Control of the pars intermedia of the lizard,Anolis carolinensis

Summary The capacity of colour change in intact lizards and in animals with a transected hypophysial stalk was studied during extended periods. It was concluded that, with certain exceptions, the skin colour of the lizards gives information on the circulating levels of MSH, and thereby on the function of the pars intermedia.After transection of the hypophysial stalk, three phases of chromatic behaviour were recognised. During Phase I, which lasted for about 6 days (average), dark skin was retained irrespective of the colour of the background (= high MSH levels), whereas Phase II (19 days) was characterised by the inability of the animals to become brown (= low MSH levels). A gradual recovery toward normal adaptive capacity was seen during Phase III.In the disconnected neuro-intermediate lobe, aldehyde fuchsin (AF)-positive material in the rostral region rapidly clumped and disappeared within a few days. In the caudal portion, the stainability and the varicose arrangement of fibres were retained longer, but disappeared within approximately 14 days after the operation. Proximal to the lesion, the preoptic system exhibited a marked increase in stainability with AF, starting in the median eminence and progressing in a retrograde direction toward the peptidergic nuclei.Revascularisation of the disconnected neuro-intermediate lobe occurred during the first few days. A reinnervation of AF-fibres across the transected area into the neural lobe was observed during Phase III in most animals, but AF-fibres did not reoccupy the entire lobe. In association with an outgrowth of capillaries, the regenerating fibres formed new neural lobules. This regenerative process was accompanied by an increase in blood supply from the primary plexus of the median eminence to the neuro-intermediate lobe.Supported by grants from the Swedish Natural Science Research Council and the Royal Physiographic Society of LundThe authors are indebted to Mrs. Ingrid Hallberg and Mrs. Kirsten Thörneby for valuable technical assistance and skillful attention to the animals and to Miss Inger Norling for photographic aid