Journal of neurophysiology
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1. In this, the fifth article in a series to assess changes in posture, hindlimb dynamics, and muscle synergies associated with backward (BWD) quadrupedal walking, we compared the recruitment of three biarticular muscles of the cat's anterior thigh (anterior sartorius, SAa; medial sartorius, SAm; rectus femoris, RF) for forward (FWD) and BWD treadmill walking. Electromyography (EMG) records from these muscles, along with those of two muscles (semitendinosus, ST; anterior biceps femoris, ABF) studied previously in this series, were synchronized with kinematic data digitized from high-speed ciné film for unperturbed steps and steps in which a stumbling corrective reaction was elicited during swing. 2. ⋯ The two forms of walking are differentiated by posture and limb dynamics, yet muscles participating in the basic flexor and extensor synergies are unchanged. Although central pattern generating (CPG) circuits determine the basic timing of these synergies, changes in the duration and waveform of muscle activity may depend on unique interactions among the CPG, supraspinal inputs that set posture and the animal's goal (to walk BWD or FWD) and motion-related feedback from the hindlimb. Output mutability to each muscle may depend on the balance of this tripartite input; muscles with immutable patterns may rely heavily on input from CPG circuits, whereas muscles with mutable patterns may rely more on form-specific proprioceptive and supraspinal inputs.
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1. Taste receptor cells produce action potentials as a result of transduction mechanisms that occur when these cells are stimulated with tastants. These action potentials are thought to be key signaling events in relaying information to the central nervous system. ⋯ These results suggest that many taste receptor cells conduct action potentials, which may be classified broadly into two groups on the basis of action potential duration and potassium current magnitude. These groups may be related to cell turnover. The physiological role of action potentials remains to be elucidated but may be important for communication within the taste bud as well as to the afferent nerve.
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1. Whole cell patch-clamp recordings of monosynaptically connected pairs of hippocampal neurons in very low-density culture were performed to determine the effects of the activation of metabotropic glutamate receptors (mGluRs) on inhibitory terminals. The mGluR agonist (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S, 3R)-ACPD] and the recently described mGluR antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) were used. ⋯ We propose that inhibition of glutamate uptake mechanisms results in activation of mGluRs on GABAergic terminals via endogenous sources of glutamate and that the uptake inhibitors (L-trans-PDC and THA) do not directly activate the metabotropic receptor. 5. Presynaptic receptors and active modulation of uptake mechanisms are clearly involved in a wide range of physiological and pathological synaptic events. The data presented here suggest that heterosynaptic modulation of inhibitory synaptic transmission by metabotropic glutamate receptors may be important for the maintenance and plasticity of the balances between excitatory and inhibitory synaptic transmission in the CNS.