J.D. Baylé

Experimental Studies on the Adrenocorticotropic Area in the Pigeon Hypothalamus

Hypothalamic control of basaland stress-induced adrenal cortical activity in the pigeon was investigated by means of hypothalamic lesions combined with adenohypophysectomy or pituitary autograft. A well-defined adrenocorticotropic area is pre-sent in the posterior medial and lateral hypothalamic region. Destruction of the area leads to the same decrease of the plasma corticosterone level as is seen after adenohypophysectomy and also prevents the progressive recovery of adrenocortical function after autografting. The adrenal cortical response to various stressful stimuli is suppressed after lesioning of this same area. It is not known whether the residual adrenocortical activity in adenohypophysectomized birds can be explained by functional autonomy of the gland or by an extrahypophysial control, although the present results do not favor the latter hypothesis. Corticotropic activity appears to be unable to function in the absence of hypothalamic maintenance and the hypothesis of a functional autonomy of the corticotropic pituitary is invalidated.

Multiple-Unit Activity in the Pineal Gland of the Japanese Quail: Spontaneous Firing and Responses to Photic Stimulations

The present study was devoted to the recording ofspontaneous multiple-unit discharges in the pineal gland of the quail to investigate the influence of light stimulation on the multiunit pineal activit

Effects of Limbic Stimulations or Lesions on Basal and Stress-Induced Hypothalamic-Pituitary-Adrenocortical Activity in the Pigeon

Limbic modulatory influences on hypothalamic adrenocorticotropic activity were investigated by means of electrical stimulation through chronically implanted deep electrodes in the conscious unrestrain

Photically evoked potentials in the gonadotropic areas of the quail hypothalamus

Abstract Gonadotropic areas were located in the quail hypothalamus by means of stereotaxic coordinates. Destruction of two regions (posterior tuber and dorsal hypothalamus) inhibited the photosexual reflex. Flash-evoked potentials were recorded in unanesthetized, unrestrained quails through chronically implanted bipolar electrodes. Characteristics of hypothalamic responses to light flashes were homogeneous throughout tuberal and dorsal gonadotropic areas, their latency being markedly longer (14 msec) than in the optic chiasma (7 msec) and shorter than in the other hypothalamic regions explored (20 msec). Changing the lighting pattern from a short to a long daily photoperiod led to classical testicular growth, whereas the latency of photically evoked responses from the gonadotropic areas became shorter (12 msec). Testosterone treatment resulted in the same decrease in latency of these evoked potentials. Bilateral section of optic nerves suppressed all hypothalamic responses to light flashes but unilateral (homo- or contralateral) optic severance affected them differently. The results are discussed in terms of mechanisms of gonadal stimulation and of nervous structures and pathways through which light elicits a gonadotropic activation.

Hypothalamic-Hypophysial Control of Adrenal Cortical Function in Birds

The hypothalamic-hypophysial control of basal adrenal cortical function was investigated in three avian species, by means of adenohypophysectomy (HE) and pituitary autografting (AG). HE led to a marke

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.

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.

Light and electron microscopic evidence of hypothalamic afferences originating from the hippocampus in the pigeon.

Degenerating nervous fibres and synaptic boutons were demonstrated in the nuclei posterior medialis hypothalami after hippocampal lesions in the pigeon (light and electron microscopy).

Thalamic-Hypothalamic Interrelationships and Stress-Induced Rebounding Adrenocortical Response in the Pigeon

Plasma corticosterone levels were determined by protein-binding assay at 2- and 5-min intervals after systemic or neurogenic stress. The same corticosterone (B) profile was observed after hemispherectomy as in intact pigeons, exhibiting episodic increase including several successive peaks after stress application. Hypothalamic stimulation of ACTH injection resulted in a simpler adrenocortical response, analogous to the first peak of the response to stress. Postero-lateral deafferentation of the hypothalamus unabled neurogenic stress to promote any plasma B increase and significantly altered the response to systemic stress since only the first peak of B occurred. Such a single peak response to both systemic and neurogenic stresses was observed after surgical interruption of neural connections between hypothalamic and thalamic structures without interferring with posterior afferents to the basal hypothalamus. The role of thalamic-hypothalamic interrelationships in modulating the stress-induced adrenocorticotropic activity is discussed.

Preoptic multiunit activity correlates of the photosexual reflex in quail

Abstract Multiunit activity (MUA) was recorded from the preoptic area in intact and blinded awake quail. Spontaneous preoptic MUA was markedly lower in photo-stimulated than in non-photostimulated animals. Blinding led to reduced spontaneous preoptic MUA in non-photostimulated birds but no modification was observed in photostimulated quail. Flask-light stimulations significantly altered preoptic MUA in intact but not in blinded birds. Influence of lighting on preoptic MUA and participation of the preoptic region in the initiation and/or development of photosexual reflex in birds are discussed.