Electrophysiology of reflexes in an isolated brainstem-spinal cord preparation of the newborn rat

An electrophysiological study was made with a brainstem-spinal cord preparation isolated from the newborn rat. In this preparation, depolarizing responses were elicited in various cranial and spinal nerves by stimulating the trigeminal or other cranial nerves. Responses were abolished by perfusion with low-Ca” medium, suggesting that synaptic transmission in the brainstem is involved in these responses. The depolarizing response of the glossopharyngeal nerve evoked by electrical stimulation of the trigeminal nerve was depressed by [D-Ala“]-Met-enkephalinamide, somatostatin or norepinephrine. In this preparation, a spontaneous periodic activity at a frequency of 5-15 cycles/min was also recorded from the phrenic nerve. Both the reflexes and the spontaneous activity could be recorded stably for several hours. The present preparation will be useful for electrophysiological, pharmacological, and biochemical studies on the mammalian central nervous system (CNS). It is generally diflicult to isolate a major part of the mammalian central nervous system (CNS) with its physiological activity unimpaired. A main reason is that mammalian central nervous tissues consume much more oxygen than do other tissues (7). To overcome this difliculty, Otsuka and Konishi used the spinal cord isolated from the newborn rat (8). In their preparation, the electrical activity can be maintained in vitro for many hours, because 1) the metabolism of neonatal central nervous tissues is more anaerobic as compared with adult tissues (1, 5, 11); and 2) the size of the spinal cord of the newborn rat is so small that the supply of oxygen by diffusion from the perfusion medium is sufficient to maintain the activity of the nervous tissues. In the present report, we describe a brainstem-spinal cord preparation from the newborn rat in which various reflex responses could be recorded for more than 7 h. 1Present address: Department of Physiology, Faculty of Medicine, Tokyo Medical and Dental University, Yushima, Bunkyoku, Tokyo 113, Japan The brain and the spinal cord were quickly isolated from 0-4-day-old Wistar rats under ether anaesthesia. The cerebrum was removed by transection at the supraor intercollicular level, and the cerebellum was removed. The preparation was placed in a 0.5-2 ml bath and perfused at a rate of 5-10 ml/min with artificial cerebrospinal fluid (9) containing 30 mM glucose, or modified Krebs solution (NaCl 123 mM, KCI 5.0 mM, KHZPO4 1.23 mM, CaCl2 2.4 mM, MgSO4 1.3 mM, NaHCO3 26 mM, and glucose 30 mM). The glucose concentration of these solutions was higher than that in the conventional Krebs solution or the artificial cerebrospinal fluid used for the spinal cord preparation (9). The supply of glucose tends to be insufficient in the brainstem because of its larger size than that of the spinal cord, therefore the higher concentration of glucose was used to improve the viability of the preparation. Solutions containing a similar concentration of glucose are often used for culture of CNS neurons (10). Solutions were equilibrated with 95% O; and 5% CO2, and the temperature of