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B Tam

Publications and source records attributed to B Tam.

5 recordsLinked to original sources
PubMed1990

Activation of the glycine site in the NMDA receptor is necessary for the induction of LTP.

The effects of 7-chlorokynurenate (7-C1KY) were examined on N-methyl-D-aspartate (NMDA) receptor-mediated synaptic mechanisms in the CA1 region of rat hippocampal slices. 7-C1KY depressed both the NMDA receptor-mediated component of synaptic transmission recorded in Mg2(+)-free medium and the induction of long-term potentiation (LTP) in Mg2(+)-containing medium. Both of these effects were reversed by D-serine, suggesting that the action of 7-C1KY was at the allosteric glycine site on the NMDA receptor.

Action Potentials↗
PubMed1986

Stimulation of corticosterone secretion in vitro by brief ACTH exposure.

We examined the relationship between ACTH concentration and exposure duration on stimulation of corticosterone (B) secretion in vitro using perifused enzymatically dispersed rat adrenocortical cells. A modular perifusion apparatus was used that permitted evaluation of 20-24 cell chambers per experimental session. In expt 1, 20-1000 pg/ml concentrations of synthetic ACTH-(1-24) were presented to cells for 1 min. In expt 2, 100 pg ACTH-(1-24) was presented to adrenal cells in five dose-duration regimens ranging from 5 pg/min for 20 min to 100 pg/min for 1 min. Perifusal rate was 1 ml/min in all sessions. B was determined by radioimmunoassay. In expt 1 (constant-duration paradigm), 1-min presentation of ACTH-(1-24) produced log-linear dose-response effects across these concentrations (r = 0.926, P less than 0.01). In expt 2 (constant-mass paradigm), identical masses administered in different dose-duration regimens had different steroidogenic efficacies (P less than 0.02): low-dose long-duration regimens provoked greater total release than high-dose short-duration regimens. Overall, every dose-duration regimen was associated with stimulation of B secretion. These results indicate that very brief exposure to physiological concentrations of ACTH-(1-24) is a significant stimulus for corticosteroid secretion; variations in the dose-duration regimen over the physiological range modifies both the maximum rate of secretion and the duration of secretion, but not the response latency; and ACTH-(1-24) presentation mass is not the sole determinant of B secretion.

Adrenal Cortex↗
PubMed1986

Dynamics of thyrotropin-releasing hormone-induced thyrotropin and prolactin secretion by acutely dispersed rat adenohypophyseal cells. Evidence for 'all-or-none' secretion by heterogeneous secretory units, each with a specific response threshold.

We have examined the dynamics of thyrotropin-releasing hormone (TRH)-stimulated secretion of prolactin (PRL) and thyrotropin-stimulating hormone (TSH) using enzymatically dispersed rat adenohypophyseal cells suspended in a perfusion chamber with a volume of 0.2 ml to minimize mixing and dilution. One-min exposure to 3-300 nM TRH, the effective dose range, elicited immediate pulses of PRL and TSH secretion with dose-dependent amplitudes. At all TRH concentrations, following a brief burst of secretion lasting less than 1 min, release of both hormones declined precipitously. Increasing the duration of stimulation up to 30 min with half-maximal TRH concentrations did not alter the dynamics of the initial response and was ineffective in maintaining the initial amplitude of secretion. This phenomenon could not be attributed to exhaustion of readily releasable intracellular PRL and TSH, since an increment in TRH concentration elicited a second pulse of hormone secretion with temporal response characteristics identical to the first. The amplitude of the second pulse was dependent on both the initial concentration of TRH and the magnitude of the increment in TRH concentration. With a stepwise increase in TRH concentration during continuous perfusion, the sum of PRL or TSH secreted from all bursts of secretory activity approximated that achieved with a single exposure to the highest concentration of TRH employed. The high-amplitude secretory response to a given concentration of TRH was restored after an 8-min perfusion with medium alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Genetic differences in anticonvulsant sensitivity in mouse lines selectively bred for ethanol withdrawal severity.

WSP (withdrawal seizure-prone) mice exhibit approximately 10-fold more severe withdrawal convulsions than WSR (withdrawal seizure-resistant) mice after identical chronic ethanol exposure. Although WSP and WSR mice do not differ in threshold for seizures elicited by electroconvulsive shock (ECS), WSR mice are more sensitive to ethanol-induced elevation of ECS seizure thresholds. The current experiments demonstrated that WSR mice showed more ECS-induced seizure threshold elevation than WSP mice when tested after the administration of C1-C5 straight-chain alcohols. Whereas the brain concentrations of the C1 and C2 alcohols did not differ between the lines, WSP mice tended to have higher brain concentrations than WSR mice of the C3-C5 alcohols, even though they exhibited the smaller behavioral response in all cases. Thus, the difference between WSP and WSR mice was one of neurosensitivity and could not be attributed to pharmacokinetic differences. The WSR line was also more sensitive to ethchlorvynol, methyprylon, barbital, phenobarbital, pentobarbital, diazepam, valproic acid and phenytoin in this test. Examining loss of righting reflex (RR), we found that WSP and WSR mice did not differ in ED50, latency to lose RR or duration of loss of RR. Thus, the genetic anticonvulsant sensitivity difference is not simply a genetic difference in sensitivity to central nervous system depression between the lines. In summary, WSR mice were more sensitive to the anticonvulsant effects of a variety of compounds than WSP mice, suggesting that some genes influence both ethanol withdrawal seizures and ethanol's anticonvulsant effects.

Alcohol Withdrawal Delirium↗