Inhibitory Synaptic Terminals Research Articles

Transneuronal changes of the inhibitory circuitry in the macaque somatosensory thalamus following lesions of the dorsal column nuclei.

The inhibitory circuitry of the ventroposterolateral nucleus (VPL) of the macaque somatosensory thalamus was analyzed in normal animals and in those surviving for a few days or several weeks following a unilateral lesion of the cuneate nucleus, the source of medial lemniscal (ML) axons carrying information from the contralateral upper extremity. Inhibitory synaptic terminals in the VPL were defined as those that contain flattened or pleomorphic synaptic vesicles and that can be shown to be immunoreactive for gamma-aminobutyric acid (GABA). There are two types of these profiles: F axon terminals that arise from neurons of the thalamic reticular nucleus, and perhaps from VPL local circuit neurons (LCNs); and the dendritic appendages of LCNs that form presynaptic dendrites (PSDs). ML terminals normally have extensive synaptic interactions with PSDs but not with F axon terminals. Electron microscopic analyses revealed that cuneatus lesions resulted in a rapid loss of ML terminals and a statistically significant reduction in both F and PSD synaptic profiles. Confocal scanning microscopy also demonstrated a profound loss of GABA immunoreactivity in the deafferented VPL. These changes persisted for more than 20 weeks, without any evidence of reactive synaptogenesis of surviving sensory afferents or of inhibitory synapses. The changes in GABA circuitry are transneuronal, and the possible mechanisms that may underlie them are discussed. It is suggested that the altered GABAergic circuitry of the VPL in the monkey may serve as a model for understanding changes in somatic sensation in the human following peripheral or central deafferentation.

Altered distribution of inhibitory synaptic terminals in reeler cerebellum with special reference to malposition of GABAergic neurons

In immunohistochemical reactions against glutamic acid decarboxylase (GAD), γ-aminobutyric acid (GABA) and glycine (Gly), neurons in the mouse cerebellum showed the following reactivities: (1) the dendrites and cell bodies of the Purkinje cells were only GAD-positive, but their axonal terminals were GABA- and GAD-positive; (2) in both stellate and basket cells, the cell bodies and terminals were GABA- and GAD-positive but Gly-negative; (3) the Golgi cells were GABA-, GAD- and Gly-positive; (4) the granule cells were negative with all antibodies. Based on the populations of each type of neuron, identified by the properties mentioned above, the reeler cerebellum was divided into four regions, namely, (1) the molecular and Purkinje cell layers covering the surface of the cerebellum, where the stellate and basket cells were present as in normai mouse, (2) the granule cell layer, where the heterotopic Purkinje and stellate-type cells (including both stellate and basket cells) were present together with the granule and Golgi cells, (3) the region beneath the granule cell layer where Purkinje cells were present as clusters of several neurons, and in addition, the superficial zone of the central cell mass, where the stellate-type and Golgi cells were present among the Purkinje cells, and (4) the deep zone of the central cell mass, where the Golgi cells were exclusively present among the Purkinje cells. The heterologous synapses originating from inhibitory interneurons were formed on the Purkinje cells closely related to the distribution of these neurons.

Neuropeptide Y-Containing Neurons are Situated Predominantly Outside Cytochrome Oxidase Puffs in Macaque Visual Cortex

Layers II/III of the primary visual cortex contain a regular pattern of histochemically detectable cytochrome oxidase (CO)-rich "puffs," which differ from the interpuff regions in their thalamo-cortical and cortico-cortical connectivity, receptive-field properties, and the density of inhibitory GABA-containing synaptic terminals. We used an immunocytochemical method, in combination with cytochrome oxidase histochemistry, to analyze the spatial relationship between neurons that contain neuropeptide Y (NPY) and the CO puffs. Of a total of 606 neurons, only 2.6% of the NPY-containing cells are located in the puffs, whereas the rest are situated in the interpuffs, or at the interface between puffs and interpuffs. The number of NPY-containing neurons in the puffs is substantially less than that expected in an equal volume of the interpuffs (X2 = 13.86; df = 1; P less than 0.001). These observations indicate that columns containing the puffs may differ also from those in the interpuff regions in that they contain a unique array of chemically and morphologically distinct local circuit neurons.

Morphology and synaptic physiology of the main closer muscle in regenerating claws ofAlpheus

1. The present paper examines the changes that take place in the synaptic physiology and morphology of the main closer (Cl1) muscle during simultaneous regeneration of pincer and snapper claws. 2. Regenerating chelipeds appear one moult cycle after removal of the original claws. Both chelipeds are small but exhibit discrete differences in skeletal structure, Cl1 muscle morphology, and synaptic physiology. 3. After the first moult cycle excitatory and inhibitory synaptic terminals on Cl1 muscle fibers are formed at about the same time. Synaptic contacts are initially made on fibers in the proximal portion of the main closer muscle, and only later during the second moult cycle are synaptic connections made on more distally located Cl1 fibers. 4. After two moult cycles, the pincer main closer muscle is composed of fibers of different diameters and sarcomeres that exhibit a bimodal length distribution. The thicker fibers are located centrally in the muscle and have sarcomeres 2 and 3 μm long, while intermediate length sarcomeres are characteristic of thinner Cl1 fibers on the lateral and medial margins. 5. Prior to the third moult cycle, snapper Cl1 sarcomeres exhibit a unimodal distribution, whereas after 3 moults the sarcomeres show a bimodal distribution. Data from a series of snapper claws in different stages of regeneration revealed that there is a close matching between the synaptic physiology and the morphology of the main closer muscle fibers.