The circuit of recurring inhibition between motor neurons and Renshaw cells in the spinal cord has been known for around 70 years, though no determined function has been outlined as of yet. Renshaw cells are thought to be part of the central pattern generator in the spinal cord establishing them as an important part of the animal’s locomotive properties. In this study we aimed to investigate the role of Renshaw cells in locomotion with the help of optogenetics and electrophysiology. Halorhodopsin was inserted into the genome of mice and driven to expression with Cre recombinase in Renshaw cells. The spinal cord of P3 mice was extracted and by inducing fictive locomotion with appropriate neurotransmitters we could inhibit the Renshaw cells in action with a green laser, opening the halorhodopsin channels for Cl- ions. In previous experiments where the ability of Renshaw cells to release inhibitory neurotransmitters was inactivated, no effect was observed in either behavioral experiments or electrophysiological experiments. In a system where the effect of Renshaw cells was knocked out acutely with optogenetics there was no discernible change in fictive locomotion cycle length, frequency or amplitude. Nor was there an effect on alternation. The access of light to the Renshaw cells area might have been limited during the experiment considering the angle of light delivery and strength of the laser. Furthermore, the maturity of Renshaw cells at P3, the exclusive ability of the marker used to target Renshaw cells and the observed nature of neonatal inhibitory neurons acting as excitatory neurons could all be called into question about whether they contributed to these results or not.

The purpose of the present study was sixfold: 1. To study the effects of x-irradiation on spinal cord activity. 2. To study the effects of CNS drugs on spinal cord function as reflected by changes in the ventral root potentials. 3. To ascertain whether one can alter the observed spinal response to ionizing radiation by applying CNS drugs prior to, during, and following x-irradiation of a given spinal cord segment. 4. To shed some light on the role of higher brain centers on spinal reflexes. 5. To shed some light on the loci of radiation insult to the spinal cord. 6. To establish evidence for a possible drug-irradiation interaction in mammals.

Metamers of the ventral stream is a model which tries to describe what information we gather from our visual field. It have previously only been tested on static images. This thesis have continued the research and applied it to dynamic images in order to investigate if the model can be seen as a functional representation of our visual field. The results show that the model, at this stage, can not be seen as a fully functional representation of the visual field, but it can be used to determine the detectability of objects in the periphery. It also shows that what we humans perceive as motion is, at least to some extent, merely a change of the statistics in our visual field.

Mu opioid receptors (MOPs) in the pain pathway contribute to morphine analgesia. Morphine also stimulates reward/reinforcement through disinhibition of dopaminergic (DA) neurones in the ventral tegmental area (VTA), an effect implicated in its abuse and dependence. We hope to develop approaches to achieve sustained analgesia without affecting reward by exploiting differential MOP signalling mechanisms in the pain and reward pathways. MOPs, delta opioid receptors (DOPs) and β-arrestin2 (BAR2) are all necessary components of the signalling complex in nociceptive neurones for morphine analgesic tolerance; c-Src (a tyrosine kinase), thought to couple to MOP receptors through BAR2 has also been implicated. To investigate opioid receptor signalling in response to morphine we used a variety of different techniques that included behavioural measures of nociception, reinforcement and locomotion and electrophysiological methods to study DRG neurones from the pain pathway and brain slices containing VTA neurones. This study in mice confirms that morphine administered subcutaneously (SC) causes analgesia, analgesic tolerance, and has psychomotor effects leading to enhanced locomotion and reinforcement. In VTA neurones morphine and the selective MOP receptor agonist DAMGO caused concentration-dependent inhibition of the frequency of IPSCs. All these actions of morphine were absent from MOP-/- mice. Morphine exhibited reduced potency as 1) an analgesic, 2) stimulator of locomotion, 3) a reinforcer in CPP and 4) an inhibitor of sIPSC frequency, when applied to MOP+/- mice or their VTA neurones. Morphine analgesic tolerance developed faster and to a greater extent in MOP+/- mice than in WT mice. DOP-/- mice exhibited morphine analgesia with less tolerance, as did BAR2-/- mice. BAR2-/- mice also exhibited reduced morphine locomotion and an increased sensitivity to morphine reinforcement. Morphine tolerance was absent from BAR2-/-//DOP-/- mice. The inhibition of sIPSC frequency by morphine was reduced in BAR2+/- and BAR2-/- VTA neurones. Dasatinib and PP2 (c-Src tyrosine kinase inhibitors) prevented the development of morphine tolerance in WT and MOP+/- mice and dasatinib caused its reversal in the latter. The drugs had no significant analgesic effect alone. Dasatinib did not affect morphine preference or locomotor activation. PP2 reduced morphine’s inhibition of sIPSC frequency. As c-Src inhibition does not appear to alter the psychomotor effects produced by morphine and it acts to reduce morphine analgesic tolerance. We believe that cSrc is an attractive target to prevent the development of morphine analgesic tolerance without affecting hedonic homeostasis.

We conducted experiments to understand the role of Ventral Hippocampus (vHPC) projections to the Nucleus Accumbens (NAc) in exploratory locomotion, and to determine if the reduced vHPC parvalbumin neuron activity can result in behaviors associated with schizophrenia. Through the use of optogenetics, we activated vHPC neurons and vHPC terminals in the NAc. Both manipulations significantly increased locomotor activity in the open field. Selective inhibition of vHPC terminals in the NAc during a test for novel environment exploration significantly reduced preference for novel environments over familiar environments. DREADD-mediated inhibition of activation of vHPC parvalbumin neuron activity did not significantly alter amphetamine-induced locomotion. Overall, these experiments provide support for the role of the vHPC-NAc pathway in mediating exploratory behavior in novel environments, but it remains inconclusive whether dysregulated vHPC activity due to the loss of parvalbumin neurons leads to behaviors associated with schizophrenia.

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Visual processing, though seemingly automatic, is complex. Typical humansprocess objects and faces routinely. Yet, when a disease or disorder disrupts face andobject recognition, the effects are profound. Because of its importance and complexity,visual processing has been the subject of many adult functional imaging studies.However, relatively little is known about the development of the neural organization andunderlying cognitive mechanisms of face and object recognition. The current projectused functional magnetic resonance imaging (fMRI) to identify maturational changes inthe neural substrates of face and object recognition in 5-8 year olds, 9-11 year olds, andadults. A passive face and object viewing task revealed cortical shifts in the faceresponsiveloci of the ventral processing stream (VPS), an inferior occipito-temporalregion known to function in higher visual processing. Older children and adults recruitedmore anterior regions of the ventral processing stream than younger children. Toinvestigate the potential cognitive basis for these developmental changes, researchersimplemented a shape-matching task with parametric variations of shape overlap,structural similarity (SS), in stimulus pairs. VPS regions sensitive to high SS emerged inolder children and adults. Younger children recruited no structurally-sensitive regions inthe VPS. Two right hemisphere VPS regions were sensitive to maturational changes inSS. A comparison of face-responsive regions from the passive viewing task and the VPSSS regions did not reveal overlap. Though SS drives organization of the VPS, it did notexplain the cortical shifts in the neural substrates for face processing. In addition to VPSregions, results indicated additional maturational SS changes in frontal, parietal, andcerebellar regions. Based on these findings, further analyses were conducted to quantifyand qualify maturational changes in face and object processing throughout the brain.Results indicated developmental changes in activation extent, signal magnitude, andlateralization of face and object recognition networks. Collectively, this project supportsa developmental change in visual processing between 5-8 years and 9-11 years of age.Chapters Four through Six provide an in-depth discussion of the implications of thesefindings.

Decisions, such as choosing between different rewards, are known to be influenced by a number of variables such as value, uncertainty and delay associated with a rewarding outcome. Various structures in the brain are responsible for handling different aspects of reward related decision making. To understand how such decisions are made, we can attempt to reverse engineer the brain. This involves understanding how brain activity is related to the representation and processing of rewards and also to subsequent behavior in response to rewarding events. One of the central elements of the reward circuitry of the brain is the ventral striatum. It has traditionally been known as the limbic-motor interface and thought to act as a link between various structures in the brain that are responsible for processing reward and reward related behavior. To study the neural processes that underlie processing rewards, I recorded from the ventral striatum of rats as they performed a cue-reward task. The aim of my project was twofold: First, to examine how rats behave in response to changes in value and uncertainty associated with a particular rewarding outcome and second, to investigate how rewards and cues that predict rewards are represented in the neural activity of the ventral striatum. Rats (n=6) were trained on a cue-reward task, where cues indicated the mean or variance of associated outcome distributions. Behavioral responses to the reward predictive cues demonstrated that the rats learned the value and risk associated with subsequent reward outcomes. Ventral striatal gamma oscillations are known to align to rewards in a variety of reward motivated tasks. However, it is not clear if these oscillations are associated with anticipation of obtaining the reward or the reward itself. In previous studies, reward delivery has been correlated with the anticipation of reward. In the current work, a delay is used to distinguish between anticipation of reward and the reward delivery itself. This is achieved by making the rats nose poke for a fixed time interval before the arrival of reward. The analysis presented in this thesis reveals that ventral striatal gamma oscillations occur both during the anticipation and delivery of reward, opening up the possibility of formal tests. They also align to arrival of cues that predict rewarding outcomes. This suggests that gamma oscillations might be essential for modulating behavior in response to cues and rewards both before and after reward delivery. Ventral striatum is ideally situated to modulate behavior in response to rewarding events. Past studies show that ventral striatal neural activity is associated with reward and reward motivated actions. However, as suggested by the research presented in this thesis, it is not clear what specific aspects of the decision making process can be attributed to the ventral striatum once learning in complete. Studying the ventral striatum is important because its malfunctioning is implicated in brain disorders such as drug addiction.

Parkinson’s disease is a common neurological disorder with a complex etiology. The disease is characterized by a progressive loss of dopaminergic cells in the substantia nigra, which leads to motor function and sometimes cognitive function disabilities. One of the pathological hallmarks in Parkinson’s disease is the cytoplasmic inclusions called Lewy bodies found in the dopamine neurons. The aggregated protein α-synuclein is a main component of Lewy bodies. In view of severe symptoms and the upcoming of problematic side effects that are developed by the current most commonly used treatment in Parkinson’s disease, new treatment strategies need to be elucidated. One such strategy is replacing the lost dopamine neurons with new dopamine-rich tissue. To improve survival of the implanted neurons, neurotrophic factors have been used. Glial cell line-derived neurotrophic factor (GDNF), which was discovered in 1993, improves survival of ventral mesencephalic dopamine neurons and enhances dopamine nerve fiber formation according to several studies. Thus, GDNF can be used to improve dopamine-rich graft outgrowth into the host brain as well as inducing sprouting from endogenous remaining nerve fibers. This study was performed on Gdnf gene-deleted mice to investigate the role of GDNF on the nigrostriatal dopamine system. The transplantation technique was used to create a nigrostriatal microcircuit from ventral mesencephalon (VM) and the lateral ganglionic eminence (LGE) from different Gdnf gene-deleted mice. The tissue was grafted into the lateral ventricle of wildtype mice. The results revealed that reduced concentrations of GDNF, as a consequence from the Gdnf gene deletion, had effects on survival of dopamine neurons and the dopamine innervation of the nigrostriatal microcircuit. All transplants had survived at 3 months independently of Gdnf genotype, however, the grafts derived from Gdnf gene-deleted tissue had died at 6 months. Transplants with partial Gdnf gene deletion survived up to 12 months after transplantation. Moreover, the dopaminergic innervation of striatal co-grafts was impaired in Gdnf gene-deleted tissue. These results highlight the role of GDNF for long-term maintenance of the nigrostriatal dopamine system. To further investigate the role of GDNF expression on survival and organization of the nigrostriatal dopamine system, VM and LGE as single or combined to double co-grafts created from mismatches in Gdnf genotypes were transplanted into the lateral ventricle of wildtype mice. Survival of the single grafts was monitored over one year using a 9.4T MR scanner. The size of single LGE transplants was significantly reduced by the lack of GDNF already at 2 weeks postgrafting while the size of single VM was maintained over time, independently of GDNF expression. The double grafts were evaluated at 2 months, and the results revealed that lack of GDNF in LGE reduced the dopamine cell survival, while no loss of dopamine neurons was found in VM single grafts. The dopaminergic innervation of LGE was affected by absence of GDNF, which also caused a disorganization of the striatal portion of the co-grafts. Small, cytoplasmic inclusions were frequently found in the dopamine neurons in grafts lacking GDNF expression. These inclusions were not possible to classify as Lewy bodies by immunohistochemistry and the presence of phospho-α-synuclein and ubiquitin; however, mitochondrial dysfunction could not be excluded. To further study the death of the dopamine neurons by the deprivation of GDNF, the attention was turned to how Lewy bodies are developed. With respect to the high levels of α-synuclein that was found in the striatum, this area was selected as a target to inject the small molecule – FN075, which stimulates α-synuclein aggregation, to further investigate the role of α-synuclein in the formation of cytoplasmic inclusions. The results revealed that cytoplasmic inclusions, similar to those found in the grafts, was present at 1 month after the injection, while impairment in sensorimotor function was exhibited, the number of dopamine neurons was not changed at 6 months after the injection. Injecting the templator to the substantia nigra, however, significantly reduced the number of TH-positive neurons at 3 months after injection. In conclusion, these studies elucidate the role of GDNF for maintenance and survival of the nigrostriatal dopamine system and mechanisms of dopamine cell death using small molecules that template the α-synuclein aggregation.

We conducted experiments to understand the role of Ventral Hippocampus (vHPC) projections to the Nucleus Accumbens (NAc) in exploratory locomotion, and to determine if the reduced vHPC parvalbumin neuron activity can result in behaviors associated with schizophrenia. Through the use of optogenetics, we activated vHPC neurons and vHPC terminals in the NAc. Both manipulations significantly increased locomotor activity in the open field. Selective inhibition of vHPC terminals in the NAc during a test for novel environment exploration significantly reduced preference for novel environments over familiar environments. DREADD-mediated inhibition of activation of vHPC parvalbumin neuron activity did not significantly alter amphetamine-induced locomotion. Overall, these experiments provide support for the role of the vHPC-NAc pathway in mediating exploratory behavior in novel environments, but it remains inconclusive whether dysregulated vHPC activity due to the loss of parvalbumin neurons leads to behaviors associated with schizophrenia.