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A R Lieberman

Publications and source records attributed to A R Lieberman.

At least 91 records · Page 5Linked to original sources
PubMed1978

The reciprocal synapse in the external plexiform layer of the mammalian olfactory bulb.

It has recently been claimed by Ramon-Moliner29, that reciprocal synapses between mitral (and tufted) cell dendrites and granule cell gemmules, which for more than 10 years have been thought to represent a major feature of the structural and functional organization of the olfactory bulb28, are non-existent or, at best, extremely rare. The challenge is based on the contention that there is little, if any, morphological evidence to substantiate the existence of the gemmulofugal component of the reciprocal synapse. We have re-examined by electron microscopy the external plexiform layer (EPL) of the olfactory bulb of adult rabbits and rats. The study was carried out in conventionally prepared material, using individual and serial sections, goniometry, and quantitative analysis of montages, and also in material stained by the E-PTA and BIUL methods. According to currently accepted morphological criteria, gemmulofugal synapses can be identified consistently and with confidence at all levels in the EPL: they are particularly clearly and unambiguously resolved in E-PTA and BIUL preparations. At least the majority of gemmulofugal and mitrofugal synapses are closely associated in reciprocal pairs, as many previous authors have reported. Furthermore, there are approximately as many gemmulofugal as mitrofugal synapses in the EPL, which supports the long-standing proposal that the overall synaptic relationship between granule cells and mitral cells is a reciprocal one. We conclude that the challenge of Ramon-Moliner to the reality and significance of the reciprocal synapse is not well-founded.

Animals↗
PubMed1977

Neurons in layer I of the developing occipital cortex of the rat.

This paper describes the neurons in layer I of the rat occipital cortex, and traces postnatal changes in the numbers and morphology of the different cell types therein. Golgi-Cox and Nissl material from adults and from 0.5,2,4,6,8,10,11,12,13,14,15,16,18,20,24,28 and 35 day-old rats, was utilized. Horizontal, vertical and classical non-pyramidal cells without axons were recognized. Horizontal cells included foetal horizontal cells (Retzius-Cajal cells) and persisting horizontal cells. The former were fully differentiated and numerous at birth and were bipolar, with dendrite and axon extending from opposite poles, and fine ascending (vertical) branches. Some such cells possessed two axons. Almost all degenerated and disappeared over the first two to three postnatal weeks. An analogy with Rohon-Beard cells is drawn and it is suggested that these cells receive an early input which is subsequently withdrawn and/or concentrated on cells in deeper layers. There is no evidence of transformation of foetal to persisting horizontal cells, which are not numerous and most commonly give rise to two dendrites from opposite perikaryal poles. Vertical cells, with spinous dendrites and descending axons, differentiate and reach adult numbers by the end of the first postnatal week. Classical non-pyramidal cells include spinous and spine-free varieties, resemble those in deeper layers, and are mature by the end of the third postnatal week. In the upper stratum of layer I are small numbers of cells without axons.

Animals↗
PubMed1977

The neurons and their postnatal development in the ventral lateral geniculate nucleus of the rat.

The morphology and distribution of neurons in the ventral lateral geniculate nucleus (vLGN) of adult rats, and the postnatal growth and differentiation of these neurons were studied in Golgi-Cox preparations. In the adult, two main cell classes were recognized: class A cells and class B cells. The former are assumed to be projection neurons. The latter closely resemble the class B cells of the dorsal lateral geniculate nucleus and are interpreted as presynaptic dendrite-bearing interneurons. Class A cells predominated and three subtypes were tentatively identified: small--medium size multipolar neurons, with short, branched spiny dendrites (most numerous in dorsolateral vLGN); medium--large fusiform cells with one or two stem dendrites at each pole (most numerous in medial vLGN); large multipolar neurons with long, sparsely branched dendrites (most numerous in ventral vLGN). Class A and B cells were distinguishable at birth and showed parallel cell body size increases up to postnatal day 24. The dendrites of both classes of cell also reached the adult stage of differentiation at about day 24 but the differentiation of class B cell dendrites lags slightly behind that of class A cell dendrites.

Animals↗
PubMed1977

The postnatal development of neurons in the dorsal lateral geniculate nucleus of the rat: a Golgi study.

The postnatal differentiation of neurons in the dorsal lateral geniculate nucleus of the albino rat was studied using the Golgi-Cox technique. At least four animals were used at postnatal ages 12 hours, 2, 4, 6, 8, 10, 11, 12, 13, 14, 15, 16, 18, 20, 24, 28, 35 days and adult. Presumptive thalamo-cortical projection cells (Class A cells of Grossman et al., '73) and non-projection, intrinsic neurons (Class B cells) are distinguishable at 12 hours after birth. At this stage both types of neuron are immature, with prominent growth cones at their dendritic extremities. Dendritic growth and differentiation appear to be complete by 18 days. Relay cells display two apparent "growth spurts" characterized by noticeable enlargement of the perikaryon and a marked increase in dendritic length and complexity. One occurs between days 4 and 6 and coincides with a period of enhanced synaptogenesis and gliogenesis: the second occurs between days 14 and 15, around the time of eye opening (day 14) and may be related to a further phase of increased synaptogenesis and gliogenesis (Karlsson, '67; Biesold et al., '76). Class B cells appear to "lag" behind class A cells in their initial postnatal differentiation, but also reach their mature condition by day 18.

Animals↗
PubMed1976

Microtubule fascicles in the stem processes of cultured sensory ganglion cells.

Microtubule fascicles, resembling those characterizing the initial segment of multipolar neurons, have been observed by electron microscopy within and close to the origin of the stem process of some unipolar ganglion cells in explant cultures of embryonic chick dorsal root ganglia. Each fascile comprised 2-6 closely spaced parallel microtubules linked by electron dense cross-bridges. Since similar observations have been made on stem processes in vivo, the possibility that linked microtubules occur commonly in this site is considered. The observations are discussed in relation to a possible correlation between the presence of microtubule fascicles and the initiation of action potentials.

Action Potentials↗