El papel del sistema opiáceo endógeno en el síndrome depresivo y en el afecto de sujetos normales / The function of the endogenous opioid system in the depressive syndrome and in the affect of normal subjec

En este artículo se revisan los diferentes abordajes que se han hecho, para el estudio del sistema endógeno opiáceo (SEO), en el síndrome depresivo y en la modulación del afecto en sujetos normales, desde un punto de vista clínico. Desde el año de 1975, cuando se identificaron los primeros péptidos opioides por Hughes y Kosterlitz, se postularon diferentes hipóteis respecto a la participación del SEO en los trastornos afectivos. Se han utilizado al menos tres estrategias para dicho fin: 1) estudios postmortem de cerebros y de líquido cerebro espinal, tanto en pacientes deprimidos como en sujetos normales, 2) estudios con agonistas del receptor opiáceo (i.g. morfina), 3) estudios con antagonistas del receptor opiáceo (i.g. naxolona). Aunque la evidencia no ha demostrado una alteración del SEO si juega un papel importante en la modulación del afecto y las respuestas neuroendócrinas, tanto en el síndrome depresivo como en los sujetos normales. Existen aún puntos por esclarecer en cuanto a la fisiopatología del trastorno afectivo

Effects of undernutrition during suckling on foot-shock escape behavior and of post-traini9ng beta-endorphin administration on inhibitory avoidance task test behavior of young rats

The hypothalamic beta-endorphin system of young Wistar rats of both sexes (21-day-old) responds in a distinct way to behavioral situations when compared to adult rats (90 to 120-day-old). In the present study we investigated whether the post-training amnestic effect of beta-endorphin previously demonstrated in Wistar adult rats is also observed young (21-day-old) well-nourished and undernourished rats. rats were undernourished since birth by feeding their dams an 8% casein diet, while well-nourished off spring were fed by dams maintained on a 20% caseindiet beta-endorphin was administered after training in a step-down inhibitory avoidance task using a 0.2 or 0.8 m-A footshock. Retention was tested 24 h later. We observed that the dose of beta-endorphin (1 ug/kg, ip) previously reported to have an amnestic effect on adult rats was ineffective in weanling rats of both nutritional groups. At a higher dose (2 ug/kg, ip) and using a 0.2-mA shock, beta-endorphin impaired the retention only of well-nourished rats. Test-to training difference (in s) in step-down latency for well-nourished beta-endorphin-treated rats was 7 vs 25 s for well-nourished rats treated with saline (P<0.05). Undernourished rats were hyperreactive to this shock intensity. Footshock escape latency (in s) for undernourished rats was 3.56 vs 5.80 for well-nourished rats (P<0.05, experiment 1) and 5.01 vs 10.89 (P<0.05 in experiment 2) and showed better retenmtion than did well-nourished rats. Test-totraining step down latency (in s) for saline-treated undernourished rats was abouth 108 vs 28 saline-treated well-nourished rats (P<0.05). At 0.8-m-A, neither beta-endorphin nor undernutrition affected performance. These resultssuggest that well-nourished rats respons in a distinct way to post-training beta-enmdorphin when compared to adult rats of both sexes. The absence of amnesia in weanling undernourished rats may be related to the enhacenced sensitivity of both sexes. The absence of amnesia in weanling undernourished rats may be related to the enhanced sensitivity of these animals to a 0.2-mA footshock

Effect of third ventricular injection of beta-endorphin on the electrophysiological responses of some regions of endocrine hypothalamus.

Multiunit activity (MUA) of arcuate nucleus and cortical EEG were recorded in the regularly cycling female rats on the day of proestrous under urethane anaesthesia. The MUA was compared before and after injection of beta-endorphin in third ventricle. In some animals MUA increased after 30-40 min and persisted for 3-4 hr, in others MUA got inhibited within 5-10 min of injection of beta-Endorphin and effect lasted for 5-6 hr. There was no change in frontoparietal EEG activity. In another group of animals medial pre-optic responses (MPO) to stimulation of medial amygdala were tested before and after ventricular infusion of beta-endorphin. Most of the facilitatory MPO responses got blocked. These observations suggest the involvement of opioid receptors in the mediation of neuroendocrine control of preovulatory events through the amygdalo-preoptico-medial basal hypothalamic axis. There seems to be heterogeneity of beta-endorphin receptors in the arcuate nucleus.