In vitro and in vivo evidence of neurotensin release from preganglionic axon terminals in the stellate ganglion of the cat

Neurotensin receptor 1 immunoreactivity in the peripheral ganglia and carotid body

In the present study we investigated, through immunohistochemistry, the presence and location of neurotensin receptor 1 (NTR1) in the peripheral ganglia and carotid body of 16 humans and 5 rats. In both humans and rats, NTR1 immunostained ganglion cells were found in superior cervical ganglia (57.4+/-11.6% and 72.4+/-11.4%, respectively, p0.05), enteric ganglia (51.9+/-10.4% and 64.6+/-6.1, p<0.05), sensory ganglia (69.2+/-10.7% and 73.0+/-13.1%, p>0.05) and parasympathetic ganglia (52.1+/-14.1% and 59.4+/-14.0%, p>0.05), supporting a modulatory role for NT in these ganglia. Positivity was also detected in 45.6+/-9.2% and 50.8+/-6.8% of human and rat type I glomic cells, respectively, whereas type II cells were negative. Our findings suggest that NT produced by type I cells acts in an autocrine or paracrine way on the same cell type, playing a modulatory role on chemoception.

Release-depletion and receptor-mediated neuronal internalization of endogenous neurotensin in the stellate ganglion of the cat

The release and depletion of neurotensin in sympathetic preganglionic axon terminals and internalization in principal ganglion cells were investigated in the cat stellate ganglion by means of combined immunohistochemical staining, image analysis and confocal microscopy. Neurotensin stored in preganglionic boutons was released by 40 or 5 Hz electrical stimulation of preganglionic nerves, being depleted to 7.4 and 19.2% of control levels by continuous stimulation lasting 20 or 160 min (both stimuli delivered 48,000 pulses). Once released, neurotensin was internalized by the principal ganglion cells as evidenced by a ring of bright spot-like granules in the perinuclear region indicating the sites of intracellular neurotensin accumulation. Neurotensin internalization was time-dependent, thus, different content was found when the time between the end of stimulation and start of perfusion was varied. The onset of neurotensin internalization appeared in the first minutes, intracellular accumulation was evident at 20 min, maximal internalization occurred at 120 min and, 24 h later internalized neurotensin content had faded. Internalization was partially blocked by the nonpeptide neurotensin antagonist SR48692. These data provide evidence of presynaptic neurotensin release and depletion by electrical stimulation with varied frequencies. They also provide evidence for in situ receptor-mediated internalization of endogenously released neurotensin, raising the possibility that internalization may represent, in addition to some kind of turnover dynamics, an important part of the mechanisms of neuropeptide signaling.

Cardiac neurones of autonomic ganglia

The properties of the postganglionic sympathetic neurones supplying the heart and arising in the stellate and adjacent paravertebral ganglia of various species are discussed with respect to their location, morphology, synaptic input and membrane characteristics. Results from our laboratory on the morphology of rat stellate neurones projecting to the heart were obtained either by intracellular injection of hexammine cobaltic (III) chloride or by retrograde labelling of cells using cobalt-lysine complex. Intracellular recordings were made from cells using electrodes filled either with potassium chloride plus hexammine cobaltic chloride or potassium acetate. Neurones which projected axons into cardiac nerve branches arising from the stellate ganglion were termed putative cardiac neurones, because of the possibility that some supply pulmonary targets. Putative cardiac neurones had unbranched axons and were ovoid or polygonal in shape, but showed considerable variation in soma size and in the complexity of dendritic trees. The mean two-dimensional surface area was 463 microns2 and the mean number of primary dendrites was seven. Other studies have found that the morphology of rat stellate ganglion neurones is similar to that of superior cervical ganglion cells. However, in strains of rat displaying spontaneous hypertension, dendritic length may be increased. Histochemical studies do not, as yet, seem to have demonstrated a distinctive neurochemical profile for stellate cardiac neurones, but various types of peptide-containing intraganglionic nerve fibres have been identified in the guinea pig. In our electrophysiological studies, putative cardiac neurones were found to receive a complex presynaptic input arising from the caudal sympathetic trunk and from T1 and T2 thoracic rami. In addition, 16% of cardiac neurones received a synaptic input from the cardiac nerve. The properties of postganglionic parasympathetic neurones distributed in the cardiac plexus and termed intrinsic cardiac neurones are discussed, including the results of studies on cultures of these neurones.

Neurotensin-mediated effects on astrocytic tumor cell proliferation

Neurotensin (NT) and neurotensin receptors (NTRs) are widely found in the brain, NT may be considered as a mitogen factor in some tissues. However, no NT-mediated effects on glioma cell proliferation have been reported so far. In our present study we investigated the influence of NT on the proliferation of astrocytic tumor cell lines. To this end we used a synthetic NT agonist (JMV-449), a protease inhibitor which blocks the natural degradation of NT (JMV-531), and NT. The in vitro biological models used in the present study included the low grade SW1088, and the high grade U87, U373 and A172 astrocytic tumor cell lines. The peptide-induced influence on astrocytic tumor cell proliferation was investigated by means of the colorimetric MTT assay. Our results show that the NT and the NT agonist significantly stimulated the proliferation in 2/4 and 3/4 of the astrocytic cell lines respectively. Similarly, compound JMV-531 also induced an increase in the proliferation of 2/4 of the astrocytic cell lines. This marked influence of the NT and NT agonists, or the enzyme-endogenous prevention of its degradation on the regulation of astrocytic tumor growth therefore suggests that NT antagonists might be used to treat certain patients with high grade astrocytic tumors that do not respond to chemotherapy and/or radiotherapy.

The role of tonic preganglionic neuron firing in the turnover of the large dense-cored vesicle store in sympathetic preganglionic nerve terminals

Large dense-cored vesicles are transported centrifugally in the cervical sympathetic trunk and are depleted in a calcium-dependent manner from synaptic boutons of the cat superior cervical ganglion during orthodromic stimulation at 20-40 Hz [P. Weldon et al. (1993) Neuroscience 55, 1045-1054]. In the present study, we tested in awake cats whether the normal tonic firing of the sympathetic preganglionic neuron contributes to the turnover of large dense-cored vesicles in synaptic boutons of the superior cervical ganglion. Tetrodotoxin was applied with a mini-osmotic pump to one cervical sympathetic trunk, while vehicle alone was applied to the contralateral cervical sympathetic trunk, for two, four or seven days. The appearance of Horner syndrome ipsilateral to the tetrodotoxin application demonstrated block of action potential propagation. Both superior cervical ganglia were excised and processed for electron microscopy. The number of large dense-cored vesicles per bouton cross-section was higher in the ganglion with tetrodotoxin-treated input than in the control. The content at four days was higher than at two days; the content at seven days was similar to that at four days. The number of lysosomes per bouton profile also increased in the ganglion with tetrodotoxin-treated input. No changes were observed in size of bouton profiles, number of boutons or of synapses per grid square and length of the presynaptic densities in the ganglion with tetrodotoxin-treated input.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of neuron soma firing in the restoration of neurotensin store in sympathetic preganglionic neuron terminals after stimulus-evoked depletion

We have previously shown that prolonged preganglionic stimulation (e.g. 40 Hz 20 min) depletes the neurotensin (NT) store of preganglionic axon terminals in the stellate ganglion (SG) of the cat and that replenishment of the store requires several days. The present study investigates the mechanisms which control turnover of the NT store in sympathetic preganglionic axon terminals. NT content of the SG and of the preganglionic axons which innervate it was determined by radioimmunoassay in the anesthetized cat. This study shows that, during the 24 h after 40-Hz 20-min stimulation of the preganglionic input to the SG, the rate of NT accumulation proximal to a ligature on the stimulated input is three times that observed in the control. The poststimulus increase in NT accumulation rate is prevented by treatment with protein-synthesis inhibitors. When the centripetal propagation of action potentials from the stimulus site on the preganglionic axons is prevented by a tetrodotoxin block applied locally during the stimulation period, the poststimulus increase in NT accumulation rate and the replenishment of the store are both prevented. These data suggest that the level of activity of the neuron regulates NT supply to the axon terminals, presumably by regulating NT synthesis. Thus, in the sympathetic preganglionic neuron, the action potential provides a mechanism for matching peptide synthesis to release.