Neonatal viral brain infection and the development of prepulse inhibition : a neurodevelopmental model of schizophrenia

Epidemiological data suggest an important role of perinatal viral infections in the etiology of schizophrenia. In this thesis the connection between neonatal viral brain infection and its consequences to the development of central nervous system was studied. In schizophrenia the symptoms are divided into three categories as positive, negative and cognitive ones. Positive symptoms refer to hallucinations and delusions, negative symptoms are defined as social withdrawal, apathy and poor motivation and cognitive symptoms include deficits in abstraction and paying attention into subjects. Symptoms suggest that in schizophrenia the received information can not be filtered properly in central nervous system, but comes into patients senses in excess i.e. there are defects in sensorimotor gating. Sensorimotor gating was studied by prepulse inhibition of acoustic startle -phenomenon. Prepulse inhibition refers to the inhibition of the startle reflex by weak prepulse presented before the startling stimulus. In schizophrenic patients prepulse inhibition is decreased and in addition to that psychotomimetic drugs disrupt prepulse inhibition in humans as well as in experimental animals. Sensorimotor gating ability is developed under neuronal development and it can be affected by several neurodevelopmental disturbances. In the present study rats were infected with herpes simplex type 1 virus at neonatal age and later challenged to dopaminergic and glutamatergic systems. Results show controversial data of effects on prepulse inhibition, still some attenuation can be seen. Challenge studies did not show clear and persistent effect either in dopaminergic or glutamatergic tests. Corticosterone, naturally occurring hormone in rats, was administered to rat mothers under gestation until weaning in terms to clarify its effects to neuronal development. Administration was carried out by implanted pellet as well as by drinking water. The latter was found to work out better as it releases corticosterone in pulsatile manner. Corticosterone was administered also in acute test to drug naïve animals. This test showed significant decrease on prepulse inhibition. The same could not be repeated in corticosterone challenge test after perinatal treatments. Nitric oxide synthase inhibitor L-NMMA was administered to neonates under days 5-9 after partus. This was supposed to prevent neonates from neurodevelopmental disturbances affected by virus and corticosterone. Despite various dose levels used, any clear effect could not be seen. In summary, the studies show some effect of treatments on neuronal development and sensorimotor gating measured by prepulse inhibition. In the test groups inspected many treatments showed effect at first, but those effects disappeared at later tests as rats grew up. This might be an outcome of the potential compensatory mechanisms of the central nervous system to counteract harmful neurodevelopmental events

AMPA-type glutamate receptors and behavioural neuroplasticity : Bidirectional role of GluA1 subunits

Neuroplasticity is defined as an ability of the nervous system to change when it responds to modified environmental or internal conditions. Functional neuroplasticity enables a change in behaviour and ultimately provides a major mechanism for enhanced survival in a given environment. There are two main types of plasticity, positive and negative plasticity. Positive plasticity describes abilities and brain processes that benefit an animal. Negative plasticity is related to processes that tend to be harmful. In this study, positive neuroplasticity was investigated in relation to aggressive behaviour and processing of novel signals; processes that are both required for successful survival in a changing habitat. Negative plasticity was studied in several stages of addiction, a psychiatric disease in which normal plasticity is interfered by drugs of abuse eventually leading to compulsive drug use. The neurotransmitter glutamate has a well-established role in chemical signalling between neurons, and an emerging role as a major component regulating neuroplasticity. Glutamate receptors of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type are tetramers composed of subunits GluA1-4 and they mediate a majority of the fast synaptic neurotransmission, that is also implicated in neuroplastic processes. Here, the AMPA receptor subunit GluA1-deficient mouse line (GluA1-KO mouse line) was studied using behavioural and neurochemical approaches. GluA1-KO mouse line provides an alternative approach to study the importance of AMPA receptors in neuroplasticity, as there are no subunit-selective pharmacological ligands available. GluA1-KO mice displayed less propensity to change their agonistic behaviour when exposed to an altered social environment in comparison with wild-type (WT) control mice, increased responsiveness towards spatial novelty followed by deficient habituation, decreased capability to develop tolerance to benzodiazepine flurazepam, and defective morphine-induced state-dependency. Taken together, these results propose a bidirectional role for GluA1 subunit in positive and negative neuroplastic processes. In summary, these results strengthen the role of GluA1 subunit in neuroplasticity, and may assist future drug development in disorders in which neuroplasticity plays a role.Muutamme käyttäytymistämme ympäristön muuttuessa. Käyttäytymisen muutos tulee esiin esimerkiksi silloin kun opimme selviytymään uudessa sosiaalisessa tilanteessa tai käsittelemään uutta tietoa. Käyttäytymisen muuttuminen perustuu aivojen rakenteen ja toiminnan muutoksiin eli aivojen muovautuvuuteen (neuroplastisuus). Aivojen muovautuvuutta voi tapahtua myös aivojen sisäisesti ilman ympäristön ärsykettä. Tästä esimerkkejä ovat aivoihin kohdistuvan vamman paraneminen tai aivojen altistuminen huumeille. Hermovälittäjäaine glutamaatti toimii aivojen pääasiallisena viestinvälitystä lisäävänä välittäjäaineena. Tämän tehtävän lisäksi glutamaatti ja sen reseptorit osallistuvat aivojen muovautuvuuden säätelyyn. Glutamaattireseptoreista α-amino-3-hydroksi-5-metyyli-4-isoksatsolipropionihappo (AMPA)-tyypin reseptorit koostuvat neljästä alayksiköstä GluA1-4, ja vastaavat glutamaatin nopeasta viestinvälityksestä. Työssä keskityttiin selvittämään GluA1 alayksikön merkitystä erilaisissa aivojen muovautuvuutta vaativissa tilanteissa. GluA1-alayksiköllisiin AMPA-reseptoreihin vaikuttavien lääkkeiden puuttuessa tutkimusmetodina käytettiin hiirikantaa, jolta oli geeniteknisesti poistettu GluA1-alayksikkö. Poistogeenisen hiirikannan käyttäytymistä ja neurokemiaa tutkittiin sosiaalisen interaktion, uuden tiedon käsittelyn ja huumealtistuksen tilanteissa. GluA1-poistogeeniselta hiirikannalta puuttui lähes täysin kyky mukautua muuttuneeseen sosiaaliseen tilanteeseen, eikä se kyennyt hiirille tyypilliseen aggressiokäyttäytymiseen. Uuteen paikkaan tuotaessa GluA1-poistogeenisen hiirikannan liikeaktiivisuus oli selvästi kontrollihiiriä suurempaa, ja tottuminen vallitsevaan tilanteeseen vei myös pidemmän ajan. Uuden paikan altistuksen aikana GluA1-poistogeenisen hiirikannan hermosolut aktivoituivat enemmän erityisesti hippokampuksessa, joka on muovautuvuuden kannalta tärkeä aivoalue. Bentsodiatsepiini fluratsepaamin aiheuttama toleranssi kehittyi vähäisemmin GluA1-poistogeeniselle hiirikannalle. Morfiinin aiheuttama ehdollistuminen puuttui GluA1-poistogeeniselta hiirikannalta silloin, kun hiiret testattiin ehdollistavaa morfiiniannosta vastaavan morfiiniannoksen vaikutuksen alaisina. Tulokset vahvistavat GluA1-alayksiköllisten AMPA-reseptoreiden merkitystä aivojen muovautuvuuden välittämisessä ja niillä voi olla merkitystä kehitettäessä lääkkeitä tai muita hoitomuotoja aivojen muovautuvuuteen liittyviin sairauksiin

Normal extinction and reinstatement of morphine-induced conditioned place preference in the GluA1-KO mouse line

Extinction and reinstatement of morphine-induced conditioned place preference were studied in glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-receptor GluA1 subunit-deficient mice (global GluA1-KO mice). In line with previous findings, both acquisition and expression of conditioned place preference to morphine (20 mg/kg, subcutaneously) were fully functional in GluA1 KO mice compared with wild-type littermate controls (GluA1-WT), thus enabling the study of extinction. With a 10-session extinction paradigm, the GluA1 KO mice showed complete extinction similar to that of the GluA1-WT mice. Morphine-induced reinstatement (10 mg/kg, subcutaneously) was detected in both mouse lines. GluA1 KO mice moved more during all the phases of the experiment, including the place conditioning trials, extinction sessions, and place preference tests. The results suggest that the GluA1 subunit may be dispensable or prone to compensation at the neural circuitries delineating extinction and reinstatement. The GluA1 KO mice show altered long-term between-session habituation, which extends longer than previously anticipated.Peer reviewe

Rapid analysis of intraperitoneally administered morphine in mouse plasma and brain by microchip electrophoresis-electrochemical detection

Animal studies remain an essential part of drug discovery since in vitro models are not capable of describing the complete living organism. We developed and qualified a microchip electrophoresis-electrochemical detection (MCE-EC) method for rapid analysis of morphine in mouse plasma using a commercial MCE-EC device. Following liquid-liquid extraction (LLE), we achieved within-run precision of 3.7 and 4.5% (coefficient of variation, CV, n = 6) and accuracy of 106.9% and 100.7% at biologically relevant morphine concentrations of 5 and 20 mu M in plasma, respectively. The same method was further challenged by morphine detection in mouse brain homogenates with equally good within-run precision (7.8% CV, n = 5) at 1 mu M concentration. The qualified method was applied to analyze a set of plasma and brain homogenate samples derived from a behavioral animal study. After intraperitoneal administration of 20 mg/kg morphine hydrochloride, the detected morphine concentrations in plasma were between 6.7 and 17 mu M. As expected, the morphine concentrations in the brain were significantly lower, ca. 80125 nM (280-410 pg morphine/mg dissected brain), and could only be detected after preconcentration achieved during LLE. In all, the microchip-based separation system is proven feasible for rapid analysis of morphine to provide supplementary chemical information to behavioral animal studies.Peer reviewe

Attenuation of Novelty-Induced Hyperactivity of Gria1-/- Mice by Cannabidiol and Hippocampal Inhibitory Chemogenetics

Gene-targeted mice with deficient AMPA receptor GluA1 subunits (Gria1-/- mice) show robust hyperlocomotion in a novel environment, suggesting them to constitute a model for hyperactivity disorders such as mania, schizophrenia and attention deficit hyperactivity disorder. This behavioral alteration has been associated with increased neuronal activation in the hippocampus, and it can be attenuated by chronic treatment with antimanic drugs, such as lithium, valproic acid, and lamotrigine. Now we found that systemic cannabidiol strongly blunted the hyperactivity and the hippocampal c-Fos expression of the Gria1-/- mice, while not affecting the wild-type littermate controls. Acute bilateral intra-dorsal hippocampal infusion of cannabidiol partially blocked the hyperactivity of the Gria1-/- mice, but had no effect on wild-types. The activation of the inhibitory DREADD receptor hM4Gi in the dorsal hippocampus by clozapine-N-oxide robustly inhibited the hyperactivity of the Gria1-/- mice, but had no effect on the locomotion of wild-type mice. Our results show that enhanced neuronal excitability in the hippocampus is associated with pronounced novelty-induced hyperactivity of GluA1 subunit-deficient mice. When this enhanced response of hippocampal neurons to novel stimuli is specifically reduced in the hippocampus by pharmacological treatment or by chemogenetic inhibition, Gria1-/- mice recover from behavioral hyperactivity, suggesting a hippocampal dysfunction in hyperactive behaviors that can be treated with cannabidiol.Peer reviewe

GABAA receptor drugs and neuronal plasticity in reward and aversion: focus on the ventral tegmental area.

Peer reviewe

Chronic Treatment with Mood-Stabilizers Attenuates Abnormal Hyperlocomotion of GluA1-Subunit Deficient Mice

Peer reviewe

Nicotinic α4 Receptor-Mediated Cholinergic Influences on Food Intake and Activity Patterns in Hypothalamic Circuits.

Nicotinic acetylcholine receptors (nAChRs) play an important role in regulating appetite and have been shown to do so by influencing neural activity in the hypothalamus. To shed light on the hypothalamic circuits governing acetylcholine's (ACh) regulation of appetite this study investigated the influence of hypothalamic nAChRs expressing the α4 subunit. We found that antagonizing the α4β2 nAChR locally in the lateral hypothalamus with di-hydro-ß-erythroidine (DHβE), an α4 nAChR antagonist with moderate affinity, caused an increase in food intake following free access to food after a 12 hour fast, compared to saline-infused animals. Immunocytochemical analysis revealed that orexin/hypocretin (HO), oxytocin, and tyrosine hydroxylase (TH)-containing neurons in the A13 and A12 of the hypothalamus expressed the nAChR α4 subunit in varying amounts (34%, 42%, 50%, and 51%, respectively) whereas melanin concentrating hormone (MCH) neurons did not, suggesting that DHβE-mediated increases in food intake may be due to a direct activation of specific hypothalamic circuits. Systemic DHβE (2 mg/kg) administration similarly increased food intake following a 12 hour fast. In these animals a subpopulation of orexin/hypocretin neurons showed elevated activity compared to control animals and MCH neuronal activity was overall lower as measured by expression of the immediate early gene marker for neuronal activity cFos. However, oxytocin neurons in the paraventricular hypothalamus and TH-containing neurons in the A13 and A12 did not show differential activity patterns. These results indicate that various neurochemically distinct hypothalamic populations are under the influence of α4β2 nAChRs and that cholinergic inputs to the lateral hypothalamus can affect satiety signals through activation of local α4β2 nAChR-mediated transmission.This work was supported by the Royal Society and the European Union (Latin America/European Liason, LAEL).This is the final version of the article. It first appeared from PLOS via http://dx.doi.org/1371/journal.pone.013332

Importance of GluA1 Subunit-Containing AMPA Glutamate Receptors for Morphine State-Dependency

Peer reviewe

Optogenetic evidence for inhibitory signaling from orexin to MCH neurons via local microcircuits.

The lateral hypothalamus (LH) is a key regulator of multiple vital behaviors. The firing of brain-wide-projecting LH neurons releases neuropeptides promoting wakefulness (orexin/hypocretin; OH), or sleep (melanin-concentrating hormone; MCH). OH neurons, which coexpress glutamate and dynorphin, have been proposed to excite their neighbors, including MCH neurons, suggesting that LH may sometimes coengage its antagonistic outputs. However, it remains unclear if, when, and how OH actions promote temporal separation of the sleep and wake signals, a process that fails in narcolepsy caused by OH loss. To explore this directly, we paired optogenetic stimulation of OH cells (at rates that promoted awakening in vivo) with electrical monitoring of MCH cells in mouse brain slices. Membrane potential recordings showed that OH cell firing inhibited action potential firing in most MCH neurons, an effect that required GABAA but not dynorphin receptors. Membrane current analysis showed that OH cell firing increased the frequency of fast GABAergic currents in MCH cells, an effect blocked by antagonists of OH but not dynorphin or glutamate receptors, and mimicked by bath-applied OH peptide. In turn, neural network imaging with a calcium indicator genetically targeted to MCH neurons showed that excitation by bath-applied OH peptides occurs in a minority of MCH cells. Collectively, our data provide functional microcircuit evidence that intra-LH feedforward loops may facilitate appropriate switching between sleep and wake signals, potentially preventing sleep disorders.This work was supported by the Royal Society Dorothy Hodgkin Fellowship (JAS) and HFSP 37 Young Investigator Award (DB and AA, award ref. RGY0076/2012).This is the final version. It first appeared at http://www.jneurosci.org/content/35/14/5435.abstract