NEUROBIOLOGY HAS ITS UNANSWERED QUESTIONS. HAROLD HILLMAN. SEPTEMBER 1996
It would be generally agreed that the identification of anomalies and
contradictions in one's belief is an important step to advance understanding.
Below is a series of 22 bona-fide questions, some of them drawing attention
to contradictions. In a spirit of scientific debate, I have put forward new
hypotheses about the histology of the nervous system, and about the mechanism
of transmission, both of which are designed to meet the objections to the
current views, which my questions have identified. I would request
neurobiologists and other interested persons: (a) to answer these questions;
(b) if they can not, to see if my theories answer them; (c) to propose their
own solutions, if they do not agree with mine; (d) to provide some references
to their key points; (e) to avoid rudeness and assumption of my ignorance;
(f) to be conscious continuously of which aspects of any evidence have been
proved, which have not, which are provable, and which are not.
A. Histology of mammalian nervous system.
1. Has anyone shown neuroglial unit cell membranes adjacent to neuronal
membranes in intact tissue by light or electron microscopy? If so, please send
me micrographs or references in intact tissue.
2. What publications have shown that the characteristic morphological and
staining properties by which neurons, astrocytes, oligodendrocytes and
microglia, were originally described are also present in cultures which are
believed to be the same cell types?
3. Why does only a small proportion of the area of a section of the
central nervous system show up with neuronal and neuroglial stains and
antibodies?
4. Why does an intracellular recording electrode, penetrating the brain
and spinal cord, record no potential difference in most of its travel, if only
5-25% of the volume of the central nervous system is extracellular space?
5. Has anyone ever seen under their electron microscopes, or in
micrographs of longitudinal or transverse sections of myelin lamellae of the
central or peripheral nervous system, the expected appearance of 'splaying'
in longitudinal sections not going through the middle of the axon, or in
oblique transverse sections - (that is, in oblique sections, the distance
between the lamellae should not be equal distances apart)? What is the
explanation for such dictates of solid geometry being disobeyed?
6. If the central nervous system is virtually full of neurons, neuroglial
cells and their processes, how can phagocytes assemble within hours around an
infection from other sites in the brain and spinal cord, in the process
described as gliosis?
7. Why are immunocytochemical markers believed to be characteristic of
different cell types nearly always demonstrated in tissue culture and not in
the intact nervous system?
8. Does anyone have micrographs - rather than diagrams - of myelinated
fibres arising from neuron somas?
9. Have fixatives, washings, ethanol, sera and permeabilisers been shown
not to affect the intensity or distribution of fluorescence as seen in
immunocytochemistry?
10. Why do some sections have to be 'permeabilised' to allow access of
antibodies, since the cells are already cut open in thin sections, and one
must assume that the permeabilisers have no effect on the immune reaction?
B. Synapses and transmission
11. Why is it assumed that findings across nerve-muscle junctions are
relevant to nerve-nerve junctions (synapses)?
12. Why are there no light micrographs in the literature - as opposed to
diagrams - showing a dendrite arising from one cell body attached to the
synapse on another cell body, since the light microscope has the resolution
to show up such pre-synaptic fibres?
13. Why are the diameters of synaptic knobs seen by light microscopy
approximately 8-10 times the diameters of those seen by electron microscopy?
14. Why are the synaptic thickenings seen by electron microscopy nearly
always normal to the plane of section, and why are they never seen obliquely
or on face view (as circles)?
15. Why are receptors to transmitters, which are believed to have been
isolated and sequenced and shown to be two to three times the diameters of the
cell membrane - which is generally believed to be seen by electron microscopy
- not seen by transmission electron microscopy, with the exception of the
acetylcholine receptor (Unwin)? There are supposed to be 'families' of
different receptors to adrenaline, nor adrenaline, gaba, glutamate, etc. Why
are all the latter individual receptors never seen by transmission?
16. How can one prove that synaptic vesicles hit the presynaptic membrane
in life, when they can only be seen by electron microscopy of fixed (dead)
tissues?
17. Why do the synaptic vesicles appear to be almost the same diameters,
when sections made for electron microscopy must cut them in a variety of
planes?
18. Why are miniature end-plate potentials uniform in amplitude despite
the belief that they arise at varying distances from the recording electrodes?
19. Since the synaptic cleft is believed to contain a high concentration
of acetylcholinesterase, how can the acetylcholine from the presynaptic
membrane cross the cleft without being broken down?
20. If action potentials can be conducted from an isolated nerve to a
recording electrode, from the heart to the electrocardiogram, from muscle
fibres to an electromyogram, from cortical neurons to an electrocorticogram,
without the intervention of synapses, why can signals not be conducted from
one dendrite to another?
C. Pathology
21. Why are there no tumours of neurons in the central nervous system?
22. Does one judge the kind of glial tumour on the clinical history of
the patient, rather than by the histology of the tumour? Can one diagnose a
glial tumour from a histological section alone without a clinical history?
My references on this subject:
(1983) Some fundamental theoretical and practical problems associated with
neurochemical techniques in mammalian studies. Neurochem. Internat. 5, 1-13.
(1985) The anatomical synapse by light and electron microscopy. Medical
Hypotheses, 17, 1-32.
(1986) Cellular Structure of the Mammalian Nervous System. MTP Press,
Lancaster, pp 1-318.
(1991) A re-examination of the vesicular hypothesis of transmission in
relation to its applicability to the mammalian nervous system. Physiol. Chem.
Phys. & Med. NMR. 23, 177-198.
(1991) A new hypothesis for electrical transmission in the mammalian nervous
system. Medical Hypotheses, 34, 220-224.
(1991) The Case for New Paradigms in Cell Biology and in Neurobiology. Mellen
Press, Lampeter, pp 1-337.
E-mail correspondence to: Rae West on 101722.35 at compuserve.com
