1. Multiple-barreled microelectrodes were used to record from neurons in the area postrema of anesthetized dogs and to test the responses of the neurons to a variety of substances in this structure, which is known to function as the chemoceptive trigger zone for emesis. 2. The neurons in area postrema were silent at rest but could be "found" by virtue of their response to ionophoretic glutamate. The glutamic response was brief and of short latency with high frequency of discharge. 3. Dog area postrema neurons were also excited by over 20 other substances, including acetylcholine, the biogenic amines, several peptides, and at least two hormones. Not all agents were excitatory, however. 4. The responses to all excitatory agents except glutamate were similar and unusual. All responses showed a relatively long latency (3-20 s), a long duration of excitation (30 s to many minutes), and a low discharge frequency (1-3 Hz). 5. There was a good correlation between substances that were excitatory on area postrema neurons and substances known to cause emesis. Because emesis due to intravenous application of these substances is known to be abolished in animals with ablation of the area postrema, it is very likely that recordings were from the neurons which trigger the response. 6. Because so many substances elicit the same type of response there is a possibility that all utilize a common second messenger. Neurons were not excited by ionophoresis of guanosine 3',5'-cyclic monophosphate (cGMP) but were excited by 8-bromo-adenosine 3',5'-cyclic monophosphate (cAMP) and by forskolin, an activator of adenylate cyclase. 7. Behavioral studies were performed looking for emetic responses in awake dogs following intravenous injection of apomorphine, insulin, angiotensin II, and leucine enkephalin. For each a threshold concentration could be determined, which would consistently evoke emesis. 8. Dogs pretreated with phosphodiesterase inhibitors (theophylline, 3-isobutyl-1-methylxanthine, or RO 1724) showed a shift in the threshold concentration of the above substances that triggered emesis, such that emesis was evoked by lower concentrations than in the control. 9. These results suggest that neurons of the dog area postrema trigger the emetic reflex in response to specific receptors for a great variety of transmitters, peptides, and hormones, and that these receptors act through a common second messenger, cAMP.

Brains fixed in paraformaldehyde or in Clarke's solution were blocked coronaily. Blocks from brains fixed in paraformaldehyde were either frozen in liquid nitrogen or embedded in paraffin. Tissue fixed in Clarke's solution was embedded in paraffin. Sections from each block were stained by the peroxidase-antiperoxidase method for adenosine deaminase or complexing protein using affinity-purified goat antibodies. Adenosine deaminase and complexing protein did not co-localize. Adenosine deaminase was detected in oligodendroglia and in endotheial cells lining blood vessels, whereas complexing protein was concentrated in neurons. The subcellular location and appearance of the peroxidase reaction product associated with individual cells was also quite distinctive. The cell bodies ofadenosine deaminase-positive oligodendroglia were filled with intense deposits ofperoxidase reaction product. In contrast to oligodendroglia, the reaction product as-If the regulatory actions of adenosine depend on binding to cell surface receptors, it seems reasonable that the concentration ofextracellular adenosine should also be subject to regulation. Wu and Phillis (1984) have suggested that uptake and metabolism of

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A study was made to determine the efferent projections of the subthalamic nucleus in the monkey. Because of the impossibility of producing lesions in this nucleus, not involving adjacent structures, lesions were produced by different stereotaxic approaches. Comparisons were made with degeneration resulting from localized lesions in substantia nigra and globus pallidus. Degeneration resulting from these lesions was studied in transverse and sagittal sections stained by the NautaGygax method.Efferent fibers from the subthalamic nucleus pass through the internal capsule into the medial pallidal segment; a few fibers are distributed to the lateral pallidum. Some subthalamic efferent fibers pass to the contralateral globus pallidus via the dorsal supraoptic decussation, but none projection to the thalamus.Nigral efferent fibers project to parts of the ventral anterior (VAmc) and ventral lateral (VLm) thalamic nuclei. The medial pallidal segment gives fibers to: (1) ventral anterior (VA), ventral lateral (VLo) and centromedian (CM) thalamic nuclei, and (2) the pedunculopontine nucleus. The lateral pallidal segment projects exclusively to the subthalamic nucleus. Thalamic projections of the substania nigra and globus pallidus are distinctive. Subthalarnic projections to the globus pallidus are more profuse than those of the substantia nigra.Subthalamic dyskinesia, due to lesions in the subthalamic nucleus, is a consequence of removal of inhibitory influences acting upon the medial segment of the globus pallidus.The following hypothesis is presented:Clinicopathological reports (Martin, '27; Whittier, '47; Juba, '65) and experimental studies (Whittier and Mettler, '49b; Carpenter, Whittier and Mettler, '50; Carpenter, '61) indicate that discrete lesions in the subthalamic nucleus, which fulfill certain criteria, almost invariably results in severe dyskinesia in the contralateral extremities. This dyskinesia, the most forceful and violent variety known, has been referred to as hemiballism or hemichorea. Experimental studies in the monkey (Carpenter, Whittier and Mettler, '50; Carpenter, '61) suggest that this dyskinesia is the physiological expression of removal of inhibitory influences that normally act upon the neurons of the globus pallidus. This thesis is supported by the fact that lesions in the medial segment of the globus pallidus abolish or ameliorate the dyskinesia. Lesions in the ventral lateral nucleus of the thalamus also can reduce or abolish this form AM. J. ANAT., 121: 41-72.of dyskinesia (Martin and McCaul, '59; Andy and Brown, '60) presumably by interruption of pallidothalamic fiber systems and thalamocortical projections.Although a number of studies (Carpenter and Brittin, '58; Carpenter, Correll and Hinman, '60; Strominger and Carpenter, '65; Carpenter, Strominger and Weiss, '65; Stein and Carpenter, '65) have been done to establish structures involved in the neural mechanism of this dyskinesia in the monkey, many questions remain unanswered. A full understanding of the basic neural me...

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The cytology of the superior olivary complex was studied in nissl stained sections of eight human brainstems, including adult, infant and fetus, and in the brains of ten juvenile rhesus monkeys. The most prominent components of the superior olivary complex of primates were specifically investigated, i.e. the medial (SOM) and lateral (SOL) superior olivary nuclei. Cell counts of these segments were done in human brainstems. The adult SOM was comprised of an average of 11,428 (7,850--15,010) perikarya; the SOL contained an average of 3,923 (2,890--5,400) neurons. These findings indicate that the SOL contains as many cells as reported in other primates, and is not reduced. The SOL appears somewhat inconspicuous in the human because it is organized into as many as six clusters of cells rather than forming one well circumscribed configuration as in the monkey and cat. The total cell population of the SOM together with the SOL was approximately the same on each side of individual brains. If one segment was larger on one side than the opposite side, the other segment was correspondingly reduced to maintain the relative symmetry. This suggests that a single mechanism controls the cell complement of at least two segments of the superior olivary complex.

Autoradiographic tracing methods were employed to study the course and distribution of the rubroolivary tract following unilateral injections of tritiated leucine into the rostral red nucleus of seven rhesus monkeys. A topographic organization of projections to the ipsilateral principal nucleus of the inferior olivary complex was demonstrated. Lateral and medial portions of the rostral red nucleus projected to medial parts of the dorsal and ventral laminae of the principal inferior olive respectively; neurons in intermediate lateralities emitted fibers which terminated in lateral parts of the principal olive. Injections involving the oral end of the rostral red nucleus elicited label overlying the medial accessory olive in addition to the principal nucleus. Projections to the medial accessory olive may have arisen from the rostral end of the red nucleus and/or the immediately adjacent tegmentum. There were no projections to the dorsal accessory olive. Fibers of rubral origin also were distributed ipsilaterally to several reticular nuclei including the pedunculopontine, pontis oralis, caudalis, and gigantocellularis.

In a series of seventeen rhesus monkeys attempts were made to produce discrete stereotaxic lesions in the anteroventral cochlear nucleus (Av). Anterograde degeneration was described in detail in four cases with lesions confined within the cochlear complex to Av. Fibers decussating at pontine levels coursed exclusively in the trapezoid body. Degenerated fibers projected: ipsilaterally to the lateral superior olivary nucleus; bilaterally to the preolivary nuclei; to the lateral side of the ipsilateral medial superior olive and the medial side of the contralateral medial superior olive; and to the contralateral medial trapezoid nucleus. A topographic projection upon the medial superior olive was Numerous behavioral and physiological investigations have been concerned with the mechanisms of audition in the cat and monkey. While the auditory system has been subject to many neuroanatomical studies, information about the auditory pathways in primates remains incomplete including the origins, course, and terminations of ascending second order fibers. Lorente de No ('33) using the Golgi method, divided the cat cochlear nuclear complex into 13 subdivisions, and recently Osen ('69b) identified nine regions with Nissl material. The results of a combined morphological and physiological study by Rose, Galambos, and Hughes ('59) indicate that in the cat the cochlear complex is comprised of three major subdivisions : dorsal, posteroventral, and anteroventral nuclei, and that the complete auditory frequency spectrum is represented in each of these subdivisions. Cells located adjacent to the anteroventral nucleus within the fascicles of the cochlear nerve are referred to as the interstitial cochlear nucleus. Although this is one of Lorente de No's 13 regions, evidence suggesting a distinctive nature of this area is lacking, and it may be related J. COMP. NEUR., 143: 217-242.to the anteroventral subdivision. The present study represents an attempt to determine the course and terminations of fibers emanating from the anteroventral cochlear nucleus in rhesus monkey. MATERIALS AND METHODSSeventeen rhesus monkeys weighing approximately 2500 gm each were used in this study. In these animals attempts were made to produce unilateral stereotaxic lesions in the anteroventral cochlear nucleus. Preliminary stereotaxic coordinates were determined using dissections of formalin fixed heads in situ as described by Carpenter and Whittier ('52) and through the use of a stereotaxic atlas (Snider and Lee, '61). Following a suboccipital craniotomy, electrodes were protruded through the cerebellum in the horizontal plane of the stereotaxic instrument at a moderate angle to the axis of the brain stem. Electrodes were angled 15" towards the midline in order to enter the lateral aspect of the anteroventral cochlear nucleus and avoid other