A simple cerebellar system: The lateral line lobe of the goldfish
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The lateral line lobe consists of two structures, a layer of cerebellar material, the crista cerebelli overlying the medullary gray. Field potentials and single cell recordings made after stimulating the lateral line nerve and the caudal lobe of the cerebellum show that the primitive Purkinje cells (pP cells) of the crista can be excited by stimulating the large parallel fibre input running from the caudal lobe and (some cells) by stimulating the lateral line nerve. The parallel fibres do not appear to be involved in these latter responses and their role is unknown.
Apart from the extrinsic origin of the parallel fibres the crista cerebelli also differs from the cerebellum by having no identifiable climbing fibres. Stellate cell inhibition however appears to be present.
The small secondary lateral line cells in the gray layer receive punctate primary afferent inputs from one lateral line organ and a diffuse polysynaptic inhibitory input which can be seen as ipsps evoked in anterior lateral line gray cells by posterior lateral line nerve stimulation.
The lateral line inputs to the pP cells are highly variable and, in contrast to the gray cells pP cells show diffuse receptive fields when tested with “natural” stimuli.
Stimulation of the pP cells inhibits the gray cells and it seems that they are responsible for the inhibitory effect noted in (3).
It is suggested that pP cells with diffuse receptive fields inhibiting gray cells with punctate receptive fields could form a sensory lateral inhibition mechanism in the lateral line lobe.
When the responses of primary fibres in the lateral line nerve and secondary lateral line gray cells to measured physiological stimuli (water displacements at 30 Hz) are compared such a lateral inhibition seems to be present in the lateral line lobe. Secondary gray cells have response attenuation curves of 6–17 dB/cm as the stimulating probe is moved away from the units receptive field. The primary fibres show symmetrical curves with slopes of 4–6 dB/cm which corresponds to the calculated stimulus attenuation.
anterior lateral line nerves
- ext gran
external granule cell layer of the caudal lobe of the corpus cerebelli
granule cell layer of the corpus cerebelli
medullary gray of Pearson
medial longitudinal fasciculus
molecular layer of corpus cerebelli
plexus of axons at the dorsal limit of the gray
posterior lateral line nerve
- pP cells
primitive Purkinje cells
- 2 gust
ascending secondary gustatory tract
descending root of nerve VII
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