ABSTRACT
Tooth and tooth-related organs play important roles in not only mastication, but also sensory perception in the oral region. In general, sensory neural inputs during the developmental period are required for the maturation of functions in the sensory cortex. However, whether maturations of oral somatosensory cortex (OSC) require certain levels of sensory input from oral regions has been unclear. The present study investigated the influence of multiple tooth-losses during the developmental period on age-dependent emergence of rhythmic activities of population neurons in the OSC. Low-frequency electrical stimulation was delivered to layer IV and field potentials were recorded from layer II/III in the OSC of rat brain slices. In control rats, N-methyl-d-aspartate (NMDA) receptor-dependent oscillation at 8-10 Hz appeared during postnatal weeks 2-3. In rats with extraction of multiple teeth at 17-18 days old, oscillation did not appear even at maturity, whereas in rats with multiple teeth extracted at 37-38 days old, oscillation appearances were maintained in maturity. Thus, emergence of oscillation in the OSC was suppressed by multiple tooth-losses during postnatal 2-3 weeks. These results suggest that sufficient neural inputs from the teeth and tooth-related organs during developmental periods are essential for maturation of neural functions in the OSC.
Subject(s)
Biological Clocks/physiology , Neurons/physiology , Somatosensory Cortex/growth & development , Somatosensory Disorders/etiology , Tooth Loss/complications , Tooth/growth & development , Action Potentials/physiology , Afferent Pathways/growth & development , Afferent Pathways/physiopathology , Aging/physiology , Animals , Denervation , Electric Stimulation , Neuronal Plasticity/physiology , Organ Culture Techniques , Rats , Receptors, N-Methyl-D-Aspartate/drug effects , Receptors, N-Methyl-D-Aspartate/metabolism , Somatosensory Cortex/physiopathology , Somatosensory Disorders/physiopathology , Tooth/innervation , Trigeminal Nerve/growth & development , Trigeminal Nerve/physiopathologyABSTRACT
Traveling neural signals may try to find suitable paths of propagation in cortical circuits. We examined the behavior of electrically evoked signals from primary visual cortex (Oc1) to granular retrosplenial cortex (RSG) in rat brain slices under caffeine application. With continued electrical stimulation, evoked signals propagated from Oc1 to RSG along the upper layer of the secondary visual cortex (Oc2) and agranular retrosplenial cortex (RSA), but on further continuation of stimulation, a new shortcut pathway along the deep layer between Oc2 and RSG was opened. Circuitry changes reduced the signal traveling time by about 40 ms. Cortical neural circuits between Oc1 and RSG may thus have the ability to open a shortcut circuit in a use-dependent manner.
Subject(s)
Evoked Potentials/physiology , Gyrus Cinguli/physiology , Visual Cortex/physiology , Visual Pathways/physiology , Animals , Animals, Newborn , Electric Stimulation/methods , Evoked Potentials/radiation effects , Gyrus Cinguli/anatomy & histology , Gyrus Cinguli/drug effects , In Vitro Techniques , Rats , Rats, Wistar , Spectrum Analysis , Time Factors , Visual Cortex/anatomy & histology , Visual Cortex/drug effects , Visual Pathways/anatomy & histologyABSTRACT
Cyclic AMP (cAMP) is a key intracellular second messenger, and the intracellular cAMP signaling pathway acts to modulate various brain functions. We have previously reported that low-frequency insular cortex stimulation in rat brain slices switches on a voltage oscillator in the parietal cortex that delivers signals horizontally back and forth under caffeine application. The oscillatory activities are N-methyl-D-aspartate (NMDA) receptor-dependent, and the role of oscillation is to strengthen functional intercortical connections. The present study investigated actions of the cAMP signaling pathway on caffeine-induced strengthening of intercortical connections and tried to confirm the role of oscillation on intercortical strengthening by focusing on the cAMP pathway. After induction of parietal oscillation by insular cortex stimulation in caffeine-containing medium, application of membrane-permeable cAMP analog, bromo-cAMP, diminished oscillatory signal delivery from the parietal cortex, but initial insulo-parietal signal propagation remained strong. When oscillatory activities were reduced with co-application of caffeine and bromo-cAMP from the beginning, initial insulo-parietal propagation was established, but amplitudes of propagating wavelets and propagating velocity were reduced. Thus, cAMP-dependent diminution of caffeine-induced NMDA-receptor-dependent oscillatory signal delivery causes attenuation of intercortical strengthening of horizontal pathways between insular and parietal cortices. This finding suggests that the intracellular cAMP signaling pathway has the ability to regulate extracellular communications at the network level, and also that full expression of strengthened intercortical signal communication requires sufficient NMDA-receptor-dependent oscillatory neural activities.
Subject(s)
Action Potentials/physiology , Biological Clocks/physiology , Cerebral Cortex/physiology , Cyclic AMP/physiology , Neural Pathways/physiology , 2-Amino-5-phosphonovalerate/pharmacology , 8-Bromo Cyclic Adenosine Monophosphate/pharmacology , Action Potentials/drug effects , Action Potentials/radiation effects , Animals , Animals, Newborn , Biological Clocks/drug effects , Caffeine/pharmacology , Central Nervous System Stimulants/pharmacology , Cerebral Cortex/anatomy & histology , Cerebral Cortex/drug effects , Cerebral Cortex/radiation effects , Drug Interactions , Electric Stimulation/methods , Excitatory Amino Acid Antagonists/pharmacology , In Vitro Techniques , Neural Pathways/drug effects , Neural Pathways/radiation effects , Rats , Rats, Wistar , Rhodanine/analogs & derivatives , Thiazolidines , Time FactorsABSTRACT
BACKGROUND: Vascular endothelial growth factor (VEGF) is an inducer of angiogenesis and permeability of small blood vessels. We determined the concentrations of VEGF in synovial fluid of patients with symptomatic internal derangement of the temporomandibular joint (TMJ). METHODS: Diluted synovial fluid was collected by a pumping procedure from 22 TMJs of patients with internal derangement and 10 control TMJs. VEGF concentration was determined by an enzyme-linked immunosorbent assay. RESULTS: The VEGF was detected in 14 of the 22 joints (64%) of patients with internal derangement, at a mean concentration of 67 pg/ml, but in only one control joint (12.5 pg/ml) (P = 0.004 for the difference in concentration). There was a significant correlation between VEGF concentration and total protein concentration in the synovial fluid (P = 0.002). CONCLUSIONS: The increased concentration of VEGF in patients with symptomatic internal derangement suggests that this growth factor may be involved in the pathogenesis of this condition.
