Medical therapies for mood disorders alter the blood-brain barrier

Blood-brain barrier permeability and electroconvulsive therapy: a systematic review

OBJECTIVE

The cause of cognitive side effects after electroconvulsive therapy (ECT) is largely unknown. Alterations in the blood-brain barrier (BBB) have been considered in several recent ECT studies. We therefore found it worthwhile to perform a systematic review of the literature to examine if electrically induced seizures affect the permeability of the BBB.

METHODS

PubMed/MEDLINE and Embase were searched 16 November 2022. Studies with a direct measurement of BBB permeability in animals treated with modified electroconvulsive stimulation (ECS) and in humans treated with ECT were included. Synthesis of results was narrative due to the low number of studies and differences in study designs.

RESULTS

Four animal and two human (31 participants) studies were included. In animals, two studies found increased BBB permeability to some smaller molecules after modified ECS, while the two other studies found marginally increased or unchanged permeability to albumin after treatment. In contrast, the human studies did not find increased BBB permeability to smaller molecules or albumin after ECT.

CONCLUSION

Animal but not human studies support increased BBB permeability to some smaller molecules after electrically induced seizures. However, this conclusion is confined by the low number of studies and the lack of studies applying state-of-the-art methods. More studies using modern approaches to measuring of BBB permeability are warranted.

FUNDING AND REGISTRATION

The study was founded by Mental Health Services in the Capital Region of Denmark (grant number 61151-05) and was registered on PROSPERO before data extraction was initiated (CRD42022331385).

Association Between Estimated Geocoded Residential Maternal Exposure to Lithium in Drinking Water and Risk for Autism Spectrum Disorder in Offspring in Denmark

Importance

Lithium is a naturally occurring and trace element that has mood-stabilizing effects. Maternal therapeutic use of lithium has been associated with adverse birth outcomes. In animal models, lithium modulates Wnt/β-catenin signaling that is important for neurodevelopment. It is unknown whether exposure to lithium in drinking water affects brain health in early life.

Objective

To evaluate whether autism spectrum disorder (ASD) in offspring is associated with maternal exposure to lithium in drinking water during pregnancy.

Design, Setting, and Participants

This nationwide population-based case-control study in Denmark identified 8842 children diagnosed with ASD born from 2000 through 2013 and 43 864 control participants matched by birth year and sex from the Danish Medical Birth Registry. These data were analyzed from March 2021 through November 2022.

Exposures

Geocoded maternal residential addresses during pregnancy were linked to lithium level (range, 0.6 to 30.7 μg/L) in drinking water estimated using kriging interpolation based on 151 waterworks measurements of lithium across all regions in Denmark.

Main Outcomes and Measures

ASD diagnoses were ascertained using International Statistical Classification of Diseases and Related Health Problems, Tenth Revision codes recorded in the Danish Psychiatric Central Register. The study team estimated odds ratios (ORs) and 95% CIs for ASD according to estimated geocoded maternal exposure to natural source of lithium in drinking water as a continuous (per IQR) or a categorical (quartile) variable, adjusting for sociodemographic factors and ambient air pollutants levels. The study team also conducted stratified analyses by birth years, child's sex, and urbanicity.

Results

A total of 8842 participants with ASD (male, 7009 [79.3%]) and 43 864 control participants (male, 34 749 [79.2%]) were studied. Every IQR increase in estimated geocoded maternal exposure to natural source of lithium in drinking water was associated with higher odds for ASD in offspring (OR, 1.23; 95% CI, 1.17-1.29). Elevated odds among offspring for ASD were estimated starting from the second quartile (7.36 to 12.67 μg/L) of estimated maternal exposure to drinking water with lithium and the OR for the highest quartile (more than 16.78 μg/L) compared with the reference group (less than 7.39 μg/L) was 1.46 (95% CI, 1.35-1.59). The associations were unchanged when adjusting for air pollution exposures and no differences were apparent in stratified analyses.

Conclusions and Relevance

Estimated maternal prenatal exposure to lithium from naturally occurring drinking water sources in Denmark was associated with an increased ASD risk in the offspring. This study suggests that naturally occurring lithium in drinking water may be a novel environmental risk factor for ASD development that requires further scrutiny.

How an Understanding of the Function of the Locus Coeruleus Led to Use of Dexmedetomidine to Treat Agitation in Bipolar Disorder: Example of Rational Development of Psychiatric Medications

This column reviews >50 years of research on the functions subsumed by the locus coeruleus (LC) (also called the central adrenergic system). A major role of the LC is monitoring acid-base balance in the brain and responding by regulating blood-brain permeability to water and other small molecules and cerebral blood flow. The LC, through its downward projections, also regulates and coordinates respiratory and cardiac functions. Through its effect regionally or more globally depending on the stimulus and its magnitude, the LC can regulate the extracellular space in the brain, which in turn can alter ionic concentrations and thus the sensitivity of neurons to signaling. As a result of these far-reaching effects, the LC has been implicated in brain functions ranging from sleep and wakefulness to psychiatric conditions such as hyperarousal/hypervigilance, fear, agitation, anxiety, and panic attacks. This understanding of the brain functions subsumed by the LC has, in turn, led to the most recent development in the use of dexmedetomidine, an alpha-2 adrenergic agonist, to treat agitation in patients with bipolar disorder. This column also illustrates a theme discussed in a series of previous columns concerning the successful development of novel psychiatric/central nervous system drugs on the basis of an understanding of relatively simple circuits or mechanisms that underlie pathologic behavior.

Locus Coeruleus and neurovascular unit: From its role in physiology to its potential role in Alzheimer's disease pathogenesis

Locus coeruleus (LC) is the main noradrenergic (NA) nucleus of the central nervous system. LC degenerates early during Alzheimer's disease (AD) and NA loss might concur to AD pathogenesis. Aside from neurons, LC terminals provide dense innervation of brain intraparenchymal arterioles/capillaries, and NA modulates astrocyte functions. The term neurovascular unit (NVU) defines the strict anatomical/functional interaction occurring between neurons, glial cells, and brain vessels. NVU plays a fundamental role in coupling the energy demand of activated brain regions with regional cerebral blood flow, it includes the blood-brain barrier (BBB), plays an active role in neuroinflammation, and participates also to the glymphatic system. NVU alteration is involved in AD pathophysiology through several mechanisms, mainly related to a relative oligoemia in activated brain regions and impairment of structural and functional BBB integrity, which contributes also to the intracerebral accumulation of insoluble amyloid. We review the existing data on the morphological features of LC-NA innervation of the NVU, as well as its contribution to neurovascular coupling and BBB proper functioning. After introducing the main experimental data linking LC with AD, which have repeatedly shown a key role of neuroinflammation and increased amyloid plaque formation, we discuss the potential mechanisms by which the loss of NVU modulation by LC might contribute to AD pathogenesis. Surprisingly, thus far not so many studies have tested directly these mechanisms in models of AD in which LC has been lesioned experimentally. Clarifying the interaction of LC with NVU in AD pathogenesis may disclose potential therapeutic targets for AD.

A double-blind randomized study comparing plasma level-targeted dose imipramine and high-dose venlafaxine in depressed inpatients

OBJECTIVE

To compare the efficacy of plasma level-targeted dose imipramine and high-dose venlafaxine in depressed inpatients in a randomized double-blind study.

METHODS

The study included 85 patients with a diagnosis of major depressive episode according to the DSM IV criteria and a 17-item Hamilton Rating Scale for Depression (HAM-D) score ≥ 17. Patients were randomized to imipramine or venlafaxine. The dose of imipramine was adjusted for each patient to a predefined blood level of 200-300 ng/ml. The dose of venlafaxine was increased gradually to 300-375 mg/day. Efficacy was evaluated after 7 weeks of treatment.

RESULTS

The mean age of the study group was 54.5 (range 29-82) years. There was no significant difference according to the primary outcome criterion of a ≥50% reduction on the HAM-D score: 17 of 43 (39.5%) patients on imipramine were responders compared to 21 of 42 (50%) patients on venlafaxine. When considering remission as outcome criterion (HAM-D score ≤ 7), 10 of 43 (23.3%) patients on imipramine were remitters compared to 15 of 42 (35.7%) patients on venlafaxine; again, no significant difference. When analysing a subpopulation of patients without psychotic features, with remission as outcome criterion, a significant difference was found: 5 of 34 (14.7%) patients on imipramine were remitters compared to 12 of 31 (38.7%) patients on venlafaxine.

CONCLUSIONS

The present study used optimal doses in depressed inpatients and showed that venlafaxine is at least equal in efficacy to imipramine. The results in the subgroup without psychotic features indicate a possible superiority of venlafaxine.

Blood-brain barrier studies with special reference to epileptic seizures

A review is given of the structure and function of the blood-brain barrier (BBB) with special reference to the situation during and after epileptic seizures including electroconvulsive therapy (ECT). Based on the literature describing different models of epilepsy the development of the theories concerning the early observations of a BBB dysfunction in connection with seizure activity is given, and gross morphology, ultrastructural and dynamic findings are briefly reviewed.

Pharmacokinetics of DGAVP in plasma following intranasal and oral administration to healthy subjects

A pharmacokinetic study was carried out to assess the bioavailability of desglycinamide-[Arg8]vasopressin (DGAVP, Org 5667). DGAVP (2 mg) was administered both intranasally and orally to healthy subjects with a treatment interval of 1 week. Blood samples were taken regularly between 15 min before and 210 min after administration and were assayed for DGAVP by radioimmunoassay. In all subjects endogenous vasopressin (AVP) levels were detectable. Peak levels of DGAVP occurred at 15 min after both treatments. The mean absorption half-life was 8.7 and 7.3 min and the mean elimination half-life was 38 and 34.6 min for the intranasal and oral route of administration, respectively. The bioavailability of orally administered DGAVP was low compared with the intranasally administered drug; the relative bioavailability of oral/nasal administration was 0.7%. The results indicate that DGAVP is absorbed rapidly after both oral and intranasal administration, but the intranasal route of administration of DGAVP is 100 times more effective in increasing plasma DGAVP levels.

Blood-brain barrier transfer of L-Trp and alpha-MTrp in Li-treated rats

Blood-brain barrier (BBB) transport for L-Trp and alpha-methyl-L-tryptophan was evaluated in Li-treated rats. Five different brain areas as well as left to right differences were examined. No left to right difference in the PS product was observed. Lithium treatment had a significant effect on the plasma concentration of Val, Leu and Ile but no effect on plasma total or free Trp. The ratio of plasma Trp to the sum of Leu, Val, Ile, Phe, Met and Tyr is increased in the Li-treated rats but not significantly. However, the ratio of Trp/(Val+Leu+Ile) is significantly increased in the Li-treated rats. The Km apparent (Kmapp) for the BBB Trp transport is significantly decreased (affinity of the carrier for Trp is increased) in the Li-treated rats. A decrease in the Kmapp is one of the possible factors responsible for an increase in the brain Trp concentration and subsequent increase in the brain serotonin synthesis in Li-treated rats.

Blood-CSF barrier permeability and central nervous system immunoglobulin G in schizophrenia

The ratio of albumin in cerebrospinal fluid (CSF) to serum may serve as an index of the integrity of the blood-CSF barrier, with increases in this ratio indicating increased permeability. The ratio of immunoglobulin G (IgG) in CSF to serum (divided by the albumin ratio to correct for variance in blood-CSF permeability) represents an index of the endogenous production of IgG in the central nervous system (CNS), with increases reflecting a possible infectious and/or autoimmune process stimulating central IgG synthesis. We analyzed simultaneously collected CSF and serum samples from 46 schizophrenic subjects, 8 of whom were studied both on and off neuroleptic treatment, and samples from 20 normal controls. The data indicated increases in CSF/serum albumin ratios or CSF/serum IgG indices in 22% and 20%, respectively, of the schizophrenic patients. Only 3 patients showed elevations in both indices. Comparison of values on and off neuroleptics indicated no significant effect of neuroleptics on these indices.

Quantitative in vivo receptor binding. IV: Detection of muscarinic receptor down-regulation by equilibrium and by tracer kinetic methods

Newly-developed methods for estimation of in vivo binding to neurotransmitter receptors should enable the detection and quantification of physiologic or pathologic changes in receptor numbers. In the present study, both equilibrium and kinetic experimental strategies for in vivo muscarinic receptor determination were applied to the detection of receptor changes induced by chronic inhibition of acetylcholinesterase in the rat. Following one week of treatment, in vitro receptor autoradiography utilizing [3H]scopolamine revealed significant losses of muscarinic binding in the cerebral cortex, hippocampus, striatum and in cranial nerve motor nuclei. The in vivo distribution of [3H]scopolamine, following infusion to approach equilibrium binding in the brain, revealed reductions in binding which paralleled the pattern and magnitude of changes detected in vitro. A simplified tracer kinetic estimation following bolus injection of the ligand also detected substantial reductions in forebrain muscarinic receptor binding. These results indicate the feasibility of detecting receptor changes underlying neuropathologic conditions in vivo, and suggest that either equilibrium or kinetic experimental approaches may be extended to clinical research applications with the use of positron or single-photon emission tomography.

Relationship between observed NMR changes and brain water content following electroconvulsive stimulation in the rat

The administration of electroconvulsive stimuli to anaesthetised rats results in changes in the relaxation times and water content of grey and white matter, but not in mid brain, hind brain or cerebellum. White matter changes occur in both T1 and T2, are biphasic in character and related to water content. Grey matter changes are confined to T1 and water content only. It is suggested that these changes are related to altered compartmentalisation of water, manifesting in a different manner in the two tissues probably due to their different cellular and biochemical composition.

MRI gradient fields increase brain mannitol space

Following nephrectomy and intravenous injection of tritiated mannitol, adult male rats were exposed to magnetic resonance imaging (MRI) procedures at 1.5 T, 0.5 T, and 0.3 T. Compared to rats similarly handled but not exposed to MRI procedures, brain mannitol concentration, expressed as a percentage of mean body concentration, was significantly increased at 0.3 T and 0.5 T but not at 1.5 T. At 0.3 T, exposure to gradient-field fluctuations used for imaging increased brain mannitol concentration, but exposures to static main field and pulsed radiofrequency energies did not. Increased brain mannitol associated with gradient-field flux may reflect increased blood-brain barrier permeability or blood volume in brain. MRI effects on brain mannitol space are of uncertain clinical significance, but are consistent with prior evidence of an MRI-induced increase of brain capillary endothelial cell transport observed with horseradish peroxidase. Further studies are needed to confirm these findings and to explore the processes underlying changes in mannitol distribution related to MRI.

Interactions between the blood-brain barrier and endogenous peptides: emerging clinical implications

The effects of peptides on brain function suggest therapeutic and pathologic roles for these substances. Many peptides cross the blood-brain barrier (BBB) by transmembrane diffusion as a function of their lipid solubilities. Other peptides, such as the enkephalins, Tyr-MIF-1, vasopressin-related peptides, and peptide T-like peptides, are transported by carrier-mediated systems. Passage is influenced by aging, stress, lighting, drugs, amino acids, and neurotoxins. Disruption of the BBB results in complex changes in the blood and CSF levels of peptides. Peptides influence the passage of glucose, amino acids, and inorganic acids and may affect the integrity of the BBB. Peptide-BBB interactions have been suggested to play direct roles in dialysis dementia and maple syrup urine disease; they may be expected to be involved in other disorders of the CNS.

Alterations by antidepressants of cerebrospinal fluid formation and calcium distribution dynamics in the intact rat brain

The formation of cerebrospinal fluid (CSF) after chronic treatment with imipramine (IMI), lithium (Li), or electroshock (EST) was studied in urethane-anesthetized rats by ventricular-cisternal perfusion with 14C-inulin. Effects of these treatments on the removal of 45Ca from the cerebroventricular perfusate were also studied. The mean value for CSF formation in control rats was 2.6 +/- 0.2 microliters/min. EST and IMI both increased CSF formation significantly (+38% and +19%, respectively). Li caused a significant decrease (-19%). Endogenous removal of 45Ca was by bulk CSF absorption to blood and by uptake to brain. In control animals, the uptake by brain accounted for 42% of the total endogenous removal at the steady state. Each of the applied treatments resulted in a significant decrease in the fraction of 45Ca taken up by the brain (EST 26%, IMI 33%, Li 29%). Thus, although chronic EST or IMI resulted in an effect opposite to that obtained by Li on CSF formation, all three treatments appear to act similarly in reducing calcium passage from the cerebroventricular compartment to brain tissue.

Penetration of DGAVP (Org 5667) across the blood-brain barrier in human subjects

To assess the penetration of desglycinamide-arginine-vasopressin (DGAVP, Org 5667) to the central nervous system, levels of DGAVP were measured in the lumbar CSF after peripheral administration. DGAVP (2 mg) was administered intranasally to 37 patients and CSF samples were collected from these patients 5 to 240 minutes later. Detectable levels of DGAVP in CSF could be found 5 minutes after administration, but levels declined rapidly during the next 90 minutes. The DGAVP levels in CSF correlated with plasma levels of DGAVP (r=0.586, p less than 0.001). According to these results, DGAVP may gain access to the central nervous system and may induce central effects.

Blood-brain barrier in Alzheimer dementia and in non-demented elderly. An immunocytochemical study

Peroxidase-antiperoxidase staining of formalin-fixed brain was employed to compare the blood-brain barrier (BBB) function in five patients with Alzheimer's disease/senile dementia of the Alzheimer type (AD/SDAT) and three patients with AD/SDAT combined with multi-infarct dementia (MID/SDAT) with that of six non-demented aged controls. The diffusion of serum proteins through the BBB was visualized with antisera to albumin, prealbumin, immunoglobulin, C1q, C3c and to fibrinogen. A similar patterns of diffusion was seen in AD/SDAT and non-demented aged individuals. Neuron and glial cells were stained with different antisera in the vicinity of the diffusion. Senile (neuritic) plaques were occasionally visualized with antisera to IgG, C1q and C3c but not with antisera to albumin, prealbumin and fibrinogen in both demented and non-demented aged individuals. Neurofibrillary tangles were not labelled with any of the antisera studied. These results indicate that the BBB is compromised equally in AD/SDAT and in the non-demented elderly.

Carrier-mediated transport of vasopressin across the blood-brain barrier of the mouse

A brain to blood carrier-mediated transport system for arginine vasopressin (AVP) was investigated in mice after intraventricular injection of iodinated AVP and varying amounts of unlabeled material or candidate inhibitors. Residual activity in the brain detected after decapitation was used as the main determinant of transport activity. The half-time disappearance of iodinated AVP from the brain was 12.4 min, the Vmax was 1.41 nmol/g-min, and the apparent Km was 28.7 nmol/g. A 30-nmol dose of AVP, mesotocin, arginine vasotocin, pressinoic amide, pressinoic acid, tocinoic acid, and lysine vasotocin, but not oxytocin, lysine vasopressin, AVP free acid, tocinoic amide, Tyr-MIF-1, or cyclo Leu-Gly, significantly (P less than 0.05) inhibited the transport of iodinated AVP out of the brain. The 30 nmol dose of AVP had no effect on the transport of iodide or iodotyrosine out of the brain. High-performance liquid chromatography showed that 59.2% of the radioactivity found in the blood 2 min after an i.c.v. injection of labeled AVP eluted at the same position as labeled AVP compared with 68.8% of radioactivity eluting at that position after material was infused i.v. for 2 min. This indicates that intact peptide is transported across the blood-brain barrier and that most of the degradation of AVP occurs during circulation in the blood. Calculations based on the appearance of radioactivity in the periphery showed that 56.2% of the material injected centrally would have been transported into the periphery by 10 min. This appearance of material in the periphery was inhibited by the simultaneous injection of an excess of unlabeled peptide. Water loading significantly decreased the brain to blood transport rate of AVP by 40%. It is concluded that a saturable system exists for brain to blood transport of AVP and some structurally similar peptides.

Tolerance to the anticonvulsant effect of clonazepam in mice: no concurrent change in plasma concentration

Clonazepam was administered for 10 or more days on three different dose regimens (0.5, 0.25 and 0.08 mg kg-1 twice daily) to mice given pentetrazol by slow intravenous infusion. Plasma concentrations of clonazepam were assayed by high performance liquid chromatography. Tolerance developed to the anticonvulsant effect of clonazepam at all doses but was incomplete and could be overcome by increasing the dose. With the 0.5 and 0.25 mg kg-1 regimens there was no significant change in the drug plasma concentrations during development of tolerance; on the lowest dose, levels were below the limits of accurate detection. Anticonvulsant tolerance does not seem to be the result of a disturbance in clonazepam metabolism.

Effect of altered blood plasma osmolalities on regional brain amino acid concentrations and focal seizure susceptibility in the rat

Blood plasma hypo- or hyperosmolality alters significantly the concentration of some amino acids in brain tissues of the medial septum and hippocampus of adult Sprague-Dawley rats. With some notable exceptions, brain amino acid concentrations decreased under hypoosmotic conditions and increased under hyperosmotic conditions. Osmotic changes and brain amino acid changes appear to be related to each other in an almost linear fashion. A comparison of rats and toads indicates that the patterns of changes in brain amino acid concentrations in response to a hypoosmotic plasma osmolality were almost identical for both species. Changes achievable under hyperosmotic conditions were considerably greater in toads. When rats with kindled epileptogenic foci were made hypoosmotic by water-loading, seizure thresholds decreased dramatically. Our data suggest a possible relationship between the hypoosmotically induced biochemical changes in brain tissues (especially some amino acid neurotransmitters and neurotransmitter precursors) and the hypoosmotically induced increase in seizure susceptibility.

Amitriptyline normalizes tetrabenazine-induced changes in cerebral microcirculation

The cerebromicrocirculation in the tetrabenzaine (TBZ) model of depression has been found to be abnormal with respect to (1) responsiveness of cerebral blood flow to increases in arterial CO2 content and (2) the effective permeability of the blood-brain barrier to water. Development of these abnormalities temporally paralleled the behavioral disturbances and catecholamine depletion induced by TBZ. These TBZ-induced changes occurred globally throughout the brain, being apparent in the forebrain, cerebellum, and medulla-pons. Pretreatment with the antidepressant amitriptyline prevented both behavioral and physiological effects of TBZ, whereas amitriptyline administered after TBZ was less effective. The results suggest that an important action of tricyclic antidepressants may be cerebromicrocirculatory effects.

Neuronal control of brain microvessel function

Cerebral capillary endothelium forms a barrier limiting and controlling the movement of ions and solutes between blood and brain. Recent anatomical, physiological and biochemical studies have suggested the possibility that capillary function may be directly controlled by neuronal structures. Alterations in neuronal systems involved in the regulation of microcirculation may account for microvascular dysfunctions which occur in different pathologic conditions.

Blood-brain barrier: endogenous modulation by adrenal-cortical function

The blood-brain barrier restricts the passage of molecules from the blood to the brain. The permeability of the barrier to iodine-125-labeled bovine serum albumin was examined in rats that had undergone adrenalectomy, adrenal demedullation, and corticosterone replacement. Adrenalectomy, but not adrenal demedullation, increased the permeability of brain tissue to the isotopically labeled macromolecule; corticosterone replacement reversed this effect. These results indicate that the blood-brain barrier may be hormonally regulated; that is, the pituitary-adrenal axis may physiologically modulate the permeability of the brain microvasculature to macromolecules.

Permeability of the blood-brain barrier to neuropeptides: the case for penetration

Evidence that peptides can cross the blood-brain barrier (BBB) is reviewed. Penetration is suggested by the observations that blood levels correlate with cerebrospinal fluid levels for many peptides and that peripheral administration of peptides results in effects on the CNS. Passage is confirmed by experiments involving administration of a peptide (immunoactive or radioactive) in one compartment and identification of its appearance in the other, supported by such methods as selective labeling, cross-reactivity with highly specific antibodies, and chromatography. The degree of passage varies among peptides and their analogs. The major route of passage is probably by a non-competitive, non-saturable mechanism, wih the physicochemical characteristics of the peptide (e.g. lipophilicity, charge, molecular weight, and protein binding) determining the degree of passage. A competitive transport mechanism also exists for some peptides. Penetration of the BBB via large pores or by pinocytosis does not appear to be of major importance for peptides. Permeability of the BBB to peptides, but not to the larger iodinated albumin, is affected by intraperitoneal administration of aluminum, apparently by an increase in the permeability of the membrane to lipophilic materials.

Cerebral blood flow and cerebrovascular permeability in an inescapable shock (learned helplessness) animal model of depression

The effects of a purported animal model of depression (inescapable shock, IS) was tested on: (a) escape behavior, (b) regional brain levels of norepinephrine (NE), serotonin (5-HT), and dopamine, and (c), the response of the cerebromicrovasculature to metabolic demand as mimicked by manipulation of arterial CO2 content (PaCO2). Multidisciplinary research has implicated central biogenic amines in the regulation of cerebromicrocirculation. IS treatment resulted in increased escape latency and lowered levels of NE and 5-HT in the locus coeruleus but not in terminal fields in distant regions. This treatment also did not alter cerebral blood flow or capillary permeability in distant regions when compared with control rats. Thus, the discrete changes in NE and 5-HT in locus coeruleus induced by IS treatment is not reflected in changes in cerebral blood flow and the effective permeability of the blood-brain barrier.

Cerebromicrocirculatory defects in animal model of depression

In the tetrabenazine (TBZ) model of depression, the cerebromicrocirculation was discovered to respond abnormally to metabolic demand as mimicked by the administration of CO2. Altered responsivity of cerebral blood flow and effective permeability of the blood--brain barrier to changes in PaCO2 were found. These physiologic defects coincided temporally with TBZ-induced depletion of central norepinephrine and dopamine and with the development of the behavioral effects of TBZ (the end points used to test the antidepressant potential of experimental drugs). Pretreatment with amitriptyline (a standard antidepressant and amine reuptake inhibitor) prevented the development of these TBZ-induced abnormalities in the cerebromicrocirculation, just as it prevented the behavioral effects.

Methods for the determination of lorazepam and chlordiazepoxide and metabolites in brain tissue. A comparison with plasma concentrations in the rat

Rapid and sensitive methods are described for determining lorazepam and for determining chlordiazepoxide and its metabolites in brain tissue of the rat. Lorazepam was determined by means of solvent extraction and electron-capture gas-liquid chromatography and concentrations as low as 5 ng/g tissue could be measured. High-performance liquid chromatography with UV detection was used to determine chlordiazepoxide and its metabolites and was sensitive to 0.1 micrograms/g tissue. The methods were used to investigate the brain and plasma pharmacokinetics of these compounds in animals that had been chronically treated with lorazepam or chlordiazepoxide. In both experiments brain and plasma levels of all compounds assayed were found to correlate highly.

Long-term effect of electroshock treatment on the entry of calcium into the cerebroventricular fluid in the rat

The rate of appearance (Ra) of calcium (Ca) in the cerebroventricular compartment of urethane-anesthesized rats was determined by two methods: one is measurement of isotope dilution during ventricular-cisternal perfusion with artificial cerebrospinal fluid (CSF) containing 45Ca, the other is estimation of the rate of entry of 45Ca from plasma after rapid injection of tracer 45CaCl2 intravenously. Electroshock treatment (EST) for 3 successive days resulted in a marked increase in the rate of entry of calcium from blood to CSF. The effect of EST on the permeability of the blood-CSF barrier to Ca could be observed even 24 hr after the generalized seizure induced by electroshock has terminated.

The immune system and the nervous system

The immune system may interfere with brain function. The central nervous system may also influence the activity of the immune system. The central nervous system is functionally protected by the blood-brain barrier. The central nervous system is functionally protected by the blood-brain barrier. The endothelial cells of the brain capillaries are linked by tight junctions, resulting in an almost continuous interior wall which restricts the transfer of plasma proteins. The barrier function is modified by inflammatory meningeal lesions, stroke and epileptic seizures. Antigenic material may penetrate the barrier and enter the nerve tissue. The phagocytic cells in the central nervous system are mainly of haematogenous origin. The number of such cells in the brain is very low. There are also few lymphocytes under normal circumstances. These cells circulate from the blood, through the vessel walls and into the perivascular spaces, along the perivascular channels and to the CSF and back to the blood. This circulation may increase enormously during inflammatory conditions. In multiple sclerosis, the number of T-lymphocytes in the CSF is increased, corresponding to a preponderance of T-lymphocytes in the perivascular cell infiltrates in and around the lesions. Thus, the individual elements of the immune system are all present in the brain, which is only partially immunologically privileged. The mechanisms underlying the brain's immunological privilege may be of a non-immunological nature. As yet there are only few data which indicate that auto-immunity is a prominent feature in diseases of the human brain. The central nervous system also exerts a modulating influence upon the immune response. This may take place both by secretion of hormones and by a nervous/neurotransmitter influence upon the immune system.

Functional tolerance to lorazepam in the rat

The nature of the tolerance that develops to the sedative action of lorazepam was investigated using a hole-board apparatus. Rats treated with lorazepam (0.125, 0.25 and 0.50 mg/kg) once daily for 3 days showed similar degrees of tolerance to the effects of a test dose of 0.25 mg/kg lorazepam. Tolerance was also observed in animals treated once every 2 days with lorazepam (0.50 mg/kg). Measurement of the plasma and brain concentrations of lorazepam immediately after the behavioural test showed that this tolerance was functional and not dispositional. In contrast, the behavioural effects of lorazepam were not reduced as a result of 3 days of treatment with a sedative dose of sodium pentobarbitone (20 mg/kg), although this led to lower brain concentrations of lorazepam at the time of testing.

A dual label radiotracer technique for the simultaneous measurement of cerebral blood flow and the single-transit cerebral extraction of diffusion-limited compounds in rats

An inexpensive method is described which permits simultaneous quantification of the cerebrovascular extraction (E) of diffusion-limited compounds and cerebral blood flow (CBF) in rats. This method involves the use of two radioisotopic tracers: (a) a diffusion-limited, test tracer such as [3H]water; and (b) a reference tracer. The reference tracer is also used in the measurement of CBF. In the development and validation of this technique, results using two different types of reference tracers were compared. The reference tracers employed were: (a) [14C]butanol, a flow-limited (i.e. freely diffusible) compound; and (b) [141Ce]microspheres which embolize in the cerebromicrocirculation. Inclusion of [3H]water in the injection bolus permitted simultaneous measurement of Ew using both butanol and microspheres as the reference as well as concomitant measurement of CBF. Both tracers provided estimates of these values which behaved physiologically with respect to increasing arterial CO2 content (paCO2). In addition, the simultaneous measurement of Ew and CBF permitted calculation of the effective permeability of water across the blood-brain barrier (PwS) which was discovered to increased with increasing paCO2.

Elevation of erythrocyte glycine levels during lithium treatment of affective disorders

An elevation of erythrocyte (RBC) glycine was observed in a group of patients with bipolar affective disorder who were being treated with lithium (Li) carbonate. A maximal increase of 90% or more was generally attained after about 100 days of Li intake and was maintained for 2 years or longer. After 3 or more years of Li therapy, the RBC glycine had often returned to the normal range. Abrupt withdrawal of Li in such a case produced an immediate, dramatic, and paradoxical increase in RBC glycine which lasted for 100 days. Plasma glycine was not affected by Li.

Cerebral endothelial cell culture. I. The presence of beta 2 and alpha 2-adrenergic receptors linked to adenylate cyclase activity

Cultured endothelial cells derived from cerebral microvessels separated from 2-day-old rat brain contain a specific beta 2 and alpha 2-adrenergic sensitive adenylate cyclase (AC). Among the various tested hormones, PGE1 and PGE2 were found to be the most potent activators, while adenosine, angiotensin I and II, gamma-aminobutyric acid and vasoactive intestinal peptide inhibited the enzyme activity. However, acetylcholine, histamine, serotonin, glycine, glutamine, bradykinin, neurotensin and vasopressin (Lysine and Arginine) had no effect on the adenylate cyclase activity in this model. The susceptibility of the cerebrovascular endothelial AC system to the vasoactive substances as well as presence of beta 2 and alpha 2-type adrenergic receptors in the cultured endothelium provides additional support for the proposed endothelial involvement in the regulation of cerebrovascular permeability and blood flow.