Neural Correlates of Behavioural Olfactory Sensitivity Changes Seasonally in European Starlings

Possibly due to the small size of the olfactory bulb (OB) as compared to rodents, it was generally believed that songbirds lack a well-developed sense of smell. This belief was recently revised by several studies showing that various bird species, including passerines, use olfaction in many respects of life. During courtship and nest building, male European starlings (Sturnus vulgaris) incorporate aromatic herbs that are rich in volatile compounds (e.g., milfoil, Achillea millefolium) into the nests and they use olfactory cues to identify these plants. Interestingly, European starlings show seasonal differences in their ability to respond to odour cues: odour sensitivity peaks during nest-building in the spring, but is almost non-existent during the non-breeding season.This study used repeated in vivo Manganese-enhanced MRI to quantify for the first time possible seasonal changes in the anatomy and activity of the OB in starling brains. We demonstrated that the OB of the starling exhibits a functional seasonal plasticity of certain plant odour specificity and that the OB is only able to detect milfoil odour during the breeding season. Volumetric analysis showed that this seasonal change in activity is not linked to a change in OB volume. By subsequently experimentally elevating testosterone (T) in half of the males during the non-breeding season we showed that the OB volume was increased compared to controls.By investigating the neural substrate of seasonal olfactory sensitivity changes we show that the starlings' OB loses its ability during the non-breeding season to detect a natural odour of a plant preferred as green nest material by male starlings. We found that testosterone, applied during the non-breeding season, does not restore the discriminatory ability of the OB but has an influence on its size

Manganese-Enhanced Magnetic Resonance Imaging: Overview and Central Nervous System Applications With a Focus on Neurodegeneration

Manganese-enhanced magnetic resonance imaging (MEMRI) rose to prominence in the 1990s as a sensitive approach to high contrast imaging. Following the discovery of manganese conductance through calcium-permeable channels, MEMRI applications expanded to include functional imaging in the central nervous system (CNS) and other body systems. MEMRI has since been employed in the investigation of physiology in many animal models and in humans. Here, we review historical perspectives that follow the evolution of applied MRI research into MEMRI with particular focus on its potential toxicity. Furthermore, we discuss the more current in vivo investigative uses of MEMRI in CNS investigations and the brief but decorated clinical usage of chelated manganese compound mangafodipir in humans

Manganese-Enhanced Magnetic Resonance Imaging: Overview and Central Nervous System Applications With a Focus on Neurodegeneration

Manganese-enhanced magnetic resonance imaging (MEMRI) rose to prominence in the 1990s as a sensitive approach to high contrast imaging. Following the discovery of manganese conductance through calcium-permeable channels, MEMRI applications expanded to include functional imaging in the central nervous system (CNS) and other body systems. MEMRI has since been employed in the investigation of physiology in many animal models and in humans. Here, we review historical perspectives that follow the evolution of applied MRI research into MEMRI with particular focus on its potential toxicity. Furthermore, we discuss the more current in vivo investigative uses of MEMRI in CNS investigations and the brief but decorated clinical usage of chelated manganese compound mangafodipir in humans

Automated Computational Processing of 3-D MR Images of Mouse Brain for Phenotyping of Living Animals

Magnetic resonance (MR) imaging provides a method to obtain anatomical information from the brain in vivo that is not typically available by optical imaging because of this organ's opacity. MR is nondestructive and obtains deep tissue contrast with 100-µm^3 voxel resolution or better. Manganese-enhanced MRI (MEMRI) may be used to observe axonal transport and localized neural activity in the living rodent and avian brain. Such enhancement enables researchers to investigate differences in functional circuitry or neuronal activity in images of brains of different animals. Moreover, once MR images of a number of animals are aligned into a single matrix, statistical analysis can be done comparing MR intensities between different multi-animal cohorts comprising individuals from different mouse strains or different transgenic animals, or at different time points after an experimental manipulation. Although preprocessing steps for such comparisons (including skull stripping and alignment) are automated for human imaging, no such automated processing has previously been readily available for mouse or other widely used experimental animals, and most investigators use in-house custom processing. This protocol describes a stepwise method to perform such preprocessing for mouse

Manganese-Enhanced Magnetic Resonance Imaging: Overview and Central Nervous System Applications With a Focus on Neurodegeneration

Manganese-enhanced magnetic resonance imaging (MEMRI) rose to prominence in the 1990s as a sensitive approach to high contrast imaging. Following the discovery of manganese conductance through calcium-permeable channels, MEMRI applications expanded to include functional imaging in the central nervous system (CNS) and other body systems. MEMRI has since been employed in the investigation of physiology in many animal models and in humans. Here, we review historical perspectives that follow the evolution of applied MRI research into MEMRI with particular focus on its potential toxicity. Furthermore, we discuss the more current in vivo investigative uses of MEMRI in CNS investigations and the brief but decorated clinical usage of chelated manganese compound mangafodipir in humans

Blast-Induced Tinnitus: A Combined Behavioral, Memri, And Electrophysiology Study

ABSTRACT BLAST-INDUCED TINNITUS: A COMBINED BEHAVIORAL, MEMRE, AND ELECTROPHYSIOLOGY STUDY by JESSICA OUYANG May 2014 Advisor: Drs. Steve Cala & Jinsheng Zhang Major: Physiology Degree: Doctor of Philosophy Tinnitus and hearing loss are the frequent auditory-related co-morbidities of blast trauma. The etiology of blast-induced tinnitus is also muddled by brain mechanisms associated with emotional and cognitive problems such as anxiety, memory loss, and depression. We set out to develop a realistic and ecologically valid model to address changes of cognitive status and psychological state that are associated with blast- induced tinnitus. In this study, 19 adult rats were randomly divided into the sham group (n=6) and the blast group (n=13). Blast exposure (14 psi) was conducted via a shock wave tube to expose the left ears of the rats in the blast group, and a sham exposure was conducted to the rats in the sham group. Blast-induced tinnitus was evaluated with gap detection and pre-pulse inhibition (PPI) acoustic startle reflex paradigms; the changes of thresholds of the hearing was evaluated with auditory brainstem response (ABRs), the change in the level of anxiety was evaluated with elevated plus maze; and the change in the status of memory was evaluated with one-day Morris water maze. To investigate blast-induced neuronal changes in the limbic structures, we utilized MEMRI technique. Obtained with MRIcro, MR intensity signal-to-noise ratios (SNRs) of 83 selected limbic structures were measured to represent the level of synaptic activity. Of the 13 rats that were exposed to blast shock wave, 8 rats developed chronic tinnitus on post-exposure day 35 (PED35) and 5 rats did not. Our results showed that compared to rats in the sham group (n=6), (1) rats in the blast group with or without tinnitus demonstrated higher level of anxiety (p\u3c0.05); (2) rats in the blast group that exhibited behavioral evidences of tinnitus (n=8) demonstrated neuronal hyperactivity in bilateral amygdaloidal complex, specifically bilateral basolateral groups and the left cortical-like group of the amygdala (p\u3c0.05); and (3) rats in the blast group demonstrated neuronal hyperactivity in bilateral nucleus accumbens core (p\u3c0.05). In conclusion, the elevated level of synaptic activity in the bilateral amygdala and nucleus accumbens core indicates central plasticity associated with blast-induced tinnitus

Alkoholin palkitseviin ominaisuuksiin ja amfetamiinin myrkkyvaikutuksiin liittyvien hermostollisten järjestelmien funktionaalinen kuvantaminen

Alcohol addiction is one of the most prevalent brain disorders in the world. A major hurdle for reducing alcohol-related harms and developing effective treatments is the poor understanding of neural processes responsible for the development of dependence and addiction. Alcohol has been shown to affect various neurotransmitter systems; however, the mesolimbic dopamine (DA) system, which projects from the ventral tegmental area (VTA) to the nucleus accumbens (NAc), has been thought to play a key role in producing the reinforcing effects of alcohol. The VTA region has also been suggested to be the anatomical site for the interaction of the dopaminergic system with the opioidergic and γ-aminobutyric acid (GABA) systems. Here, manganese-enhanced magnetic resonance imaging (MEMRI) and behavioral tests were used to study drug-induced alterations in brain activity of the alcohol-preferring AA (Alko Alcohol) and heterogeneous Wistar rats. MEMRI is based on the ability of paramagnetic Mn2+ ions to accumulate in excitable neurons, thus enhancing the T1-weighted signal in activated brain regions. Mn2+ ions can also be transported anterogradely and retrogradely in neurons, released to the synaptic cleft, and taken up by other neurons. These properties allow MEMRI to measure long-term changes in brain activity, as well as map neural pathways involved in acute and long-term drug actions, including drug reward and toxicity. The AA rats exposed to alcohol compared to water controls displayed a widespread and persistent activation in brain regions that have been previously linked with alcohol reinforcement. Similarly, activity in neural pathways originating in the NAc and projecting caudally to the midbrain was enhanced in alcohol drinking rats. Moreover, this alcohol-induced activation was blocked by systemic naltrexone (NLX) administration. Comparison of naïve AA and Wistar rats revealed a lowered basal activity in the caudal linear nucleus (CLi) of AA rats, which was restored by voluntary alcohol drinking. The intra-CLi γ-aminobutyric acid type A receptor (GABAA) agonist muscimol produced a dose-dependent increase in alcohol drinking, blocked by co-administration of the GABAA antagonist bicuculline, suggesting that the CLi GABAergic system is involved in the regulation of alcohol reward. MEMRI was also employed for assessing stimulant-induced toxicity. Methamphetamine and mephedron displayed disparate effects on brain activity, as methamphetamine produced widespread decreases in activity, whereas mephedron increased activity in limited brain areas. Taken together, the use of MEMRI for mapping alcohol- and stimulant-induced alterations in functional brain activity revealed networks and specific pathways that have potential for guiding further translational efforts to develop medications for drug abuse disorders, as well as for evaluating drug-induced toxicity.Alkoholismi on maailman yleisimpiä aivosairauksia. Alkoholin aiheuttamien haittojen vähentämistä ja tehokkaiden hoitomuotojen kehittämistä haittaa se, että päihderiippuvuuden kehittymiseen vaikuttavat aivojen toiminnan muutokset ymmärretään yhä huonosti. Alkoholin vaikutukset syntyvät monien hermoston välittäjäaineiden toiminnan kautta, ja etenkin nk. mesolimbisellä dopamiinijärjestelmällä on arveltu olevan keskeinen rooli alkoholin tuottamassa mielihyvässä. Töissämme käytettiin mangaanitehosteista magneettiresonanssikuvantamista (MRI) selvitettäessä alkoholin ja stimulanttien vaikutuksia alkoholiin mieltyneiden AA-rottien ja normaalien Wistar-rottien aivoissa. Kyseinen kuvantamismenetelmä perustuu siihen, että magneettisia ominaisuuksia omaavat mangaani-ionit kulkeutuvat hermopäätteiden kalsiumkanavien kautta hermosoluihin niiden aktivoituessa. Mangaani-ioneja sisältävien hermosolujen muodostamat radat ja aivoalueet tuottavat mitattavissa olevan signaalin. Mangaani voi myös siirtyä synapsiraon ylitse viereiseen hermosoluun ja tuottaa siten MRI-kuvan aktiivisista hermoverkoista. Viikkoja kestänyt alkoholin juominen johti aivojen aktiivisuusmuutoksiin sellaisilla aivojen alueilla, joiden on aikaisemmin oletettu liittyvän alkoholin positiivisiin vaikutuksiin. Selvitettäessä tarkemmin yksittäisten hermoratojen merkitystä havaittiin, että etuaivojen accumbens-tumakkeen keskiaivoihin lähettävä rata aktivoitui alkoholin juomisen seurauksena, kun taas alkoholismin hoidossa käytettävä lääkeaine, naltreksoni, vähensi alkoholin aiheuttamaa aktivaatiota. Verrattaessa alkoholiin mieltyneitä rottia tavalliseen rottakantaan löydettiin keskiaivoista tumake (kaudaalinen lineaaritumake), jonka aktiivisuus oli ennen alkoholin juomista tavallista alhaisempi, mutta jota alkoholi aktivoi. Kun tähän tumakkeeseen annettiin ainetta, joka salpasi gamma-aminovoihapon (GABA) vastaanottokohdat, alkoholin kulutus lisääntyi huomattavasti. Tämä löydös viittasi keskiaivojen GABA-järjestelmän merkitykseen alkoholin kulutuksen säätelyssä. Kaikkiaan kehittämämme mangaanitehosteinen magneettiresonanssikuvantaminen tuotti uutta tietoa alkoholin juomista säätelevistä hermoradoista ja yksittäisistä aivojen alueista. Tätä tietoa voidaan käyttää hyväksi, kun suunnitellaan ja testataan alkoholismin hoitoon tarkoitettuja lääkeaineita

In vivo identification of brain structures functionally involved in spatial learning and strategy switch

Spatial learning is a complex behavior which includes, among others, encoding of space, sensory and motivational processes, arousal and locomotor performance. Today, our view on spatial navigation is largely hippocampus-centrist. Less is known about the involvement of brain structures up- and downstream, or out of this circuit. Here, I provide the first in vivo assessment of the neural matrix underlying spatial learning, using functional manganese-enhanced MRI (MEMRI) and voxel-wise whole brain analysis. Mice underwent place-learning (PL) vs. response-learning (RL) in the water cross maze (WCM) and its readout was correlated to the Mn2+ contrasts. Thus, I identified structures involved in spatial learning largely overlooked in the past, due to methods focused on region of interest (ROI) analyses. These structures include several sensory-related structures and differ between place-learners and response-learners, with the former (PL) comprising mostly structures involved in different properties of visual processing, such as horizontal gaze (e.g. nucleus prepositus) and saccade (e.g. fastigial nucleus), or provide vision-input and eye movement information from parahippocampal (e.g. presubiculum, perirhinal, postrhinal and ectorhinal areas) and other regions (e.g. orbital area, superior colliculus and vestibular ocular-reflex from the vestibular nucleus) likely to head-direction, grid- and place-cells; and the latter (RL) presenting structures related to more basic rodent sensory computations, like odor (e.g main and accessory olfactory bulb, cortical amygdala, piriform, endopiriform and postpiriform areas) and acoustic stimuli representation (e.g. auditory area, nucleus of the lateral lemniscus and superior olivary complex), or sensory-motor properties, such as body representation (e.g. somatosensory area – upper limbs) and head-direction signal. Add-on experiments pointed to preferential Mn2+ accumulation towards projection terminals, suggesting that our mapping was mostly formed by projection sites of the originally activated structures. This is corroborated by in-depth analysis of MEMRI data after WCM learning showing mostly downstream targets of the hippocampus. These differ between fornical afferences from vCA1 and direct innervation from dCA1/iCA1 (for PL), and structures along the longitudinal association bundle originating in vCA1 (for RL). To elucidate the pattern of Mn2+ accumulation seen on the scans, I performed c-fos expression analyses following learning in the WCM. This helped me identify the structures initially activated during spatial learning and its underlying connectivity to establish the matrix. Finally, to test the causal involvement of selected structures from our previous findings I inhibited them (through DREADDs) while mice performed the WCM task. I also focused on the causal involvement of the vHPC-mPFC circuit on strategy switch during WCM learning. I believe that this study might shed light into new brain structures involved in spatial learning and strategy switch and complement the current knowledge on these circuits’ connectivity. Moreover, I elucidated some functional mechanisms of MEMRI, clarifying the interpretation of data obtained with this method and its possible future applications

Volumetric Manganese Enhanced Magnetic Resonance Imaging in mice (mus musculus)

The present doctoral thesis introduces a method for semi-automatic volumetric analysis of the hippocampus and other distinct brain regions in laboratory mice. The method of volumetric manganese enhanced magnetic resonance imaging (vMEMRI) makes use of the paramagnetic property of the manganese ion, Mn2+, which results in a positive contrast enhancement of specific brain areas on the MR image and enables a more detailed image of brain morphology. The chemical similarity of Mn2+ to Calcium leads to an accumulation of Mn2+ in excited cells and consequentially an enhanced signal in certain brain regions in an activity dependent manner. However, one major drawback for vMEMRI is the toxicity of Mn2+. Therefore, the aims of the thesis have been: (1) Establishment of a MEMRI protocol in mice (2) Optimization of a Mn2+ application procedure to reduce toxic side effects (3) Development of an automatized method to determine hippocampal volume (4) Validation of vMEMRI analysis (5) Application of volumetric analysis in mouse models of psychopathology This thesis splits into 3 studies. Study 1 deals with Mn2+ toxicity and introduces an application method that considerably reduces the toxic side effects of Mn2+. Study 2 validates vMEMRI as a method to reliably determine hippocampal volume and explores its utilization it in animals with genetically and chemically modified hippocampi. Study 3 displays the application vMEMRI in a mouse model of a psychiatric disorder. Study 1 shows that a single application of Mn2+ in dosages used in current MEMRI studies leads to considerable toxic side effects measurable with physiological, behavioral and endocrine markers. In contrast, a fractionated application of a low dose of Mn2+ is proposed as an alternative to a single injection of a high dose. Repeated application of low dosages of 30 mg/kg Mn2+ showed less toxic side effects compared to the application schemes with higher dosages of 60 mg/kg. Additionally, the best vMEMRI signal contrast was seen for an injection protocol of 30 mg/kg 8 times with an inter-injection interval of 24 h (8x30/24 protocol). The impact of the 8x30/24 application protocol on longitudinal studies was tested by determining whether learning processes are disturbed. Mice were injected with the 8x30/24 protocol 2 weeks prior to receiving a single footshock. Manganese injected mice showed less contextual freezing to the shock context and a shock context reminder one month after shock application. Furthermore, mice showed increased hyperarousal and no avoidance of shock context related odors. This impairment in fear conditioning indicates a disturbed associative learning of Mn2+ injected mice. Therefore, it was investigated whether Mn2+ application shows a specific disturbance of hippocampus dependent learning. Mice were subjected to habitual and spatial learning protocols 12 h after each injection in a water cross-maze. There was no impairment in learning protocols which allowed for hippocampus-independent habitual learning. However, Mn2+ injected mice were specifically impaired in the hippocampus-dependent spatial learning protocol. Furthermore, it was shown that only mice with higher Mn2+ accumulation showed this impairment. Altogether, the results of this chapter argue for a fractionated application scheme such as 30 mg/kg every 24 h for 8 days to provide sufficient MEMRI signal contrast while minimizing toxic side effects. However, the treatment procedure has to be further improved to allow for an analysis of hippocampus-dependent learning processes as well. Because of the potential side effects, the vMEMRI method was applied as a final experiment in study 2 and 3. Study 2 introduces the method of vMEMRI, which allows, for the first time, an in vivo semi-automatic detection of hippocampal volume. Hippocampal volume of mice with genetically altered adult neurogenesis and those with chemically lesioned hippocampi could be analyzed with vMEMRI. Even the highly variable differences in hippocampal volume of these animals could be detected with vMEMRI. vMEMRI data correlated with manually obtained volumes and are in agreement with previously reported histological findings, indicating the high reliability of this method. Study 3 investigates the ability of vMEMRI to detect even small differences in brain morphology by examining volumetric changes of the hippocampus and other brain structures in a mouse model of PTSD supplemented with enriched housing conditions. It was shown, that exposure to a brief inescapable foot shock led to a volume reduction in both the left hippocampus and right central amygdala two months later. Enriched housing decreased the intensity of trauma-associated contextual fear independently of whether it was provided before or after the shock. vMEMRI analysis revealed that enriched housing led to an increase in whole brain volume, including the lateral ventricles and the hippocampus. Furthermore, the enhancement of hippocampal volume through enriched housing was accompanied by the amelioration of trauma-associated PTSD-like symptoms. Hippocampal volume gain and loss was mirrored by ex vivo ultramicroscopic measurements of the hippocampus. Together, these data demonstrate that vMEMRI is able to detect small changes in hippocampal and central amygdalar volumes induced by a traumatic experience in mice. In conclusion, vMEMRI proves to be very reliable and able to detect small volumetric differences in various brain regions in living mice. vMEMRI opens up a great number possibilities for future research determining neuroanatomical structure, volumes and activity in vivo as well as the ability to repeatedly determine such characteristics within each subject, given an improvement of the Mn2+ treatment protocols to minimize potential toxic side effects