Actions of Acidic Amino Acids on the Excitability of Medial Hypothalamic Neurons in the Rat
Notice bibliographique
Résumé
Systemic administration of acidic amino acids produces selective neurotoxic effects on neurons in the arcuate nucleus. However, little is known on the comparative or topographical actions of various acidic amino acids within the hypothalamus. In the present study, microiontophoretic methods were utilized to compare the sensitivity of arcuate nucleus neurons with other medial hypothalamic neurons during applications of glutamate, aspartate, homocysteate, and two conformationally restricted glutamate analogs, kainate and ibotenate. An increase in excitability to all test substances was observed from the majority of 62 neurons identified both as to location (arcuate, ventromedial and dorsomedial nuclei, and periventricular area) and to response to electrical stimulation in the median eminence, amygdala, and posterior pituitary. There was little difference in the sensitivity of neurons to glutamate, aspartate, or homocysteate. In contrast, kainate produced a more prominent and long-lasting excitation at lower application currents, frequently leading to spike inactivation and excessive depolarization followed by a prolonged recovery period. Ibotenate was also a potent excitatory agent, but its actions were biphasic, with an initial excitation followed by a decrease in excitability that influenced both spontaneous and glutamate-evoked firing; the latter is considered due to conversion of ibotenate to muscimol, a GABA analog. These observations suggest a homogeneity among arcuate and other medial hypothalamic neurons in terms of their membrane receptors and sensitivity to all acidic amino acids tested. Since acidic amino acids are also viewed as possible excitatory neurotransmitters within the hypothalamus, the diethyl esters of glutamic acid (GDEE) and kainic acid (KDEE), two proposed glutamate antagonists, were applied by microiontophoresis and assessed for their ability to alter glutamate- and aspartate-evoked activations and synaptically evoked excitations. Each agent depressed both glutamate- and aspartate-evoked activity nonselectively; thus, while they do affect acidic amino acid actions, they appear to be of limited use in differentiating between glutamate- and aspartate-activated receptors on medial hypothalamic neurons. Neither GDEE nor KDEE altered synaptically evoked excitations from the median eminence, amygdala, or posterior pituitary. Owing to the extensive dendritic arborization of hypothalamic neurons, it is possible that these agents attained a low potency at active synaptic sites. We suggest that further evaluations of the role of acidic amino acids as medial hypothalamic neurotransmitters include in vitro testing where it is possible to achieve a uniform application of their antagonists in known concentrations.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,003 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,002 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».