Final results of a randomized phase III trial of induction chemotherapy followed by concurrent chemoradiotherapy versus concurrent chemoradiotherapy alone in patients with stage IVA and IVB nasopharyngeal carcinoma-Taiwan Cooperative Oncology Group (TCOG) 1303 Study.

Background: Concurrent chemoradiotherapy (CCRT) is superior to radiotherapy alone for treating locoregionally advanced nasopharyngeal carcinoma (NPC). Whether adding induction chemotherapy (IC) further improves the outcome warrants investigation. Patients and methods: This open-label multicenter phase III trial was conducted at 11 institutions in Taiwan. Patients with stage IVA or IVB NPC were randomized to receive IC followed by CCRT (I-CCRT) or CCRT alone. Patients in the I-CCRT arm received three cycles of mitomycin C, epirubicin, cisplatin, and 5-fluorouracil/leucovorin (MEPFL). All patients received 30 mg/m2 cisplatin weekly during radiotherapy, which was delivered as 1.8-2.2 Gy per fraction with five daily fractions per week, to a total dose of 70 Gy or greater to the primary tumor and 66-70 Gy to the involved neck. The primary end point was disease-free survival (DFS). Results: In this study, 240 and 239 patients were randomized to CCRT and I-CCRT arm, respectively. The most prominent toxicities of induction were leukopenia (grade 3 and 4: 47% and 12%) and thrombocytopenia (grade 3 and 4: 24% and 3%). During radiotherapy, severe mucositis was the major side-effect in both arms; an increased number of patients in the I-CCRT arm had myelosuppression; hence, discontinuation of weekly cisplatin was more common. After a median follow-up of 72.0 months, the I-CCRT arm had significantly higher DFS than that of the CCRT arm [5-year rate 61% versus 50%; hazard ratio=0.739, 95% confidence interval (CI)=0.565-0.965; P = 0.0264], after stratified for N3b and LDH, and adjusted for T stage. Conclusion: Induction with MEPFL before CCRT was tolerable and significantly improved the DFS of patients with stage IVA and IVB NPC though overall survival not improved. Clinical trial information: NCT00201396.

Tunable nanoblock lasers and stretching sensors.

Reconfigurable, reliable, and robust nanolasers with wavelengths tunable in the telecommunication bands are currently being sought after for use as flexible light sources in photonic integrated circuits. Here, we propose and demonstrate tunable nanolasers based on 1D nanoblocks embedded within stretchable polydimethylsiloxane. Our lasers show a large wavelength tunability of 7.65 nm per 1% elongation. Moreover, this tunability is reconfigurable and reliable under repeated stretching/relaxation tests. By applying excessive stretching, wide wavelength tuning over a range of 80 nm (spanning the S, C, and L telecommunication bands) is successfully demonstrated. Furthermore, as a stretching sensor, an enhanced wavelength response to elongation of 9.9 nm per % is obtained via the signal differential from two nanoblock lasers positioned perpendicular to each other. The minimum detectable elongation is as small as 0.056%. Nanoblock lasers can function as reliable tunable light sources in telecommunications and highly sensitive on-chip structural deformation sensors.

Randomised clinical trial: comparison of two everolimus dosing schedules in patients with advanced hepatocellular carcinoma.

BACKGROUND: Deregulation of mammalian target of rapamycin (mTOR) signalling is common in human hepatocellular carcinoma (HCC). AIM: To determine the maximum tolerated dose (MTD) of the oral mTOR inhibitor everolimus in advanced HCC patients. METHODS: Patients with locally advanced or metastatic HCC (Child-Pugh class A or B) were enrolled in an open-label phase 1 study and randomly assigned to daily (2.5-10 mg) or weekly (20-70 mg) everolimus in a standard 3 + 3 dose-escalation design. MTD was based on the rate of dose-limiting toxicities (DLTs). Secondary endpoints included safety, pharmacokinetics and tumour response. In a post hoc analysis, serum hepatitis B virus (HBV) DNA levels were quantified. RESULTS: Thirty-nine patients were enrolled. DLTs occurred in five of 21 patients in the daily and two of 19 patients in the weekly cohort. Daily and weekly MTDs were 7.5 mg and 70 mg respectively. Grade 3/4 adverse events with a ≥10% incidence were thrombocytopenia, hypophosphataemia and alanine transaminase (ALT) elevation. In four hepatitis B surface antigen (HBsAg)-seropositive patients, grade 3/4 ALT elevations were accompanied by significant (>1 log) increases in serum HBV levels. The incidence of hepatitis flare (defined as ALT increase >100 IU/mL from baseline) in HBsAg-seropositive patients with and without detectable serum HBV DNA before treatment was 46.2% and 7.1% respectively (P < 0.01, Fisher exact test). Disease control rates in the daily and weekly cohorts were 71.4% and 44.4% respectively. CONCLUSIONS: The recommended everolimus dosing schedule for future hepatocellular carcinoma studies is 7.5 mg daily. Prophylactic anti-viral therapy should be mandatory for HBsAg-seropositive patients (ClinicalTrials.gov NCT00390195).

Trends of mortality and causes of death among HIV-infected patients in Taiwan, 1984-2005.

BACKGROUND: The aim of this study was to analyse the trends of mortality and causes of death among HIV-infected patients in Taiwan from 1984 to 2005. METHODS: Registered data and death certificates for HIV-infected patients from Taiwan Centers for Disease Control were reviewed. Mortality rate and causes of deaths were compared among patients whose HIV diagnosis was made in three different study periods: before the introduction of highly active antiretroviral therapy (HAART) (pre-HAART: from 1 January 1984 to 31 March 1997), in the early HAART period (from 1 April 1997 to 31 December 2001), and in the late HAART period (from 1 January 2002 to 31 December 2005). A subgroup of 1161 HIV-infected patients (11.4%) followed at a university hospital were analysed to investigate the trends of and risk factors for mortality. RESULTS: For 10 162 HIV-infected patients with a mean follow-up of 1.97 years, the mortality rate of HIV-infected patients declined from 10.2 deaths per 100 person-years (PY) in the pre-HAART period to 6.5 deaths and 3.7 deaths per 100 PY in the early and late HAART periods, respectively (P<0.0001). For the 1161 patients followed at a university hospital (66.8% with CD4 count <200 cells/microL), HAART reduced mortality by 89% in multivariate analysis, and the adjusted hazard ratio for death was 0.28 (95% confidence interval 0.24, 0.33) in patients enrolled in the late HAART period compared with those in the pre-HAART period. Seventy-six per cent of the deaths in the pre-HAART period were attributable to AIDS-defining conditions, compared with 36% in the late HAART period (P<0.0001). The leading causes of non-AIDS-related deaths were sepsis (14.7%) and accidental death (8.3%), both of which increased significantly throughout the three study periods. Compared with patients acquiring HIV infection through sexual contact, injecting drug users were more likely to die from non-AIDS-related causes. CONCLUSIONS: The mortality of HIV-infected patients declined significantly after the introduction of HAART in Taiwan. In the HAART era, AIDS-related deaths decreased significantly while deaths from non-AIDS-related conditions increased.

Surrogate estimates of insulin sensitivity in subjects with hypertension.

The purpose of the study is to compare surrogate estimates of insulin sensitivity with a directly measured insulin sensitivity index, steady-state plasma glucose (SSPG) from insulin suppression test (IST), in subjects with hypertension. Two hundred and twenty-eight hypertensive patients who received IST for SSPG were included for analysis. Estimates from fasting measurements alone, homeostasis model assessment for insulin resistance (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI)), and indices from fasting and/or 2 h samples (ISI(0,120) and ISI(TX)) were calculated. In addition to Pearson and partial correlations, variance-component models were used to test the relationship between surrogate estimates of insulin sensitivity and SSPG. A large proportion of variance owing to covariates in the variance-component models indicated the goodness of model fit, irrespective of the independence among variables. SSPG was positively correlated with logarithmic transformation (Log) (HOMA-IR) and negatively correlated with QUICKI, Log (ISI(0,120)) and ISI(TX) (all P<0.0001). Log (ISI(0,120)) seemed to have a better correlation with SSPG (r=-0.72) than other measures in partial correlation. The proportion of variance owing to all covariates of Log (ISI(0,120)) and ISI(TX) were larger than those of Log (HOMA-IR) and QUICKI in the variance-component models. After adjustments for demographic and obesity covariates, the proportion of variance explained by Log (ISI(0,120)) were largest among the surrogate measures in the variance-component models. Our results showed that ISI(0,120) and ISI(TX) correlated better with SSPG than those used fasting measures alone (HOMA-IR and QUICKI). Log (ISI(0,120)) currently showing the strongest association with SSPG than other estimates is adaptable for use in large studies of hypertension.

Endemic fungal infections caused by Cryptococcus neoformans and Penicillium marneffei in patients infected with human immunodeficiency virus and treated with highly active anti-retroviral therapy.

This study compared the clinical presentations of 58 episodes of cryptococcosis in 50 patients and 26 episodes of penicillosis in 25 patients infected with human immunodeficiency virus (HIV) between June 1994 and June 2004, and assessed the safety of discontinuation of secondary prophylaxis for endemic fungal infections in those patients responding to highly active anti-retroviral therapy (HAART). Neurological symptoms were seen more commonly in patients with cryptococcosis, whereas respiratory symptoms, lymphadenopathy, hepatomegaly and/or splenomegaly, and non-thrush-related oral presentations were seen more commonly in patients with penicillosis. Patients with penicillosis were more likely to have abnormal chest radiography results and radiographic presentations of interstitial lesions, cavitations, fibrotic lesions and mass lesions. At the end of the study, maintenance antifungal therapy had been discontinued in 27 patients with cryptococcosis and in 18 patients with penicillosis in whom the median CD4 count had increased to 186 cells/microL (range, 9-523 cells/microL) and 95 cells/microL (range, 15-359 cells/microL), respectively, after HAART. Only one episode of penicillosis recurred (a relapse rate of 1.72/100 person-years; 95% CI, 1.44-2.10/100 person-years) after a median follow-up duration of 35.3 months (range, 2.6-91.6 months). No relapses occurred in patients with cryptococcosis after a median follow-up duration of 22.3 months (range, 1-83.4 months). These findings suggest that there are differences in the clinical presentations between endemic cryptococcosis and penicillosis in patients with HIV infection, and that it is safe to discontinue secondary antifungal prophylaxis for cryptococcosis and penicillosis in patients responding to HAART.

Betel nut chewing and other risk factors associated with obesity among Taiwanese male adults.

OBJECTIVE: The research aimed at examining betel nut chewing and other risk factors associated with obesity among Taiwanese male adults. DESIGN: The research analyzed the data obtained by the 2001 National Health Interview Survey in Taiwan that covered all the administrative divisions in Taiwan. Multistage stratified systematic sampling design was adopted for survey. All members of a sampled household received the interview. SUBJECTS: The research analyzed questionnaires answered by nonaboriginal male respondents aged between 20 and 59 years old, and the total number of samples analyzed read 6126. Since very few female subjects chewed betel nut, they were excluded from the analysis. MEASUREMENTS: Criteria of obesity was defined as body mass index > or = 27 kg/m2. The variables incorporated for analysis included the respondents' status of betel nut chewing, age, educational background, presence of hypertension and diabetes mellitus, drinking and smoking status, exercise status, and demand for physical strength at job. Generalized estimating equations model was employed to estimate the odd ratios (with 95% CI) of obesity of each independent variable. RESULTS: Approximately 16.2% of respondents were obese. The distribution of betel nut chewing was current chewers 15.9%, ex-chewers 4.3%, and nonchewers 79.8%. After controlling above-mentioned independent variables, hypertension, diabetes mellitus, betel nut chewing, never exercising, and sedentary jobs were closely associated with obesity. CONCLUSION: The research found that betel nut chewing closely associated with obesity. The increased appetite of betel nut chewers is speculated as the underlying cause. The prospective study is needed to clarify this issue. In addition to increasing the risk of developing oral cancer, betel nut chewing seemed to be related with another health hazard: obesity.

Prevalence of Toxoplasma gondii infection and incidence of toxoplasma encephalitis in non-haemophiliac HIV-1-infected adults in Taiwan.

We assessed the seroprevalence of Toxoplasma gondii infection and incidence of toxoplasma encephalitis (TE) in 844 non-haemophiliac HIV-infected patients in Taiwan between June 1994 and April 2003. Approximately 70% (69.3%) of them had a baseline CD4+ lymphocyte count of 200 x 10(6)/L or less, and more than 70% (73.9%) having initiated highly active antiretroviral therapy. The seroprevalence of T. gondii infection was 10.2%, which did not differ with sex,age,route of transmission, birth inside or outside of Taiwan, or CD4+ lymphocyte stratifications. After a median observation duration of 603 days (range, 1-3264 days), 10 (1.2%) patients developed 11 episodes of TE after a median interval of 30 days (range, 1-941 days) between enrolment and diagnosis of TE, with an incidence of 0.59 per 100 person-years (PY) (95% confidence interval, 0.56-0.63 per 100 PY). We concluded that the incidence of TE of HIV-infected patients in Taiwan was lower than that reported in western countries because of a lower seroprevalence of T. gondii infection and use of antimicrobial prophylaxis and antiretroviral therapy, although most of the patients were at the late stage of HIV infection.

Impact of chronic hepatitis C infection on outcomes of patients with an advanced stage of HIV-1 infection in an area of low prevalence of co-infection.

To ascertain whether hepatitis C (HCV) co-infection affects the progression of HIV infection, we initiated an eight-year prospective observational study at a university hospital in Taiwan where seroprevalences of HCV antibody and HIV antibody were low. Fifty-three (12.0%) consecutive non-haemophiliac HIV1-infected patients with HCV co-infection and 387 (88.0%) patients without HCV and hepatitis B co-infection were enrolled between June 1994 and June 2002 and observed until December 2002. Outcomes evaluated included the risk for acute hepatitis, hepatic decompensation, HIV disease progression and mortality, and changes of CD4+ count and plasma viral load (PVL) after initiation of highly active antiretroviral therapy (HAART) at the end of the study. The baseline CD4+ count, PVL and proportion of patients with AIDS-defining opportunistic illnesses (OI) at study entry were similar between patients with HCV co-infection and those without co-infection, but HCV-co-infected patients were older (39 versus 35 years, P = 0.01) and had a higher proportion of intravenous drug use (17.0% versus 0.8%, P < 0.001). After a total observation duration of 1137 patient-years (PY) (median, 791 days; range, 3-3053 days), the incidence of acute hepatitis in HCV-co-infected patients was 13.89 per 100 PY (95% confidence interval [CI], 13.31-14.49) and that in patients without co-infection was 6.39 per 100 PY (95% CI, 6.24-6.55 per 100 PY), with an adjusted odds ratio (OR) of 2.769 (95% CI, 1.652-4.640). At the end of the study, CD4+ count increased by 137 x 10(6) and 157 x 10(6)/L in patients with and without HCV co-infection, respectively, (P = 0.47). The proportions of achieving undetectable PVL (<400 copies/mL) after HAART was similar (76.7% versus 74.9%, P = 0.79). The adjusted OR for development of new AIDS-defining OI was 1.826 (95% CI, 0.738-4.522) in HCV-co-infected patients as compared with HCV- uninfected patients. The adjusted hazards ratio for death of HCV-co-infected patients when compared with those without co-infection was 0.781 (95% CI, 0.426-1.432). Our findings suggested that HCV co-infection was associated with a significantly higher risk for acute hepatitis in HIV-infected patients receiving antiretroviral therapy, but it had no adverse impact on virological, immunological and clinical responses to HAART and survival when compared with patients without HCV and HBV co-infection.

Sagittal abdominal diameter is associated with insulin sensitivity in Chinese hypertensive patients and their siblings.

The purpose of the study is to observe the relation between anthropometric measurements, focusing on sagittal abdominal diameter (SAD), and insulin sensitivity indices in Chinese hypertensive patients and their siblings. In total, 907 participants, 537 hypertensive and 370 nonhypertensive, from 311 Taiwanese families were drawn from the Stanford Asia and Pacific Program for Hypertension and Insulin Resistance for the study. The participants received anthropometric measurements and 75-g oral glucose tolerance tests after an overnight fast. Fasting insulin, homeostasis model assessment for insulin resistance (HOMA-IR), and the insulin sensitivity index ISI(0,120) were chosen as surrogate measures of insulin sensitivity. In addition to Pearson and partial correlations, we used generalized estimating equations (GEEs) to examine the association between anthropometric measurements and insulin sensitivity indices. A small deviance in the GEEs indicates the goodness of model fit, irrespective of the independence among variables. The hypertensive patients were older in age, wider in waist circumference (WC), larger in body mass index (BMI) and SAD, and more insulin resistant than the nonhypertensive counterparts. The logarithmic transformation of fasting insulin, HOMA-IR, and ISI(0,120) significantly correlated with SAD, WC, and BMI before and after adjustments for age and sex. The deviances of SAD in the GEEs were similar to those of WC in all subjects, while BMI had smaller deviances than SAD and WC in the hypertensive patients. Our results suggest that the performance of SAD in predicting insulin sensitivity is comparable with WC in Chinese hypertensive patients and their siblings. BMI, however, seems to have better association with insulin sensitivity than SAD and WC in the patients with hypertension.

Genetic variation in aldosterone synthase predicts plasma glucose levels.

The mineralocorticoid hormone, aldosterone, is known to play a role in sodium homeostasis. We serendipitously found, however, highly significant association between single-nucleotide polymorphisms in the aldosterone synthase gene and plasma glucose levels in a large population of Chinese and Japanese origin. Two polymorphisms--one in the putative promoter (T-344C) and another resulting in a lysine/arginine substitution at amino acid 173, which are in complete linkage disequilibrium in this population--were associated with fasting plasma glucose levels (P = 0.000017) and those 60 (P = 0.017) and 120 (P = 0.0019) min after an oral glucose challenge. A C/T variant in intron 1, between these polymorphisms, was not associated with glucose levels. Arg-173 and -344C homozygotes were most likely to be diabetic [odds ratio 2.51; 95% confidence interval (C.I.) 1.39-3.92; P = 0.0015] and have impaired fasting glucose levels (odds ratio 3.53; 95% C.I. 2.02-5.5; P = 0.0000036). These results suggest a new role for aldosterone in glucose homeostasis.

High-throughput genotyping with single nucleotide polymorphisms.

To make large-scale association studies a reality, automated high-throughput methods for genotyping with single-nucleotide polymorphisms (SNPs) are needed. We describe PCR conditions that permit the use of the TaqMan or 5' nuclease allelic discrimination assay for typing large numbers of individuals with any SNP and computational methods that allow genotypes to be assigned automatically. To demonstrate the utility of these methods, we typed >1600 individuals for a G-to-T transversion that results in a glutamate-to-aspartate substitution at position 298 in the endothelial nitric oxide synthase gene, and a G/C polymorphism (newly identified in our laboratory) in intron 8 of the 11-beta hydroxylase gene. The genotyping method is accurate-we estimate an error rate of fewer than 1 in 2000 genotypes, rapid-with five 96-well PCR machines, one fluorescent reader, and no automated pipetting, over one thousand genotypes can be generated by one person in one day, and flexible-a new SNP can be tested for association in less than one week. Indeed, large-scale genotyping has been accomplished for 23 other SNPs in 13 different genes using this method. In addition, we identified three "pseudo-SNPs" (WIAF1161, WIAF2566, and WIAF335) that are probably a result of duplication.

Membrane resonance and subthreshold membrane oscillations in mesencephalic V neurons: participants in burst generation.

Trigeminal mesencephalic (Mes V) neurons are critical components of the circuits controlling oral-motor activity. The possibility that they can function as interneurons necessitates a detailed understanding of the factors controlling their soma excitability. Using whole-cell patch-clamp recording, in vitro, we investigated the development of the ionic mechanisms responsible for the previously described subthreshold membrane oscillations and rhythmical burst discharge in Mes V neurons from rats ages postnatal day (P) 2-12. We found that the oscillation amplitude and frequency increased during development, whereas bursting emerged after P6. Furthermore, when bursting was initiated, the spike frequency was largely determined by the oscillation frequency. Frequency domain analysis indicated that these oscillations emerged from the voltage-dependent resonant properties of Mes V neurons. Low doses of 4-aminopyridine (<100 microm) reduced the oscillations and abolished resonance in most neurons, suggesting that the resonant current is a steady-state K(+) current (I(4-AP)). Sodium ion replacement or TTX reduced substantially the oscillations and peak amplitude of the resonance, suggesting the presence of a persistent Na(+) current (I(NaP)) that functions to amplify the resonance and facilitate the emergence of subthreshold oscillations and bursting.

Outward currents influencing bursting dynamics in guinea pig trigeminal motoneurons.

To initiate and maintain bursts (and plateau potentials) in the presence of serotonin, guinea pig trigeminal motoneurons utilize L-type Ca2+ and persistent Na+ inward currents. However, the intrinsic currents that contribute to burst termination and determine the duration of the interburst interval are unknown. Therefore we investigated the roles of outward currents, whose slow activation is coupled to cytosolic cation (Ca2+ and Na+) accumulation. First we examined a Ca2+-dependent K+ current (IK-Ca) with apamin and Ba2+-substituted, low-Ca2+ solution. Blockade of IK-Ca lengthened burst duration and cycle time but did not abolish bursting. Next we studied the Na+/K+-ATPase pump current (Ip) with cardiac glycosides. In the presence of apamin or low-Ca2+/Ba2+ solution, blocking Ip (with ouabain or strophanthidin) decreased both burst duration and cycle time and ultimately transformed bursting into tonic spiking. We conclude that IK-Ca and Ip contribute to burst termination in trigeminal motoneurons. These currents influence temporal bursting properties such as burst duration and cycle time and may help determine the phasic activity of motoneurons during rhythmic oral-motor behaviors.

Evidence for a novel bursting mechanism in rodent trigeminal neurons.

We investigated bursting behavior in rodent trigeminal neurons. The essential mechanisms operating in the biological systems were determined based on testable predictions of mathematical models. Bursting activity in trigeminal motoneurons is consistent with a traditional mechanism employing a region of negative slope resistance in the steady-state current-voltage relationship (Smith, T. G. 1975. Nature. 253:450-452). However, the bursting dynamics of trigeminal interneurons is inconsistent with the traditional mechanisms, and is far more effectively explained by a new model of bursting that exploits the unique stability properties associated with spike threshold (Baer, S. M., T. Erneux, and J. Rinzel. 1989. SIAM J. Appl. Math. 49:55-71).

Ionic basis for serotonin-induced bistable membrane properties in guinea pig trigeminal motoneurons.

Intracellular recordings and pharmacological manipulations were employed to investigate the ionic basis for serotonin-induced bistable membrane behaviors in guinea pig trigeminal motoneurons (TMNs). In voltage clamp, 10 microM serotonin (5-HT) induced a region of negative slope resistance (NSR) in the steady-state current-voltage (I-V) relationship at potentials less negative than -58 mV, creating the necessary conditions for membrane bistability. The contributions of sustained Na+ and Ca2+ currents to the generation of the NSR were investigated using specific ion channel antagonists and agonists. The NSR was eliminated by the L-type Ca2+ channel antagonist nifedipine (5-10 microM), indicating the contribution of L channels. In nifedipine, inward rectification was present in the I-V relationship in a similar voltage range (greater than -58 mV). This region was subsequently linearized by tetrodotoxin (TTX), indicating the presence of a persistent Na+ current. When the 5-HT-induced NSR was eliminated by perfusion in low Ca2+ solution (0.4 mM), it was restored by the Na+ channel agonist veratridine (10 microM). Commensurate with bistability, in current clamp during bath application of 5-HT, plateau potentials were elicited by transient depolarizing or hyperpolarizing stimuli. Plateau potentials evoked by depolarization were observed under control and TTX conditions, but were blocked by nifedipine, suggesting the participation of an L-type Ca2+ current. Plateau potentials initiated after release from hyperpolarization (anode break) were blocked by 300 microM Ni2+, suggesting the responses relied on deinactivation of a T-type Ca2+ current. Conditional bursting was also observed in 5-HT. Nifedipine or low Ca2+ solutions blocked bursting, and the L-channel agonist Bay K 8644 (10 microM) extended the duration of individual bursts, demonstrating the role of L-type Ca2+ currents. Interestingly, when bursting was blocked by nifedipine or low Ca2+, it could be restored by veratridine application via enhancement of the persistent Na+ current. We conclude that bistable membrane behaviors in TMNs are mediated by L-type Ca2+ and persistent Na+ currents. 5-HT is associated with enhancement of TMN activity during oral-motor activity; the induction of bistable membrane properties by 5-HT represents a cellular mechanism for this enhancement.

Multiple effects of serotonin on membrane properties of trigeminal motoneurons in vitro.

Intracellular recordings from guinea pig trigeminal motoneurons (TMNs) in brain stem slices were used to determine the underlying ionic mechanisms responsible for our previously demonstrated enhancement of TMN excitability during jaw movements by serotonin (5-HT). 5-HT (0.5-100 microM) depolarized motoneurons and increased input resistance in the majority of neurons tested. Additionally, 5-HT reduced the amplitude of the postspike medium-duration afterhyperpolarization, decreased the current threshold for maintained spike discharge, and increased the maximum slope of the steady-state spike frequency-current relationship. Under voltage clamp, from holding potentials close to resting potential, 5-HT produced an inward current and a decrease in instantaneous slope conductance, suggesting a reduction in a resting K+ leak conductance (I(leak)). The instantaneous current-voltage (I-V) relationship for the inward 5-HT current (I(5-HT)) was linear throughout most of the voltage range tested. However, the steady-state I-V relationship showed some degree of inward rectification at potentials starting around -70 mV. The mean reversal potential for the instantaneous I(5-HT) was -86.2 +/- 4.5 (SE) mV (n = 9), a value slightly negative to the predicted potassium equilibrium potential of -82 mV in these neurons. In the presence of 2 mM Ba2+, 5-HT application did not produce a further reduction in input conductance, but did expose a Ba2+-insensitive residual inward current that was resistant to Cs+ application. The instantaneous I-V relationship during 5-HT application in the presence of Ba2+ was shifted downward and parallel to control, suggesting that Ba2+ and 5-HT block the same resting I(leak). The residual Ba2+- and Cs+-insensitive component of the total inward I(5-HT) was voltage independent and was blocked when the extracellular Na+ was replaced by choline, suggesting that the predominant charge carrier for this residual current is Na+. 5-HT enhanced a hyperpolarization-activated cationic current, I(h). In the presence of Ba2+, the time course of I(5-HT) resembled that of I(h) and showed a similar voltage dependence that was blocked by extracellular Cs+ (1-3 mM). The effects of 5-HT on membrane potential, input resistance, and I(h) were partially mimicked by 5-HT2 agonists and suppressed by 5-HT2 antagonists. It is concluded that 5-HT enhances TMN membrane excitability through modulation of multiple intrinsic membrane conductances. This provides for a mechanism(s) to fine tune the input-output discharge properties of these neurons, thus providing them with greater flexibility in output in response to time-varying synaptic inputs during various movements of the jaw.

Characteristics of a fast transient outward current in guinea pig trigeminal motoneurons.

A fast transient voltage dependent outward current (TOC) in trigeminal motoneurons (TMNs) was studied in guinea pig brainstem slices by use of sharp electrodes in combination with single electrode voltage clamp techniques. In solutions containing TTX, low Ca2+/Mn2+ and 20 mM TEA this current activated around -55 to -60 mV from holding potentials negative to resting potential, obtained its peak amplitude within 5 ms and decayed as a single exponential with a time constant of 6-8 ms. Half maximal values for inactivation and activation were -72 and -37 mV, respectively. Bath application of 5 mM 4-AP suppressed this current by approximately 90% and eliminated the early depolarizing transient membrane rectification observed in response to a constant depolarizing current pulse, prolonged the action potential duration, and reduced the threshold voltage and delay to onset of the action potential. It is suggested that this current resembles the typical A-current observed in many CNS neurons and, as a result of its voltage and time dependent properties, could contribute to control of motoneuronal discharge and timing of burst onset during rhythmical jaw movements. Therefore, any cellular models of masticatory activity should include the properties of this current.

Identification of cell types from action potential waveforms: cerebellar granule cells.

We have recorded 404 single units extracellularly in the cerebellar cortex of the rat with tungsten microelectrodes. Waveforms of action potentials were analyzed in order to develop criteria for on-line identification of cell types. Two of the four most frequently recorded waveforms were simple and complex spikes from Purkinje cells. The other two originated from granule cells and glomeruli. Presumed granule cells showed biphasic action potentials with half-widths (0.78 +/- 0.14 ms, n = 51) broader than those of the simple spikes of Purkinje cells (0.22 +/- 0.06 ms, n = 54), whereas presumed glomerular potentials had complex action potentials with narrower half-widths (0.14 +/- 0.05 ms, n = 35). The mean inter-spike interval of presumed granule cells (333.3 +/- 195.4 ms, n = 53) was longer than that of Purkinje cells (47.3 +/- 31.8 ms, n = 59) and the presumed glomerular potentials (77.7 +/- 50.8 ms, n = 20). Results were virtually identical from 17 cerebellar units recorded extracellularly in the cat. Intracellular recording and staining of 20 granule cells with HRP-filled microelectrodes provided further support for our assessment. These results suggest that action potentials from granule cells may be identified on-line by waveform.