Random or selective neuroanatomical connectivity. Study of the distribution of fibers over two populations of identified interneurons in cerebral cortex

3-D reconstruction of neurons from multichannel confocal laser scanning image series

A confocal laser scanning microscope (CLSM) collects information from a thin, focal plane and ignores out-of-focus information. Scanning of a specimen, with stepwise axial (Z-) movement of the stage in between each scan, produces Z-series of confocal images of a tissue volume, which then can be used to 3-D reconstruct structures of interest. The operator first configures separate channels (e.g., laser, filters, and detector settings) for each applied fluorochrome and then acquires Z-series of confocal images: one series per channel. Channel signal separation is extremely important. Measures to avoid bleaching are vital. Post-acquisition deconvolution of the image series is often performed to increase resolution before 3-D reconstruction takes place. In the 3-D reconstruction programs described in this unit, reconstructions can be inspected in real time from any viewing angle. By altering viewing angles and by switching channels off and on, the spatial relationships of 3-D-reconstructed structures with respect to structures visualized in other channels can be studied. Since each brand of CLSM, computer program, and 3-D reconstruction package has its own proprietary set of procedures, a general approach is provided in this protocol wherever possible.

Neuroanatomical identification of crossmodal auditory inputs to interneurons in somatosensory cortex

Multisensory convergence is the first, requisite step in the process that generates neural responses to events involving more than one sensory modality. Although anatomical studies have documented the merging of afferents from different sensory modalities within a given area, they do not provide insight into the architecture of connectivity at the neuronal level that underlies multisensory processing. In fact, few anatomical studies of multisensory convergence at the neuronal level have been conducted. The present study used a combination of tract-tracing, immunocytochemistry, and confocal microscopic techniques to examine the connections related to crossmodal auditory cortical inputs to somatosensory area SIV. Axons labeled from auditory cortex were found in contact with immunolabeled interneurons in SIV, some of which also colocalized vesicular glutamate transporter 1, indicating the presence of an active, glutamatergic synapse. No specific subtype of inhibitory interneuron appeared to be targeted by the crossmodal contacts. These results provide insight into the structural basis for multisensory processing at the neuronal level and offer anatomical evidence for the direct involvement of inhibitory interneurons in multisensory processing.

A double dissociation of subcortical hippocampal efferents for encoding and consolidation/retrieval of spatial information

CA3 lesions impair encoding, whereas CA1 lesions impair retrieval during learning of a Hebb-Williams maze. CA3 efferents in the fimbria were transected, taking care to spare cholinergic and GABAergic afferents. CA1 efferents in the dorsal fornix were similarly transected. Fimbria transections, but not dorsal fornix transections, resulted in deficits for the encoding of spatial information during learning of a Hebb-Williams maze. Dorsal fornix, but not fimbria, transections resulted in deficits for retrieval of spatial memory during learning of a Hebb-Williams maze. These results reveal a double dissociation for the roles of CA3 and CA1 subcortical efferents in encoding and retrieval processes that mirror the double dissociation seen after excitotoxic lesions of CA1 and CA3. These data provide support for the theory that the cholinergic projections from the septal nuclei modulate the dynamics for encoding and consolidation/retrieval in the hippocampus.

3-D reconstruction of neurons from multichannel confocal laser scanning image series

A confocal laser scanning microscope (CLSM) collects information from a thin, focal plane and ignores out-of-focus information. The operator configures separate channels (laser, filters, detector settings) for each fluorochrome used in a particular experiment. Then, 3-D reconstructions are made from Z-series of confocal images: one series per channel. Channel signal separation is extremely important and measures to avoid bleaching are vital. Post-acquisition deconvolution of the image series is then performed to increase resolution. In the 3-D reconstruction program described in this unit, reconstructions can be inspected in real time from any viewing angle. By altering viewing angles and by switching channels off and on, the spatial relationship of 3-D-reconstructed structures with respect to structures seen in other channels can be studied. Since each brand of CLSM, computer program, and 3-D reconstruction package has its own proprietary set of procedures, a general approach is provided wherever possible.

Role of dCA3 efferents via the fimbria in the acquisition of a delay nonmatch to place task

Dorsal CA3, but not dorsal CA1, lesioned rats are impaired in the acquisition of a delay nonmatch to place task. In this study, dorsal CA3 efferent fibers in the fimbria were transected; while taking care to spare afferent fibers from the medial septum. Neurophysiological, anatomical tracing, and histochemical data suggest that the transection was selective to dorsal CA3 efferent fibers and spared afferents from the medial septum. Rats showed a deficit for acquisition, but not for performance once learned. One possible explanation is that a small change to the cholinergic inputs to dCA3 caused by a decrease in dorsal CA3 efferent signals reaching the medial septum may impair new learning but not performance of a task once learned.

Evidence for histamine as a neurotransmitter in the cardiac sympathetic nervous system

The colocalization of histamine (HA) and norepinephrine (NE) immunoreactivities was identified within the superior cervical ganglia neurons of the guinea pig. HA and NE immunoreactivity levels were significantly attenuated after chemical sympathectomy with 6-hydroxydopamine (6-OHDA). Coexistence of NE and HA was also visualized in the cardiac sympathetic axon and varicosities labeled with anterograde tracer biotinylated dextran amine. Depolarization of cardiac sympathetic nerve endings (synaptosomes) with 50 mM potassium stimulated endogenous HA release, which was significantly attenuated by 6-OHDA or a vesicular monoamine transporter 2 (VMAT2) inhibitor reserpine pretreatments. Compound 48/80, a mast cell releaser, did not affect cardiac synaptosome HA exocytosis. Furthermore, K+-evoked HA release was abolished by the N-type Ca2+-channel blocker ω-conotoxin but was not affected by the L-type Ca2+-channel blocker lacidipine. Cardiac synaptosome HA exocytosis was augmented by the enhanced synthesis of HA or the inhibition of HA metabolism. HA H3-receptor activation by ( R)-α-methylhistamine inhibited high K+-evoked histamine release. The HA H3receptor antagonist thioperamide enhanced K+-evoked HA release and blocked the ( R)-α-methylhistamine effect. The K+-evoked endogenous NE release was attenuated by preloading the cardiac synaptosomes with l-histidine or quinacrine. These inhibitory effects were reversed by thioperamide or antagonized by α-fluoromethylhistidine. Our findings indicate that high K+-evoked corelease of NE and HA may be inhibited by endogenous HA via activation of presynaptic HA H3-receptors. The H3-receptor may function as an autoreceptor, rather than a heteroreceptor, in the regulation of sympathetic neurotransmission and HA may be a novel sympathetic neurotransmitter.