NATURE OF THE NERVOUS CONTROL OF PARS INTERMEDIA FUNCTION IN AMPHIBIANS: RATE OF FUNCTIONAL RECOVERY AFTER DENERVATION

Water-balance response to salt loads in the toad Bufo bufo: independence of hypophysial pars nervosa function

1. In water, injection of 1 ml of 1 mol/l NaCl/100 g body mass increased the rates of cutaneous water uptake and reduced the rates of bladder urine accumulation both in unoperated and sham operated controls and in toads with denervated or extirpated neuro-intermediate lobe. 2. This initial antidiuretic effect of the salt load gradually changed to a diuretic effect, when the volume expansion caused by cutaneous water uptake overrode the effect of increased osmolarity. 3. In a saturated atmosphere, injections of 0.3 or 0.5 ml of 0.7 mol/l NaCl/toad (mean body mass 33 g) reduced urine accumulation. Only to the largest load was the antidiuretic response significantly smaller in the toads with denervated or extirpated neuro-intermediate lobe. 4. It is argued that the reduced antidiuretic response was due to interference with pars distalis function rather than caused by lack of pars nervosa function.

Vision and the skin camouflage reactions of Ambystoma larvae: the effects of eye transplants and brain lesions

Salamander larvae typically adapt their dermal melanophores to achieve camouflage, and it has been known for some time that removal of the eyes abolishes the response. Here we survey the contribution of the optic system to the bright and dark camouflage reactions and report that: the stimulus depends on an interaction between the direct and reflected light; an eye mounted atop the head and oriented vertically tended not to support camouflage, even though the animal responded to visual cues and learned a vision-dependent task; deviating the transplanted eye off the vertical axis enhanced the recovery of camouflage reactions; amputating or reorienting the telencephalon, epithalamus, pretectum or tectum did not abolish either camouflage reaction whereas lesions of the ventral optic pathway blocked brightening; transection near the midbrain-hindbrain junction--well posterior to known optic terminals--retarded the dark reaction; when the latter lesion was combined with disconnection of the telencephalon and epithalamus, contrary to predictions from the lesions executed separately, the animals lost the bright reaction; the hypophysis is necessary for darkening, but the organ supported this reaction even though detached, displaced or reoriented; and the pineal body was not essential for the grosser aspects of camouflage in Ambystoma larvae but may play an adjunctive role in fine tuning.

Seasonal changes in luteinizing hormone-releasing hormone concentrations in microdissected brain regions of male rough-skinned newts (Taricha granulosa)

Luteinizing hormone-releasing hormone (LHRH) concentrations were measured in specific brain areas of male rough-skinned newts collected from a single population throughout the reproductive cycle. Plasma androgen and corticosterone (B) concentrations were also measured. Androgen concentrations were highest during the breeding season (winter) and lowest during the summer. In contrast, plasma B was lowest during the breeding season and highest in the summer. Concentrations of LHRH in the infundibulum (I) and rostral hypothalamus (RH) were positively correlated throughout the reproductive cycle; LHRH was always higher in the I than in the RH. Concentrations of LHRH in the ventral preoptic area (POA) fluctuated independently of concentrations of LHRH in the I and RH. However, LHRH concentrations decreased to undetectable levels in all three brain areas in March and April, which was before the end of the breeding season and before plasma androgen concentrations had decreased. An injection of LHRH into postbreeding males resulted in a significant increase in plasma androgen concentrations, indicating that the pituitary-gonad axis was still functional at the end of the breeding season. These results support the hypothesis that an abrupt decline in LHRH secretion is the initial endocrine event that signals the end of the breeding season in this amphibian.

Changes in formaldehyde-induced fluorescence of the hypothalamus and pars intermedia in the frog, Rana temporaria, following background adaptation

Adaptation of the frog, Rana temporaria, to a white background for 12 hr has resulted in an intense formaldehyde-induced fluorescence (FIF) in the neurons of the preoptic recess organ (PRO), paraventricular organ (PVO), nucleus infundibularis dorsalis (NID) and their basal processes permitting visualization of the PRO- and PVO-hypophysial tracts that extend into the median eminence (ME) and pars intermedia (PI); the FIF is reduced in all the structures by 3 days. In frogs adapted to a black background, for 12 hr and 3 days, there was a general reduction in the FIF of the PRO neurons and PRO-hypophysial tract. By 12 hr black background adaptation, the PVO/NID neurons and only their adjacent basal processes show FIF which was sharply reduced by 3 days, making the PVO-hypophysial tract undetectable. In the PI fibers the fluorescence was more intense in black-adapted frogs than in white-adapted ones at both the intervals studied. The simultaneous changes in the FIF of the hypothalamic nuclei, tracts and PI suggest that the PRO and PVO/NID neurons participate in PI control through release of neurotransmitter(s) at the axonal ends.

Light and electron microscopic studies on the pars intermedia of the chameleon

The neurointermediate lobe of the hypophysis in the Chameleon (Chamaeleo dilepis) was examined with light and electron microscopic methods, with special reference to the cytology of the pars intermedia (PI). The PI is the largest lobe of the hypophysis consisting of (1) dark cells with secretory granules ranging from 200-600 nm; (2) light cells, far fewer in number, containing granules 150-300 nm in diameter; (3) stellate, non-secretory cells. The secretory cells abut onto the perivascular basal lamina of the capillary sinusoids while their apical part borders an intercellular space. This surface of the cells often bears a cilium. The granules arise from the Golgi cisternae while small detached vesicles are found between circumscribed sites of the cell membrane and the Golgi apparatus. No nervous elements were found in the pars intermedia and it is assumed that the regulation of this lobe is purely humoral. This is supported by the presence of three types of nerve terminals in the pars nervosa: (a) terminals with large secretory granules and small vesicles; (b) terminals with dense-core vesicles and small vesicles; (c) terminals with small vesicles only. All of these are secretory as indicated by the presence of the synaptic semidesmosomes formed with the perivascular basal lamina.