s57

-327 GABAA RBCEPTOR-MEDIATED INHIBITION IN RESPIRATORY NEURONS IN THE NUCLEUS AMBIGUUS

IN RATS. YUKIO Ym, YASUMASA HAYASHI, Dept. of Phvsiol., Hvogo College of Medicine, Nishinomiva. Hvogo, 663 Japan.

Inspiratory and expiratory phases in respiration are known to be generated by a group of neurons in the retrofacial nucleus and Botzinger complex in the rostra1 nucleus ambiguus complex. In our previous study we have indicated that most ambiguous neurons showing spontaneous rhythmic activity in phase with the respiration did not respond to the recurrent laryngeal nerve stimulation, while the laryngeal motoneurons activated and identified antidromically by the recurrent laryngeal nerve stimulation possess GABAA receptors probably on the cell body. These respiratory neurons were tested if they had the GABAA receptors by extracellular application of GABA antagonist and agonist. Iontophoretic application of bicuculline through the barrel electrode caused remarkable increase. in the maximum bust discharge rate while muscimol reversed this effect. Simultaneous application of GABA with either bicuculline or muscimol increased or decreased the discharge rate, respectively. These results suggest strongly that most ambiguous respiratory neurons possess GABAA receptors and that they may function as the inhibitory interneuron in the respiratory oscillation in the ventral respiratory group.

328 A PATCH CLAMP ON D2 AND 33 RECEPTORS ON NEURONS IN STRIATUM USING SLICE PREPARATIOI. TAKU AMANO, KUMATOSHI ISHIHARA AND MASASHI SASA,

Dept. of Pharmacol., Hiroshima Univ. Sch. of Med., Hiroshima, 734, Japan.

We have previously reported that dopamine elicits excitatory effects in striatal neurons via D2-like receptors. A meager number of D3 receptors are also found in the striatum. ?atch clamp studies using slice preparations were performed to elucidate the role of D2 and D3 receptors in striatum. Whole-cell patch clamp recording under current-ciamp conditions was performed on visually identified striatal neurons in slice preparations obtained from young rats aged 7-14 days. in large neurons, bath application of dopamine 32 receptor agonist (talipexoie) and D3 receptor agonist (7-OH-DPAT and PDi28907) induced depolarization concomitantly with an increase in firing in concentration-dependently. These effects were similarly observed in Ca"'-free and high Mg" solution containing tetrodotoxin. The 32 and D3 agonists-induced depolarization was inhibited in the presence of U99194A, a D3 antagonist. However, in medium-size neurons were hyperpolarized with talipexole, aithough they were unaffected with 7-OH-DPAT. These findings indicate that large neurons are activated by dopamine via D2 and/or D3 receptors, while medi.Jm-sized neurons are inhibited via the D2 receptors.

329 INVOLVEMENT OF THE NMDA RECEPTOR CHANNEL SUBUNIT ~2 IN DEVELOPMENT OF THE TRIGEMINAL BARRELETTE STRUCTURE. SHIMA WADA,

CHITOSHI TAKAYAMA, MASAHIKO WATANABE, MASAYOSHI MISHINA*, YOSHIRO INOUE. Dept. of Anat., Hokkaido Univ. Sch. of Med., Sapporo 060, and *Dept. of Pharmacol., Tokyo Univ. Faculty of Med., Tokvo 113, Japan

Development of the somatosensory barrel system is known to depend on nerve activities during a limited period, termed “critical period”. To understand the molecular mechanism, neuroanatomical analyses were undertaken, using mutant mice with inactivated GluR~2 subunit gene. Cytochrome oxidase histochemistry displayed the presence of barrelettes in the neonatal trigeminal nucleus of the wild-type mouse, being observed as five distinct rows of patchy stainings corresponding to the five rows of whiskers. However, the histochemical barrelette structure was missing in the mutant mouse. We labeled a limited number of the trigeminal primary sensory nerves by injecting cholera toxin B subunit into a single vibrissa follicle. In the wild-type, terminal arbors of the labeled sensory nerves formed distinct clusters, which coincided with the hi&chemical barrelettes. Labeled nerves and terminals were distributed in a similar region of the trigeminal nucleus, but no discrete clusters were observed in the mutant. Expression analyses with oligonucleotide probes revealed that the ~2 subunit was transcribed in the neonatal trigeminal nucleus, but not in the trigeminal ganglion. These findings suggest that activation of NMDA receptor channels containing then ~2 subunit on trigeminal nucleus neurons is essential for development of the barrelette formation and of barrelette-related clustering of the primary afferent terminals.