Aims: (1) Analyze the roles of α7 and α4β2 nicotinic receptors (nAChRs) in nicotine sensitization in adolescent male and female rats neonatally treated with quinpirole as well as their effects on brain-derived neurotrophic factor (BDNF) and mammalian target of rapamycin (mTOR) 1 h and 24 h post drug treatment. (2) Analyze the effects of behavioral sensitization to nicotine on α7 and α4β2 nAChR density in the nucleus accumbens and dorsal striatum. Methods: Animals were neonatally treated with quinpirole (1 mg/kg) or saline from postnatal days (P)1-21. Beginning on P33, animals were ip injected with nicotine (0.5 mg/kg free base) or saline and tested every second day from P33-49. Approximately 30 min before injection, animals were ip injected with either the α7 nicotinic receptor (nAChR) antagonist methllycacontine (MLA; 2 or 4 mg/kg) or the α4β2 nAChR antagonist dihyro-β-erythrodine (DhβE; 1 or 3 mg/kg). Brain tissue was taken either 1 h or 24 h after the last day of testing. In a second experiment, animals were identically treated and brain tissue analyzed for nAChR density using the autoradiographic technique. Results: Neonatal quinpirole enhanced nicotine sensitization and the 3 mg/kg dose DhβE effectively blocked nicotine sensitization on Day 9 but enhanced the hypoactive response to nicotine on Day 1. MLA appears more important in the acute response to nicotine. Neonatal quinpirole sensitized the accumbal BDNF response to nicotine, but resulted in a decrease of accumbal mTOR. The nAChR density data will be presented. Conclusions: The α4β2 receptor played a critical role in the development of adolescent nicotine sensitization, and both nAChRs appear to be important in accumbal BDNF and in the mTOR response, demonstrating their important role in synaptic strength.

No description available.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 126-135). Also available in electronic version.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

The establishment of neuronal polarity constitutes a central phase in neuronal development and synaptogenesis. In my thesis, I study factors that regulate the development of neuronal polarity and its relationship with neurotransmitter receptor expression. For my experiments, I have investigated the development of sensory neurons from neonatal rat nodose ganglia in culture. Sensory neurons have a pseudo-unipolar morphology, do not extend dendrites, and are devoid of synaptic connections on their somata. However, nodose neurons form synapses de novo in cultures, and I show that the neurons have retained the ability to extend dendrites. Extrinsic factors control dendrite extension by these neurons: the ganglionic satellite cells inhibit the growth of dendrites and induce the neurons to develop a unipolar morphology. In the absence of satellite cells, nodose neurons establish a new multipolar morphology and, in response to nerve growth factor (NGF), extend several dendrites. However, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) do not induce the neurons to extend dendrites, but promote the expression of properties typical of nodose neurons in vivo. / As nodose neurons acquire a new dendrite-axonal polarity in the presence of NGF, they increase the density of functional neuronal nicotinic acetylcholine receptors (nAChRs) on their somato-dendritic domains. To learn more about the relationship between dendrites extension and nAChR gene expression, I have examined the changes in transcript levels of nAChR subunits in neonatal rat sympathetic neurons developing in culture. I show that the developmental pattern of nAChR subunit expression in the cultured neurons follows closely that of sympathetic neurons developing in vivo, with the exception of one specific subunit $ alpha sb7$. I show that the increase in $ alpha sb3$ mRNA levels correlates well with an increase in the density of functional nAChRs on the neurons. In addition, my results suggest that these increases are regulated by mechanisms intrinsic to neonatal sympathetic neurons. On the other hand, the changes in $ alpha sb7$ gene expression, which correlate with changes in $ alpha$-bungarotoxin binding, are activity-dependent and regulated by a calcium/calmodulin-dependent protein kinase pathway. The results presented in this thesis provide insights on how neurons are influenced in their extension of dendrites and how this extension affects neurotransmitter receptor expression.

Thesis (M.S.)--Brigham Young University. Dept. of Physiology and Developmental Biology, 2006. / Includes bibliographical references (p. 47-50).

Thesis (Ph.D.)--Ohio University, March, 2008. / Abstract only has been uploaded to OhioLINK. Includes bibliographical references (leaves 145-160).

Thesis (Ph. D.)--University of Chicago, Committee on Neurobiology, December 2002. / Includes bibliographical references. Also available on the Internet.

The caudal nucleus tractus solitarius (cNTS) is the key recipient of the primary afferents from visceral sensory neurons and also an important site that processes and integrates gastrointestinal, cardiovascular and respiratory functions. Glutamate and gamma-aminobutyric acid are the major neurotransmitters within the NTS, but studies have suggested that nicotinic acetylcholine receptors (nAChRs) and transient receptor potential (TRP) channels can modulate excitatory/inhibitory neurotransmission. I have designed studies to understand the role of nAChRs and TRP channels in the modulation of neurotransmission in the cNTS. In the first aim, experiments were designed to test the hypothesis that the cNTS contains function-specific subsets of neurons whose responsiveness to nicotine correlates with the target of their axonal projections. cNTS neurons send axonal projections to brain regions such as parabrachial nucleus (PBN), hypothalamic paraventricular nucleus (PVN), nucleus ambiguous (NA), dorsal motor nucleus of the vagus (DMV) and the caudal ventrolateral medulla (CVLM) and are involved in integrating autonomic and neuroendocrine functions. Presynaptic/postsynaptic modulation by nAChRs differ in the axonal projections of cNTS neurons, studying of which would provide better understanding of this complex integration. In vivo fluorescent tracing combined with in vitro slice patch-clamp electrophysiological recordings from anatomically identified caudal NTS neurons were used to study the expression and function of nAChRs (mainly á3â4 containing nAChRs) in the cNTS. Results from these studies demonstrate that presynaptic and postsynaptic responsiveness of caudal NTS neurons to nicotine correlates with the areas the neurons project to in the following order of prevalence: DMV>PVN>NA>CVLM>PBN (for presynaptic responses) and DMV>CVLM>PBN>NA>PVN (for postsynaptic responses). In the second aim, experiments were designed to test the hypothesis that nociceptive TRP channels TRPV1 (vanilloid) and TRPA1 (ankyrin) modulate synaptic transmission in the NTS. As a result of this modulation, the efferent functions that control autonomic and visceral functions will be regulated and account for the changes in autonomic neuropathy as patients with diabetes develop significant alterations in blood pressure and heart rate as well as silent myocardial ischemia as a result of blunted pain carrying ability. Results obtained from these studies demonstrated that TRPV1 and TRPA1 mRNA were detected in the dorsal root ganglion (DRG), but not in the NTS. Immunofluorescence studies revealed that TRPV1 and TRPA1 were expressed in the solitary tract central sensory terminals inputs to NTS but not in NTS neurons. This suggests that TRPV1 and TRPA1 are expressed only in solitary tract. Administration of capsaicin (TRPV1 agonist) and allyl isothiocyanate (AITC, TRPA1 agonist) both increased the frequency of s/mEPSCs without affecting spontaneous and miniature inhibitory postsynaptic currents (s/mIPSCs). Next, the modulation of TRPV1- and TRPA1-induced responses by utilizing a PKC activator (PDBu) was examined. Incubation of slices with PDBu synergistically increased the mEPSC frequency following capsaicin application suggesting an increased receptor affinity; however following application of AITC there was no significant change, suggesting that activation by covalent modification does not enhance binding affinity. Finally, the specificity of TRPV1 and TRPA1 effect on synaptic transmission by ablating TRPV1 and TRPA1were tested. There was no modulation of synaptic transmission in these animals, further confirming that capsaicin- and AITC-mediated modulation of synaptic transmission are specifically mediated by TRPV1 and TRPA1, respectively. Furthermore, animals with painful diabetic peripheral neuropthy exhibited enhanced synaptic activity at the NTS, suggesting a role in nociception and other visceral functions. In summary, nAChRs, TRPV1 and TRPA1 are expressed in the NTS and activation of which modulate excitatory synaptic transmission. The results obtained from these studies and their interpretation may provide a better understanding of the central mechanism of modulation on efferent functions from NTS that regulate cardiovascular, respiratory and gastrointestinal functions.

The current project examined the ability of nicotine to modulate dopamine transporter (DAT) function. Initial experiments determined the dose-response for nicotine to modulate dopamine (DA) clearance in rat striatum and medial prefrontal cortex (MPFC) using in vivo voltammetry and determined if this effect was mediated by nicotinic receptors (nAChRs). In both striatum and MPFC, nicotine increased DA clearance in a mecamylamine-sensitive manner, indicating nAChR-mediation. The effect of acute nornicotine on DAT function was also determined. In contrast to nicotine, nornicotine in a dose-related manner decreased striatal DA clearance in a mecamylamine-sensitive manner, indicating nAChR mediation. To determine if tolerance developed to the nicotine effect nicotine, separate groups of rats were injected once daily for 5 days with nicotine or saline. DA clearance in striatum and MPFC was determined 24 hrs after the last injection. Nicotine increased DA clearance only 10-15% in the group repeatedly administered nicotine, demonstrating that tolerance developed. To determine if nicotine altered striatal DAT efficiency, following nicotine injection, DAT density and maximal velocity of [3H]DA uptake was determined using [3H]GBR12935 binding and saturation analysis of [3H]DA uptake in rat striatum, respectively. Nicotine did not alter the Bmax or Kd of maximal binding of [3H]GBR12935 binding. However, an increase in Vmax was observed at 10 and 40 min following nicotine injection, suggesting that nicotine increases DAT efficiency. To determine if systemic nicotine enhanced DAT function via an action at nAChRs on striatal DA terminals, [3H]DA uptake was determined in striatum in vitro in the absence or presence of nicotine in the buffer. Nicotine did not alter the Vmax for [3H]DA uptake in vitro, suggesting that the nicotine-induced increase in DAT function observed in vivo is mediated by nAChRs on DA cell bodies or another site which indirectly alters DAT function. To determine if the increase in DAT efficiency was due to increased surface expression of striatal DAT, biotinylation and Western blot analyses were performed. Nicotine did not alter striatal DAT, suggesting that the nicotine-induced increase in DA clearance in vivo and DAT efficiency in vitro is not the result of increased trafficking of this protein to the cell surface.