactive steroids concurrently modulate the GABA(A) receptor and regulate gene expression via the progesterone receptor after intracellular oxidation. Animal studies showed that progesterone is converted rapidly into GABAergic neuroactive steroids in vivo. Progesterone reduces locomotor activity in a dose dependent fashion in male Wister rats. Moreover, progesterone and 3alpha,5alpha-tetrahydroprogesterone produce a benzodiazepine-like sleep EEG profile in rats and humans. In addition, there is a dysequilibrium of such 3alpha-reduced neuroactive steroids during major depression which is corrected by successful treatment with antidepressants. Neuroactive steroids may further be involved in the treatment of depression and anxiety with antidepressants in patients during ethanol withdrawal. First studies in patients with panic disorder suggest that neuroactive steroids may also play a pivotal role in human anxiety. The genomic and non-genomic effects of steroids in the brain contribute to the pathophysiology of psychiatric disorders and the mechanisms of action of antidepressants. Neuroactive steroids affect a broad spectrum of behavioral functions through their unique molecular properties and may constitute a yet unexploited class of drugs.

The clinical role of computerized EEG in the evaluation and treatment of learning and attention disorders in children and adolescents.

Quantitative EEG (QEEG) can play an important role in the evaluation and treatment of children and adolescents with attention deficit and learning disorders. Children with learning disorders are a heterogeneous population with QEEG abnormality in 25% to 45% of reported cases. EEG slowing is the most common abnormal finding, and the nature of the QEEG abnormality may be related to future academic performance. Children with attention disorders are a more homogeneous population, with QEEG abnormalities in up to 80%. In this population, frontal/polar regions are most likely to show deviations from normal development, with the thalamocortical and/or septal-hippocampal pathways most likely to be disturbed. QEEG shows high sensitivity and specificity for distinguishing normal children and children with learning disorders and attention disorders from each other and may provide useful information for determining the likelihood that children with attention problems will respond to treatment with stimulant medication.

Invariant reversible QEEG effects of anesthetics.

Continuous recordings of brain electrical activity were obtained from a group of 176 patients throughout surgical procedures using general anesthesia. Artifact-free data from the 19 electrodes of the International 10/20 System were subjected to quantitative analysis of the electroencephalogram (QEEG). Induction was variously accomplished with etomidate, propofol or thiopental. Anesthesia was maintained throughout the procedures by isoflurane, desflurane or sevoflurane (N = 68), total intravenous anesthesia using propofol (N = 49), or nitrous oxide plus narcotics (N = 59). A set of QEEG measures were found which reversibly displayed high heterogeneity of variance between four states as follows: (1) during induction; (2) just after loss of consciousness (LOC); (3) just before return of consciousness (ROC); (4) just after ROC. Homogeneity of variance across all agents within states was found. Topographic statistical probability images were compared between states. At LOC, power increased in all frequency bands in the power spectrum with the exception of a decrease in gamma activity, and there was a marked anteriorization of power. Additionally, a significant change occurred in hemispheric relationships, with prefrontal and frontal regions of each hemisphere becoming more closely coupled, and anterior and posterior regions on each hemisphere, as well as homologous regions between the two hemispheres, uncoupling. All of these changes reversed upon ROC. Variable resolution electromagnetic tomography (VARETA) was performed to localize salient features of power anteriorization in three dimensions. A common set of neuroanatomical regions appeared to be the locus of the most probable generators of the observed EEG changes.

Increased behavioral neurosteroid sensitivity in a rat line selectively bred for high alcohol sensitivity.

Acute administration of a neurosteroid 5beta-pregnan-3alpha-ol-20-one induced a greater impairment in motor performance of the selectively bred alcohol-sensitive (ANT) than alcohol-insensitive (AT) rats. This difference was not associated with the sensitivity of gamma-aminobutyrate type A (GABA(A)) receptors, as 5alpha-pregnan-3alpha-ol-20-one (allopregnanolone) decreased the autoradiographic signals of t-butylbicyclophosphoro[35S]thionate binding to GABA(A) receptor-associated ionophores more in the brain sections of AT than ANT rats. Nor was the difference associated with baseline levels of neuroactive progesterone metabolites, as 5alpha-pregnan-3,20-dione (5alpha-DHP) and 5alpha-pregnan-3alpha-ol-20-one were lower in the ANT rats. After ethanol (2 g/kg, i.p.) administration and the subsequent motor performance test, the increased brain concentrations of these metabolites were still lower in the ANT than AT rats, although especially in the cerebellum the relative increases were greater in the ANT than AT rats. The present data suggest that the mechanisms mediating neurosteroid-induced motor impairment are susceptible to genetic variation in rat lines selected for differences in ethanol intoxication.

Fluoxetine decreases concentrations of 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone (THDOC) in major depression.

There is evidence for a differential alteration in the concentrations of 3 alpha-reduced neuroactive steroids in major depression. Because it has been suggested that fluoxetine may shift the activity of the 3 alpha-hydroxysteroid oxidoreductase towards the reductive direction, treatment of major depression may be accompanied by a further increase in plasma 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone (THDOC) concentration. We studied eight male depressed patients before and after treatment with fluoxetine and compared them to healthy age-matched control subjects. Blood samples were quantified for 3 alpha, 5 alpha-tetrahydroprogesterone, 3 alpha,5 beta-tetrahydroprogesterone (THP) and THDOC by means of a highly sensitive combined gas chromatography/mass spectrometry analysis. Compared to control subjects, concentrations of THDOC were higher in depressed patients and decreased after fluoxetine treatment. In contrast, THP concentrations were lower in depressed patients and increased after fluoxetine treatment. Our results give further evidence for a disequilibrium of 3 alpha-reduced neuroactive steroids in major depression, which is normalized by treatment with fluoxetine.

Increased neurosteroids synthesis after brain and spinal cord injury in rats.

We studied the effect of brain and spinal cord injury induced by fluid-percussion on the local synthesis of neurosteroids as measured by a gas-chromatographic/mass-spectrometric method. In the nervous system of sham operated rats i.v. infusion of pregnenolone (PREGN)-sulfate results in a 2-4 fold increase in PREGN, progesterone (PROG), 5alpha-dehydroprogesterone (5alpha-DHP) and 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha5alpha-THP, allopregnanolone) concentrations, as compared to vehicle treated rats. When PREGN-sulfate was infused 1, 3 or 7 days after brain or spinal cord injury it was observed a large time-dependent increase of PROG, 5alpha-DHP and 3alpha5alpha-THP levels in the peri-focal but not in the focal site. This increase in neurosteroids content may be due essentially to the glial cells hyperplasia in the peri-focal area and to an activation of the pathways involved in the metabolism of PREGN-sulfate to PROG, 5alpha-DHP and 3alpha5alpha-THP.

Effects of fluoxetine, indomethacine and placebo on 3 alpha, 5 alpha tetrahydroprogesterone (THP) plasma levels in uncomplicated alcohol withdrawal.

OBJECTIVE: The purpose of this study was to investigate the effects of fluoxetine (F) and indomethacine (I), two drugs that regulate the synthesis of the GABAergic neurosteroid 3 alpha, 5 alpha tetrahydroprogesterone (allopregnanolone, THP) on THP plasma levels and on symptoms of anxiety and depression in alcoholics during ethanol withdrawal. METHOD: Patients who met DSM-IV criteria for alcohol abuse were randomly assigned to treatment with F (40 mg/day) plus misoprostol (M) (500 mg/day) or I (100 mg/day) plus M or placebo (PL) plus M. Patients were rated with the Hamilton Anxiety (14-HAS) and Depression (17-HDS) scales on days 1, 5, 7, 15 and 28 of ethanol withdrawal and with a Visual Analogue Scale for Depression (VASD) and a Visual Analogue Scale for Anxiety (VASA) on days 1, 2, 4, 5, 7, 15 and 28 of withdrawal. On the same days a plasma sample was collected to measure the concentrations of THP by means of a very sensitive gas chromatographic mass spectrometric method. RESULTS: During withdrawal at days 1, 2, 4 and 5, THP plasma values were lower and symptoms of anxiety and depression were significantly higher compared to the late withdrawal phase at days 15 and 28. In the F or I treatment, the depression and anxiety score, measured by VASD and VASA, decreased significantly at day 5-7 whereas THP plasma levels significantly increased compared to PL condition CONCLUSIONS: Treatment of alcohol withdrawal either with F or I reduced the extent of anxiety and depression and normalised THP plasma levels that were decreased during withdrawal.

Concentrations of 3 alpha-reduced neuroactive steroids and their precursors in plasma of patients with major depression and after clinical recovery.

BACKGROUND: There is preclinical and clinical evidence that plasma concentrations of 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-tetrahydroprogesterone; 3 alpha,5 alpha-THP), a neuroactive steroid that is a positive allosteric modulator of the GABAA receptor, are altered in depression and normalize as a result of antidepressant treatment. However, no data are available on the concentrations of 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-tetrahydrodeoxycorticosterone; 3 alpha,5 alpha-THDOC), another GABA ergic neuroactive steroid, in depression. METHODS: We studied nine depressed patients before and after treatment with various antidepressants and compared them to healthy matched control subjects. Blood samples were quantified by means of a highly sensitive combined gas chromatography/mass spectrometry analysis. RESULTS: Compared to control subjects, plasma concentrations of 3 alpha,5 alpha-THDOC and its precursor 5 alpha-dihydrodeoxycorticosterone (5 alpha-DHDOC) were increased in depressed patients and were not significantly influenced by antidepressant treatment. However, 3 alpha,5 alpha-THP plasma concentrations were decreased in depression and clinically effective antidepressant treatment was accompanied by an increase of 3 alpha,5 alpha-THP concentrations in these patients. CONCLUSIONS: Our results provide the first evidence for a differential alteration in the plasma concentrations of the 3 alpha-reduced neuroactive steroids 3 alpha,5 alpha-THDOC and 3 alpha,5 alpha-THP in major depression, which is only partially reversed by successful antidepressant treatment.

Neuroactive steroid concentrations following metyrapone administration in depressed patients and healthy volunteers.

BACKGROUND: There is evidence that treatment with the 11 beta-hydroxylase inhibitor metyrapone may represent an alternative treatment strategy in major depression. As a consequence of inhibition of cortisol synthesis the overdrive of corticotropin leads to an accumulation of precursor steroids. However, the effects of metyrapone on the concentrations of endogenous neuroactive steroids that modulate ion channels, e.g., the GABAA receptor, have not yet been studied systematically. METHODS: Therefore, we quantified the concentrations of an array of neuroactive steroids following administration of 1.5 g metyrapone before and after pretreatment with 1 mg dexamethasone in 19 patients suffering from severe depression in comparison to 13 healthy controls by means of a highly sensitive gas chromatography/mass spectrometry analysis. RESULTS: The administration of metyrapone induced a pronounced increase in all neuroactive steroids studied both in patients and controls that was prevented by dexamethasone pretreatment. CONCLUSIONS: Thus, the psychotropic properties of endogenous neuroactive steroids may contribute to the antidepressant properties of metyrapone in the treatment of major depression.

Effects of antidepressant treatment on neuroactive steroids in major depression.

OBJECTIVE: There is evidence from animal studies that fluoxetine may enhance the concentrations of neuroactive steroids. Therefore, the authors investigated whether clinically effective treatment with antidepressants may alter the concentrations of neuroactive steroids in patients suffering from a major depressive episode. METHOD: In the first study, eight drug-naive outpatients with major depression were studied during treatment with fluoxetine. In a complementary study, 11 inpatients with major depression were studied during a severe depressive episode and after recovery following treatment with different antidepressants. Plasma samples were quantified for neuroactive steroids by means of a highly sensitive and specific combined gas chromatography/mass spectrometry analysis. RESULTS: During depression, there was a significant decrease in 3 alpha, 5 alpha-tetrahydroprogesterone (3 alpha, 5 alpha-THP) and 3 alpha, 5 beta-THP concentrations, both of which are positive modulators of the gamma-aminobutyric acidA receptor, and a concomitant increase in 3 beta, 5 alpha-THP levels. This dysequilibrium of neuroactive steroids could be corrected by treatment with different antidepressants. CONCLUSIONS: These results provide the first clinical evidence of a possible role of neuroactive steroids in successful antidepressant therapy.

Allopregnanolone affects sleep in a benzodiazepine-like fashion.

Recent research in rats and humans has shown that exogenous progesterone evokes a sleep profile similar to that induced by agonistic modulators of gamma-aminobutyric acid(A) receptors, such as benzodiazepines. This finding suggests the involvement of the neuroactive metabolite of progesterone, allopregnanolone. In the vehicle-controlled study reported here, we assessed the sleep effects of two doses of allopregnanolone (7.5 and 15 mg/kg), mixed with oil, administered intraperitoneally at light onset in 8 rats. The electroencephalogram (EEG) and electromyogram were recorded during the first 6 postinjection hr. Compared with vehicle, both doses of allopregnanolone reduced the latency to non-rapid eye movement sleep (non-REMS) and 15 mg/kg allopregnanolone significantly increased the time spent in pre-REMS, an intermediate state between non-REMS and REMS. Furthermore, allopregnanolone dose-dependently influenced EEG activity during non-REMS and REMS. In non-REMS, EEG activity was decreased in the lower frequencies (< or =7 Hz) and enhanced in the frequencies of > or =13 Hz. In REMS, allopregnanolone enhanced high-frequency EEG activity (> or =17 Hz). The effects were most pronounced during the first postinjection hours and gradually diminished thereafter. Analysis of the plasma and brain concentrations of allopregnanolone in 45 rats revealed long-lasting increases, which reached maximal levels during the first postinjection hour. The sleep effects of allopregnanolone are very similar to those elicited by larger doses of progesterone, which produce comparable brain levels of allopregnanolone. These data indicate that the steroid allopregnanolone has benzodiazepine-like effects on sleep.