Ontogenetic development of 5-HT1D receptors in human brain: an autoradiographic study

The pattern of pre- and postnatal appearance of 5-HT1D receptors throughout the different areas of the human brain was studied by quantitative in vitro autoradiography, using [125I]GTI (serotonin O-carboxymethyl-glycyl-[125I]tyrosinamide) as a ligand. The anatomical distribution of 5-HT1D receptors in neonatal, infant and children's brain was in good agreement with that observed in the adult, the basal ganglia and substantia nigra being the most intensely labelled areas. The development of these receptors throughout the human brain was mainly postnatal: low densities of [125I]GTI binding sites were observed at the fetal/neonatal stage in most regions analyzed, in contrast with the high levels of labelling found in infant and children's brains. Indeed, in a number of regions, including the globus pallidus, substantia nigra and visual cortex, a peak of overexpression of 5-HT1D receptors was observed in the first decade of life. Such overexpression could support a regulatory role for 5-HT1D receptors in advanced periods of the CNS developmental process. Our results also indicate that the administration of drugs acting on 5-HT1D receptors during the early postnatal period of life could result in modifications of their properties, as these receptors are already functional in this period.

Differential expression of alpha-CGRP and beta-CGRP genes within hypoglossal motoneurons in response to axotomy

In this study we have analysed, by in situ hybridization, the expression of the genes for both alpha-CGRP and beta-CGRP in hypoglossal motor nuclei following transection of the left hypoglossal nerve. Our results show that the gene for alpha-CGRP displays a peculiar sequence of regulation (a successive up-down-up-recovery sequence) within ipsilateral hypoglossal motoneurons in response to axotomy. It is initially up-regulated, then down-regulated (displaying mRNA levels below basal), and later again up-regulated before recovery. By contrast, the gene for beta-CGRP displays a successive and distinct up-down-recovery sequence of regulation (it does not display a second increase in mRNA production). The first up-regulation of the alpha-CGRP gene occurs just during the early period of perineuronal glial reaction and the second up-regulation just during the period of delayed astrocyte reaction and muscle reinnervation. Because alpha-CGRP is a neuron-derived factor for many types of cells, including astrocytes and skeletal myocytes, our results suggest that the pleiotropic alpha-CGRP may be a motoneuron-derived trophic signal for both glial and skeletal muscle cells in order to maintain the motoneuron itself and, in consequence, might be of therapeutic interest in treating degenerative disease of motoneurons. beta-CGRP might be redundant within the hypoglossal motoneurons.

Autoradiographic analysis of 5-HT receptor subtypes labeled by [3H]5-CT ([3H]5-carboxamidotryptamine)

This work examines the autoradiographic distribution of serotonin (5-HT) receptor subtypes in rat, guinea pig and human brain, using [3H]5-HT and [3H]5-CT as ligands. Different displacers were used to mask radioligand binding to 5-HT1A, 5-HT1B/1D and 5-HT2C receptors, in an attempt to visualize other receptor populations, which presumably would correspond to 5-HT1E and 5-HT1F sites. Brain areas enriched in 5-HTnon1A/1B/1D sites in guinea pig were the hilus, dentate gyrus, striatum, claustrum, substantia nigra and superior colliculus, among others. In humans, however, the claustrum, a structure supposed to contain 5-HT1E sites, showed significant densities of [3H]5-CT binding. An interesting finding was that blockade [3H]5-CT binding to 5-HT1A receptors by 8-OH-DPAT could only be achieved at very high concentrations of the displacer. This could be due to differences in the affinity of ligands in intact tissue sections compared to membrane homogenates or cell lines. Another possibility would be that [3H]5-CT labels 5-HT1A receptors in the low-affinity state. These hypotheses remain to be investigated.

Neurotransmitter receptor histochemistry: the contribution of in situ hybridization

Molecular cloning of neurotransmitter receptors has enabled the application of in situ hybridization histochemistry to the study of the regional distribution and cellular localization of receptor mRNAs with an unprecedented degree of selectivity. This has resulted in a large body of information including detailed maps of the distribution of receptor subtype transcripts, the establishment of neurotransmitter phenotype and connectivity of receptor-expressing cells, and the relationship between receptor transcripts and binding sites. In this minireview, we discuss and illustrate with a number of examples the contributions of in situ hybridization histochemistry to the study of receptor distribution in brain tissue.

In situ hybridization for vasopressin mRNA in the human supraoptic and paraventricular nucleus; quantitative aspects of formalin-fixed paraffin-embedded tissue sections as compared to cryostat sections

In order to study the suitability of formalin-fixed paraffin-embedded brain tissue for vasopressin (AVP)-mRNA detection, we used symmetric halves of 5 human hypothalami. In every case, one half was formalin fixed for 10-35 days and paraffin embedded while the other half was frozen rapidly. Following in situ hybridization (ISH) histochemistry on systematically obtained sections of the supraoptic (SON) and paraventricular nucleus (PVN) of both halves, total amounts of AVP-mRNA in these nuclei were estimated using densitometry of film autoradiographs. Total amounts of radioactivity were found to vary considerably between patients and amounted to 1297 +/- 302 arbitrary units (AU) (PVN) (mean +/- SEM) and 2539 +/- 346 (SON) for the cryostat sections and 868 +/- 94 (PVN) and 1259 +/- 126 (SON) for the paraffin tissue. Variations introduced by the method itself yielded a coefficient of variation of only 0.19. Furthermore, a non-significant negative trend with postmortem delay was found in cryostat tissue, but not in paraffin sections. No effect of fixation time was observed in the paraffin tissue. Both ways of tissue treatment have specific advantages and disadvantages that may be different for other probes or other brain areas. For ISH of a highly abundant mRNA like AVP in a very heterogeneous brain area such as the human hypothalamus, formalin-fixed paraffin-embedded tissue sections can be used for quantitative analysis of entire brain nuclei because of the small variation in this tissue, the remarkably good signal recovery (some 75% as compared to cryostat sections) and its practical advantages with regards to anatomical orientation, storage and sampling of the tissue.

Increased beta-amyloid precursor protein expression in astrocytes in the gerbil hippocampus following ischaemia: association with proliferation of astrocytes

Increases in beta-amyloid precursor proteins (APP), which include the beta-amyloid senile plaque protein present in patients with Alzheimer's disease, have been shown to occur in models of neuronal damage and neurotoxic cell injury. This observation led us to examine the expression of these proteins after transient ischaemic episodes in the gerbil. Animals were killed 2-28 days after ischaemia and APP were detected by immunocytochemistry at the light and electron microscopic levels with an antibody raised against the C-terminal region of these proteins. The gliotic reaction was also examined using glial fibrillary acid protein (GFAP) immunoreactivity. Two days after ischaemia, neuronal cell death was observed in the hippocampal CA1 region accompanied by astrocyte hypertrophy. These hypertrophic astrocytes were found to be GFAP positive but stained weakly for APP. Seven days after ischaemia both astrocyte hypertrophia and hyperplasia, with identified mitotic figures, were observed. These hyperplasic astrocytes were intensely stained by the APP antibody, and were observed up to 28 days after ischaemia. This shows that neuronal cell death produced by transient ischaemia is followed by an increased APP expression which appears to be associated with the hyperplasic astrocytes but not with the initial hypertrophy of this cell population. These results, when taken together with those obtained in other models of neuronal damage or death, clearly suggest that APP expression follows neuronal death and is associated with astrocyte proliferation.

Rapid increase in amyloid precursor protein immunoreactivity in the supraoptic and paraventricular nuclei of the rat hypothalamus after osmotic stress

The effects of water deprivation or i.p. injection of hypertonic salt solution on the expression of the amyloid precursor polypeptide (APP) were studied immunohistochemically in the rat brain, in particular in the supraoptic and paraventricular nuclei, both known to be involved in electrolytic and water homeostasis and to contain mRNAs coding for the various forms of APP. In parallel, the expression of the immediate early gene c-fos was also studied by immunohistochemistry. Both hypertonic saline injection and water deprivation resulted in a rapid and dramatic increase in the levels of amyloid precursor protein-like immunoreactivity in neurones of the supraoptic and paraventricular nuclei. These increases paralleled those seen using c-fos immunohistochemistry. In contrast, no changes were observed in other brain areas, including the subfornical organ, which also contained mRNA and APP-like immunoreactivity. The results indicate that levels of the beta-amyloid precursor protein can be rapidly increased by stressors affecting the activity of well characterized cell populations in the rat hypothalamus. These results suggest the involvement of the beta-amyloid precursor protein in the secretory activities of these cells, or in the initiation of morphological changes which are known to occur after osmotic stress in the supraoptic and paraventricular neurones. Interestingly, the changes were limited to neurones and no modification of beta-amyloid precursor protein levels was observed in glial cells, which are also known to be modified by osmotic stress.

Differential regulation of the expression of nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 mRNAs in adult rat brain after intrahippocampal injection of quinolinic acid

Intrahippocampal injection of the endogenous excitotoxin quinolinic acid (QUIN) induces seizures together with local, delayed neurodegeneration in specific cell layers. In situ hybridization histochemistry was used to study the spatio-temporal pattern of expression of neurotrophins (NTFs) after this treatment. As in other excitatory paradigms, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNA levels increased dramatically and transiently in dentate gyrus after the administration of 120 nmol of QUIN to the left hippocampus. BDNF, but not NGF, mRNA also increased in the hippocampal pyramidal cell layer, mainly in the CA1 field. Neurotrophin-3 (NT3) mRNA levels decreased in dentate gyrus, practically disappeared around 12 h after the insult and returned to basal levels four days later. A very different pattern of expression of NTFs was found locally: (a) upregulation of NGF and BDNF mRNAs expression was prevented in a spherical region of 1-2 mm diameter around the injection site, (b) a delayed increase in NT3 mRNA levels, beginning at 12 h and lasting for at least 4 days after the administration of QUIN, was found in the same region, in cell layers showing neurodegeneration. Pretreatment with the non-competitive NMDA antagonist MK-801 (2 mg/kg, 30 min before the insult), partially blocked the increase in both BDNF and NGF mRNAs, as well as the decrease in NT3, in the contralateral hippocampus. However, this treatment did not prevent the QUIN-induced local downregulation of NGF and BDNF. Treatment with the AMPA/kainate antagonist NBQX (30 mg/kg, 15 and 5 min before, and 10 min after the insult) did not influence the effect of QUIN upon NGF or BDNF mRNA levels, although it partially prevented the hippocampal contralateral decrease in NT3 mRNA. In conclusion, the present study strongly supports previous work concerning different regulation of BDNF/NGF respect to NT3 in seizure inducing paradigms. Moreover, the different and to some extent opposite regulation of NTFs in the hippocampal region contiguous to the injection site, respect to the remaining hippocampus, suggests a differential regulation of NTFs in QUIN-induced neurodegenerative and seizural processes. Finally, our pharmacological data, (i) show that the upregulation of NGF and BDNF mRNAs, indirectly induced by QUIN, is not mediated by AMPA receptors, and (ii) suggest other effects for QUIN, apart from the stimulation of NMDA receptors.

De novo synthesis of GAP-43: in situ hybridization histochemistry and light and electron microscopy immunocytochemical studies in regenerating motor neurons of cranial nerve nuclei in the rat brain

In order to investigate the modulation of the synthesis and the subcellular localization of the growth associated protein GAP-43 in neuronal cell bodies we have taken advantage of the well known regenerative properties of axotomized motor neurons of the facial and hypoglossal nuclei. Alterations in the levels of GAP-43 mRNA containing cells were studied by in situ hybridization histochemistry. The protein localization was examined using immunohistochemistry at the light and electron microscopic levels. Neurons from the control side showed undetectable levels of both GAP-43-like immunoreactivity and GAP-43 mRNA levels. Whereas axotomized neurons exhibited a marked increase in GAP-43 mRNA levels and in GAP-43-like immunoreactivity. Three to 50 days after axotomy, motor neurons ipsilateral to the lesion displayed a dense reticular or filamentous perinuclear distribution of the immunoreactivity in somata and proximal dendritic processes, corresponding to the location of the Golgi apparatus in these neurons. At the electron microscopic level the immunoreactivity was located in the cisternae of the Golgi complex and found to be associated with trans-side vesicles of these complexes. The myelinated fibers of the transectomized facial nerve also presented an intense GAP-43-like immunoreactivity. Twenty-one days after the axotomy a decay in the number of immunostained neurons and in the intensity of immunolabeled somata was observed. Our study reveals a rapid induction of GAP-43 mRNA and protein after axotomy. The localization of the newly synthesized GAP-43-like immunoreactivity to the Golgi apparatus seen in the present work suggests an early association of this protein with newly formed membranes prior to transport toward the terminals through the axons.

Expression and localization of somatostatin receptor SSTR1, SSTR2, and SSTR3 messenger RNAs in primary human tumors using in situ hybridization

Somatostatin receptor gene expression of SSTR1, SSTR2, and SSTR3 subtypes was evaluated by in situ hybridization in 55 human primary tumors shown to contain a high density of somatostatin receptors in binding assays. All 55 tumors expressed at least one SSTR subtype. Of 55 somatostatin receptor-positive tumors, 46 had SSTR2 mRNA; all 46 were characterized as having receptors with a high affinity for the synthetic analogue octreotide. Of 55 tumors, 12 expressed SSTR1, and 14 expressed SSTR3 mRNA. The subtype SSTR1 was expressed alone in 4 cases, SSTR2 was expressed alone in 33 cases, and SSTR3 was expressed alone in one case. In 4 cases, all 3 SSTR were expressed simultaneously. The cases having SSTR1 mRNA were identified in binding experiments with 125I-labeled somatostatin-14 and -28 analogues rather than with 125I-[Tyr3]-octreotide. Whereas meningiomas, neuroblastomas, pituitary adenomas, small cell lung carcinomas, lymphomas, and breast tumors expressed primarily a high abundance of SSTR2, carcinoids, islet cell carcinomas, medullary thyroid carcinomas, and ovarian tumors had a mixed distribution of the somatostatin receptor subtypes. This is the first demonstration of the presence of SSTR1, SSTR2, and SSTR3 in primary human tumors using in situ hybridization. Since these somatostatin receptor subtypes probably mediate distinct somatostatin actions, it may be worthwhile to search for subtype-specific analogues to use for the treatment and diagnosis of these tumors.

Distribution of the serotonin 5-HT2 receptor family mRNAs: comparison between 5-HT2A and 5-HT2C receptors

Because of their similarities, serotonin 5-HT2, 5-HT1C, and the recently described 5-HT2F receptors have been classified as members of the 5-HT2 receptor family, and they have been renamed 5-HT2A, 5-HT2C and 5-HT2B, respectively. The regional distribution and cellular localization of mRNA coding for the members of 5-HT2 receptor family were investigated in consecutive tissue sections from the rat brain by in situ hybridization histochemistry. No evidence for the expression of 5-HT2B receptor was found. High levels of 5-HT2A (formerly 5-HT2) receptor mRNA were observed only in few areas, as the frontal cortex, piriform cortex, ventro-caudal part of CA3, medial mammillary nucleus, the pontine nuclei and the motor cranial nerve nuclei in the brainstem, and the ventral horn of the spinal cord. The distribution of 5-HT2A receptor mRNA is generally in good agreement with that of the corresponding binding sites, although discrepancies were sometimes observed. 5-HT2C (formerly 5-HT1C) mRNA was present at very high levels in the choroid plexuses. However, very high levels were also seen in many other brain regions, as the retrosplenial, piriform and entorhinal cortex, anterior olfactory nucleus, lateral septal nucleus, subthalamic nucleus, amygdala, subiculum and ventral part of CA3, lateral habenula, substantia nigra pars compacta, several brainstem nuclei and the whole grey matter of the spinal cord. These results confirm and extend previous observations that 5-HT2C receptor mRNA is present in many brain areas in addition to those autoradiographically shown to have the corresponding binding sites and that 5-HT2C receptor subtype is a principal 5-HT receptor in the brain. From the comparison between their distributions, 5-HT2A and 5-HT2C receptor mRNAs appeared to be expressed in distinct but overlapping sets of brain regions. Both mRNAs coexisted at high levels in the anterior olfactory nucleus, piriform cortex, endopiriform nucleus, claustrum, pyramidal cell layer of the ventral part of CA3, taenia tecta, substantia nigra pars compacta, and several brainstem nuclei. In other regions both mRNAs were present but with different distributions, as the caudate-putamen. These results are also discussed in relation to the physiological meaning of the existence of two so similar receptor subtypes in the brain.

Localization of 5-HT1B, 5-HT1D alpha, 5-HT1E and 5-HT1F receptor messenger RNA in rodent and primate brain

In situ hybridization histochemistry (ISHH) was used to study the distribution of various 5-HT1 receptor messenger RNAs (mRNA) in the mammalian nervous system. Since the cDNAs encoding the different 5-HT1 receptors, have not been cloned in one single species, brains of the species appropriate for the 5-HT1 receptor messenger RNA (mRNA) have been used. Thus, 5-HT1B and 5-HT1D alpha mRNA were determined in rat and mouse brain, while 5-HT1E and 5-HT1F mRNA were studied in human (and monkey) and guinea-pig brain, respectively. 5-HT1B and 5-HT1D alpha hybridization signals were predominantly present in caudate-putamen and cortical areas; in addition, 5-HT1B mRNA was also detected in hippocampus, cerebellum and cerebral arteries. In general, the distribution of 5-HT1B mRNA was characterized by high densities, whereas 5-HT1D alpha mRNA was expressed at very low levels. Comparison of the localization of the mRNAs to the regional distributions of the 5-HT1B and 5-HT1D binding sites in rat brain (described in a previous study), revealed that both receptor subtypes could be putative presynaptic heteroreceptors, modulating the release of various neurotransmitters in the central nervous system. The mRNA encoding the recently cloned 5-HT1E receptor, which has low affinity for the 5-HT1 receptor ligand 5-carboxamidotryptamine (5-CT), was localized in human brain. It was found to be present in cortical areas, caudate, putamen and amygdala, areas known to contain 5-CT insensitive 5-HT1 binding sites. The regional distribution of the 5-HT1F mRNA was determined in guinea-pig brain: high densities were observed in various cortical areas, the hippocampal formation and claustrum, which are regions known to contain 5-CT insensitive 5-HT1 or non 5-HT1A/1B/IC/ID [3H]5-HT binding sites. Altogether, this ISHH study describes the distribution of mRNAs of recently cloned 5-HT1 receptors in rodent and primate brain and compares these results to the distribution of the heterogeneous population of 5-HT1 binding sites.

Excitatory amino acid AMPA receptor mRNA localization in several regions of normal and neurological disease affected human brain. An in situ hybridization histochemistry study

In situ hybridization histochemistry was used to localize the mRNAs coding for four alpha-aminoisoxazole propionic acid-sensitive glutamate receptor subunits in human brain (age range 51-95 years, postmortem delay 4.5-10 h). High levels of the B receptor subunit mRNA were present in all the studied regions, followed by the A-subunit and the C-subunit. Only very low levels of the D-subunit mRNA were detected. In hippocampus, the mRNA coding for the B-subunits of the glutamate receptor was observed in granule cells of dentate gyrus and in the pyramidal cells of Ammon's horn. In cortex, the highest levels of glutamate receptor subunit mRNAs were found in layer I and layers III-IV of entorhinal and temporal cortex, although significant levels were also observed in the other cell layers. A differential distribution was seen in cerebellum where the A-subunit mRNA is expressed mainly by Purkinje cells, while the B-subunit mRNA is present in the internal granule cell layer. These results correlate well with previous data from autoradiographic studies on the localization of excitatory amino acid binding sites in human brain and pinpoint the cells where these receptors are synthesized. In situ hybridization in the hippocampus of patients affected by Alzheimer's disease (age range 77-82 years, postmortem delay 19-25.5 h) revealed a decrease on the content of the mRNAs coding for these excitatory amino acid receptors, while an increase was detected in surgically dissected epileptic human hippocampi. These results corroborate and extend the previous data from in vitro autoradiography and suggest alteration of the excitatory amino acid disfunction during these neurodegenerative processes.

Multiplicity of muscarinic autoreceptor subtypes? Comparison of the distribution of cholinergic cells and cells containing mRNA for five subtypes of muscarinic receptors in the rat brain

In situ hybridization was used to compare the microscopic distribution in the rat brain of cells containing mRNA for choline acetyltransferase (ChAT) (i.e. cholinergic cells) with that of cells containing mRNA for the five subtypes of muscarinic receptors, in an attempt to establish the potential role as autoreceptors (i.e. muscarinic cholinoceptors present in cholinergic cells) of the different muscarinic receptor subtypes. [32P]alpha-dATP-labelled synthetic oligonucleotides were used as hybridization probes in serial sections. Transcripts for all five subtypes of muscarinic receptors were detected in cells co-distributing with ChAT mRNA-containing cells in one or more regions of the brain. Cells containing m2, m3, m4 or m5 mRNAs were observed in the regions of the basal forebrain where cholinergic cells are located (medial septum/diagonal band nuclei, ventral pallidum, basal nucleus of Meynert). m2, m3 and m5 mRNAs were abundant in the parabigeminal nucleus. m2, m3 and m4 transcripts were detected in the pedunculopontine and laterodorsal tegmental nuclei. m1, m2 and m3 mRNAs were present in several cranial nerve nuclei. The present results suggest that muscarinic autoreceptors belonging to the five subtypes cloned to date may exist.

Expression of acetylcholinesterase messenger RNA in human brain: an in situ hybridization study

The distribution of messenger RNA coding for acetylcholinesterase was studied in human post mortem brain and rhesus monkey by in situ hybridization histochemistry and compared to the distribution of acetylcholinesterase activity. Acetylcholinesterase messenger RNA had--similar to acetylcholinesterase enzymatic activity--a widespread distribution in human bain. Acetylcholinesterase messenger RNA positive cells corresponded to perikarya rich in acetylcholinesterase activity in most but not all regions. Examples for mismatches included the inferior olive and human cerebellar cortex. The presence of hybridization signals in cerebral cortex and an enrichment in layer III and V of most isocortical areas confirmed that perikaryal acetylcholinesterase in cerebral cortex is of postsynaptic origin and not derived from cholinergic projections. In striatum the expression of high levels of acetylcholinesterase messenger RNA was restricted to a small population of large striatal neurons. In addition, low levels of expression were found in most medium sized striatal neurons. Cholinergic neurons tended to express high levels of acetylcholinesterase messenger RNA whereas in cholinoceptive neurons the levels were moderate to low. However, some noncholinergic neurons like dopaminergic cells in substantia nigra, noradrenergic cells in locus coeruleus, serotoninergic cells in raphé dorsalis, GABAergic cells in thalamic reticular nucleus, granular cells in cerebellar cortex and pontine relay neurons expressed levels comparable to cholinergic neurons in basal forebrain. It is suggested that neurons expressing high levels of acetylcholinesterase messenger RNA may synthesize acetylcholinesterase for axonal transport whereas neurons with an expression of acetylcholinesterase confined to somatodendritic regions tend to contain lower levels of acetylcholinesterase messenger RNA.

Regional distribution of amyloid beta-protein precursor, growth-associated phosphoprotein-43 and microtubule-associated protein 2 messenger RNAs in the nigrostriatal system of normal and Weaver mutant mice and effects of ventral mesencephalic grafts

Using in situ hybridization histochemistry with [32P]oligonucleotide probes, we studied the cellular localization of RNA transcripts for amyloid beta-protein precursor (beta APP), growth-associated phosphoprotein-43 (GAP-43) and microtubule-associated protein 2 (MAP2) in the mesostriatal system of normal (+/+) and weaver (wv/wv) mutant mice, which lose mesencephalic dopamine neurons. In addition, expression of the same messages was studied in ventral mesencephalic cell suspensions transplanted to the weaver striatum. Transcripts encoding GAP-43, MAP2 and isoforms beta APP695, beta APP714 and beta APP751 were present in normal substantia nigra and progressively reduced in weaver substantia nigra; such a reduction was correlated with dopamine neuron loss. The survival of dopamine neurons in unilateral intrastriatal grafts was documented by methamphetamine-induced rotational asymmetry tests and by tyrosine hydroxylase immunocytochemistry. High hybridization signals were obtained for GAP-43, MAP2, beta APP695, beta APP714 and beta APP751 RNA transcripts in the grafted tissue; the beta APP770 species--normally seen in striatum and not substantia nigra--was not expressed in the grafts, but it was present in the recipient striatum. Following immunocytochemical labelling with antibodies, GAP-43 and MAP2 immunoreactivities were seen in cell processes in the grafts and surrounding tissue, whereas beta APP immunoreactivity was mainly found in grafted cell bodies. These results suggest that the transplanted mesencephalic cells mature very similarly to those in the normal substantia nigra, expressing different mRNAs that are normally present in the ventral midbrain and which are reduced in the weaver mutant as a consequence of dopamine neuron loss.

Beta APP gene expression is increased in the rat brain after motor neuron axotomy

The response of the beta APP gene to neuronal injury was studied in the facial and hypoglossal nerve nuclei of the rat after corresponding nerve axotomy. Increased levels of beta APP 695, 714, 751 and 770 mRNAs were observed after either facial or hypoglossal nerve axotomy in the parent ipsilateral motor neurons. The increase was gradual, with maximal values 7 days after axotomy. beta APP mRNA expression returned to normal values 60 days after the lesion. Increased beta APP immunostaining was also detected in ipsilateral chromatolytic motor neurons. No change in beta APP immunoreactivity was observed in oligodendrocytes, another cell type expressing beta APP under normal conditions. A rapid increase in the expression of the GFAP gene was observed in reactive astrocytes surrounding chromatolytic neurons in the ipsilateral facial or hypoglossal nuclei. Thus, in contrast with other models of neuronal injury, where only the Kunitz protease inhibitor-containing beta APP mRNA isoforms are increased, all beta APP mRNAs are increased in the axotomy model. Furthermore, although beta APP expression has been shown to be increased in reactive astrocytes following neuronal injury, in the present study the increase was essentially found in the motor neurons reacting to axotomy.

Dopamine D3 receptor mRNA and binding sites in human brain

Dopamine D3 receptors (Sokoloff et al., 1990) have been shown to be related to dopamine D2 receptors and have been suggested to play a role in mediating the antipsychotic effects of neuroleptics. So far studies on the expression of D3 mRNA and of binding sites with pharmacological characteristics of D3 receptors have been restricted to rat brain. Using in situ hybridization histochemistry, we demonstrate that D3 mRNAs are enriched in human n, accumbens and in the islands of Calleja. In addition, D3 mRNA was detected at very low levels in anterior caudate and putamen with a rostro-caudally decreasing gradient and in hypothalamic mammillary nuclei. In receptor autoradiographic binding studies, the islands of Calleja were found to be labeled by [125I]iodosulpride and [3H]CV 205 502 but not by [3H]raclopride and [3H]YM 09151-2. Pharmacological analysis of binding of the D2/D3 ligand [3H]CV 205 502 in n. accumbens and caudate-putamen is consistent with the presence of D3 receptor sites in ventral striatum. Overall distribution and pharmacology of D3 sites in human and rat brain appear to be similar. Presence and distribution of D3 receptors in human brain are compatible with the notion that D3 receptors might be involved in mediating the clinical effects of antipsychotics.

Neuronal death and neurotrophin gene expression: long-lasting stimulation of neurotrophin-3 messenger RNA in the degenerating CA1 and CA4 pyramidal cell layers

Neurotrophin-3 has been characterized as the product of a gene cloned by homology with nerve growth factor and brain-derived neurotrophic factor. Recombinant neurotrophin-3, like nerve growth factor and brain-derived neurotrophic factor, has been shown to enhance survival and differentiation of specific neuronal populations in vitro. However, little is known about its function and regulation in vivo. Both brain-derived neurotrophic factor and nerve growth factor messenger RNAs increased in adult rat brain, in a wide range of excitatory paradigms. In contrast, neurotrophin-3 messenger RNA decreased in some of them. Neurotrophin-3 is the most highly expressed neutrophic factor in immature areas of the central nervous system. However, no stimulation of its expression in the mature central nervous system, either in physiological or pathological conditions, has been described to date. This behaviour suggests that neurotrophin-3 could be involved in biological roles different from the prototypes nerve growth factor and brain-derived neurotrophic factor. Excitatory amino acid receptor-mediated neurotoxicity (excitotoxicity) is believed to contribute to neuronal loss in a wide range of neurodegenerative conditions (for a review, see Ref. 17). Moreover, locally increased levels of the endogenous excitotoxin quinolinic acid may be involved in the natural development of neurodegenerative diseases. The unilateral intrahippocampal injection of 120 nmol of quinolinic acid induced seizures together with local neurodegeneration in specific cell layers. In situ hybridization histochemistry was used to analyse the spatiotemporal pattern of expression of neurotrophin-3. As in other excitotoxic paradigms, neurotrophin-3 messenger RNA clearly decreased, nearly disappearing, in the contralateral hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatostatin (SRIH) messenger ribonucleic acid expression in human neuroendocrine and brain tumors using in situ hybridization histochemistry: comparison with SRIH receptor content

Somatostatin (SRIH) receptors are expressed in a large number of neuroendocrine and brain tumors. To evaluate the potential of these tumors locally to produce the SRIH required to bind to SRIH receptors, we have investigated in 158 human tumors whether they express mRNA for SRIH, using in situ hybridization. Among 78 neuroendocrine tumors tested, 13 of 13 medullary thyroid carcinomas, 19 of 34 pheochromocytomas, 3 of 11 paragangliomas, 0 of 4 small cell lung cancers, 4 of 9 adrenal neuroblastomas, and 4 of 7 gastroenteropancreatic tumors contained SRIH mRNA. Among 47 central nervous system and meningeal tumors tested, including 23 meningiomas, 9 astrocytomas, 4 oligodendrogliomas, and 11 glioblastomas, none expressed SRIH mRNA. Unexpectedly, 16 of 33 ovarian tumors, including adenocarcinomas and borderline tumors, expressed SRIH mRNA. These results suggest that a large proportion of neuroendocrine tumors have the ability to express SRIH mRNA, whereas central nervous system tumors do not. The presence of SRIH mRNA in half of the tested ovarian tumors suggests that those tumors may be hormone producing and have neuroendocrine features. The presence of SRIH receptors in most of the neuroendocrine tumors together with the ability of many of those tumors to synthesize SRIH point toward an autocrine regulatory feedback mechanism of SRIH in these tissues.

Differential regional and cellular distribution of beta-amyloid precursor protein messenger RNAs containing and lacking the Kunitz protease inhibitor domain in the brain of human, rat and mouse

The beta-amyloid precursor protein is the precursor of the main component of senile plaques (the beta-amyloid peptide or beta/A4) found in the brain of aged humans and, in higher amounts, in the brain of Alzheimer's disease and Down's syndrome subjects. Four different forms of beta-amyloid precursor protein messenger RNAs have been described in humans and rodents: beta-amyloid precursor protein 695, beta-amyloid precursor protein 714, beta-amyloid precursor protein 751 and beta-amyloid precursor protein 770 messenger RNAs (numbers corresponding to the number of encoded amino acids). The two latter forms are characterized by containing in their sequence a region with high homology to the Kunitz family of serine protease inhibitors. We have used oligonucleotide probes to study the distribution of the different messenger RNAs encoding each of the four beta-amyloid precursor proteins by in situ hybridization histochemistry in human, rat and mouse brain. We found that beta-amyloid precursor protein 695, beta-amyloid precursor protein 714 and beta-amyloid precursor protein 751 messenger RNAs were widely distributed in the human, rat and mouse brain and that their distribution was roughly similar in most brain areas in these three species. The distribution of beta-amyloid precursor protein 770 messenger RNA was not so wide and differed among the three species studied. beta-amyloid precursor protein 751 and 770 messenger RNAs were the only forms present at significant levels in rodent choroid plexus and meninges, while beta-amyloid precursor protein messenger RNA isoforms containing and lacking the Kunitz domain were detected in the human choroid plexus. We also observed that the relative levels of beta-amyloid precursor protein 751 and 770 messenger RNAs in the rat cerebral white matter as well as in the mouse and human striatum were higher than those of the beta-amyloid precursor protein messenger RNAs lacking the Kunitz domain. While the most abundant beta-amyloid precursor protein messenger RNAs in the brain of all three species under study were, in descending order, beta-amyloid precursor protein 695 and beta-amyloid precursor protein 751 messenger RNAs, the least abundant form was not the same for all species: in human it was beta-amyloid precursor protein 714 messenger RNA and in rat and mouse brain it was beta-amyloid precursor protein 770 messenger RNA. Our results show differences both inter- and intraspecies of the relative abundance and distribution of four beta-amyloid precursor protein messenger RNAs in rat, mouse and human brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional distribution of the alternatively spliced isoforms of beta APP RNA transcript in the brain of normal, heterozygous and homozygous weaver mutant mice as revealed by in situ hybridization histochemistry

The cellular localization of amyloid beta-protein precursor (beta APP) RNA transcripts was studied by in situ hybridization histochemistry in normal, heterozygous and homozygous weaver (wv) mutant mice, which lose midbrain dopamine (DA) neurons, cerebellar granule cells, and Purkinje cells. The beta APP gene is located at the distal end of mouse chromosome (MMU) 16, on which the wv locus has been assigned as well. Transcripts encoding isoforms beta APP695, beta APP714 and beta APP751 were present in several different brain areas of normal (+/+) mice, including hippocampus, substantia nigra (SN) pars compacta and cerebellum. The same transcripts were progressively reduced in homozygous weaver (wv/wv) SN, in correlation with DA neuron loss. The beta APP770 species--normally seen in striatum and not SN--was present in the mutant striatum. There were not any obvious changes in beta APP expression in the nigrostriatal system of weaver heterozygotes (wv/+). In normal cerebellum, Purkinje cells showed very high levels of hybridization signal for beta APP695, beta APP714 and beta APP751 RNA transcripts, and a moderate signal for the beta APP770 species. In weaver heterozygotes and homozygotes, Purkinje cells, which are typically not arranged in a monolayer, showed strong hybridization signal. No changes in beta APP mRNAs were observed in brain areas other than the cerebellum and ventral midbrain of weaver mutants. These findings suggest that the decreased beta APP gene expression seen in the cerebellum and SN of weaver mutants most likely represents an epiphenomenon of the regional nerve cell loss and, therefore, the wv gene defect on MMU 16 does not seem to influence the expression of the closely linked beta APP gene in brain areas outside the nigrostriatal pathway and cerebellar cortex.

p-chlorophenylalanine increases tryptophan-5-hydroxylase mRNA levels in the rat dorsal raphe: a time course study using in situ hybridization

The effects of a single dose of p-chlorophenylalanine on the mRNA encoding tryptophan-5-hydroxylase (EC 1.14.16.4) in the rat dorsal raphe nucleus were analyzed using in situ hybridization. The levels of tryptophan-5-hydroxylase mRNA were markedly increased in cell bodies located in the ventromedial part of the dorsal raphe 1-2 days after p-chlorophenylalanine (300 mg/kg, i.p.) administration. This was followed by a decrease in the amount of tryptophan-5-hydroxylase mRNA, which returned to basal values by 5 days after treatment. An almost symmetric time course was observed for the midbrain serotonin concentration. Our results on the temporal pattern of changes in tryptophan-5-hydroxylase mRNA levels in the ventromedial part of the dorsal raphe are opposite to those reported for the enzyme activity and serotonin concentration after p-chlorophenylalanine treatment. These changes may result from modifications in enzyme mRNA expression, suggesting that tryptophan-5-hydroxylase gene transcription is involved in feedback mechanisms regulating serotonin synthesis.

Differential visualization of dopamine D2 and D3 receptor sites in rat brain. A comparative study using in situ hybridization histochemistry and ligand binding autoradiography

At least five members of the dopamine receptor family have been characterized at the gene level. D2, D3 and D4 dopamine receptors are related pharmacologically. In order to visualize the differential expression of D1, D2 and D3 receptors in rat brain we have combined in situ hybridization histochemistry with receptor autoradiography. Regions enriched with D3 messenger RNA (mRNA) included the islands of Calleja (ioC) and nucleus accumbens. Very low or undetectable levels were present in the caudate-putamen. In contrast, no D2 transcripts were observed in the islands of Calleja, but there were high levels in the nucleus accumbens, caudate-putamen (CP) and pyramidal layer of the olfactory tubercle. A comparison of the binding pattern of six dopamine receptor radioligands hitherto regarded as D2 receptor-selective showed that the islands of Calleja were intensely labelled by [125I]iodosulpride, [3H]CV 205 502 and [3H]SDZ 205 501, while the binding of [3H]spiperone, [3H]raclopride and [3H]YM 09151-2 was much lower or undetectable. Pharmacological analysis of the binding of D2/D3 ligands to the islands of Calleja and caudate-putamen suggests that binding sites in these two regions are of different pharmacology, consistent with the presence of D3 sites in the islands of Calleja and the predominance of D2 sites in the caudate. These results demonstrate the expression of D3 binding sites in the rat brain and provide a procedure to differentiate D2 and D3 receptor populations in binding studies.