A role for bursa fabricii and bursin in the ontogeny of the pineal biosynthetic activity in the chicken.

The tripeptide bursin (Lys-His-Gly-NH2) is a B cell differentiation hormone derived from the bursa fabricii. The latter is a cloacal diverticulum and the site of B lymphocyte differentiation and selection in aves; also the bursa fabricii is involved in endocrine functions. Herein we demonstrate that in the chicken, the bursa fabricii and bursin are crucial to the ontogeny of both the pineal response to antigenic challenge and pineal circadian synthetic activity. In early embryonically bursectomized chickens, the plasma melatonin response to immunization by porcine thyroglobulin (Tg) was abolished. Also, the amplitudes of both plasma melatonin and pineal N-acetyltransferase (NAT) circadian rhythms were reduced by 50%, whereas the activity of hydroxyindole-O-methyltransferase (HIOMT) remained unchanged. Conversely, administration of either minute amounts (100 pg, 100 fg) or highly dilute (5 x 10(-27) g) bursin, with the exception of a highest dose (100 micrograms), to bursaless embryos induced recovery of normal antigen-induced melatonin response and normal amplitudes of melatonin and NAT rhythms. These findings establish that early in embryonic life, the bursa fabricii and its derived signal (bursin) are essential for normal development of pineal synthetic activity and underline the efficacy of very dilute bursin as an informative signal.

Bursine diluee: validation des hautes dilutions / Diluted bursin: validation of the high dilutions

L'article est une etape important vers la reconnaissance et la generalisation du concept d'immunomodulation a tres faibles doses developpe par le professeur M. Bastide il y a maintenant plus de 15 ans. La thymuline... (AU)

Effects of early embryonic bursectomy and opotherapic substitution on the functional development of the adrenocorticotropic axis.

Functional development of the adrenocorticotropic axis was inferred from plasma ACTH and corticosterone levels in intact and embryonically bursectomized (BFX) embryos and chicks from 8 days before to 56 days after hatch. Bursectomy was surgically made at 80 h of incubation and resulted in various alterations in developing adrenocorticotropic axis: ether stress-induced hormonal stimulation could be detected more precociously in BFX (day-6) than in intact embryos; the non stress-responsive period of newly hatched controls did not appear in BFX chicks; BFX young adult chicken exhibited quite smaller responses to stress than controls. In ovo injection of bursin (Lys-His-Gly-NH2) to 6- and 9-days old BFX embryos could restore normal adrenocorticotropic development provided convenient doses of tripeptide were used: administration of 100 fg or 100 pg of bursin was effective to restore normal hormonal levels at all stages studied whereas 100 micrograms was effective at embryonic stages only. The tripeptide Lys-His-Gly-NH2 is suggested as a possible signal from the immune B system directed at the hypothalamo-hypophysial-adrenocortical axis.

Adaptation of the adrenocorticotropic response to chronic intermittent stress was altered by intracerebroventricular infusion of hemicholinium-3.

The role of diencephalic cholinergic neurotransmission in regulating hypothalamic-pituitary-adrenocortical (HPA) axis was investigated by means of administration of hemicholinium-3 (HC-3), a blocker of acetylcholine synthesis, in the third ventricle of hemispherectomized pigeons. Except for an early increase in ACTH and corticosterone levels following injection as a bolus of HC-3 that was ascribed to some stress-like situation, all data indicated that hypothalamic acetylcholine depletion resulted in inhibiting effects on the HPA axis. Twenty-four hours after injection of 6 micrograms of HC-3, the response to acute stress was markedly reduced in both magnitude and duration. Permanent instillation of HC-3 in the third ventricle at the rate of 0.25 microgram/h for 9 days led to lowered basal resting HPA activity and severely affected the development of adaptation to chronic intermittent stress. The anticipatory conditioned, endocrine response did not appear whereas attenuation of the poststress component was amplified. It is suggested that cholinergic mechanisms are involved in modulating the HPA function and particularly the conditioning process that takes place in the course of adaptation of the HPA response to chronic intermittent application of the same stressor.

[Effects of systemic administration of muscimol (gamma-aminobutyric acid agonist) on the corticotropic adenohypophysis]. / Effets de l'administration systémique de muscimol (agoniste de l'acide gamma-aminobutyrique) sur l'adénohypophyse corticotrope.

A short and moderate increase in plasma ACTH and corticosterone levels was observed after i.v. injection of the GABA-agonist, muscimol as a bolus of 0.5 mg . kg-1. Doses lower than 0.3 mg . kg-1 were ineffective. 6 hrs. after i.v. injection of 1 ml of an undiluted immune serum raised against oCRF41, resting hormone levels were markedly diminished, stress-induced responses were almost completely suppressed, whereas i.v. injection of muscimol still resulted in an unaltered adrenocorticotropic stimulation. Adenohypophysectomized animals displayed a low basal adrenal function, no stress-induced response and interestingly enough no longer responded to i.v. muscimol injection. Consequently, acute GABA-ergic stimulation appears to act directly onto the pituitary corticotroph cells. It cannot be inferred so far whether this action is of physiological importance but it can at least contribute to elucidate some controversial data prevailing in this field.

[Comparison of plasma ACTH and corticosterone levels after embryo bursectomy]. / Comparaison des taux plasmatiques d'ACTH et de corticostérone après bursectomie embryonnaire.

Plasma levels of both adrenocorticotropic hormone (ACTH) and corticosterone (B) were determined in embryos (day 15 of incubation), chicks (day 3 after hatch) and young chickens (8 weeks). Experimental animals were bursectomized at 80 hr of incubation, i.e., before any anlage of the bursa of Fabricius could develop. Bursectomized (BFX) animals were compared to sham-operated controls (T), in basal, resting condition and 7 (ACTH) or 14 min (B) after ether stress was delivered for 30 sec. Basal B and ACTH levels seemed not to be significantly modified in BFX embryos, chicks and chickens. Hypophysial and adrenocortical response to stress appeared more precociously in BFX embryos (day 15 of incubation) than in intact ones (day 19). The non stress-responsive period that was observed for one week after hatch of T birds did not appear in 3-day-old BFX chicks whose both B and ACTH stress-induced levels were as high as in intact adults. In contrast, adrenocortical and pituitary corticotropic responses to stress were markedly impaired (by 50%) in adult BFX chickens as compared to intact controls.

[Effect of ACTH injection and graft of bursa of Fabricius on the adrenocortical activity of bursectomized chicks at 80 hours of incubation]. / Effets de l'injection d'ACTH et de la greffe de bourse de Fabricius sur l'activité corticosurrénalienne des poussins et poulets bursectomisés à 80 heures d'incubation.

Early embryonic bursectomy (BFX) disturbed the adrenocortical functioning. The stress-unresponsive period that occurred in controls, and lasted for 2-3 weeks after hatching, no longer appeared in BFX chicks. In contrast, the magnitude of the stress-induced hypercorticosteronemia was much lower in BFX than in sham-operated 5 week-old chicken. It was assumed that such adrenocortical dysfunction was due to bursal deprivation, since grafting bursal buds onto the chorio-allantoic membrane of BFX embryos restored all the parameters under study, i.e., the post-hatching stress unresponsive period and the high magnitude of stress-induced responses in adults. Factor(s) involved in such interregulation are not known but do not seem to affect directly adrenocortical cells because intramuscular injection of a moderate dose of ACTH resulted in the same hypercorticosteronemia whether 3 day-old and 5 week-old chicks had been bursectomized or sham-operated.

Effect of GABAergic treatment on resting and stress-induced adrenocortical activities in the thalamic pigeon.

Muscimol was injected (0.5 mg kg-1) intravenously to either intact or thalamic-lesioned animals through a chronic catheter. Plasma samples were obtained at 7-min intervals and exhibited a moderate and transient increase in corticosterone levels in both groups, together with some symptoms of light discomfort (e.g., ptiloerection or panting). All these signs disappeared within 45 to 60 min. Intraventricular injection of bicuculline (3.5 micrograms) provoked a corticosterone profile quite similar to a stress-induced polyphasic pattern. Acute stress (electrical footshocks for 30 sec) was applied 2 hr after drug treatment. In controls, the stress-induced adrenocortical response appeared to be markedly modified after muscimol injection. The usual polyphasic rebounding profile was replaced by a monophasic one. This effect of muscimol did not occur when bicuculline had been injected in the 3rd ventricle. Bicuculline alone did not alter the stress-induced profile. GABAergic treatment had no effect on the monophasic response of thalamic-lesioned birds.

[Development of blood testosterone in the embryo and young chick after precocious bursectomy]. / Evolution de la testostéronémie chez l'embryon et le jeune Poulet après bursectomie précoce.

The effect of bursa of Fabricius on the endocrine function of the chick testes was studied in vivo by comparing plasma testosterone levels from 48 h before hatch to 16 weeks of age in both intact and bursectomized chicken. Early bursectomy was performed at 80 h of incubation. Post surgery survival was low (12% at 1 week). In controls, plasma testosterone levels were found to be low (100-200 pg. ml-1) from 48 h before to 48 h after hatch, then to raise up to a plateau (2,200 pg. ml-1) at 6 weeks. After bursectomy, values were first higher than in intact (210-440 pg. ml-1 from 48 h before/after hatch and 515 vs 300 pg.ml-1 at 3 days) but no difference could be further detected from 1 to 16 weeks of age. It is suggested that, in addition to the effect of androgen on bursa of Fabricius, the later reciprocally influences the gonadotropic axis during the early stage of development.

[Persistence of the acquisition of an endocrine response to conditioned stress in the thalamic pigeon by chronic GABAergic treatment]. / Persistance de l'acquisition d'une réponse endocrine au stress conditionnée chez le pigeon thalamique sous traitement GABAergique chronique.

The thalamic pigeon was taken as a model to investigate mechanisms of adaptation to chronic intermittent stress. Muscimol was infused into the 3rd ventricle at the rate of 0.25 microgram.hr-1 by means of an osmotic minipump. In controls, pumps were filled in with saline. Animals were placed under constant light regimen and electrical foot shocks were delivered, thrice a day, at fixed time interval following a short dark period (3 min). In controls, adaptation of the adrenocortical response to chronic intermittent stress was achieved within 7 days, including both attenuation of the post-stress hypercorticosteronemia and occurrence of a pre-stress conditioned peak of corticosterone. The anticipating conditioned constituent subsisted in muscimol treated animals whereas no attenuation of the post-stress peak could be detected. GABAergic chronic treatment also resulted in decreased basal plasma corticosterone levels. In controls, extinction of the conditioned endocrine response was not obtained after conditioning stimulus (dark period) was presented alone for 2 weeks.

Effects of chronic intracerebroventricular GABAergic treatment on basal and chronic or acute stress-induced adrenocortical activities in the thalamic pigeon.

Muscimol was chronically administrated to the third ventricle of thalamic pigeons by means of osmotic minipumps at the rate of 0.25 microgram X h-1 for 28 days. No abnormal behavioural sign was noted. The animals were subjected daily to chronic intermittent stress for the same 28-day period. Basal and stress-induced adrenocortical activities were evaluated by recording serial plasma corticosterone levels at the end of the experimental session. Untreated controls exhibited both components of the adaptation of the adrenocortical response to chronic stress: attenuation, i.e., a decrease in magnitude and disappearance of the late rebounding phenomenon, and anticipation, i.e., the occurrence of a conditioned component before stress itself. The adaptation to chronic stress was partly impaired by GABAergic treatment. The anticipatory conditioned peak subsisted but the magnitude of the post-stress peak was found not to be reduced whereas rebounding events were suppressed after chronic as well as acute stress. The basal resting levels of corticosterone were significantly lowered in muscimol-treated animals. A lesion placement in the anterior dorsomedial thalamus (ADMT) resulted in the same profile of stress-induced plasma corticosterone levels as seen after muscimol administration. Adaptation did not develop in ADMT animals and GABAergic stimulation, either acute or chronic, had no effect on their response to stress.

Seasonal changes in plasma testosterone, thyroxine, and cortisol levels in wild rabbits (Oryctolagus cuniculus algirus) of Zembra island.

Annual variations in testosterone, thyroxine, and cortisol concentrations were recorded in plasma samples obtained monthly from male wild rabbits living in their natural biotope. For comparison, a group of animals was held in semicaptivity close to Tunis. Zembra is an uninhabited, hardly accessible island, north of the bay of Tunis and is a part of a large, protected zone of natural reserve. Warrens of Zembra appear to subsist from a very remote past, without any contact with other strains. In both natural and captive environments, testosterone levels peak sharply in October, decline in November-December, and are low from January to September. Thyroxine titers also peak in October but a second peak occurs in spring, the magnitude of which is markedly higher in natural than in captive conditions. As to cortisol, netting in Zembra results in stress-induced high values but semicaptive specimens exhibit a clear-cut annual rhythm peaking in January.

[Effect of muscimol (GABA-agonist) on thalamo-hypothalamic regulation by corticotropic efferents (thalamic model)]. / Influence du muscimol (GABA-agoniste) sur une boucle de régulation thalamo-hypothalamique à efférence corticotrope (modèle thalamique).

It can be assumed from previous data that the stress-induced polyphasic adrenocortical response involves two phenomenons. First, direct hypothalamic afferents stimulate the adrenocorticotropic axis resulting in a rapid increase in plasma corticosterone levels up to a maximum of about 40 ng . ml-1 at 15 min. Then, a thalamic-hypothalamic loop generates the late rebounding components. Intravenous injection of muscimol (0.5 ml . kg-1) produces only slight and short duration (45 min) disturbances (piloerection; panting; corticosteronemia). Stress application, 1 hr after muscimol administration, elicits only the first peak of corticosterone with magnitude and delay similar to that in control. However, the late rebounding component is no more visible. Thus, GABA-ergic stimulation leads to a situation similar to that seen after section of neural connections between thalamic nuclei and infundibular complex. The hypothalamic-adrenocorticotropic reactivity itself is not affected whereas the function of the regulating thalamo-hypothalamic loop is markedly impaired.

Effect of short exposure to cold on plasma thyroxine in Coturnix quail: role of the infundibular complex and its neural afferents.

Exposure of control quail to low ambient temperature (4 degrees) for a short duration (15 min) led to a rapid increase in plasma thyroxine (T4) levels. A peak appeared 40 min after the cold began and was followed by a progressive and slow decline. T4 levels were elevated in birds maintained for up to 3 hr at 4 degrees. Restraint stress could be accompanied by a slight and late decrease in thyroxine concentration, indicating that glucocorticoids could partly inhibit thyroid function. Both cold and restraint stresses elicited sustained adrenocortical activation. No thyroid response to cold appeared after complete or partial neural deafferentation of the hypothalamus, indicating that cold signals were conveyed to the thyrotropic centers from peripheral and/or deep thermoreceptors through neural posterior-lateral afferents to the hypothalamus. No thalamic relay appeared to be necessary since normal thyroidal stimulation was observed after thalamic-hypothalamic disconnection. Such a response persisted in hemispherectomized quail.

Adaptation of the adrenocortical response during repeated stress in thalamic pigeons.

Chronic vascular catheterization allowed to obtain serial blood samples before and after stress application to thalamic pigeons. Daily repetition of the same stress, at the same hour, for 5 weeks led to drastic changes in the stress-induced adrenocortical reaction. The rebounding, long-lasting rise in plasma corticosterone occurring after initial presentation of electrical footshocks was replaced by a single peak of corticosterone, lower and shorter than the initial response. Moreover, an anticipatory conditioned rise in corticosterone appeared before stress. Random distribution of stressful stimuli, thrice a day, for 5 weeks resulted in the single peak pattern of post-stress adrenocortical reaction, without any anticipatory component. When electrical footshocks were omitted after 5 weeks of daily regular presentation of stress, only the anticipatory peak in plasma corticosterone occurred. Shifting the daily lighting from the usual 06.00 a.m. to 04.00 a.m. led to a shift in the anticipatory conditioned endocrine response which appeared 2 h sooner than usual. Thalamic involvement in the process of adaptation to chronic stress is discussed.

Adrenocortical adaptation to chronic intermittent stress in hemispherectomized pigeon.

Hemispherectomized pigeons were exposed daily to electrical footshocks delivered for 15 sec, at the same hour, for 8 weeks. Serial blood samples were obtained through a chronic vascular catheter. The adrenocortical response to chronic intermittent stress was measured kinetically at one week intervals. The initial response including several successive peaks of plasma corticosterone progressively adapted: Late peaks disappeared and only the first one subsisted 12-14 min after stressor application; this first peak diminished in magnitude; furthermore, an anticipatory peak occurred, starting 14 min before stress. In pigeons lesioned in the anterior dorsomedial thalamus, the only response to the stressor was of the single peak (12-14 min) type without any development of anticipatory conditioned response. This phenomenon was consistant all over the experimental period. Thalamic-hypothalamic interrelationships may be suggested to provide neuronal loops that underlie the long lasting, pulsatile repetitive components of the adrenocortical response to acute stress and also the adaptative process of such a response to chronic intermittent stress, including a conditioned, anticipatory endocrine activation.

[Seasonal cycles of plasma testosterone and cortisol in the wild rabbit (Oryctolagus cuniculus algirus Loche) of Zembra Island, studied in its natural biotope and in captivity]. / Cycles saisonniers de la testostérone et du cortisol plasmatiques chez le Lapin sauvage de l'île de Zembra (Oryctolagus cuniculus algirus Loche), étudié dans son biotope naturel et en captivité.

Annual variations in plasma testosterone and cortisol levels were determined in male wild rabbits caught monthly in their natural biotope (Zembra island). For comparison, a group of warrens was hold in semi-captivity close to Tunis. In both conditions plasma testosterone concentrations were low from January to September and peak values were observed in October. Captive warrens exhibited a clear cut annual rhythm in plasma cortisol levels also and ether stress resulted in a very large increase of cortisolemia. In rabbits caught in ther habitat however, cortisol concentrations were always extremely high throughout the year, probably due to stressing conditions. Interestingly, wild rabbits of Zembra island appear to subsist from a very remote past without any contact with other strains. As to Zembra, it is a hardly get-at-able, uninhabited island which is a part of a strictly protected natural reserve and constitutes a fairly useful and valuable ecosystem.

Gonadotropic and photosensitive abilities of the lobus paraolfactorius: electrophysiological study in quail.

Spontaneous and flash-altered multiunit activity MUA was recorded from the lobus paraolfactorius of young male quail reared in either long or short daily photoperiods. The birds were subjected to testosterone administration, castration, optic nerve section or retroparaolfactory disconnection and compared to intact controls. In all experimental and intact quail, iterative flashes led to decreased paraolfactory MUA. Spontaneous firing rates were found to be significantly higher during the light than during the dark part of the photoperiods, indicating some direct effect of environmental lighting on the paraolfactory neuronal populations. However, blinded as well as paraolfactory disconnected animals failed to exhibit any difference in firing rates according to the daily short and long photoperiods as seen in controls, suggesting that the light regime might also indirectly influence the paraolfactory activity.