Intracranial Hypertension Is Painless!

INTRODUCTION: Headache is usually considered a key symptom of intracranial hypertension (ICHT). However, there are no published experimental data to support the concept that increased intracranial pressure (ICP) is painful in humans. MATERIALS AND METHODS: This prospective study was performed in 16 patients with suspected normal-pressure hydrocephalus, necessitating a lumbar infusion test with measurement of cerebrospinal fluid (CSF) hydrodynamics. During the test, ICP was increased from baseline to a plateau. Headache was scored on a visual analog scale (VAS) (0 = no pain, 10 = very severe pain) at baseline ICP and when ICP plateaued. RESULTS: At baseline, mean ICP was 11 ± 3.6 mmHg and VAS was 0. At plateau, mean ICP was 28 ± 9.5 mmHg and VAS was 0. There was a significant increase in ICP (p <0.001), but no increase in headache intensity (VAS). An acute (20-min) moderate increase in ICP was not accompanied by a headache. DISCUSSION: We demonstrate that an acute, isolated increase in CSF pressure does not produce a headache. To occur, a headache needs activation of the pain-sensitive structures (dura and venous sinuses) or central activation of the cerebral nociceptive structures. This peripheral or central activation does not occur with an isolated increase in CSF pressure.

Guillain-Barré syndrome following severe head trauma and spine surgery.

Guillain-Barré syndrome (GBS) is an acute-onset inflammatory polyradiculoneuropathy usually triggered by an infectious disease. In some cases, GBS can occur without any preceding infectious episode, like after vaccination, epidural anaesthesia or surgery. A 73 years old woman had head and spine trauma. Body-TDM showed bilateral temporal and right frontal haematomas and fracture of the first lumbar vertebrae. Sextant and kyphoplasty were performed. She presented 14 days after surgery tetraparesis, swallowing difficulties and bilateral facial palsy. Electromyography was consistent with demyelinating neuropathy. Cerebrospinal fluid examination found albumino-cytological dissociation. Viral and bacterial serology and antiganglioside antibodies were negative. She was treated with intravenous immunoglobulins. Four months after discharge she had fully recovered except left peripheral facial palsy. GBS can rarely be triggered by head trauma or spine surgery. Physician must keep in mind this diagnosis whenever their patients present acute-onset neurological worsening in such context.

Neurogenesis inhibition in the dorsal vagal complex by chronic immobilization stress in the adult rat.

The dorsal vagal complex (DVC) is the brainstem integrative center that mediates the satiety reflex and relays autonomic neural responses to stress. The DVC displays adult neurogenesis, intrinsic neural stem cells and a high brain-derived neurotrophic factor (BDNF) content, effectors of plasticity that are modulated by stress in the hippocampus. In this study we asked whether neurogenesis and BDNF expression in the DVC are altered by stress, in parallel with food intake reduction. To this end, neurogenesis was assessed in adult rats in vivo by repetitive 5-bromo-2'-deoxyuridine (BrdU) administration without (controls) or with daily sessions of immobilization stress (1 h/day), and were allowed to survive for 2 weeks after the end of BrdU treatment. Neurogenic proliferation in the brainstem was detected by immunohistochemistry and confocal microscopy mainly in the area postrema and the nucleus tractus solitarius; newly formed neurons amounted to about 35% of all BrdU-labeled cells in the DVC of control rats. Chronic immobilization stress induced a significant decrease in neurogenic proliferation in the DVC which reached 50% in the area postrema. The number of newly-formed neurons was also decreased by chronic immobilization stress in the DVC, and this effect was again maximal in the area postrema; the proportion of BrdU-labeled cells that were neurons was unchanged. In vitro neurosphere assay was then performed on microdissected DVC tissue from another cohort of chronically stressed and control rats. Chronic immobilization stress induced a significant decrease of the total neurosphere number per rat DVC in both primary and secondary cultures, indicating that intrinsic neural stem cell frequency was decreased by chronic stress in DVC tissue. Tissue BDNF concentration in the DVC, as assessed by enzyme-linked immunosorbent assay, was not significantly altered when compared with controls after 3, 6, 9 or 13 days of chronic immobilization stress. These results further characterize neurogenesis in the DVC and suggest its involvement in the long-term regulation of food intake.

Diagnostic value of the pulmonary vein-to-right pulmonary artery ratio in dogs with pulmonary hypertension of precapillary origin.

INTRODUCTION: Non-invasive diagnosis of pulmonary hypertension (PH) relies on estimation of pulmonary arterial pressure (PAP) via Doppler echocardiographic measurement of tricuspid regurgitation pressure gradient (TRPG). The pulmonary vein-to-right pulmonary artery ratio (PV/PA) recently has been described for the detection of pulmonary venous congestion. Whether this variable could be used to detect the presence of precapillary PH is unknown. The objective of the present study was to investigate the diagnostic value of PV/PA for prediction of TRPG, as a surrogate of PAP, in dogs with PH of precapillary origin. ANIMALS: Sixty-seven client-owned dogs were included in the study. METHODS: This was a retrospective study. Dogs with a measurable TRPG were included and classified into group 1 (TRPG < 30 mmHg), group 2 (TRPG 30-49 mmHg), group 3 (TRPG 50-80 mmHg), or group 4 (TRPG > 80 mmHg). The PV/PA, acceleration time-to-ejection time ratio of pulmonary artery flow, main pulmonary artery diameter-to-aortic diameter ratio, and right pulmonary artery distensibility index were measured retrospectively from cineloops in each dog. RESULTS: The PV/PA measured by both two-dimensional (2D) and time-motion mode(MM) echocardiography decreased proportionally with PH severity. Using regression analysis, PV/PA (2D) was identified as the strongest predictor for TRPG (R2 = 0.70, p < 0.0001) among other variables studied, with a good diagnostic accuracy (area under the curve = 0.94) for moderate PH (TRPG > 50 mmHg) using a cutoff value of < 0.70 (sensitivity = 96%, specificity = 82%). CONCLUSIONS: Results of the present study suggest that PV/PA can be useful as an additional, non-invasive, and indirect variable to identify precapillary PH in dogs.

Characterization of neural stem cells in the dorsal vagal complex of adult rat by in vivo proliferation labeling and in vitro neurosphere assay.

The dorsal vagal complex, located in the brainstem, is the major integrative center of the autonomic nervous system. By combining in vivo bromodeoxyuridine incorporation and phenotypic immunolabeling, we have previously reported that neurogenesis occurs in the adult rat dorsal vagal complex [Bauer S, Hay M, Amilhon B, Jean A, Moyse E (2005) In vivo neurogenesis in the dorsal vagal complex of the adult rat brainstem. Neuroscience 130:75-90.]. In the present study we asked whether adult dorsal vagal complex contains proliferative and/or neural stem cells. Using Ki-67 immunolabeling and cyclin D1 Western blot, we showed intrinsic cell proliferation in the dorsal vagal complex and its stimulation by vagotomy. Detailed time-course analysis revealed that vagotomy-induced proliferation in the dorsal vagal complex peaked three days after lesion. In order to directly assess the presence of intrinsic stem cells, primary cell cultures from adult rat dorsal vagal complex were performed in the presence of epidermal growth factor and basic fibroblast growth factor (neurosphere assay). A discrete subpopulation of dorsal vagal complex cells proliferated as neurospheres, self-renewed when passaged, and differentiated into neurons, astrocytes and oligodendrocytes. Proliferation and neuron-differentiating potentials of dorsal vagal complex neurospheres were both lower than those of subventricular zone neurospheres from the same rats. The relationship between in vitro neurosphere-forming cells of dorsal vagal complex and in vivo dorsal vagal complex neurogenesis is discussed and remains to be directly addressed. The present data demonstrate the occurrence of neural stem cells in the dorsal vagal complex of adult rat brain.

Leukemia inhibitory factor is a key signal for injury-induced neurogenesis in the adult mouse olfactory epithelium.

The mammalian olfactory epithelium (OE) is composed of primary olfactory sensory neurons (OSNs) that are renewed throughout adulthood by local, restricted neuronal progenitor cells. The molecular signals that control this neurogenesis in vivo are unknown. Using olfactory bulb ablation (OBX) in adult mice to trigger synchronous mitotic stimulation of neuronal progenitors in the OE, we show the in vivo involvement of a cytokine in the cellular events leading to the regeneration of the OE. We find that, of many potential mitogenic signals, only leukemia inhibitory factor (LIF) is induced before the onset of neuronal progenitor proliferation. The rise in LIF mRNA expression peaks at 8 hr after OBX, and in situ RT-PCR and immunocytochemistry indicate that LIF is upregulated, in part, in the injured neurons themselves. This rise in LIF is necessary for injury-induced neurogenesis, as OBX in the LIF knock-out mouse fails to stimulate cell proliferation in the OE. Moreover, delivery of exogenous LIF to the intact adult OE using an adenoviral vector stimulates BrdU labeling in the apical OE. Taken together, these results suggest that injured OSNs release LIF as a stimulus to initiate their own replacement.

Serine protease inhibitor Spi2 mediated apoptosis of olfactory neurons.

The olfactory epithelium of adult mouse, where primary sensory neurons are massively committed to apoptosis by removal of their synaptic target, was used as a model to determine in vivo mechanisms for neuronal cell death induction. A macro-array assay revealed that the death of olfactory neurons is accompanied with over-expression of the serine protease inhibitor Spi2. This over-expression is associated with decreased serine protease activity in the olfactory mucosa. Moreover, in vitro or in vivo inhibition of serine proteases induced apoptotic death of olfactory neuronal cells. Interestingly, Spi2 over-expression is not occurring in olfactory neurons but in cells of the lamina propria, suggesting that Spi2 may act extracellularly as a cell death inducer. In that sense, we present evidence that in vitro Spi2 overexpression generates a secreted signal for olfactory neuron death. Hence, taken together these results document a possible novel mechanism for apoptosis induction that might occur in response to neurodegenerative insults.

In vivo neurogenesis in the dorsal vagal complex of the adult rat brainstem.

The dorsal vagal complex (DVC) encompasses the nucleus tractus solitarii (NTS), the dorsal motor nucleus of the vagus nerve (DMX) and the area postrema (AP), that altogether provide the major integrative center for the mammalian autonomic nervous system. The adult rat DVC has been reported to contain afferent-dependent concentration of the plasticity-promoting polysialylated form of neural cell adhesion molecule [J Neurosci 21 (2001) 4721; Eur J Neurosci 14 (2001) 1194]. This prompted us to assess the occurrence of neurogenesis in the DVC of adult rats. Cumulative in vivo labeling of cell proliferation with i.p. bromodeoxyuridine (BrdU) injections was combined with phenotypic markers and confocal microscopy on serial brainstem sections throughout the DVC extent. In basal condition, sparse BrdU+ nuclei were selectively detected in the DVC according to a discrete and reproducible pattern. Some of them were found to colocalize with the neuronal markers doublecortin, HuC/D, or neuronal-specific antigen (NeuN), demonstrating that neurogenesis does occur within the DVC of adult rat. In the NTS, 10% of the BrdU+ nuclei were also NeuN+. A comparable proportion of astrogliogenesis was found in the DVC. Nestin immunohistochemistry yielded a highly specific labeling pattern at the border between AP and NTS. These data may relate to the neural stem cells that have been reported in the floor of the IVth ventricle [J Neurosci 16 (1996) 7599]. In order to assess a possible modulation of neurogenesis by afferent input in vivo, unilateral vagotomy was performed prior to cumulative BrdU treatment. Such DVC deafferentation triggered a large increase of BrdU incorporation in the ipsilateral DVC, which was associated with microglial proliferation in the DMX and with increased genesis of neurons and astrocytes in the NTS. These findings establish DVC as a novel model of adult neurogenesis that is reactive to deafferentation.

Guanine nucleotide sensitivity of [125I]-Iodo NTyr somatostatin binding in rat adenohypophysis and cerebral cortex.

Specific [125I]-Iodo-NTyr somatostatin binding sites are present in adenohypophyseal and cerebral cortical membranes. Guanine nucleotides reduce the maximal binding capacity of adenohypophyseal binding sites without significantly affecting their apparent affinity. In pituitary as well as in cortex, GTP is the most potent nucleotide followed by GDP and guanylyl imidodiphosphate (GMP-PNP). The effect appears specific of guanine nucleotides since ATP, ADP and AMP are inactive on [125I]-Iodo-NTyr somatostatin binding. These results, showing the nucleotide sensitivity of [125I]-Iodo-NTyr somatostatin binding in pituitary and cerebral cortex, are compatible with a coupling of somatostatin receptors with adenylate cyclase.

Somatostatin receptors in human growth hormone and prolactin-secreting pituitary adenomas.

[125I-Tyr]Somatostatin [( 125I-Tyr]SRIH) binding was found in 11 GH-secreting pituitary adenomas [Kd = 0.46 +/- 0.15 (+/- SE) nM; maximum binding, 165 +/- 35 fmol/mg protein). This binding was specific, since it was displaced by somatostatin-14 (SRIH-14), N-Tyr-SRIH-14, and SRIH-28. In contrast, a number of peptides and drugs not structurally related to SRIH, such as bombesin, dopamine, LHRH, met-enkephalin, naloxone, neurotensin, secretin, substance P, TRH, or vasoactive intestinal peptide, did not affect [125I-Tyr]SRIH binding. [125I-Tyr]SRIH specific binding also was found in PRL-secreting pituitary adenomas. The kinetic characteristics of the specific binding were similar to those of GH-secreting adenomas. However, maximal binding was one quarter that of GH-secreting adenomas (37 +/- 9 fmol/mg protein). In contrast, nonsecreting (chromophobe) tumors were devoid of any specific binding. Finally, in acromegaly, the density of [125I-Tyr]SRIH-binding sites in the adenomas was negatively correlated with plasma GH levels before surgery (r = -0.80). This suggests that somatostatinergic control is involved in GH secretion in acromegalic patients.

Dopamine receptor coupling to adenylyl cyclase in rat olfactory pathway: a combined pharmacological-radioautographic approach.

Dopamine binding sites of D1 and D2/D3 subtypes had been detected in the rat peripheral olfactory system and postulated to account for dopamine-dependent enhancement of olfactory memory and retro-inhibition of olfactory input within the olfactory bulb, respectively. We further assessed, in the present study, the mechanisms of these dopamine actions by using adenylyl cyclase activity assay and [35S]GTP radioautography in rat olfactory bulb and mucosa. The D1 agonist SKF 38393 increased adenylyl cyclase activity on membranes of the olfactory bulb, but not on those of the olfactory mucosa. Stimulation of adenylyl cyclase by SKF 38393 in the olfactory bulb was dose dependent, with a half-maximal effect (EC50) at 0.16 microM SKF 38393, reaching 40% over basal adenylyl cyclase activity, and was blocked by the D1 antagonist SCH 23390. The D2 agonists bromocriptine and quinpirole inhibited both basal and forskolin-stimulated adenylyl cyclase activities in the olfactory bulb and mucosa. These adenylyl cyclase inhibitions were dose dependent, with EC50 values of 0.1-0.3 microM for bromocriptine and 1-3 microM for quinpirole, equal to 25% of basal enzyme activity at concentrations of 1-10 microM, and were blocked by the D2 antagonist eticlopride. The D2 antagonist was devoid of any effect on basal and forskolin-stimulated adenylyl cyclase activities in the olfactory bulb and mucosa. Odorant-induced stimulation of adenylyl cyclase was blocked by D2 agonist in olfactory mucosa membranes, which suggests dopaminergic regulation of odor detection in the olfactory mucosa. By using microdissected fractions of the olfactory mucosa, D2 agonist-induced inhibition of adenylyl cyclase was shown to occur only in lamina propria, thus co-localizing with D2 binding sites. [35S]GTP radioautography on tissue sections revealed D2 agonist-induced G-protein activation in olfactory nerve and glomerular layers of the olfactory bulb, and in the chorion of the olfactory mucosa. Taken together, these data demonstrate functional coupling of the dopamine receptors with adenylyl cyclase in both the olfactory bulb and mucosa, and document novel aspects of dopamine's physiological involvement in olfaction and of D2-mediated signal transduction.

Accumulation of Ym1/2 protein in the mouse olfactory epithelium during regeneration and aging.

A unique feature of the olfactory system is its efficiency to produce new neurons in the adult. Thus, destruction of the olfactory receptor neurons (ORNs) using chemical (intranasal perfusion with ZnSO4) or surgical (axotomy or bulbectomy) methods, leads to an enhanced rate of proliferation of their progenitors and to complete ORNs regeneration. The aim of our study was to identify new factors implied in this regenerative process. Using an electrophoretic method, we observed the accumulation of a 42 kDa protein after axotomy in the olfactory mucosa, but not in the olfactory bulb. Its expression started after a few days following injury and increased massively during the phase of ORN regeneration. The purification and the sequence characterization revealed that this protein was Ym1/2, recently identified in activated macrophages present in various tissues during inflammation. Western blotting analysis of Ym1/2 confirmed the accumulation of this protein in the regenerating olfactory mucosa consecutively to olfactory axotomy or bulbectomy but also after ZnSO4 irrigation of the nasal cavity. In the olfactory mucosa of control mice, Ym1/2 was hardly detectable in young animals and became more and more abundant with increasing age. In injured and aged mice, Ym1/2 mainly accumulates in the cytoplasm of supporting cells as well as in other cells located throughout the olfactory epithelium. Our results suggest that Ym1/2 is involved in olfactory epithelium remodeling following several kinds of lesions of the adult olfactory mucosa and support the view of a critical role of inflammatory cues in neurodegeneration and aging.

Distribution of neurotensin binding sites in the caudal brainstem of the rat: a light microscopic radioautographic study.

Specific high-affinity neurotensin binding sites were labeled in sections of the rat caudal brainstem using a monoiodinated ligand, and their distribution was examined by light microscopic radioautography after fixation with glutaraldehyde. In the medulla, labeled binding sites were mainly concentrated within the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, the external cuneate nucleus, the lateral reticular nucleus, the medial vestibular nucleus, the retrofacial nucleus, the linearis nucleus, the paragigantocellular nucleus and the nucleus raphe pallidus. Within the pons, neurotensin binding sites were detected in the reticulotegmental nucleus, the pontine nuclei, the dorsal tegmental nucleus, the laterodorsal and pedunculopontine tegmental nuclei and the nuclei raphe dorsalis and medianus. Most nuclei found here to contain high densities of neurotensin binding sites have been shown to stain intensely for acetylcholinesterase, suggesting a possible association between this enzyme and neurotensin receptors.

Localization of mu opioid receptors on the membranes of nerve endings and tanycytes in the guinea-pig median eminence by electron microscopic radioautography.

The high density of opioid-containing nerve endings in the median eminence together with the absence of direct effects of opioids upon pituitary suggest a local action of opioids in the median eminence. The aim of this work was to address the occurrence of mu-opioid binding sites in the median eminence at the electron microscopic level, using the highly selective radioligand [125I]FK 33-824. mu-Opioid receptors were labeled in vitro on slightly prefixed slices of mediobasal hypothalamus. The labeling was essentially detected in the external part of the median eminence. Most of the silver grains overlaid membrane appositions. Two overall types of appositions were concerned: nerve terminal-nerve terminal or nerve terminal-tanycyte. Detailed analysis of the silver grain distribution indicated that mu receptors were observed on membranes of different types of nerve endings but also of tanycytes. All the binding sites were localized out of synaptic junctions since the median eminence is totally devoid of these structures. Our results suggest that in the median eminence, opioid peptides have a paracrine and/or autocrine action occurring at least via mu receptors located on nerve terminals but also on tanycytes.

Dopaminergic modulation of mitral cell activity in the frog olfactory bulb: a combined radioligand binding-electrophysiological study.

Dopamine content in the amphibian olfactory bulb is supplied by interneurons scattered among mitral cells in the external plexiform/mitral cell layer. In mammals, dopamine has been found to be involved in various aspects of bulbar information processing by influencing mitral cell odour responsiveness. Dopamine action in the bulb depends directly on the localization of its receptor targets, found to be mainly of the D2 type in mammals. The present study assessed, in the frog, both the anatomical localization of D2-like, radioligand-labelled receptors of dopamine and the in vivo action of dopamine on unitary mitral cell activity in response to odours delivered over a wide range of concentrations. The [125I]iodosulpride-labelled D2 binding sites were visualized on frozen sagittal sections of frog brains by film radioautography. The sites were found to be restricted to the external plexiform/mitral cell layer; other layers of the olfactory bulb were devoid of specific labelling. Electrophysiological recordings of mitral unit activity revealed that dopamine or its agonist apomorphine induced a drastic reduction of spontaneous firing rate of mitral cells in most cases without altering odour intensity coding properties of these cells. Moreover, pre-treatment with the D2 antagonist eticlopride blocked the dopamine-induced reduction of mitral cell spontaneous activity. In the frog olfactory bulb, both anatomical localization of D2-like receptors and functional data on dopamine involvement in information processing differ from those reported in mammals. This suggests a phylogenetic evolution of dopamine action in the olfactory bulb. In the frog, anatomical data perfectly corroborate electrophysiological results, together strongly suggesting a direct action of dopamine on mitral cells. In a physiologically operating system, such an action would result in a global improvement of signal-to-noise ratio.

Effects of the alpha 2-adrenoreceptor antagonist dexefaroxan on neurogenesis in the olfactory bulb of the adult rat in vivo: selective protection against neuronal death.

A dysfunction of noradrenergic mechanisms originating in the locus coeruleus has been hypothesised to be the critical factor underlying the evolution of central neurodegenerative diseases [Colpaert FC (1994) Noradrenergic mechanism Parkinson's disease: a theory. In: Noradrenergic mechanisms in Parkinson's disease (Briley M, Marien M, eds) pp 225-254. Boca Raton, FL, USA: CRC Press Inc.]. alpha(2)-Adrenoceptor antagonists, presumably in part by facilitating central noradrenergic transmission, afford neuroprotection in vivo in models of cerebral ischaemia, excitotoxicity and devascularization-induced neurodegeneration. The present study utilised the rat olfactory bulb as a model system for examining the effects of the selective alpha(2)-adrenoceptor antagonist dexefaroxan upon determinants of neurogenesis (proliferation, survival and death) in the adult brain in vivo. Cell proliferation (5-bromo-2'-deoxyuridine labelling) and cell death associated with DNA fragmentation (terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling assay) were quantified following a 7-day treatment with either vehicle or dexefaroxan (0.63 mg/kg i.p., three times daily), followed by a 3-day washout period. The number of terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling-positive nuclei in the olfactory bulb was lower in dexefaroxan-treated rats, this difference being greatest and significant in the subependymal layer (-52%). In contrast, 5-bromo-2'-deoxyuridine-immunoreactive nuclei were more numerous (+68%) in the bulbs of dexefaroxan-treated rats whilst no differences were detected in the proliferating region of the subventricular zone. Terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling combination with glial fibrillary acidic protein or neuronal-specific antigen immunohistochemistry revealed that terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling-positive nuclei were associated primarily with a neuronal cell phenotype. These findings suggest that dexefaroxan increases neuron survival in the olfactory bulb of the adult rat in vivo, putatively as a result of reducing the apoptotic fate of telencephalic stem cell progenies.

Distribution of neurotensin binding sites in rat brain: a light microscopic radioautographic study using monoiodo [125I]Tyr3-neurotensin.

The topographic distribution of specifically labeled neurotensin binding sites was examined by light microscopic radioautography in rat brain sections incubated with monoiodo [125I]Tyr3-neurotensin. Preliminary experiments indicated that under the present experimental conditions [125I]neurotensin specifically binds to a single apparent population of sites with a dissociation constant of 7.7 +/- 0.3 nM, and that fixation of the labeled sections with glutaraldehyde ensures regionally proportional retention of more than 70% of bound [125I]neurotensin molecules. High concentrations of [125I]neurotensin binding sites were detected in the olfactory bulb and tubercle, parts of the neocortex, the lateral septum, the diagonal band of Broca, the caudate putamen, the amygdala, the dentate gyrus, the anterior dorsal nucleus of the thalamus, the suprachiasmatic nucleus of the hypothalamus, the medial habenula, the zona incerta, the substantia nigra and the ventral tegmental area. In certain areas, such as in the diagonal band of Broca, the substantia innominata, the nucleus basalis and the pars compacta of the substantia nigra, discrete accumulations of silver grains were apparent over neuronal perikarya and their proximal dendrites. In most areas, however, the label appeared more or less uniformly distributed over nerve cell bodies and surrounding neuropil. In several instances, the labeling conformed with the distribution of cell bodies of origin and terminal aborizations of specific projection systems, suggesting that neurotensin receptors might be distributed both proximally and distally on the plasma membrane of certain neurons. Such putative "neurotensinoceptive" projection systems might involve part of the mesostriatal, mesocortical and mesolimbic dopamine systems, as well as the raphe-prosencephalic serotonin system and the habenulo-interpeduncular and basal forebrain-cortical cholinergic systems. Finally, areas of dense [125I]neurotensin labeling often corresponded to zones previously shown to exhibit intense acetylcholinesterase staining, suggesting the existence of a possible link between the expression of neurotensin binding sites and that of acetylcholinesterase in certain neuronal populations.

Differential effects of passive immunization with somatostatin antiserum on adenohypophysial hormone secretions in starved rats.

The role of somatostatin (SRIF) on adenohypophysial hormone secretion in starved rats was reassessed by passive immunization. Because of the absence of pulsatile GH secretion in starved rats, the effects of the injection of SRIF antiserum on GH levels can be clearly demonstrated. To determine whether starvation modifies the sensitivity of the adenohypophysis to SRIF, we measured 125I-labelled iodo-N-Tyr-SRIF binding. There was no difference in the dissociation constant (Kd) nor in the maximal binding capacity (Bmax) in fed (n = 15) and starved (n = 15) animals (Kd = 0.38 +/- 0.09 (S.E.M.) and 0.45 +/- 0.09 nmol; Bmax = 204 +/- 39 and 205 +/- 30 fmol/mg protein respectively). Administration of SRIF antiserum resulted in a dose-dependent increase in plasma concentrations of GH, TSH and prolactin. The minimal effective dose of SRIF antiserum was 50 microliters for GH, 100 microliters TSH and 200 microliter for prolactin. Our results show that: starvation does not modify adenohypophysial SRIF-binding sites, in starved male rats endogenous SRIF exerts a negative control on prolactin secretion in vivo and sensitivity to endogenous SRIF seems to be different for each hypophysial cell type.

Somatostatin and regulation of prolactin secretion.

In addition to its classical growth hormone (GH) inhibiting action, somatostatin (SRIF) inhibits prolactin (PRL) secretion in man and rat under specific endocrine conditions. Furthermore, SRIF counteracts the thyrotropin releasing hormone (TRH) and vasoactive intestinal peptide (VIP) stimulated prolactin release from rat adenohypophysis in vitro. Two criteria are needed to demonstrate a physiological role of SRIF in PRL control: specific receptors must be present on prolactin secreting cells, and antagonization of endogenous SRIF must affect PRL secretion in vitro. In fact [125I]N--Tyr--SRIF binds to membranes not only of human GH-secreting adenomas, but also of prolactinomas. Specific binding characteristics are comparable in both cell types, but the density of sites in PRL-secreting adenomas is only one-quarter that in GH-secreting adenomas. In contrast, non-PRL-secreting chromophobe adenomas are devoid of specific binding. On the other hand, administration of SRIF antisera (SRIF-AS) affects both GH and PRL secretion in starved rats (a model in which pulsatile GH secretion is abolished); a marked increase in PRL plasma levels occurs, but the needed SRIF-AS concentration is higher than that for GH disinhibition. This demonstrates that endogenous SRIF may exert a negative control over PRL secretion, although lactotroph cells appear less sensitive to SRIF than somatotrophs. Since the apparent affinity of SRIF binding sites is similar on both GH and PRL secreting cells, at least in human tumor tissues, a lower density of SRIF receptors on PRL cells could account for this reduced responsiveness. Alternatively, different coupling mechanisms may be involved in the two cell types.

Combined autoradiographic and immunohistochemical evidence for an association of somatostatin binding sites with growth hormone-releasing factor-containing nerve cell bodies in the rat arcuate nucleus.

Abstract The regulation of growth hormone secretion depends upon the complex interplay between two hypothalamic hypophysiotropic factors: growth hormone-releasing factor and somatotropin release inhibiting factor or somatostatin. Interactions between these two neurohormones appear to be exerted both distally, at the level of pituitary somatotropes, and proximally, within the hypothalamus. In an attempt to detect a possible anatomical substrate for central interactions between the two neurohormones, we compared the autoradiographic distribution of specifically labeled somatostatin binding sites with the immunohistochemical distribution of growth hormone-releasing factor-containing neurons in the hypothalamus of adult rats. Somatostatin binding sites were labeled in vitro by incubating serial brain sections with [(125)l]TyrO-DTrp8-somatostatin. Growth hormone-releasing factor-immunoreactive neurons were visualized in a second set of animals, using an antiserum raised against synthetic rat growth hormone-releasing factor (1-29) NH(2). In light microscopic autoradiograms of sections incubated with [(125)l]somatostatin the label was found to be concentrated over small, round or oval neuronal perikarya clustered within the ventrolateral aspect of the arcuate nucleus. The topographic distribution of these [(125)l]somatostatin-labeled cells was similar to that of growth hormone-releasing factor-immunoreactive neurons detected within the same region. Moreover, the number of [(125)l]somatostatin-labeled cells was found to vary in parallel with that of growth hormone-releasing factor-immunoreactive neurons throughout the rostro-caudal extent of the arcuate nucleus (coefficient of correlation r = 0.80). These results suggest that somatostatin binding sites may be directly associated with the perikarya of arcuate growth hormone-releasing factor neurons. Such an association would provide an anatomical substrate for a direct regulation of growth hormone-releasing factor secretion by somatostatin at the hypothalamic level.