Renata Ferrari

[14C]Deoxyglucose uptake of the rat visual centres under monocular optokinetic stimulation

Monocular optokinetic stimulation ( OKS ) in Long-Evans rats enhances the uptake of [14C]2-deoxy-D-glucose (2-DG) in the pretectal nucleus of the optic tract (NOT) and superior colliculus (SC) contralaterally to the open eye regardless of the movement direction. Metabolic increases in NOT and SC are therefore found to be unrelated to the ocular nystagmus that in monocularly viewing rats follows only to OKS nasalward for the seeing eye. Since the oculomotor asymmetry has been attributed to the directional selective properties of NOT neurons responding to nasalward movement in the contralateral visual field but being inhibited by opposite ( temporalward ) movement, the enhanced 2-DG uptakes observed in the present experiments seem to represent the NOT excitatory metabolic work in the case of nasalward movement and the NOT inhibitory metabolic expenditure in the case of temporalward movement.

Correlation between retinal afferent distribution, neuronal size, and functional activity in the guinea pig medial terminal accessory optic nucleus

SummaryThe intrinsic morpho-functional organization of the medial terminal nucleus of the accessory optic system was investigated in the guinea pig. The distribution of the retinal afferents, as assessed by the axoplasmic transport of 14C-valine, showed a remarkable asymmetry within the nucleus. Thus, while the retinal terminal field covered the entire medial terminal nucleus, by far the largest density of labeled retinofugal axon terminals was found within its dorsal division. In this same portion of the nucleus, we found the greatest density of large cells and the maximum intensity of functional activation, this latter as estimated by the increase in metabolic activity of neurons using the 14C-2-deoxyglucose autoradiographie method in the vertical and horizontal whole-field movement in the visual field.

The commissural transfer of the horizontal optokinetic signal in the rat: a c-Fos study.

We applied the Fos method in rats subjected to horizontal optokinetic stimulation (OKS) to study whether optokinetic information is transferred through the commissural pretectal fibres from one optic tract nucleus (NOT) to the opposite. In binocular as well as in monocular nasalward OKS, the highest Fos immunoreactivity was found in the NOT contralateral to the nasalward stimulation, as expression of the activation either of direction-selective cells and of commissural neurons. Even the opposite NOT showed many Fos-positive cells activated by the opposite nucleus throughout the commissural pretectal pathway. They might be the GABA positive cells, which are thought to allow the activation in one nucleus to be transformed into inhibition of the opposite side. In monocular temporalward OKS, the inhibition on direction-selective cells and the consequent silencing of commissural neurons caused the faint immunoreactivity in the NOT contralateral to eye stimulated. In the opposite nucleus the few Fos-positive cells emerged as a consequence of the lack of the normal tonic commissurally mediated inhibition.

Abnormal c-fos-like immunoreactivity in the superior colliculus and other subcortical visual centers of pigmented royal college of surgeons rats

Neurons in the central nervous system often show a transient up‐regulation of expression of the immediate early gene c‐fos when presented with precise novel stimuli. In normal rats, neurons in most subcortical visual centers show low levels of fos‐like immunoreactivity (FLI) expression, but there is a substantial and transient increase in FLI expression if the animal is exposed to a flashing light. This is especially evident in the superior colliculus (SC). We have examined here FLI expression in the subcortical visual centers of the Royal College of Surgeons rat, focusing specifically on the SC. In this animal, as a result of a genetic defect, there is early loss of rod photoreceptors over the first few months of life, along with slower disappearance of cones. Although light stimulation showed that FLI expression was very similar to that seen in normal rats, the basal levels of FLI expression under dark‐maintained conditions were much higher than normal, even exceeding the levels seen after visual stimulation. In the SC, the elevation of FLI expression was already evident by 6 weeks of age and reached a plateau by 17 weeks. Other subcortical visual centers also showed elevated basal levels of FLI expression, although in general the increases were less dramatic than the increase in the SC. The elevated FLI expression in dark‐maintained condition seen in the SC was abolished by contralateral optic nerve section. It was also severely diminished by subretinal cell transplantation at 3 weeks of age with the objective of limiting photoreceptor loss over part of the retina. These results suggest that the elevated basal FLI expression is a retina‐driven event. Although it correlates with the loss of rod photoreceptors, it is unlikely to reflect reduced photoreceptor drive but rather some form of bursting activity generated in the inner retina, as a result of circuit reorganization or receptor up‐regulation. J. Comp. Neurol. 472:100–112, 2004.

Correlation between amount of retinal afferents to the pretectal nucleus of the optic tract and dorsal terminal accessory optic nucleus and performance of horizontal optokinetic reflex in rat

Intraocular kainic acid injection in Long-Evans rats induces loss of retinal afferents to subcortical visual centers as assessed by the axoplasmic transport of [14C]valine. The optical terminal fields of the pretectal nucleus of the optic tract (NOT), superior colliculus and accessory optic system (AOS) nuclei appear particularly affected. Since NOT and the AOS dorsal terminal nucleus (DTN) represent the first relay station of the visuomotor pathway mediating horizontal optokinetic nystagmus (HOKR), we have studied the characteristics of HOKR after various degrees of retinal deafferentation of these nuclei induced by intraocular KA injection. Taking advantage of the arrangement of the primary optic projections to NOT-DTN, that in rats are almost entirely crossed, in each animal, monocular HOKR induced by stimulation of the injected eye was compared to monocular HOKR elicited by stimulation of the intact, ipsilateral eye. Following NOT-DTN optic denervation, HOKR gain always worsened, and in a way, that the greater the deficits of retinal afferents, the greater the HOKR inability to compensate for visual motion. Furthermore, for any given retinal denervation the higher the stimulus velocity, the greater the HOKR deficit. While the correlation between HOKR gain and the amount of retinal afferents to NOT-DTN would seem to indicate a functional homogeneity of the retinal ganglion cells sending axons to these nuclei, the finding that the extent of HOKR impairment also varied with velocity might not support the above view.

Cholesterol synthesis in isolated rat hepatocytes: effect of homologous and heterologous serum lipoproteins

The present study investigated the effect of serum lipoproteins on sterol synthesis by isolated rat hepatocytes. These cells were maintained in culture medium for 24 hr and incubated for the same period of time with increasing concentrations of serum lipoproteins (5-150 microgram of lipoprotein-protein per ml) isolated from different animal species. The viability of the cells was ascertained by their ability to synthesize cholesterol and protein and to secrete serum proteins into the medium. Rat VLDL and LDL did not alter sterol synthesis, which was stimulated instead by HDL. Rat serum chylomicrons were also ineffective. Human LDL significantly reduced the synthesis of sterols from both acetate and tritiated water; this effect was also induced by human VLDL to a reduced extent. VLDL isolated from hypercholesterolemic rabbit (VLDLC) strongly inhibited sterol synthesis from acetate but not from mevalonate. Cholesteryl-ester-rich VLDL isolated from a patient with type III hyperlipidemia (type III VLDL) were more effective than normal VLDL in suppressing sterol synthesis from acetate. The implications of these findings are discussed with regard to the possible role of cholesteryl-ester-rich lipoproteins on the in vivo regulation of sterol synthesis in the liver.

Functional cerebral activation detected by an integrated system combining CW-NIR spectroscopy and EEG

The aim of this study is to explore the possibility of correlating hemodynamic changes and neural activities in the brain by using an integrated system combining Near Infrared Spectroscopy (NIRS) and electroencephalographic activity (EEG). We present brain hemodynamic changes and EEG recordings obtained from four volunteers during the performance of two different sequential thumb-finger opposition tasks, with and without a related mental activity. The optical and electrical signals were recorded simultaneously on the subject forehead. The coupling of the two systems could be useful to demonstrate correlation between cognitive paradigms and hemodynamic signals.

Kainic acid differently affects retinal projections to different pretectal nuclei

Kainic acid (KA) damages retinal cells, thus impairing axonal anterograde transport of labeled aminoacids when injected intravitreally. In this study, Long-Evans rats were injected with KA into one eye, and seven days later were binocularly injected with 14C-valine. The extent of residual retinal afferents to two pretectal nuclei was calculated as the percentage of the contralateral, intact side. Projections to the nucleus of the optic tract (first relay station of the optokinetic pathway) appear significantly more affected than those to the olivary pretectal nucleus (involved in the pupillary light response). These results suggest a correlation between the functional properties of retinal ganglion cells and distinctive biochemical characteristics, such as their susceptibility to KA.

Dyslipidemia in rats with hypothyroidism

Publisher Summary This chapter discusses a study to analyze dyslipidemia in rats with hypothyroidism. Male Wistar rats with an initial weight ranging from 160 to 200 g were used. They were divided into two groups. The rats of the first group received daily subcutaneous injections of 6-propyl-2-thiouracil (PTU) dissolved in 0.9% NaCl, pH 8.5. The rats of the other group (control rats) received an equivalent volume of 0.9% NaCl pH 8.5. The rats treated with PTU became hypophagic after 8 days of treatment. To assure equicaloric consumption of food, pair feeding procedure was introduced. Therefore, the amount of food given to the control rats was restricted to the amount consumed daily by the PTU-treated animals. At the end of treatment, nonfasting rats were anesthetized with Nembutal and bled from the carotid artery. It was found that after 25 days of treatment with propylthiouracil, the level of T 4 fell to 24% of that found in the control rats. The level of T 3 also diminished but to a lesser extent.

C-fos Expression in the Optokinetic Nuclei of the Rat Following Different Visual Stimulus Conditions

In the present study we characterised by means of the c-Fos method the neuronal populations of the optokinetic nuclei system of the rat activated by different directions of external visual world motion as well as by saccadic exploration of a patterned stationary scene. A major difference was found between the nucleus of the optic tract (NOT) and the nuclei of the accessory optic system (AOS): dorsal terminal (DTN), lateral terminal (LTN) and medial terminal (MTN). c-Fos-positive cells are expressed in the AOS nuclei only after optokinetic stimulation (OKS) according to the direction for which each nucleus is strictly committed: in the DTN after horizontal OKS, in the LTN and MTN after vertical OKS. No segregation of direction-selective cells was observed in the MTN for opposite directions of motion. In the NOT, c-Fos cells became immunoreactive after OKS of any direction, with the greatest expression induced by horizontal OKS in the nucleus contralateral to the eye stimulated nasalward, and even following the presentation of a non-rotating drum. However, the spatial location of the activated neurones is distributed along the nucleus for horizontal OKS and strongly restricted to its rostral region for other stimuli. Given these findings, a larger spectrum of competencies than previously supposed should be attributed to the NOT.