Hypocalcemia with hypoparathyroidism and renal tubular dysfunction associated with aminoglycoside therapy

Seventeen patients with malignant disease developed a complex metabolic syndrome of 2-8 weeks' duration characterized by hypocalcemia, hypomagnesemia and hypokalemia following administration of the aminoglycoside group of antibiotics. Gentamicin, Tobramycin, Amikacin, and Sisomicin were all involved. Other features noted were hypoalbuminemia, hypophosphatemia, and hypouricemia. Low immunoreactive parathyroid hormone (i-PTH) levels in the presence of hypocalcemia and absence of hyperplastic changes in the parathyroid gland examined at postmortem confirmed a diagnosis of hypoparathyroidism. Immunoreactive calcitonin levels (i-CT) were not elevated. Renal tubular wasting of potassium and magnesium was documented in six patients and excessive urinary loss of sodium, phosphate, and uric acid was noticed. Twelve patients died before recovering from the metabolic stress and five patients developed progressive renal impairment. A possible potentiating action of chemotherapeutic agents, especially Adriamycin, is suggested.

Binocular interaction and intertectal neuronal connexions: dependence upon developmental stage

The functional synaptic relationships in a system of neuronal connexions linking the two optic tecta in Xenopus laevis may change following rotation of one eye. This ability of the intertectal connexions to adjust to an altered spatial relationship between the two eyes was examined at various developmental stages. It was found that the system could respond to eye rotations as large as 180° provided that such rotations were performed before stage 58. The system did not respond even to small eye rotations if the latter were performed in adult life. For eye rotations performed during metamorphic climax (stages 60–66), alterations of intertectal connexions occurred if the rotations were 90° or less but not if the rotation were larger than 90°. The capacity of the intertectal system to modify its pattern of connexions in response to changes in the relative positions of the two eyes thus reduces with increasing age. A possible role, for this intertectal plasticity, in normal development is discussed.

Visual deprivation and intertectal neuronal connexions in Xenopus laevis

The role of visual function in ( a ) the normal development of intertectal neuronal connexions, and in ( b ) the production of the modified patterns of intertectal connexions that may develop in animals with an eye rotation, was examined. Normal animals were dark-reared from stage 58, before the first appearance of intertectal responses, until the terminal recording experiment in adult life. The general pattern of intertectal connexions was normal in these animals, but the organization was less precise than normal. It was concluded that visual function was required for the development or maintenance of the normal spatial precision of functional intertectal connexions. Animals with one eye rotated at stage 54 or stage 58 were reared sub­sequently in darkness until the terminal recording experiment. Such ani­mals reared in a normal laboratory environment would have shown a modified pattern of intertectal connexions. The dark-reared animals did not. It was concluded that visual function was necessary for the reorganiza­tion of intertectal connexions that follows larval eye rotation.

The time course of experience-dependent synaptic switching of visual connections in Xenopus laevis

Following the rotation of one larval eye in Xenopus laevis , the pattern of functional connections linking the two optic tecta may change. The time necessary for the elaboration of the new pattern of connections was studied by mapping the connections at various time intervals after the right eye had been rotated by 90°, this eye rotation being performed at stage 63. The minimal time necessary for the emergence of a new pattern of intertectal connections was of the order of 8-12 days. Visual deprivation during this period prevented the development of a new pattern of intertectal connections.

The synaptic organization of optic afferents in the amphibian tectum

Potentials in the amphibian tectum, evoked by stimulation of the optic nerve, were recorded extracellularly. Four discrete potentials, referred to as the m 1 , m 2 , u 1 and u 2 waves, occur at different latencies after stimulation. We have shown that these waves represent summed post-synaptic potentials generated by synchronous activation of four different groups of optic nerve fibres. The m 1 and m 2 waves are generated by two classes of myelinated optic nerve fibres, previously characterized as ‘dimming’ and ‘event’ fibres. The maximum amplitude of the m 2 wave occurs just below, and of the m 2 wave just above, cell layer 8 of P. Ramón. The u 1 and u 2 waves are generated by ‘edge’ and ‘convexity’ fibres, respectively. The maximum amplitude of the u 1 wave occurs near the surface of the tectum, and of the u 2 wave some 100 μm below it. Postsynaptic cell bodies for all four classes of optic fibre are located in layer 8.

Functional synaptic relations during the development of the retino-tectal projection in amphibians

Stimulation of the optic nerve elicited pronounced, monophasic potentials in the larval amphibian tectum. These potentials are identified as summed postsynaptic potentials generated by synchronous activation of optic nerve fibres. Functioning synaptic junctions are present in the rostrolateral portion of the tectum in early larval Xenopus . With development, the area on the tectum from which synaptic potentials are recorded expands caudally, until the whole tectal area can be synaptically activated just prior to metamorphic climax. These findings, taken in conjunction with other related studies, demonstrate that connexions between pre- and postsynaptic neurons in this system are not invariant but shift continuously throughout development.

The evolution of the retinotectal map during development in Xenopus

The retinotectal projection was mapped eleetrophysiologically in tadpoles of Xenopus laevis . Recording was performed with the animals immersed in saline inside a transparent hemisphere. Visual responses could be recorded from the optic tectum from about stage 43 onwards. The visual map on the tectum of the tadpole was found to differ in several respects from that in the adult. The earliest responses recorded showed very large multi-unit receptive fields and no discernible retinotopic organization. From about stage 47 the map showed the adult type of order; nasal field projected rostrally, temporal field caudally, superior field medially and inferior field laterally. However, in tadpoles up to stage 63/64 the projection was markedly distorted in that nasal field was confined to the most rostral region of the tectum and theie was an expanded representation of the temporal pole of the field. In tadpoles the entire visual projection covers only the rostral one-half to two-thirds of the tectum. These results, in conjunction with the results of previous studies on the mode of growth of the retina and tectum, indicate a progressive shift of the retinotectal projection with development which may involve changing synaptic relations between retinal fibres and tectal cells.

Binocular interaction in the formation of specific intertectal neuronal connexions

The mechanisms concerned in the formation of the ipsilateral visual projection in Xenopus have been investigated by examining the results in the adult of various surgical manoeuvres on the embryonic eye: 1. In animals with one double-nasal compound eye, the ipsilateral projection from the compound eye was normal while that from the normal eye was abnormal but internally organized. 2. In animals with one double-temporal compound eye the ipsilateral projection from both operated and normal eyes was normal. 3. In animals with one rotated eye, the ipsilateral projection from the operated eye was normal while that from the normal eye was rotated. 4. In animals reared with only one eye the ipsilateral projection was abnormal in that it was diffuse. The observations are interpreted as indicating that the formation of the retinotopically organized intertectal projection which forms part of the ipsilateral projection is dependent upon a process by which regions of the two tecta that generally receive similar spatiotemporal patterns of excitation become neurally interconnected.