Central neural motor programs underlying short- and long-term patterns of \u3cem\u3eLimulus\u3c/em\u3e respiratory activity

Isolated, unstimulated abdominal ventral nerve cords ofLimulus display patterns of motor output characteristic of rhythmic gill ventilation and of gill cleaning (Fig. 2). The motor output may occur as long-term patterns of alternate gill cleaning and ventilation (Fig. 3), or alternate gill cleaning and tonic activity (Fig. 4). Two patterns of gill cleaning motor output, apparently corresponding to the left-leading and right-leading patterns observed in intact animals, persist in the isolated ventral cord (Fig. 4). These two patterns occur with the same rough alternation as in intact animals. Thus all the patterns of gill-plate movement in intact animals, except those involving swimming, have underlying motor programs that are expressed in isolated nerve cords in the absence of stimulation or of sensory feedback. These findings extend the concept of central pattern generators to include complex and long-duration patterns of stereotyped behavior such as those underlying the movements of theLimulus abdominal appendages

Characterization of auditory synaptic inputs to gerbil perirhinal cortex

The representation of acoustic cues involves regions downstream from the auditory cortex (ACx). One such area, the perirhinal cortex (PRh), processes sensory signals containing mnemonic information. Therefore, our goal was to assess whether PRh receives auditory inputs from the auditory thalamus (MG) and ACx in an auditory thalamocortical brain slice preparation and characterize these afferent-driven synaptic properties. When the MG or ACx was electrically stimulated, synaptic responses were recorded from the PRh neurons. Blockade of GABA-A receptors dramatically increased the amplitude of evoked excitatory potentials. Stimulation of the MG or ACx also evoked calcium transients in most PRh neurons. Separately, when fluoro ruby was injected in ACx in vivo, anterogradely labeled axons and terminals were observed in the PRh. Collectively, these data show that the PRh integrates auditory information from the MG and ACx and that auditory driven inhibition dominates the postsynaptic responses in a non-sensory cortical region downstream from the auditory cortex

Developmental hearing loss eliminates long-term potentiation in the auditory cortex

Severe hearing loss during early development is associated with deficits in speech and language acquisition. Although functional studies have shown a deafness-induced alteration of synaptic strength, it is not known whether long-term synaptic plasticity depends on auditory experience. In this study, sensorineural hearing loss (SNHL) was induced surgically in developing gerbils at postnatal day 10, and excitatory synaptic plasticity was examined subsequently in a brain slice preparation that preserves the thalamorecipient auditory cortex. Extracellular stimuli were applied at layer 6 (L6), whereas evoked excitatory synaptic potentials (EPSPs) were recorded from L5 neurons by using a whole-cell current clamp configuration. In control neurons, the conditioning stimulation of L6 significantly altered EPSP amplitude for at least 1 h. Approximately half of neurons displayed long-term potentiation (LTP), whereas the other half displayed long-term depression (LTD). In contrast, SNHL neurons displayed only LTD after the conditioning stimulation of L6. Finally, the vast majority of neurons recorded from control prehearing animals (postnatal days 9–11) displayed LTD after L6 stimulation. Thus, normal auditory experience may be essential for the maturation of synaptic plasticity mechanisms