Role of nitric oxide in the development of retinal projections.

Synthesis of nitric oxide (NO) occurs downstream from activation of NMDA receptors and NO acts as a retrograde messenger, influencing the refinement and stabilization of coactive afferent terminals. Cells and neuropil in the rat superior colliculus (SC) and lateral geniculate body (LGB) show intense, developmentally regulated activity for NO synthase (NOS). To study the role of NO in the development of retinogeniculate and retinotectal axon arbors, we examined primary visual projections of rats that had received daily i.p. injections of L-NoArg (an NOS inhibitor) for 4-6 weeks starting from postnatal day 0. Retinal fibers labeled by intraocular injection of the B subunit of cholera toxin were revealed immunohistochemically and the density of fibers in the superficial SC and in the dorsal LGB was measured by computerized image analysis. Single retinocollicular terminal arbors were reconstructed at the computer (Neurolucida). Treated rats showed significant alterations in ipsilateral retinotectal projections, in the mediolateral and anteroposterior axes: there was an increase in the density of fibers entering the SC, in branch length, and in numbers of boutons on retinotectal arbors in the treated group. Ipsilaterally projecting retinal axons also showed an increase in density and distribution in the dorsal nucleus of the LGB. If animals were allowed to survive for several months after stopping treatment, similar changes were also noted, but these were much less striking. Our results suggest that, in the mammalian visual system, NO released from target neurons in the SC and LGB serves as a retrograde signal which feeds back on retinal afferents, influencing their growth.

Optimizing efficacy of quick parathyroid hormone determination in the operating theater.

The usefulness of intraoperative parathyroid hormone (PTH) monitoring has been extensively documented in primary hyperparathyroidism (HPT), whereas few data have been published on its use in reoperations or in secondary and tertiary HPT. We report our initial experience with a rapid (12 min response) PTH immunochemiluminometric assay performed in the operating room during surgery in 12 patients with primary HPT, 16 end-stage renal disease patients with secondary HPT and five kidney transplanted subjects with tertiary HPT. Blood samples were taken at baseline, within 10 min after resection and subsequently at various intervals whenever needed. The mean PTH levels before and after parathyroidectomy were 230.5 pg/mL (range 69-842) and 47.3 pg/mL (range 5-184), respectively, in primary HPT, 855.0 pg/mL (416-1655) and 202.2 pg/mL (53-440) in secondary HPT, and 205.6 pg/mL (116-301) and 45.4 pg/mL (18-97) in tertiary HPT. All patients but one had a significant percentage decline from pre-excision values (mean 76.9%, 76.0%, and 76.1% in primary, secondary and tertiary HPT, respectively). While a reduction of more than 50% was observed in 30 out of 33 patients after the first intraoperative sampling, additional measurements were performed in 10 cases. On-site PTH monitoring with this user-friendly and reliable system has proved helpful in targeting PTH tests to give the surgeon a rapid and accurate assessment of the intervention. The development of optimal PTH sequence strategies with decision-focused analytical and clinical limits will improve the efficacy of "point-of-care" PTH assay and resource utilization.

NOS inhibition during postnatal development leads to increased ipsilateral retinocollicular and retinogeniculate projections in rats.

Synthesis of nitric oxide (NO) occurs downstream from activation of N-methyl-D-aspartate (NMDA) receptors; NO reportedly acts as a retrograde messenger, influencing the refinement and stabilization of coactive afferent terminals. Cells and neuropil in the rat superior colliculus (SC) and lateral geniculate body (LGB) show intense, developmentally regulated activity for NO synthase (NOS). To study the role of NO in the development of retinogeniculate and retinotectal axon arbors, we examined primary visual projections of rats that had received intraperitoneal injections of Nomega-nitro-L-arginine (L-NoArg, an NOS inhibitor) on postnatal day 0, and daily thereafter for 4-6 weeks. Treated rats showed significant alterations in ipsilateral retinotectal projections, in the mediolateral and anteroposterior axes; there was an increase in the density of fibres entering the SC, in branch length, and in the numbers of boutons on retinotectal arbors in the treated group. Ipsilaterally projecting retinal axons also showed an increase in density and distribution in the dorsal nucleus of the LGB. If animals were allowed to survive for several months after stopping treatment, similar changes were also noted, but these were much less striking. Our results support the hypothesis that, in the mammalian visual system, NO released from target neurons in the SC and LGB serves as a retrograde signal which feeds back on retinal afferents, influencing their growth. The effects of NOS inhibition are partially reversed after treatment is stopped, indicating that lack of NO synthesis delays the maturation of retinofugal connections, and also that NO plays a constitutive role in their development.

Maturation of NADPH-d activity in the rat's barrel-field cortex and its relationship to cytochrome oxidase activity.

Histochemical detection of NADPH-d activity in rat barrel-field cortex reveals four types of distributions. (i) A transient, diffuse neuropil staining is visible in the cortical plate and in deeper layers until postnatal day (P) 4. Thereafter, until P15, it is segregated in whisker-specific patches in layer IV, then the pattern gradually disappears, becoming virtually indistinct by P21. This transient patterning of diffuse NADPH-d activity in layer IV disappears after cortical injections of kainic acid and is affected by neonatal damage to the contralateral snout. An intense labeling (ii) of scattered cells and (iii) of a plexus of fibers is present. With maturation, the cells become localized mostly in layers II/III, in the lower part of layer V, and in layer VI. They are sparse in layer I, in upper layer V, and in layer IV where their somata are located primarily in the interbarrel septa. (iv) Light staining of cortical neurons is detected mostly in layers II-IV but occasionally also in layers V-VI. Cytochrome c oxidase (CO)-positive patches associated with barrels are first detected in layer IV around P4-P5; their staining density increases with development, then stays high. In the adult, CO activity is moderate in supragranular layers, highest in the barrels in layer IV, low in upper layer V, medium dense in the deeper half of layer V, and low in lamina VI. Thus, NADPH-d and CO activities are not necessarily colocalized in the rodent barrel-field cortex. The varied (transient and long-lasting) distributions of NADPH-d activity indicate that the enzyme and its associated production of NO serve multiple roles in developing and adult barrel-field cortex.

Sex steroids modulate NADPH-diaphorase expression in the postnatal adrenal neurons of the rat.

The rat adrenal gland contains nitric oxide-producing ganglion cells, contributing to its innervation. In a previous study postnatal number and morphology of these adrenal neurons were analyzed by NADPH-diaphorase histochemistry in the two sexes. A transient sex-related difference in the number of NADPH-diaphorase positive neurons per adrenal gland was found at postnatal day 10, when the number of stained neurons in males was nearly twice that found in females. In the present work we studied the effects of perinatal hormonal manipulation on the number of adrenal NADPH-diaphorase-positive neurons during the second postnatal week. The number of labeled adrenal neurons at postnatal day 10 was higher in females receiving perinatal androgen treatment than in control untreated females, and was similar to that of control untreated males. In contrast, in males that underwent perinatal deprivation of testosterone the number of labeled adrenal neurons was lower than in control males, and similar to that of control females. These differences were found in both the adrenal cortex and medulla. In males and in testosterone-treated females there was a higher proportion of stained multipolar neurons than in females and in androgen-deprived males. No intergroup differences were found in the size of stained neurons. Thus, we demonstrated that the postnatal difference in the number of NADPH-diaphorase-positive adrenal neurons in the two sexes is related to the epigenetic action of gonadal hormones during perinatal maturation.