Lateral Pons Research Articles

Neurones in the ventrolateral pons are required for post‐hypoxic frequency decline in rats.

1. The breathing pattern following acute hypoxia (arterial O2 pressure (Pa,O2), 27.4 +/- 7.7 mmHg) was measured in intact, anaesthetized and spontaneously breathing adult rats (n = 4) and in anaesthetized, vagotomized, paralysed and ventilated animals (n = 14). Measurements were made both before and after bilateral lesions or chemical inactivation of neurones in the lateral pons. Respiratory motor activity was recorded as an index of the respiratory cycle. We tested the hypothesis that the ventrolateral pons is required for expression of post-hypoxic frequency decline, defined as a decrease in respiratory frequency below steady-state baseline levels following brief exposures to hypoxia. 2. We identified an area in the ventrolateral pons where brief (1 ms) low current (< or = 20 microA) pulses evoked a short-latency inhibitor of phrenic nerve activity. At this site, bilateral electrical or chemical lesions (n = 3) were performed, or neural activity was inhibited by focal injections of 10 mM muscimol (n = 9). In six control animals, neural activity was inhibited by muscimol injections into the lateral pons, dorsal to the target site. 3. Prior to pontine intervention, respiratory frequency decreased below baseline levels following 20-110 s of 8% O2. The decrease in frequency resulted from a prolongation of expiration (up to 276%), which gradually returned to baseline levels (tau = 45 s). 4. Following lesions or inhibition of neural activity in the ventrolateral pons, baseline inspiratory (TI) and expiratory (TE) durations were altered, albeit minimally, in the animals with intact vagus nerves. Expiratory duration following hypoxia was not different from baseline levels either in vagotomized (P = 0.18) or intact (P > 0.05) animals. In contrast, injections of muscimol at more dorsal sites did not alter the decrease in frequency normally seen following hypoxia. 5. Histological examination revealed that effective lesion or injection sites were within the lateral pontine tegmental field and included portions of the noradrenergic A5 cell group. 6. We conclude that the mechanism responsible for post-hypoxic frequency decline involves an active neural process that depends on the integrity of the ventrolateral pons.

Two types of corticopulvinar terminations: round (type 2) and elongate (type 1).

Corticopulvinar axons were anterogradely labeled by Phaseolus vulgaris-leucoagglutinin injections in the occipitotemporal cortex of the macaque to determine quantitative parameters of divergence and convergence, arbor size and shape, and distribution of terminal specializations. Forty individual axons were analyzed by serial section reconstruction and divided into two major groups. The majority of axons have numerous (typically 500-1,000) small, spinous endings (boutons terminaux). These axons have terminal fields that are beam-like or elongated (E, corresponding to classical type 1) and highly divergent (1.0-3.0 mm). These frequently innervate several of the traditionally designated pulvinar subdivisions; namely inferior pulvinar (PI) and the ventral part of interal pulvinar (PL); medial pulvinar (PM) and dorsal PL, and (one axon) PM, dorsal PL, and PI. Some axons, however (R or round, corresponding to classical type 2), have a small number (typically 70-160) of primarily large, beaded endings (boutons en passant), which concentrate in sharply delimited, round arbors (diameters 100-125 microns). R axons appear to be larger caliber than E axons (1.0-1.5 microns vs. 0.5-1.0 micron, respectively). These differences in phenotype are probably associated with distinct types of projection neurons. In visual areas, corticopulvinar terminations are reported to originate from pyramidal cell subpopulations in layer 5. Indirect evidence, presented here, suggests that the more numerous medium-sized neurons give rise to E axons, and the sparser giant pyramids give rise to R corticopulvinar axons. If this is correct, corticopulvinar connectivity may be involved in multiple transformations. Spatially, axons of giant neurons (with basal dendrites that collect intracortically from a disc-like area, about 1.0 mm in diameter) converge onto a small number of pulvinar neurons. Axons of medium neurons (with basal dendrites that occupy a small intracortical disc, about 0.3 mm in diameter) diverge over 1.0-3.0 mm in the pulvinar and may form many contacts. Giant neurons, although numerically few in relation to medium pyramids (1 or 2: 50?), are likely to have distinctive membrane properties (functionally equivalent to bursting neurons?). Their larger boutons and axon caliber may be associated with a faster transmission that compensates for their small numbers. In primates, the E and R duality does not characterize cortical projections to the caudate, lateral geniculate nucleus, pons, or superior colliculus and thus may be essentially linked to pulvinar-specific processes.

Modulation of a novel RNA in brain neurons by glucocorticoid and mineralocorticoid receptors.

A novel cDNA clone, CR16, was isolated from a rat hippocampal cDNA library and characterized for responses to corticosteroids and regional expression. The 4-kb RNA was increased 3-fold by treatment of adrenalectomized (ADX) rats with corticosterone (CORT). Overlapping cDNA totaling 4,374 nt were used to define an open reading frame of 1,356 nt beginning 191 nt from the 5'-end and encoding a 45-kD protein containing 32% proline. CR16 has no obvious homologies to GenBank or protein databases. CR16 RNA was detected by in situ hybridization in neuron-rich layers of the hippocampal formation, layers II, III and VI of the cerebral cortex, thalamus, ventromedial nucleus of the hypothalamus, bed nucleus of the stria terminalis, lateral septal nucleus, nucleus accumbens, olfactory bulb, inferior colliculus, pons and inferior olive. The CR16 RNA has low prevalence in the hippocampus and cortex (< 10 pg/micrograms total RNA) and is elevated 3-fold in both structures in a dose-dependent manner by CORT in ADX rats. Treatment of ADX rats with aldosterone (ALDO), CORT, or RU28362 increased CR16 RNA to similar levels in the hippocampus while ALDO had minimal effects on the level of CR16 RNA relative to CORT or RU28362 in the cortex. Neither shaking stress (2 h) nor 2 h CORT significantly elevated CR16 RNA in the hippocampus, suggesting that its response to elevated CORT is not rapid. ADX lowered CR16 RNA levels by 50% relative to intact rats while low-level CORT replacement (> or = 4 ng/ml serum CORT) significantly elevated CR16 RNA 2-fold in ADX rats. These results are consistent with both the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) regulating the CR16 gene. This gene will be useful in dissecting the role of MR and GR in CNS neurons.

Fetal chemoreception: a developing story.

The central and peripheral chemoreceptors are critical to the efficient uptake and delivery of oxygen and the removal of carbon dioxide after birth. However, the importance and activity of fetal chemoreception has been questioned, since oxygen uptake and carbon dioxide removal are not regulated in the lungs in the fetus. Early studies suggested that chemotransduction-the conversion of a chemical stimulus to cardiovascular and ventilatory responses via the integration of chemoreceptor stimulation, neural afferent activity and neurohormonal effector mechanisms-was immature in its individual components or their interaction. However, it now appears that the chemoreceptor cascade is structurally and functionally intact in the late-term fetus, and responds actively to normal and other chemical stimuli. The differences between fetal and postnatal chemotransduction appear to be primarily dependent on the central inhibition of the ventilatory response, the inhibitory area being localized to the lateral pons. It appears to be mediated in part by a placental factor which is removed at birth, allowing for the expression of the ventilatory response. The suppression of this response is also responsible for the difference in the heart rate response: the postnatal tachycardia is caused by the lung inflation reflex; when abolished, bradycardia is seen, just as in the fetus. Despite the suppression of the ventilatory component of chemoreception, the fetal carotid chemoreceptor is more important than the aortic, even though it has been considered to be more important to ventilatory than to cardiovascular stability. This review discusses current knowledge of the various components of the mature chemoreceptor cascade, and presents the fetal story within that framework.

Spinal cord and trigeminal projections to the pontine parabrachial region in the rat as demonstrated with Phaseolus vulgaris leucoagglutinin

In order to determine the regions within the parabrachial nucleus that receive synaptic input from nociceptive regions of the spinal cord and medulla in the rat, we analyzed the "Golgi-like" labeling produced by anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L) from discrete iontophoretic injections confined to either the superficial dorsal horn of the lumbar spinal cord or to the superficial dorsal horn of the trigeminal nucleus at the level of the obex. Labeled fibers from both the spinal cord and the medulla ascended through the ventral lateral pons and coursed with the ventral spinocerebellar tract toward the parabrachial nuclei. Spinal cord injections led to labeling of fine caliber fibers and en passant and terminal enlargements in the rostral part of the contralateral lateral parabrachial nucleus (PBL), mostly in the central lateral and dorsal lateral subnuclei. Medullary injections revealed fiber and enlargement labeling primarily in the ipsilateral caudal PBL, mostly in the central lateral, external lateral, and medial subnuclei. Injections in both regions resulted in labeled terminations in the Kölliker-Fuse nucleus. These results indicate that the nociceptive regions of the spinal cord and medulla terminate in regions of the parabrachial nucleus that have been associated with autonomic functions because of their interconnections with the hypothalamus, brainstem cardiovascular and respiratory control centers, and the amygdala.

Peripheral chemoreceptors respond to hypoxia in pontine-lesioned fetal lambs in utero.

Acute hypoxia inhibits, rather than stimulates, fetal breathing movements (FBM), but there has been controversy as to the activity and role of the peripheral arterial chemoreceptors in the regulation of breathing movements in the unanesthetized fetus in utero. However, after midcollicular brain stem transection or lateral pontine lesion, hypoxia causes FBM to become continuous and stimulated in rate and depth. To determine whether this stimulatory response involves peripheral chemoreceptors, we used a two-stage approach to examine the response to hypoxia after peripheral chemodenervation in lateral pontine-lesioned fetal lambs. The lateral pons was lesioned at 119-121 days, and the response to hypoxia was tested in the unanesthetized fetus 4 days afterward. Fourteen fetuses in which hypoxia stimulated FBM underwent either peripheral chemodenervation or sham denervation in a second operation. Hypoxia had no effect when the fetus was tested 4-5 days after peripheral chemodenervation, and the basal incidence of FBM was significantly lower. The stimulatory response was unchanged by sham denervation. We conclude that the peripheral chemoreceptors are active in fetal life and that they mediate the stimulation of FBM seen in response to hypoxia after removal of the lateral pontine inhibition. In addition, after pontine lesion there is evidence of tonic chemoreceptor-mediated influences on FBM, which are normally overriden in the intact fetus.

Evaluation of the Pelorus Stereotactic Surgical System for CT-guided stereotactic brain biopsy.

The Pelorus Stereotactic Surgical System is a relatively new, commercially available device that can be used to perform computed tomography (CT)-guided stereotactic brain biopsy. It has been promoted as being a relatively simple and inexpensive system that is more rapid, less cumbersome, and generally easier to use than conventional stereotactic frames. In this paper, we describe the Pelorus System, and report on its diagnostic accuracy and associated morbidity, based on our experience with 49 consecutive patients in two institutions. Patients ranging from 7 months to 85 years of age had CT-guided stereotactic biopsy, primarily for diagnosis of lesions deep within the cerebral hemispheres. Two transfrontal biopsies of the lateral pons were also done. Satisfactory tissue for histologic diagnosis was obtained in 42 of 49 patients (86%). In this series, there were two deaths in the immediate postoperative period, unrelated to the use of the Pelorus System. One patient suffered a transient neurologic deficit, which resolved over a period of 3 days. Although the Pelorus System has some limitations, we found it easy to use, well-tolerated by patients, and useful for performing CT-guided stereotactic biopsy.

Myelin acquisition in the central nervous system of the mouse revealed by an MBP-Lac Z transgene

Myelin has pronounced effects upon the morphology, function, and growth of axons in the mammalian CNS. Consequently, oligodendrocyte development and myelination have been investigated using a wide variety of histological, immunocytochemical, ultrastructural, and biochemical techniques. While many of the spatial and temporal features of myelin appearance have been characterized, for any one species only limited regions of the CNS have been investigated. To address this limitation, we have derived transgenic mice in which the bacterial Lac Z gene is regulated by promoter elements of the myelin basic protein gene. When differentiating oligodendrocytes begin to elaborate recognizable myelin, they initiate expression of the MBP-Lac Z transgene and accumulate readily detectable levels of beta-galactosidase. Here, we exploit the sensitivity, resolution, and ease of beta-galactosidase histochemical assays to characterize the temporal and spatial patterns of CNS myelination in the mouse. Many features of the myelination program revealed by this approach were predicted by the immunocytochemical and ultrastructural data derived from other species. Nonetheless, previously undocumented patterns were also encountered. beta-Galactosidase was expressed first by oligodendrocytes in the ventral spinal cord, 1 d prior to birth. There, myelination proceeded in a strictly rostral-caudal direction, whereas in the dorsal cord, myelination initiated in the cervical enlargement and proceeded in both rostral and caudal directions. In the cerebellum, deep regions myelinated first, and in the optic nerve, myelination initiated at the retinal end. In contrast, the lateral olfactory tracts, pons, and optic chiasm initiated myelination along their entire course.(ABSTRACT TRUNCATED AT 250 WORDS)

Almitrine mimics hypoxia in fetal sheep with lateral pontine lesions

Almitrine bimesylate is a potent and long-lasting respiratory stimulant in adult species. It acts by stimulating the peripheral chemoreceptors, where it has been shown to accumulate specifically, although its exact mechanism of action is uncertain. In the fetal lamb, however, it produces a profound inhibition of breathing even after denervation of the peripheral chemoreceptors. In this respect its action is similar to hypoxia. To investigate whether almitrine is hypoxia mimetic, we examined the effect of almitrine in nine fetal lambs of 120-130 days gestation. Five had lesions in the lateral pons that changed the fetal depressive response to hypoxia to one of stimulation. In the remaining four fetuses, the lesions did not bilaterally encompass the appropriate area of the pons; thus they still showed the normal fetal depressive response to hypoxia and so acted as controls. Almitrine (10 mg iv) caused a pronounced stimulation of breathing that lasted 406 +/- 26 min in all five fetuses with lesions that caused a stimulatory response to hypoxia. However, in the remaining four fetuses, in which the response to hypoxia was inhibitory, almitrine caused an inhibition of breathing that lasted 184 +/- 28 min. We conclude that the action of almitrine is like that of hypoxia and that, because it acts specifically on the chemoreceptors, it may prove to be a useful tool in the study of possible central chemoreceptor mechanisms.

CEREBELLAR INFARCTION IN THE TERRITORY OF THE ANTERIOR AND INFERIOR CEREBELLAR ARTERY

Clinicopathological reports on infarction in the territory of the anterior inferior cerebellar artery (AICA) are rare. In the present series cerebellar infarcts involved only the AICA territory in 13 cases. They were bilateral in 3 cases. In these pontocerebellar infarcts the middle cerebellar peduncle was the core of the affected territory. It was seldom selectively affected. In a few cases, the infarction extended to the flocculus. Next most frequently involved was a thin band of tissue in the adjacent cerebellar white matter, comprising laterally the neighbouring cerebellar lobules. The largest infarcts extended to the anterior and inferior aspects of the cerebellum. In these cases, the posterior inferior cerebellar artery (PICA) was hypoplastic. In most infarcts, the inferolateral pontine territory was involved, the infarction sometimes extending up to the middle third of the lateral pons and down to the superior part of the lateral medulla. No brainstem compression or tonsillar herniation were observed with infarcts affecting the AICA territory alone. Clinically, involvement of several cranial nerves (facial palsy, multimodal trigeminal sensory impairment, deafness, sometimes with tinnitus, a vestibular syndrome, or lateral gaze palsy) was constant. Cerebellar signs and motor weakness occurred frequently. Contralateral pain and temperature sensory loss was present at times. Horner's syndrome or skew deviation was rare. Study of the arteries showed that arterial occlusion was mainly due to thrombosis superimposed on atheromatous stenosis. In 7 cases, the infarction also involved the PICA territory or the PICA and the superior cerebellar artery territories. These extensive infarcts were often associated with tonsillar herniation and massive paramedian brainstem infarction. The cases in which the territories of the three cerebellar arteries were affected presented in deep coma, together with tetraplegia in some patients. Those in which PICA and AICA territories were involved together presented with similar clinical features as in the cases in which only the AICA territory was involved.

Spontaneous Lateral Pontine Hemorrhage with Associated Trigeminal Nerve Root Hematoma

Abstract Spontaneous hemorrhage into the lateral part of the pons with sequelae compatible with survival has been documented previously. The author describes an unusual case with spontaneous hemorrhage into the lateral pons, with intraneural extension into the right trigeminal nerve root. Radiological features were of an expanding mass of the cerebellopontine angle. The patient was treated surgically with success.

Lateral pontine lesions affect central chemosensitivity in unanesthetized fetal lambs.

The mechanisms underlying the apnea associated with both hypoxia and high-voltage electrocortical activity (HV ECOG) in the fetal lamb are not clearly understood. We have previously shown that lesions in the rostral lateral pons change the depressive response to hypoxia to one of stimulation. We now present evidence that lesions in this area also affect the fetal response to H+/CO2. Lactic acidemia and 5-6% hypercapnia both caused almost continuous breathing throughout both HV and low-voltage (LV) ECOG in seven of eight fetuses with lesions that reversed the depressive response to hypoxia. In five intact control fetuses and seven fetuses with lesions that did not affect the response to hypoxia, neither CO2 nor lactic acidemia induced continuous breathing. We conclude that the lateral pontine area, which is involved in the hypoxic depression of breathing in the fetus, is also involved in the inhibitory mechanisms operating during HV ECOG. Furthermore the inhibition of breathing during HV ECOG appears to be related to a raised threshold for fetal breathing, which is sensitive to H+/CO2.

Projections of the retinorecipient pretectal nuclei in the pigeon (Columba livia).

We have used anterograde autoradiographic and retrograde HRP techniques to investigate the efferent connections of the retinorecipient pretectal nuclei in the pigeon. In the accompanying paper we identified these nuclei in the pigeon as the nucleus lentiformis mesencephali--pars lateralis and pars medialis, the tectal gray, the area pretectalis, and pretectalis diffusus. Although there are reports of a few of the projections of these nuclei, they had not previously been the subject of a detailed study. We found that different cell types in the lentiformis mesencephali, pars medialis and the lentiformis mesencephali, pars lateralis have descending projections to different targets. These targets include the inferior olive, the cerebellum, the lateral pontine nucleus, the nucleus papillioformis, the nucleus of the basal optic root, the nucleus mesencephalicus profundus, pars ventralis, the nucleus principalis precommissuralis, and the stratum cellulare externum. We found that a few cells in the lentiformis mesencephali project to the medial pontine nucleus, but that a much heavier projection arises from the nucleus laminaris precommissuralis, which is medial to the nucleus lentiformis mesencephali, pars medialis. The tectal gray has predominantly ascending projections to the diencephalon. The nuclei that it projects to are the nucleus intercalatus thalami, the nucleus of the ventral supraoptic decussation, the nucleus posteroventralis, the ventral lateral geniculate nucleus, the nucleus dorsolateralis medialis, and the nucleus dorsolateralis anterior. The tectal gray also projects topographically to layers 4 and 8-13 of the optic tectum. Area pretectalis has both ascending and descending projections. It has ipsilateral ascending projections to the nucleus dorsolateralis anterior, pars magnocellularis, the nucleus lateralis anterior, and the nucleus ventrolateralis thalami. It has ipsilateral descending projections to the central gray, the nucleus of the basal optic root, pars dorsalis, the lateral pontine nucleus, and the deep layers of the optic tectum. It has contralateral projections to the area pretectalis, the nucleus Campi Foreli, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the cerebellum, and the Edinger-Westphal nucleus. The efferent projections of pretectalis diffusus are limited. It projects contralaterally to the pretectalis diffusus, and ipsilaterally to the nucleus of the ventral supraoptic decussation, the lateral pons, and the cerebellum.4

Lesions in the upper lateral pons abolish the hypoxic depression of breathing in unanaesthetized fetal lambs in utero.

1. The effects of stereotaxically placed lesions made throughout the mid-brain and upper pons were studied in chronically instrumented fetal lambs from 120 days gestation, after recovery in utero. 2. Isocapnic hypoxia caused an increase in the rate and depth of breathing movements in fetuses in which bilateral lesions encompassed the upper lateral pons in the region of and slightly rostral to the principal sensory and motor nuclei of the trigeminal nerve. 3. Fetal lambs with lesions which did not bilaterally encompass the upper lateral pons showed the normal fetal depressive response to hypoxia. 4. None of the lesions induced permanent continuous breathing as previously described in mid-brain transected fetuses, although periods of continuous breathing lasting several hours were seen at times in some fetuses with lesions in the upper lateral pons. 5. It is concluded that an area in the lateral pons close to areas with well known involvement in respiratory control is involved in the hypoxic depression of breathing in the fetal lamb.

Location of the systems generating REM sleep: Lateral versus medial pons

Location of the systems generating REM sleep: Lateral versus medial pons

Localization of central rhythm generator involved in cortically induced rhythmical masticatory jaw-opening movement in the guinea pig.

The location of the central rhythm generator involved in the cortically induced rhythmical masticatory jaw-opening movement was studied in the ketamine-anesthetized guinea pig. These studies show that a population of neurons is activated by a nonrhythmical input from the cortical masticatory area (CMA) and produces a rhythmical output to the trigeminal motoneurons innervating the jaw-opening muscles. Repetitive stimulation (30 Hz) of the pyramidal tract (PT) rostral to the middle level of the medulla oblongata, in the animal with a precollicular transection as well as with an intact neuraxis, induced a rhythmical reciprocal EMG activity in the anterior digastric and masseter muscles. The rhythmical activity could be monitored by a rhythmical burst in the efferent discharge in the mylohyoid nerve innervating the anterior digastric muscle. Essentially the same pattern was observed when stimulating the PT as that induced by repetitive stimulation of the CMA. The rhythmical efferent burst in the mylohyoid nerve could still be induced after paralyzing the animal. Repetitive PT stimulation in the isolated brain stem after precollicular and bulbospinal transections induced a rhythmical pattern in the anterior digastric EMG and an efferent activity in the mylohyoid nerve. The rhythmical mylohyoid nerve burst could be induced after paralyzing the animal. After section of the medial part of the brain stem at the pontobulbar junction, including the PT, repetitive PT stimulation at the pontine level did not induce any masticatory activity either in the digastric EMG or in the efferent discharge in the mylohyoid nerve, while stimulation at the rostral bulbar level still induced a rhythmicity that was essentially the same pattern as before the section. By testing the effects of total and partial transections of the brain stem in coronal and sagittal planes at various locations, we found that the medial bulbar reticular formation, the lateral pons including the trigeminal motor nucleus and nerve, and the reticulotrigeminal motoneuronal pathways composed the minimum structures that must be left intact to induce a rhythmicity in the anterior digastric EMG and the efferent discharge in the mylohyoid nerve by repetitively stimulating the PT. Repetitive PT stimulation induced a field potential in the medial bulbar reticular formation, which periodically fluctuated in the masticatory rhythm coincident with the rhythmical activity in the digastric EMG. This fluctuation persisted in the same rhythm after paralysis of the animal.(ABSTRACT TRUNCATED AT 400 WORDS)

The squirrel monkey as an experimental model in the study of cerebral organization of emotional vocal utterances.

The different human nonverbal emotional vocal utterances (e.g., laughing, shrieking, moaning) and emotional intonation patterns (e.g., scolding, lamenting, caressing) can be shown to have their acoustic and emotional counterparts in the vocal repertoire of the squirrel monkey. This makes the latter an attractive model for investigations on the neural control of human emotional vocal utterances. Neurophysiological investigations in the squirrel monkey suggest that the cerebral control of emotional vocal utterances is organized hierarchically (Fig. 3). The lowest level - above that of the motor neurons - is represented by the reticular formation of the lateral pons and medulla; here, the motor coordination of laryngeal, respiratory and articulatory movements takes place. The next level is represented by the periaqueductal grey and laterally bordering tegmentum of the caudal midbrain. This area serves to couple specific motivational states to their corresponding vocal expressions. It is a necessary relay station for all vocalization-inducing stimuli. The periaqueductal area receives its input partly from limbic motivation-controlling regions (amygdala, hypothalamus, midline thalamus), partly from sensory pathways (collaterals of spinothalamic tract, fibers from superior and inferior colliculus), and partly from the anterior cingulate cortex. The latter represents the highest level within the system and seems to be responsible for the volitional control of emotional vocal utterances.

The effects of brainstem lesions on vocalization in the squirrel monkey

The present study is an attempt to find out the brain areas involved in the motor coordination of species-specific vocalization. For this purpose, high-frequency coagulations were placed in a systematic manner throughout the brainstem and posterior diencephalon in altogether 43 squirrel monkeys ( Saimiri sciureus). The effect of these lesions on different call types elicited by electrical brain stimulation was studied spectrographically. It was found that bilateral destruction of the ventrolateral, ventroposterior and intralaminar thalamus, periventricular and rostral periaqueductal gray, ventral tegmental area of Tsai, nucl. interpeduncularis, nucl. ruber, anterodorsolateral midbrain tegmentum, superior and inferior colliculi, pontine gray, cerebral peduncles, medial pontine reticular formation, raphe and vestibular nuclei did not affect the acoustic structure of the calls tested. On the other hand, lesions in the ventrolateral midbrain involving the substantia nigra and overlying reticular formation, in the midbrain tegmentum just below the inferior colliculus, in the lateral pons and almost the whole medulla (minimal lesion size: 2.5 mm 3) changed vocalization significantly. It is suggested that the latter areas are more or less directly involved in the motor coordination of vocalization, while the first are not.

Serotonin levels and turnover in different brain areas of isolated aggressive or non-aggressive strains of mice

o 1. After eight weeks of individual housing DBA/2 but not C57 B1/6 (C57) mice showed high levels of aggressive responses in comparison with grouped mice. 2. Social isolation did not modify serotonin (5-HT) levels in either strain of mice, while it produced a decrease of turnover rate in amygdala, lateral hypothalamus and pons in C57 mice and in lateral hypothalamus and pons of DBA mice. 3. When isolated mice of both C57 and DBA strains are compared, no differences in turnover rate in amygdala and pons are evident, while isolated DBA mice show significant lower turnover values in lateral hypothalamus in comparison with isolated C57 mice. 4. A possible suggestion emerging from our results is that aggressive responses exhibited by isolated DBA mice but not by isolated C57 mice may be related to lower 5-HT turnover rate in lateral hypothalamus.

Role for lateral tegmental noradrenergic neurons in the vasopressin response to hypertonic saline

Lesions to the dorsal and ventral noradrenergic pathways were achieved by injecting 6-hydroxydopamine in the periaqueductal midbrain or lateral pons, respectively. Four to 6 weeks after surgery the rats were anaesthetized with pentobarbitone, and hypertonic saline was administered into the peritoneum. Rats with lesions of the ventral noradrenergic pathways showed a significant reduction in the saline-induced rise in plasma vasopressin concentrations, while lesions to the dorsal pathway or control injections were without effect.