An integrated, temporal study of the behavioural, electrophysiological and neuropathological consequences of murine prion disease

We have conducted an integrated study of ME7 prion disease by examining the electrophysiological and neuropathological features of hippocampal slices from behaviourally characterised C57Bl/6J mice 12, 14, 16, 18, 20 and 24 weeks after intracerebral micro-injection of ME7 or normal brain homogenate. We describe the pathogenesis of ME7 as a three-stage process. STAGE ONE: PrPSc deposition, synaptic pathology and abnormal synaptic plasticity. STAGE TWO: Onset of behavioural changes, exemplified by an increase in open-field activity, enhancement of the slow AHP and development of vacuolation. Membrane depolarisation is also an early feature, but its exact timing remains to be confirmed. STAGE THREE: Clinical disease, substantial neurodegeneration and further disruption of the action potential profile. We suggest that the mechanisms underlying the electrophysiological changes of Stages one and two may provide novel approaches to treatment of prion disease, and that those seen in Stage three may be relevant to neurodegenerative diseases more generally.

Re-examination of the medullary rootlets of the accessory and vagus nerves

The vagus (X) and cranial root of the accessory nerve (crXI) are traditionally described as arising from a series of rootlets from the medulla oblongata. Descriptions of the number of rootlets vary, and the existence of the crXI is contested. Here we report the results of dissections in six embalmed adult human specimens (11 sides). The rootlets forming the vagus were counted at three positions. At emergence from the brainstem there were between 12 and 21 rootlets, at the jugular foramen the range was 12-17, and midway between these two points it was 6-12. In addition, the origin of the most caudal X rootlet (cX) and the most rostral XI rootlet (rXI) was recorded in relation to the spino-medullary junction, defined as the caudal border of the olivary eminence. The position of the cX varied between -1 and +8 mm (median = +2 mm on left, +3.75 mm on right). The rXI varied between -5 and +7 mm (median = -0.5 mm on left, +1.75 mm on right). In five sides, rXI was above the caudal border of the olivary eminence and as such can be defined as being of cranial origin. These observations show the arrangement of rootlets contributing to the vagus to be more complex than what was described previously and provide evidence for the variable existence of a cranial root of the accessory nerve.

Hyperpolarization-activated current (Ih): A characterization of subicular neurons in brain slices from socially and individually housed rats

The hyperpolarization and cyclic nucleotide activated current Ih is thought to have a role in rhythmic brain activity that is important in complex behaviors and might be perturbed in some neuropsychiatric diseases. We have used whole-cell voltage and current clamp techniques to characterize Ih in neurons from the subiculum-the major output region of the hippocampal formation. Subicular projection neurons are themselves classifiable as intrinsically bursting (IB) or regular spiking (RS) and Ih is present in both. Given the possible involvement of Ih in neuropsychiatric diseases, we have also characterized Ih in subicular neurons from rats that have been housed in individual cages (though still able to see, smell, and hear other rats) as these rats can display behavioral changes similar to those seen in schizophrenia. Individual housing is associated with a 4.4-mV depolarization of the Ih activation curve (P=0.0027) and an increase in mean firing rate measured in response to current injection (P=0.037) specifically in RS neurons and a change in the relative amplitude of Ih between IB and RS neurons. Thus, we have shown significant changes in a current thought to be relevant to psychiatric disease in a partial model of schizophrenia. Its further investigation might reveal chemical targets for novel antipsychotic drugs.

Post-weaning social isolation of rats leads to a diminution of LTP in the CA1 to subiculum pathway

Post-weaning social isolation of rats produces psychological and physiological changes that are relevant to schizophrenia. Here, we report that long-term potentiation (LTP) in the CA1 to subiculum pathway is lower by 34%, (P<0.0001) in brain slices from isolates compared with those from socially housed rats. We also report that LTP in this pathway is NMDA receptor-dependent.

Effects of detailed information about dissection on intentions to bequeath bodies for use in teaching and research

Almost all UK medical schools teach anatomy using human bodies that have been bequeathed specifically for the purpose. Persons intending to make this most generous gift should be fully informed about how their body will be used. If detailed descriptions of dissection reduce the number of bequests, then this traditional and effective approach to anatomy teaching will have to change. To determine what effect detailed information has on intentions to bequeath, the Department of Anatomy at Bristol University sent all 139 people who asked for information, between July and December 2001, a description of dissection that included the statement 'Anatomical examination requires that bodies be dissected (taken apart) so that the fine detail of internal structures can be seen. Organs, such as the heart, lungs and brain, are often removed from the body to allow for more detailed study.' Views were sought by questionnaire (response rate 88%). Ninety-nine per cent of respondents intended to bequeath their body and 88% would allow it to be used in research or teaching with the department to make the final decision. Thus the provision of detailed information about dissection should not reduce the number of bequests and this mechanism could, subject to law, make bodies available for research as well as for teaching.