Differential expression of Nk1 and NK3 neurokinin receptors in neurons of the nucleus tractus solitarius and the dorsal vagal motor nucleus of the rat and mouse.

Tachykinins (substance P, neurokinin A and neurokinin B) influence autonomic functions by modulating neuron activity in nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMV) through activation of neurokinin receptors NK1 and NK3. Our purpose was to identify and define by neurochemical markers, the subpopulations of NK1 and NK3 expressing neurons in NTS and DMV of rat and mouse. Because the distribution of the NK1 and NK3 expressing neurons overlaps, co-expression for both receptors was tested. By double labeling, we show that NK1 and NK3 were not co-expressed in NTS neurons. In the DMV, most of neurons (87%) were immunoreactive for only one of the receptors and 34% of NK1 neurons, 7% of NK3 neurons and 12% of NK1-NK3 neurons were cholinergic neurons. None of the neurons immunoreactive for NK1 or NK3 were positive for tyrosine hydroxylase, suggesting that catecholaminergic cells of the NTS (A2 and C2 groups) did not express neurokinin receptors. The presence of NK1 and NK3 was examined in GABAergic interneurons of the NTS and DMV by using GAD65-EGFP transgenic mouse. Immunoreactivity for NK1 or NK3 was found in a subpopulation of GAD65-EGFP cells. A majority (60%) of NK3 cells, but only 11% of the NK1 cells, were GAD65-EGFP cells. In conclusion, tachykinins, through differential expression of neurokinin receptors, may influence the central regulation of vital functions by acting on separate neuron subpopulations in NTS and DMV. Of particular interest, tachykinins may be involved in inhibitory mechanisms by acting directly on local GABAergic interneurons. Our results support a larger contribution of NK3 compared with NK1 in mediating inhibition in NTS and DMV.

Epileptiform activity triggers long-term plasticity of GABA(B) receptor signalling in the developing rat hippocampus.

GABA(B) receptor (GABA(B)R)-mediated presynaptic inhibition regulates neurotransmitter release from synaptic terminals. In the neonatal hippocampus, GABA(B)R activation reduces GABA release and terminates spontaneous network discharges called giant depolarizing potentials (GDPs). Blocking GABA(B)Rs transforms GDPs into longer epileptiform discharges. Thus, GABA(B)R-mediated presynaptic inhibition of GABA release (GABA auto-inhibition) controls both spontaneous network activity and excitability in the developing hippocampus. Here we show that extensive release of endogenous GABA during epileptiform activity impairs GABA auto-inhibition, but not GABA(B)R-mediated inhibition of glutamate release, leading to hyperexcitability of the neonatal hippocampal network. Paired-pulse depression of GABA release (PPD) and heterosynaptic depression of glutamate release were used to monitor the efficacy of presynaptic GABA(B)R-mediated inhibition in slices. PPD, but not heterosynaptic depression, was dramatically reduced after potassium (K+)-induced ictal-like discharges (ILDs), suggesting a selective impairment of GABA(B)R-dependent presynaptic inhibition of GABAergic terminals. Impairing GABA auto-inhibition induced a 44% increase in GDP width and the appearance of pathological network discharges. Preventing GABA-induced activation of GABA(B)Rs during ILDs avoided PPD loss and most modifications of the network activity. In contrast, a partial block of GABA(B)Rs induced network discharges strikingly similar to those observed after K+-driven ILDs. Finally, neither loss of GABA auto-inhibition nor network hyperexcitability could be observed following synchronous release of endogenous GABA in physiological conditions (during GDPs at 1 Hz). Thus, epileptiform activity was instrumental to impair GABA(B)R-dependent presynaptic inhibition of GABAergic terminals. In conclusion, our results indicate that endogenous GABA released during epileptiform activity can reduce GABA auto-inhibition and trigger pathological network discharges in the newborn rat hippocampus. Such functional impairment may play a role in acute post-seizure plasticity.

Acute desensitization of presynaptic GABAB-mediated inhibition and induction of epileptiform discharges in the neonatal rat hippocampus.

The consequences of sustained activation of GABA(B) receptors on GABA(B)-mediated inhibition and network activity were investigated in the neonatal rat hippocampus using whole-cell and extracellular field recordings. GABA(B)-mediated presynaptic control of gamma-aminobutyric acid (GABA) release progressively diminished with time in spite of the continued presence of the agonist (100 microM baclofen, 15 min), indicating acute desensitization of presynaptic GABA(B)-mediated inhibition on GABAergic terminals. By contrast, neither GABA(B)-mediated inhibition of glutamate release nor postsynaptic GABA(B)-mediated inhibition seemed to produce this desensitization. Efficacy of presynaptic GABA(B) receptors was still reduced by 49% 30 min after baclofen washout, suggesting a long timeframe for recovery from desensitization. The 15-min baclofen application was followed by a dramatic modification of the spontaneous network activity, with the occurrence of epileptiform events called ictal-like discharges (ILDs). Extracellular field recordings confirmed the epileptic nature of the discharges that could be recorded up to 4 h after baclofen washout. ILDs did not occur when the GABA(B) receptor antagonist CGP35348 was coapplied with baclofen. This indicates that ILD induction is a consequence of the sustained activation of GABA(B) receptors and the correlated changes in GABA(B)-mediated inhibition. Furthermore, ILDs were also induced when blocking with CGP35348 an amount of GABA(B) receptors that exactly mimicked the loss of inhibition obtained with desensitization. These results show that presynaptic GABA(B)-mediated inhibition of GABA release acutely and specifically desensitizes following a sustained application of the GABA(B) receptor agonist baclofen. Conditions that induce desensitization of the GABA(B)-mediated responses also trigger persistent epileptiform discharges in the neonatal rat hippocampus.

[Epithelial-myoepithelial carcinoma of the salivary glands: report of a case]. / Carcinome épithélial-myoépithélial des glandes salivaries. Etude à propos d'un cas.

Epithelial-myoepithelial carcinoma (E.M.C.) is a rare lowgrade salivary gland neoplasm that occurs in both major and minor salivary glands. It is characterized by tubular and solid growth pattern with a dual cell population including an inner layer of epithelial cells which are peripherically bounded by a layer of clear myoepithelial cells. This differentiation is confirmed by electron microscopic and immunohistochemical studies. The differential diagnosis included clear cell tumor of the salivary gland and metastatic renal carcinoma. The majority of these tumours arise in the parotid in women with a peak incidence from the 6th to the 8th decade. We report a case of parotidic E.M.C. in a 33 year old man.

Dual role of the C34 subunit of RNA polymerase III in transcription initiation.

The C34 subunit of yeast RNA polymerase (pol) III is part of a subcomplex of three subunits which have no counterpart in the other two nuclear RNA polymerases. This subunit interacts with TFIIIB70 and is therefore thought to participate in pol III recruitment. To study the role of C34 in transcription, we have mutagenized RPC34, the gene encoding C34, and found that mutations affecting growth also altered C34 interaction with TFIIIB70. The two mutant pol III that were purified had catalytic properties indistinguishable from those of the wild-type pol III on a poly[d(A-T)] template, while specific transcription of pol III genes in the presence of general transcription factors was impaired. The defect of the C34-1124 mutant enzyme could be compensated by increasing the amount of pol III present in the reaction, suggesting that the enzyme had a lower affinity for pre-initiation complexes. In contrast, the C34-1109 mutant enzyme was defective in transcription initiation due to impaired open complex formation. These observations demonstrate that the C34 subunit is a major determinant in pol III recruitment by the pre-initiation complex and further acts at a subsequent stage that involves the configuration of an initiation-competent form of RNA polymerase.

Mutations in the alpha-amanitin conserved domain of the largest subunit of yeast RNA polymerase III affect pausing, RNA cleavage and transcriptional transitions.

The alpha-amanitin domain or domain f of the largest subunit of RNA polymerases is one of the most conserved of these enzymes. We have found that the C-terminal part of domain f can be swapped between yeast RNA polymerase II and III. An extensive mutagenesis of domain f of C160, the largest subunit of RNA polymerase III, was carried out to better define its role and understand the mechanism through which C160 participates in transcription. One mutant enzyme, C160-270, showed much reduced transcription of a non-specific template at low DNA concentrations. Abortive synthesis of trinucleotides in a dinucleotide-primed reaction proceeded at roughly wild-type levels, indicating that the mutation did not affect the formation of the first phosphodiester bond, but rather the transition from abortive initiation to processive elongation. In specific transcription assays, on the SUP4 tRNA gene, pausing was extended but the rate of RNA elongation between pause sites was not affected. Finally, the rate of cleavage of nascent RNA transcripts by halted mutant RNA polymerase was increased approximately 10-fold. We propose that the domain f mutation affects the transition between two transcriptional modes, one being adopted during abortive transcription and at pause sites, the other during elongation between pause sites.