L-Citrulline Immunoreactivity Reveals Nitric Oxide Production in the Electromotor and Electrosensory Systems of the Weakly Electric Fish, Apteronotus leptorhynchus

Cell type-specific plasticity at parallel fiber synapses onto Purkinje cells in the posterior caudal lobe of the mormyrid fish cerebellum

It has been demonstrated that there are two morphological subtypes of Purkinje cells (PCs)-fan-shaped Purkinje cells (fPCs) and multipolar Purkinje cells (mPCs)-in the posterior caudal lobe of the mormyrid fish cerebellum, but whether these cell types are also functionally distinct is unknown. Here, we have used electrophysiological and pharmacological tools in a slice preparation to demonstrate that pairing parallel fiber (PF) and climbing fiber (CF) inputs at a low frequency induces long-term depression (LTD) in fPCs but long-term potentiation (LTP) in mPCs. The induction of plasticity in both cell types required postsynaptic Ca²⁺ and type 1α metabotropic glutamate receptors. However, the LTD in fPCs was inducted via a calcium/calmodulin-dependent protein kinase II cascade, whereas LTP induction in mPCs required calcineurin. Moreover, the LTD in fPCs and LTP in mPCs were accompanied by changes to the corresponding paired-pulse ratios and their coefficients of variation, suggesting presynaptic modes of expression for the plasticity at PF terminals for both cell types. Hence, the synaptic plasticity at PF synapses onto PCs in the posterior caudal lobe of the mormyrid cerebellum is cell type specific, with both pre- and postsynaptic mechanisms contributing to its induction and expression. NEW & NOTEWORTHY Much has been learnt about the cerebellar long-term depression (LTD) in the cortex. More recent work has shown that long-term potentiation (LTP) is equally important for cerebellar motor learning. Here we report for the first time that plasticity in the mormyrid cerebellum is cell type specific, e.g., following the conventional pairing of parallel and climbing fiber inputs in an in vitro preparation leads to LTD in one Purkinje cell subtype and LTP in another.

Recent advances in enteric neurobiology: mechanosensitive interneurons

Until recently, it was generally assumed that the only intrinsic sensory neuron, or primary afferent neuron, in the gut was the after-hyperpolarizing AH/Type II neuron. AH neurons excited by local chemical and mechanical stimulation of the mucosa appear to be necessary for activating the peristaltic reflex (oral excitation and anal inhibition of the muscle layers) and anally propagating ring like contractions (peristaltic waves) that depend upon smooth muscle tone. However, our recent findings in the guinea-pig distal colon suggest that different neurochemical classes of interneuron in the colon are also mechanosensitive in that they respond directly to changes in muscle length, rather than muscle tone or tension. These interneurons have electrophysiological properties consistent with myenteric S-neurons. Ascending and descending interneurons respond directly to circumferential stretch by generating an ongoing polarized peristaltic reflex activity (oral excitatory and anal inhibitory junction potentials) in the muscle for as long as the stimulus is maintained. Some descending (nitric oxide synthase +ve) interneurons, on the other hand, appear to respond directly to longitudinal stretch and are involved in accommodation and slow transit of faecal pellets down the colon. This review will present recent evidence that suggests some myenteric S interneurons, in addition to AH neurons, behave as intrinsic sensory neurons.

Breaking the silence: brain-computer interfaces (BCI) for communication and motor control

Brain-computer interfaces (BCI) allow control of computers or external devices with regulation of brain activity alone. Invasive BCIs, almost exclusively investigated in animal models using implanted electrodes in brain tissue, and noninvasive BCIs using electrophysiological recordings in humans are described. Clinical applications were reserved with few exceptions for the noninvasive approach: communication with the completely paralyzed and locked-in syndrome with slow cortical potentials, sensorimotor rhythm and P300, and restoration of movement and cortical reorganization in high spinal cord lesions and chronic stroke. It was demonstrated that noninvasive EEG-based BCIs allow brain-derived communication in paralyzed and locked-in patients but not in completely locked-in patients. At present no firm conclusion about the clinical utility of BCI for the control of voluntary movement can be made. Invasive multielectrode BCIs in otherwise healthy animals allowed execution of reaching, grasping, and force variations based on spike patterns and extracellular field potentials. The newly developed fMRI-BCIs and NIRS-BCIs, like EEG BCIs, offer promise for the learned regulation of emotional disorders and also disorders of young children.