Extensive serotonin (5-HT) fiber innervation throughout the brain corroborates 5-HT’s modulatory role in numerous behaviors including social behavior, emotion regulation, and learning and memory. Abnormal brain 5-HT levels and function are implicated in Autism Spectrum Disorder (ASD) which often co-occurs with other neuropsychiatric conditions. While 5-HT therapeutics are used to treat ASD, variable improvements in symptomatology require further investigation of 5-HT-mediated pathology. Neurexins (Nrxns) are presynaptic cell adhesion molecules that maintain synapse function for proper neural circuit assembly. Given that aberrant Nrxn and 5-HT function independently contribute to signaling pathology and behavioral impairments, it is critical to understand how Nrxn-mediated 5-HT neurotransmission participates in pathological mechanisms underlying ASD. Using fluorescence in situ hybridization, I found that the three Nrxn genes (Nrxn1, Nrxn2, and Nrxn3) are differentially expressed in 5-HT neurons in the dorsal raphe nucleus (DRN) and median raphe nucleus which contain the primary source of 5-HT neurons in the brain. Our lab generated a mouse model with selective deletion of Nrxns in 5-HT neurons to investigate the function of Nrxns in 5-HT signaling. The loss of Nrxns at 5-HT release sites reduced 5-HT release in the DRN and hippocampus and altered 5-HT innervation in specific brain regions. The lack of 5-HTergic Nrxns also reduced sociability and increased depressive-like behavior in males. This mouse model provides mechanisms to shed new light on 5-HT neurotransmission in the generation of complex behaviors.

Prenatal opioid exposure has been studied in relation to infants' medical outcomes. However, large gaps exist in the literature supporting early identification of atypical neurobehavior and motor development of infants with prenatal opioid exposure. The purpose of the study was to investigate whether prenatal opioid exposure has a negative influence on a newborn infant’s neurobehavior and motor development to aid in the early identification of potential delays. Using a prospective quasi experimental design, infants motor development using the Test of Infant Motor Performance (TIMP) and neurobehavior using the NICU Neonatal Network Scale (NNNS) was assessed on 58 infants in a hospital setting. Even after statistically controlling for covariates both the TIMP and the six out of twelve subscales of the NNNS: attention, handling, self-regulation, arousal, excitability, and stress were significantly different between the two groups of infants. Infants’ TIMP z-scores were significantly correlated with the NNNS subscales of attention, handing, self-regulation, arousal, excitability, hypertonicity, non-optimal reflexes, and stress. The findings highlight the similarities between the two groups and the outcome measures used for early identification of infants at-risk for delays following prenatal opioid exposure. The neonatal outcomes described here, including growth deficits, motor delays and altered neurobehavior are critical given their association with longer-term health and developmental impacts.

Environmental conditions imposed onto organisms during certain phases of their life cycles such as embryogenesis or puberty can not only impact the organisms’ own health, but also affect subsequent generations. The underlying mechanisms causing intergenerational phenotypes are not encoded in the genome, but the result of reversible epigenetic modifications. This work investigates in a mouse model the impact of paternal nicotine exposure on the next generation regarding addictive behavior modulation, metabolic changes, and molecular mechanisms. It provides evidence that male offspring from nicotine-exposed fathers (NIC offspring) is more resistant to lethal doses of nicotine. This phenotype is gender-specific and depends on short-term environmental challenges with low doses of nicotine prior to the LD50 application. The observed survival phenotype is not restricted to nicotine as drug of abuse, but also presents itself, when NIC offspring is challenged with a cocaine LD50 after acclimatization to low doses of either nicotine or cocaine. Functionally, NIC offspring metabolizes nicotine faster than control. Mechanistically, NIC offspring livers show global up-regulation of xenobiotic processing genes (XPG), an effect that is even more pronounced in primary hepatocyte cultures. Being known targets of Constitutive Androstane Receptor (CAR) and Pregnane X Receptor (PXR), these XPGs show higher baseline expression in naïve NIC offspring livers. Nicotine’s action on the brain’s reward circuitry does not appear to be of biological significance in our model system. Taken together, paternal nicotine exposure leads to a non-specific and conditional phenotype in male NIC offspring that may provide a general survival advantage against xenobiotic challenges.

<p>Small nematode model organisms such as <em>Caenorhabditis elegans</em> are widely used in the fields of neurobiology, toxicology, drug discovery, etc. They are advantageous due to their fully characterized genomic and cellular system. Traditional screening methods involve the exposure of animals to chemicals/drugs inside multiwell-plates while its effects on growth, movement and other cellular/sub-cellular processes are monitored by visual inspection. Yet, these methods are time-consuming, low-throughput, expensive, tedious, difficult to control, hard to modulate instantaneously, prone to subjectivity and not suitable for movement-based behavioural assays. Hence, a method to induce and to quantify movement on-demand in a rapid, sensitive, precise and reversible manner would greatly facilitate biological studies. In this thesis, microfluidic engineering approaches have been utilized in nematode-based assays due to their potential to obtain high precision measurements in a low-cost, rapid and automated manner. Movement response of worms to a diverse range of electric signals has been quantitatively characterized. DC and pulse-DC electric fields have been shown to stimulate worms’ swimming towards the negative electrode inside a microchannel (electrotaxis). AC electric fields were used to inhibit movement on-demand. Animals’ movement has been characterized in terms of speed and range of motion, body-bend frequency and turning time. Electrotaxis was shown to be mediated by neuronal activities and correlations between animal’s behaviour and neuronal signalling has also been demonstrated. Using this basic understanding, multiple microfluidic components such as position sensors and electric immobilizers have been developed. Electrotaxis has then been applied as a technique to sort worms in accordance to their size/age and phenotype as well as to perform drug screening at a single-animal level. Integration of the techniques and components developed during this research is expected to have a significant impact on the development of an integrated microfluidic platform for high throughput automated behavioural screening of nematodes with applications in drug discovery, toxicology, neurobiology and genetics.</p> / Doctor of Philosophy (PhD)