PROCEEDINGS OF THE PHYSIOLOGICAL SOCIETY OXFORD MEETING

8-9 July 1977 DEMONSTRATIONS

Automated measurement of potentials BY E. M. VAUGHAN WiuxAms. Department of Pharmacology, Oxford University Until recently the measurement of various parameters of intracellularly recorded potentials and contractions was laborious and time-consuming. Oscilloscope screens had to be photographed, and it was often found, on subsequent development of the film, that good records had been lost because a micro-electrode had been dislodged from contracting muscle while the camera or oscilloscope sweep was being manipulated. The developed film had to be projected and nine individual measurements made by eye on each frame. The results had to be written down, and later re-entered into a calculator for statistical treatment. In the system demonstrated a 4-channel recorder tapes intracellular potentials, contractions, stimulus synchronization pulses, and voice continuously, permitting undivided concentration on the experimental procedures. Instantaneous playback of any desired section of recording is available. Subsequently the experiment can be viewed at leisure in real time, and displayed via three analogue-todigital (ADO) transient recorders. The memory of one of them displays in a 'roll' mode the intracellular records. The other two display the associated contraction, and the initial segment of the intracellular potential, at appropriate sweep speeds, the individual sweeps being triggered by the pulses recorded on channel 3. When a 'good' record is found, this section is played back at i or i real time, and the desired segment is locked into the ADO memories. The digital information is then transferred to a Hewlett Packard 9830 calculator, and processed, and the results are printed out. Meanwhile the next segment of tape can be examined until another good record is found. When all records have been measured, the data is analysed statistically, and the computations are printed. The raw data is then stored on an appropriate data file, to which similar data acquired subsequently can be added. Data from entire series of experiments can

2P PROCEEDINGS OF THE then be recalled, and statistical computations carried out on the complete sets, and printed. The advantages of the system are: no loss of records, and instant verification of capture; greatly increased accuracy of measurement; a tenfold saving of data-processing time; complete objectivity, because no measurement is made by eye, or written down. Thanks are expressed to the British Heart Foundation for an equipment grant.

Dietary obesity: permanent changes in body weight BY BARBARA J. ROLLS AND E. A. ROWE. Department of Experimental Psychology, University of Oxford Studies of obesity in animals have usually employed genetically obese strains, or rats with lesions in the ventromedial hypothalamus. An animal model of obesity was presented which accords closely with a major cause of obesity in man, that of dietary obesity. The dietary obesity model. Adult male rats were offered either a mixed high-calorie diet (potato chips, cheese crackers, chocolate chip cookies and dates) in addition to laboratory chow, or chow alone. The rats on the mixed diet became obese, gaining 102 g more than the controls in 13 weeks. Carcass analysis indicated that the body length and femur length in the two groups were similar, but that the animals fed on the mixed diet had significantly (P < 0.01) greater fat deposits. After 13 weeks the mixed diet was withdrawn and both groups were maintained on chow. The obese rats maintained the elevated body weight. If the body weight of the obese group was reduced to that of the control group by restricting food intake, they subsequently regained the lost weight when given free access to chow. The influence of exercise. Adult male and female rats were maintained either in standard cages or in cages with a running wheel attached. Both groups were offered either the mixed diet with chow or chow alone. Under both conditions of feeding, exercise had little effect on female body weights, and sedentary and exercising females became obese on the mixed diet. But in the males both mixed diet and chow fed exercising groups weighed less (P < 0 02) than the sedentary groups; only the sedentary males on the mixed diet became obese. The mixed diet was withdrawn after 10 weeks. The body weights ofthe sedentary females were maintained at the mixed diet level, but in the exercising females body weights fell but were regained 4-6 weeks later. Thus once body weight is established at a new high level it is maintained at that level in this model of obesity. Furthermore there are sex differences in the effects of exercise on the maintenance of body weight in rats. Supported by the Medical Research Council.

PHYSIOLOGICAL SOCIETY, JULY 1977

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The superfused rat cerebellar cortex as an in vivo preparation for studies of neurotransmitter release BY J. A. AsuIMPVrXo, N. BERNARDI, C. G. DACKE and N. DAVIDSON. Department of Physiology, Marischal College, University of Aberdeen, Broad Street, Aberdeen AB9 lAS, Scotland The rat cerebellar cortex offers a number of advantages to the investigator of central neurotransmitters. Although not lissencephalic, as is the rat cerebrum, it is dorsally located and easy of access. The well-identified and relatively uniform distribution of cerebellar excitatory and inhibitory synapses makes it a promising region of the brain in which to study the in vivo release of putative neurotransmitters.

. : : : : ................ .:: ...:.:

5 mm

Fig. 1. Tracing from a photograph of the dorsal aspect of the exposed surface of the rat vermis cerebelli. Arrows indicate the lambdoid suture (L) and the obex (0). The stippled area indicates the region of the tuber and declive enclosed within the superfusion chamber.

Techniques for the superfusion of the cerebellar cortex of the chloraloseurethane anaesthetized rat were demonstrated. Supraoccipital and interparietal skull are removed, exposing the mid line cerebellar structures, or vermis cerebelli, including tuber and declive of the posterior lobe (Fig. 1). A small Perspex ring, internal volume 30 pzl. is sealed in place over the exposed pial surface with petroleum jelly. A Watson-Marlow MHRE Flow Inducer is used to superfuse the area of cerebellum within the ring with surrogate cerebrospinal fluid (c.s.f.) at approximately 50 I1M. min'. A mini-peristaltic pump is used to collect suitable fractions for chemical or isotopic measurement. Data were shown of (a) potassium evoked release of

4P PROCEEDINGS OF THE 4P [3H]taurine (Assumpga9o, Bernardi, Dacke & Davidson, 1977) and [14C]GABA, putative neurotransmitters present in significant amounts in the cerebellum, (b) calcium dependency of the evoked taurine release and (c) atomic absorption spectrophotometric estimations of calcium levels present in superfusates recovered from the cerebellar surface after superfusion with normal and calcium-free surrogate c.s.f. This research was supported by grants from the Medical Endowment Funds of Aberdeen University to N.D. and C.G.D. and from CNPq and FAPESP (Brazil) to J.A.A. and CAPES and FAPESP (Brazil) to N.B. REFERENCE AssumrPAo, J. A., BERNARDI, N., DACKE, C. G. & DAvmsoN, N. (1977). J. Physiol. 270, 48-49 P.

Analysis of drinking in the chronically cannulated monkey BY S. MADDISON, BARBARA J. RoiLs, E. T. Rou~s and R. J. WOOD. Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OXi 3UD The preparation of rhesus monkeys with two chronic cannulas (one in the greater curvature of the stomach 5 cm above the pylorus, and one in the duodenum 2 cm below the pylorus) was illustrated. The following studies of drinking in the primate have been made possible by this preparation. Drinking with the cannulas closed. Analysis of blood samples drawn from the water-deprived monkey during drinking with both cannulas closed indicated that drinking stopped before major plasma dilution occurred. This suggests that satiety signals for thirst involved in the cessation of drinking may be of peripheral origin. The following experiments utilized one or both cannulas in an attempt to localize the site of origin of such signals. Drinking with the gastric cannula open. In this situation ingested water is immediately recovered from the gastric cannula. This is referred to below as 'gastric sham drinking'. The monkeys drank several times their normal intake on the first trial in which the gastric cannula was opened. Gastric sham drinking was vigorous and sustained throughout the 60 min test period. Pauses were short and infrequent. Gastric sham drinking had no effect on plasma osmolality. These data suggest that any oropharyngeal and gastric factors involved in this situation are weak satiety signals when acting alone. Drinking with the duodenal cannula open. In this situation ingested water passes through the stomach (gastric cannula closed) and is recovered as it

PHYSIOLOGICAL SOCIETY, JULY 1977 5P leaves the stomach, 1*5-20 cm below the pylorus. This is referred to as 'duodenal sham drinking'. Excessive drinking was observed on the first trial with the duodenal cannula open. The monkeys drank vigorously and with few pauses, though at a lower rate than during gastric sham drinking. These data suggest pre- or post-absorptive signals arising in or after the intestine are important in the satiation of thirst in the monkey. Duodenal infusions during drinking. Duodenal infusions were made via the duodenal cannula and began at the same time as drinking with the gastric cannula open. Duodenal infusions of water in the range 25-100 ml. slowed or stopped gastric sham drinking. Volumes of isotonic saline up to 155 ml. infused in the same way did not affect gastric sham drinking. The data suggest that important pre- or post-absorptive signals in the satiation of thirst in the monkey originate at the level of the intestine.

An automatic thermal data recording system for use in high performance aircraft By J. R. ALLAN, M. H. HARRISON and C. HIGENBOTTAM. Royal Air Force Institute of Aviation Medicine, Farnborough, Hants (U14 6SZ High performance aircraft are increasingly being required to fly at high speeds at very low altitudes, and under these flight conditions the cabin aerodynamic heat load can approach 9 kW. Solar radiation and cockpitmounted avionic equipment can each add another 2 kW. The net effect of these heat inputs on cockpit temperature depends upon the efficiency of the cabin conditioning system. However, there seems to be little doubt that cockpit temperatures can rise to high levels during flight, even in the temperate climate of mid Europe, and that the resulting thermal strain induced in the pilot could adversely affect his operational efficiency. Only recently has it became possible, using an automatic data recording system, to measure cockpit and pilot temperatures during operational sorties. This recording system, which is man-mounted, connects with physiological sensors applied to the pilot's body, and with environmental sensors mounted on the ejection seat. Measured are the pilot's skin temperature (at four sites), aural canal temperature, heart rate, the cockpit air temperature, black globe (50 mm) temperature, humidity and air flow. The recorder employs a multiplexing technique to reduce the number of data amplifiers required to service the thirty-two channels which are available. To preserve linearity and resolution, thermistor temperature data are grouped into three full-scale ranges appropriate to the site of measurement (aural temperature 35-40 0C; skin temperature 5-30 0C or 15-40 0C; environmental temperature 10-60 0C). A frequency-to-voltage

6PAPROCEEDINGS OF THE 6P converter records heart rate from e.c.g. electrodes in the range 50-200 beats min-, and a Valsala capacitive detector (with associated circuit) provides a voltage proportional to humidity in the range 0-100 % r.h. Air velocity is monitored by a hot-thermistor anemometer in the range 0-3 m. sec-'. After analogue-to-digital conversion, data are recorded on magnetic tape in a seven-bit serial bipolar code format, interspersed with tone bursts for channel identification. Each data scan occupies a 2 see period, and the scan interval may be set at 1, 2 or 5 min. By using low-power linear and digital microcircuits, a recording life of 50 hr can be obtained from four disposable mercury batteries. The man-mounted electronic unit and tape recorder each weighs 0-6 kg, and they are both sufficiently compact to fit into the pilot's coverall pockets. A voice-commentary recording facility is provided to log relevant flight information. Post-flight recovery of data is accomplished using a field-replay system which generates a digital print-out. Laboratorybased facilities include an eight-channel analogue replay unit for graphical presentation of data on a trace recorder, and a computer digital interface.

A sequence timer for on-line experiments BY W. J. BANNISTER. University Laboratory of Physiology, South Paris Road, Oxford. A four-channel sequence timer was demonstrated, to enable the programming of on-line experiments. The device shown was built at a component cost of less than £200, and consists of a master clock (1-10-100-1000 Hz, crystal-controlled), and four identical timing modules, with pre-settable periods from 1 to 9999 counts at the chosen clock rate, i.e. a total range of 1 msec to 9999 sec. The device can be triggered manually or electronically, with the four modules acting independently, or in 'single sequence' or 'ring of four' mode. Each module has two TTL outputs: a 0/1 level (busy) and a 1/0 pulse of 50 ,psec duration (reached). Effects of pre- and perinatal restricted food intake on the rat cerebellum By K. F. HOWELLS, T. C. JORDAN and S. M. PIGGOTT. Department of Biology, Oxford Polytechnic, Headington, Oxford OX3 OBP Restriction of food supply during pregnancy and lactation is known to bring about marked and permanent changes in the central nervous system

PHYSIOLOGICAL SOCIETY, JULY 1977 7P together with associated deficits in motor coordination (Dobbing & Smart, 1974). We report here possible specific links between motor coordination, cerebellar structure, differentiation of fast and slow skeletal muscles, and suggested sex differences due to such undernutrition. Undernutrition was achieved by giving female Wistar rats approximately 50 % of their normal ad libitum intake during pregnancy and lactation; litters were standardized at eight for both experimental and control animals. Body weights between experimental and control animals were significantly different when weighed at 3 and 25 days (P < 0.001). After weaning all animals received an ad lib. diet. Animals were tested at 20 weeks for motor coordination by being run backwards on a revolving drum (Lynch, Smart & Dobbing, 1975). Significant differences were found (P < 0.01) with the suggestion that the females were less severely affected by the undernutrition than the males. Previous studies seem to have used only male rats. At 36 weeks animals were sacrificed. Body weights remained significantly different (P < 0.001). Whole-brain weights showed a 9 % drop, cerebellar weight showed a 14 % drop compared with controls. This was reflected in decreases in sagittal cross-sectional area of the vermis. Further analysis revealed that this decrease was significant in males only (P < 0 01), females showing relatively little total decrease and no proportional change between the molecular and granular layers. Males, however, showed decreases in both layers with greater losses in the granular layer. Decreases in muscle weight were found in the undernourished group with fast muscle being more severely affected. This appeared to be due to decreases in muscle fibre size rather than changes in connective tissue content. Further work is in progress investigating specific losses in cerebellar cell types, together with physiological and histochemical analyses of the muscles. REFERENCES DOBBING, J. & SmART, J. L. (1974). Br. med. Bull. 30, 164-168. LYNcH, A., SMART, J. L. & DOBBING, J. (1975). Brain Re8. 83, 249-259.

A substitute for hermeticity in implantable pressure sensors BY G. S. BRINDLEY. M.R.C. Neurological Prostheses Unit, Institute of Psychiatry, London SES 8AF Pressure sensors for long-term implantation into patients or animals (Mackay, 1970; Watson, Currie, Riddle & Meldrum, 1974; Van den Bos, Dolfing, Nassenstein, Heerooms, Buitenweg, Engel & Dijkema, 1974) have hitherto consisted of gas-filled or empty capsules impermeable to water

8P PROCEEDINGS OF THE 8P and gases ('hermetic'), fitted with sensitive mechano-electrical transducers. The transducers need to be sensitive because known materials that are totally impermeable to gases and water are stiff, and those that are also electrically non-conducting (often a requirement) are very stiff. Sensitive transducers rarely have good long-term stability. A pressure-sensitive capsule in an environment of extracellular fluid need not have walls that are impermeable to water and gases if these walls are sufficiently impermeable to sodium and chloride; osmosis keeps the water out, or, if the capsule is saline-filled, keeps its quantity constant. There are silicone rubbers (Dow Coming Silastic sheet and Medical Adhesive Type A) that are sufficiently impermeable to sodium and chloride. These rubbers are very flexible, so that an insensitive transducer with excellent long-term stability can be used (a radio-interrogated tuned circuit, frequency-modulated by movement of a cylinder of ferrite within its inductor). Sensors of the difference in pressure between two regions can conveniently be saline-filled. If their diaphragms are of silicone rubber, saltimpermeability easily suffices to give an expected implanted life of over 100 years. Sensors of absolute pressure must be gas-filled, and for them lives exceeding 10 years cannot yet be confidently predicted. They also have the disadvantage that the contained gas equilibrates with the tissue, so that changes in respiratory state can be confused with changes in ambient pressure. Radio-interrogated implantable sensors for the difference in pressure between the urinary bladder and the abdomen and for that between the cranial cavity and the loose tissues of the neck were demonstrated. The sensor for the urinary bladder is implanted so that it invaginates the wall of the bladder, and is thus hydrostatically inside the bladder though topologically outside. Besides its frequency-modulated tuned circuit, it contains four switches operated by vesical pressure. The same equipment serves for interrogating both the intracranial and the vesical sensor; it was designed and made by Mr P. E. K. Donaldson. REFERENCES MAcKAY, R. S. (1970). Biomedical Telemetry, chapter 5. New York: Wiley. VAN DEN Bos, G. S., DOLIWNG, J., NASSENSTEIN, F., HEERoOMS, B., BuiTENWE, R., ENGEL, W. &]DIJKEMA, F. K. (1974). Cardiovascular Research 8, 290-295. WATSON, B. W., CuIpRIE, J. C. M., RIDDLE, H. C. & MELDRum, S. J. (1974). Phys. Med. Biol. 19, 86-95.

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Skeletal transients associated with heel strike BY L. H. LIOGF and G. McLErA. Clinical Re8earch Centre and Northwick Park Ho8pital, Harrow, Middle8ex Walking on soft ground feels different from walking on hard, and the 'feel' of different footwear can likewise be distinguished. The sensation associated with heel-strike in particular varies greatly, yet conventional gait analysis instrumentation barely differentiates between the impact of soft and hard heels (Hull & Perkins, 1977). Tibia

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"

P

I%..

Skin

50 msec

TeethN 1 g

(a)

I

Barefoot

Hard leather

Shock absorbing

Soft crepe

(b)

Fig. 1. (a) Transducer positions on leg. (b) Vertical acceleration transients on heel strike in normal walking with different footwear. Top pair: simultaneous tracings from tibia/shin surface; bottom pair: simultaneous tracings from tibialbite bar.

As part of an investigation of whether shock-absorbing footwear may ameliorate symptoms in sufferers from joint or back pain, we have studied the transients associated with heel-strike. Gunther (1968) has shown that peak accelerations of 300 m/sec2 (30 g) can be measured on shoe heels, but simultaneous measurements at hip and head level were taken through soft tissue and are therefore difficult to interpret. We have investigated the effect of walking barefoot, with normal and with shock-absorbing footwear on the accelerations observed in a normal subject with lightweight transducers of extended frequency response, one of which was mechanically coupled to the tibia. A Kulite accelerometer type GYN 155-50 (resonance 2 8 kHz) was firmly attached to two Kirschner wires of 1-14 mm diameter driven through vertical slits in the skin into the tibia of one of the investigators (G. McL., age 31 years, weight 72 kg) 5 cm below the tibial tubercle (A in Fig. 1 a). Another transducer was attached to a moulded high-density Plastazote spreader plate which was glued and 8-2

PROCEEDINGS OF THE loP strapped to the skin 15 cm lower down (B). Vertical acceleration was also recorded from a transducer held between the teeth. High peak accelerations (20-80 m/sec2, i.e. 2-8 g) of short duration (Fig. 1 b) are seen to occur in the tibia during normal walking; joints are thus subjected to substantial force transients on heel strike. The acceleration wave is attenuated, filtered and delayed in passage to the head. High-frequency components are lost also in transit to the skin mounted transducer on the leg. The amplitude and shape of the transient depend on heel construction. In particular, hard heels are associated with a large transient of abrupt onset, while subsequent reverberation was greater for crepe rubber heels than ones of shock-absorbing construction including a high-hysteresis polymer. Modification of heel strike transients by footwear construction offers a way of assessing their relevance to osteoarthritis degeneration and may have implications on prevention and palliation. REFERENCES

GwNHER, R. (1968). tYber Stosserschiitterungen beim Gang des Menschen. Int. Z. angew. Phyuiol. 25, 130-141. HuLL, W. & PERKINS, P. J. (1977). Effect of heel hardness on contact forces during wear. Internal Report 687, Shoe and Allied Trades Research Association, Kettering, Northants.

A proposal regarding the significance of simple mechanical events, such as the development of the choroid fissure, in the organization of central visual projections By S. M. BUNT* and T. J. HORDER. Department of Human Anatomy, South Parks Road, Oxford OXi 3QX Optic fibres reach the tectum in a mirror image of the arrangement in which they originated in the retina. This re-ordering of the fibres' dorso-ventral sequence independently of their naso-temporal relations might seem to require complex guidance, such as could be provided by tectal 'neural specific' cues. However, the necessary reorganization could be achieved as follows. Suppose that, developmentally, the first optic fibres formed are led directly by tissue continuity from their origin dorsally in the optic cup on to the ventral surface of the optic stalk. Later retinal growth is by addition of new ganglion cells peripherally. If the new axons follow the earlier fibres on their vitreous surface, more dorsal retinal fibres will come to lie in more ventral positions in the stalk. Progressive cupping of the *

M.R.C. Scholar.

PHYSIOLOGICAL SOCIETY, JULY 1977 lip optic rudiment occurs due to growth of its lateral wings which, by their downward extension, eventually meet to form definitive ventral retina. Simply by following the most direct route into the stalk and maintaining the relations to already formed fibres that they had at their retinal origins, laterally originating fibres will become disposed around the lateral walls of the stalk with the result that fibres from more and more ventral retina will come to lie increasingly dorsal to the original fibres from dorsal retina. Patterns of organization consistent with these proposals have been seen in the optic nerve of mature goldfish. Fibres of dorsal retinal origin pass progressively down through the centre of the optic nerve as they are traced centripetally while, at the same time, fibres of ventral retinal origin split into nasal and temporal groups which spiral around the lateral borders of the nerve to arrive dorsally. The continued addition of fibres during later retinal growth will have caused distortion in the directness of the paths initially followed by the fibres. Addition of fibres from peripheral retina centrally at the optic nerve head will cause fibres from central ventral retina to be stretched out around the periphery of the nerve as they travel dorsally and eventually descend the vertical meridian to the centre of the nerve. In their train fibres from peripheral ventral retina will arrive in successively more dorsal positions. Throughout this reorganization no fibres have departed from direct contact with the fibres which immediately surrounded them when they originated in the retina - a feature which is indeed rigidly adhered to in the goldfish optic pathway - except that ventrally, nasal and temporal fibres reorganize independently. Thus a complex and integrated pattern of adult organization can result from a simple mechanical event of precisely the kind that occurs in choroid fissure formation. The fissure provides a tissue plane which connects, in the most direct fashion, the sites of the earliest, prospective dorsal, retinal ganglion cells with the ventral wall of the optic stalk where it remains uninvaginated. A significant feature of this proposal is that the entire organization of the retinotectal map is achieved through guidance of each growing fibre by the mechanical constraints provided by the paths of previously formed fibres in neighbouring retina. It then only remains for central nuclei to determine the orientation and extent of the projection. Relatively mirror imaged projections such as may occur in mesencephalic and diencephalic nuclei could be formed by reversal of the process described here or, if the nuclei are back to back on each side of the optic array, as the result of first formed fibres terminating in proximal nuclear tissue and later formed in distal tissue.

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Do fibres from neighbouring retinal ganglion cells maintain their interrelationships throughout the length of the optic nerve in all vertebrate species? By S. M. BUNT and T. J. HORDER. University of Oxford, Department of Human Anatomy, South Parks Road, Oxford, OX1 3QX

Michael Foster's correspondence with Henry Bowdich from July 1877 concerning the founding of the Journal of Physiology.

COMMUNICATIONS Directional Doppler measurements of foetal breathing By J. D. GOUGH and E. R. POORE. Nuffield Institute for Medical Research University of Oxford Foetal breathing in man can be recorded by means of continuous Doppler ultrasound from a transducer applied to the maternal abdomen. The peak velocities of fluid movement sometimes reach values of 1-5 m/sec. We have undertaken experiments in vivo to decide whether this rapid movement is in the lung, as demonstrated in vitro (Boyce, Dawes, Gough & Poore, 1976) or in the great vessels as suggested by observations in man (C. Mantell, personal communication). Records using a 2 MHz directional Doppler ultrasound instrument showed that the audible Doppler-shift frequencies associated with foetal breathing recorded from the maternal abdomen had directional properties. When the position of the foetus in utero was known, the high velocities in phase with foetal breathing were directed cephalad. Foetal lambs near term were delivered supine into a warm saline bath under maternal epidural anaesthesia. If breathing movements were not already present, they were induced by warming or cooling the bath. Audible Doppler-shift frequencies similar to those in man were identified using a 1-8 cm diameter twin-crystal ultrasound transducer operated at 2 MHz, from the lower thorax and upper abdomen to the right of the mid line. Directional analysis showed that high velocities, in phase with inspiratory movements recorded from an oesophageal catheter, were directed cephalad. Similar velocities in phase with breathing movements were recorded from a 1-2 mm diameter single-crystal transducer, mounted on a coaxial cable and operated at 10 MHz to detect flow locally; it was introduced into the inferior vena cava via a femoral or jugular vein. Peak signals, with flow directed cephalad, were recorded from the region of the diaphragm. No comparable signals were observed with an external trans-