Schizencephaly: case report of familial incidence.

Two half-siblings with schizencephaly are presented. They have the same mother who had a normal cerebral imaging study. Only one other kindred was found in which 2 siblings had this cerebral lesion. In the present patients, autosomal inheritance from the mother is possible, but other explanations should include familial, as well as genetic, factors. Family counseling should stress the sporadic nature of this entity but a recurrence in the same sibship is possible. Details of the clinical and magnetic resonance imaging studies are presented.

Thrombosis in a congenitally bifurcated superior sagittal sinus.

A 26-year-old woman had a peripartum venous thrombotic stroke involving the right parietal lobe. The initial thrombus was present only in the right channel of a congenitally bifurcated superior sagittal sinus. This diagnosis and subsequent thrombus extension were readily shown by magnetic resonance imaging in contrast to equivocal angiography. A subsequent, prospective review of 100 patients undergoing cranial magnetic resonance imaging showed the presence of similarly bifurcated superior sagittal sinuses in two. The patient stabilized after therapy with intravenous heparin, but switching her medication to oral warfarin sodium was followed by clinical deterioration and propagation of the thrombus, necessitating resumption of intravenous heparin. No coagulopathy was identified.

A sensitive period for the neural induction of taste buds.

Taste buds mature postnatally in the vallate papilla of the rat and reach a mean number of 610 by day 90. Although taste buds are neurotrophically dependent, the presence of widespread bilateral innervation permits more than 80% of the 610 vallate taste buds to survive after one IXth nerve is removed in adults. However, after a IXth nerve is removed at 0-3 d postpartum, about two-thirds of the vallate taste buds fail to develop. In the present investigation, the timing of the neural induction of taste buds was examined by unilaterally removing the IXth nerve at 12 different postnatal ages, from 0 to 75 d. Unilateral denervation revealed the existence of a sensitive period that is maximal from 0 to 10 d, when unilateral or bilateral interruption of the IXth nerve profoundly impairs the formation of taste buds. The number of taste buds that form is nonlinearly dependent upon the number of axons; at low levels of innervation, a doubling of the number of myelinated axons quintuples the number of taste buds. Thus, taste axons interact synergistically. In studying regeneration, we found that axons of both neonatal and adult IXth nerves elongate approximately 1.8 mm/d. Taste buds were re-formed more rapidly and a higher proportion were bilaterally innervated when regenerating axons and the sites of former taste buds were numerous. The proportion of bilaterally innervated taste buds could be approximated from the likelihood of random overlap of axons from the right and left IXth nerves. The greater ease with which taste buds are re-formed than developed suggests that taste bud regeneration does not recapitulate taste bud development.

Neural induction of taste buds.

Bilateral innervation allows more than 80% of the 610 vallate taste buds to survive removal of one IXth nerve in adult rats. Removal of both IXth nerves in neonatal or adult rats results in the absence of taste buds. In studying development, we found that removing or crushing one IXth nerve in three-day-old neonates profoundly decreased the number of vallate taste buds that subsequently developed. Specifically, after removal of one IXth nerve at 3 days, only 228 taste buds formed, compared with 496 taste buds that one nerve would maintain in adults. Thus, during normal development, the right and left IXth nerves interact synergistically, as at least 150 more taste buds develop than predicted by the sum of the independent action of each IXth nerve. This suggests that vallate taste buds are induced by the IXth nerve. A second example of synergism, representing evidence for the neural induction of taste buds, came from experiments in which we crushed the left IXth nerve 3 days after birth and found that these regenerated IXth nerve axons induced 4 times as many taste buds in the presence of the normal right IXth nerve (118 taste buds) as in its early absence (30 taste buds). We conclude that taste buds are neurally induced and that axons of the IXth nerve interact synergistically in inducing them, rather than competing for targets. We propose that in development innervated progenitor cells form stem cells which lead to taste bud cells.

Postnatal development of the vallate papilla and taste buds in rats.

The postnatal maturation of the vallate papilla and its taste buds was quantitatively investigated in rats by ligh microscopy. Specifically, we measured postnatal increases in the size of mature vallate taste buds and the vallate papilla, increases in the thickness of the gustatory epidermis, and increases in the number of mature taste buds and taste cells per bud. Mature taste buds, defined as those having a taste pore, are rare at birth but proliferate rapidly during the first postnatal month until an average of 610 mature taste buds has accumulated by 90 days. Throughout this postnatal period, mature taste buds adjust to the developmental thickening of the epidermis by continuously increasing in length. Mature taste buds also increase in width, in part due to a threefold increase from 10 and 45 days in the number of taste cells per bud. From 10 to 21 days there is an average daily net increase of three cells per mature taste bud. The maturational increase in taste buds and cells may contribute to the functional changes in taste nerve responses known to occur over the course of several generations of taste receptor cells. The dimensions of the vallate papilla and the surface area of the gustatory epithelium increase logarithmically with age. Although mature taste buds continue to increase in number until 90 days, both taste bud density (178/mm2) and the number of cells per mature taste bud (70-75 cells) reach ceilings by 45 days. Thus, density-dependent factors appear to control vallate taste bud maturation. The immaturity of lingual taste buds in newborn rats supports the view that odor, rather than taste, is the chemosensory signal that guides suckling in altricial rodents.

The effect of nerve stump length upon mammalian taste responses.

A decline in the magnitude of the summated responses evoked by taste solutions began about 1 h following IXth nerve transection. In 41 IXth nerves transected at different lengths we found a linear relationship between the length of the IXth nerve stump remaining attached to the tongue and the time for the taste response amplitude to fall to 50% of its control magnitude. The existence of a nerve stump length dependency suggests that IXth nerve taste responses in the gerbil are maintained by the axonal transport of trophic substances to the tongue.