Immunocytochemical study of parvalbumin, calbindin D-28k, and calretinin in the superficial dorsal horn of the rat spinal cord following unilateral hindpaw inflammation

The effect of noxious stimulation on the immunore-activity of the calcium-binding proteins parvalbumin (PV), calbindin-D-28k (CB) and calretinin (CR) was investigated in the superficial dorsal horn of lumbar levels L5-L3 of the rat spinal cord. Freund's adjuvant was injected unilaterally into the hindpaw to induce inflammation. Immunohistochemical techniques were utilized to investigate changes in the calcium-binding proteins 2h and 1, 2, 4, and 7 days after injection. At 24h after injection, a decrease in the intensity of fluorescence of PV-immunoreactive (IR) fibers was observed in the superficial layer (substantia gelatinosa) of the ipsilateral dorsal horn (L5-L3) in most animals. Comparatively fewer animals exhibited changes in the CB- and CR-IR fibers, except at the L3 level 2 days after, and at the L4 level 7 days after the hindpaw injection. After the peak response, at 24h in most animals, there was a decline in the number of responders at 2 days and no differences were noted at 4 days. However, at 7 days, there was again an increase in the number of animals revealing diminished fluorescence intensity in the ipsilateral substantia gelatinosa. Changes in immunoreactivity of calcium binding proteins in the interneurons of the superficial lumbar dorsal horn may reflect hyperactivity within these neurons following noxious stimulation.

Calretinin-containing neurons which co-express parvalbumin and calbindin D-28k in the rat spinal and cranial sensory ganglia; triple immunofluorescence study

The co-expression of calretinin with parvalbumin and calbindin D-28k was examined in the rat cranial and spinal sensory ganglia by triple immunofluorescence method. In the trigeminal and nodose ganglia, 9% and 5% of calretinin-immunoreactive neurons, respectively, also contained both parvalbumin- and calbindin D-28k immunoreactivity. These neurons had large cell bodies. In the trigeminal ganglion, they were restricted to the caudal portion. Such neurons were evenly distributed throughout the nodose ganglion. The co-expression could not be detected in the dorsal root, jugular or petrosal ganglia. Nerve fibers which co-expressed all the three calcium-binding proteins were observed in the inferior alveolar nerve but not the infraorbital nerve or palate. In the periodontal ligament, these nerve fibers formed Ruffini-like endings. These findings suggest that (1) the co-expression in trigeminal neurons is intimately related to their peripheral receptive fields; (2) the three calcium-binding proteins (calretinin, parvalbumin, calbindin D-28k) co-expressed in the trigeminal neurons may have mechanoreceptive function in the periodontal ligament.

Flotillin-1 in the substantia nigra of the Parkinson brain and a predominant localization in catecholaminergic nerves in the rat brain

The substantia nigra cells of a normal and Parkinson's disease human brain were obtained by the micropunch procedure and total RNA was isolated. Differential display RT-PCR of the total RNA revealed differentially expressed cDNAs that were identified by sequencing. This resulted in the identification of a panel of known and unknown differentially expressed genes. Complex I (NADH ubiquinone oxidoreductase) and Complex IV (cytochrome oxidase) whose expressions are decreased in Parkinson's disease were reduced in the Parkinson brain. Of the various differentially expressed genes, flotillin-1, also known as reggie-2, was of great interest to us. It is a relatively new protein which is an integral membrane component of lipid rafts and has been implicated in signal transduction pathway events. In situ hybridization histochemical studies with human and rat brain sections revealed the presence of this mRNA in discrete neuronal (and possibly glial) cells of the substantia nigra, locus coeruleus, cortex, hippocampus, hypothalamus, thalamus, motor nuclei, nucleus basalis, raphe nucleus, and other brain regions. Immunohistochemical studies revealed that flotillin-1 is not present in all the regions where the message was found. In the rat brain, the most prominent observation was the revelation of all catecholamine cells (dopamine, norepinephrine, epinephrine) by the flotillin-1 antibody (1:100 dilution). At a more concentrated dilution (1:10) other neuronal cells (e.g., cortex, thalamus, hindbrain) were observed. At both dilutions dense dopaminergic fibers were observed in the rat caudate-putamen, nigrostriatal tract, and substantia nigra. It is significant that there is an increased gene expression of flotillin-1 in the Parkinson substantia nigra/ventral tegmental area. The role of flotillin in these cells is unclear although it is interesting that the reggie-2/flotillin-1 gene was upregulated during retinal axon regeneration in the goldfish visual pathway (Schulte et al., Development 124:577-87, 1997) which suggests that flotillin-1/reggie-2 might play a role in axonal growth from the remaining substantia nigra cells of the Parkinson brain.

Effect of Brn-3a deficiency on parvalbumin-, calbindin D-28k-, calretinin- and calcitonin gene-related peptide-immunoreactive primary sensory neurons in the trigeminal ganglion

Immunohistochemistry for parvalbumin, calbindin D-28k, calretinin and calcitonin gene-related peptide (CGRP) was performed on the trigeminal ganglion and oro-facial tissues in Brn-3a wildtype and knockout mice at embryonic day 18.5 and postnatal day 0. In wildtype mice, the trigeminal ganglion contained abundant parvalbumin-, calbindin D-28k- and CGRP-immunoreactive neurons while the ganglion was almost devoid of calretinin-immunoreactive neurons. In Brn-3a knockout mice, a 63% decrease of parvalbumin-immunoreactive neurons was detected. In contrast, the absence of Brn-3a dramatically increased the number of calbindin D-28k-immunoreactive (3.5-fold increase) and calretinin-immunoreactive neurons (91-fold increase). The number of CGRP-immunoreactive neurons, however, was not altered by the Brn-3a deficiency. Cell size analysis indicated that loss of Brn-3a increased the proportions of small (<100 microm (2)) parvalbumin-, calbindin D-28k- and CGRP-immunoreactive neurons while it decreased those of large (>200 microm(2)) immunoreactive cells. Calretinin-immunoreactive neurons were either small or medium (100-200 microm (2)) in mutant mice. The oro-facial tissues contained parvalbumin-, calbindin D-28k- and CGRP-immunoreactive fibers, but not calretinin-immunoreactive ones in wildtype mice. In Brn-3a knockout mice, the number of parvalbumin-immunoreactive fibers markedly decreased in the infraorbital nerve and parvalbumin-immunoreactive endings disappeared in the vibrissa. In contrast, the number of calbindin D-28k-immunoreactive fibers increased significantly in the infraorbital and mental nerves. In addition, calbindin D-28k-immunoreactive endings appeared in the vibrissa. As well, some fibers showed calretinin-immunoreactivity in the infraorbital nerve of the mutant. However, no obvious change of CGRP-immunoreactive fibers was observed in the oro-facial region of knockout mice. Taken together, our data suggest that Brn-3a deficiency has effects on the expression of neurochemical substances in the trigeminal ganglion.

Stiff person syndrome: quantification, specificity, and intrathecal synthesis of GAD65 antibodies

OBJECTIVE

To characterize the specificity of anti-GAD(65) antibodies in patients with stiff person syndrome (SPS), quantify antibody titers, and examine antibody production within the CNS.

METHODS

The authors studied 18 patients with SPS and positive serum immunoreactivity to gamma-aminobutyric acid (GABA)-ergic neurons. The reactivity of serum and CSF to purified GAD antigen was examined by Western blots, and the anti-GAD(65) antibody titers in serum and CSF were quantified by ELISA and compared with 70 disease controls (49 with other autoimmune disorders and 11 with insulin-dependent diabetes mellitus). The intrathecal synthesis of anti-GAD(65) IgG was calculated, and the functional significance of the antibodies was examined by measuring the GABA levels in the CSF.

RESULTS

The serum and CSF of all selected patients with SPS had high anti-GAD(65) titers (from 7.0 to 215 microg/mL in serum and from 92 to 2500 ng/mL in CSF) and immunoreacted strongly with recombinant GAD(65) on Western blots and with GABA-ergic neurons on rat cerebellum. Among controls, only the serum of eight patients with insulin-dependent diabetes mellitus had low anti-GAD(65) antibody titers (from 200 to 1760 ng/mL) but no reactivity to recombinant GAD(65). The CSF showed oligoclonal IgG bands in 10 (67%) of 15 patients and an increased anti-GAD(65)-specific IgG index in 11 (85%) of 13. The mean level of GABA in the CSF was lower in patients with SPS than in controls.

CONCLUSIONS

In patients with SPS, there is marked intrathecal antibody response against neuronal GAD(65) epitopes, indicating a clonal B cell activation in the CNS. Anti-GAD(65) antibodies at high titers, when confirmed with immunoblots, are highly specific for SPS and appear to impair GABA synthesis.

Vulnerability to calcium-induced neurotoxicity in cultured neurons expressing calretinin

Calretinin (CR) is a calcium-binding protein purported to have neuroprotective properties. This study was designed to characterize the types of neurons containing CR in two different primary cultures and to determine which, if any, CR-immunoreactive (CR-ir) neurons are resistant to excitotoxic insults. Calretinin-containing neurons in cortical primary cultures derived from E14 rat embryos were not resistant to either kainic acid or a brief calcium overload induced by the calcium ionophore A23187. Equal proportions of CR-ir and GABAergic cortical neurons were lost after a 24-h exposure to 100 or 500 microM kainic acid. A 3 microM, 3-h exposure to A23187 induced equivalent amounts of cell loss in both the total cell and CR-ir cortical neuron culture populations. Cortical cultures grown for 6-7 days were more vulnerable than 12- to 13-day-old cultures to short-term, low-concentration treatments of A23187. Older cultures, however, were more severely affected when examined 24 h after a 3-h exposure to A23187. Calretinin-immunoreactive neurons derived from the diencephalon were relatively more resistant than cortical neurons to kainic acid at 6-7 days in vitro. In cortical or diencephalic cultures, CR was rarely coexpressed with GABA or calbindin D-28k. No vasoactive intestinal peptide, substance P, or parvalbumin was detected in CR-ir neurons in either culture system. We suggest that the presence of CR alone is not sufficient to spare neurons from a toxic calcium overload. Calretinin may still buffer calcium at low concentrations or be a component in a calcium-based signal transduction system.

Calbindin D28k and calretinin in oxytocin and vasopressin neurons of the rat supraoptic nucleus. A triple-labeling immunofluorescence study

The aim of the present study was to examine quantitatively whether two calcium-binding proteins, calbindin D28k and calretinin, are localized in oxytocin and vasopressin neurons of the supraoptic nucleus of the male rat. We used a triple-labeling immunofluorescence method with a confocal laser scanning microscope. Of the oxytocin-labeled cells, 70% were stained for both calbindin D28k and calretinin, 15% were stained for only calbindin D28k, 13% were stained for only calretinin, and 2% were stained for neither protein. Of the vasopressin-labeled cells, 73% were stained for neither calbindin D28k nor calretinin, 21% were stained for only calbindin D28k, 4% were stained for only calretinin, and 2% were stained for both proteins. Calbindin D28k and calretinin have been shown previously to contribute to calcium homeostasis by buffering [Ca2+]i. Therefore, these findings suggest that most of the oxytocin neurons may have a higher Ca(2+)-buffering capacity than most of the vasopressin neurons.

Migration defects of cdk5(-/-) neurons in the developing cerebellum is cell autonomous

Cyclin-dependent kinase 5 (Cdk5) is a member of the family of cell cycle-related kinases. Previous neuropathological analysis of cdk5(-/-) mice showed significant changes in CNS development in regions from cerebral cortex to brainstem. Among the defects in these animals, a disruption of the normal pattern of cell migrations in cerebellum was particularly apparent, including a pronounced abnormality in the location of cerebellar Purkinje cells. Complete analysis of this brain region is hampered in the mutant because most of cerebellar morphogenesis occurs after birth and the cdk5(-/-) mice die in the perinatal period. To overcome this disadvantage, we have generated chimeric mice by injection of cdk5(-/-) embryonic stem cells into host blastocysts. Analysis of the cerebellum from the resulting cdk5(-/-) left arrow over right arrow cdk5(+/+) chimeric mice shows that the abnormal location of the mutant Purkinje cells is a cell-autonomous defect. In addition, significant numbers of granule cells remain located in the molecular layer, suggesting a failure to complete migration from the external to the internal granule cell layer. In contrast to the Purkinje and granule cell populations, all three of the deep cerebellar nuclear cell groupings form correctly and are composed of cells of both mutant and wild-type genotypes. Despite similarities of the cdk5(-/-) phenotype to that reported in reeler and mdab-1(-/-) (scrambler/yotari) mutant brains, reelin and disabled-1 mRNA were found to be normal in cdk5(-/-) brain. Together, the data further support the hypothesis that Cdk5 activity is required for specific components of neuronal migration that are differentially required by different neuronal cell types and by even a single neuronal cell type at different developmental stages.

The function and expression of sproutin, a novel neurite outgrowth factor

TA20 cDNA was previously cloned as a neurite outgrowth factor from a hybridoma of mouse and rat cells, NG108-15. To clarify the detailed function and tissue distribution of this gene, homologous sequences of rat and mouse were identified. The cloned sequences had no homology with known genes, and was designated as sproutin. A predicted open reading frame of rat sproutin was transfected into human SK-N-SH cells. The over-expressed protein was distributed in cytoplasm and neurites, and caused an increase in the levels of microtuble associated proteins, but not that of phosphorylated neurofilament-H. The percentage of cells with neurites, the length of neurites and the number of neurites per cell were increased by sproutin transfection. Sproutin mRNA was brain specific. These results suggest that an increase in sproutin promotes dendritic extension.

Developmental expression of calretinin-immunoreactivity in the thalamic eminence of the fetal mouse

An investigation of the developmental expression of calretinin immunoreactivity and mRNA expression was carried out in the developing mouse diencephalon. Attention was focused on the thalamic eminence, which is a prominent structure previously described in the thalamus of the fetal mammalian diencephalon and adult lower vertebrates. Calretinin-positive staining was first observed in the thalamic eminence beginning at embryonic day 11. In situ hybridization histochemistry confirmed the presence of calretinin mRNA in the thalamic eminence. During subsequent embryonic development calretinin expression was very intense in neurons in the thalamic eminence though embryonic day 17, and thereafter, was increasingly difficult to distinguish. By postnatal day 0 the thalamic eminence was no longer discernable. Additional neurons within the murine diencephalon also expressed calretinin positive cell bodies and, or neuronal processes, including the stria medullaris, the habenular commissure and the paraventricular thalamic nucleus. It is possible that the thalamic eminence may form during development in order to act as an organizing center for the diencephalon.

Kir6.2 oligoantisense administered into the globus pallidus reduces apomorphine-induced turning in 6-OHDA hemiparkinsonian rats

ATP-sensitive inwardly rectifying potassium channels (KATPs) couple cell metabolism with its membrane potential. The best characterized KATP is the pancreatic KATP which is an heteromultimer of Kir6.2 and SUR1 protein subunits. KATPs are found in a variety of excitable cells, including neurons of the central nervous system. Basal ganglia (BG), especially in the substantia nigra (SN) reticulata and the globus pallidus (GP), have a high density of KATPs. Pharmacological modulation of the KATPs within the BG alters GABAergic activity and produces behavioural changes. However, the relatively high concentrations of drugs used might not have been entirely selective for the KATPs and may have acted at presynaptic nerve terminals as well as on the post-synaptic neurons. As an alternative means of examining the role of KATPs in regulating motor behavior, we used oligoantisense technology to diminish selectively Kir6.2 formation in the GP neurons. We then examined the effect of reduction in Kir6.2 expression on apomorphine-induced turning behavior in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the SN. Two weeks after injection of 6-OHDA, contralateral circling in response to apomorphine (0.25 mg/kg sc) was recorded. Kir6.2 antisense oligodeoxyribonucleotide (ODN) was then administered daily for 6 days into the GP ipsilateral to the 6-OHDA injection. Responses to apomorphine were then tested again and the animals killed to determine the effect of the antisense ODN on Kir6. 2 mRNA. Administration of Kir6.2 antisense ODN significantly attenuated apomorphine-induced contralateral turning and specifically reduced Kir6.2 mRNA in the injected GP. These results are consistent with pharmacological experiments which suggest that KATP channels in the GP are involved in motor responses to apomorphine in 6-OHDA lesioned rats, localizing the effects to the GP neurons, probably through modulation of the GABAergic system.

Distribution and possible functions of neuropeptides in the nervous system

Neuropeptides have now been localized throughout the nervous system. This talk focuses attention on (1) the interplay of peptides and other neurotransmitter systems in the hypothalamus--median eminence--pituitary gland. The multiplicity of neurochemicals is perceived to be responsible for the integrated control of pituitary hormone releasing factors; (2) the role of neuropeptides in the regulation of cardiovascular function in the hypothalamus-preoptic area. We investigated the effects of discrete intrahypothalamic injections of a variety of peptides on blood pressure and heart rate. We concluded that neuropeptides have a diversity of central cardiovascular actions and that not all areas containing a given peptide respond with cardiovascular change when the peptide is injected. Also, peptide specific actions originating within the same nucleus have been demonstrated, and the same peptide may have different vascular effects in different segments of the same nucleus; (3) the colocalization of neuropeptides with other classical neurotransmitters. We have found modulatory behavioral effects ("boxing") of combinations of transmitters and peptides injected into the postsynaptic site in the brain.

Chymotrypsin gene expression in rat peripheral organs

Prior studies have revealed the presence of chymotrypsinlike protease in peripheral organs, although no definitive evidence for the synthesis of this enzyme in tissue other than the pancreas is available. In an attempt to detect chymotrypsinogen mRNA in peripheral organs, a fragment of the pancreatic chymotrypsin mRNA from rat was amplified using PCR. The sequence was identified as a portion of the rat chymotrypsin B gene overlapping exon 5 through exon 7. It was subcloned into the pGEM-4Z vector and used as a template for the vitro transcription of an antisense riboprobe. Using ribonuclease protection and Northern blot analyses, chymotrypsin mRNA was detected in the rat pancreas, stomach, duodenum, ovary, and spleen. Monoclonal and polyclonal antisera against chymotrypsin detected chymotrypsinlike immunoreactivity in rat and human pancreas, rat stomach, duodenum and jejunum. Electrophoresis and immunoblotting revealed chymotrypsin-chymotrypsinogen bands (25-29 kDa) in the stomach and duodenum. Synthesis of a potent protease such as chymotrypsin in tissue other than pancreas is significant, suggesting a potential physiological and/or pathological role in these tissues.

Brain-derived neurotrophic factor stimulates neurite outgrowth in a calretinin-enriched neuronal culture system

A calretinin enriched cell culture system which comprised approximately 40% of the total neuronal population of the E14 rat embryo was established from the region of the thalamic eminence (TE), and the effects of several neurotrophins on the neurite growth of calretinin-immunoreactive (CR-IR) neurons was investigated. A 4-day treatment of BDNF significantly increased the ratio of CR-IR to microtubule-associated protein 2-immunoreactive neurons at concentrations between 50 and 250 ng/ml. IGF-I at 100 ng/ml and TGF-alpha at 250 ng/ml also increased this ratio. None of the neurotrophins examined increased the number of primary neurites. BDNF did, however, increase the number of secondary neurites. BDNF-treated primary and secondary neurites were also significantly longer than neurites from neurons in control cultures. IGF-I elicited an increase in primary neurite length, but did not affect either number or length of secondary neurites. TGF-alpha had no effect on either number or length of the primary and secondary neurites. These results indicate that the maturation and development of CR-IR neurites is specifically affected by BDNF. It is suggested that BDNF increases the CR concentration above the threshold of detection by immunohistochemistry in cells and stimulates the sprouting of secondary CR-IR neurites.

A method for the rapid analysis of neuronal proportions and neurite morphology in primary cultures

This article provides basic guidelines for a rapid analysis of subpopulation proportions and neurite morphology in primary cultures. We describe, in E14 mesencephalic primary cultures, an immunohistochemical method for the simultaneous identification of multiple neuronal phenotypes and an estimation of the ratio of subpopulations. In addition, we describe the use of the Renaissance TSA-Direct kit (NEN, DuPont) to enhance the visualization of neurites when the antigen is in low abundance. Finally, a modified sholl analysis is used to rapidly and reliably estimate neurite number and length.

The mouse calretinin gene promoter region: structural and functional components

The 5' flanking region of the mouse calretinin gene was cloned and a 1.8 kbp region adjacent to exon 1 was sequenced. Putative upstream promoter and enhancer elements were identified, including appropriately positioned TATA and CAAT boxes (positions -50 and -68, respectively). There was considerable sequence and structural homology between mouse and human upstream elements. Neuron-restrictive activity was demonstrated via transfection of calretinin promoter-reporter constructs into primary embryonic mouse brain cultures expressing calretinin. In promoterless reporter constructs, the proximal upstream 1.5 kbp of the mouse calretinin gene boosted luciferase activity (up to 100-fold) exclusively in the neuronal population. Deletion analysis revealed the minimal promoter to be within the 95-bp proximal to the transcription start site. Transfections with SV40 promoter constructs in these cultures resulted in reporter gene expression predominantly in non-neuronal cells. Inserting the proximal 1.5 kbp of mouse calretinin upstream in SV40 promoter-reporter constructs reduced luciferase activity. Thus, calretinin upstream sequences increased reporter expression in cultured neurons and decreased expression from the SV40 promoter in non-neuronal cultured brain cells. The calretinin promoter contained relevant regulatory element consensus motifs and demonstrated in vitro neuron-restrictive bioactivity.

Coexpression of calretinin and parvalbumin in Ruffini-like endings in the rat incisor periodontal ligament

The coexpression of calretinin- (CR) and parvalbumin-immunoreactivities (irs) was examined in oro-facial tissues of the rat. Nerve fibers coexpressing these calcium-binding proteins (CaBPs) were observed in the lingual periodontal ligament of incisors but not other tissues. In the part of periodontal ligament adjacent to the alveolar bone, such nerve fibers left nerve bundles and formed bush-like endings, i.e., they ramified repeatedly and terminated with one to four twigs. An immunoelectron microscopic method indicated that these endings were identical to Ruffini-like endings, 4% of trigeminal neurons retrogradely labeled from the inferior alveolar nerve coexpressed CR- and parvalbumin-irs. The present observations suggest that the coexpression of these CaBPs may be a specific marker for low-threshold mechanoreceptors in the trigeminal ganglion.

Calretinin-immunoreactive dopaminergic neurons from embryonic rat mesencephalon are resistant to levodopa-induced neurotoxicity

Levodopa, which is used in the treatment of Parkinson's disease, has known cytotoxic effects on dopaminergic neurons grown in culture. Calretinin (CR) is a cytosolic calcium-binding protein found in specific subpopulations of neurons as well as in some nonneuronal tissue. CR is expressed in 10% of rat embryo dopaminergic neurons grown in vitro. Since it has been postulated that CR provides neuroprotection due to its calcium-binding properties, we investigated whether CR-containing dopaminergic neurons were spared from levodopa toxicity. Incubation of mesencephalic cells with 10(-5) to 10(-7) M levodopa on Days 1-6 in vitro produced no significant effects on the number of dopaminergic neurons containing CR, but resulted in the loss of approximately 65% of the dopaminergic cells which did not contain CR. The remaining CR-negative dopaminergic neurons exhibited dose-dependent reductions in neurite length. The neuronal processes in CR-containing dopaminergic cells retained a smooth bipolar appearance. CR-immunoreactive cells which did not contain dopamine showed slight neurite length decreases at the highest drug concentrations but no changes in neuron number. These results indicate that CR may protect dopaminergic neurons from levodopa-induced toxicity.

Calretinin expression in the chick brainstem auditory nuclei develops and is maintained independently of cochlear nerve input

The expression of the calcium-binding protein calretinin (CR) in the chick brainstem auditory nuclei angularis (NA), laminaris (NL), and magnocelularis (NM) was studied during normal development and after deafening by surgical removal of the otocyst (embryonic precursor of the inner ear) or columella (middle ear ossicle). CR mRNA was localized by in situ hybridization by using a radiolabeled oligonucleotide chick CR probe. CR immunoreactivity (CR-IR) was localized on adjacent tissue sections. CR mRNA signal in the auditory nuclei was expressed at comparable levels at embryonic day (E)9 and E11 and increased thereafter to reach the highest levels in posthatch chicks. CR-IR neurons were apparent in NM and NA at E11 and in NL by E13, and CR-IR increased in all three auditory nuclei thereafter. Neither unilateral nor bilateral otocyst removal caused detectable changes in the intensity of CR mRNA expression or CR-IR in the auditory nuclei at any of the several ages examined. Similarly, columella removal at posthatching day 2 or 3 failed to significantly affect CR mRNA or CR-IR levels at 3 hours, 1 day, or 3-4 days survival times. We conclude that cochlear nerve input is not necessary for expression of either calretinin mRNA or protein and that the profound decrease in sound-evoked activity caused by columella removal does not affect the maintenance of CR expression after hatching.

Calretinin in the rat pituitary: colocalization with thyroid-stimulating hormone

The purpose of this study was to examine the distribution of calretinin immunoreactivity (CR) in the male rat pituitary gland by immunofluorescence microscopy. CR was found in cells of the anterior pituitary and in granules in the posterior pituitary. In the intermediate lobe, nerve fibers in close proximity to the melanotropes were CR-immunoreactive (CR-ir). Fine CR-ir varicose fibers were also observed in the anterior and posterior pituitary. Colocalization studies revealed that the majority of the CR-containing cells of the anterior pituitary also contained thyroid-stimulating hormone (TSH). These CR/TSH cells represented about 32% of the thyrotrope population. Following thyroidectomy, a massive increase in both the number of CR-ir cells and in the expression of CR mRNA was observed in the anterior pituitary. Thyroxine treatment, however, resulted in a reduction in the number and size of the CR-ir cells in the same lobe. In the intermediate lobe, CR-ir was colocalized with tyrosine hydroxylase (TH) immunoreactive dopaminergic fibers. These intermediate lobe fibers disappeared following pituitary stalk section, as did the CR/TH fibers and the CR-ir granular material in the posterior pituitary. The findings in the anterior pituitary suggest that consideration be given to the idea that CR might function in the synthesis and/or release mechanism of TSH in thyrotropes and that its expression is modulated by the hypothalamo-pituitary-thyroid axis.

S100 protein-immunoreactive primary sensory neurons in the trigeminal and dorsal root ganglia of the rat

The cell body size (cross-sectional area) of S100-immunoreactive (-ir) primary neurons was measured in the trigeminal (TG) and lumbar dorsal root ganglia (DRG). About a half of neurons exhibited S100-immunoreactivity (-ir) in the DRG (44.0%) and TG (59.0%). DRG neurons with cell bodies > 1200 microm2 mostly exhibited S100-ir (96.5%), whereas S100-ir DRG neurons < 600 microm2 were rare (8.0%). 36.6% of DRG neurons in the cell size range 600-1200 microm2 showed the ir. TG neurons > 800 microm2 mostly exhibited S100-ir (93.1%), whereas those < 400 microm2 were devoid of it (positive cells 10.5%). 58.3% of TG cells in the range 400-800 microm2 contained S100-ir. Double-immunofluorescence method revealed the co-expression of S100 and other calcium-binding proteins. Parvalbumin-ir neurons mostly exhibited S100-ir in the DRG (97.4%) and TG (97.0%). The co-expression of S100 and calbindin D-28k was very rare in the DRG, because the DRG contained few calbindin D-28k-ir neurons. Unlike in the DRG, numerous neurons co-expressed S100- and calbindin D-28k-ir in the TG. Most calbindin D-28k-ir TG neurons were also immunoreactive for S100 (90.7%). Sub-populations of calretinin (CR)-ir neurons co-expressed S100-ir in both the DRG (68%) and TG (50.0%). Virtually all CR-ir neurons > 1400 microm2 co-expressed S100-ir in the DRG (100%) and TG (95.9%). CR-ir neurons < 800 microm2 were rarely exhibited S100-ir (DRG 18.0%, TG 21.9%). 71.3 and 60.5% of CR-ir neurons in the range 800-1400 microm2 co-expressed S100-ir in the DRG and TG, respectively. The present study indicates that S100 is closely correlated to the primary neuronal cell size in the DRG and TG.

Calretinin-containing neurons in rat cerebellar granule cell cultures

Using an antiserum against calretinin, a calcium-binding protein, we discovered two distinct neuronal cell types that stain intensely in enriched cerebellar granule cells. One neuronal cell type resembles unipolar brush cells, whereas the other resembles Lugaro cells. During early culture times, these calretinin-positive neurons are most numerous but represent less than one percent of the total neuronal population. In cultured cells, calretinin mRNA levels peak at day three in vitro, followed by a rapid decline to undetectable levels by day six in vitro. However, calretinin-immunoreactive neurons are observed up to 29 days in vitro. Excitotoxic concentrations of glutamate receptor agonists failed to elicit an excitotoxic response on the intensely staining calretinin-positive neurons, whereas greater than 95% of the cerebellar granule cells were susceptible to the excitotoxic actions of the glutamate receptor agonists. To distinguish between the two possibilities that calretinin-positive neurons either do not express glutamate receptors or they are not susceptible to the excitotoxic effects of glutamate receptor agonists, we performed immunocytochemistry using glutamate receptor antibodies to detect the presence of receptor protein. We found that the AMPA/kainate glutamate receptor (GluR2R3) colocalized with calretinin, suggesting that calretinin-immunoreactive neurons express the AMPA/kainate receptor; cerebellar granule cells, which are known to express this receptor, were also immunoreactive for the GluR2R3 receptor.

Calretinin mRNA and immunoreactivity in the medullary reticular formation of the rat: colocalization with glutamate receptors

Calretinin-positive cells were identified in the medullary reticular formation of the rat by both immunohistochemistry and in situ hybridization histochemistry. In addition, double immunocytochemical labeling was used to examine the degree of colocalization of calretinin with GluR2/R3, GluR4 and GluR5-7 glutamate receptor subtypes. Results indicated regional variation in calretinin expression across reticular formation regions with the exception of the largest cells which were mostly calretinin-positive. Calretinin mRNA was particularly abundant in the parvocellular reticular nucleus. Most calretinin-immunoreactive cells also expressed at least one of the glutamate receptor subtypes examined with the exception of the smallest calretinin-positive cells of the parvocellular reticular formation which were generally not immunoreactive for any of the glutamate receptors examined. Calretinin immunoreactivity was colocalized with immunoreactivity for all three glutamate receptor subtypes examined in most of the large cells of the reticular formation. Immunoreactivity for the GluR4 antibody was least abundant in the reticular formation and GluR4 immunoreactive cells were least likely to co-express calretinin. These results suggest that calretinin and glutamate receptor antibodies may be used to identify specific subsets of reticular formation neurons.

The expression of calretinin in transfected PC12 cells provides no protection against Ca(2+)-overload or trophic factor deprivation

To address the question whether calretinin (CR) may protect cells against Ca2+ overload or trophic factor deprivation, PC12 cells were transfected with plasmids containing a CR coding region under control of a cytomegalovirus promoter. Nerve growth factor (NGF) treatment induced differentiation, increased transfection efficiency (at least 10-fold) and activated the CR gene (as found by RNase protection method and immunohistochemistry). Exogenous CR expression was identified either in living cells by fluorescence of green fluorescent protein (when the CR coding region was fused to this protein) or in fixed cells by CR immunoreactivity. Undifferentiated and NGF-differentiated populations of transfected cells were incubated in the presence of a Ca(2+)-ionophore or in media deprived of serum or NGF. Expression of exogenous CR in undifferentiated or NGF-treated cells (due to transfection) or endogenous CR (due to gene activation by NGF) did not render PC12 cells more resistant to insults such as Ca(2+)-overload and trophic factor deprivation.

Calretinin is differentially localized in magnocellular oxytocin neurons of the rat hypothalamus. A double-labeling immunofluorescence study

By use of a double-labeling immunofluorescence method with a confocal laser scanning microscope, we have examined whether a calcium-binding protein, calretinin, is localized in magnocellular oxytocin and vasopressin neurons of the rat hypothalamus. In the supraoptic nucleus, all oxytocin-labeled cells were stained for calretinin. However, in the magnocellular part of the paraventricular nucleus, almost all oxytocin-stained cells were devoid of calretinin immunoreactivity. All vasopressin-positive cells of both the supraoptic nucleus and the magnocellular part of the paraventricular nucleus lacked calretinin immunoreactivity. No calretinin immunoreactivity was found in oxytocin-labeled cells of the the anterior commissural nucleus or in vasopressin-labeled cells of the suprachiasmatic nucleus. We previously showed that another calcium-binding protein, calbindin-D28k, was localized in magnocellular oxytocin neurons of the supraoptic nucleus but not in those of the paraventricular nucleus. These findings suggest that, in general, magnocellular oxytocin neurons of the supraoptic nucleus and those of the paraventricular nucleus can be chemically distinguished, that is, the former contain both calretinin and calbindin-D28k but the latter lack the two calcium-binding proteins.

Cellular expression of MAP 2 kinase in rat brain

The cellular localization of microtubule-associated protein (MAP) 2 kinase mRNA in rat brain was examined by in situ hybridization histochemistry using a synthetic oligonucleotide probe. MAP 2 kinase was expressed in both neuronal and non-neuronal cells. Areas of high density of mRNA label by the MAP 2 kinase probe appeared to be associated with high cellular packing density. Thus, MAP 2 kinase expression was particularly high in regions such as the locus coeruleus, the piriform cortex, the dentate gyrus granule cell layer, pyramidal cells of the hippocampus, the mitral cells of the olfactory bulb, and the large motor neurons of the V and VII nerves. This apparent ubiquitous distribution suggests an important role of MAP 2 kinase in the cellular functions in most cells of the adult brain.

Calbindin-D28k-immunoreactivity in the trigeminal ganglion neurons and molar tooth pulp of the rat

The cell body size and coexpression of carbonic anhydrase (CA), calretinin (CR) and calcitonin gene-related peptide (CGRP) of primary neurons with calbindin-D28k (CB) was examined in the trigeminal ganglion (TG) of the rat. CB-immunoreactive (-ir) cells were mostly large and preferentially distributed in the maxillary and mandibular divisions of the TG. 48% of CB-ir TG cells exhibited enzyme CA activity. 10% of CB-ir TG cells contained CR-ir. Most TG cells coexpressing CB- and CR-irs were localized to the maxillary and mandibular divisions and exhibited CA activity. 6.5% of CB-ir TG cells coexisted with CGRP-ir. 46% of TG cells coexpressing CB and CGRP exhibited CA activity. The innervation of the molar tooth pulp by CB-ir TG primary neurons was also examined. CB-ir thick and smooth nerve fibers projected from the root pulp to the pulp horn and the roof of the pulp chamber, where they became thinner and rarely entered the subodontoblastic layer. However, they could not be traced to the odontoblastic layer, predentin or dentine. The distribution pattern of CB-ir pulpal fibers was different from that of CR-ir ones. The trigeminal neurons cells retrogradely labeled with fast blue (FB) from the maxillary molar tooth pulp contained CB- and CR-irs. 23% and 1% of the labeled cells were immunoreactive for CB and CR, respectively. The coexpression of CB- and CR-immunoreactivities (-irs) in FB-labeled cells was negligible. An immunoelectron microscopic method revealed that 21% of pulpal nerve fibers were immunoreactive for CB, and that all CB-ir nerve fibers in the root pulp were myelinated. The present study indicated that the tooth pulp primary neurons contained CB-ir but did not coexpress CB- and CR-irs and that these neurons projected their myelinated axons to the pulp.

Differential effects of excitatory amino acids on mesencephalic neurons expressing either calretinin or tyrosine hydroxylase in primary cultures

In mesencephalic primary cultures derived from E14 rat embryos, calretinin- and tyrosine hydroxylase-immunoreactive neurons comprised 2% and 5% of the total cell population, respectively, at 6-7 days in vitro. The number of calretinin-immunoreactive neurons was unchanged after a 12- or 24-h exposure to 500 microM kainic acid (KA), but a 50% cell loss was detected after a 48-h exposure to KA. Tyrosine hydroxylase-immunoreactive neurons demonstrated a 50% and 67% cell loss at 24- and 48-h exposures to 500 microM KA. A 500 microM N-methyl-D-aspartic acid (NMDA) incubation for 24 h had no effect on calretinin-immunoreactive cell number, but did significantly reduce tyrosine hydroxylase-immunoreactive cell numbers by 26%. In tyrosine hydroxylase-immunoreactive cells, exposure to KA appeared to stimulate the retraction of the neuritic tree and to cause somatic swelling. In contrast, calretinin-immunoreactive neurons developed larger and more complex neuritic trees after a 24-h exposure to 500 microM KA but not NMDA. Immunohistochemical colocalization studies revealed that all tyrosine hydroxylase-immunoreactive and the majority of calretinin-immunoreactive neurons expressed the glutamate receptor subunits GluR2-R3. Very low levels of NMDAR1 receptor subunits were detected on cells in this culture and GluR4 receptor subunits were not detectable. Our experiments showed that glutamate receptors present in both calretinin- and tyrosine hydroxylase-immunoreactive cells were functional, since phosphorylated cAMP/Ca2+ response element-binding protein levels were increased in both cell types after 10 or 30 min exposures to 500 microM KA. The present results indicate that in the mesencephalic cultures tyrosine hydroxylase-immunoreactive cells are more vulnerable to KA excitotoxicity than calretinin-immunoreactive neurons.

Calretinin-containing pathways in the rat forebrain

The anatomy of pathways containing the calcium binding protein calretinin was investigated in the forebrain of the rat, using a combination of immunohistochemical and retrograde tract tracing techniques. Numerous well identified pathways do contain calretinin, whereas others do not. Pathways arising from the substantia nigra/ventral tegmental area, the dorsal raphe, the lateral mammillary nucleus, the supramammillary nucleus, the triangular septal and septo-fimbrial nuclei, several thalamic nuclei, the parabrachial nucleus, the peripeduncular nucleus, the medial amygdala contain at least some calretinin. The proportion of projection neurons containing calretinin ranged from 2% (dorsal raphe to caudate) to about 75% (triangular septal nucleus to habenula, medial amygdala to the ventromedial hypothalamus). More than 50% of the nigro-striatal neurons contain calretinin immunoreactivity. In contrast, other pathways do not contain any calretinin immunoreactivity (for instance the pathways arising from cerebral cortex, locus coeruleus, cholinergic forebrain nuclei), although calretinin may be present in local neurons in these structures. The present study demonstrates that calretinin is not associated specifically with projection neurons or local neurons, identified transmitter systems or functionally related pathways in the forebrain of the rat.

Conformational changes and calcium binding by calretinin and its recombinant fragments containing different sets of EF hand motifs

Four recombinant fragments, representing different sets of EF-hand motifs of rat calretinin (CR) (I-II, I-III, III-VI, IV-VI), were prepared, and their Ca2+ -induced conformational changes were compared with those of full-length recombinant CR. All fragments were able to bind calcium ions as shown by 45Ca2+ overlay method on nitrocellulose and fluorescence measurements. The intrinsic tryptophan fluorescence intensity (FI) of apo-CR reversibly increased about 3-fold upon addition of calcium, indicating a change of conformation. The FI of fragments I-II (Trp 25) and I-III (Trp 25 and 116) increased about 1.4-fold on calcium binding, but that of fragment III-VI (Trp 116) increased 3.5-fold. Calcium titration of CR monitored by Trp fluorescence intensity showed that recombinant CR and some fragments bound Ca2+ with high affinity (Kd below 0.4 microM) and with high cooperativity. An apparent Hill coefficient for Ca2+ -induced fluorescence changes in CR was about 3.7. CR bound to organomercurial-agarose Cys 101 and 266 did not form cystine. The fluorescence intensities of cysteine-linked fluorescent probes 5-iodoacetamidofluorescein and N-(1-pyreneiodoacetamide) were increased approximately 1.3-fold upon calcium binding by CR. These data indicate that CR binds Ca2+ with high affinity and cooperativity and that this binding induces a change of conformation that involves the interaction of different parts of the molecule. Taken together, our results suggest that CR works as an on/off switch within a narrow range of free Ca2+ by interacting with as yet unidentified targets.

Alteration in levels of expression of brain calbindin D-28k and calretinin mRNA in genetically epilepsy-prone rats

Variations in the concentration of free calcium in neurons is believed to play a major role in regulating neuronal excitability. Because calcium-binding proteins such as calbindin D-28k and calretinin help to regulate intracellular calcium, we investigated the possibility that the expression of these proteins may be affected in genetically epilepsy-prone rats (GEPRs). The mRNA levels of both proteins were compared across several brain regions using in situ hybridization histochemistry and Northern blot analysis with semiquantitation by optical density measures in autoradiograms from two GEPR strains that differ in the severity of audiogenic seizures (GEPR9 and GEPR3) and from Sprague-Dawley rats. Results revealed a lower level of expression in calbindin D-28k mRNA in the in the caudate putamen-accumbens nuclei in GEPR3 (-30%) and GEPR9 (-60%) relative to controls. The calbindin D-28k mRNA level was also lower in the reuniens nucleus of the thalamus (-41% in GEPR3; -34% in GEPR9). The calretinin mRNA level was lower in the substantia nigra compacta of both GEPR rat strains (-31% in GEPR3 and -34% in GEPR9 relative to controls). No changes in mRNA were detected in other brain regions expressing calbindin D-28k or calretinin mRNA. These results indicate that the expression of these related calcium-binding proteins is altered in the GEPRs before the induction of seizures. This initial defect could alter either the calcium-buffering capacity or regulation of calcium-mediated processes by these proteins and thus play a role in the molecular cascade of events inducing the genetic susceptibility to, and the generalization of, seizures in these rat strains.

Chemically defined neuron groups and their subpopulations in the glomerular layer of the rat main olfactory bulb

Chemically-defined neuron groups and their subpopulations in the glomerular layer of the rat main olfactory bulb were revealed immunocytochemically using antibodies against gamma-amino butyric acid (GABA), tyrosine hydroxylase (TH), methionin-enkephalin-Arg6-Gly7-Leu8 (ENK), calretinin (CR), calbindin-D28K (calbindin) and thyrotropin-releasing hormone (TRH). GABA-like immunoreactive (GABA-LIR) neurons and CR immunoreactive (CR-IR) neurons were most numerous; they were about 1.5-3 times more numerous than calbindin immunoreactive (calbindin-IR), TH immunoreactive (TH-IR), ENK-like immunoreactive (ENK-LIR) and THR-like immunoreactive (TRH-LIR) neurons. We identified at least three distinct chemically-defined neuron groups, GABA-LIR neurons, CR containing neurons and calbindin containing neurons, since these three neuron groups were almost separate from one another. On the other hand, TH-IR and ENK-LIR neurons were nearly included in and thus considered to be subpopulations of GABA-LIR and CR-IR neurons, respectively, for about 80% of these two neuron groups contained GABA-L and CR immunoreactivities, respectively. TRH-LIR neurons appeared to be divided into two subpopulations, one containing the GABA-L immunoreactivity and the other containing the CR immunoreactivity. Thus in the glomerular layer of the rat olfactory bulb, GABA-LIR, CR-IR and calbindin-IR cells could be considered to be three distinct chemically-defined neuron groups, whereas TH-IR, TRH-LIR and ENK-LIR neurons were regarded as their subpopulations. Furthermore, some neurons groups, whereas TH-IR, TRH-LIR and ENK-LIR neurons were regarded as their subpopulations. Furthermore, some neurons are supposed to contain three substances (e.g. GABA + TH + TRH, GABA + TRH + EnK, CR + TRH + ENK, GABA + TRH + CR) or a few might even contain four substances (e.g. GABA + TRH + CR + ENK). Preliminary quantitative analysis using the optical disector method showed percentages of these three main neuron groups to total cells in the glomerular layer; that is, neuron groups containing GABA, CR and calbindin were about 20%, 20% and 10%, respectively.

Comparative immunohistochemical distribution of amylin-like and calcitonin gene related peptide like immunoreactivity in the rat central nervous system

Using the indirect immunofluorescence method with a polyclonal antiserum raised in rabbits and directed against amylin (AMY), we have investigated the distribution of AMY-like immunoreactivity (-ir) throughout the central nervous system of the rat. The widespread distribution of AMY-ir was much more abundant than that previously reported for calcitonin gene related peptide (CGRP) immunoreactivity. In most brain areas there was no overlap between AMY- and CGRP-ir cell body groupings, with the exception of the motor nuclei of the hindbrain and spinal cord, which were found to contain large numbers of AMY- and CGRP-immunoreactive cell bodies. Areas with a moderate to dense appearance of AMY-ir were the rhinencephalon, the nucleus of the diagonal band, the magnocellular, dorso- and ventro-medial and mammillary nuclei of the hypothalamus, the habenula, the compact part of the substantia nigra, the ruber and pontine nuclei, and the inferior olive and the cerebellar nuclei. The widespread immunohistochemical distribution of AMY-ir in the rat brain is in partial agreement with the distribution of AMY-binding sites.

Quadruple colocalization of calretinin, calcitonin gene-related peptide, vasoactive intestinal peptide, and substance P in fibers within the villi of the rat intestine

Double-labeling immunofluorescent histochemistry demonstrates that calretinin, a calcium-binding protein, coexists with calcitonin gene-related peptide, vasoactive intestinal peptide, and substance P in the fibers innervating the lamina propria of the rat intestinal villi. An acetylcholinesterase histochemical stain revealed that the majority of calretinin-containing cells in the myenteric ganglia were cholinergic and that about one half of the submucosal calretinin-containing cells colocalized with acetylcholinesterase. In situ hybridization studies confirmed the presence of calretinin mRNA in the dorsal root ganglia, and a ribonuclease protection assay verified the presence of calretinin message in the intestine. The coexistence of calretinin in calcitonin-gene-related-peptide-containing cells that also contained substance P and vasoactive intestinal polypeptide in the dorsal root ganglia suggest that these ganglia are the source of the quadruple colocalization within the sensory fibers of the villi. Although the function of calretinin in these nerves is unknown, it is hypothesized that the coexistence of three potent vasodilatory peptides influences the uptake of metabolized food products within the vasculature of the villi.

Localization of Ca(2+)-dependent conformational changes of calretinin by limited tryptic proteolysis

Calretinin is an EF-hand Ca(2+)-binding protein expressed predominantly in some neurons. We have found that the tryptic digestion pattern of rat recombinant calretinin depends on Ca2+ concentration as determined by SDS/PAGE, amino-acid-sequence analysis and electrospray-ionization MS. Ca(2+)-saturated calretinin was cleaved between amino acids 60 and 61 to yield two fragments, which accumulated during cleavage. Small amounts of the larger fragment (amino acid residues 61-271) were further cleaved from the C-terminal end. Ca(2+)-free calretinin was also cleaved between residues 60 and 61; however, under the latter conditions the fragment 61-271 was further cleaved from the N-terminal end. Native rat calretinin was cleaved by trypsin in a similar Ca(2+)-dependent fashion. All identified fragments of recombinant calretinin bound 45Ca2+ on nitrocellulose filters, although to a different extent. The 61-271 fragment was released by EGTA from an octyl-agarose column in a manner similar to intact calretinin, while fragment 61-233 was not eluted by EGTA. These observations show that there are trypsin cleavage sites in calretinin that are available regardless of Ca2+ binding, other sites that are completely protected against trypsin on Ca(2+)-binding and sites which become partially available on Ca(2+)-binding. Together these data show that calretinin changes its conformation on Ca2+ binding and identify the regions which are exposed in apo and Ca(2+)-bound form.

Development of calretinin-immunoreactive unipolar brush-like cells and an afferent pathway to the embryonic and early postnatal mouse cerebellum

In the developing mouse hindbrain, immunoreactivity for calretinin, a calcium-binding protein, was first observed at embryonic day 10, and was localized to neuronal cell bodies in the reticular formation. By embryonic day 12, fibers emanated rostrally from the calretinin-immunoreactive neurons, extended dorsally and then caudally in the uncinate fasciculus to reach the developing cerebellar plate. These fibers crossed the cerebellar midline and were distributed to the contralateral side of the cerebellum. The number and intensity of staining of cell bodies in the reticular formation was reduced in postnatal mice. After postnatal day 1, it was no longer possible to discern the calretinin-immunoreactive fiber bundle in the brainstem, although fibers were still visible at the level of the uncinate fasciculus and in the cerebellum. We also observed intensely calretinin-immunoreactive, smaller cells in the cerebellum (embryonic day 14) and dorsal cochlear nuclei (embryonic day 18), most of which we believe are destined to become the "unipolar brush", (also known as "pale" or "monodendritic") cells observed in the adult mammalian brain. An immature form of these cells exists in the developing mouse cerebellum. Thus, using calretinin antiserum as a marker, an afferent neuronal system was described which projects to the cerebellar primordium. It is suggested that the calretinin-containing hook bundle is an afferent projection which provides a feed-forward neuronal system to the cerebellum which, in turn, projects afferent fibers to the calretinin-containing and other cells of the reticular formation.

Parvalbumin- and calretinin-immunoreactive trigeminal neurons innervating the rat molar tooth pulp

Calcium-binding proteins and neuropeptides were examined in trigeminal neuronal cell bodies retrogradely labeled with Fast blue (FB) from the maxillary molar tooth pulp of the rat. FB-labeled cells were located in the maxillary division of the trigeminal ganglion. Approximately 30 and 50% of the labeled cells were immunoreactive for parvalbumin and calcitonin gene-related peptide (CGRP), respectively. The coexpression of these substances was observed in 9.5% of FB-labeled cells. On the other hand, 2.4% of FB-labeled cells exhibited calretinin-immunoreactivity (CR-ir) and 20% tachykinin (TK)-ir. The coexpression of CR and TK was observed in 1.9% of FB-labeled cells, i.e., most of CR-ir FB-labeled neurons coexpressed TK-ir. An immuno-EM method revealed that all parvalbumin-ir nerve fibers in the root pulp were myelinated and that CGRP-ir nerve fibers were both myelinated (15%) and unmyelinated (85%). The present study indicated that primary nociceptors innervating the rat molar tooth pulp contained parvalbumin and CR and coexpressed these calcium-binding proteins and neuropeptides. It was suggested that peripheral axons of parvalbumin-ir tooth pulp primary neurons are all myelinated. Most peripheral CR-ir axons are probably unmyelinated because TK-ir myelinated axons have never been demonstrated in any peripheral organ.

Effects of unilateral cochlea ablation on the distribution of calretinin mRNA and immunoreactivity in the guinea pig ventral cochlear nucleus

The predominantly neuronal, calcium-binding protein calretinin is highly expressed in the guinea pig auditory system. Within the ventral cochlear nucleus (VCN), calretinin-positive auditory nerve fibers terminate on many calretinin-containing bushy, octopus, and multipolar cells. The abundance of calretinin in the cochlear nucleus provides an ideal system for examining the effects of altered neuronal input on the expression of this calcium-binding protein. The present experiments examined the effects of unilateral cochlea ablation on calretinin immunoreactivity and mRNA levels in the VCN. Calretinin mRNA was labeled by in situ hybridization histochemistry using a radioactive oligonucleotide probe and was quantified by optical density measures on autoradiograms. Survival times of 1, 7, and 56 days postlesion were examined. The results revealed a consistent increase in calretinin mRNA in the rostral portion of the ipsilateral anterior VCN 1 day postlesion but no effect on calretinin mRNA in this region at 7 and 56 days postlesion. The intensity of immunohistochemical label was also increased at 1 and 7 days after surgery. In contrast, calretinin mRNA was not affected 1 day postlesion in the ipsilateral posterior VCN but was decreased at both 7 and 56 days postlesion. The decrease in calretinin mRNA in the posterior VCN at longer survival times was accompanied by decreased immunolabeling of fibers projecting from VCN cells to the superior olivary complex. These results suggest that calretinin gene expression is regulated in part by auditory nerve activity in some cochlear neurons but that additional factors related to the unique cellular milieu also control calretinin expression.

Up-regulation of calretinin in the supraoptic nucleus of the rat after chronic salt loading

We immunocytochemically examined the effect of chronic salt loading on the content of calretinin, a calcium-binding protein, in both the supraoptic nucleus and the magnocellular parts of the hypothalamic paraventricular nucleus. In control rats that were given water for drinking, the supraoptic nucleus contained a cluster of calretinin-stained cells. Drinking 2% sodium chloride solution for 7 days resulted in an increase of the staining intensity of calretinin in cells of the suprasoptic nucleus. In both the control and salt-loaded rats, the magnocellular parts of the paraventricular nucleus were almost devoid of calretinin-labeled cells. It is suggested that expression of calretinin in cells of the supraoptic nucleus is up regulated by chronic salt loading.

Corticosterone effects on rat calretinin mRNA in discrete brain nuclei and the testes

Calretinin is an EF-hand calcium binding protein found predominantly in discrete sets of neurons in the central system, and in the sex hormone producing cells of the gonads. Calretinin mRNA levels were measured in discrete brain areas from vehicle and corticosterone treated rats (subcutaneous injections of 0, 0.1, 1, or 10 mg, 7 days) using a micropunch ribonuclease protection assay. Treatment with high dose corticosterone (10 mg) caused a 93% decrease in calretinin mRNA levels in the hypothalamic paraventricular nucleus compared to controls. Two other brain regions, the medial amygdaloid nucleus and the nucleus reuniens, demonstrated an approximately 40% decrease in calretinin mRNA following high dose corticosterone. In separate experiments, adrenalectomy and diurnal corticosterone variations had no effect on calretinin mRNA in the brain areas examined. In the testes, corticosterone treatment decreased calretinin protein in a dose dependent fashion (to 81%, 68%, and 39% of controls at doses of 10, 1, and 0.1 mg/day, respectively). Low dose corticosterone treatments decreased testicular but not neuronal calretinin mRNA, whereas high dose corticosterone reduced calretinin mRNA in testes and several discrete brain areas. This suggests that corticosterone's effects on brain calretinin may be due to its pathological effects, e.g. energy depletion of brain cells or interference with the normal support functions of glia.

Detailed mapping of CGRP mRNA expression in the rat central nervous system: comparison with previous immunocytochemical findings

The localization of CGRP mRNA in neurons of the rat brain and spinal cord was assessed by in situ hybridization histochemistry (ISH) using a radiolabeled synthetic 57-mer oligodeoxynucleotide probe complementary to the rat prepro CGRP mRNA. Results were compared with previously published findings of CGRP-immunoreactive (CGRP-IR) cell bodies revealed by an indirect immunofluorescence technique. The highest numbers of CGRP mRNA expressing neurons as well as the greatest intensity of staining were found in the lateral hypothalamic area, the parabrachial nuclei, and among the cranial motor nuclei, especially in the nuclei of the 7th and 12th nerve and the ambiguus nucleus, which is generally in good agreement with findings assessed by immunocytochemistry (ICH). However, some mismatches between the localization of the peptide by ICH and the localization of the CGRP mRNA were also observed. Thus, ISH was not able to confirm CGRP-IR in cells of the amygdaloid complex and parts of the medial hypothalamus, the central gray, and the inferior colliculus, but ISH revealed considerably more CGRP mRNA expressing cells in the lateral hypothalamic area, arcuate nucleus, posterior and peripeduncular thalamic nuclei, and all cranial motor nuclei than CGRP-IR containing cells found by ICH. Moreover, ISH also revealed CGRP mRNA synthesis in the nucleus of the lateral olfactory tract and in the perihypoglossal nuclei that were devoid of CGRP-IR. The reasons for the observed mismatches still remain to be elucidated; however, intracerebroventricular colchicine pretreatment used to increase immunocytochemical signals also might have induced or suppressed gene expression in certain brain regions in an unpredictable matter. On the other hand, detection of only the mRNA in a certain region does not necessarily mean that also the active peptide is synthesized there.

Calretinin is expressed in the Leydig cells of rat testis

Calretinin, a highly evolutionarily conserved E-F hand calcium binding protein, is expressed predominantly in neurons, with a few exceptions. The function of calretinin is not known. We demonstrate the expression of calretinin mRNA and protein in rat testes. Immunocytochemistry and in situ hybridization reveal that calretinin expression in testis is localized to the interstitial Leydig cells. Western blot and ribonuclease protection analyses show that calretinin protein and mRNA in testis is the same as that expressed in brain. It is suggested that calretinin may play a role in the production of testosterone.

Parvalbumin, calretinin and carbonic anhydrase in the trigeminal and spinal primary neurons of the rat

The cell-body size of parvalbumin-immunoreactive (-ir) primary neurons was measured in the trigeminal (TG) and lumber dorsal root ganglia (DRG). In the DRG, parvalbumin-ir was mostly detected in large cells (94% in the range of 600-2800 microns2). Parvalbumin-ir TG cells were smaller than similar DRG cells and yet parvalbumin-ir TG cells of < 400 microns2 (2.86%) were rare. Trichrome stains for parvalbumin, calretinin (CR) and carbonic anhydrase (CA), and for parvalbumin, calcitonin gene-related peptide (CGRP) and CA were performed to estimate possible overlap of these substances. Virtually all parvalbumin-ir DRG cells contained CA activity while a small subpopulation (28.5%) of CR-ir DRG cells lacked CA activity. All the CR-ir DRG cells that exhibited CA were also ir for parvalbumin. 31.1% of parvalbumin-ir DRG cells exhibited CR-ir while 71.5% of CR-ir DRG cells showed parvalbumin-ir. All the CR-ir DRG cells of < 400 microns2 lacked CA activity and parvalbumin-ir while all those of > 800 microns2 exhibited both activities. Approximately 30% of CR-ir DRG cells in the size range of 400-800 microns2 co-expressed CA. DRG cells co-expressing parvalbumin and CGRP were rare (approximately 1%). As was the case for the DRG, most of parvalbumin-ir TG cells exhibited CA activity (89.24%) and lacked CGRP-ir (96.6%). CR-ir TG cells were also subdivided into two groups; one with and the other without co-expression of CA. Unlike in the DRG, however, co-expression of parvalbumin and CR could never be detected in the TG.

Dietary calcium deficiency causes a reduction in calretinin mRNA in the substantia nigra compacta-ventral tegmental area of rat brain

Dietary calcium deprivation (3 weeks) affected neuronal gene expression of calretinin. Calcium deprived rats exhibited calcium appetite, weight loss, and a 28% decrease in calretinin mRNA in the substantia nigra compacta-ventral tegmental area, compared to controls. No changes were detected in 2 other mRNAs (tyrosine hydroxylase, beta-actin) and 5 other brain regions examined. This region-specific reduction of calretinin mRNA may relate to the altered physiology or behavior.

Ca(2+)-dependent and independent interactions of calretinin with hydrophobic resins

The ability of rat calretinin to bind to hydrophobic resins in a Ca(2+)-dependent manner was examined. Both native calretinin present in cerebellum extract and purified recombinant calretinin bound similarly to hydrophobic resins such as phenyl-, hexyl-, octyl-, and W7-agarose. Hydrophobic interactions of calretinin were partially Ca(2+)-dependent since 1/3 of bound protein was released from the resins by EGTA under varied conditions. Some calretinin tryptic fragments bound to octyl-agarose in a manner similar to uncleaved calretinin, while others bound to the resin in a Ca(2+)-independent manner. These and other results suggest that calretinin has several hydrophobic regions of varied strength and sensitivity to Ca2+. It is proposed that the local changes in hydrophobicity induced by Ca2+ binding might be relevant for calretinin functions.

The unipolar brush cells of the rat cerebellar cortex and cochlear nucleus are calretinin-positive: a study by light and electron microscopic immunocytochemistry

Cell class-specific markers are powerful tools for the study of individual neuronal populations. The peculiar unipolar brush cells of the mammalian cerebellar cortex have only recently been definitively identified by means of the Golgi method, and we have explored markers of cerebellar neurons with the purpose of facilitating the analysis of this new cell population and, especially, its distribution and ultrastructural features. By light microscopic immunocytochemistry, we demonstrate that, in the rat, the unipolar brush cells are the cortical neurons that are most densely immunostained with antiserum to calretinin, a recently discovered calcium-binding protein. The unipolar brush cells are highly concentrated in the flocculo-nodular lobe, the ventral uvula and the ventral paraflocculus, occur at relatively high density in the lingula, at moderate-to-low density in other folia of the vermis and in the narrow intermediate cortex, and at low to very low density, with the exception of a few hot spots, in the lateral regions of the cerebellar hemispheres and in the dorsal paraflocculus. Unipolar brush cells are also found in the cochlear nucleus. In addition to the unipolar brush cells, calretinin antibody distinctly stains certain mossy fibers, and weakly to moderately stains other cerebellar elements, such as granule neurons and climbing fibers. In the lobules containing high densities of unipolar brush cells, the granule cell bodies and the parallel fibers are much less immunoreactive, and there are many more densely immunostained mossy fibers than in the lobules, where these cells are rare, which suggests some relationships between these elements. In the cerebellar nuclei, small neurons are densely immunostained, while large neurons are immunonegative. The unipolar brush cells reside nearly exclusively in the granular layer. They are small neurons, intermediate in size between granule cells and Golgi cells, and their features are remarkably similar across all lobules. They usually have a single, relatively thick dendrite of varying length that terminates in a brush-like tip consisting of several short branchlets. Utilizing a pre-embedding protocol, we have identified unipolar brush cells with the electron microscope. The cytoplasm of these cells is partially obscured by the electron dense product of calretinin immunoreaction in all regions of the soma and processes. The cells are often covered with non-synaptic appendages and contain a peculiar cytoplasmic inclusion consisting of ringlet subunits. Other characteristic components are numerous neurofilaments, mitochondria and large, dense-core vesicles. Individual brushes enter one or two glomeruli, where the dendritic branchlets establish an unusually extensive synapse with mossy fiber rosettes.(ABSTRACT TRUNCATED AT 400 WORDS)

Neural parvalbumin and calretinin in the tooth pulp

Parvalbumin- and calretinin-immunoreactivities (CR-irs) were examined in the molar tooth pulp of the rat using immunohistochemical methods. CR-ir fibers were further classified based on the tachykinin-ir revealed by a double immunofluorescence method. The rat root pulp contained three types of nerve fibers; parvalbumin-ir smooth fibers, CR-ir (TK-negative) smooth fibers and CR-ir (TK-ir) varicose fibers. These fibers projected toward the roof of the pulp chamber and pulp horn without marked ramification. In the subodontoblastic layer at the roof of the pulp chamber and pulp horn, parvalbumin-ir smooth fibers repeatedly ramified and extended varicose terminals into the odontoblastic layer. CR-ir (TK-negative) smooth fibers reached the subodontoblastic layer without marked ramification and gave rise to varicose terminals that appeared to terminate within the subodontoblastic layer. On the other hand, CR-ir (TK-ir) varicose fibers proceeded to the subodontoblastic layer at the roof of the pulp chamber and pulp horn, where they ramified and penetrated the odontoblastic layer. The present study indicates that the rat tooth pulp contains myelinated parvalbumin-ir and CR-ir (TK-negative) fibers, and unmyelinated CR-ir (TK-ir) fibers, and that they project varicose terminals to the subodontoblastic and odontoblastic layers. The central projection sites of these sensory fibers have yet to be revealed.

Mapping of the colocalization of calretinin and tyrosine hydroxylase in the rat substantia nigra and ventral tegmental area

The distribution of calretinin (CR), a calcium binding protein, was compared with that of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine, throughout the rostrocaudal extent of the rat substantia nigra (SN) and ventral tegmental area (VTA). After mapping the cells using double-labelling immunofluorescence, it was possible to distinguish three distinct cell types: cells immunoreactive for CR only, cells immunoreactive for TH only, and cells in which the two proteins were colocalized (CR + TH). Colocalized cells in rat brain sections comprised approximately 40-55% of the fluorescent labelled cells in the SN compacta, 30-40% in the VTA, and 55-80% in the SN lateralis. Colocalized cells in the SN reticulata were infrequent except in the more caudal sections where a majority of the TH-immunoreactive cells also contained CR. The percentage of CR cells that contained TH was approximately 80% in the SN compacta and averaged 65% in the VTA. Overall, the percentage of TH-immunoreactive cells which also contained CR was approximately 50% in the SN compacta and 45% in the VTA. These data reveal a significant degree of colocalization of CR in dopamine-producing cells of the SN and VTA and suggest the need for studies concerning the fate of these individual cell types following experimental manipulations.