Ultrastructure and electrical activity of the rat neurohypophysis.

Ultrastructural and electrophysiological studies of the rat neurohypophysis was carried out following stimulation to cause vasopressin release. Unit activity was investigated with microelectrodes, filtered, integrated, and recorded simultaneously with blood pressure in a polygraph. The basal unit activity was challenged by perfusing the hypothalamus and pituitary gland with hypertonic, hypotonic, and isotonic solutions through the internal carotid and by bleeding. Posterior lobes were fixed in osmium tetroxide and stained with uranyl acetate for electron microscopy. Single unit activity from the neural lobe showed mostly a continuous pattern of activity with a rate of discharge (RD) of 7 to 30 pulses per 10 s during control periods. Following hypertonic stimulation, out of 20 units studied, 35% increased, 10% decreased, and 55% did not change their RD. The effect of bleeding was studied in 34 units. Following the withdrawal of 1 ml of blood from the jugular vein, 29% increased, 32% decreased, and 38% did not change their RD. It is concluded that the existence in the neurohypophysis of fibers which are excited or inhibited by stimuli known to cause vasopressin release supports the hypothesis of the existence of a modulatory mechanism for neuropeptide release in the neural lobe.

Brainstem cells of origin of the cervical vagus and cardiopulmonary nerves in the neonatal pig (Sus scrofa).

The distribution of the cells of origin of the cervical vagus and cardiopulmonary nerves has been studied in neonatal piglets (Sus scrofa) ranging in age from 1 to 60 days. Cardiopulmonary nerves were identified physiologically and anatomically prior to injection of horseradish peroxidase (HRP) into the nerves. Following injection of HRP into the cervical vagus nerve retrogradely labeled neurons were present in the dorsal motor nucleus of the vagus nerve (DMV), the nucleus of the solitary tract, the nucleus ambiguus (NA), ventrolateral to the NA and in an intermediate zone between the DMV and the NA. Two unique clusters of neurons were also retrogradely labeled after injections into the vagus nerve. One group was located lateral to the most caudal levels of the DMV and extended as far caudally as the C1 spinal segment. The second distinctive group was located ventrolateral to the nucleus ambiguus in a cell column identified as the ventrolateral nucleus ambiguus (VLNA). After injections of HRP into cardiopulmonary nerves, the majority of neurons were found in the VLNA and the distinct clusters of neurons in this cell column were particularly heavily labeled. Small numbers of cells were labeled in the DMV and NA and none were labeled in the solitary nucleus after cardiopulmonary nerve injections. There were no apparent age-related differences in the degree or distribution of retrograde labeling. The distribution of neurons in the medulla oblongata projecting into cardiopulmonary nerves in the piglet is similar to that described in other species, i.e., the nucleus ambiguus, particularly its ventrolateral cell column, is the primary site of cardiomotor neurons. In addition, in the piglet there is a morphologically distinct cluster of cells related to the heart, and possibly the lungs, which does not appear to be present in other species.