Contrasting patterns in the localization of glutamic acid decarboxylase and Ca2+/calmodulin protein kinase gene expression in the rat central nervous system

Synaptic distribution of afferents from reticular nucleus in ventroposterior nucleus of cat thalamus

This study was aimed at determining the synaptic circuitry that contributes to the alterations in thalamic function that accompany changes in behavioral states. The somatosensory sector of the thalamic reticular nucleus (RTN) was identified by microelectrode recording in cats and injected with Phaseolus vulgaris-leucoagglutinin (PHA-L). The axons of labeled RTN cells gave rise to collaterals within the RTN and continued into the dorsal thalamus where they terminated predominately in the ventral posterior lateral nucleus (VPL). After small injections in the upper limb representation of RTN, most labeled terminations in VPL were confined to its medial part, suggesting the presence of a topographic organization in the projection. Terminations were concentrated in localized, focal aggregations of boutons. Combined electron microscopic immunocytochemistry, using immunogold labeling for gamma-aminobutyric acid (GABA), showed that the PHA-L labeled boutons were GABA-positive terminals that ended in symmetrical synapses. Eighty-two percent of these synapses were on dendrites of relay neurons, 8.5% on dendrites of interneurons, and 9.3% on somata. The terminals of RTN axons form the majority of axon terminals ending in symmetrical synapses in VPL. Their concentration on relay neurons probably underlies the capacity of the RTN projection to reduce background activity of VPL relay neurons in the awake state and to maintain oscillatory behavior of these neurons in drowsiness and early phases of sleep.

Distribution of four types of synapse on physiologically identified relay neurons in the ventral posterior thalamic nucleus of the cat

This study was aimed at providing quantitative data on the thalamic circuitry that underlies the central processing of somatosensory information. Four physiologically identified thalamocortical relay neurons in the ventral posterior lateral nucleus (VPL) of the cat thalamus were injected with horseradish peroxidase and subjected to quantitative electron microscopy after pre- or postembedding immunostaining for gamma-aminobutyric acid to reveal synaptic terminals of thalamic inhibitory neurons. The four cells all had rapidly adapting responses to light mechanical stimuli applied to their receptive fields, which were situated on hairy or glabrous skin or related to a joint. Their dendritic architecture was typical of cells previously described as type I relay cells in VPL, and they lacked dendritic appendages. Terminals ending in synapses on the injected cells were categorized as RL (ascending afferent), F (inhibitory), PSD (presynaptic dendrite), and RS (mainly corticothalamic) types and were quantified in reconstructions of serial thin sections. RL and F terminals formed the majority of the synapses on proximal dendrites (approximately 50% each). The number of synapses formed by RL terminals declined on intermediate dendrites, but those formed by F terminals remained relatively high, declining to moderate levels (20-30%) on distal dendrites. RS terminals formed moderate numbers of the synapses on intermediate dendrites and the majority (> 60%) of the synapses on distal dendrites. Synapses formed by PSDs were concentrated on intermediate dendrites and were few in number (approximately 6%). They formed synaptic triads with F terminals and rarely with RL terminals. On somata, only a few synapses were found, all made by F terminals. The total number of synapses per cell was calculated to be 5,584-8,797, with a density of 0.6-0.9 per micrometer of dendritic length. Of the total, RL terminals constituted approximately 15%, F terminals approximately 35%, PSD terminals approximately 5%, and RS terminals approximately 50%. These results provide the first quantitative assessment of the synaptic architecture of thalamic somatic sensory relay neurons and show the basic organizational pattern exhibited by representatives of the physiological type of relay neurons most commonly encountered in the VPL nucleus.

Specific distribution of Ca2+/calmodulin-dependent protein kinase II alpha and beta isoforms in some structures of the rat forebrain

The immunohistochemical distribution of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) alpha and beta isoforms in the rat forebrain was examined by using monoclonal antibodies specific to each isoform. The present study confirmed that alpha and beta immunoreactivities are localized only in neuronal elements. At the light microscopic level, specific distribution patterns of these isoforms and staining characteristics were recognized in some regions of the forebrain as follows. Firstly, alpha-immunoreactive neurons were more homogeneously distributed throughout the cellular layers of the cerebral cortex (i.e., layers II-VI) than beta-immunoreactive ones. Secondly, neurons in the globus pallidus were immunostained by the anti-beta antibody, but not by the anti-alpha antibody. Thirdly, neurons in the medial habenular nucleus, the subthalamic nucleus and the reticular thalamic nucleus were more densely stained with the anti-beta antibody than with the anti-alpha antibody. However, marked differences were not observed in the hippocampal formation at the light microscopic level. The electron microscopic analysis of the cerebral cortex demonstrated that subcellular localizations of alpha- and beta-immunoreactive products within the cortical neurons were quite dissimilar: (i) the nucleus was stained only with the anti-alpha antibody, but not with the anti-beta antibody, and (ii) beta-immunoreactive products were more sporadically localized in the cytoplasms of the perikarya and dendrites than the alpha-immunoreactive ones. These regional and subcellular differences between the distribution patterns of alpha and beta immunoreactivities suggest the functional diversity of CaM kinase II alpha and beta isoforms in the central nervous system.

Cellular localization of type II Ca2+/calmodulin-dependent protein kinase in the rat basal ganglia and intrastriatal grafts derived from fetal striatal primordia, in comparison with that of Ca2+/calmodulin-regulated protein phosphatase, calcineurin

We investigated immunohistochemically the cellular localization of multifunctional type II Ca2+/calmodulin-dependent protein kinase in the rat basal ganglia and intrastriatal grafts derived from fetal striatal primordia, in comparison with that of calcineurin, a reliable marker for striatal medium-sized spinous neurons. The type II Ca2+/calmodulin-dependent protein kinase-positive neurons were of medium size, with a mean diameter of 16.1 +/- microns (average +/- S.D., n = 72, range 13.6-18.3 microns) and comprised approximately 70% of the total neuronal population in the striatum. Light microscopy showed that the type II Ca2+/calmodulin-dependent protein kinase-positive cells had round, triangular or polygonal cell bodies with relatively little cytoplasm. Analysis of serial sections showed that type II Ca2+/calmodulin-dependent protein kinase and calcineurin immunoreactivities were co-localized in the striatal neurons examined with a similar distribution pattern. Type II Ca2+/calmodulin-dependent protein kinase-positive cells were always immunoreactive for calcineurin and cells negative for type II Ca2+/calmodulin-dependent protein kinase showed no apparent calcineurin immunoreactivity. Type II Ca2+/calmodulin-dependent protein kinase-positive nerve fibers in the globus pallidus and substantia nigra almost disappeared following striatal ischemic injury produced by transient middle cerebral artery occlusion and cerebral hemitransection, respectively, suggesting that these immunopositive fibers were striatal projections. Thus, most type II Ca2+/calmodulin-dependent protein kinase-positive neurons in the rat striatum are considered to be of the medium-sized spinous type. Type II Ca2+/calmodulin-dependent protein kinase or calcineurin immunoreactivity was also observed in a large number of neurons in transplants derived from fetal striatal primordia grafted into striatal ischemic lesions. In addition, type II Ca2+/calmodulin-dependent protein kinase- or calcineurin-immunoreactive nerve fibers appeared in the deafferented globus pallidus of the host rats, suggesting that the striatopallidal pathway was reformed by striatal projection neurons of the transplants. This finding may also indicate that Ca2+/calmodulin-regulated enzymes are useful for tracing striatal projection fibers as endogenous marker proteins.

Differential regulation of brain-derived neurotrophic factor and type II calcium/calmodulin-dependent protein kinase messenger RNA expression in Alzheimer's disease

The relative levels of messenger RNA for brain-derived neurotrophic factor and the alpha subunit of calcium/calmodulin-dependent protein kinase type II were examined in hippocampal sections from Alzheimer's diseased and age matched non-diseased brains by in situ hybridization histochemistry. Consistent with previous reports in monkey and rodent, calcium/calmodulin-dependent protein kinase II messenger RNA was prevalent throughout the dentate gyrus, all the principal hippocampal subfields, and adjacent cortical regions. A distribution consistent with the dendritic localization of calcium/calmodulin-dependent protein kinase II was also observed. In contrast, brain-derived neurotrophic factor messenger RNA levels were much lower than calcium/calmodulin-dependent protein kinase II messenger RNA levels and were less widely distributed. Within the hippocampus of Alzheimer's diseased brains, levels of calcium/calmodulin-dependent protein kinase II messenger RNA were increased and levels of brain-derived neurotrophic factor messenger RNA were decreased in comparison with matched controls. These changes were consistently seen in four out of six cases processed for both messenger RNA species and ranged from 150-300% relative to non-diseased brain tissue for calcium/calmodulin-dependent protein kinase II and 20-70% for brain-derived neurotrophic factor. These results suggest that within the Alzheimer's hippocampus an altered program of gene expression is occurring leading to aberrant levels of both calcium/calmodulin-dependent protein kinase II and brain-derived neurotrophic factor messenger RNA. Previous studies of the activity-dependent regulation of these messenger RNA species suggest these results are consistent with a decrease in afferent activity within the Alzheimer's hippocampus.

Immunohistochemical detection of calcium/calmodulin-dependent protein kinase II in the spinal cord of the rat and monkey with special reference to the corticospinal tract

Calcium/calmodulin-dependent protein kinase II is a prominent enzyme in the mammalian brain that phosphorylates a variety of substrate proteins. In the present study, monoclonal antibodies that specifically recognize either the alpha or the beta isoforms of this enzyme were used to determine the distribution of these isoforms within the rat and monkey spinal cord. In the rat, the corticospinal tract consists of two components: the dorsal corticospinal tract, which occupies the ventralmost aspect of the dorsal funiculus; and the ventral corticospinal tract, which occupies an area adjacent to the ventral median fissure. Both dorsal and ventral corticospinal tract fibers were strongly immunopositive for the alpha-antibody. Unilateral ablation of the sensorimotor cortex of the rat eliminated the alpha-immunoreactive staining in the contralateral dorsal corticospinal tract. The neuropil in the superficial laminae of the dorsal horn (Rexed's laminae I and II) was densely stained with the alpha-antibody, whereas the neuropil in laminae IV-X was immunonegative. Dense alpha-immunopositive neurons were also distributed in the head of the dorsal horn (laminae I-IV). In contrast to the strong alpha-immunoreactivity seen in the dorsal corticospinal tract fibers, only very weak beta-immunoreactivity was observed in this tract. Moderate beta-immunoreactive products were distributed homogenously throughout the neuropil of the gray matter, although the neuropil of the superficial laminae of the dorsal horn (laminae I and II) was stained more strongly than the other regions of the gray matter (laminae III-X). Neuronal components in all laminae were immunopositive for the beta-antibody. Thus, motoneurons in the ventral horn, which were immunonegative for the alpha-antibody, were immunopositive for the beta-antibody. This selective distribution pattern of immunoreactivity of alpha- and beta-antibodies in the rat was also present in the monkey spinal cord, although the alpha-immunopositive corticospinal tract fibers in the monkey descended in the lateral funiculus as the lateral corticospinal tract instead of passing through the dorsal funiculus, as is the case in the rat. The differential distribution of immunoreactivity in the spinal cord suggests that these two isoforms of calcium/calmodulin-dependent protein kinase II may have different functional roles in the spinal cord.

Immunohistochemical localization of Ca2+/calmodulin-dependent protein kinase II in the rat retina

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) consisting of alpha and beta isoforms is highly expressed in the central nervous system and is implicated in the regulation of various Ca(2+)-dependent physiological processes. We investigated the immunohistochemical distribution of the alpha and beta isoforms of this enzyme in the rat retina, using highly specific monoclonal antibodies which recognize each isoform. Immunoblotting revealed that not only the alpha but also the beta isoform of CaM kinase II were expressed in the retina. The immunohistochemical study showed that highly alpha-immunoreactive products were localized in amacrine cells in the inner nuclear layer and displaced amacrine cells and ganglion cells in the ganglion cell layer. In addition, two well-defined bands within the inner plexiform layer were densely stained with the anti-alpha antibody. By contrast, immunoreactivity against the anti-beta antibody was very weak in the same neuronal components of the retina. beta-Immunoreactive products were homogeneously distributed throughout the inner plexiform layer and no well-defined bands were detected in this layer. Glial cells such as Müller cells were immunoreactive neither to alpha nor beta antibody. A possible co-existence of choline acetyl transferase (ChAT) within CaM kinase II alpha-immunopositive neurons was examined by evaluating adjacent sections stained with anti-CaM kinase II alpha antibody and anti-ChAT antibody, respectively. The distribution of CaM kinase II alpha immunoreactivity in the rat retina was remarkably similar to that of ChAT immunoreactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of RNAs present in synaptodendrosomes: dendritic, glial, and neuronal cell body contribution

"Synaptodendrosomes" are subcellular fractions that contain pinched-off axon terminals and dendrites. These fractions are a potential source of RNAs that are localized in dendrites. However, these fractions may also contain RNAs that are seen in situ in neuronal cell bodies and glia. To evaluate whether synaptodendrosomes could be used as a source of dendritic RNA, we studied the RNA content of this fraction as compared with RNA isolated from total forebrain and a cell body-enriched fraction. RNA was analyzed by gel electrophoresis, oligo-dT chromatography, and northern blot hybridization. RNA from synaptodendrosomes contained a greater proportion of low-molecular-weight nonpolyadenylated RNAs. RNAs known to be present in dendrites (mRNA for the alpha subunit of the calcium/calmodulin-dependent protein kinase II and the polymerase III transcript BC1) were detected in synaptodendrosomes; RNAs that are restricted to neuronal and glial cell bodies (mRNAs for the 68-kDa neurofilament protein, 43-kDa growth-associated protein, beta-tubulin, and beta-actin) were present only at low levels. However, the mRNA for glial fibrillary acidic protein (seen in situ in glial cell bodies and processes) was present at high levels in the synaptodendrosomes. These results support and extend previous studies indicating that a limited subset of mRNAs is present in neuronal and astrocyte processes and reveal that both of these types of mRNAs are present in synaptodendrosomes. Thus, synaptodendrosomes may be useful as a source of dendritic RNAs, but it will be necessary to develop strategies to subtract mRNAs present in astroglial processes.

Comparative localization of mRNAs encoding two forms of glutamic acid decarboxylase with nonradioactive in situ hybridization methods

Nonradioactive in situ hybridization methods with digoxigenin-labeled cRNA probes were used to localize two glutamic acid decarboxylase (GAD) mRNAs in rat brain. These mRNAs encode two forms of GAD that both synthesize GABA but differ in a number of characteristics including their molecular size (65 and 67 kDa). For each GAD mRNA, discrete neuronal labeling with high cellular resolution and low background staining was obtained in most populations of known GABA neurons. In addition, the current methods revealed differences in the intensity of labeling among neurons for each GAD mRNA, suggesting that the relative concentrations of each GAD mRNA may be higher in some groups of GABA neurons than in others. Most major classes of GABA neurons were labeled for each GAD mRNA. In some groups of GABA neurons, the labeling for the two mRNAs was virtually identical, as in the reticular nucleus of the thalamus. In other groups of neurons, although there was substantial labeling for each GAD mRNA, labeling for one of the mRNAs was noticeably stronger than for the other. In most brain regions, such as the cerebellar cortex, labeling for GAD67 mRNA was stronger than for GAD65 mRNA, but there were a few brain regions in which labeling for GAD65 mRNA was more pronounced, and these included some regions of the hypothalamus. Finally, some groups of GABA neurons were predominantly labeled for one of the GAD mRNAs and showed little or no detectable labeling for the other GAD mRNA, as, for example, in neurons of the tuberomammillary nucleus of the hypothalamus where labeling for GAD67 mRNA was very strong but no labeling for GAD65 mRNA was evident. The findings suggest that most classes of GABA neurons in the central nervous system (CNS) contain mRNAs for at least two forms of GAD, and thus, have dual enzyme systems for the synthesis of GABA. Higher levels of one or the other GAD mRNA in certain groups of GABA neurons may be related to differences in the functional properties of these neurons and their means of regulating GABA synthesis.

The inferior colliculus of GEPRs contains greater numbers of cells that express glutamate decarboxylase (GAD67) mRNA

Previous studies have shown significantly greater GABA levels and numbers of GABAergic neurons in the central nucleus of the inferior colliculus (ICCN) of genetically epilepsy-prone rats (GEPR-9s). In the present study, in situ hybridization and emulsion autoradiographic techniques were used to determine whether there are also elevated numbers of ICCN cells that contain the 67-kD form of mRNA for the GABA synthesizing enzyme, glutamate decarboxylase (GAD), in GEPR-9s as compared to normal Sprague-Dawley (SD) rats. Hybridization with a 35S-labeled RNA probe complementary to a span of monkey GAD mRNA labeled cells throughout the brain including the ICCN. Labeled cells in the ICCN appeared to be of different sizes that corresponded with previous descriptions of GABAergic neurons from immunocytochemical studies. In the GEPR-9s, a larger number of GAD67 cRNA labeled neurons was observed in the ICCN as compared to SD rats. The external nucleus of the inferior colliculus was also found to contain significantly greater numbers of GAD67 cRNA labeled neurons whereas in the frontal cortex, a region of the brain that is not required for audiogenic seizure activity in GEPR-9s, there were no significant differences in hybridization between GEPR-9s and SD rats. Interestingly, within the superficial layers of the superior colliculus there was a higher density of hybridization in GEPR-9s than in SD rats indicating higher levels of GAD expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Dendritic localization of type II calcium calmodulin-dependent protein kinase mRNA in normal and reinnervated rat hippocampus

In situ hybridization histochemistry has revealed a diffuse distribution of the alpha subunit of type II calcium calmodulin-dependent protein kinase (CaM II kinase alpha) mRNA in the neuropil of regions containing CaM II kinase alpha-expressing cells and has led some to propose that it may be expressed in dendrites. In order to determine if CaM II kinase alpha mRNA is expressed in dendrites and if the gene encoding CaM II kinase alpha is regulated in response to synaptic reinnervation, we examined its expression in the hippocampus of normal rats, of rats that had received a unilateral injection of kainic acid and of rats with a unilateral entorhinal cortex lesion. The relatively specific elimination of the CA3 pyramidal cells by kainate lesions precisely correlated with the loss of CaM II kinase alpha cRNA hybridization in the stratum radiatum as well as the stratum pyramidale. Following entorhinal cortex lesions, during the period of new synapse formation in the dentate gyrus, there was no detectable change in the level of CaM II kinase alpha gene expression. These data suggest that CaM II kinase alpha mRNA is expressed in the dendrites of hippocampal pyramidal cells and, therefore, is likely to be expressed in dendrites in other regions of the central nervous system exhibiting CaM II kinase alpha cRNA labeling in the neuropil. However, changes in expression were not found to accompany new synapse formation.