The supraspinal control of descending inhibition of genital reflexes (such as ejaculation) is poorly understood but is important in our global comprehension of how neural signals are integrated to produce sexual behavior, and in our understanding of sexual dysfunction. Sexual dysfunctions, such as premature ejaculation/delayed ejaculation in men, and involuntary vaginal spasms, dyspareunia, and anorgasmia in women, are common. An underlying dysregulation of genital reflexes may produce these dysfunctions, especially in those individuals being treated for depression and anxiety with serotonergic drugs. The nucleus paragigantocellularis (nPGi) of the rat medulla has been described as a descending inhibitory system for genital reflexes in rats, and a homologue is known in humans. Through retrograde tracing of nPGi afferents with the tracer Fluorogold in rats, we found that a number of brain regions implicated in sexual behavior, such as the medial preoptic area, paraventricular nucleus of the hypothalamus, and periaqueductal gray (PAG) provide sexually dimorphic projections to the nPGi, and that many of these regions contain receptors for gonadal steroids and are active during sexual behavior. We also found that excitotoxic lesions of the nPGi with N-methyl-D-aspartate facilitate male sexual behavior by reducing the number of intromissions required for ejaculation, and decreasing ejaculation latency. In females, such lesions attenuated sexual behavior by reducing the amount of time the female spent mating and reducing the reinforcement value of vaginocervical stimulation. Lastly, we found that by removing the source of serotonin to the nPGi (from the ventrolateral PAG) with the serotonergic neurotoxin 5,7-DHT in male rats, we were able to mimic the effects of nPGi lesions and facilitated male sexual behavior indicating that serotonin neurotransmission at the level of the nPGi is critical for genital reflex control. Taken together our results indicate that the nPGi is an important site of integration of internal signals for the regulation of sexual behavior that is sexually dimorphic and under serotonergic control. Our understanding of normal and dysfunction genital reflex control, and possible treatment options in people, is complemented by these results.

Neurons in the Locus coeruleus (LC) play an important role in the central CO2 chemosensitivity. However, the molecular mechanisms for neuronal CO2 chemosensitivity remain unclear. To demonstrate the expression of pH/CO2 sensitive ion channels, we screened the inward rectifier K+ channels (Kir) and transient receptor protein (TRP) channels, as parallel studies in this lab suggested that certain Kir and TRP channels are involved in neuronal responses to high levels of CO2. Our results showed that several members of the Kir and TRP channel families were robustly expressed in the LC neurons at the mRNA level. Of particular interest are TRPC5, Kir4.1 and Kir5.1 channels that are all pH-sensitive. The rich expression of various pH-sensitive Kir and TRP channels suggests that these ion channels are likely to play a role in the chemosensitivity of LC neurons.

Professional research project (Au.D.)--University of South Florida, 2000. / Title from PDF of title page. / Document formatted into pages; contains 48 pages. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The primary objective of the project was to survey recognized "experts" in the field of neurodiagnostic audiology and practicing audiologists regarding their referral criteria and referral patterns for administering an auditory brainstem response test (ABR). For purposes of this study, "expert" was defined as any recognized audiologist with at least two or more publications and/or seminarsin the field of auditory evoked potentials. / Responses of experts and practicing audiologists were compared and contrasted to establish: a) if there was a standard referral pattern; b) what, if any, were the apparent critical components of referral patterns; and, c) whether or not current practice reflected the utilization of such critical components. The survey was designed to establish whether the respondent was practicing, in what type of practice setting, and how often ABRs were performed. Specificity and sensitivity of ABR outcomes was also requested. / The survey was administered verbally, via telephone, to 3 experts and was sent via e-mail to 178 randomly selected audiologists in the United States. Of the latter 53 returned, 38 reported conducting ABRs. Thus, data analysis was reported on 38 respondents. The survey results did not reveal a consistent standard referral pattern. Critical components for referral were hypothesized based on the "expert" majority response. These include ABR referral based on the presence of: (1) asymmetric sensorineural hearing loss; (2) unilateral tinnitus; (3) positive reflex decay; and, (4) word recognition rollover. The majority of "non-expert" practitioners surveyed reported that these symptoms warranted consideration for referral, thus reflecting utilization of apparent critical components. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Auditory evoked potentials (AEPs) have become commonly used to measure hearing thresholds in fish. However, it is uncertain how well AEP thresholds match behavioral hearing thresholds and what effect variability in electrode placement and tank composition has on AEPs. In the first experiment, the effect of testing tank composition and electrode placement on AEPs was determined by recording AEPs in the same individual fish in a steel and PVC cylindrical testing tank, and simultaneously recording AEPs from four locations and two different depths on each of 12 goldfish, Carassius auratus. Results from these studies show that tank composition has an effect AEP strength and hearing thresholds, with steel producing lower thresholds for all frequencies. Electrode placement and depth showed no significant effect on hearing thresholds.In the second experiment, the hearing sensitivity of 12 goldfish was measured using both classical conditioning and AEPs in the same setup. For behavioral conditioning, the fish were trained to reduce their respiration rate in response to a 5s sound paired with a brief shock. Once the behavioral audiogram was completed, the AEP measurements were made without moving the fish. The same sound stimuli were presented and the resultant evoked potentials were recorded for 1,000-6,000 averages. AEP input-output functions were then compared to the behavioral audiogram to compare techniques for estimating behavioral thresholds from AEP data. Results show a large range in variability between behavioral and evoked potential thresholds between fish, with the linear regression evoked potential analysis method producing closer thresholds to behavioral methods. In the third study, the effects of masking were examined on the behavioral and evoked potential audiograms. Behavioral thresholds were first determined with a constant masking noise for two frequencies, followed by threshold measurements with no masking noise.

This study tested the hypothesis that decreasing the control O2 level from 95% to 40% (5% CO2 + 55% N2) maintains viability in caudal solitary complex (cSC) neurons in transverse slices (~300-400ꝳ) prepared from neonatal rat (P2-22) maintained at 32-34°C. The underlying rationale is to reduce exposure to redox and nitrosative stimuli generated during several hours of exposure to 95% O2 that produces a tissue O2 tension throughout the slice which is in excess of 203 kPa (2.0 atmospheres absolute,ATA) oxygen. Whole cell recordings of cSC neurons maintained in 40% O2 exhibited spontaneous firing and had similar membrane potentials (Vm) and input resistances (Rin) as cSC neurons maintained in 95% O2. Neurons maintained in 40% O2, however, had significantly lower intrinsic firing rates than those maintained in 95% O2. 67% of neurons maintained in 40% O2 control were stimulated by hyperoxia, compared to 81% of neurons maintained in 95% O2 that were stimulated by reoxygenation from relative hypoxia. cSC neurons maintained in 40% O2 also exhibited CO2/H+-sensitivity, including CO2/H+-excitation (31%) and CO2H+-inhibition (31%) and most CO2/H+-sensitive neurons were also stimulated by hyperoxia and reoxygenation or inhibited by lower O2. It is also suggested that acute exposure to lower concentrations of O2 may increase the incidence of CO2-inhibited cSC neurons. Anoxia reduced or eliminated all firing in essentially all cSC neurons. Our findings indicate that brainstem slice viability is retained in 40% O2 control and that hyperoxia is a general stimulant of many cSC neurons, including chemosensitive neurons. We therefore recommend that 40% O2 be used for brainstem electrophysiology studies.

No description available.

This study examined the effects of temperature and chronic hypoxia (CH) on pH/CO2- sensitive fictive breathing, and central pH/CO2 chemosensitivity, in cane toads (Bufo marinus). Toads were exposed to CH (10% or 15% O2) or control conditions (21% O2) for 10 days at either room temperature (controls), 10°C or 30°C following which in vitro brainstem-spinal cord preparations were used to examine central pH/CO2-sensitive fictive breathing (i.e., motor output from respiratory nerves which is the neural correlate of breathing). A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation (TFV). Cold temperature reduced and hot temperature increased fR and TFV under control conditions. CH attenuated fictive breathing independently of temperature. Additional experiments in which the aCSF temperature was varied indicate that the effects of temperature acclimation result from neural plastic changes within respiratory control centres in the brain.

This study examined the effects of temperature and chronic hypoxia (CH) on pH/CO2- sensitive fictive breathing, and central pH/CO2 chemosensitivity, in cane toads (Bufo marinus). Toads were exposed to CH (10% or 15% O2) or control conditions (21% O2) for 10 days at either room temperature (controls), 10°C or 30°C following which in vitro brainstem-spinal cord preparations were used to examine central pH/CO2-sensitive fictive breathing (i.e., motor output from respiratory nerves which is the neural correlate of breathing). A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation (TFV). Cold temperature reduced and hot temperature increased fR and TFV under control conditions. CH attenuated fictive breathing independently of temperature. Additional experiments in which the aCSF temperature was varied indicate that the effects of temperature acclimation result from neural plastic changes within respiratory control centres in the brain.

This thesis tests the hypothesis that increased neuronal cell death in SIDS infants is related to the ability of risk factors, such as prone sleeping, to expose infants to intermittent hypercapnic hypoxia (IHH). Based on the hypothesis that the NMDA system is linked to neuronal death, by way of excitotoxicity, correlations were also sought between cell death and changes in NMDA receptor (NR1) expression in brainstem nuclei controlling cardiorespiratory function. The first aim of this study was to verify that increased neuronal cell death occurs in SIDS infants. To verify a piglet model of SIDS risk factors, brainstem changes were examined in piglets exposed to IHH, and comparisons were made to changes seen in SIDS infants. The NMDA receptor was characterised in controls for both the human infant and the piglet groups. Comparisons of neuronal changes were made with SIDS infants, and piglets exposed to IHH. Non-radioactive in-situ hybridisation and immunohistochemistry were performed on formalin fixed and paraffin embedded brainstem tissue to identify markers of cell death (caspase-3, active caspase-3, and TUNEL), and to examine NR1 mRNA and protein expressions. Staining was quantified using computerised image analysis software. Eight nuclei from the brainstem medulla (caudal in piglets, and mid in infants), and two nuclei from the rostral pons (infants) were studied. The first dataset included human infants aged 1-6 months with a diagnosis of SIDS (n=15) or non-SIDS (n=10). The second dataset comprised developing piglets aged 13-14 days, with controls (n=6), against those exposed to IHH for 2 (n=6) or 4 (n=5) days. Increased neuronal cell death was not verified in the SIDS infants, but abnormalities in NR1 expression were present in selected nuclei of the medulla. Piglets exposed to IHH had increased neuronal cell death and changes in NR1 in selected nuclei of the medulla. There was also a positive correlation between increased cell death and high NR1 levels. Preliminary data showed that SIDS infants who usually slept prone had some differences in NR1 compared to those who did not usually sleep prone. From these findings, it was concluded that IHH may underlie the abnormalities in NMDA receptor expression that are present in the brainstem of SIDS infants. Although IHH can induce an increase in neuronal cell death, its significance in the aetiology of SIDS is not known. In piglets, IHH induced cell death correlated with high NMDA expression in some brainstem nuclei, supporting the hypothesis that excitotoxicity may be involved in the mechanism for cell death. Moreover, this thesis presents for the first time, �preliminary pathological proof� of an association between prone sleeping and abnormal NMDA receptor expression in SIDS infants.

Doctor of Philosophy(PhD) / This thesis addresses the neurochemistry and function of specific nuclei in the autonomic nervous system that are crucial mediators of cardiorespiratory regulation. The primary aim is to build on previous knowledge about muscarinic cholinergic mechanisms within cardiorespiratory nuclei located in the ventrolateral medulla oblongata. The general focus is characterisation of gene expression patterns of specific muscarinic receptor subtypes in central nuclei involved in blood pressure control and respiratory control in normal rats. The findings were subsequently extended by characterisation of muscarinic receptor gene expression patterns in 1) a rat model of abnormal blood pressure control (hypertension) (Chapter 3) 2) a rat model of cholinergic sensitivity (Chapter 5) 3) the rat ventral respiratory group (Chapter 6) The results of a series of related investigations that ensued from the initial aims more finely characterise the neurocircuitry of the ventrolateral medulla, from a specifically cholinoceptive approach. All five muscarinic receptor subtypes are globally expressed in the ventrolateral medulla but only the M2R mRNA was significantly elevated in the VLM of hypertensive animals compared to their normotensive controls and in the VLM of animals displaying cholinergic hypersensitivity compared to their resistant controls. Surprisingly, M2R mRNA is absent in catecholaminergic cell groups but abundant in certain respiratory nuclei. Two smaller projects involving gene expression of other neurotransmitter / neuromodulators expressed in cardiorespiratory nuclei were also completed during my candidature. Firstly, the neurochemical characterisation of enkephalinergic neurons in the RVLM, and their relationship with bulbospinal, catecholaminergic neurons in hypertensive compared to normotensive animals was carried out (Chapter 4). A substantial proportion of sympathoexcitatory neurons located in the RVLM were enkephalinergic in nature. However, there was no significant difference in preproenkephalin expression in the RVLM in hypertensive compared to normotensive animals. Secondly, the identification and distribution of components of the renin-angiotensin aldosterone system (RAAS) within the brainstem, and differences in gene expression levels between hypertensive and normotensive animals was also investigated. The RAAS data was not included in this thesis, since the topic digresses substantially from other chapters and since it is published (Kumar et al., 2006). The mRNA expression aldosterone synthase, mineralocorticoid receptor (MR1), 12-lipoxygenase (12-LO), serum- and glucocorticoid- inducible kinase and K-ras) were found to be present at all rostrocaudal levels of the ventrolateral medulla. Expression of MR1 mRNA was lower in the RVLM of SHR compared with WKY rats and 12-LO mRNA levels were lower in the CVLM in SHR compared with WKY rats. Otherwise, there was no difference in gene expression level, or the method of detection was not sensitive enough to detect differences in low copy transcripts between hypertensive and normotensive animals.