The electroretinogram and visual evoked potential of freely moving rats

The vascularised rat retina could be one of the most useful experimental objects in visual neuroscience to understand human visual physiological and pathological processes. We report here on a new method of implantation for studying the visual system of freely moving rats that provides a rat model for simultaneous recording at corneal and cortical level and is stable enough to record for months. We implanted light emitting diodes onto the skull behind the eyeball to stimulate the eye with flashes and to light adapt the retina with constant light levels. A multistrand, stainless steel, flexible fine wire electrode placed on the eyeball was used for electroretinogram recording and screw electrodes (left/right visual and parietal cortical) were used to record the visual evoked potential and the electroencephalogram. In the present report we focus on the new method of implantation for recording the corneal flash electroretinogram of normal, freely moving rats simultaneously with the visual evoked cortical potential showing examples in various visual experiments. We also introduce a program for retinogram and visual evoked potential analysis, which defines various measures (latencies, areas, amplitudes, and durations) and draw attention to the benefits of this method for those involved in visual, functional genomic, pharmacological, and human ophthalmologic research.

An in vitro temporomandibular joint-nerve preparation for pain study in rats

A novel in vitro TMJ-nerve preparation was developed to quantitatively study peripheral sensory mechanisms of temporomandibular joint (TMJ). The TMJ region on one side (including mandibular head, disc, retrodiscal tissue and mandibular fossa) of adult Wistar albino rats was excised together with the auriculo-temporal nerve. The block was preserved in a modified Krebs-Henseleit solution saturated with O(2)/CO(2) (95/5%) gas mixture. Using a calibrated von Frey type apparatus, mechanical noxious stimulation was applied directly to various sites within the TMJ region. In addition, thermal and chemical noxious stimuli were also attempted. Stable recordings of single unit activities from the auriculo-temporal nerve could be obtained for as long as 5 h, which was sufficient to analyze the response properties of the TMJ units to various stimuli. This new preparation would be useful for investigating TMJ peripheral sensory mechanisms, especially pain, and potentially makes it possible to reveal neural mechanisms of temporomandibular arthralgia, a syndrome that has recently shown an increased incidence in clinical dentistry.

An improved version of embolic model of brain ischemic injury in the rat

A modified version of focal embolic stroke model has been developed in rats. Ischemic injury was induced by injection of a pre-formed clot into the middle cerebral artery (MCA). In the first series of experiments, the model was validated. Embolizing a pre-formed clot resulted in an infarction in the territory irrigated by the MCA. At 48 h after embolization, 2,3,5-triphenyltetrazolium chloride (TTC) staining showed that infarction volume was 42.1+/-15.6% (mean+/-S.D.) when 5 microl clot was injected (n=8) and 28.4+/-8.6% in the animals received 3.5 microl clot (n=8). The infarction volume between these two groups showed a significant difference (P<0.05). In the second series of experiments, the natural dissolution of the clot in the MCA was studied. Five min after embolization (n=6), clots were observed in the MCA of all the animals. Clots in the MCA were seen in 68 and 29% of the animals at 1 and 3 h, respectively, after embolization. These results suggest that the procedure described here produces a reliable and reproducible ischemic injury. The clots injected were dissolved in the MCA in relatively short period of time. The model shows a close similarity to thromboembolic stroke in human, and it provides a useful tool to investigate mechanisms and test thrombolytic agents in ischemic brain injury.

Increase of the ornithine decarboxylase/polyamine system and transglutaminase upregulation in the spinal cord of aged rats

We have investigated changes in ornithine decarboxylase (ODC) activity and in polyamine levels in the central nervous system of aged rats. We measured a significant increase of ODC catalytic activity in the spinal cord from 30 month-old rats (+105%) as compared to 4 month-old rats. No changes were noticed in the cerebellum, cortex and hippocampus from the same animals. A related putrescine increase was measured in the spinal cord of 30 month-old rats (+168%), together with a smaller increase of spermidine (+33%). A parallel increase (+78%) of the Ca2+-dependent transglutaminase activity was detected in the spinal cord of 30 month-old rats, while no changes were apparent in the cortex and cerebellum. Our observations indicate a possible role of the ODC/polyamine system during the normal process of ageing in rats and point to the spinal cord as the most sensitive area for this kind of modification. A possible role of protein polyamination by transglutaminase is discussed.

Distribution of Ca(2+)/calmodulin-dependent protein kinase I beta 2 in the central nervous system of the rat

Recently, we reported the mRNA localization of Ca(2+)/calmodulin-dependent protein kinase I beta 2 isoform (CaMKIbeta2) in the mouse nervous system. In the present study, polyclonal antibody against CaMKIbeta2 was generated and used to investigate the distribution of the enzyme within the central nervous system of the rat. Interestingly some differences were observed between the enzyme localization and previous mRNA detection [J. Neurochem. 268 (1999) 26512]. The strongest expression of the enzyme was found in pontine nuclei. Immunopositive fibers could be traced through the middle cerebellar peduncle until they reached the cerebellum. Quite strong staining could also be observed in almost all of the neurons in the neocortex, hippocampus, amygdala, hypothalamus, brainstem and cerebellum, including the nuclei of the cranial nerves and Purkinje cell layer of the cerebellar cortex which was not clearly detected in the previous in situ hybridization study. In the spinal cord, CaMKIbeta2 could be detected in the gray matter with stronger expression in the dorsal horn. CaMKIbeta2 showed very strong nuclear localization but was also present in the cytoplasm of some neurons. Such localization suggests that CaMKIbeta2 may be involved in many neuronal functions in the central nervous system, including the possibility of important roles in nuclear signal transduction.

Continual replacement of newly-generated olfactory neurons in adult rats

It has been known that stem cells do exist in the central nervous system, and adult neurogenesis is continually taking place in the olfactory bulb during life. We report here, with the combined method of autoradiography using (3)H-thymidine and immunohistochemistry for a neuronal marker, that 65.3-76.9% of calretinin-immunoreactive bulbar neurons are replaced during the short period of 6 weeks in the adult rodent. The results indicate that neuronal replacement is a common phenomenon in the olfactory bulb during life.

Phylogenetic study on distribution and chromogranin/secretogranin content of histamine immunoreactive elements in the gut

The distribution of histamine-immunoreactive (HA-IR) elements and possible coexistence of chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII) were immunohistochemically studied in gut specimens of various vertebrate species. In fish, HA-IR cells were distributed mainly within the gastric and duodenal mucosa, and nerve fibres in the gastric myenteric plexus. Only the gastric HA-IR cells co-stored SgII. In frog specimens, HA-IR endocrine cells and nerve fibres were found in the distal stomach wall, but SgII coexisted only in the nerve fibres. In lizard, HA-IR endocrine cells were widely distributed from the oesophagus to the small intestine, but only those in the stomach co-stored CgA, CgB and SgII. In chick, HA-IR cells were found in the proventriculus and almost all co-stored all three proteins. In rat, HA-IR cells were accumulated in the oxyntic mucosa and all of them constantly immunostained for CgA only.

Different patterns in the histology and autofluorescence of the Harderian glands of the Syrian Hamster, rat, mouse, Mongolian gerbil and guinea pig

The purpose of this study was to compare the natural fluorescence in the Harderian glands of the Syrian hamster, rat, mouse, Mongolian gerbil and guinea pig (both sexes). For each species, 10 animals (five males and five females) were used. Histological autofluorescence studies were performed using a fluorescence microscope (450-490 nm filter). Two different types of fluorescent cells were observed in both hamster (type AFI high intensity and type AFII, low fluorescence) and rat (type AFI, low fluorescence and type AFII, high fluorescence) Harderian glands. The fluorescence was basally located in all mice cells, whereas it was observed near the epithelial cell nuclei in the Mongolian gerbil (occupying two-thirds and one-third of the cells in males and females, respectively). A high intensity of fluorescence was present throughout the acinar cells in the guinea pig. The patterns of fluorescence identified exhibited a sexual dimorphism in all species studied. These results demonstrate that the Harderian glands of the animal species examined exhibit a variety of histological autofluorescence patterns.

Neurohistological and behavioral evidence for lordosis-inhibiting tract from lateral septum to periaqueductal gray in male rats

To verify the anatomical and functional connection of the lateral septum (LS) and periaqueductal gray (PAG) in inhibiting female sexual behavior, lordosis, in male rats, retrograde (Fluoro-Gold, FG) or anterograde (Phaseolus vulgaris-leucoagglutinin, PHA-L) tracer was injected into the PAG or LS on the right side, respectively, and FG-labeled cells or PHA-L-labeled axons in the forebrain and mesencephalon were determined in estrogen-treated castrated male rats. A ventral cut (VC) of the septum and a behavioral test were also conducted in some FG-injected rats. Furthermore, lordosis behavior was observed after chemical destruction of the septum by ibotenate. As a result, the lordosis quotient (LQ) in VC males was higher than that in control males without VC. FG-labeled neuronal cell bodies were found in the ipsilateral intermediate part of the LS in the control males but not in this area of the VC males. When neuronal cells in the intermediate part of the bilateral LS were completely destroyed by ibotenate, the LQ was higher than that in sham-lesioned male rats. These results suggest that a direct neural connection of the intermediate LS to the PAG has an inhibitory role in regulating lordosis in male rats. In addition, neuronal cell bodies in the intermediate LS exert an inhibitory influence. In the PHA-L experiment, labeled axons were seen in the ventral part of the LS, the medial forebrain bundle at the chiasmatic level, the lateral hypothalamus, the median region of the mesencephalon, and the rostral PAG in the side ipsilateral to the tracer injection site of the LS. Thus, these areas are thought to be involved in the pathway for lordosis-inhibition from the intermediate part of the LS to the PAG in male rats.

Ultrastructural features of the nitric oxide synthase-containing interneurons in the nucleus accumbens and their relationship with tyrosine hydroxylase-containing terminals

The ultrastructural features of neuronal nitric oxide synthase (NOS) -immunoreactive interneurons of rat nucleus accumbens shell and core were studied and compared. The NOS-containing subpopulation displayed characteristics similar to those previously described for nicotinamide adenine dinucleotide phosphate diaphorase-, neuropeptide Y, or somatostatin-containing striatal neurons, but also showed properties not previously associated with them, particularly the formation of both asymmetric and symmetric synaptic junctions. Inputs derived mainly from unlabeled terminals, but some contacts were made by NOS-immunolabeled terminals, by means of asymmetric synapses. Immunopositive endings that formed symmetric synapses were mainly onto dendritic shafts, whereas those that formed asymmetric synapses targeted spine heads. Morphometric analysis revealed that the core and shell NOS-stained neurons had subtly different innervation patterns and that immunostained terminals were significantly larger in the shell. A parallel investigation explored synaptic associations with dopaminergic innervation identified by labeling with an antibody against tyrosine hydroxylase (TH). In both shell and core, TH-positive boutons formed symmetric synapses onto NOS-containing dendrites, and in the core, TH- and NOS-immunolabeled terminals converged on both a single spiny dendrite and a spine. These results suggest that, in the rat nucleus accumbens, NOS-containing neurons may be further partitioned into subtypes, with differing connectivities in shell and core regions. These NOS-containing neurons may be influenced by a dopaminergic input. Recent studies suggest that nitric oxide potentiates dopamine release and the current study identifies the medium-sized, densely spiny neurons as a possible site of such an interaction.

Immunohistochemical analyses of DNA topoisomerase II isoforms in developing rat cerebellum

In mammalian cells, two isoforms of DNA topoisomerase II (topo IIalpha and topo IIbeta) have been identified. Topo IIalpha is essential in mitotic cells, whereas the function of topo IIbeta remains unclear. In the present study, we investigated the developmental control of topo II isoforms in two different neuronal lineages, cerebellar Purkinje cells and granule cells, by immunohistochemical analysis with isoform-specific monoclonal antibodies. As expected, proliferating cells in the neuroepithelium and in the external germinal layer (EGL) were topo IIalpha immunopositive. The migrating as well as differentiating Purkinje cells and granule cells showed an enhanced topo IIbeta immunoreactivity. The postmitotic granule cells in the postnatal EGL showed an abrupt transition of expressed topo II isoforms from IIalpha to IIbeta. The transition was clearly coincident with the completion of final cell division and the initiation of terminal differentiation because no increase of the topo IIbeta immunoreactivity was observed in the spreading EGL cells that are still in the cell division cycle. The topo IIbeta signal was detected in both nucleoplasm and nucleolus of differentiating cells. However, the nucleoplasmic signal decreased significantly as the cells reached terminal differentiation. The residual topo IIbeta in nucleoli was shown to occupy an unique location with respect to other nucleolar proteins, nucleolin and DNA topoisomerase I. Our findings indicate that both Purkinje cells and granule cells express the topo II isoforms in a similar timing during the cerebellar development and also suggest that topo IIbeta localized in nucleoplasm is the functional entity involved in neuronal differentiation.

Characterization of microglial cells and their response to stimulation in an organotypic retinal culture system

An organotypic culture system of the early postnatal rat retina was developed to study microglial activation within a tissue environment. One day after tissue preparation, microglial cells of the ganglion cell/nerve fiber layer revealed features of activation. Cells acquired an ameboid morphology as revealed by Bandeiraea simplicifolia lectin staining. Proliferation-as revealed by Ki67 immunocytochemistry-resulted in higher cell densities. In the supernatant, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and monocyte chemoattractant factor-1 (MCP-1) were detected by using specific enzyme-linked immunosorbent assay systems, activated microglia being the most likely source of their release. After 6 days in vitro (div), microglial cells regained their resting morphology, and cell counts returned to control levels. Concomitantly, the release activity decreased to undetectable levels. When slices were treated at this later stage of cultivation (>6 div) with bacterial lipopolysaccharide (LPS; 100 ng/ml for 24 hours), microglial cells became activated, as revealed by a change in morphology. In parallel, the LPS treatment also resulted in high levels of TNF-alpha, IL-6, and MCP-1 in the culture medium. Both the release from the tissue and the morphological changes of the microglia were reversible. Seventy-two hours after LPS removal, only microglia with ramified morphology were found, and release activities returned to baseline. These data suggest that the organotypic culture of the retina is a useful model for studying microglial activation from its resting form.

Persistence of vibrissal motor representation following vibrissal pad deafferentation in adult rats

The effect of sensory vibrissal pad denervation on M1 organization was studied in adult rats 2 weeks after the infraorbital nerve was severed. Cortical motor output organization was assessed mapping the representation size and thresholds of vibrissa movements evoked by intracortical electrical microstimulation (ICMS). Motor cortex output patterns of control and sham groups of rats were compared with those of rats that had received unilateral or bilateral infraorbital nerve lesions. The mean size of the vibrissa representation in both unilateral and bilateral input-deprived hemispheres was not significantly different from those in control and sham hemispheres. The mean threshold required to evoke vibrissa movements was significantly higher in both groups of deafferented hemispheres than in control and sham groups of hemispheres. In contrast, the mean threshold required to evoke other types of movements from both groups of input-deprived hemispheres were similar to those found in the control and sham groups of hemispheres. These results indicate that input-deprived vibrissal motor representation reflects lower-than-normal excitability, although the size and topographic relationship with neighboring representations are normal.

Interconnectivity between the amygdaloid complex and the amygdalostriatal transition area: a PHA-L study in rat

The amygdala orchestrates the formation of behavioral responses to emotionally arousing stimuli. Many of these responses are initiated by the central nucleus, which converges information from other amygdaloid nuclei. Recently, we observed substantial projections from the amygdala to the amygdalostriatal transition area, which is located dorsal to the central nucleus. These projections led us to question whether the amygdalostriatal transition area has a role in the initiation of behavioral responses in emotionally arousing circumstances. To explore this anatomically, we traced the interconnections between the amygdalostriatal transition area and the amygdaloid complex using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. The lateral (the medial division and the caudal portion of the dorsolateral division) and the accessory basal nuclei (the parvicellular division) provide moderate-to-heavy projections to the amygdalostriatal transition area. Projections back to the amygdala are light and are composed of thin, faintly stained varicose fibers that resemble the labeling of cholinergic terminals. The extra-amygdaloid outputs of the amygdalostriatal transition area are sparse and include moderate projections to the caudoventral globus pallidus, the ansa lenticularis, and the substantia nigra pars lateralis. These data suggest that the amygdalostriatal transition area is one of the major targets for projections originating in the lateral and accessory basal nuclei of the amygdala. Via these pathways, emotionally significant stimuli can evoke behavioral responses that are different from those initiated via projections from the amygdala to the central nucleus. One such candidate response is the orienting response (i.e., saccadic eye movements and head direction) in a pathway that includes a projection from the lateral/accessory basal nucleus of the amygdala to the amygdalostriatal transition area, and from there to the substantia nigra, pars lateralis.

Multiple zonal projections of the basilar pontine nuclei to the cerebellar cortex of the rat

This study revealed a sagittal zonal pattern of projections to the cerebellar cortex after hydraulic or iontophoretic injections of anterograde tracers (tritiated leucine, wheat germ agglutinin-horseradish peroxidase, or biotinylated dextrane amine) in the basilar pontine nuclei of Wistar rats. The zonal pattern of projection was observed only after injections of small size, whereas large injections labeled diffusely wide areas of the cerebellar cortex, masking the zonal projection because the fusion of contiguous stripes. Diverging projections to discrete sets of sagittal stripes in the two sides of the cerebellar cortex arose from single injections. The stripes of fiber terminals were sharply delimited on both sides by areas, interstripes, either virtually void of labeling or with a much lower density of labeling. Thus, the areas of the cerebellar cortex were parceled in sets of sagittal compartments, stripes and interstripes, by the pontine projections. Up to five compartments (three stripes and two interstripes) were observed in the paraflocculus, in the copula pyramidis, and in vermal lobule IX. Up to nine compartments (five stripes and four interstripes) were found in the crus I, the lobulus simplex, the paramedian lobule, and vermal lobules VI-VIII. Up to seven compartments (four stripes and three interstripes) were found in the crus II. Single injections into the basilar pontine nuclei usually labeled symmetric areas of the cerebellar cortex, which, in some cases, showed similar number of stripes. When this was not the case, the stripes were usually more numerous in the contralateral than in the ipsilateral side. All areas of the cerebellar cortex were projected upon, with zonation patterns from different regions of the basilar pontine nuclei. The projections of the basilar pontine nuclei to the cerebellar cortex were arranged according to a fixed pattern specific for each cortical area, independently of the number of stripes labeled within. The mean width of the stripes visualized in the single cortical areas of different rats was similar, despite the different size of the injections. The length of the stripes ranged widely in the various areas of different rats. The data collected in this study are consistent with the idea that all the mossy afferents to the cerebellar cortex are arranged with a zonal pattern.

Morphology of pulmonary rapidly adapting receptor relay neurons in the rat

The term rapidly adapting pulmonary stretch receptor (RAR) refers to one of the major pulmonary sensory receptors that responds to inflation and deflation of the lungs as well as to irritant stimuli with rapidly adapting irregular discharges. The functional role and central pathways are largely unknown. The aim of this study was to elucidate morphological characteristics of second-order neurons (RAR cells) activated by vagal afferent fibers originating from RARs. A mixture of horseradish peroxidase (HRP) and Neurobiotin was injected intracellularly into physiologically identified RAR cells in Nembutal-anesthetized, immobilized, and artificially ventilated Wister rats. Direct visualization of individual RAR cells (n = 12), including their somata, dendritic arborizations, and fine axonal branches with terminal boutons, was possible for the first time. Their somata were located in the commissural or medial subdivision of the nucleus of the solitary tract, caudal to the level of the area postrema. The RAR cells had, in addition to dendrites extending into the NTS area, one or two long dendrites extending laterally and/or ventrolaterally into the medullary reticular formation. The stem axons issuing from the RAR cells first coursed ventrolaterally toward the reticular formation in the vicinity of the ambiguus nucleus and then bifurcated into ascending and descending axons: three RAR cells possessed only ascending axons. Some of the ascending axons could be traced as far as the level of the facial nucleus and some of the descending axons beyond the spinomedullary junction. These ascending and/or descending axons gave off extensive axon collaterals distributing boutons within and in the vicinity of the ambiguus nucleus. These results, showing an anatomical substrate for the network implicated in RAR-evoked reflexes, provide useful clues for study of the RAR system.

Morphology of local axon collaterals of electrophysiologically characterised neurons in the rat medial septal/ diagonal band complex

Neurons in the medial septal/diagonal band complex (MS/DB) in vivo exhibit rhythmic burst-firing activity that is phase-locked with the hippocampal theta rhythm. The aim was to assess the morphology of local axon collaterals of electrophysiologically identified MS/DB neurons using intracellular recording and biocytin injection in vitro. Cells were classified according to previous criteria into slow-firing, fast-spiking, regular-spiking, and burst-firing neurons; previous work has suggested that the slow-firing neurons are cholinergic and that the other types are GABAergic. A novel finding was the existence of two types of burst-firing neuron. Type I burst-firing neurons had significantly longer duration after hyperpolarisation potentials when held at -60 mV, and at -75 mV, type I neurons exhibited a low-threshold spike with more rapid activation and inactivation kinetics than those of type II neurons. We have, also for the first time, described the main features of the local axon collaterals of the five neuron types. All filled neurons possessed a main axon that gave forth 1-12 local primary axon collaterals. All electrophysiological types, except for the type I burst-firing neuron, had a main axon that coursed toward the fornix. Myelination of the main axon was a prominent feature of all but the slow-firing neurons. Branching of the primary axon collaterals of the fast-spiking and type I burst-firing neurons was more extensive than that of the other cell types, with those of the slow-firing neurons exhibiting the least branching. All cell types possessed axon collaterals of the en passant type, and some in addition had twiglike or basketlike axon terminals. All cell types made synapses on distal dendrites; a proportion of the fast-spiking and burst-firing cells in addition had basketlike terminals that made synaptic contacts on proximal dendrites and on somata. Two morphological types of somata were postsynaptic to the basket cells: large (20-30-microm) oval cells with dark cytoplasm, and large oval cells with paler cytoplasm, often with an apical dendrite. The presence of lamellar bodies in the large dark neurons suggests that they may be cholinergic neurons, because previous work has localised these structures in some neurons that stain for choline acetyltransferase. Our work suggests therefore that there may be GABAergic neurons in the MS/DB that form basket synaptic contacts on at least two types of target cell, possibly cholinergic and GABAergic neurons, which means that the basket cells could play a key role in the generation of rhythmic activity in the MS/DB.

Androgen stimulates neuronal plasticity in the perineal motoneurons of aged male rats

Ten aged male rats (24 months of age) were castrated and implanted subcutaneously with Silastic capsules containing testosterone (T)(5 males) or nothing (5 males). Five sham-castrated males (25 months of age) served as controls. Four weeks after castration, cholera toxin-horseradish peroxidase (CT-HRP) was injected into the bulbocavernosus muscles and animals were killed 2 days later. The spinal cords containing the spinal nucleus of the bulbocavernosus (SNB) were dissected, processed with a modified tetramethylbenzidine method for visualization of retrogradely transported CT-HRP, and examined ultrastructurally. Neuronal structures apposing the membranes of 150 CT-HRP-labeled SNB motoneurons were analyzed by measuring the percentage of somatic membranes covered by synaptic contacts, synaptoid contacts, and neuron-neuron contacts. Most of the neuronal structures in the control and experimental SNB motoneurons consisted of synaptic contacts. The mean percentage of somatic membranes covered by synapses in castrated, aged males treated with T was significantly greater than that in control or castrated animals. Size and number of synaptic contacts per unit length of somatic membranes in castrated, aged males treated with T were also significantly greater than those in control or castrated animals. Plasma levels of T in castrated, aged males treated with T were significantly greater than that in controls. These results suggest that the SNB motoneurons of aged male rats retain a considerable synaptic plasticity in response to androgen, and that androgen may be, at least in part, involved in the process of aging of the SNB system in male rats.

Local differences in vagal afferent innervation of the rat esophagus are reflected by neurochemical differences at the level of the sensory ganglia and by different brainstem projections

The objective of the present study was to characterize further the vagal afferent fibers in the rat esophagus, particularly those in its uppermost part, their cell bodies in vagal sensory ganglia, and their central projections. We applied immunohistochemistry for calretinin, calbindin, and calcitonin gene-related peptide (CGRP); retrograde tracing with FluoroGold; and transganglionic tracing with wheat germ agglutinin-horseradish peroxidase in combination with neurectomies. Vagal terminal structures in the muscularis propria of the whole esophagus consisted of calretinin-immunoreactive intraganglionic laminar endings that were linked to cervical vagal and recurrent laryngeal nerve pathways. The mucosa of the uppermost esophagus was innervated by a very dense net of longitudinally arranged, calretinin-positive fibers that were depleted by section of the superior laryngeal nerve. Distal to this area, the mucosa was virtually devoid of calretinin-immunoreactive vagal afferents. Calretinin-positive mucosal fibers in the upper cervical esophagus were classified into four types. One type, the finger-like endings, was sometimes immunoreactive also for CGRP. About one-third of cell bodies in vagal sensory ganglia retrogradely labeled from the upper cervical esophagus expressed CGRP, whereas two-thirds coexpressed calretinin and calbindin but not CGRP. In addition to the central subnucleus of the nucleus of the solitary tract, vagal afferents from the upper cervical esophagus also projected heavily to the interstitial subnucleus. This additional projection was attributed to mucosal afferents traveling through the superior laryngeal nerve. The present study provides a possible morphological basis for bronchopulmonary and aversive reflexes elicited upon stimulation of the esophagus.

Laminar organization of the pyramidal cell layer of the subiculum in the rat

The distribution of neurons in the subiculum of the rat that give rise to subcortical connections was studied using retrograde labeling with horseradish peroxidase conjugated to wheat germ agglutinin. Injections were made into the anteroventral thalamic nucleus, the medial mammillary nucleus, the nucleus accumbens, and the lateral septal nucleus. To facilitate the analysis, the hippocampal formation with adjacent cortices were "flattened," which allowed the cutting of sections perpendicular to the full septotemporal axis. Cells projecting to the anteroventral thalamic nucleus (AV cells), the medial mammillary body (MMB cells), and the nucleus accumbens (ACC cells) were observed consistently throughout the entire septotemporal (dorsoventral) and transverse extent of the subiculum (from field CA1 of the hippocampus to the presubiculum). In the transverse plane, the three kinds of projection cells were arranged in a laminar fashion: The AV cells were observed in the deepest portion of the subicular pyramidal cell layer, the ACC cells were observed in the most superficial portion of the layer, and the MMB cells were observed in the middle portion of the layer. Although this laminar arrangement was observed at all septotemporal levels of the subiculum, it was most apparent at the septal level. At more temporal levels, the "laminae" shifted such that the superficially located ACC cells were more prominent in the proximal half of the subiculum, whereas the AV cells were shifted toward the distal half of the subiculum. The average size of somata of the AV cells was 72.3 microm(2), that of the ACC cells was 105.2 microm(2), and that of the MMB cells was 121.8 microm(2). The connectional and cytoarchitectonic data indicate that there is a distinct sublamination of the subicular pyramidal cell layer, suggesting that the subiculum may be analogous to the infragranular layer (layers V and VI) of the isocortex.

Ultrastructural features of myenteric ganglia of adult Wistar rats (Rattus norvegicus)

The ultrastructural features of the ganglia of the myenteric plexus exhibit changes according to the animal species. These myenteric ganglia in the duodenum of adult rats of the Wistar strain were characterized ultrastructurally in this work. Those ganglia were depicted as compact structures, composed of neurones and glial cells, forming a dense neuropil surrounded by a continuous basal lamina and collagen fibrils. Glial cell bodies were smaller and apparently more frequent than neuronal cell bodies, being morphologically distinguished by nuclear features. In the neuronal extensions granular and agranular synaptic vesicles of different sizes predominate, in addition to mitochondria and myelinized profiles. Gliofilaments were not observed on the glial extensions of the rats.

Simultaneous intrastriatal and intranigral dopaminergic grafts in the parkinsonian rat model: role of the intranigral graft

The current transplantation strategy in experimental and clinical Parkinson's disease (PD) has been to place nigral dopaminergic grafts not in their ontogenic site (substantia nigra) but in their target area (striatum). Although intrastriatal dopaminergic grafts are capable of reinnervating the striatum, they fail to reinnervate the nigra, which may be an important factor limiting the efficacy of fetal tissue transplantation in parkinsonian patients. We have previously shown that simultaneous intrastriatal and intranigral dopaminergic grafts (double grafts) may provide a more complete restoration of the nigrostriatal circuitry (Mendez et al. [1996] J Neurosci 16:7216-7227; Mendez and Hong [1997] Brain Res 778:194-205). In the present study, we investigated the contribution of the intranigral graft to functional recovery in double-grafted hemiparkinsonian rats. Twenty Wistar rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway were divided into two groups and received either double grafts (n = 10) or intrastriatal grafts alone (n = 10). Following transplantation, both intrastriatally and double-grafted animals had a significant decrease in rotational behavior. However, only animals with double grafts exhibited a significant increase in contralateral adjusting step performance. The intranigral graft was subsequently lesioned by a second 6-OHDA injection. Following the second lesion, animals with double grafts exhibited a significant reversal of rotational behavior and a 51% reduction in contralateral adjusting step performance. The reversal in functional recovery correlated with a significant loss of intranigral grafted neurons. These results suggest that the intranigral graft has an important role in the functional recovery of double-grafted animals. Restoration of dopaminergic innervation to both the nigra and the striatum may be crucial for optimizing graft efficacy and may be a superior strategy in neural transplantation for PD.

Innervation pattern of different cartilaginous tissues in the rat

BACKGROUND

The innervation of skeletal tissues by sensory nerves is poorly understood - especially of nerve fibres which reach into the bony and cartilaginous tissue.

METHODS

Samples of rat cartilaginous tissues from different locations (knee joint, vertebral column, temporomandibular joint) were fixed by perfusion and decalcified. The distribution of protein gene product (PGP) 9.5-, calcitonin gene-related peptide (CGRP)- and tachykinin (TK)-immunoreactive axons was analysed using fluorescence immunohistochemistry.

RESULTS

Nerve fibres were detected in the outer regions of the hyaline cartilage of the knee joint, in the hyaline cartilage of the vertebral body, in the fibrocartilage of the intervertebral disc and menisci, and in the articular disc of the temporomandibular joint. Predominantly, they were found to be CGRP-immunoreactive.

CONCLUSION

The neuropeptidergic innervation of the hyaline cartilage in different locations and the presence of nerve fibres in the fibrocartilage might indicate that in addition to the classical neuronal afferent and efferent pathway these fibres may also mediate trophic actions like tissue adaptation and repair.

Tyrosine hydroxylase-expressing and/or aromatic L-amino acid decarboxylase-expressing neurons in the mediobasal hypothalamus of perinatal rats: differentiation and sexual dimorphism

In this quantitative and semiquantitative immunocytochemical study, the authors evaluated the differentiation of neurons expressing tyrosine hydroxylase (TH) and/or aromatic L-amino acid decarboxylase (AADC) in the mediobasal hypothalamus (MBH) of male and female rats on embryonic day 18 (E18), E20, and postnatal day 9 (P9). Four neuronal populations were distinguished according to either enzyme expression or neuron location. The earliest and most prominent first population was represented by TH-immunoreactive (IR)/AADC-immunonegative (IN) neurons that were detected initially at E18 and always were located in the ventrolateral region of the MBH. The second population of TH-IN/AADC-IR neurons was observed first at E20 and, after that time, was distributed dorsomedially. The third minor population of TH-IR/AADC-IR neurons initially was detected at E20 and was located dorsomedially. The fourth population was represented by TH-IR/AADC-IN neurons that were distributed in the dorsomedial region at any studied age. The numbers of TH-IR and AADC-IR neurons increased from their initial detection at E18 and E20 until P9. The area of TH-IR and AADC-IR neurons also increased from E18 to E20 and from E20 to P9, respectively. Both TH-IR and AADC-IR neurons showed sex differences in the neuron number, size, and optic density (OD). The numbers of TH-IR neurons in males exceeded those of females at E20 and at P9, although, at P9, sexual dimorphism was a characteristic only of the ventrolateral population. The area and OD of TH-IR neurons from females exceeded those from males in the entire mediobasal hypothalamus (MBH) at E18 and E20 but only in its dorsomedial region at P9. Sexual dimorphism also was an attribute of AADC-IR neurons at E20 and P9. Their number, size, and OD were significantly higher in females than in males. Thus, the MBH of perinatal rats contained two major populations of TH-IR/AADC-IN or TH-IN-AADC-IR neurons and a minor population of TH-IR/AADC-IR neurons. The differentiating neurons expressing either enzyme showed sexual dimorphism.

Calretinin in the entorhinal cortex of the rat: distribution, morphology, ultrastructure of neurons, and co-localization with gamma-aminobutyric acid and parvalbumin

Calretinin is a marker that differentially labels neurons in the central nervous system. We used this marker to distinguish subtypes of neurons within the general population of neurons in the entorhinal cortex of the rat. The distribution, morphology, and ultrastructure of calretinin-immunopositive neurons in this cortical area were documented. We further analyzed the co-localization of the marker with gamma-aminobutyric acid (GABA) and studied whether calretinin-positive neurons project to the hippocampal formation. Methods used included single-label immunocytochemistry at the light and electron microscopic level, retrograde tracing combined with immunocytochemistry, and double-label confocal laser scanning microscopy (CLSM). The entorhinal cortex contained calretinin-positive cells in a scattered fashion, in all layers except layer IV (lamina dissecans). Bipolar and multipolar dendritic configurations were present, displaying smooth dendrites. Bipolar cells had a uniform morphology whereas the multipolar calretinin cell population consisted of large neurons, cells with long ascending dendrites, horizontally oriented neurons, and small spherical cells. Retrograde tracing combined with immunocytochemistry showed that calretinin is not present in cells projecting to the hippocampus. Few synapic contacts between calretinin-positive axon terminals and immunopositive cell bodies and dendrites were seen. Most axon terminals of calretinin fibers formed asymmetrical synapses, and immunopositive axons were always unmyelinated. Results obtained in the CLSM indicate that calretinin co-exists in only 18-20% of the GABAergic cell population (mostly small spherical and bipolar cells). Thus, the entorhinal cortex contains two classes of calretinin interneurons: GABA positive and GABA negative. The first class is presumably a classical, GABAergic inhibitory interneuron. The finding of calretinin-immunoreactive axon terminals with asymmetrical synapses suggests that the second class of calretinin neuron is a novel type of a (presumably excitatory) interneuron.