Heterogeneous calretinin expression in the avian cochlear nucleus angularis.

Multiple calcium-binding proteins (CaBPs) are expressed at high levels and in complementary patterns in the auditory pathways of birds, mammals, and other vertebrates, but whether specific members of the CaBP family can be used to identify neuronal subpopulations is unclear. We used double immunofluorescence labeling of calretinin (CR) in combination with neuronal markers to investigate the distribution of CR-expressing neurons in brainstem sections of the cochlear nucleus in the chicken (Gallus gallus domesticus). While CR was homogeneously expressed in cochlear nucleus magnocellularis, CR expression was highly heterogeneous in cochlear nucleus angularis (NA), a nucleus with diverse cell types analogous in function to neurons in the mammalian ventral cochlear nucleus. To quantify the distribution of CR in the total NA cell population, we used antibodies against neuronal nuclear protein (NeuN), a postmitotic neuron-specific nuclear marker. In NA neurons, NeuN label was variably localized to the cell nucleus and the cytoplasm, and the intensity of NeuN immunoreactivity was inversely correlated with the intensity of CR immunoreactivity. The percentage of CR + neurons in NA increased from 31 % in embryonic (E)17/18 chicks, to 44 % around hatching (E21), to 51 % in postnatal day (P) 8 chicks. By P8, the distribution of CR + neurons was uniform, both rostrocaudal and in the tonotopic (dorsoventral) axis. Immunoreactivity for the voltage-gated potassium ion channel Kv1.1, used as a marker for physiological type, showed broad and heterogeneous postsynaptic expression in NA, but did not correlate with CR expression. These results suggest that CR may define a subpopulation of neurons within nucleus angularis.

The effects of acute hypoglycemia on relative cerebral blood flow distribution in patients with type I (insulin-dependent) diabetes and impaired hypoglycemia awareness.

To examine the hypothesis that in diabetic patients with impaired hypoglycemia awareness the relative regional distribution of cerebral blood flow (rCBF) would be abnormal in a specific area, namely the frontal lobes, rCBF was examined in 20 type I diabetic patients, of whom 10 had a normal awareness of hypoglycemia and 10 had a history of impaired hypoglycemia awareness. rCBF was determined sequentially using single photon emission computed tomography (SPECT) during (1) normoglycemia (arterialized blood glucose 4.5 mmol. L-1) and (2) hypoglycemia (blood glucose 2.5 mmol.L-1) induced by a hyperinsulinemic glucose clamp technique. Distribution of the isotope, 99mTc-Exametazime, was detected using a single-slice multi-detector head scanner. A split-dose technique was used, with 250 MBq being injected during steady-state normoglycemia and 250 MBq during subsequent hypoglycemia. rCBF was estimated in 30 regions of interest, derived from a standard neuroanatomical atlas on two parallel slices at 40 and 60 mm above the orbitomeatal line (OML). No between-group differences in the pattern of overall rCBF or changes in regional tracer uptake were demonstrated. In comparison to the rCBF during normoglycemia, both patient groups exhibited significant changes in the pattern of rCBF during hypoglycemia, with increments of rCBF to both superior frontal cortices and the right thalamus and reduced rCBF to the right posterior cingulate cortex and the right putamen. This pattern of relative redistribution of rCBF during hypoglycemia was preserved in patients who had impaired hypoglycemia awareness.