Differential vulnerability of the rat retina, suprachiasmatic nucleus and intergeniculate leaflet to malnutrition induced during brain development.

We investigated in young rats the effects of malnutrition on the main structures of the circadian timing system: retina, hypothalamic suprachiasmatic nuclei (SCN), thalamic intergeniculate leaflet, retinohypothalamic- and geniculohypothalamic tracts. Control rats were born from mothers fed a commercial diet since gestation, and malnourished rats from mothers fed a multideficient diet since gestation (GLA group) or lactation (LA group). After weaning, pups received the same diet as their mothers, and were analysed at postnatal days 27, 30-33 and 60-63. Brain sections were processed to visualise in the SCN neuropeptide Y immunoreactivity and terminal labeling after intraocular tracer injections. Nissl staining was used to assess cytoarchitectonic boundaries of the SCN and cell features in retinal whole mounts. Cell counts, morphometric and densitometric analysis were performed. Compared with controls, the total retinal surface was reduced and the topographical distribution of retinal ganglion cells was altered in malnourished rats, with changes in their density. Alterations were also detected in the SCN dimensions in the GLA and LA groups at one and two postnatal months, as well as in the SCN portion occupied by the retinal input in the GLA group at days 30-33, but not in the NPY-containing geniculohypothalamic tract. The present data point to subtle changes, with a low and differential vulnerability to early malnutrition, of structures involved in circadian timing regulation. Furthermore, the present findings suggest that the altered circadian rhythmicity previously documented in malnourished rats cannot be ascribed to impaired development of the retino- and geniculohypothalamic projections to the SCN.

Effect of essential fatty acid deficiency on membrane fatty acid content and growth hormone stimulation of rat pituitaries during postnatal development.

Fatty acid composition of anterior pituitary cell membranes of rats deprived of essential fatty acids (EFA) and of rats receiving a standard diet was determined during postnatal development and in adults. Pregnant rats were fed an EFA-deficient diet and the offspring were fed the same diet after weaning. In parallel, effects of the diet on growth and on growth hormone (GH) responsiveness to GHRH stimulation were determined in control animals. Membrane content of arachidonic acid (20:4n-6) and of its elongation product adrenic acid (22:4n-6) increased regularly from day 2 to day 12 after birth. EFA-deficiency resulted on day 2 in increased oleic acid and in substitution of arachidonic and adrenic acids by corresponding elongation-desaturation products of oleic acid: eicosatrienoic (20:3n-9) and docosatrienoic (22:3n-9) acids. At the age of 24 days, n-9 series fatty acid reached the same level as in adult animals. Two-day-old EFA-deficient rats paradoxically exhibited a higher level of 20:4n-6 as compared to control rats. EFA-deficiency also decreased growth rate and GH pituitary responses to GHRH during the prepubertal period. These results suggest that changes in the lipid structure and in pituitary secretion properties elicited by EFA-deficiency depend upon the stage of development.

Effect of an essential fatty acid deficiency on the phospholipid composition in anterior pituitary membranes.

The effects of an essential fatty acid deficient diet were investigated on the phospholipid fatty acids of several membrane fractions of the rat anterior pituitary, the secretion of which is known to be partly dependent on the membrane phospholipidic constituents. In standard dietary conditions, arachidonic acid (20:4n-6) and its elongation product, adrenic acid (22:4n-6), were the two main polyunsaturated fatty acids in all fractions studied. In rats deprived of EFA for 6 weeks after weaning, the levels of both 20:4n-6 and 22:4n-6 were not changed in microsomal + plasma membrane and nuclear fractions, whereas they were decreased in heavy mitochondrial and light mitochondrial fractions. The present data suggest a mechanism of compensation between membrane fractions which may preferentially preserve 20:4n-6 and 22:4n-6 in discrete membrane fractions.

Distribution of motoneurones innervating extraocular muscles in the brain of the marmoset (Callithrix jacchus).

Extraocular muscle motoneurones were localised in the oculomotor nucleus (ON), trochlear nucleus (TN) and abducens nucleus (AN) in the marmoset brain using the horseradish peroxidase (HRP) retrograde labelling technique. HRP pellets injected into individual extraocular muscles revealed one or more groups of labelled neurones occupying discrete loci within these nuclei. Relatively little overlap of motoneurone pools was observed, except in the case of the inferior oblique and superior rectus muscles. Injections of HRP into the medial rectus muscle revealed three separate populations of labelled cells in the ipsilateral ON. Motoneurones innervating the inferior rectus muscle were mainly localised in the lateral somatic cell column of the ipsilateral ON. A second smaller grouping was observed in the medial longitudinal fasciculus. The inferior oblique muscle motoneurones were localised in the ipsilateral medial somatic cell column intermingled with motoneurones supplying the superior rectus muscle of the opposite eye. The superior oblique muscle motoneurones occupied the entire TN and the lateral rectus muscle motoneurones the AN. It was concluded that the organisation of nuclei and subnuclei responsible for controlling the extraocular muscles in the marmoset is broadly similar to that of other primates.

Oculomotor areas involved in the parasympathetic control of accommodation and pupil size in the marmoset (Callithrix jacchus).

The motoneurons of the oculomotor complex responsible for controlling accommodation and pupil size of the marmoset were identified by injecting horseradish peroxidase (HRP) into the ciliary ganglion. The anatomical organization of accommodation and pupil constrictor motoneurons was determined using electrical stimulation techniques. HRP-labelled cells were found through the whole length of the Edinger-Westphal nucleus (EW) and also just ventral to this nucleus in caudal sections. A projection from the antero-median nucleus to the ciliary ganglion could not be demonstrated. Electrical stimulation data showed that currents of less than 1 microampere applied inside the EW evoked accommodation responses. Pupil constriction responses, on the other hand, were evoked with weak currents at sites ventral to those in the EW generating accommodation at caudal and central levels. It was concluded that the EW was responsible for accommodation and areas containing HRP-labelled cells ventral to the caudal part of the EW were responsible for pupil constriction.