How does the brain develop differently to support nocturnality in some mammals, but diurnality in others? To answer this question, one might look to the suprachiasmatic nucleus (SCN), the pacemaker of the mammalian brain, which is required for all circadian biological and behavioral rhythms. Light arriving at the retina entrains the SCN to the daily light-dark cycle via the retinohypothalamic tract (RHT). However, in all mammals studied thus far, whether nocturnal or diurnal, the SCN exhibits a rhythm of increased activity during the day and decreased activity at night. Therefore, structures downstream of the SCN are likely to determine whether a species is nocturnal or diurnal. From an evolutionary perspective, nocturnality appears to be the primitive condition in mammals, with diurnality having reemerged independently in some lineages. However, it is unclear what mechanisms underlie the development of one or the other circadian phase preference. In adult Norway rats (Rattus norvegicus), which are nocturnal, the RHT also projects to the ventral subparaventricular zone (vSPVZ), an adjacent region that expresses an in-phase pattern of SCN-vSPVZ neuronal activity (in other words, activity in the SCN and vSPVZ increase and decrease together). In contrast, in adult Nile grass rats (Arvicanthis niloticus), a diurnal species that is closely related to Norway rats, an anti-phase pattern of SCN-vSPVZ neuronal activity is expressed (in other words, activity in the SCN increases as activity in the vSPVZ decreases, and vice versa). We hypothesized that these species differences in activity pattern result in part from a weak or absent RHT-to-vSPVZ projection in grass rats. Using a developmental comparative approach, we assessed differences in behavior, hypothalamic activity, and RHT and SCN connectivity to the vSPVZ between these two species. We report that a robust retina-to-vSPVZ projection develops in Norway rats around the end of the second postnatal week when nocturnal wakefulness and the in-phase pattern of SCN-vSPVZ activity emerge. In grass rats, however, such a projection does not develop and the emergence of the anti-phase SCN-vSPVZ activity pattern during the second postnatal week is accompanied by increased diurnal wakefulness. When considered within the context of previously published reports on RHT projections in a variety of other nocturnal and diurnal species, our current findings suggest that how and when the retina connects to the hypothalamus differentially shapes brain and behavior to produce animals that occupy opposing temporal niches.

The mesolimbic dopamine (DA) system has been implicated in providing the basis of pleasure, guiding the general mechanism of reinforcement as well as motivation. Support for these roles have grown from neurochemical research in the field of addiction. It is now well known that DA activity increases in the nucleus accumbens septi (NAcc) with exposure to addictive substances. Moreover, pharmacological manipulation of this system produces predictable changes in the administration of drugs of abuse, as well as natural reinforcers. This system is responsive to natural reinforcers and addiction may be the transference of routine mesolimbic function to environmental stimuli predictive of drug administration. The role of the NAcc in addiction specifically appears to be the facilitation of attention to drug-paired stimuli and addiction may be the behavioral manifestation of conditioned NAcc DA reactivity to the presence of drug-related stimuli. Although these findings have been reported in adults, few studies have focused on adolescence, the time when drug use/abuse begins. Adolescents may be particularly susceptible to addiction when considered in the light of this hypothesis. Recent research has revealed that the mesolimbic system of periadolescent animals is undergoing dramatic transition in functional tone. DA receptor and transporter levels are up regulated, synthesis rates are altered, and innervation from prefrontal cortex (PFC), involved in regulating tonic and phasic DA activity, is increasing. Consequently, during adolescence there is a dramatic change in tonic DA levels, variations in phasic responses to acute drug administration and alterations in how the system adapts to repeated drug exposure. The present study utilizes the procedures of conditioned place preference, Novelty preference and in vivo microdialysis to determine how this conditioning process changes during the period of adolescence. The results indicate that adolescents are different from adults not only on behavioral measures associated with drug abuse, but in their neurochemical responsiveness to alcohol, and that these differences are related to a general developmental aspect of adolescence that renders them susceptible to addiction.

Back pain is one of the most common physical conditions in the United States, for which approximately 15% of the population will visit a doctor every year. The most common type of back pain is low back pain (LBP) and millions of dollars are spent every year healthcare are a due to LBP. Although poorly understood, low back pain has been associated to interveterbral disc (IVD) degeneration. The IVD is an important structure that helps maintaining normal skeletal support. It is composed of three different tissues called the annulus fibrosus (AF), and the nucleus pulposus (NP), attached to a cartilage endplate (CEP) at its top and bottom surfaces. The AF tissue is composed of chondrocyte-like cells, while the NP tissue is composed of notochordal cells at a young age, which are replaced by mature NP cells later in life. Common signs of degeneration are the inability to maintain extracellular matrix integrity and calcification of the cartilage endplate. Extracellular matrix synthesis and cartilage endplate calcification are closely related to production of adenosine triphosphate (ATP) or energy metabolism of the cells. AF and NP tissues are known to be structurally and compositionally different; therefore it is believed that their metabolic pathways are also distinct. The objective of this study was to determine the differences between AF and NP cells, specifically in their energy metabolism with and without dynamic loading.

Neutrophils are implicated in many inflammatory lung disorders. However, the mechanisms regulating neutrophil migration in acute lung inflammation are incompletely understood. Although, integrin β2 mediates neutrophil migration in lungs in response to many stimuli such as E. coli, integrin involved in <i>S. pneumoniae</i> induced neutrophil migration is not known. Therefore, the role of integrin αvβ3 in neutrophil recruitment was tested. First, it was found that the number of neutrophils expressing the integrin subunits αv and β3 is reduced or remains in lung inflammation induced by E. coli or <i>S. pneumoniae</i>, respectively. Next, the role of integrin αvβ3 using β3 knockout mice (β3-/-) and function blocking antibodies was addressed. Neutrophil recruitment did not vary between wild type and β3-/- mice. Although β3 antibodies reduced neutrophil recruitment, similar effect was observed with isotype antibodies. Therefore, one can conclude that integrin αvβ3 is not critical for neutrophil recruitment in <i>S. pneumoniae</i> induced pneumonia. <p>Apart from integrins, TLR4 also regulate neutrophil migration. Because, the pattern of TLR4 expression at various times of lung inflammation is not known, TLR4 expression during different phases of lung inflammation in a rat model of LPS-induced inflammation was studied. TLR4 expression in the septum increased and decreased at 6h and 12-36h of inflammation, respectively. Since these correlate with the time of increase and decline of neutrophil recruitment, the findings support previously observed requirement for TLR4 in neutrophil recruitment. <p>Neutrophils recruited into the lungs regulate the inflammatory process by controlling subsequent monocyte/macrophage recruitment. The mechanisms involved and the pattern of monocyte/macrophage recruitment in lungs are not completely understood. Therefore, the possible involvement of monocyte chemoattractant protein (MCP)-1, which is a premier chemokine in monocyte/macrophage migration and produced by neutrophils and other cells was tested. This was addressed by quantification of monocytes/macrophages at various times and using neutrophil depletion experiments in LPS-induced lung inflammation in rats. It was found that monocytes/macrophages migrate very early and before neutrophils in addition to their migration in the late phase of acute lung inflammation. Neutrophil depletion abrogated both early as well as the late monocyte/macrophage recruitment without altering the expression of MCP-1. Therefore, possibly other chemokines and not MCP-1 are involved in neutrophil dependent monocyte/macrophage recruitment. <p>To conclude, the experiments further the understanding on acute lung inflammation by ruling-out the involvement of integrin αvβ3 and MCP-1 in β2-independent neutrophil migration and neutrophil dependent monocyte/macrophage recruitment, respectively. Further studies are essential to find the integrins and chemokines operating in the above situations. Equally important will be to understand the functional significance of early recruited monocytes/macrophages in the lung.

This thesis tested the hypothesis that ethanol suppresses respiratory muscle activity by effects at the central motor pool and/or by state-dependent regulation of motor activity via influences on sleep/arousal processes. Ten rats were implanted with electroencephalogram and neck electrodes to record sleep-wake states, and genioglossus and diaphragm electrodes for respiratory recordings. Studies were performed following intraperitoneal injection of ethanol (1.25g/kg) or vehicle. The effects on genioglossus activity of ethanol (0.025-1M) or vehicle applied directly to the hypoglossal motor nucleus were also determined in sixteen isoflurane-anaesthetized rats. The results of these studies suggest that ethanol at physiologically relevant concentrations promoted sleep, and altered electroencephalogram and postural motor activities indicative of a sedating effect. The lack of effect on genioglossus activity with ethanol applied directly to the hypoglossal motor pool suggests that the suppression observed with systemic administration may be mediated via effects on state-dependent processes rather than direct effects at the motor pool per se.

The mechanisms underlying the generation of rapid eye movement (REM) sleep are poorly understood. Despite a lack of direct support, neurons maximally active during REM sleep (REM sleep-active) located in the pedunculopontine tegmental nucleus (PPTn) are hypothesized to generate this state and its component phenomenology. This hypothesis has never been directly tested, since the results of selectively inhibiting this cell-group have never been determined. Using microdialysis, electrophysiology, histochemical and pharmacological methods in freely-behaving rats (n=22) instrumented for sleep-wake state and respiratory muscle recordings, I selectively inhibited REM sleep-active PPTn neurons. Contrary to the prevailing hypothesis, I showed that REM sleep-active PPTn neurons suppress REM sleep by limiting the frequency of its onset. These neurons also shape the impact of REM sleep on breathing. REM sleep-active PPTn neurons restrain behavioural activation of upper-airway musculature during REM sleep, while depressing breathing rate and respiratory activation of the upper-airway musculature across sleep-wake-states.

The naked mole-rat (Heterocephalus glaber) demonstrates a strict social and reproductive hierarchy. Oxytocin (OXT) is a peptide hormone that acts both peripherally and centrally in the regulation of a number of sexual and social behaviours. The main area of central production of this peptide is the paraventricular nucleus of the hypothalamus (PVN). The present study characterized differences that exist in OXT neurons in this region. Breeders and subordinates from established colonies were sacrificed and brains were processed for OXT-immunoreactivity. Four further groups of paired animals underwent various social and hormonal manipulations (opposite-sex paired, same sex-paired, opposite-sex/gonadectomised paired, opposite-sex/vasectomized paired) and were also used for analysis. Results showed that subordinate naked mole-rats had significantly more OXT-immunoreactive neurons in the PVN than either breeders or paired animals that had been gonadectomised. However, no differences were found on measures of OXT cell volume. Possible functional significance of these differences is discussed.

This thesis tested the hypothesis that ethanol suppresses respiratory muscle activity by effects at the central motor pool and/or by state-dependent regulation of motor activity via influences on sleep/arousal processes. Ten rats were implanted with electroencephalogram and neck electrodes to record sleep-wake states, and genioglossus and diaphragm electrodes for respiratory recordings. Studies were performed following intraperitoneal injection of ethanol (1.25g/kg) or vehicle. The effects on genioglossus activity of ethanol (0.025-1M) or vehicle applied directly to the hypoglossal motor nucleus were also determined in sixteen isoflurane-anaesthetized rats. The results of these studies suggest that ethanol at physiologically relevant concentrations promoted sleep, and altered electroencephalogram and postural motor activities indicative of a sedating effect. The lack of effect on genioglossus activity with ethanol applied directly to the hypoglossal motor pool suggests that the suppression observed with systemic administration may be mediated via effects on state-dependent processes rather than direct effects at the motor pool per se.

The mechanisms underlying the generation of rapid eye movement (REM) sleep are poorly understood. Despite a lack of direct support, neurons maximally active during REM sleep (REM sleep-active) located in the pedunculopontine tegmental nucleus (PPTn) are hypothesized to generate this state and its component phenomenology. This hypothesis has never been directly tested, since the results of selectively inhibiting this cell-group have never been determined. Using microdialysis, electrophysiology, histochemical and pharmacological methods in freely-behaving rats (n=22) instrumented for sleep-wake state and respiratory muscle recordings, I selectively inhibited REM sleep-active PPTn neurons. Contrary to the prevailing hypothesis, I showed that REM sleep-active PPTn neurons suppress REM sleep by limiting the frequency of its onset. These neurons also shape the impact of REM sleep on breathing. REM sleep-active PPTn neurons restrain behavioural activation of upper-airway musculature during REM sleep, while depressing breathing rate and respiratory activation of the upper-airway musculature across sleep-wake-states.

The naked mole-rat (Heterocephalus glaber) demonstrates a strict social and reproductive hierarchy. Oxytocin (OXT) is a peptide hormone that acts both peripherally and centrally in the regulation of a number of sexual and social behaviours. The main area of central production of this peptide is the paraventricular nucleus of the hypothalamus (PVN). The present study characterized differences that exist in OXT neurons in this region. Breeders and subordinates from established colonies were sacrificed and brains were processed for OXT-immunoreactivity. Four further groups of paired animals underwent various social and hormonal manipulations (opposite-sex paired, same sex-paired, opposite-sex/gonadectomised paired, opposite-sex/vasectomized paired) and were also used for analysis. Results showed that subordinate naked mole-rats had significantly more OXT-immunoreactive neurons in the PVN than either breeders or paired animals that had been gonadectomised. However, no differences were found on measures of OXT cell volume. Possible functional significance of these differences is discussed.