Jerome Sutin

The Periventricular Stratum of the Hypothalamus

Publisher Summary This chapter discusses the anatomical studies and neurophysiological studies of the periventricular stratum (PVS) of the hypothalamus. The periventricular stratum consists of small neuronal cell bodies in a matrix of fine axonal processes and the bulk of the experimental evidence indicates that the posterior division of the PVS is not associated with a readily definable function or functions. Stimulation of the PVS shows participation of the anterior division in several types of response, and the posterior division in some, but only for pupillary dilatation is there a continuous zone along the entire extent of the PVS, and virtually all the hypothalamus is involved. Correlation of the locations from which autonomic or somatic responses are evoked with hypothalamic structure offers insight to the functions of the PVS. The lesion studies, together with anatomical studies, strongly support the argument that the posterior PVS is afferent to the medial hypothalamus. The organization of the anterior PVS is less certain.

Slow-wave activity in the ventral tegmental area of Tsai related to barbiturate anesthesia

Abstract Rhythmic 6 to 8 per second high-voltage activity has been observed in a restricted region of the mesencephalon under barbiturate anesthesia. This region is situated ventral to the red nucleus and encompasses the ventral tegmental area of Tsai. This phenomenon is not seen in conscious animals, in normal sleep, or under nonbarbiturate sedation, and bears no apparent relationship to cortical spindling. Stimulation of the rostromedial portion of the globus pallidus blocks or disrupts the rhythmic activity. Evoked responses in the same tegmental area are seen following stimulation of the thalamic ventralis anterior nucleus and the immediately subadjacent dorsal hypothalamus. Repetitive stimulation of ventralis anterior at 3 to 8 per second drives the tegmental rhythm at the stimulus frequency. These observations suggest a relationship between the globus pallidus, ventralis anterior, and the ventral tegmental area of Tsai.

Septal projections to the dorsomedial thalamic nucleus in the cat

Abstract 1. 1. Stimulation of the septal region situated dorsal to the anterior commissure evoked responses in the medial portion of the thalamic dorsomedial nucleus. Evoked responses were usually seen to turn over in polarity in the region of the vertical center of the dorsomedial nucleus. 2. 2. Stimulation of the medial and lateral preoptic region and nucleus of the diagonal band of Broca ventral to the anterior commissure failed to evoke dorsomedial responses. It was from this region that degenerating fibers have been traced to the dorsomedial nucleus by other investigators. 3. 3. Previously placed lesions in the preoptic region blocked septo-dorsomedial evoked responses. As discussed in the text, this observation together with other studies, suggests that a synaptic relay in the septo-dorsomedial pathway may occur in the region ventral to the anterior commissure. 4. 4. Criteria for the identification of the source of evoked potentials are discussed.

POSTERIOR THALAMIC AND SEPTAL INFLUENCE UPON PALLIDAL AND AMYGDALOID SLOW-WAVE AND UNITARY ACTIVITY.

Abstract Stimulation of the magnocellular medial geniculate nucleus evoked slow-wave responses in the globus pallidus, amygdala, temporal cortex, and ventromedial nucleus of the hypothalamus. The stimulation discharged units after a 3 to 9-msec latency in the globus pallidus and after 12 to 23-msec latency in the basal nuclei of the amygdala. Pallidal units that fired both spontaneously and upon stimulation of the nucleus were facilitated by 100 per sec stimulation, while similarly characterized units in the amygdala were inhibited. Spontaneously active amygdaloid cells responded to auditory stimulation with a decrease in firing rate, while a nasal air puff caused an increased firing rate. Units affected by sensory stimulation were not confined to any particular amygdaloid nucleus.

Ascending pathways from an osmotically sensitive region of the medulla oblongata

Abstract Ascending projections from the region of the area postrema of the cat have been investigated by the evoked potential technique. A postremal region is defined which includes the area postrema, nucleus intercalatus, and the solitary and dorsal motor vagal nuclei. Evidence is presented that an ascending pathway links the postremal region with a region bordering the central gray matter of the midbrain. This projection ascends in the medial reticular formation in the vicinity of the tectospinal tract. Responses resulting from stimulation of the postremal region may be distinguished from those following direct stimulation of the medial longitudinal fasciculus and medial reticular formation by their latencies and by the distribution of the sites from which they may be evoked and recorded. The results are discussed with respect to the report of osmotically evoked responses recorded in the region of the area postrema.

Trigeminal and pretectal influences upon slow-wave activity of the ventral tegmental area in the cat.

Abstract The influence of the posterior brain stem on the 6 to 10 per sec slow-wave rhythm of the ventral tegmental area of Tsai (VTA) associated with barbiturate anesthesia in cats was investigated. The VTA slow-wave activity was augmented by stimulation (6–10/sec) of the descending trigeminal tract or trigeminal ganglion. Augmentation of the VTA rhythm was also observed during stimulation of the inferior alveolar nerve, the supraorbital nerve and the greater occipital nerve, but not the infraorbital nerve. Lesions in the caudal part of the descending tract of the trigeminal nerve, in the medial forebrain bundle, the lateral habenular nucleus, or brain-stem transection at a rostral pontine level had no effect upon the VTA rhythm. Lesions in the pretectal region or centrum-medianum-parafascicular nucleus complex markedly diminished or abolished the rhythm.

Effect of lesions of the medulla oblongata on electrolyte and water metabolism in the rat

Abstract Lesions in the region of the obex of the medulla oblongata destroying the area postrema and solitary nucleus result in a marked elevation of the urinary Na + K+ excretion ratio during the 24-hour period following placement of the lesion. Potassium retention appears responsible for the increase of the Na+ K+ ratio from a preoperative average of 0.52 ± 0.04 (S.E.) to a first postoperative day average of 0.92 ± 0.13 (S.E.). Animals with control lesions more laterally in the medulla oblongata did not show an elevated urinary Na+ K+ ratio.

DIFFERENTIAL EFFECTS OF NOREPINEPHRINE ON RESPONSES EVOKED IN THE HYPOTHALAMIC VENTROMEDIAL NUCLEUS.

Abstract The injection of 20–55 μg norepinephrine directly into the hypothalamic ventromedial nucleus (HVM) or the ipsilateral carotid artery increased the amplitude of the HVM response to septal stimulation and suppressed the HVM response to amygdaloid stimulatio.. Similar results were obtained with comparable concentrations of epinephrine. d -Amphetamine produced a suppression of both septal-HVM and amygdaloid-HVM responses. Local injection of 0.85 per cent saline, pitressin or sodium nitrite did not alter the HVM evoked responses.

SUSTAINED RESPONSE OF THE DIFFUSE THALAMIC PROJECTION SYSTEM.

Summary When certain intralaminar thalamic nuclei are stimulated at intensities slightly above threshold for the cortical recruiting response, a response of similar wave form, latency and cortical distribution maintains a sustained amplitude between epochs of recruitment. This sustained response differs from the recruiting response in its reaction to reticular activating system stimulation and barbiturate anesthesia.

BRAIN STEM PATHWAYS MODIFYING ACTIVITY IN THE TUBERAL REGION OF THE HYPOTHALAMUS

1. Two ascending pathways are described which influence responses evoked in the hypothalamic ventromedial nucleus by septal and amygdaloid stimulation.