No description available.

Developmental nicotine exposure (DNE) is associated with increased risk of cardiorespiratory, intellectual, and behavioral abnormalities in neonates, and is a risk factor for apnea of prematurity, altered arousal responses and Sudden Infant Death Syndrome. Alterations in nicotinic acetylcholine receptor signaling (nAChRs) after DNE lead to changes in excitatory neurotransmission in neural networks that control breathing, including a heightened excitatory response to AMPA microinjection into the hypoglossal motor nucleus. Here, we report on experiments designed to probe possible postsynaptic and presynaptic mechanisms that may underlie this plasticity. Pregnant dams were exposed to nicotine or saline via an osmotic mini-pump implanted on the 5th day of gestation. We used whole-cell patch clamp electrophysiology to record from hypoglossal motoneurons (XIIMNs) in thick medullary slices from neonatal rat pups (N = 26 control and 24 DNE cells). To enable the translation of our findings to breathing-related consequences of DNE, we only studied XIIMNs that were receiving rhythmic excitatory drive from the respiratory central pattern generator. Tetrodotoxin was used to isolate XIIMNs from presynaptic input, and their postsynaptic responses to bath application of L-glutamic acid (glutamate) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were studied under voltage clamp. DNE had no influence on inward current magnitude evoked by either glutamate or AMPA. However, in cells from DNE animals, bath application of AMPA was associated with a right shift in the amplitude distribution (P = 0.0004), but no change in the inter-event interval distribution of miniature excitatory postsynaptic currents (mEPSCs). DNE had no influence on mEPSC amplitude or frequency evoked by glutamate application, or under (unstimulated) baseline conditions. Thus, in the presence of AMPA, DNE is associated with a small but significant increase in quantal size, but no change in the probability of glutamate release.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 91-102).

Developmental nicotine exposure (DNE) is known to cause abnormal development of multiple brain regions and results in impaired control of breathing and altered behaviors that rely on proper coordination of the muscles of the tongue. The adverse effects of nicotine are presumably caused by its actions on nicotinic acetylcholine receptors (nAChRs), which modulate fast-synaptic transmission and play a prominent role during brain development. Previous work has shown that DNE alters nAChR function in multiple brainstem regions (Pilarski et al., 2012, Wollman et al, 2016). Moreover, DNE causes multiple changes to XIIMNs, which innervate the muscles of the tongue (Powell et al., 2016, Powell et al., 2015, Pilarski et al., 2011). These changes likely reflect both altered development as a primary outcome of the chronic presence of nicotine, as well as, homeostatic adjustments made in an attempt to maintain normal motoneuron output. With the experiments described here, we tested the hypothesis that DNE alters the development of fast-synaptic transmission to XIIMNs, which, along with intrinsic properties of these neurons, is a main determinant of motor output to the muscles of the tongue. Additionally, we tested the hypothesis that DNE alters the function of nAChRs located on multiple brainstem neurons, including those that modulate fast-synaptic transmission to XIIMNs. For these experiments, we used whole cell patch clamp recordings from XIIMNs in a transverse slice of the medulla, and extracellular recordings from the 4th cervical ventral root in the brainstem spinal cord, split bath preparation. All preparations were obtained from control or DNE neonatal rats in the first week of life. Overall, the results of these experiments show that DNE alters fast-synaptic transmission to XIIMNs, which likely reflects appropriate homeostatic adjustments aimed at maintaining normal motor output at rest. However, these results also show that nAChR function is significantly altered by DNE, indicating fast-synaptic transmission may not be appropriately modulated in response to increased release of acetylcholine (ACh), the endogenous neurotransmitter for nAChRs.

To effect movement, the central nervous system must appropriately coordinate the activities of pools of motoneurons (MNs), the cells which control muscle fibers. Sources of neural drive are often distributed to many MNs of a pool, and thus can synchronize the activities of targeted MNs. In this thesis, synchronization among MNs is used to investigate the strength, temporal progression, and anatomical distribution of neural drive to the hypoglossal motor nucleus (HMN), which controls muscles of the tongue. The HMN is an ideal target for such an investigation because it processes a host of functionally diverse inputs, such as those related to breathing, speaking, and swallowing. Study 1 characterizes motor unit (MU) synchronization within and across bellies of the human genioglossus (GG) muscle when MUs are activated by cortical drive (during voluntary tongue protrusion) or by automatic, brainstem-mediated drive (during rest breathing). We show that voluntary tongue protrusion synchronizes MU spike timing and firing rates within but not across bellies of the GG, whereas during rest breathing, MU firing rates are moderately synchronized both within and across muscle bellies. Study 2 documents respiratory-related synchronization of MU activities in muscles of the tongue and respiratory pump using an anesthetized rat model. The results of this study indicate that upper airway and respiratory pump MN pools share a low frequency respiratory-related drive, but that higher frequency (>8 Hz) synchronization is strongest in MU pairs of the chest-wall. Finally, Study 3 examines the potential for GG multi-unit and single MU activities to be entrained by cortical input. We show that during voluntary tongue protrusion, cortical oscillations in the 15-40 Hz range weakly synchronize MU population activity, and that EEG oscillations in this range intermittently influence the spike timing of individual GG MUs. These studies are the first to characterize MU synchronization by different sources of neural input to the HMN and establish a broad foundation for further investigation of hypoglossal motor control.

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.

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.

No description available.

Developmental nicotine exposure (DNE) is known to cause deleterious effects in neonatal mammals through nicotine's actions on nicotinic acetylcholine receptors (nAChRs). In this work, we studied how DNE altered the structure and function of the hypoglossal motoneurons (XIIMNs) over the first few days post-parturition. Previous work in XIIMNs demonstrated an increase in cellular excitability (Pilarski et al., 2011), alterations in synaptic transmission among respiratory-related neurons (Wang et al., 2006; Pilarski et al., 2012; Jaiswal et al., 2013), and a reduction in inspiratory drive currents in DNE animals (Pilarski et al., 2011). Here we show that the effects of DNE extend to alterations in the spike-timing precision and reliability of XIIMNs, as well as spike-frequency adaptation. Additionally, simple morphological analysis of XIIMNs following nicotine exposure in utero has revealed a reduction in soma cross-sectional area. We were interested in studying the complete morphology of XIIMNs following DNE to discern its effects on more complex morphological parameters. We advanced this research using a combination of techniques in thin brainstem slices of neonatal rats, including whole cell patch clamp recordings and immunohistochemistry of intracellularly labeled hypoglossal motoneurons. Furthermore, morphological analysis revealed significant differences in the complexity of the dendritic arborization, showing that neurons from DNE animals had shorter dendrites that branched less often. We also used computational analysis to gain insight into mechanisms that may underlie the changes in spike-timing precision and reliability. In a single cell model of XIIMNs, decreases in potassium-dependent conductances such as the calcium-activated potassium current could potentially replicate the alterations seen in vitro. Finally, we also did a systems-level study of the hyoglossus muscle, a tongue retractor, to determine the relation between tongue retraction force and motor unit discharge characteristics. These experiments utilized adult, anesthetized rats to record single motor units, whole muscle electromyography (EMG) activity and tongue retraction force during spontaneous breathing. We determined that during inspiration-related tongue retractions in low and high force conditions, recruitment of motor units plays a crucial role in the control of tongue force output, whereas rate coding of single motor units is present, but appears to play a lesser role. Overall, this study shows that DNE effects the input-output properties of XIIMNs, potentially through changes in intrinsic channel properties; DNE also alters XIIMN morphology, particularly dendritic arborization; and that organization of a tongue retractor muscle depends primarily on recruitment, but also rate coding, to increase force output.

Nicotine from smoking or from other products containing nicotine has adverse effects on the fetus during pregnancy, such as respiratory problems. Our laboratory has previously shown that exposure to nicotine during development (DNE) alters hypoglossal motor neuron (XII MN) function, including decreased excitatory synaptic input, desensitized nicotinic acetylcholine receptors, increased input resistance, and differences in the precision and reliability of spike timing in XIIMNs. Evidence of DNE effects on XIIMN function prompted us to test the hypothesis that DNE will affect the development of primary dendrites and the soma. Brainstem slices were collected from neonates and motoneurons were filled with neurobiotin via whole-cell patch clamp. Filled cells were visualized with heavy metal intensified-3,3'-Diaminobenzidine (DAB) reaction. DAB-stained cells were analyzed using Neurolucida hardware and software. On average, the maximum soma diameter of more rostral XIIMNs was larger than that in more caudal cells. Also, caudal XIIMNs had more primary nodes than rostral XIIMNs, and there was a significant treatment effect on minimum soma diameter (Control, 13.76 ± 0.71 µm; DNE, 18.09 ± 1.22 µm). The results from this study uncovered potential effects of nicotine on XIIMNs found in rostral and caudal regions of the hypoglossal nucleus.