Quantitative non-radioactive in situ hybridization of preproenkephalin mRNA with digoxigenin-labeled cRNA probes

Non-radioactive detection of mRNA with in situ hybridization histochemistry has emerged as an important new technology for the study of gene expression. Quantitative in situ hybridization studies have generally relied upon counting of autoradiographic grains in the emulsion overlying cells containing hybridized, radioactively labeled probe. However, such high resolution studies require tedious grain counting over individual cells, frequently in addition to weeks of exposure to nuclear emulsion. The present report describes a quantitative, non-radioactive approach to the detection of a specific mRNA in the brain with the advantages of comparatively rapid tissue processing and computerized image analysis. The validity of this approach was tested by measuring the haloperidol-induced increase in the level of preproenkephalin mRNA in striatal sections of the rat brain using an RNA probe labeled with digoxigenin-11-UTP. Detection of probe hybridized to tissue sections was carried out enzymatically following complex formation with an antidigoxigenin-alkaline phosphatase conjugate. Using computerized image analysis, it was found that chronic treatment of rats with haloperidol resulted in a 50 +/- 6% increase in striatal neuronal optical density, a value in good agreement with previous studies using low-resolution radioactive methods, showing a 30-80% increase in striatal preproenkephalin mRNA hybridization signal.

Ontogeny of somatostatin mRNA-containing perikarya in the rat central nervous system

The distribution of neuronal perikarya containing somatostatin mRNA in the developing rat brain was investigated with in situ hybridization histochemistry. This study describes the expression of somatostatin mRNA during selected perinatal stages and demonstrates regional changes in somatostatin mRNA expression at the single cell level. The mRNA expression closely parallels previously reported developmental localization of the peptide (Inagaki et al., 1982; Shiosaka et al., 1982). As early as embryonic day 13 (E13), somatostatin mRNA was observed in discrete spinal cord and brainstem regions. At birth, densely hybridized somata could be seen primarily in ventral and caudal brain areas with small scattered neurons in the hippocampus and dorsal neocortex. After birth, somatostatin mRNA increased in forebrain regions, such as the hippocampus, dorsal neocortex, and caudate. By postnatal day 14 (P14), the distribution in the telencephalic and diencephalic regions approached that of the adult brain. Several brain regions manifested large changes in the density of somatostatin mRNA hybridization during development. For example, the cerebellar vermis and brainstem contained somatostatin mRNA perikarya during early postnatal development but decreased in these regions in the adult. During perinatal development, increases in somatostatin mRNA content were the results of increases in both the number of neurons containing somatostatin mRNA as well as in the amount of this mRNA expressed in each cell. As the brain differentiates, the apparent numbers of somatostatin mRNA containing neurons in certain brain regions are reduced. These data provide evidence for transient somatostatinergic neurons during early development in discrete areas of the occipital cortex, pyriform cortex, cerebellum, and brainstem and suggest that this peptide may play a role in the development of these regions.

Non-radioactive detection of nerve growth factor receptor (NGFR) mRNA in rat brain using in situ hybridization histochemistry

Radioactively labeled RNA probes in conjunction with in situ hybridization histochemistry have become a useful method for studying gene expression in the central nervous system. We used digoxigenin-labeled uridine triphosphate to synthesize cRNA probes for localization of nerve growth factor receptor (NGFR) mRNA in the rat basal forebrain. Detection of cells containing digoxigenin-labeled NGFR mRNA was accomplished using a digoxigenin antibody conjugated with alkaline phosphatase. NGFR mRNA-positive cells were distributed in three major cell groups in the basal forebrain: the medial septal nucleus, vertical and horizontal limbs of the diagonal band of Broca, and nucleus basalis. This technique provides a rapid and sensitive method for high-resolution detection of mRNA species in the central nervous system, as well as the potential for co-localization of two different mRNA species within individual cells.

Localization of nerve growth factor receptor mRNA in the rat basal forebrain with in situ hybridization histochemistry

1. In situ hybridization histochemistry was used to localize nerve growth factor receptor (NGFR) mRNA in the adult rat basal forebrain. 2. In emulsion-dipped sections 35S-labeled RNA antisense probes produced a high density of silver grains over cells located in the medial septum, vertical and horizontal limbs of the diagonal band of Broca, and nucleus basalis. 3. This distribution of NGFR mRNA overlaps with the distribution of NGFR protein localized using immunocytochemical techniques. 4. No hybridization signal was detected when sections were hybridized with a 35S-labeled RNA sense (control) probe. 5. We suggest that NGFRs are synthesized in these basal forebrain nuclei and transported to terminal areas where NGF is thought to be bound and internalized, an initial step in the many actions of this neurotrophic factor.

Neuronal localization of cholecystokinin mRNA in the rat brain by using in situ hybridization histochemistry

The distribution of cholecystokinin (CCK) mRNA in the rat brain was determined by means of in situ hybridization histochemistry. Our results demonstrate a widespread distribution of neurons containing CCK mRNA throughout the rat brain. Hybridization-positive neurons were distributed throughout the neocortex, olfactory bulb, claustrum, amygdala, the dentate gyrus and hippocampus proper, and several subnuclei of the thalamus and the hypothalamus. The most abundant and most heavily labeled neurons were found in the endopiriform/piriform cortex, tenia tecta, and the ventral tegmental area. The distribution of neurons positive for CCK mRNA paralleled that of CCK-like immunoreactive neurons. These results detail the distribution of CCK mRNA and clearly identify the existence of CCK-synthesizing neurons in regions such as the paraventricular and supraoptic nuclei of the hypothalamus, where the presence of CCK cell bodies was previously uncertain.

Synchronized neuronal activities in neocortical explant cultures

Intracellular recordings revealed that in neocortical explant cultures prepared on the day of birth and examined 3-6 weeks later, neurons mature and establish complex synaptic relationships that lead to spontaneous and triggered synchronous discharge. The spontaneous synchronous activity took several forms, including periodic generation of epileptiform depolarizing waves, prolonged periods of seizure-like discharge, and periodic, intense barrages of IPSPs. Synchronous depolarizations were associated with a marked increase in membrane conductance. Intracellular injection of currents of varying polarity and intensity affected their amplitudes and polarities without influencing the probability of their occurrence, indicating that the discharge reflected the synchronous activities of a neuronal population. This conclusion was confirmed with simultaneous recordings from pairs of neurons. Effects of the GABAa receptor antagonist, bicuculline, and the NMDA receptor antagonist, 2-aminophosphonvalerate (2APV), were used to assess the contributions of impairment of inhibition and enhancement of excitation to the initiation of synchronous discharge. The frequency with which spontaneous depolarizations were generated in normal medium was markedly reduced by 2APV. Moreover, seizure-like activity was induced by removing Mg++ from the medium, a condition that enhances conductance through NMDA receptor-coupled channels. This behavior was also attenuated by 2APV. Perfusion of bicuculline was potently epileptogenic. 2APV cut short the late, voltage-dependent phase of bicuculline-induced paroxysmal depolarizations, indicating a role of NMDA receptors in generating this component of the wave. Epileptiform activities induced by withdrawal of Mg++ were greatly augmented by bicuculline, indicating that blockade of inhibition was not a prerequisite for seizure-like activity. This conclusion is supported by the finding that in many neurons in untreated cultures, paroxysmal generation of trains of IPSPs was the primary manifestation of spontaneous, synchronous population discharge.

Electrophysiological characteristics of neurons in neocortical explant cultures

We examined the electrophysiological and morphological properties of neocortical neurons maintained in explant cultures prepared from the parietal cortex of newborn Sprague-Dawley rats. After 3-6 weeks in vitro, cultures showed regional differences in cellular density reminiscent of cortical layering, and an abundance of axonal processes. Pyramidal-shaped neurons with spinous dendrites were the dominant elements revealed by Lucifer yellow injections. Intracellular recordings revealed that many electrophysiological properties of neurons in the explants resembled those of neocortical neurons in vivo and in slice preparations. In response to depolarizing current injection, neurons in the explants showed the same three patterns of repetitive firing described in neocortical slices, as well as a similar array of responses. Spontaneous synaptic potentials were recorded from all neurons and complex PSPs were evoked in response to focal extracellular stimulation. GABAa receptors mediated a significant component of the evoked responses. Fifteen of sixty neurons generated action potentials that arose spontaneously from resting potentials. Neurons in many slices generated large, prolonged depolarizing potentials that reflected coordinated synaptic activity within the explants. These results underscore the usefulness of the neocortical explant as a valuable model for studying aspects of the behavior of circuits of cortical neurons.

Nonradioactive detection of vasopressin mRNA with in situ hybridization histochemistry

In situ hybridization histochemistry has been used successfully by many laboratories to detect mRNAs within single cells in the CNS. The detection of these hybrids in CNS tissue sections has been accomplished mainly with radioactive probes. However, radiolabeled probes have intrinsic limitations, including the long exposure time required for high resolution autoradiography and the inability to detect multiple RNA species within the same neuron. Here we report a new method to detect mRNA in situ using a synthetic DNA probe conjugated to alkaline phosphatase (AP). The probe was synthesized to be complementary to the glycoprotein coding region of vasopressin mRNA. Under normal hybridization conditions high resolution detection of vasopressin mRNA within individual neurons was routinely obtained within 8 h. The distribution of hybridization signal obtained with the AP-conjugated probe was identical to that observed with the same probe radiolabeled with [35S]dATP. Hybridization-positive neurons were found in all regions of the CNS that have been previously reported to synthesize vasopressin, including magnocellular neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus. Small diameter neurons were also observed in the suprachiasmatic nucleus, the accessory PVN, the bed nucleus of the stria terminalis, and a cell group along the ventral surface of the optic tract. These results suggest that nonradioactive detection of neuropeptide mRNA in situ can be easily accomplished within 24 h. Furthermore, the improved resolution with AP-conjugated oligonucleotide probes should enhance efforts to study the regulation of gene expression in the nervous system.

Lactation elevates vasoactive intestinal peptide messenger ribonucleic acid in rat suprachiasmatic nucleus

Vasoactive intestinal peptide (VIP) has been suggested to play a role in lactation; indeed several studies implied that VIP induces the release of PRL in the pituitary. Quantitative RNA studies from our laboratory show an increase in the VIP messenger RNA (mRNA) content in the hypothalamus of lactating rats. The purpose of this investigation is to determine which hypothalamic neurons are increasing the expression of VIP. A sensitive in situ hybridization assay employing synthetic oligodeoxynucleotide probes corresponding to specific exons of the VIP gene was used to study VIP gene expression at the neuronal level. We were able to detect VIP-encoding transcripts in various brain regions including the ventrolateral thalamus, neocortex, pyriform cortex, and hypothalamus with a particularly high concentration in the suprachiasmatic nucleus. When lactating animals were compared to non-lactating animals, a 2-fold increase was observed in VIP transcripts in the suprachiasmatic nucleus. Since the suprachiasmatic nucleus is not directly associated with the physiology of lactation, the response of the VIP gene to lactation may be, in part, indirect. Taken together, our results suggest that lactation and the expression of the VIP gene are interrelated.

In situ hybridization of mRNA for beta-preprotachykinin and preprosomatostatin in adult rat dorsal root ganglia: comparison with immunocytochemical localization

In situ hybridization histochemistry was used to identify neurons in rat dorsal root ganglia that contained mRNAs encoding beta-preprotachykinin and preprosomatostatin. The distribution of these neurons was compared with the distribution of neurons containing tachykinins or somatostatin, identified using immunocytochemical techniques. Neurons labelled for beta-preprotachykinin mRNA constituted 20% of the total neuronal population and belonged to the small cell class. Neurons labelled for preprosomatostatin mRNA with either RNA or DNA hybridization probes constituted approximately 10% of the total cells and comprised a small cell group that differed in average size from the beta-preprotachykinin labelled population. The distribution of cells containing tachykinin- or somatostatin-like immunoreactive material was identical to the distribution of cells containing the respective mRNAs and, in addition, individual somata in adjacent sections contained both the mRNA precursor and the peptide. These results suggest that for these neuropeptides the sensitivity of the two methods is equivalent and the respective mRNAs and peptides are co-localized in the same neurons.

Telencephalic projections of the A8 dopamine cell group

The telencephalic projections of the A8 dopamine cell group of the rat were assessed using both anterograde and combined retrograde-immunohistochemical methods. The projections of the A8 neurons onto the forebrain were more extensive than hitherto realized, and encompassed striatal, limbic, and allocortical regions. The A8 neurons were shown to contribute to the dopaminergic innervation of the striatum, nucleus accumbens, olfactory tubercles, amygdala, and bed nucleus of the stria terminalis, and also innervate the pyriform and entorhinal cortices. In addition, projections within the midbrain were observed, and suggested that there may be direct interconnections between the dopaminergic neurons of the A8, A9, and A10 cell groups. These data therefore suggest that the A8 dopamine cell group is uniquely situated to modulate functional activity within both nigrostriatal and mesocorticolimbic regions, and further suggests that heterogeneities of the midbrain dopamine neurons are embedded within a larger homogeneous mesotelencephalic dopamine system.

Coordinate hormonal and synaptic regulation of vasopressin messenger RNA

Previous studies have shown that adrenalectomy augments arginine vasopressin (AVP) messenger RNA levels in the adult paraventricular nucleus. It is now demonstrated that unilateral lesions in the lateral septal nucleus enhance the adrenalectomy-induced expression of AVP mRNA. This effect was entirely ipsilateral to the lesion and most prominent in the rostral paraventricular nucleus and related nuclei. Moreover, AVP and AVP mRNA were found to be colocalized with oxytocin in a few neurons. These results indicate that mRNA expression is modulated by synaptic influences and raise the possibility that synaptically mediated selection of neuronal phenotypes is a dynamic feature of the mature central nervous system.

Neuronal localization of prosomatostatin mRNA in the rat brain with in situ hybridization histochemistry

Individual neurons containing prosomatostatin mRNA were identified with in situ hybridization histochemistry. Our results demonstrate a widespread distribution of prosomatostatin mRNA in several regions of the rat central nervous system. Neurons containing this transcript were most abundant in the anterior olfactory nucleus, hypothalamus, hippocampus, and amygdala as well as in all regions of the cerebral cortex. Moreover, the distribution of mRNA-containing perikarya was coextensive with the location of neurons containing somatostatin-like immunoreactivity in all areas of the brain examined. Somatostatin neurons varied in their morphology and amount of hybridization signal from region to region. The widespread distribution and regional variations in neuronal morphology and the amount of hybridization signal are consistent with a neurotransmitter and/or a neuromodulator role for somatostatin in addition to its well-established neuroendocrine role. These results demonstrate that both the peptide and its mRNA are found in perikarya in the same areas and that they are therefore the sites of synthesis for somatostatin.

Steroid regulation of somatostatin mRNA in the rat hypothalamus

The participation of gonadal steroid hormones in the regulation of the expression of the somatostatin gene in the hypothalamus and cerebral cortex was studied by using a quantitative densitometric hybridization assay which allows the direct measurement of specific somatostatin mRNA levels. The levels of somatostatin mRNA in hypothalamus were found to be significantly decreased following gonadectomy in both male and female rats (67% in males and 75% in females). Moreover, with in situ hybridization histochemistry somatostatin mRNA was similarly reduced following gonadectomy in the dorsal portion of the periventricular region and in the ventromedial nucleus. Estradiol dibenzoate treatment reversed the decrease in somatostatin mRNA in females within 24 h and testosterone treatment reversed the decrease in castrated males. In contrast, there was no significant change in cerebral cortex somatostatin mRNA levels after gonadectomy. These results suggest that sex steroids are involved in the regulation of the somatostatin gene in the hypothalamus, possibly at the transcriptional level.

Localization of vasopressin-, vasoactive intestinal polypeptide-, peptide histidine isoleucine- and somatostatin-mRNA in rat suprachiasmatic nucleus

Messenger RNAs (mRNA) coding for vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), somatostatin and vasopressin were localized in the suprachiasmatic nucleus (SCN) of the rat hypothalamus using in situ hybridization histochemistry. Specific mRNA coding for each of these peptides was distributed in areas coextensive with the immunohistochemical localization of the appropriate peptide. The autoradiographic signal produced with probes to VIP and PHI created dense concentrations of silver grains over neuronal perikarya in the ventrolateral SCN, and the coextensive distribution of both VIP- and PHI-mRNAs suggests that both peptides are synthesized within the same neurons. The distribution of somatostatin-mRNA was distinct from the of VIP and PHI. Labeled neurons are observed at the interface of the two SCN subdivisions and the distribution of these neurons is identical to those shown to contain somatostatin immunoreactivity. Vasopressin-mRNA is also differentially concentrated within neurons in the dorsomedial subdivision of the SCN in an area that is coextensive with vasopressin-immunoreactive perikarya. The discrete pattern of hybridization for each of these mRNAs indicates that each of these peptides are synthesized in SCN neurons and reaffirms the differential distribution of each of these chemically defined cell populations within cytoarchitecturally distinct subdivisions of the nucleus.

Hormonal regulation of somatostatin messenger RNA

The ability of gonadal steroids to regulate the expression of the somatostatin gene in several regions of the CNS was investigated with in situ hybridization histochemistry. The amount of somatostatin mRNA was found to be significantly decreased 2-3 weeks after ovariectomy or orchidectomy in the periventricular hypothalamus, the ventromedial nucleus of the hypothalamus, and the medial and central nuclei of the amygdala. Treatment of gonadectomized rats with estradiol benzoate or testosterone enanthate reversed this decrease in somatostatin mRNA. No significant effect was noted in the cerebral cortex or bed nucleus of the stria terminalis. In some regions, there was a high degree of convergence between the distribution of neurons containing estrogen/androgen receptors and somatostatin neurons that were responsive to gonadectomy. These results suggest that sex steroids regulate the expression of somatostatin through an action at the level of transcription.

Neuropeptide modulation of apomorphine-induced stereotyped behavior

The nucleus accumbens contains many neuropeptides whose functions are presently unknown. The purpose of this study was to determine the extent to which these neuropeptides act in conjunction with the mesolimbic dopamine system. Microinjections of cholecystokinin, neurotensin, met-enkephalin, somatostatin, bombesin, as well as glutamate and muscimol, were made into the medial nucleus accumbens after systemic injection of apomorphine. Cholecystokinin and neurotensin, in nanogram doses, potentiated apomorphine-induced stereotypy. Met-enkephalin reduced, while somatostatin and bombesin were without effect on, apomorphine-induced stereotypy. In addition, both glutamate and muscimol potentiated this effect. These results suggest that several neuropeptides and amino acids act in the nucleus accumbens to modulate apomorphine-induced stereotyped behaviors.

An N-methyl-D-aspartate (NMDA) receptor antagonist reduces bicuculline-induced depolarization shifts in neocortical explant cultures

We investigated the actions of a specific N-methyl-D-aspartate (NMDA) antagonist, 2-amino-5-phosphonovaleric acid (2-APV), on bicuculline-induced epileptogenesis in organotypic explant cultures from neonatal rat neocortex. Explants were maintained in roller tubes for 3-5 weeks. The late, plateau phase of the intracellularly recorded paroxysmal depolarization shift was sensitive to both intracellularly injected hyperpolarizing currents and 2-APV, suggesting that this component is generated by a voltage-dependent, regenerative process that is mediated by activation of NMDA receptors. The results support the hypothesis that NMDA receptors play an important role in the generation of epileptiform activity by localized circuits of neocortical neurons.

Glucocorticoid sensitivity of vasopressin mRNA levels in the paraventricular nucleus of the rat

Immunocytochemical studies have shown that adrenalectomy produces changes in the content and distribution of [arginine-8]vasopressin (AVP) immunoreactivity in the paraventricular nucleus of the hypothalamus. The purpose of this study was to determine whether manipulation of adrenal hormones affects the levels of AVP mRNA. In situ hybridization assays with highly specific synthetic oligodeoxyribonucleotide probes and immunocytochemistry were used to detect the distribution of AVP mRNA and AVP-immunoreactive perikarya. AVP mRNA is codistributed with AVP immunoreactivity in the posterior magnocellular subdivision of the paraventricular nucleus and its accessory nuclei, the supraoptic nucleus and the suprachiasmatic nucleus. In adrenalectomized rats, the density and distribution of the hybridization signal were increased in the paraventricular nucleus; a 2-fold increase in the area comprising the signal was observed. At the cellular level, silver grains were detected in corticotropin-releasing-factor-immunoreactive neurons throughout the medial parvocellular subdivision of the paraventricular nucleus. No changes were seen in the distribution of AVP mRNA in the supraoptic or suprachiasmatic nuclei. Treatment with dexamethasone prevented the increase in AVP mRNA produced by adrenalectomy. In contrast, adrenalectomy did not alter the hybridization signal obtained with a probe for alpha-tubulin mRNA. These results suggest, at the cellular level, that adrenalectomy induces a glucocorticoid-sensitive stimulation of AVP mRNA synthesis in the central nervous system. Thus, considerable plasticity in gene expression is retained in the hypothalamus of the adult rat.

Rapid, high-resolution in situ hybridization histochemistry with radioiodinated synthetic oligonucleotides

In situ hybridization histochemistry is a valuable technique for localizing specific messenger RNA (mRNA) and detecting changes in gene expression. Generally, the mRNA of interest has been detected by probes obtained from cloned DNA and labelled to high specific activity by nick translation. Such probes have a number of disadvantages which can be circumvented by the use of short synthetic oligonucleotides designed to be complementary to a known mRNA sequence. We report here that synthetic oligonucleotides complementary to part of the mRNA coding for rat arginine-vasopressin (AVP) can be labelled to high specific activity with [125I], using either the primer extension method with the Klenow fragment of DNA polymerase I or the 3'-tailing method with terminal deoxynucleotidyl transferase. Both AVP probes hybridized well to the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. A strong autoradiographic signal was present by 2 days, with grains largely confined to the perikaryon. These results compare favorably to those obtained with [32P]- or [3H]-labelled probes. Given the ease of the 3'-tailing method, [125I]-labelled oligonucleotides appear to be especially useful probes for in situ hybridization histochemistry.

Structure-activity studies with carboxy- and amino-terminal fragments of neurotensin on hypothalamic neurons in vitro

The purpose of this study was to determine the structural requirements for the activity of neurotensin (NT1-13) on preoptic/anterior hypothalamic (POAH) neurons in vitro. Standard explant culture electrophysiological techniques were employed. NT was administered to POAH cultures through the superfusion fluid, or, to the vicinity of individual neurons by pressure ejection (0.5-10 psi) from micropipettes. Computer-generated, peri-event histograms were used to quantitate neuronal responses. Pressure ejection of NT1-13 (50 pM to 1 microM) consistently produced an excitatory effect on 30 of 42 neurons. The remaining cells were either inhibited or unaffected. Application of the C-terminal hexapeptide, NT8-13, but not the N-terminal octapeptide, NT1-8 (less than or equal to 1 mM), produced an excitatory response in 21 of 30 neurons, but was less potent than NT1-13. Application of an N-acetylated NT8-13 fragment (NTAC8-13) produced a response that was similar to that produced by NT8-13. The excitatory effects of NT1-13 and NT8-13 were maintained in medium which effectively blocked synaptic transmission (0 mM Ca2+/12 mM Mg2+ 1 mM EGTA). These data indicate that the C-terminal hexapeptide, but not the N-terminal octapeptide, produces a dose-related, excitatory effect on single neurons in the POAH in vitro. The persistence of these effects in Ca2+-free medium supports a postsynaptic site of action for these peptides.

The application of enzyme-linked immunosorbent assays (ELISA) to neuropeptides

Procedures are presented for routine evaluation of antibody specificity, titre, and quantitation of antigen levels in tissue extracts without the use of radiolabeled probes. A colorimetric, enzyme-linked immunosorbent assay (ELISA) is described for general use with neuropeptides, using neurotensin as a primary example. These assays use rabbit anti-neurotensin immune serum which is colorimetrically identified after combination with an alkaline phosphatase-conjugated, affinity purified, goat anti-rabbit IgG and reaction with the chromogenic substrate, p-nitrophenyl phosphate. Because the principle of these methods can be adapted for use with various proteins and neuropeptides, they should find widespread applicability in neurobiology.

Co-localization of corticotropin releasing factor and vasopressin mRNA in neurones after adrenalectomy

The discrete anatomical distribution of arginine vasopressin and corticotropin releasing factor (CRF) immunoreactivity in the paraventricular nucleus (PVN) of the rat hypothalamus is altered after adrenalectomy. Not only is the immunostaining of both peptides enhanced, but vasopressin immunoreactivity, normally confined to the magnocellular subdivision, becomes clear in a large percentage of CRF neurones in the parvocellular subdivision. These changes in immunoreactivity may reflect changes in post-translational events, peptide metabolism or genomic activity that lead indirectly or directly to the enhanced expression of vasopressin. Here we report that levels of transcripts homologous to vasopressin messenger RNA increase in the PVN after adrenalectomy, in parallel with increases in vasopressin immunoreactivity. In fact, after adrenalectomy, vasopressin mRNA can be detected in CRF-immunoreactive neurones. These results indicate that a considerable degree of plasticity is retained by the adult neuronal genome of the rat and that this plasticity may be modulated by the endocrine environment.

Primary explants as a model of the hypothalamus in situ

Anatomical and electrophysiological studies with neurotensin and somatostatin were performed to assess the integrity of primary explants of the preoptic anterior hypothalamus (POAH) maintained in organ culture as a model to study peptidergic neurons in vitro. POAH neurons maintained in vitro were found to be morphologically similar to those visualized histologically in situ. Somatostatin- and neurotensin-immunoreactive neurons were also present in both preparations. Additionally, electrophysiological responses of neurons in vitro to neurotensin and somatostatin were qualitatively similar to neuronal responses in situ. The striking morphological and pharmacological similarity between POAH neurons in vitro and in situ suggests that primary explants of the POAH are organotypic.

A quantitative, immunochemical demonstration of the postnatal development of neurotensin in the medial preoptic area of the rat

The postnatal ontogeny of neurotensin (NT) in the medial preoptic area (MPO) of the rat was quantitatively investigated using immunocytochemical and neurochemical techniques. On postpartum day 0, NT-like immunoreactive neurons could not be identified within the MPO by peroxidase-antiperoxidase histochemistry and, in fact, did not appear until 9 days postpartum. After this age, the number of NT cells in the MPO increased ontogenetically, as did concentrations of NT in MPO extracts measured by radioimmunoassay and enzyme-linked immunosorbent assay. In organotypic MPO explants derived from neonatal rats, NT-like immunoreactivity was detected only after the explants were maintained 14 days in vitro, after which, the number of NT-like immunoreactive somata increased as the time in vitro was extended. These findings indicate that a substantial amount of differentiation occurs postnatally in the MPO both in vivo and in vitro and, more specifically, that the ontogenetic expression of NT may be an intrinsic property of the MPO.

Postsynaptic actions of neurotensin on preoptic-anterior hypothalamic neurons in vitro

This study examines the effects of neurotensin (NT) on single neurons in explants of the preoptic-anterior hypothalamus (POAH) in vitro. Standard in vitro electrophysiological techniques were employed. Cultures were prepared from newborn rats and maintained in roller tubes for 3-4 weeks. NT was administered either through the superfusion fluid or via micropressure ejection (0.5-10 psi). Pressure ejection of NT produced a consistent, dose-related, excitatory effect on 71% of the cells studied. The remaining cells were either unresponsive to NT or inhibited by it. In addition, the excitatory effects of microiontophoretically applied glutamate (10-100 nA) were markedly enhanced by NT applied at concentrations that did not alter spontaneous rate. The effects of NT at higher concentrations were additive with glutamate. The effects of NT persisted in Ca2+-free medium when synaptic activity was suppressed. These data indicate that NT exerts a potent excitatory effect on single neurons in the POAH in vitro. Moreover, this effect proved to be additive with that of glutamate. The persistence of these effects in Ca2+-free medium suggests that the actions of NT are postsynaptic in nature.

In situ hybridization of putative somatostatin mRNA within hypothalamus of the rat using synthetic oligonucleotide probes

The distribution of mRNA with high sequence homology to somatostatin mRNA within the periventricular hypothalamus of rat was assessed using in situ hybridization techniques with synthetic oligodeoxyribonucleotide probes, complementary to the 3' coding region of rat somatostatin mRNA. The probes (22- and 24-mers) were 5'-end labeled using T4 polynucleotide kinase and gamma-32P-ATP. They were used either individually or after ligation with T4 DNA ligase to form a 46-mer. Serial tissue sections (less than 10 microns) were taken from the level of the preoptic/anterior hypothalamus through the paraventricular hypothalamus. In situ hybridizations were conducted at room temperature in hybridization buffer. Neurons immunoreactive with antiserum raised against somatostatin were identified in alternate sections using standard immunocytochemical procedures. The anatomical location of the hybridization signal was determined by autoradiography. Our results show that the peri- and paraventricular hypothalamus is rich in transcripts putatively coding for somatostatin and that these transcripts are co-distributed with neurons immunoreactive with antisomatostatin immunoglobulin.

Anticonvulsant actions of fominoben: possible involvement of benzodiazepine receptors

The purpose of this study was to examine the benzodiazepine-like activity of fominoben-HCl, a compound with prominent antitussive and respiratory stimulant actions. Towards this end we examined the anticonvulsant actions of fominoben as well as its ability to displace benzodiazepine (BDZ) binding from brain membranes. Scatchard analysis of binding data demonstrated that fominoben displaced 3H-flunitrazepam binding from rat cortical membrane preparations. Furthermore when tested against 3H-ethyl-beta-carboline-3-carboxylate, the addition of GABA resulted in a mean (+/- SE) shift of the IC50 from 4.05 +/- 0.10 microM to 2.2 +/- 0.05 microM, a characteristic of benzodiazepine agonists. Seizures were induced in male, Swiss Webster mice with pentylenetetrazol (PTZ) or 3-mercaptoproprionic acid (3-MP). Fominoben (50 and 100 mg/kg) completely protected mice from seizures induced by 50 mg/kg PTZ and elevated the seizure latency against 75 mg/kg of PTZ. The anticonvulsant effects of fominoben were less pronounced against 3-MP-induced seizures. The benzodiazepine antagonist Ro 15-1788 antagonized the anticonvulsant action of fominoben against both convulsants. Taken together, these data suggest that the anticonvulsant action of fominoben may be mediated by agonistic actions at benzodiazepine binding sites.

Anxiolytic-like properties of fominoben

Fominoben, a centrally acting antitussive, has been shown recently to bind to the brain benzodiazepine binding site and to antagonize pentylenetetrazol-induced seizures. The present study reports the ability of fominoben to produce anti-anxiety effects analogous to diazepam in a mouse exploratory model for anxiolytics. This action of fominoben was blocked by Ro15-1788, a benzodiazepine receptor antagonist, implicating a brain benzodiazepine binding site in this anxiolytic action of fominoben.

Effects of iontophoretically applied (+)- and (-)-naloxone on rat hypothalamic and septal neurons

The purpose of this study was to investigate the possible independent actions of both (+)-and (-)-naloxone on individual neurons in the preoptic/anterior hypothalamus (POAH) and septal area (SA) of the rat brain. Morphine and (-)-naloxone were applied to 31 neurons in the SA (n = 11) and the POAH (n = 20). Morphine depressed the spontaneous activity in 19 of 31 neurons. (-)-Naloxone at currents less than 10 nA did not influence these neurons. However, (-)-naloxone applied in excess of 10 nA reduced spontaneous activity in 28 of 29 neurons. This effect of (-)-naloxone was stereospecific; (+)-naloxone did not alter the spontaneous rate in 12 of 14 cells when alternately applied with (-)-naloxone at the same current intensity. Application of (+)- and (-)-naloxone at supramaximal currents produced a diminution of spike amplitude and an increase in the duration of the action potential. The results of this study indicate that naloxone reduces spontaneous activity via two mechanisms. One involves a direct stereospecific action, and a second produces a non-specific reduction in spike amplitude and a prolongation of spike duration.

Electrophysiological analysis of neuronal thermosensitivity in rat preoptic and hypothalamic tissue cultures

1. Ninety-six neurones in forty-six explant tissue cultures of rat medial basal hypothalamus (m.b.h.) and preoptic area (p.o.a.h.) were subjected to thermal stimulation. 2. Neuronal response to temperature was determined on the basis of an extrapolated Q10 calculated from the regression line relating mean spontaneous activity to bath temperature. 3. Thermal stimulation (28-41 degrees C) of p.o.a.h. cultures resulted in the identification of three distinct groups of neurones: (1) temperature-insensitive (0.5 less than or equal to Q10 less than or equal to 2), (2) warm-sensitive (Q10 greater than 2), and (3) cold-sensitive (Q10 less than 0.5). 4. No temperature-sensitive neurones were identified in m.b.h. cultures. 5. In the presence of a medium which effectively blocks synaptic transmission (12 mM-Mg2+ and 0.25 mM-Ca+) the sensitivity of both warm- and cold-sensitive neurones was preserved. 6. These data indicate that thermosensitivity is a characteristic not only of the preoptic neuronal network in vitro but also is an intrinsic characteristic of individual neurones.

Effect of sodium valproate on hypothalamic neurons in vivo and in vitro

The effects of sodium valproate on extracellularly recorded spontaneous neuronal activity and its interaction with GABA-induced inhibition were assessed in the rat medial basal hypothalamus both in situ and in explant culture. In situ, valproate enhanced the spontaneous rate in 14 of 20 neurons sampled, 6 neurons were unaffected. In vitro, valproate had an inconsistent effect on firing rate; the spontaneous rate was decreased in 6 cells, elevated in 1, while 17 either were unchanged or demonstrated no consistent pattern of response. Both in vivo and in vitro, valproate produced a variable effect on GABA induced inhibition. In vivo, the modal response of valproate on GABA inhibition was antagonism whereas the response in vitro was less consistent, favoring no change in GABA inhibition. The results of this study suggest that valproate exerts an inconsistent action on hypothalamic neurons. These findings are in contrast to those from the cerebral cortex, suggesting that the action of valproate in the brain may be regionally specific.

Sodium valproate enhancement of gamma-aminobutyric acid (GABA) inhibition: electrophysiological evidence for anticonvulsant activity

The purpose of this study was to gain further insight into the mechanism of action of the anticonvulsant sodium valproate. The effects of valproate on spontaneous neuronal activity and its interaction with locally applied gamma-aminobutyric acid (GABA) were assessed in the rat cerebral cortex. Extracellular neuronal potentials were recorded using standard procedures. Valproate, glycine, GABA and bicuculline methiodide were applied through microiontophoresis. Valproate at 30, 50, and 100 nA did not affect the spontaneous activity of the majority of cells (21), increased the firing rate in four and slowed right cells. When applied simultaneously with GABA, valproate significantly enhanced GABA inhibition in a dose-related manner. Bicuculline methiodide antagonized the combined effects of valproate and GABA. Glycine inhibitions were not significantly enhanced by valproate. Our results indicate that valproate enhances GABA inhibition in the cerebral cortex, an action which is independent of its effect on spontaneous activity. The specificity of valproate for GABA suggests that this interaction may be an important mechanism through which valproate exerts its anticonvulsant properties.

Effects of antipsychotic and antianxiety drugs on the morphine abstinence syndrome in rats

The effects of representative antipsychotic and antianxiety drugs on the abstinence syndrome in morphine-dependent rats were compared. Groups of 10 to 22 male albino Sprague-Dawley rats (250-300 g) were individually implanted s.c. with either two 75-mg morphine base pellets or two placebo pellets. After 72 hr, chlorpromazine (CPZ 1,2 and 4 mg/kg), haloperidol (0.2, 0.4 and 0.8 mg/kg), thioridazine (10, 20 and 40 mg/kg), chlordiazepoxide (2,4 and 8 mg/kg), diazepam (DPM, 1, 2 and 4 mg/kg) or vehicle was injected s.c. 55 min before precipitation of abstinence with naloxone (1 mg/kg s.c.). Jumping was exacerbated by CPZ (4 mg/kg), chlordiazepoxide (4 and 8 mg/kg) and DPM (1, 2 and 4 mg/kg); haloperidol and thioridazine had no significant effect on this sign. Weight less over 1 hr was decreased by CPZ (4 mg/kg) and DPM (4 mg/kg). Wet-dog shakes were decreased by all doses of haloperidol but increased by chlordiazepoxide (8 mg/kg) and DPM (1, 2 and 4 mg/kg). CPZ (2 and 4 mg/kg) significantly increased the incidence of teeth chattering. Other abstinence signs were not affected in a dose-related manner. Although the antipsychotic agents each decrease dopamine availability at the postsynaptic receptor, this mechanism alone cannot explain their actions on individual signs of abstinence. Perhaps it is therefore time to question how modifying agents can be meaningfully compared in morphine-abstinent rats.