Interaction between piloting and beacon homing by rats in a swimming pool

In three experiments, rats in a swimming pool were trained to find a submerged platform with a beacon attached to it. For some rats this beacon unambiguously identified the location of the platform; for others the beacon was made ambiguous by placement of an identical beacon in a different part of the pool. Test trials, in the absence of the platform and the beacons, revealed more persistent searching near the original location of the platform if the beacon attached to the platform had been ambiguous. These results show that learning about the location of the platform, with regard to cues that lie beyond the pool, is influenced by the extent to which an animal can find the platform by relying on other cues. The final experiment shows that this interaction between cues is influenced by an animal's prior experience.

Longus cervicis colli "myositis" (syn: retropharyngeal tendinitis)

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Acquisition of conditioned inhibition in rats is impaired by ablation of serotoninergic pathways

The effects of chronically ablating the serotoninergic inputs to various regions of the rat brain on the ability to solve a feature-negative discrimination was measured. After intracerebroventricular administration of the specific neurotoxin 5,7-dihydroxytryptamine, the rats exhibited an impaired capacity to solve such a discrimination, irrespective of whether auditory or visual stimuli were used. Further behavioural analysis revealed that this effect was not due to a reduced capacity to form excitatory associations, since both groups responded equally to reinforced stimuli. By contrast, the lesion more likely resulted in a failure to endow the non-reinforced stimuli with inhibitory properties. This suggestion was supported by the observation that, in a retardation test, the conditioned inhibitor aroused less inhibition in the lesioned group than in vehicle-injected controls. Furthermore, the conditioned inhibitor failed to pass a summation test in lesioned animals, again indicating that their hampered ability to master the discrimination was the result of an impairment in the formation of inhibitory associations. It is concluded that destruction of central 5-hydroxytryptamine-containing pathways impairs the functioning of brain areas underlying inhibitory associative learning.

Cervicogenic headache: a personal view

Cervicogenic headache describes pain referred along the upper three cervical roots and is a common source of headache in the over fifties. A review of clinical features, anatomy, and investigations using neural blockade shows several clinical pictures. Diseases of the cranio-vertebral junction, e.g. syringomyelia, and tonsilar descent, can produce mechanical or hydrodynamic head and neck pain. Pre-existent migraine and tension headache may be precipitated or aggravated by cervical spondylosis, but the anatomical mechanism is unclear. Headaches which arise from and are primarily caused by disorders in the cervical spine are exemplified by spondylosis and acute whiplash injury, but are usually transient. Evidence for a cervicogenic mechanism of chronic whiplash headache is, however, lacking.