The electrophysiological properties of dentate granule cells and hippocampal pyramidal neurons were examined with extracellular and intracellular recording techniques in the hippocampal slice. Intracellular analysis revealed that there may exist two populations of granule cells distinguishable by the presence or absence of non-linear current-voltage (I-V) membrane properties (anomalous rectification, AR). The granule cells exhibiting AR also maintained greater resting membrane potentials and action potential (AP) amplitude values. The membrane input resistance (Rn) and time constant (Tc) measurements were similar between the populations in response to hyperpolarizing current injection, but granule cells displaying AR had significantly higher Rn and Tc values in response to depolarizing pulses. Both groups also responded to maintained depolarizing current injection with repetitive AP discharges; however, this response accommodated. Upon termination of the depolarizing current injection, an afterhyperpolarization (AHP) resulted, the amplitude of which appeared to depend on the duration of the depolarizing pulse and not on the number of APs generated during the pulse. Stimulation of either the lateral (LPP) or medial (MPP) perforant paths evoked a monosynaptic EPSP followed by a depolarizing afterpotential (DAP) and a long afterhyperpolarization (LHP). In contrast, antidromic stimulation elicited a depolarizing-IPSP (D-IPSP) and a LHP. Both the DAP and D-IPSP were reversed by membrane depolarization, whereas, the LHP was inverted by membrane hyperpolarization. In all cases, however, the EPSP could not be inverted. Afterpotentials were associated with an increase in conductance, but the change accompanying the LHP was less than the DAP and D-IPSP. In addition, by reducing the [Ca]₀ and increasing the [Mg]₀, the DAP was attenuated and the LHP eliminated. Similar results were also obtained with the GABAB agonist, baclofen. Paired pulse stimulation of either the LPP or MPP resulted in the potentiation of the intracellular EPSP at condition-test (C-T) intervals less than 100 ms; however, simultaneous extracellular records from the granule cell layer (GCL) illustrated depression of the EPSP. The discrepancy between the extra- and intracellular recordings was shown to be related to the presence of the DAP. In addition, the MPP evoked test EPSP at C-T intervals greater than 150 ms exhibited inhibition regardless of whether it was recorded inside or outside the granule cell and this EPSP depression was partially due to the granule cell LHP. The LPP evoked test EPSP potentiated at all C-T intervals less than 1s when recorded from the outer molecular layer (OML) but was inhibited at both the GCL and intracellular recording sites. These data confirmed that postsynaptic processes contribute to the short-term alterations observed with paired pulse stimulation. The typical inhibition-potentiation-inhibition sequence of the perforant path (PP) evoked population spike (PS) was noted at C-T intervals of 20, 80 and 400 ms, respectively. The inhibition of the PS at 20 ms was abolished with perfusion of the GABA antagonist, bicuculline. In contrast, the PS inhibition at 400ms was unaffected by this treatment but was slightly attenuated by the gKca antagonist TEA. A number of factors appeared to contribute to the potentiation of the PS: 1) reduction in AP threshold; 2) the presence of the DAP; and 3) extrasynaptic events. In addition to the PS data from normal tissue, hippocampal slices from chronically kindled rats exhibited depression of the PS at all C-T intervals tested. This augmentation of inhibition was dependent on the presence of hippocampal afterdischarges but not on motor seizures. Perfusing the kindled slices with either bicuculline or lowered [Cl]₀ did not markedly reverse the enhanced inhibition at C-T intervals which displayed dramatic facilitation in normal slices. Intracellular recordings of granule cells obtained from kindled slices also exhibited an increase in the Rn and Tc. Both the alterations in inhibition and membrane characteristics appear to be localized to.the granule cells, since these changes were not observed in CA1 pyramidal neurons. These data indicate that short-term and long-term alterations in granule cell neuronal excitability are partially due to changes in the postsynaptic membrane. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

Psychopathy is a complex personality disorder denned by a constellation of affective and behavioral characteristics. There is accumulating behavioral evidence suggesting that the condition is associated with impairments in affective, cognitive, and language functions. However, relatively little is known regarding the neural systems underlying these abnormalities. The present thesis is comprised of five experiments designed to elucidate and characterize the abnormal functional architecture underlying these abnormalities in psychopathic criminals. In Experiments 1 and 2, functional magnetic resonance imaging (fMRI) was used to elucidate the neural systems underling abnormal semantic and affective processes in these individuals. In Experiments 3, 4 and 5, event-related potentials (ERPs) were used to characterize the temporal features of cognitive and language functions in psychopaths. The results from Experiment 1 revealed that compared to control participants, psychopaths performed more poorly and failed to showed the appropriate neural differentiation between abstract and concrete stimuli during a lexical decision task. These deficits were located in the right anterior superior temporal gyrus. The results from Experiment 2 indicated that psychopaths, relative to control participants, showed less activation for processing affective stimuli than for neutral stimuli in several neural regions, including the right amygdala/hippocampal formation, left parahippocampal gyrus, ventral striatum, and in the anterior and posterior cingulate. Psychopaths did show greater activation for processing affective than for neutral stimuli in regions located outside the limbic system, including bilateral inferior frontal gyrus. These latter data suggesting that psychopaths used different neural systems than did controls for performing the task. The results from Experiments 3 and 4 indicated that psychopathy is associated with abnormalities in the P3 ERP component elicited by target stimuli during visual and auditory oddball tasks. In addition, the psychopaths' ERPs to visual and auditory target stimuli were characterized by large fronto-central negativities in the 350-600 millisecond time window. These fronto-central ERP negativities are similar to those observed for patients with temporal lobe damage. In Experiment 5, using a standard sentence processing paradigm, no group differences were observed between psychopaths and nonpsychopaths in the amplitude of the N400 potential elicited by terminal words of sentences that were either congruent or incongruent with the previous sentence context. These results indicate that the abnormal fronto-central ERP negativities observed in previous studies of language function in psychopaths are not related to processes involved in the generation of the N400. Taken together, these data suggest that one of the cardinal abnormalities in psychopathy is abnormal semantic processing of conceptually abstract information and affective information and that these abnormalities are related to the function of neural circuits in the anterior temporal lobes and lateral frontal cortex. / Arts, Faculty of / Psychology, Department of / Graduate

Excitatory glutamatergic inputs from limbic regions such as the hippocampus and the basolateral amygdala (BLA), and dopaminergic inputs from the ventral tegmental area converge in the nucleus accumbens (NAc). It has been proposed that interactions between these glutamatergic and dopaminergic pathways play an important role in adaptive behaviors. The present thesis employed a multidisciplinary approach to study these interactions, with a specific emphasis on the importance of mesoaccumbens dopamine (DA) transmission, in order to obtain a better understanding of the neural mechanisms by which the NAc transforms signals from the temporal lobes into behavior. The experiments of Chapter 2 utilized extracellular single-unit recordings of individual NAc neurons in combination with electrochemical measures of DA efflux in the NAc. Recordings from NAc neurons which received input from the hippocampus but not the BLA revealed that increased efflux of mesoaccumbens DA, evoked by tetanic stimulation of the fimbria, potentiated hippocampal-evoked neural activity in these cells. These effects were mediated by both DA and NMDA receptors. Similar recordings from neurons which received converging input from both the hippocampus and the BLA revealed tetanic stimulation of the fimbria again potentiated hippocampal evoked spiking activity, while concurrently suppressing BLA-evoked spiking activity in the same neurons. The suppression of BLA-evoked spiking activity was activity-dependent, and was mediated by both D, and adenosine A, receptors. Chapter 3 showed that random foraging on a radial-arm maze, which is dependent on a neural circuit linking the hippocampus to the NAc, was correlated with an increase in mesoaccumbens DA extracellular levels, as measured with microdialysis. In Chapter 4, pharmacological blockade of DA or NMDA receptors in the NAc, or selective disruption of dopaminergic modulation of ventral subicular inputs to the NAc (using an asymmetrical infusion procedure) significantly disrupted random foraging. These effects were mediated by the Dl receptor. In Chapter 5, the present data are integrated with previous research to formulate a model of ventral striatal function. It is proposed that the NAc mediates behavior through distinct patterns of activity and inactivity driven by excitatory limbic input projecting to different groups of neural ensembles. Mesoaccumbens DA transmission plays an essential role in regulating the synchrony ensemble activity, augmenting activity in one ensemble while suppressing activity in another. It is argued that the modulatory effects of DA appears to be essential when an organism must switch from one form of adaptive behavior to another in response to a constantly changing environment. / Arts, Faculty of / Psychology, Department of / Graduate

Le bien-être animal est considéré un phénomène multidimensionnel basé sur les conditions et les expériences de vie de chaque individu, et lié aux fonctions organiques et à la sensibilité de l’individu même. L’étude des émotions animales est complexe mais les hypothèses sur leurs états émotifs peuvent être formulées sur la base de mesures neurophysiologiques, comportementales et cognitives. Des études récentes ont montré que la latéralité cérébrale et comportementale, la fréquence cardiaque et l'activité cérébrale (mesurée par électroencéphalographie sont des paramètres qui permettent d’évaluer la perception de la valence et du niveau stimulant des émotions chez l’animal et l'Homme. Le but principal de ce projet de thèse était d’étudier la perception que les chiens et les chevaux ont du contenu émotionnel des signaux humains et l’impact potentiel que peuvent avoir ces signaux sur l’état émotionnel de ces animaux et par conséquent sur leur bien-être. Dans ce but, nous avons présenté à ces animaux des stimuli exprimant diverses émotions. Nous avons utilisé une approche intégrée combinant l’analyse de la latéralité comportementale, de la fréquence cardiaque, de l’activité cérébrale et du comportement des sujets afin de répondre à 2 questions: 1) les chiens et les chevaux perçoivent-ils le contenu émotionnel des signaux humains? 2) Les chiens et les chevaux attribuent-ils une valence et une intensité différentes selon les émotions humaines perçues. Les résultats de ce travail de thèse montrent que les chiens et les chevaux traitent différemment les signaux émotionnels en fonction de leur valence et de leur intensité. La perception de la voix de l'homme par le cheval est modulée par la valence des interactions homme-cheval antérieures et par les conditions de vie des chevaux. En ce qui concerne les chiens, nos résultats montrent qu’ils discriminent et perçoivent les émotions contenues dans les signaux visuels, auditifs et olfactifs humains différemment, et nous fournissent de nouvelles connaissances sur le fonctionnement émotionnel du cerveau du chien. Les résultats de ce travail de thèse apportent un cadre théorique pour définir des paramètres utiles à l'évaluation du bien-être animal. / Animal welfare is considered to be a multidimensional phenomenon based upon life experiences and conditions, characterized by how an individual feels and functions. The study of emotions in animals is difficult but assumptions of emotional states are usually derived from neurophysiological, behavioral and cognitive measurements. Recent literature shows that cerebral and behavioral laterality, cardiac activity and brain activity (measured by electroencephalography) are suitable parameters to examine animals’ and human emotional processing along the valence and arousal dimensions. The main aim of the present research project was to investigate dogs and horses perception of the emotional content of human signals that potentially affects animals’ affective state and welfare. An integrated approach combining the analysis of behavioral lateralization, cardiac and brain activity, and subjects’ behavior was applied in order to answer to the following questions: 1) Do dogs and horses perceive the different emotional content of human signals? 2) Do dogs and horses attribute a different valence and intensity to the human emotions perceived? Overall, the results of this thesis project demonstrate that dogs and horses process differently emotional signals according to their valence and intensity. In particular, horses perception of a human voice is modulated by the valence of the prior horse-human interactions and by subjects’ living conditions. As for dogs, results demonstrate that they discriminate and perceive differently the emotional content of human visual, auditory and olfactory signals, providing new insights into the emotional functioning of the canine brain. The current research offers a theoretical framework for defining useful parameters to evaluate animal welfare.

While three decades of intensive cortical electrophysiology using a variety of sustained visual stimuli has made a significant contribution to many aspects of visual function, it has not supported the existence of intracortical circuit operations in cortical processing. This study investigated cortical processing by a comparison of the response of primary visual cortical neurones to transient electrical and strobe-flash stimulation. Experiments were performed on 74 anaesthetised Long Evans rats. Standard stereotaxic and extracellular electrophysiological techniques were employed. Continuous (on-line) raster plots and peri-stimulus time histograms (PSTHs) of the extracellular spikes from 81 visual cortical and 55 lateral geniculate nucleus (LGN) neurones were compiled. The strobe-flash stimuli (0.05 ms) were applied to the contralateral eye while the monopolar or bipolar electrical stimuli (0.2 ms, 80-400 μA) were applied to the ipsilateral LGN. 60 of the 81 (74%) tested cortical units were found to be responsive to visual stimuli. A distinct and consistent difference in the cortical response to the two types of transient stimuli was found: (a) Electrical stimulation evoked a prolonged period (197 ± 61 ms) of inhibition in all cortical neurones tested (n=20). This was the case even in those cortical units that were completely unresponsive to visual stimulation. The protracted inhibition was usually followed by a 100-200 ms phase of rebound excitation. (b) Flash stimulation evoked a prominent excitatory discharge (5-30 ms duration) after a latency of 30-60 ms from the onset of the stimulus (n = 59). This was followed by either moderate inhibition or return to a firing rate similar to control activity, for a maximum of 40 ms. Thereafter, cortical neurones showed a sustained increased level of activity with superimposed secondary excitatory phases. The duration of this late re-excitatory phase was 200-300 ms. In 17 of 20 (85%) tested units, the temporal profile of the cortical response to flash stimulation was modulated by small changes in the level of background illumination. In 16 of the 17 units, this sensitivity was reflected primarily as an emergence of a brief secondary inhibitory phase at the lowest level of background illumination (0 lux). Only 1 of the 17 cortical units displayed a flash-evoked primary inhibitory phase at O lux. We explored the possibility that neurones in the lateral geniculate nucleus (LGN) of the thalamus were responsible for the late phase of cortical reexcitation. 49 of the 55 (89%) LGN neurones could be classified as either of the "ON type" i.e. excited by visual stimuli, or the "OFF type" i.e. inhibited by visual stimuli. The response of ON-like LGN neurones to strobe-flash stimulation of the contralateral eye was characterised by a primary excitatory or early discharge (ED) phase after a latency of 25-40 ms. Thereafter, a 200- 400 ms period of inhibition was observed. In 57% of the sample, a rebound excitatory or late discharge (LD) phase completed the response. OFF-like LGN neurones were inhibited by the strobe-flash stimuli after a latency of 30- 35 ms. This flash-evoked inhibition was maintained for 200-400 ms. The sensitivity of the flash-evoked LGN response to the level of background illumination was tested in 11 ON-like and 10 OFF-like neurones. No sustained secondary excitatory events, as observed in visual cortical neurones, were found in any of the ON- and OFF-like LGN neurones, irrespective of the level of background illumination. In conclusion, the data show that the late re-excitatory phase evoked in cortical neurones upon strobe-flash stimulation, is not due to sustained LGN (thalamic) input. Rather, it suggests that these re-excitatory phases are due to intracortical processing of the transient stimuli. These findings emphasize the independent role of the cortex in computing the response to visual stimuli, and cast doubt on traditional theories that have emphasised the role of the thalamus in shaping cortical responses. The difference in the flash and electrically evoked cortical response suggests that even though substantial inhibition is available to the cortex, only a small fraction of this inhibitory capacity is utilised during natural stimulation.

The work presented in this thesis investigates whether primitive pallial brain circuits such as those found in teleost fish may also encode complex information such as spatial memory despite its circuitry being “simpler” than those found in species with much larger brains such as primates and rodents. Previous behavioral studies have already shown that most teleost fish are capable of spatially orienting themselves and remembering past food locations. Behavioral studies combined with selective brain lesions and related anatomical studies have identified a hippocampal-like region in the fish’s pallium; however, it is unknown whether the neurons located in this structure can also perform cortical-like computations as those found in the mammalian hippocampus. Consequently, this thesis will first present an anatomical characterization of the intrinsic circuitry of this hippocampal-like structure, followed by an in vitro electrophysiological characterization of its constituent neurons. Surprisingly, we have found that this hippocampal-like structure possesses many features reminiscent of the mammalian cortex, including recurrent local connectivity as well as a laminar/columnar-like organization. Furthermore, we have also identified many biophysical properties which would describe these hippocampal-like neurons as sparse coders, including a prominent after-hyperpolarizing potential and an adapting spike threshold with slow recovery. Since this particular dynamic spike threshold mechanism has not been thoroughly characterized in the mammalian hippocampus, we have further investigated the dynamic threshold in the major rodent hippocampal cell types. We have found that only a subset of excitatory neurons displayed this dynamic spike threshold on the time scale that was observed in teleost pallial cells, which allowed us to discuss its potential role in encoding spatial information in both species. Nevertheless, the fact that this teleost hippocampal homologue possesses characteristics that are both akin to the cortex and hippocampus suggest that it may perform computations that, in a mammalian brain, would require both structures and makes this ancestral structure a very interesting candidate to study the mechanism(s) underlying spatial memory.

This work deals with the electrophysiology of cardiac cells, their electro-stimulation and design of stimulation device to extend their life. The first part is focused on the action potential in general, in muscle cells, followed by an analysis of the process and characteristics of the action potential in cardiomyocytes. The next section provides a procedure for isolating and process of changes that lead to cell death and of a method that the process would be eliminated. Part of this work is a program for processing and evaluation of pictures obtained during electro-stimulation process.

Background: A single infusion of ketamine has rapid antidepressant properties, although the drawback is a lack of sustained effect. A previous study showed a rapid enhancement (within 2 hours) in ventral tegmental area (VTA) dopamine (DA) neuron population and locus coeruleus (LC) norepinephrine (NE) firing and bursting activity following a single ketamine administration. The current study investigated whether these changes are present 24 hours after a single administration and if they are maintained with repeated administration. Additionally, we examined dorsal raphe nucleus (DRN) serotonin (5-HT) neurons to assess the effects of single and repeated ketamine administration on these neurons. Methods: Ketamine (10 mg/kg, i.p.) was administered to male Sprague Dawley rats once or repeatedly (3 times/week) for 2 weeks. After single and repeated administration of ketamine, electrophysiological recordings were done in the VTA, LC and DRN in anesthetized rats, 24 hrs, 3 or 7 days post-administration. Spike frequency, bursting, and for VTA neurons, spontaneously active neurons/trajectory were assessed. Results: In the VTA, LC and DRN, 24 hrs after ketamine was injected acutely there was no significant difference between controls and treated animals in all parameters assessed. However, after repeated administration, there was an increase in bursting and number of spontaneously discharging neurons per tract of VTA DA neurons as well as an increase in frequency of discharge of LC NE neurons. While the increased number of spontaneously discharging neurons per tract had dissipated after 3 days, the enhanced bursting was still present but dissipated after 7 days. As for LC NE neurons, the increased frequency of discharge was no longer present after 3 days. No significant differences in the firing of DRN 5-HT neurons were observed between controls and treated animals even after ketamine was administered repeatedly. Conclusion: These results indicate that repeated but not acute administration of ketamine maintained the increase in population activity of DA neurons and firing activity of NE neurons.

Indiana University-Purdue University Indianapolis (IUPUI) / Hydrocephalus is a neurological disorder characterised by the pathological accumulation of cerebrospinal fluid (CSF) within the brain ventricles. Surgical interventions, including shunt placement, remain the gold standard treatment option for this life-threatening condition, despite these often requiring further revision surgeries. Unfortunately, there is currently no effective, pharmaceutical therapeutic agent available for the treatment of hydrocephalus. CSF is primarily produced by the choroid plexus (CP), a specialized, branched structure found in the ventricles of the brain. The CP comprises a high resistance epithelial monolayer surrounding a fenestrated capillary network, forming the blood-CSF barrier (BCSFB). The choroid plexus epithelium (CPe) critically modulates CSF production by regulating ion and water transport from the blood into the intraventricular space. This process is thought to be controlled by a host of intracellular mediators, as well as transporter proteins present on either the apical or basolateral membrane of the CPe. Though many of these proteins have been identified in the native tissue, exactly how they interact and modulate signal cascades to mediate CSF secretion remains less clear. Transient potential receptor vanilloid 4 (TRPV4) is a non-selective cation channel that can be activated by a range of stimuli and is expressed in the CP. TRPV4 has been implicated in the regulation of CSF production through stimulating ion flux across the CPe. In a continuous CP cell line, activation of TRPV4, through the addition of a TRPV4 specific agonist GSK1016790A, stimulated a change in net transepithelial ion flux and increase in conductance. In order to develop a pharmaceutical therapeutic for the treatment of hydrocephalus, we must first understand the mechanism of CSF secretion in health and disease. Therefore, a representative in vitro model is critical to elucidate the signaling pathways orchestrating CSF production in the CP. This research aims to characterize an in vitro culture model that can be utilized to study both the BCSFB and CSF production, to investigate and identify additional transporters, ion channels and intracellular mediators involved in TRPV4-mediated signaling in the CPe, primarily through a technique called Ussing-style electrophysiology which considers electrogenic ion flux across a monolayer. These studies implicated several potential modulators, specifically phospholipase C (PLC), phosphoinositide 3-kinase (PI3K), protein kinase C (PKC), intermediate conductance K+ channel (IK), transmembrane member 16A (TMEM16A), cystic fibrosis transmembrane conductance regulator (CFTR) and protein kinase A (PKA), in TRPV4-mediated ion flux.

Mouse hepatocytes respond to osmotic stress with adaptive changes in transmembrane potential, Vm, such that hypotonic stress hyperpolarizes cells and hypertonic stress depolarizes them. These changes in Vm provide electromotive force for redistribution of ions such as CI−, and this comprises part of the mechanism of hepatocyte volume regulation. We conducted the present study to determine whether ethanol administered in vitro to mouse liver slices increases hepatocyte water volume, and whether this swelling triggers adaptive changes in the Vm. Cells in mouse liver slices were loaded with tetramethylammonium ion (TMA). Changes in hepatocyte water volume were computed from measurements with Ion sensitive micro‐electrodes of changes in intracellular activity of TMA (a1TMA) that resulted from water fluxes. Ethanol (70 mM) increased hepatocyte water volume Immediately, and this peaked at 17% by 7 to 8 min, by which time a plateau was reached. Liver slices also were obtained from mice treated 12 hr prior with 4‐methylpyrazole (4 mM). The effect of ethanol on their hepatocyte water volume was identical to that from untreated mice, except that the onset and peak were delayed 2 min. Hepatocyte Vm showed no differences between control or ethanol‐treated cells during the course of volume changes. In contrast, hyposmotic stress, created by dropping external osmolality 50 mosm, increased Vm from –30 mV to –46 mV. Ethanol did not inhibit this osmotic stress‐induced hyperpolarization, except partially at high concentrations of 257 mM or greater. We infer that ethanol‐induced swelling of hepatocytes differs from that resulting from hyposmotic stress. Cellular events associated with increased activity of intracellular water most likely trigger the hyperpolarization of Vm that accompanies the latter. We conclude, therefore, that ethanol‐induced swelling occurs without change in cell water activity. This may result from the retention of macromolecules by ethanol in cells that constitutively secrete protein.