Hope for vascular cognitive impairment: Ac-YVAD-cmk as a novel treatment against white matter rarefaction

Vascular cognitive impairment (VCI) is the second leading cause of dementia with limited treatment options, characterised by cerebral hypoperfusion-induced white matter rarefaction (WMR). Subcortical VCI is the most common form of VCI, but the underlying reasons for region susceptibility remain elusive. Recent studies employing the bilateral cortical artery stenosis (BCAS) method demonstrate that various inflammasomes regulate white matter injury and blood-brain barrier dysfunction but whether caspase-1 inhibition will be beneficial remains unclear. To address this, we performed BCAS on C57/BL6 mice to study the effects of Ac-YVAD-cmk, a caspase-1 inhibitor, on the subcortical and cortical regions. Cerebral blood flow (CBF), WMR, neuroinflammation and the expression of tight junction-related proteins associated with blood-brain barrier integrity were assessed 15 days post BCAS. We observed that Ac-YVAD-cmk restored CBF, attenuated BCAS-induced WMR and restored subcortical myelin expression. Within the subcortical region, BCAS activated the NLRP3/caspase-1/interleukin-1beta axis only within the subcortical region, which was attenuated by Ac-YVAD-cmk. Although we observed that BCAS induced significant increases in VCAM-1 expression in both brain regions that were attenuated with Ac-YVAD-cmk, only ZO-1 and occludin were observed to be significantly altered in the subcortical region. Here we show that caspase-1 may contribute to subcortical regional susceptibility in a mouse model of VCI. In addition, our results support further investigations into the potential of Ac-YVAD-cmk as a novel treatment strategy against subcortical VCI and other conditions exhibiting cerebral hypoperfusion-induced WMR.

The Effects of CYP2C19 Genotype on Proxies of SSRI Antidepressant Response in the UK Biobank

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly used psychopharmaceutical treatment for major depressive disorder (MDD), but individual responses to SSRIs vary greatly. CYP2C19 is a key enzyme involved in the metabolism of several drugs, including SSRIs. Variations in the CYP2C19 gene are associated with differential metabolic activity, and thus differential SSRI exposure; accordingly, the CYP2C19 genotype may affect the therapeutic response and clinical outcomes, though existing evidence of this link is not entirely consistent. Therefore, we analysed data from the UK Biobank, a large, deeply phenotyped prospective study, to investigate the effects of CYP2C19 metaboliser phenotypes on several clinical outcomes derived from primary care records, including multiple measures of antidepressant switching, discontinuation, duration, and side effects. In this dataset, 24,729 individuals were prescribed citalopram, 3012 individuals were prescribed escitalopram, and 12,544 individuals were prescribed sertraline. Consistent with pharmacological expectations, CYP2C19 poor metabolisers on escitalopram were more likely to switch antidepressants, have side effects following first prescription, and be on escitalopram for a shorter duration compared to normal metabolisers. CYP2C19 poor and intermediate metabolisers on citalopram also exhibited increased odds of discontinuation and shorter durations relative to normal metabolisers. Generally, no associations were found between metabolic phenotypes and proxies of response to sertraline. Sensitivity analyses in a depression subgroup and metabolic activity scores corroborated results from the primary analysis. In summary, our findings suggest that CYP2C19 genotypes, and thus metabolic phenotypes, may have utility in determining clinical responses to SSRIs, particularly escitalopram and citalopram, though further investigation of such a relationship is warranted.

The putative role of the relaxin-3/RXFP3 system in clinical depression and anxiety: A systematic literature review

The relaxin-3/RXFP3 system is one of several neuropeptidergic systems putatively implicated in regulating the behavioural alterations that characterise clinical depression and anxiety, making it a potential target for clinical translation. Accordingly, this systematic review identified published reports on the role of relaxin-3/RXFP3 signalling in these neuropsychiatric disorders and their behavioural endophenotypes, evaluating evidence from animal and human studies to ascertain any relationship. We searched PubMed, EMBASE, PsycINFO and Google Scholar databases up to February 2021, finding 609 relevant records. After stringent screening, 51 of these studies were included in the final synthesis. There was considerable heterogeneity in study designs and some inconsistency across study outcomes. However, experimental evidence is consistent with an ability of relaxin-3/RXFP3 signalling to promote arousal and suppress depressive- and anxiety-like behaviour. Moreover, meta-analyses of six to eight articles investigating food intake revealed that acute RXFP3 activation had strong orexigenic effects in rats. This appraisal also identified the lack of high-quality clinical studies pertinent to the relaxin-3/RXFP3 system, a gap that future research should attempt to bridge.

A Flexi-PEGDA Upconversion Implant for Wireless Brain Photodynamic Therapy

Near-infrared (NIR) activatable upconversion nanoparticles (UCNPs) enable wireless-based phototherapies by converting deep-tissue-penetrating NIR to visible light. UCNPs are therefore ideal as wireless transducers for photodynamic therapy (PDT) of deep-sited tumors. However, the retention of unsequestered UCNPs in tissue with minimal options for removal limits their clinical translation. To address this shortcoming, biocompatible UCNPs implants are developed to deliver upconversion photonic properties in a flexible, optical guide design. To enhance its translatability, the UCNPs implant is constructed with an FDA-approved poly(ethylene glycol) diacrylate (PEGDA) core clad with fluorinated ethylene propylene (FEP). The emission spectrum of the UCNPs implant can be tuned to overlap with the absorption spectra of the clinically relevant photosensitizer, 5-aminolevulinic acid (5-ALA). The UCNPs implant can wirelessly transmit upconverted visible light till 8 cm in length and in a bendable manner even when implanted underneath the skin or scalp. With this system, it is demonstrated that NIR-based chronic PDT is achievable in an untethered and noninvasive manner in a mouse xenograft glioblastoma multiforme (GBM) model. It is postulated that such encapsulated UCNPs implants represent a translational shift for wireless deep-tissue phototherapy by enabling sequestration of UCNPs without compromising wireless deep-tissue light delivery.

Intranasal administration of a stapled relaxin-3 mimetic has anxiolytic- and antidepressant-like activity in rats

Background and Purpose

Depression and anxiety are common causes of disability, and innovative tools and potential pharmacological targets are actively sought for prevention and treatment. Therapeutic strategies targeting the relaxin‐3 peptide or its primary endogenous receptor, RXFP3, for the treatment of major depression and anxiety disorders have been limited by a lack of compounds with drug‐like properties. We proposed that a hydrocarbon‐stapled mimetic of relaxin‐3, when administered intranasally, might be uniquely applicable to the treatment of these disorders.

Experimental Approach

We designed a series of hydrocarbon‐stapled relaxin‐3 mimetics and identified the most potent compound using in vitro receptor binding and activation assays. Further, we assessed the effect of intranasal delivery of relaxin‐3 and the lead stapled mimetic in rat models of anxiety and depression.

Key Results

We developed an i,i+7 stapled relaxin‐3 mimetic that manifested a stabilized α‐helical structure, proteolytic resistance, and confirmed agonist activity in receptor binding and activation in vitro assays. The stapled peptide agonist enhanced food intake after intracerebral infusion in rats, confirming in vivo activity. We showed that intranasal delivery of the lead i,i+7 stapled peptide or relaxin‐3 had orexigenic effects in rats, indicating a potential clinically translatable route of delivery. Further, intranasal administration of the lead i,i+7 stapled peptide exerted anxiolytic and antidepressant‐like activity in anxiety‐ and depression‐related behaviour paradigms.

Conclusions and Implications

Our preclinical findings demonstrate that targeting the relaxin‐3/RXFP3 receptor system via intranasal delivery of an i,i+7 stapled relaxin‐3 mimetic may represent an effective treatment approach for depression, anxiety, and related neuropsychiatric disorders.

Hydrocarbon stapled B chain analogues of relaxin-3 retain biological activity

Relaxin-3 or insulin-like peptide 7 (INSL7) is the most recently discovered relaxin/insulin-like family peptide. Mature relaxin-3 consists of an A chain and a B chain held by disulphide bonds. According to structure activity relationship studies, the relaxin-3 B chain is more important in binding and activating the receptor. RXFP3 (also known as Relaxin-3 receptor 1, GPCR 135, somatostatin- and angiotensin- like peptide receptor or SALPR) was identified as the cognate receptor for relaxin-3 by expression profiles and binding studies. Recent studies imply roles of this system in mediating stress and anxiety, feeding, metabolism and cognition. Stapling of peptides is a technique used to develop peptide drugs for otherwise undruggable targets. The main advantages of stapling include, increased activity due to reduced proteolysis, increased affinity to receptors and increased cell permeability. Stable agonists and antagonists of RXFP3 are crucial for understanding the physiological significance of this system. So far, agonists and antagonists of RXFP3 are peptides. In this study, for the first time, we have introduced stapling of the relaxin-3 B chain at 14th and 18th positions (14s18) and 18th and 22nd position (18s22). These stapled peptides showed greater helicity than the unstapled relaxin-3 B chain in circular dichroism analysis. Both stapled peptides bound RXFP3 and activated RXFP3 as observed in an inhibition of forskolin-induced cAMP assay and a ERK1/2 activation assay, although with different potencies. Therefore, we conclude that stapling of the relaxin3 B chain does not compromise its ability to activate RXFP3 and is a promising method for developing stable peptide agonists and antagonists of RXFP3 to aid relaxin-3/RXFP3 research.

A role for sorting nexin 27 in AMPA receptor trafficking

Sorting nexin 27 (SNX27), a PDZ domain-containing endosomal protein, was recently shown to modulate glutamate receptor recycling in Down's syndrome. However, the precise molecular role of SNX27 in GluA1 trafficking is unclear. Here we report that SNX27 is enriched in dendrites and spines, along with recycling endosomes. Significantly, the mobilization of SNX27 along with recycling endosomes into spines was observed. Mechanistically, SNX27 interacts with K-ras GTPase via the RA domain; and following chemical LTP stimuli, K-ras is recruited to SNX27-enriched endosomes through a Ca(2+)/CaM-dependent mechanism, which in turn drives the synaptic delivery of homomeric GluA1 receptors. Impairment of SNX27 prevents LTP and associated trafficking of AMPARs. These results demonstrate a role for SNX27 in neuronal plasticity, provide a molecular explanation for the K-ras signal during LTP and identify SNX27 as the PDZ-containing molecular linker that couples the plasticity stimuli to the delivery of postsynaptic cargo.

NogoR1 and PirB signaling stimulates neural stem cell survival and proliferation

Neural stem cells (NSCs) and neural progenitors (NPs) in the mammalian neocortex give rise to the main cell types of the nervous system. The biological behavior of these NSCs and NPs is regulated by extracellular niche derived autocrine-paracrine signaling factors on a developmental timeline. Our previous reports [Plos One 2010;5:e15341; J Neurochem 2011;117:565-578] have shown that chondroitin sulfate proteoglycan and ApolipoproteinE are autocrine-paracrine survival factors for NSCs. NogoA, a myelin related protein, is expressed in the cortical ventricular zones where NSCs reside. However, the functional role of Nogo signaling proteins in NSC behavior is not completely understood. In this study, we show that NogoA receptors, NogoR1 and PirB, are expressed in the ventricular zone where NSCs reside between E10.5 and 14.5 but not at E15.5. Nogo ligands stimulate NSC survival and proliferation in a dosage-dependent manner in vitro. NogoR1 and PirB are low and high affinity Nogo receptors, respectively and are responsible for the effects of Nogo ligands on NSC behavior. Inhibition of autocrine-paracrine Nogo signaling blocks NSC survival and proliferation. In NSCs, NogoR1 functions through Rho whereas PirB uses Shp1/2 signaling pathways to control NSC behavior. Taken together, this work suggests that Nogo signaling is an important pathway for survival of NSCs.

A digitally assisted, signal folding neural recording amplifier

A novel signal folding and reconstruction scheme for neural recording applications that exploits the 1/f(n) characteristics of neural signals is described in this paper. The amplified output is 'folded' into a predefined range of voltages by using comparison and reset circuits along with the core amplifier. After this output signal is digitized and transmitted, a reconstruction algorithm can be applied in the digital domain to recover the amplified signal from the folded waveform. This scheme enables the use of an analog-to-digital convertor with less number of bits for the same effective dynamic range. It also reduces the transmission data rate of the recording chip. Both of these features allow power and area savings at the system level. Other advantages of the proposed topology are increased reliability due to the removal of pseudo-resistors, lower harmonic distortion and low-voltage operation. An analysis of the reconstruction error introduced by this scheme is presented along with a behavioral model to provide a quick estimate of the post reconstruction dynamic range. Measurement results from two different core amplifier designs in 65 nm and 180 nm CMOS processes are presented to prove the generality of the proposed scheme in the neural recording applications. Operating from a 1 V power supply, the amplifier in 180 nm CMOS has a gain of 54.2 dB, bandwidth of 5.7 kHz, input referred noise of 3.8 μVrms and power dissipation of 2.52 μW leading to a NEF of 3.1 in spike band. It exhibits a dynamic range of 66 dB and maximum SNDR of 43 dB in LFP band. It also reduces system level power (by reducing the number of bits in the ADC by 2) as well as data rate to 80% of a conventional design. In vivo measurements validate the ability of this amplifier to simultaneously record spike and LFP signals.

A 0.45 V 100-channel neural-recording IC with sub- μW/channel consumption in 0.18 μm CMOS

Neural prosthetics and personal healthcare have increasing need of high channel density low noise low power neural sensor interfaces. The input referred noise and quantization resolution are two essential factors which prevent conventional neural sensor interfaces from simultaneously achieving a good noise efficiency factor and low power consumption. In this paper, a neural recording architecture with dynamic range folding and current reuse techniques is proposed and dedicated to solving the noise and dynamic range trade-off under low voltage low power operation. Measured results from the silicon prototype show that the proposed design achieves 3.2 μVrms input referred noise and 8.27 effective number of bits at only 0.45 V supply and 0.94 μW/channel power consumption.

Selective lesioning of nucleus incertus with corticotropin releasing factor-saporin conjugate

The nucleus incertus (NI), a brainstem nucleus found in the pontine periventricular grey, is the primary source of the neuropeptide relaxin-3 in the mammalian brain. The NI neurons have also been previously reported to express several receptors and neurotransmitters, including corticotropin releasing hormone receptor 1 (CRF₁) and gamma-aminobutyric acid (GABA). The NI projects widely to putative neural correlates of stress, anxiety, depression, feeding behaviour, arousal and cognition leading to speculation that it might be involved in several neuropsychiatric conditions. On the premise that relaxin-3 expressing neurons in the NI predominantly co-express CRF₁ receptors, a novel method for selective ablation of the rat brain NI neurons using corticotropin releasing factor (CRF)-saporin conjugate is described. In addition to a behavioural deficit in the fear conditioning paradigm, reverse transcriptase polymerase chain reaction (RT-PCR), western blotting (WB) and immunofluorescence labelling (IF) techniques were used to confirm the NI lesion. We observed a selective and significant loss of CRF₁ expressing cells, together with a consistent decrease in relaxin-3 and GAD65 expression. The significant ablation of relaxin-3 positive neurons of the NI achieved by this lesioning approach is a promising model to explore the neuropsychopharmacological implications of NI/relaxin-3 in behavioural neuroscience.

Corticotropin-releasing factor infusion into nucleus incertus suppresses medial prefrontal cortical activity and hippocampo-medial prefrontal cortical long-term potentiation

The medial prefrontal cortex (mPFC) in the rat has been implicated in a variety of cognitive processes, including working memory and expression of fear memory. We investigated the inputs from a brain stem nucleus, the nucleus incertus (NI), to the prelimbic area of the mPFC. This nucleus strongly expresses corticotropin-releasing factor type 1 (CRF1 ) receptors and responds to stress. A retrograde tracer was used to verify connections from the NI to the mPFC. Retrogradely labelled cells in the NI expressed CRF receptors. Electrophysiological manipulation of the NI revealed that stimulation of the NI inhibited spontaneous neuronal firing in the mPFC. Similarly, CRF infusion into the NI, in order to mimic a stressful condition, inhibited neuronal firing and burst firing in the mPFC. The effect of concurrent high-frequency stimulation of the NI on plasticity in the hippocampo-prelimbic medial prefrontal cortical (HP-mPFC) pathway was studied. It was found that electrical stimulation of the NI impaired long-term potentiation in the HP-mPFC pathway. Furthermore, CRF infusion into the NI produced similar results. These findings might account for some of the extra-pituitary functions of CRF and indicate that the NI may play a role in stress-driven modulation of working memory and possibly other cognitive processes subserved by the mPFC.

Nicotine and clozapine cross-prime the locus coeruleus noradrenergic system to induce long-lasting potentiation in the rat hippocampus

A priming-challenge schedule of nicotine treatment causes long-lasting potentiation (LLP), a form of synaptic plasticity closely associated with the norepinephrine (NE) neurotransmitter system, at the medial perforant path (MPP)-dentate gyrus (DG) synapse in the rat hippocampus. Previous reports revealed that nicotine activates the locus coeruleus (LC) noradrenergic (NAergic) system and this mechanism may underlie its beta-adrenoceptor sensitive LLP effects. Clozapine, an atypical antipsychotic, is also known to activate the LC. Interactions between nicotine and clozapine are of interest because of the prevalence of smoking in patients with schizophrenia and increasing interest in the use of nicotinic receptor ligands as cognitive enhancers. Rats were subchronically primed with nicotine, clozapine or saline. Twenty-one to twenty-eight days later, the effects of the nicotine, clozapine or saline challenge on the evoked field excitatory postsynaptic potentials (fEPSP) at the MPP-DG monosynaptic pathway were recorded as a measure of LLP. We confirmed the hypothesis that a challenge dose of either nicotine or clozapine induces LLP exclusively in nicotine- and clozapine-primed rats, and not in saline-primed rats, thus indicating a cross-priming effect. Moreover, unilateral suppression of LC using lidocaine abolished the LLP induced by nicotine in clozapine-primed rats. Furthermore, systemic treatment with clonidine (an α2 adrenoceptor agonist that reduces NAergic activity via autoreceptors) prior to the challenge doses blocked the nicotine/clozapine-induced LLP in nicotine- and clozapine-primed rats. These findings may add to understanding of the cognitive enhancing effects of nicotine.

Therapeutic effect of hydrogen sulfide-releasing L-Dopa derivative ACS84 on 6-OHDA-induced Parkinson's disease rat model

Parkinson’s disease (PD), characterized by loss of dopaminergic neurons in the substantia nigra, is a neurodegenerative disorder of central nervous system. The present study was designed to investigate the therapeutic effect of ACS84, a hydrogen sulfide-releasing-L-Dopa derivative compound, in a 6-hydroxydopamine (6-OHDA)-induced PD model. ACS84 protected the SH-SY5Y cells against 6-OHDA-induced cell injury and oxidative stress. The protective effect resulted from stimulation of Nrf-2 nuclear translocation and promotion of anti-oxidant enzymes expression. In the 6-OHDA-induced PD rat model, intragastric administration of ACS84 relieved the movement dysfunction of the model animals. Immunofluorescence staining and High-performance liquid chromatography analysis showed that ACS84 alleviated the loss of tyrosine-hydroxylase positive neurons in the substantia nigra and the declined dopamine concentration in the injured striatums of the 6-OHDA-induced PD model. Moreover, ACS84 reversed the elevated malondialdehyde level and the decreased glutathione level in vivo. In conclusion, ACS84 may prevent neurodegeneration via the anti-oxidative mechanism and has potential therapeutic values for Parkinson’s disease.

Antipsychotic drugs dose-dependently suppress the spontaneous hyperactivity of the chakragati mouse

The chakragati (ckr) mouse has been proposed as a model of aspects of schizophrenia. The mice, created serendipitously as a result of a transgenic insertional mutation, exhibit spontaneous circling, hyperactivity, hypertone of the dopamine system, reduced social interactions, enlarged lateral ventricles, deficits in pre-pulse inhibition of acoustic startle and deficits in latent inhibition of conditioned learning. In this study, the dose-dependent effects of antipsychotic drugs (haloperidol, pimozide, risperidone, clozapine, olanzapine, ziprasidone, quetiapine and aripiprazole) on the spontaneous hyperactivity of the mice were investigated. All the antipsychotic drugs tested dose-dependently suppressed spontaneous hyperactivity. Aripriprazole, which is known to be a dopamine D2 receptor partial agonist, exhibited a tri-phasic dose-response, initially suppressing hyperactivity at low doses, having little effect on hyperactivity at intermediate doses, and suppressing activity again at high doses. These data suggest that the spontaneous circling and hyperactivity of the ckr mouse may allow screening of candidate antipsychotic compounds, distinguishing compounds with aripriprazole-like profiles.

Effective cryopreservation of neural stem or progenitor cells without serum or proteins by vitrification

Development of effective cryopreservation protocols will be essential to realizing the potential for clinical application of neural stem and progenitor cells. Current cryopreservation protocols have been largely employed in research, which does not require as stringent consideration of viability and sterility. Therefore, these protocols involve the use of serum and protein additives, which can potentially introduce contaminants, and slow cooling with DMSO/glycerol-based cryopreservation solutions, which impairs cell survival. We investigated whether serum- and protein-free vitrification is effective for functional cryopreservation of neurosphere cultures of neural stem or progenitor cells. To protect the samples from introduction of other contaminants during handling and cryostorage, an original "straw-in-straw" method (250 microl sterile straw placed in 500 microl straw) for direct immersion into liquid nitrogen and storing the samples was also introduced. The protocol employed brief step-wise exposure to vitrification solution composed of ethylene glycol (EG) and sucrose (40% v/v EG, 0.6 M sucrose) and removal of vitrification solution at room temperature. Evaluation of the effects of vitrification revealed that there were no differences between control and vitrified neural stem or progenitor cells in expression of the neural stem or progenitor cell markers, proliferation, or multipotent differentiation. This sterile method for the xeno-free cryopreservation of murine neurospheres without animal or human proteins may have the potential to serve as a starting point for the development of cryopreservation protocols for human neural stem and progenitor cells for clinical use.

Hydrogen sulphide in the hypothalamus causes an ATP-sensitive K+ channel-dependent decrease in blood pressure in freely moving rats

Hydrogen sulfide (H2S) is a naturally occurring gas that may act as an endogenous signaling molecule. In the brain, H2S is mainly produced by cystathionine beta-synthase (CBS) and its cellular effects have been attributed to interactions with N-methyl-D-aspartate (NMDA) receptors and cyclic adenosine 3',5'-monophosphate (cAMP). In contrast, direct vasodilator actions of H2S are most probably mediated by opening smooth muscle ATP-sensitive K+ (K(ATP)) channels. In the hypothalamus, K(ATP) channel-dependent mechanisms are involved in CNS-mediated regulation of blood pressure. In this report, we investigated the hypothesis that H2S may act via K(ATP) channels in the hypothalamus to regulate blood pressure. Mean arterial blood pressure (MAP) and heart rate were monitored in freely moving rats via a pressure transducer placed in the femoral artery. Drugs were infused via a cannula placed in the posterior hypothalamus. Infusion of 200 microM sodium hydrogen sulfide (NaHS), an H2S donor, into the hypothalamus of freely moving rats reduced MAP and heart rate. Infusion of 300 nM to 3 microM gliclazide dose-dependently blocked the effect of 200 microM NaHS. Infusion of the CBS activator, s-adenosyl-L-methionine (0.1 mM and 1 mM), likewise decreased MAP. Infusion of the CBS inhibitors aminooxyacetic acid (10 mM) and hydroxylamine (20 mM) increased MAP but did not block the effects of infusion of 200 microM NaHS. These data indicate that actions of H2S in the hypothalamus decrease blood pressure and heart rate in freely moving rats. This effect appears to be mediated by a K(ATP) channel-dependent mechanism and mimicked by endogenous H2S.

Theta driving both inhibits and potentiates the effects of nicotine on dentate gyrus responses

The medial septal area of conscious rats was stimulated through previously implanted electrodes at a frequency of 7.7 Hz for 20 min each day for 7 days to evoke rhythmic slow activity in CA1 at a similar frequency to spontaneous theta. Two weeks later in the anaesthetized rats the effects of a single subcutaneous injection of nicotine (0.4 mg/kg) on fEPSPs, evoked in the dentate gyrus by separate stimulation of the MPP and LPP, were studied and compared with those obtained in controls. Nicotine increased the firing of locus coeruleus neurons and the slope of the fEPSPs evoked by LPP stimulation, but not by MPP stimulation. Prior theta driving considerably increased the effect of nicotine on the responses evoked by stimulation of the MPP and abolished the nicotine-induced potentiation of the responses evoked by stimulation of the LPP. The results are attributed to theta driving increasing the amount of noradrenaline released by nicotine and to noradrenaline producing a beta-adrenoceptor long-lasting potentiation at the medial perforant path synapse and a long-lasting depression at the lateral perforant path synapse.

Effects of short-term and chronic olanzapine treatment on immediate early gene protein and tyrosine hydroxylase immunoreactivity in the rat locus coeruleus and medial prefrontal cortex

Atypical antipsychotic drugs, such as olanzapine, have been reported to activate the locus coeruleus (LC) and lead to acute expression of the Fos-like immediate early gene (IEG) protein in the LC and medial prefrontal cortex (mPFC). Stimuli that activate the LC have been reported to increase expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. However, the effects of chronic treatment with olanzapine on IEG expression and the dose-dependence of the effects of olanzapine on IEG and TH expression are not known. Thus, we examined Fos-like, c-Jun, activating transcription factor 2 (ATF-2), early growth response 1 (Egr-1), early growth response 2 (Egr-2), and TH immunoreactivity expression in the LC and mPFC in rats receiving 2, 4, 8, or 15 mg/kg/day olanzapine by s.c. osmotic minipump for 4 h, 1 week, 2 weeks, or 4 weeks. ATF-2 expression was up-regulated at all treatment durations, while Egr-1 and Egr-2 were down-regulated in both the LC and mPFC. Fos-like expression was up-regulated through 2 weeks, but not 4 weeks, in both the LC and mPFC. C-Jun expression was up-regulated for 4 weeks in the LC and for 2 weeks, but not 4 weeks, in the mPFC. At all doses, there were rapid and sustained increases in TH immunoreactivity in the LC, but only delayed increases in the mPFC. These data indicate that olanzapine has rapid effects on IEG in the LC and mPFC, many of which are sustained through four weeks of treatment. Further, these data indicate that the delayed increase in TH expression in the mPFC parallels, and may play an important role in, the increased efficacy of olanzapine that emerges over time in humans.

Biphasic effects of atropine on sensory-evoked hippocampal rhythmical slow activity in urethane-anaesthetized rats

This study investigated the response of hippocampal RSA, recorded from electrodes in CA1 and the contralateral dentate gyrus of urethane-anaesthetized rats, to atropine sulphate administered at 15 min intervals in a cumulative dose-response schedule (1, 3, 10, 50 and 50 mg x kg(-1) i.p.). The power of CA1 and dentate gyrus RSA in the 3-7 Hz band was increased after administering the first 3 doses of atropine (1, 3 and 10 mg x kg(-1) cumulatively) in rats held in the stereotaxic frame or removed from the frame and given electrical sensory stimulation to the base of the tail. This increase in RSA was dependent on sensory input, since it was not seen in animals outside the frame unless sensory stimulation was given, and it was abolished by increasing the dose of atropine (an additional 50 and 50 mg x kg(-1) cumulatively). Methylatropine (6 mg x kg(-1) i.p.) did not increase RSA power. The biphasic effect of atropine on sensory-evoked hippocampal RSA activity may be explained by differential effects at pre- and post-synaptic sites e.g. in the septo-hippocampal system or on pathways processing sensory information.

Theta driving both inhibits and potentiates the effects of nicotine on dentate gyrus responses

The medial septal area of conscious rats was stimulated through previously implanted electrodes at a frequency of 7.7 Hz for 20 min each day for 7 days to evoke rhythmic slow activity in CA1 at a similar frequency to spontaneous theta. Two weeks later in the anaesthetized rats the effects of a single subcutaneous injection of nicotine (0.4 mg x kg(-1)) on fEPSPs, evoked in the dentate gyrus by separate stimulation of the MPP and LPP, were studied and compared with those obtained in controls. Nicotine increased the firing of locus coeruleus neurones and the slope of the fEPSPs evoked by LPP stimulation, but not by MPP stimulation. Prior theta driving considerably increased the effect of nicotine on the responses evoked by stimulation of the MPP and abolished the nicotine-induced potentiation of the responses evoked by stimulation of the LPP. The results are attributed to theta driving increasing the amount of noradrenaline released by nicotine and to noradrenaline producing a beta-adrenoceptor long-lasting potentiation at the medial perforant path synapse and a long-lasting depression at the lateral perforant path synapse.

Endogenous dopamine modulates corticopallidal influences via GABA

Acute experiments on Sprague-Dawley rats were performed to study the effects of local application of D1 and D2 receptor antagonists (SCH 23390 and raclopride) on the responses of neurons in the globus pallidus induced by stimulation of the somatosensory cortex. SCH 23390 induced short-latency inhibition in response to stimulation of the cortex and blocked long-latency inhibition. Application of raclopride suppressed short-latency inhibition and induced a long-latency inhibitory response to stimulation of the cortex. It is suggested that these changes are based on modulation of GABA release from striopallidal terminals by endogenous dopamine.

[Endogenous dopamine modulates cortico-pallidal influence via GABA]

Sprague-Dawley rats were used to study the influence of local application of antagonists of D1 and D2 receptors (SCH 23390 and raclopride, respectively) on neuronal responses in globus pallidus evoked by somatosensory cortex stimulation. SCH 23390 was found to produce a short-latency inhibition in response to cortical stimulation and to block the long-latency inhibition. Raclopride application suppressed the short-latency inhibition and revealed the long-latency inhibition in response to cortical stimulation. It is suggested that the observed phenomena are based on the modulation of GABA releasing in stria-pallidar terminals by endogenous dopamine.

Olanzapine activates the rat locus coeruleus: in vivo electrophysiology and c-Fos immunoreactivity

BACKGROUND

Activation of central noradrenergic pathways by atypical antipsychotics has been hypothesized to play a role in their efficacy in treating the negative symptoms and cognitive impairment of schizophrenia. Because acute administration of the atypical antipsychotic olanzapine has been shown to increase extracellular levels of norepinephrine in the medial prefrontal cortex, we examined the effects of olanzapine on the noradrenergic cells of the locus coeruleus (LC).

METHODS

The effects of olanzapine (0.25-16 mg kg(-1), IV) on the firing rates and patterns of LC neurons were determined by extracellular, single-unit recordings in chloral hydrate-anaesthetized rats. The effects of olanzapine and clozapine on c-Fos expression in the LC, nucleus subcoeruleus part alpha (SubCA), and nucleus A5 (A5) were studied by immunohistochemistry.

RESULTS

Olanzapine increased LC cell firing rates, de-regularized firing, and induced burst firing. Induction of c-Fos expression in the LC by olanzapine and clozapine was confirmed and was also found in the SubCA, but not in A5.

CONCLUSIONS

Acute administration of olanzapine activates the noradrenergic neurons of the rat LC. This increased activity of LC neurons may play an important role in the efficacy of olanzapine and clozapine in treating both the negative symptoms and cognitive impairment observed in schizophrenic patients.

Changes in sensitivity of cholinoceptors and adrenoceptors during transhemispheric cortical reorganisation in rat SmI

The reorganisation of primary somatosensory cortex that occurs after lesioning the corresponding cortex of the contralateral hemisphere in rat has been termed, 'transhemispheric cortical reorganisation'. Cholinergic and noradrenergic innervations are hypothesized to be involved in cortical plasticity. The present study investigated the change in responses of somatosensory neurones in the hindpaw representation area to muscarinic cholinoceptor and beta-adrenoceptor receptor stimulation, by iontophoretic application of acetylcholine, noradrenaline, propranolol and atropine, during the process of transhemispheric cortical reorganization at 3-4 days and at 20-21 days after lesioning the corresponding area in the contralateral hemisphere. Most neurones in control rats showed excitatory atropine-sensitive responses to acetylcholine, and inhibitory propranolol-sensitive responses to noradrenaline. A marked reduction in neurones exhibiting muscarinic responses (from 69% to 22%) and beta-noradrenoceptor-mediated responses (from 62% to 24%) were seen in rats 3-4 days post lesion. The proportion of neurones responding had recovered by 3 weeks but the direction of the responses had changed with muscarinic response becoming predominantly inhibitory and beta-noradrenoceptor responses predominantly excitatory. It is concluded that transhemispheric cortical reorganization involves both receptor types and that the reciprocal changes at different stages after injury maintain cortical plasticity.

Changes in neurite outgrowth but not in cell division induced by low EMF exposure: influence of field strength and culture conditions on responses in rat PC12 pheochromocytoma cells

The effects of low electromagnetic field (EMF) exposure (4.5-15.8 microT, 50 Hz AC) on neurite outgrowth and cell division in rat PC12 pheochromocytoma cells were examined. The study involved two separate experimental series in which culture conditions during exposure to the magnetic fields differed. In series 1 (14 experiments in which culture conditions were not strongly conducive to cell differentiation [15% serum]), exposure to 4.5-8.25 microT for 23 h significantly inhibited neurite outgrowth by 21.5 +/- 1.3% (by Manova, p = 0.003). In contrast, in series 2 (12 experiments in which culture conditions promoted cellular differentiation [4% serum]), exposure to 4.35-8.25 microT for 23 h significantly stimulated neurite outgrowth by 16.9 +/- 1.1% (by Manova, p = 0.009). Thus, in both series, exposure to a narrow range of low EMF has significant, but opposite effects on neurite outgrowth. Exposure to higher fields, 8.25-12.5 microT (series 1) and 8.25-15.8 microT (series 2) had no significant effect on neurite outgrowth. These data, when considered with other reports, suggest that neuronal differentiation can be altered by low level EMF exposure. While this may not be detrimental, it merits further research. At present, the reasons for the significant changes in neurite outgrowth being confined to the same narrow field strength are unclear. As stated above, culture conditions in series 2 were more conducive to cell differentiation than those in series 1. This is reflected in the lower number of cells in control samples in series 2, at the end of the 23-h incubation, than in series 1 (- 16.9 +/- 1.7%, p = 0.003). As the same numbers were plated in both series, the medium used in series 1 allows more of the PC12 cells to divide; this is consistent with some cells reverting to a non-neuronal adrenal chromaffin phenotype [L. Greene, A. Tischler. Establishment of a noradrenergic clonal line of rat adrenal pheochromocytoma cells which respond to nerve growth factor. Proc. Natl. Acad. Sci. U. S. A., 73 (1976) 2424-2426]. Exposure to both ranges of magnetic fields (4.35-8.25 and 8.25-15.8 microT) has no effect on cell division. Thus, there is no evidence in this study that there is a mitogenic effect arising from low EMF exposure.

Aboulia: neurobehavioural dysfunction of dopaminergic system?

Recent advances in the understanding of the neural substrates of goal-directed behaviour have created new interest in unlocking the mystery behind those disorders that are characterized by poverty of thought and action. In this review, various studies will be considered which proffer converging evidence that the dopaminergic brain circuitry running from ventral tegmental areas in the midbrain, via nucleus accumbens in the forebrain, to the frontal cortex, tends to produce aboulia when its restitutive function fails. Such aboulic deficits occur in various neurological and psychiatric disorders in which they have profound implications for the patients' management, rehabilitation and social interactions. We begin by examining the consequences of dopamine agonism and antagonism in pre-clinical studies and draw on the inferences that can be made from studies in humans. We then go on to discuss aboulic features in neuropsychiatric conditions, focusing on clinical manifestation, animal models, abnormal dopamine activity and pharmacological interventions.

Lesions of the nucleus basalis magnocellularis do not alter the proportions of pirenzepine- and gallamine-sensitive responses of somatosensory cortical neurones to acetylcholine in the rat

The effects of S-alpha-amino-3-hydroxy-4-isoxozolepropionic acid (AMPA) lesions of the nucleus basalis magnocellularis on the M1/M2 nature of the responses of somatosensory cortical neurones to acetylcholine (ACh) in Sprague-Dawley rats were investigated by iontophoretic application and extracellular single unit recording. The responses were characterised using pirenzepine, an M1 receptor antagonist, and gallamine, an M2 antagonist. Eighty two neurones in control and 94 neurones in lesioned animals were studied. In control animals, 37% of responses to ACh were sensitive to pirenzepine, gallamine or to both antagonists. This increased to 62% in lesioned animals, the proportions of pirenzepine- and gallamine-sensitive responses remaining unchanged. These results provide the first electrophysiological confirmation that both pirenzepine- and gallamine-sensitive (M1 and M2) receptors occur postsynaptic to afferent cholinergic terminals and that their postsynaptic stimulation may produce both inhibition and excitation.

Nicotine induces long-lasting potentiation in the dentate gyrus of nicotine-primed rats

A challenge dose of nicotine (0.4 mg kg-1 s.c.) produced a long-lasting potentiation (LLP) of field EPSPs evoked in the dentate gyrus by stimulation of the medial perforant path of urethane-anaesthetized rats primed four weeks previously with seven daily injections of nicotine (0.8 mg kg-1 s.c.). The same dose of nicotine did not alter EPSPs evoked in rats primed with saline vehicle. Systemic injection of either mecamylamine or propranolol, 30 min before nicotine challenge, prevented induction of LLP without affecting baseline EPSPs but neither drug affected LLP when given after it was established. Since the nicotine-priming regime is known to increase tyrosine hydroxylase activity and hippocampal noradrenaline release in response to nicotine challenge, the results suggest that systemic injection of nicotine released sufficient noradrenaline in nicotine-primed rats to induce a beta-adrenoceptor-mediated LLP.

Cholinergic facilitation and inhibition of long-term potentiation of CA1 in the urethane-anaesthetized rats

Responses were evoked in the hippocampal CA1 field by stimulating the medial septal area (MSA) and ventral hippocampal commissure (VHC) of urethane-anaesthetized rats. Tetanic stimulation of the MSA resulted in a homosynaptic long-term potentiation (LTP) of a slow synaptic response in the hippocampus, and heterosynaptic LTP of the evoked VHC response. Both forms of LTP were blocked by MK801. Tetanization of the VHC resulted in homosynaptic LTP but did not produce heterosynaptic LTP of the evoked MSA response. Atropine pretreatment increased commissural homosynaptic LTP and unveiled a heterosynaptic LTP of MSA-evoked responses. In contrast, atropine pretreatment partially blocked the homosynaptic LTP produced by tetanization of the MSA and prevented the heterosynaptic LTP of VHC-evoked responses.

Changes in paired-pulse facilitation correlate with induction of long-term potentiation in area CA1 of rat hippocampal slices

The phenomenon of long-term potentiation is widely used as an experimental model of memory. An approach that has been used to study its underlying mechanisms is to analyse its interaction with presynaptic paired-pulse facilitation. Several studies found no evidence for an interaction in the CA1 hippocampal area, whereas other data, for example from quantal analysis, suggested that presynaptic mechanisms contribute to the maintenance of long-term potentiation. In the present study, initial slopes of field potentials in area CA1 were measured in rat hippocampal slices. "Conventional" long-term potentiation was induced by high-frequency (100 Hz) afferent tetanization of the testing input. "Associative" long-term potentiation was induced by combining lower frequency (40 Hz) tetanization of a testing input with high-frequency tetanization of a second input. The paired-pulse facilitation ratio decreased in the majority of experiments in which long-term potentiation was induced conventionally, but it decreased, increased or did not change after inducing associative potentiation. Decreases in the paired-pulse facilitation correlated inversely with the initial (pre-tetanic) facilitation ratio. A more detailed regression analysis suggests that this correlation results from two other correlations: (i) that between changes in paired-pulse facilitation and the magnitude of long-term potentiation, and (ii) that between initial paired-pulse facilitation and the magnitude of long-term potentiation. The first correlation prevailed during the initial 10 min following tetanization, while the second prevailed 40-60 min later. A post-tetanic decrease in paired-pulse facilitation is evidence for an involvement of presynaptic mechanisms in the maintenance of long-term potentiation. The lack of significant changes in some studies could be due to the inclusion in the analyses of experiments with long-term potentiation of small magnitude, in which changes in paired-pulse facilitation ratios would have been inconsistent. The present study suggests that the early (10-20 min) and late (40-50 min) phases of long-term potentiation were mediated by different mechanisms, with a mixture of these mechanisms during the intermediate period. On the basis of the present and previous studies, the following scheme of involvement of several mechanisms in long-term potentiation maintenance is proposed. The early phase includes two major mechanisms: an increase in the probability of transmitter release, leading to an apparent increase in the number of effective release sites, and an increase in efficacy of one transmitter quantum, probably due to an increased number of postsynaptic receptors. The later phase of long-term potentiation is attributed to an increase in the number of transmitter zones, presumably due to structural modifications.

Extracellular recordings in the colchicine-lesioned rat dentate gyrus following transplants of fetal dentate gyrus and CA1 hippocampal subfield tissue

Grafts of fetal dentate gyrus (DG) and CA1 hippocampal subfield tissue were extruded into the dentate gyri of adult male Sprague-Dawley rats, 7-10 days after lesioning the granule cells with colchicine (0.06 microliter of 7 mg/ml solution at each of 5 sites/hippocampus). Graft area-host and host-graft area connectivities were investigated 4-6 months post-transplantation by recoding extracellular evoked response in hippocampal slice preparations. Following stimulation of the host mid-molecular layer, evoked field potential responses, showing considerable variation, were recorded in both types of graft. Evoked responses in the lesioned DG without grafts were recorded in very few slices. Stimulation of the area of DG tissue grafts occasionally evoked responses in the host CA3/CA4 and there was no evidence for CA1 graft area-CA3/CA4 connectivity; stimulation of DG and CA1 graft areas occasionally evoked responses in the host CA1. Responses in the area of both DG and CA1 grafts supported short-term potentiation following stimulation of the host mid-molecular layer but only DG graft areas supported long-term potentiation of the population spike amplitude. In the area of both types of transplant a tonic bicuculline-sensitive inhibition was present and paired-pulse stimulation paradigms provided some evidence for inhibition. It is possible that responses recorded within the area of grafted tissue to stimulation of the host are attributable to host-graft connectivity and similarly, responses recorded in the host to stimulation of the area of the graft may be attributable to graft-host connectivity. Only DG graft areas received host inputs which were capable of sustaining a long-term potentiation and establishing efferent contacts with the host CA3/CA4 subfield, suggesting that these would be more likely than CA1 grafts to reinstate normal functional circuitry.

Contacts between group Ia muscle spindle afferent axons and GABA-immunoreactive perikarya in lamina VI of cat spinal cord

Three group Ia muscle spindle afferent axons were labelled with horseradish peroxidase and terminations in lamina VI examined. Eleven perikarya were contacted by the three fibres; these were examined using a post-embedding immunostaining technique for GABA. Three neurons were found to be positively labelled for GABA. It is likely that these cells are involved in inhibition of primary afferent fibres and non-reciprocal inhibition of motoneurons.