Visual pretectal neurons projecting to the dorsal lateral geniculate nucleus and pulvinar nucleus in the cat

We observed morphological subtypes of visual pretectal neurons ascending to the dorsal thalamus, following injections of wheat germ agglutinin conjugated to horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or the pulvinar nucleus. These neurons are composed of fusiform cells and small-sized multipolar cells in the olivary pretectal nucleus, superficial horizontal cells, fusiform cells, small-, medium- and large-sized multipolar cells in the optic tract nucleus, and small- and medium-sized multipolar cells in the posterior pretectal nucleus. When somal size of the neurons projecting to the LGNd was compared to the size of neurons projecting to the pulvinar, the neuronal groups were not identical.     

Properties of cells responding to visual stimuli in the rat ventral lateral geniculate nucleus

Single-unit recordings were made of the ventral lateral geniculate nucleus (LGv) in the albino rat anesthetized with urethane. Visual receptive field properties as well as the characteristics of responses elicited by electrical stimuli to the optic tract and to the visual cortex were examined. Compared with the relay cells of the dorsal lateral geniculate nucleus (LGd), LGv cells were characterized by the following properties. (i) They responded to visual cortex stimuli orthodromically as well as to optic tract shocks. (ii) The postexcitatory inhibition they showed after single optic tract or visual cortex stimuli was only short-lasting, at most 100 ms. (iii) Conduction velocities of the optic nerve afferent fibers were mostly in the range of slow fibers, 2 to 10 m/s. (iv) The receptive fields were essentially homogeneous in type; about 90% of the sample of 53 cells were On-tonic. (v) Receptive field sizes were substantially large, from 6.3 to 45.6° (mean, 22.3°). (vi) On-tonic cells revealed a regular maintained discharge whose level changed monotonically as a function of the luminous intensity of the stimulating light. The functional implications of these findings were compared with those of the relay cells in the LGd.     

Ventral lateral geniculate nucleus projects to the dorsal lateral geniculate nucleus in the cat

The lamina C3 of the dorsal lateral geniculate nucleus of the cat does not receive retinal projections but instead receives visual information from the small subpopulation of W-type ganglion cells via the upper substratum of the stratum griseum superficiale of the superior colliculus. We herein report a projection from the lateral division of the ventral lateral geniculate nucleus into the lamina C3 of the dorsal lateral geniculate nucleus. As the lateral division receives projections from the contralateral retina and the ipsilateral upper stratum griseum superficiale of the superior colliculus, we suggest that these regions make up a small cell type W-cell neuronal network that provides visual information to layer I of the striate cortex via the lamina C3.     

Subdivisions of the dorsal raphe nucleus projecting to the lateral geniculate nucleus and primary visual cortex in the Mongolian gerbil

The mammalian dorsal raphe nucleus (DRN) is composed of sub-divisions with different anatomical and functional properties. Using cholera toxin subunit B as a retrograde tracer, DRN subdivisions projecting to the lateral geniculate nucleus and to the primary visual cortex were examined in the Mongolian gerbil. DRN neurons projecting to the lateral geniculate nucleus were observed in the lateral DRN (rostrally) and in the ventromedial DRN (caudally), while DRN cells projecting to the primary visual cortex were observed at all rostral-caudal levels in the ventromedial DRN. These results demonstrate a significant overlap between the DRN projections to the lateral geniculate and superior colliculus, and show that only the caudal ventromedial DRN projects to all three major visual targets: the lateral geniculate nucleus, primary visual cortex, and superior colliculus. Since the DRN is involved in depression and other neuropsychiatric disorders, as well as is affected by many psychotropic substances, these data may help to develop new treatments and therapies targeting specific DRN subdivisions.     

Response properties of cells in the dorsal lateral geniculate nucleus of the albino rat

The response patterns of cells in the dorsal lateral geniculate nucleus of the albino rat were studied in order to examine the functional organization of the lateral geniculate nucleus. Both photic stimulation and electrical stimulation of the optic tract were used to activate single units in the lateral geniculate nuclei. Three different types of response patterns were found for principal cells, while interneurons all had similar response patterns. The first class of principal cells, E-S cells, responded to stimulation with a period of excitation, followed by a period when activity was suppressed. A second class of cells, S cells, responded to photic stimulation with an initial period when activity was suppressed. The final class of cells, E cells, responded with a period of excitation followed by a return to spontaneous rates of firing. The response patterns of E cells suggest that this type of principal neuron does not receive feedback inhibition of the type proposed in previous models of the lateral geniculate nuclei. Based on these and other observations, a new model of the functional organization of the lateral geniculate nuclei is proposed.     

Retinal ganglion cells projecting to the dorsal raphe and lateral geniculate complex in Mongolian gerbils

Injections of rhodamine-B into the dorsal raphe nucleus (DRN) and Fluoro-Gold into the lateral geniculate nucleus (LGN) revealed double-labeled retinal ganglion cells (DL RGCs) projecting to both nuclei. The soma-size distribution of DL RGCs was compared with three other distributions: DRN-projecting RGCs, LGN-projecting RGCs, and a large sample of RGCs labeled via the optic nerve with DiI. DL RGC soma diameters fell primarily within the mid-to-upper size range of all three distributions. DL RGCs may provide information to both nuclei concerning comparable aspects of light and visual stimulation via collateralized axons.     

Morphology and distribution of retinal ganglion cells projecting to different layers of the dorsal lateral geniculate nucleus in normal and Siamese cats

Electrophoretic injections of horseradish peroxidase were made into physiologically characterized sites within the different layers of the dorsal lateral geniculate nuclei (LGNd) of normal and Siamese cats. The histochemical procedures used stained the cell bodies, dendrites, and axons of retrogradely labeled ganglion cells. In both normal and Siamese cats, only alpha and beta ganglion cells are labeled by injections restricted to the A laminae. In normal cats, the alpha/beta ratios (number of labeled alpha cells/number of labeled alpha + beta cells) resulting from injections into lamina A increase from about 0.045 at 0.5 mm from the area centralis to about 0.12 in the far periphery. The alpha/beta ratios observed outside of the area centralis in normal cats following injections into different parts of lamina A1 were lower at each eccentricity than those resulting from injections into corresponding parts of lamina A. Also, the cell bodies and dendritic fields of alpha and beta cells projecting to lamina A1 are somewhat larger than those projecting to corresponding parts of lamina A. Outside of the area centralis, the relative numbers of alpha and beta cells projecting to Siamese lamina A are normal. However, alpha cells comprise an abnormally small proportion of ganglion cells projecting to the normal segments of Siamese lamina A1 and an abnormally large proportion of cells projecting to the abnormal segments of lamina A1. In Siamese cats, alpha and beta cells projecting to lamina A1 are distributed continuously throughout virtually all of the ipsilateral and contralateral temporal retinas. Since large parts of the ipsilateral and contralateral hemifields are not represented in Siamese lamina A1, it seems that some of the retinal afferents to this lamina are being suppressed. Injections into the C laminae of the LGNd show that the same morphological classes of ganglion cells project to these laminae in normal and Siamese cats. The classes projecting to the contralateral as C laminae (laminae C and C2) include alpha, beta, gamma, and epsilon as well as two other groups of cells referred to g1 and g2 cells, gamma, epsilon, g1, and g2 cells project to the ipsilateral C lamina (lamina C1). In siamese, but not in normal cats, examples of all of these types are found far into the contralateral temporal retina following injections involving lamina C1. This indicates that all classes projecting to the ipsilateral C lamina misproject in Siamese cats.     

Dendritic morphologies of retinal ganglion cells projecting to the lateral geniculate nucleus in the rabbit.

Small injections of fluorescent Rhodamine-latex microspheres and Fast Blue were made into the dorsal lateral geniculate nucleus (dLGN) of fifteen rabbits. After 8-15 day survival times, the somas of projecting ganglion cells were found to be labelled in the contralateral retinas by retrograde transport. The dendritic morphologies of the labelled ganglion cells were revealed by intracellular injection of Lucifer Yellow or horseradish peroxidase while superfusing the retinas. At least ten distinct dendritic morphologies were observed among 161 injected ganglion cells. The three most commonly recovered dendritic morphologies were those of: (1) alpha-like cells; (2) large, complex dendritic field cells; and (3) cells with small, dense dendritic fields that resemble intracellularly identified brisk sustained cells (Amthor et al., J. Comp. Neurol. 1989; 280:72-96). Smaller percentages of cells whose dendritic morphologies resembled those of several physiologically identified sluggish and complex receptive field ganglion cell classes (Amthor et al., J. Comp. Neurol. 1989; 280:72-96, 97-21) were also recovered. Several morphological types were also found that were previously unknown or could not be confidently related to those of previously known classes. Most dLGN injections labelled many different types of ganglion cells, but restricted injections in some dLGN loci labelled only a limited number of ganglion cell classes.     

Neurons of the dorsal lateral geniculate nucleus of the albino rat.

Light and electron microscopic observations were made on the dorsal lateral geniculate nucleus (DLGN) of 33 young adult male albino rats. Three variants of the Golgi silver impregnation technique were employed in the light microscopic studies. Neurons were classified into three categories based on location, dendritic pattern, and dendritic appendages. Type 1 and type 3 neurons were distributed throughout the DLGN. Type 2 neurons were located in the superficial zone. Dendritic appendages of type 1 and type 2 neurons indicated these cells may function as geniculo-cortical relay neurons. The type 3 neurons had lobulated dendritic appendages and an axon that terminated withinthe nucleus. Type 3 neurons may represent Golgi-type-II interneurons. Camera lucida drawings, photomicrographs, and electronmicrographs illustrate the characteristics ofthe three cell types. The literature on ultrastructural and neurophysiological findings may substantiate the presence of three neuronal types. Initially, the rat DLGN does not appear as elaborately organized as the nucleus observed in cats and primates; however, there are notable similarities in neuronal morphology and synaptology.     

Identification of ventral lateral geniculate nucleus cells projecting to the pretectum and superior colliculus in the cat

Among 235 histologically identified cells of the ventral lateral geniculate nucleus (LGV) in the cat, 66 responded antidromically to electrical stimulation of the pretectum (PT) and/or superior colliculus (SC): 22 projected to PT, 22 to SC and 22 to both sites. The LGV cells were innervated by optic tract fibers corresponding to axons of X- as well as W-type retinal ganglion cells.     

Noradrenaline-stimulated inositol phospholipid breakdown in rat dorsal lateral geniculate nucleus neurones

Noradrenaline-stimulated inositol phospholipid breakdown in matched vibratome sections through the rat dorsal lateral geniculate nucleus (dLGN). The response was measured as a large accumulation of [3H]inositol labelled inositol monophosphate and was mediated via activation of alpha 1-adrenergic receptors. Accumulation of [3H]inositol phosphates was reduced in kainic acid-lesioned animals, indicating that this response occurred within dLGN neurones and not afferent terminals. The results implicate inositol phospholipid breakdown as part of the mechanism of noradrenergic neurotransmission within the dLGN.     

Serotonergic inhibition of the dorsal lateral geniculate nucleus

Electrophysiological studies were conducted on chloral hydrate-anesthetized rats to determine if the dorsal raphe nucleus (DR) exerts an inhibitory influence upon the dorsal lateral geniculate nucleus (dLGN), and if this inhibition is mediated by the release of serotonin (5-HT). Conditioning stimuli presented to the DR 100-400 ms before an optic tract (OT) shock significantly lowered the amplitude of OT shock-elicited, postsynaptic, field potentials of less than 3 ms latency. Rare, long-latency, field potentials (greater than 5 ms) were diminished in amplitude when preconditioning intervals were less than 15 ms. Six days after intracerebral injection of the 5-HT neurotoxin, 5,7-dihydroxytryptamine (8 micrograms), into the dLGN, significant reductions were observed in 5-HT and 5-hydroxyindole acetic acid in the dLGN. Field potentials recorded on the sixth day in indoleamine-depleted dLGN were significantly less inhibited by DR preconditioning. Intracerebral injections of a control solution neither altered monoamine levels nor the degree of inhibition by DR preconditioning. These data provide further evidence that inhibition of dLGN by DR is mediated by release of 5-HT.     

Activity-evoked extracellular pH shifts in slices of rat dorsal lateral geniculate nucleus

Activity-dependent extracellular pH shifts were studied in slices of the rat dorsal lateral geniculate nucleus (dLGN) using double-barreled pH-sensitive microelectrodes. In 26 mM HCO₃⁻-buffered media, afferent activation (10 Hz, 5 s) elicited an early alkaline shift of 0.04±0.02 pH units associated with a later, slow acid shift of 0.05±0.03 pH units. Extracellular pH shifts in the ventral lateral geniculate nucleus were rare, and limited to acidifications of approximately 0.02 pH units. The alkaline shift in the dLGN increased in the presence of benzolamide (1–2 μM), an extracellular carbonic anhydrase inhibitor. The mean alkaline shift in benzolamide was 0.10±0.05 pH units. In 26 mM HEPES-buffered saline, the alkaline response averaged 0.09±0.03 pH units. The alkaline shifts persisted in 100 μM picrotoxin (PiTX) but were blocked by 25 μM CNQX/50 μM APV. If stimulation intensity was raised in the presence of CNQX/APV, a second alkalinization arose, presumably due to direct activation of dLGN neurons. The direct responses were amplified by benzolamide, and blocked by either 0 Ca²⁺/EGTA, Cd²⁺ or TTX. In 0 Ca²⁺, addition of 500 μM–5 mM Ba²⁺ restored the alkalosis. Alkaline shifts evoked with extracellular Ba²⁺ were larger and faster than those elicited by equimolar Ca²⁺. In summary, synchronous activation in the dLGN results in an extracellular H⁺ sink, via a Ca²⁺-dependent mechanism, similar to activity-dependent alkaline shifts in hippocampus.     

Receptive field properties of rat ventral lateral geniculate cells projecting to the superior colliculus

Cells of the ventral lateral geniculate nucleus (LGV) in rats sending their axons to the superior colliculus (SC), were identified electrophysiologically as the ones responding antidromically to electrical stimulation of SC. They were located in the external part of LGV. Visual receptive fields of these cells were mostly of ON-tonic types and some of movement-sensitive ones. Evidence was presented supporting existence of the reciprocal fiber connection between the LGV and the SC.