Effects of hypothalamic deafferentation on basal and stress-induced adrenocortical acitivity in the pigeon.

Partial and complete deafferentation of the hypothalamus of the pigeon was performed using a modified Halasz-Pupp microknife. After complete neural isolation the plasma corticosterone level stabilized at a point intermediate between the morning and evening levels found in intact pigeons. No diurnal rhythm was observed and the response to neurogenic stimulus (restraint) was suppressed. Ether stress, however, induced a rise in plasma corticosterone. Posterior deafferentation had no effect on the diurnal corticosterone rhythm but did block the rise normally found after restraint. Anterior deafferentation did not suppress the stress-induced response but provided the cuts were large enough they inhibited the diurnal corticosterone rhythm. It is suggested therefore that the neural afferents to the hypothalamus which are necessary for diurnal fluctuations in pituitary-adrenal function pass through a sector located anteriorly between 45 degrees and 60 degrees on either side of the mod-line while stress-induced adrenocortical activation is triggered through posterior connexions.

The adrenocortical response to stress from the pre-hatching period to the adult state in the pigeon: Thalamic participation.

The stress-induced adrenocortical response was kinetically evaluated for 100 min after ether vapor exposure in late embryos (30 h before hatching) and in 1, 2, 3 and 6-wk-old squabs. An-adult-pattern of corticosterone profile was seen in intact 6-wk-old pigeons, i.e. a polyphasic increase of corticosterone including successive peaks at 12-15, 35, 60 and 90 min after stress application. In 1-wk-old squabs, a small adrenocortical response to stress included only a single peak of corticosterone at 12-15 min. The early peak was found again, with the same magnitude, 2 wk after hatching but it was followed by two later and smaller peaks 35 and 60 min after stress. The adult pattern was visible in 3-wk-old stressed pigeons, although the magnitude of the response was still smaller than in adult controls. A single, high peak of corticosterone occurred 12-15 min after stress application, without any later peak, in embryos and a similar monophasic response was seen in thalamic lesioned adult birds. Therefore, it can be suggested that the polyphasic reverberating adrenocortical response to stress depends upon relationships between the adrenocorticotrophic hypothalamus and the anterior mediodorsal thalamus. Such thalamic-hypothalamic interrelations appear to mature during the early post-hatching weeks.

Hypothalamic multiunit activity correlates of the adrenocortical response to stress.

The corticotropic response to stress was studied by means of multiple unit activity (MUA) recording from the adrenocorticotropic region of the hypothalamus, and plasma corticosterone (B) determination. MUA was permanently obtained and B was measured at 2, then 5 and 10 min intervals before and after neurogenic (electrical shocks) or systemic (ether inhalation) stress was applied. Experiments were made on steady unanesthetized, unrestrained thalamic pigeons. Post-stress alterations of MUA and B were closely in parallel, exhibiting a rapid and sustained increase in firing rate and shifting by 5-10 min, in corticosteronemia. Three successive and progressively decreasing peaks of MUA and B could be observed. Basal resting values were restored by approximately 90 min. Adrenocorticotropic responses to stress appear to be modulated through neural thalamic and/or rhombencephalic mechanisms.

Retrograde transport of horseradish peroxidase from the preoptic-anterior hypothalamic region to retinal ganglion cells in quail.

Horseradish peroxidase was injected in the preoptic-anterior hypothalamic area of intact male quail and reacted with 3,3'-diaminobenzidine and hydrogen peroxide in eye sections. Cells labelled with peroxidase reaction product were found in the ganglion layer of the retina. One possible function of such retinal-hypothalamic connections might be to participate in the photosexual reflex.

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.

Basal and stress-induced adrenal cortical activities in the chronic thalamic pigeon.

The plasma corticosterone level was determined in chronic thalamic pigeons. Basal resting adrenocortical activity did not show any diurnal variation and kept a steady intermediate level. The peak and nadir in the morning and in the evening were completely suppressed. Neurogenic stress (restraint) resulted in a sharp increase in the plasma corticosterone concentration 15 min after immobilization. This response was as important in magnitude (three-fold the resting level) in thalamic pigeons as in intact birds. These results can be compared with data obtained after complete or partial deafferentation of the hypothalamus, and after hippocampal or archistriate lesions, and are discussed in terms of sleep-walking alternation in these various experimentally-prepared pigeons.

[Basal and stress-induced adrenocortical activity in young pigeons during pre- and post-hatching periods (author's transl)]. / Evaluation de l'activité hypophyso-corticosurrénalienne basale et de sa réponse au stress au cours de la période précédant et suivant l'éclosion chez le pigeon.

The functioning of the hypothalamic pituitary-adrenocortical system was tested in young pigeons before and after hatching, by radiocompetitive assay of plasma corticosterone (B) at rest and under stress. 1 degree B was expressed in ng/ml. Resting adult values (8-10) could not be observed before the birds were 6 week-old. B levels were very low 36 h before and 24 and 48 h after hatching (3-5). Then, they progressively increased. 2 degrees B concentrations soared during the 24 h immediately preceding hatching to rise to 45 ng/ml at the time of hatching. After that, corticosteronemia rapidly decreased. 3 degrees Neurogenic stress was applied by means of electrical stimulation of the led skin for 15 sec. Ten to 12 min later, B rose markedly (30 ng/ml) in 6 week-old pigeons as well as in adult ones. No response could be observed from 36 h before to 24 h after hatching. Significant adrenocortical activation was obtained in 3-7 day old squabs (18 ng/ml). 4 degrees Systemic stress (ether vapor) led to significant hypercorticosteronemia (30-40 ng) in pre-hatching embryos. No response could be observed for 24 h after hatching. Ether-induced adrenocortical activation appeared again in 2-3 day-old pigeons. 5 degrees The development of both resting and stress-altered corticosteronemia did not seem to be related to the increase in body weight of young birds. One can present the hypothesis that a strongly stressfull situation occurring during the period which immediately precedes hatching, results in a rapid activation of the adrenocortex. The period following hatching corresponds to the "non stress responsive period" of mammals and could be explained by some feedback mechanisms.

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.

[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.

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.

[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.

Multiple unit activity patterns of neuronal populations in gonadotropic areas of the quail hypothalamus: spontaneous and photically-induced firing.

Multiple-unit activity (MUA) was obtained from neuronal pools in the gonadotropic hypothalamus of quails. A special device allowed for exploration of various hypothalamic structures in unanesthetized birds. All recording sessions were made in the dark. Spontaneous and flash light-evoked MUAs were recorded from both tuberal and dorsal gonadotropic areas, either in the morning or in the afternoon, and were compared to extragonadotropic firing patterns. Firing rates (spikes/10 sec) and integrated MUA (200 addresses) provided distinctive spontaneous neuronal activities for various cell clusters. These spontaneous salient features appeared to be changeable throughout the photoperiod. Flash stimulations resulted in a marked increase in MUA recorded from the gonadotropic regions of the hypothalamus.

Adrenal cortical activation induced by hypothalamic stimulation and stress in pigeons bearing ectopic pituitary autografts.

Adrenocorticotropic abilities in basal and stress conditions, and the responsiveness of ectopically-transplanted pituitaries to hypothalamic stimulation were investigated in adult red Carneau pigeons. In birds with pituitary autografts, both electrical stimulation of the hypothalamus and restraint stress elicited a significant increase in the plasma corticosterone level, however these adrenal cortical responses were not so important as those in intact pigeons. Ether stress, which was a very effective stimulus of adrenocortical activity in controls, did not result in any plasma corticosterone elevation in pigeons that had been operated on. Such a decrease in the functional abilities of ectopic adrenocorticotropic cells was interpreted as the result of an impaired hypothalamic control acting via the systemic bloodstream. This hypothesis was corroborated by a moderate reduction in diurnal variations of the plasma corticosterone level in birds with autografts with respect to intact pigeons. Adenohypophysectomized controls did not show any adrenocortical response either to hypothalamic stimulation or to stress application.

[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.

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.