title: Stimulation-induced responses of the trigeminal caudal neurons in the brainstem preparation isolated from newborn rats.
abstract: The brainstem preparation with the trigeminal mandibular nerve attached was isolated from rats postnatal day 0-6 (P0-P6) to test if the potentiation could be induced in neonatal neurons in the trigeminal subnucleus caudalis by stimulation of the primary afferents. The stimulation-induced potentials in 92 neurons recorded extracellularly, and the synaptic potentials in 16 neurons recorded by the whole-cell patch clamp technique were examined. The extracellularly recorded neurons responded to stimulation (0.5 Hz) with either an increase, a decrease, or little change in spike numbers, and were classified as Type 1, Type 2, and Type 3, respectively. Type 1 neurons at P4 and older responded in a low Mg2+ solution with a progressive increase in spike number lasting for several minutes after the cessation of stimulation, i.e., short-term potentiation, STP. This potentiation was antagonized by 20 microM of (+)-MK-801 hydrogen maleate (MK-801) or 25 microM of 2-amino-5-phosphonovaleric acid. In contrast, Type 1 at P3 and younger did not exhibit STP. The age-related distinct response properties were observed between Type 1 neurons at P4-P6 and at P0-P3. The percentage of Type 1 in studied neurons increased from 24% at P0-P3 to 53% at P4-P6. In the intracellular experiment, the mean latency of excitatory postsynaptic potential (EPSP) of recorded neurons indicated that the conduction velocity of the convergent afferents was 0.37 m/s, in the range of C-fiber. Neurons were classified as Type E and Type I. Type E responded with EPSP only, or with both EPSP and inhibitory postsynaptic potentials (IPSP), while Type I responded with IPSP only. In Type E at P4 and older, a single stimulation produced a burst of spike discharges that lasted for several seconds. Stimulation at a hyperpolarized membrane potential showed that aggregated slow EPSPs lay under a burst of spike discharges, and that slow EPSPs, but not a short-latency EPSP, were completely blocked by MK-801. In contrast, Type E at P3 and younger did not evoke a burst of spikes. Morphological examination of recorded neurons showed that the formation of networks was sparse at P1 and rapidly developed up to P4. The results suggest that: (1) short-term potentiation is induced with the development of synaptic network formation in the caudal nucleus at P4 and older; (2) the summation of N-methyl-d-aspartate (NMDA)-mediated slow EPSPs build up a prolonged depolarization; and (3) the brainstem preparation is applicable for neurophysiological studies on the trigeminal pain system.
authors.affiliation: Department of Physiology, Showa University, School of Dentistry, Tokyo 142, Japan. hamba@dent.showa-u.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Hamba
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000344:Afferent Pathways / Q000502:physiology; D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000494:pharmacology; D001931:Brain Mapping; D001933:Brain Stem / Q000254:growth & development / Q000502:physiology*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D007839:Functional Laterality; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008340:Mandibular Nerve / Q000254:growth & development / Q000502:physiology*; D008526:Medulla Oblongata / Q000502:physiology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011930:Reaction Time; D014276:Trigeminal Nerve / Q000254:growth & development / Q000502:physiology*
chemical_list: D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; D008274:Magnesium; D001640:Bicuculline