Cholinergic amacrine cells are not required for the progression and atropine-mediated suppression of form-deprivation myopia.

Muscarinic cholinergic pathways have been implicated in the visual control of ocular growth. However, the source(s) of acetylcholine and the tissue(s) which regulate ocular growth via muscarinic acetylcholine receptors (mAChRs) remain unknown. We sought to determine whether retinal sources of acetylcholine and mAChRs contribute to visually guided ocular growth in the chick. Cholinergic amacrine cells were ablated by intraocular injections of either ethylcholine mustard aziridinium ion (ECMA; a selective cholinotoxin) or quisqualic acid (QA; an excitotoxin that destroys many amacrine cells, including those that release acetylcholine). Disruption of cholinergic pathways was assessed immunocytochemically with antibodies to the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT) and three different isoforms of mAChR, and by biochemical assay for ChAT activity. ECMA (25 nmol) destroyed two of the four subtypes of cholinergic amacrine cells and attenuated retinal ChAT activity, but left retinal mAChR-immunoreactivity intact. QA (200 nmol) destroyed the majority of all four subtypes of cholinergic amacrine cells, and ablated most mAChR-immunoreactivity and ChAT activity in the retina. ECMA and QA had no apparent effect on mAChRs or cholinergic fibres in the choroid, only marginally reduced choroidal ChAT activity, and had little effect on ChAT activity in the anterior segment. Toxin-treated eyes remained emmetropic and responded to form-deprivation by growing excessively and becoming myopic. Furthermore, daily intravitreal injection of 40 microg atropine for 6 days into form-deprived toxin-treated eyes completely prevented ocular elongation and myopia. We conclude that neither cholinergic amacrine cells nor mAChRs in the retina are required for visual regulation of ocular growth, and that atropine may exert its growth-suppressing influence by acting upon extraretinal mAChRs, possibly in the choroid, retinal pigmented epithelium, or sclera.

Neural barriers affect the action of nitric oxide synthase inhibitors in the intact chicken retina.

Nitric oxide synthase (NOS) activity, as measured by the formation of L-[3H]citrulline from L-[3H]arginine, was blocked by micromolar concentrations of NOS inhibitors in retinal homogenates, but concentrations approximately 20-3000 times higher were needed in intact retina. The higher concentrations could be related to transport of the NOS inhibitors into neuronal cells and/or their sequestration within glial cells. NG-monomethyl-L-arginine and N-iminoethyl-L-ornithine significantly inhibited L-[3H]arginine uptake, whereas N omega-nitro-L-arginine methyl ester and N omega-nitro-L-arginine had little or no effect on L-[3H]arginine uptake. The high concentrations of the inhibitors needed to inhibit nitric oxide production in intact tissue and their different interactions with arginine uptake systems may explain some of the conflicting results on the activity of NOS inhibitors on a range of physiological parameters in vivo.

Parallel suppression of retinal and pineal melatonin synthesis by retinally mediated light.

We have recently shown that light, over a narrow range of low intensities suppresses the activity of the enkephalin-immunoreactive amacrine cells of the chicken retina. In this paper, we show that over the same range of low light intensities the rate of melatonin synthesis in both the retina and the pineal of the chicken is suppressed. We further show that the effects of light on the pineal at these low intensities are mediated by the retina and not by direct actions on the pineal. Combined with our evidence that dopaminergic pathways within the retina are involved in controlling the state of activity of the pineal, these results suggest, but do not prove, that the change in state of a microcircuit within the retina involving the photoreceptors, dopaminergic amacrine cells and enkephalin-immunoreactive amacrine cells may be causally related to changes in the state of the pineal.

Pineal activity is under the control of retinal D1-dopaminergic pathways.

The role of dopaminergic pathways in the retina in controlling the functional state of the pineal was investigated. Dopaminergic agents were injected into the eyes of dark-adapted chickens which were maintained in the dark. Changes in the activity of N-acetyltransferase (NAT) in the retina and pineal were then monitored. Injection of the non-specific dopamine agonist 6,7-ADTN depressed retinal and pineal NAT. The D1-specific agonist SKF38393 did not affect retinal NAT but depressed pineal NAT. In contrast, quinpirole, a D2-specific agonist, depressed retinal NAT, but did not depress pineal NAT. Thus, D1- rather than D2-dopaminergic pathways in the retina are involved in the retinal circuit which control pineal function.

Is nitric oxide a transmitter of the centrifugal projection to the avian retina?

The chicken retina contains a population of prominent elements in the inner nuclear layer, which stain for NADPH-diaphorase. In distribution and morphology, these elements resemble the terminals of the centrifugal projection from the isthmo-optic nucleus. This identification was confirmed by showing that the NADPH-diaphorase-positive elements in the retina degenerated after destruction of the isthmo-optic nucleus or tract. These results indicate that the centrifugal projection to the retina in birds uses nitric oxide as a messenger or transmitter, in addition to a more conventional but as yet unidentified transmitter.

Anopheles farauti No. 3, a hitherto unrecognized biological species of mosquito within the taxon A. farauti Laveran (Diptera: Culicidae).

A hitherto unrecognized mosquito species, Anopheles farauti No. 3 has been found in Australia. This species occurs in sympatry with both A. farauti No. 1 and A. farauti No. 2 but we have found no evidence of introgression. Hybrids between A. farauti No. 3 and either A. farauti No. 1 or A. farauti No. 2 were found to be sterile.

Trisomy 4p and deletion 4p- in a family having translocation, t(4p-; 12p+).

Chromosome studies on a newborn infant with the clinical features of 4p-syndrome revealed a 46,XY,4p-karyotype with deletion of bands distal to 4p14. Investigation of the family revealed normal chromosomes in the mother and a balanced translocation rcp(4;12) (p14;p13) in the father, the paternal grandfather and an uncle. A severely retarded and malformed aunt is a partial trismoy for the short arms of chromosome 4, with the unbalanced karyotype 45,XX,12p+. It appears that monosomy of bands 4p15 and 4p16 leads to the full clinical features of 4p-syndrome, while trisomy of this region causes disabilities consistent with the rather more variable 4p trisomy syndrome. From currently reported cases, a summary is presented of the results of pregnancies of both male and female translocation carriers.

Major karyotypic abnormality in a child born to a woman with untreated malignant melanoma.

The karyotype of a 7-month-old child had 46 chromosomes, including five abnormal chromosomes in cultured lymphocytes. G-banding indicated the presence of reciprocal translocation products between chromosomes 1 and 7 and between chromosomes 4 and 15. A probable third translocation involved the same chromosome 4p arm and 12q. All metaphases showed these changes. C-band markers and the presence of reciprocal exchange products indicated that the chromosome changes occurred in the zygote or a post-zygotic cell of the child. The mother developed malignant melanoma while carrying the child but did not receive therapy before its birth. The suggestion is made that an undetected common agent was involved in the aetiology of the mother's tumour and the clastogenic change to the child's chromosomes.

Premature centromere division: a mechanism of non-disjunction causing X chromosome aneuploidy in somatic cells of man.

Apparent acentric fragments which replaced a C-group chromosome in cultured blood lymphocytes from a woman patient were shown by autoradiography, G-banding and C-banding to be complete X chromosomes in which the centromere had divided prematurely in relation to the centromeres of other chromosomes in the same metaphase. Metaphases with multiple 'fragments' suggested that non-disjunction of the 'fragments' had occurred. This anomaly of the X chromosome was associated with increased aneuploidy of a C-group chromosome, presumed to be X. Premature centromere division of the X chromosome (PCD, X) appeared to be a mechanism of non-disjunction which caused significant monosomy and trisomy of the X chromosome in blood cells and skin fibroblasts. The frequency of cells with multiple fragments and the extent of the aneuploidy in 48 hr. blood cultures indicated that this mechanism of non-disjunction operated during mitosis both in vivo and in vitro. Premature centromere division occurred at a lower frequency in normal women donors, and was age-related, being four times more frequent in women 60 years and older than in women under 40. Associated with the higher frequency of PCD, the older women also showed evidence of increased X chromosome aneuploidy. Premature centromere division of the X chromosome is considered to be the mechanism of non-disjunction, causing the well-documented increased number of 45, -C metaphases in ageing women. Premature centromere division was rare in men, but an age effect was again suggested.