Biomedical subjects

S R Engel

Publications and source records attributed to S R Engel.

9 recordsLinked to original sources

PubMed2001

Conditioned place preference for cocaine is attenuated in mice over-expressing the 5-HT(3) receptor.

The serotonin 5-HT(3) receptor is thought to play a role in the reward pathway and drug abuse by modulating dopamine release within the mesolimbic pathway. Dopamine release stimulated by cocaine and methamphetamine is blocked by administration of 5-HT(3) receptor antagonists. Animal studies demonstrate that 5-HT(3) receptor antagonists decrease cocaine and methamphetamine preference. We have developed a 5-HT(3) receptor over-expressing mouse to study the role of this receptor in substance abuse. No changes in either the dopamine receptors (D1, D2, D3, and D4) or in the dopamine transporter (DAT) were found over a wide range of brain regions. 5-HT(3) receptor over-expressing mice failed to develop conditioned place preference to 10 mg/kg or 6 mg/kg cocaine but showed a modest preference for 4 mg/kg cocaine. 5HT(3) receptor over-expressing mice were more sensitive to the locomotor activating effects of low dose cocaine and methamphetamine. Further, brain slices from the transgenic mice release more dopamine in response to low concentrations of cocaine. These data suggest that 5HT(3) receptor over-expression in the forebrain decreases cocaine preference and increases acute sensitivity with a corresponding increase in the amount of dopamine released in response to cocaine.

Animals↗

PubMed2001

Neurosteroids and behavior.

Neurosteroid production may be a mechanism to counteract the negative effects of stress and return organisms toward homeostasis. Stress induces an increase in neurosteroid production. Neurosteroids affect two of the most widely distributed neurotransmitter and receptor systems in the central nervous system (CNS): gamma-aminobutyric acid (GABA) and glutamate. This ability of this class of compounds to affect both the primary excitatory and the inhibitory systems in the CNS allows the modulation of a wide array of behaviors. For example, neurosteroids modulate anxiety, cognition, sleep, ingestion, aggression, and reinforcement. In general, neurosteroids that are positive modulators of N-methyl-D-aspartate receptors enhance cognitive performance and decrease appetite. Neurosteroids that are positive modulators of GABAA receptors decrease anxiety, increase feeding and sleeping, and exhibit a bimodal effect on aggression that may be secondary to effects on anxiety and cognition. Some data suggest that neurosteroids have reinforcing effects, which could affect their clinical utility. Drug discrimination studies are helping scientists to dissect more closely the receptor systems affected by neurosteroids at the behavioral level.

Aggression↗

PubMed2001

Characterization of discriminative stimulus effects of the neuroactive steroid pregnanolone.

Reduced pregnane neurosteroids such as allopregnanolone and pregnanolone are potent neuromodulators able to affect a number of membrane receptors, including gamma-aminobutyric acid (GABA)(A), N-methyl-D-aspartate (NMDA), 5-hydroxytryptamine (5-HT)(3), and sigma(1) receptors. The present study used a drug discrimination procedure to assess further the receptor effects of pregnanolone in vivo. Rats were trained to discriminate 5 mg/kg pregnanolone from saline in a two-lever operant task maintained by food reinforcement. The opiate agonist morphine and the negative GABA(A) modulator dehydroepiandrosterone sulfate did not substitute for pregnanolone. All of the GABA(A) positive modulators tested (allopregnanolone, epipregnanolone, androsterone, pentobarbital, midazolam, and zolpidem) dose dependently substituted for pregnanolone. The direct GABA-site agonists 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol and muscimol failed to substitute for pregnanolone. Ethanol and the sigma(1) receptor agonist SKF 10047 fully substituted for pregnanolone, and the NMDA antagonist MK-801 partially substituted for pregnanolone. The 5-HT(3) antagonist tropisetron did not substitute at any dose tested. The 5-HT(3) agonist SR 57227A reached full substitution, whereas the other 5-HT(3) agonist tested, m-chlorophenylbiguanide, produced partial substitution. These results suggest that positive GABA(A) modulation, but not direct agonism, confers a discriminative stimulus effect similar to pregnanolone. Additionally, antagonism of NMDA receptors and activation of 5-HT(3) and sigma(1) receptors modulate stimulus effects similar to the pregnanolone cue. Overall, the data suggest that pregnanolone produces discriminative stimulus effects representative of a wide-spectrum sedative hypnotic.

Animals↗

PubMed2000

5-HT(3) receptor function and potentiation by alcohols in frontal cortex neurons from transgenic mice overexpressing the receptor.

The function of 5-hydroxytryptamine (5-HT)(3) receptors was examined by whole-cell patch-clamp recording in dissociated frontal cortex neurons from 5-HT(3) receptor overexpressing transgenic, and wild-type mice. The effect of acute exposure to alcohols on the 5-HT(3) receptor-mediated ion current was also investigated. The 5-HT(3) receptors expressed on frontal cortex neurons in transgenic mice were activated by 5-HT and a selective 5-HT(3) receptor agonist, 2-methyl-5-HT. This current was blocked by zacopride, a specific 5-HT(3) receptor antagonist. Dissociated frontal cortex neurons from wild-type mice exhibited little or no 5-HT(3) receptor-mediated current. Ethanol (EtOH) and trichloroethanol (TCEt) potentiated the function of 5-HT(3) receptors overexpressed in transgenic mice. This is the first evidence that 5-HT(3) receptors exhibit sensitivity to alcohols when expressed by a central neuron.

Alcohols↗

PubMed1999

5-HT3 receptor over-expression enhances ethanol sensitivity in mice.

Ethanol sensitivity may play a role in the risk of developing alcoholism. The role of 5-HT3 receptors in sensitivity to ethanol was assessed in mice over-expressing the 5-HT3 receptor in the forebrain. Sleep time and ED50 for loss of righting reflex (LRR) were used to assess the effect of a high dose of ethanol in transgenic versus non-transgenic mice. The ED50 for ethanol-induced increase in open field activity was used to measure differences in sensitivity to low dose ethanol. The ED50 for ethanol-induced increase in activity was 41% lower in the 5-HT3 receptor over-expressing transgenic mice compared to non-transgenic mice. However, 5-HT3 receptor over-expressing mice did not differ from control mice in ethanol metabolism, ED50 for LRR, and ethanol sleep time. Over-expression of 5-HT3 receptors in mouse forebrain results in an enhanced sensitivity to the stimulating effects of a low dose of ethanol without altering ethanol sedating effects or ethanol metabolism. These data suggest that 5-HT3 receptors modulate low dose ethanol sensitivity and may explain why, in previous studies, these mice consume less ethanol.

Alcohol Drinking↗

PubMed1998

5-HT3 receptor over-expression decreases ethanol self administration in transgenic mice.

The 5-HT3 receptor is thought to play a role in the reward pathway and the phenomena of drug abuse by modulating dopamine release in the mesolimbic pathway. Studies involving this receptor have been hampered due to the low level of 5-HT3 receptors in the CNS. A 5-HT3 receptor over-expressing mouse was produced to study the role of this receptor in the rewarding properties of drugs of abuse. Over-expression was restricted to the forebrain by controlling gene expression with the Ca2+ calmodulin (CAM) kinase IIalpha promoter. No over-expression was detected in other body organs nor the cerebellum, as measured by ligand binding and Northern analysis. 5-HT3 receptor over-expressing mice drank less alcohol than non-transgenic mice in a two-bottle free choice test. Over-expression of the 5-HT3 receptor in these mice resulted in a decrease in ethanol consumption. These mice should prove useful in testing hypothesis regarding a common reward pathway for drugs of abuse and the role 5-HT3 receptors play in this pathway.

Animals↗

PubMed1998

Molecular systematics and paleobiogeography of the South American sigmodontine rodents.

The murid rodent subfamily Sigmodontinae contains 79 genera which are distributed throughout the New World. The time of arrival of the first sigmodontines in South America and the estimated divergence time(s) of the different lineages of South American sigmodontines have been controversial due to the lack of a good fossil record and the immense number of extant species. The "early-arrival hypothesis" states that the sigmodontines must have arrived in South America no later than the early Miocene, at least 20 MYA, in order to account for their vast present-day diversity, whereas the "late-arrival hypothesis" includes the sigmodontines as part of the Plio-Pleistocene Great American Interchange, which occurred approximately 3.5 MYA. The phylogenetic relationships among 33 of these genera were reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3, ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the same rate. A molecular clock was calibrated for these genes using published fossil dates, and the genetic distances were estimated from the DNA sequences in this study. The molecular clock was used to estimate the dates of the South American sigmodontine origin and the main sigmodontine radiation in order to evaluate the "early-" and "late-arrival" scenarios. We estimate the time of the sigmodontine invasion of South America as between approximately 5 and 9 MYA, supporting neither of the scenarios but suggesting two possible models in which the invading lineage was either (1) ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to the akodonts and phyllotines and accompanied by the oryzomyines. The sigmodontine invasion of South America provides an example of the advantage afforded to a lineage by the fortuitous invasion of a previously unexploited habitat, in this case an entire continent.

Animals↗

PubMed1996

Effect of in vivo administration of anesthetics on GABAA receptor function.

In research involving tissue derived from animals, the use of anesthesia before sacrifice is recommended by the American Veterinary Medical Association and is strongly encouraged by university committees on the use of animals in research. In this study, the effects of anesthesia on the modulation of the GABAA receptor complex by ethanol, a benzodiazepine, and a barbiturate were determined. In vivo administration of the anesthetic methoxyflurane and CO2 before sacrifice resulted in a decrease in Cl- flux in mouse brain microsacs. These treatments also resulted in the loss of the ability of the GABAA receptor modulatory agents flunitrazepam and ethanol to enhance the Cl- flux in this assay system.

Anesthesia↗

PubMed1991

The induction and repair of (6-4) photoproducts in Neurospora crassa.

The (6-4) photoproduct lesion found in DNA after UV irradiation is repaired by germinating Neurospora crassa conidia. Wild-type Neurospora removes 80% of the (6-4) photoproduct in approximately 20 min and maximal repair is accomplished by 30 min with approximately 89% of the original lesions removed. Mutagen-sensitive Neurospora mutants belonging to the established excision repair epistasis group, UVS-2, are not defective in the removal of cyclobutane pyrimidine dimers. Furthermore, we find these mutants capable of removing (6-4) photoproducts from their DNA at a rate similar to wild type. Comparable kinetics are also observed in key members of the other two epistasis groups.

DNA Damage↗