Spread of excitation from the ventromedial hypothalamus to the limbic-reticular structure of the brain

The sequence of origination of the evoked potentials in different regions of the septum amygdale and the reticular formation in response to the gradually increasing stimulation of the hypothalamic ventromedial nucleus was studied. As demonstrated, excitation that initially occurs in the hypothalamic ventromedial nuclei embraced first the structures of the septum and rostral reticular formation and then more caudal region of the reticular formation and amygdala.     

The destruction of perikaryas of the mesencephalic reticular formation and the posterior hypothalamus does not cause major disorders of awakening in the cat

Ibotenic acid microinjections have been realized at the level of the mesencephalic reticular formation and the posterior hypothalamus in 7 cats. This technique has led to a quasi-total destruction of cell bodies in the two areas (including the histaminergic neurons). 2 to 3 days after such lesions, there were no major effects on behavioral waking. These results do not favor the hypothesis of the existence of a waking system at the level of the mesencephalic reticular formation and/or posterior hypothalamus.     

Distribution of somatostatinlike immunoreactivity in the brain of the little brown bat (Myotis lucifugus)

The distribution of somatostatinlike immunoreactive (SLI) perikarya, axons, and terminals was mapped in subcortical areas of the brain of the little brown bat, Myotis lucifugus, using light microscopic immunocytochemistry. A preponderance of immunoreactivity was localized in reticular, limbic, and hypothalamic areas including: 1) in the forebrain: the bed nucleus of the stria terminalis; lateral preoptic, dorsal, anterior, lateral and posterior hypothalamic areas; amygdaloid, periventricular, arcuate, supraoptic, suprachiasmatic, ventromedial, dorsomedial, paraventricular, lateral and medial mammillary, and lateral septal nuclei; the nucleus of the diagonal band of Broca and nucleus accumbens septi; 2) in the midbrain: the periaqueductal gray, interpeduncular, dorsal and ventral tegmental, pretectal, and Edinger-Westphal nuclei; and 3) in the hindbrain: the superior central and parabrachial nuclei, nucleus incertus, locus coeruleus, and nucleus reticularis gigantocellularis. Other areas containing SLI included the striatum (caudate nucleus and putamen), zona incerta, infundibulum, supramammillary and premammillary nuclei, medial and dorsal lateral geniculate nuclei, entopeduncular nucleus, lateral habenular nucleus, central medial thalamic nucleus, central tegmental field, linear and dorsal raphe nuclei, nucleus of Darkschewitsch, superior and inferior colliculi, nucleus ruber, substantia nigra, mesencephalic nucleus of V, inferior olivary nucleus, inferior central nucleus, nucleus prepositus, and deep cerebellar nuclei. While these results were similar in some respects to those previously reported in rodents, they also provided interesting contrasts.     

Steroids as Potential Modulators of Thyroid Hormone Activity in Anuran Metamorphosis

SYNOPSIS. Anuran metamorphosis is controlled by the complexinteraction of several hormones. Although thyroid hormone isthe major stimulatory hormone in metamorphosis and likely regulatesall of the metamorphic genes directly, other hormones are involvedin regulating thyroid hormone secretion and activity. Corticoids(in particular corticosterone) and the sex steroids (especially17ß estradiol) all potentially regulate thyroid hormoneactivity both by affecting hypothalamic and pituitary controlof thyroid hormone secretion and by interacting with thyroidhormones peripherally. Although there is likely a role for endogenouscorticoids in anuran metamorphosis, the role for endogenousestrogens remains to be shown. The role of these "modulators"must be fully understood, if our understanding of hormonal controlof metamorphosis is to be complete.     

Bilateral brainstem connections of the rat supratrigeminal region

Efferent and afferent connections of the supratrigeminal region were studied in the rat using iontophoretically delivered horseradish peroxidase and Phaseolus vulgaris leuco-agglutinin. Projections of supratrigeminal efferents were found to the contralateral supratrigeminal region, to the ipsi- and contralateral trigeminal motor nuclei and the medullary reticular formation, and to the ipsilateral facial and hypoglossal motor nuclei. Neurons projecting to the supratrigeminal region were located in the contralateral supratrigeminal nucleus, in the ipsilateral mesencephalic trigeminal nucleus and bilaterally in the medullary reticular formation. This organization is discussed with respect to bilateral oral motor control mechanisms.     

Effect of arginine-vasopressin on the rat thyroid gland in vitro

The response of the rat thyroid gland to arginine-vasopressin in vitro was studied to clear a possibility of a direct regulation of this gland by hypothalamic nonapeptide neurohormones. The function of the thyroid gland was estimated by thyrocyte height and quantity of the autoradiographs on a thyrocyte. AVP makes more active hormone synthesis in thyrocytes after 30 min of incubation and it stimulates both synthesis and secretion of the thyroid hormones in 2 hours of incubation. The higher concentrations of AVP activate the thyroid hormone synthesis but not the secretion.     

Afferent projections to the mesencephalic locomotor region of the cat brain

Afferent projections to the functionally identified mesencephalic locomotor region were investigated in cats using the horseradish peroxidase retrograde axonal transport technique. Sources of afferent projections to this region were discovered in different structures of the fore-, mid-, and hindbrain. Numbers of horseradish peroxidase-labeled neurons were calculated in different brain structures after injecting this enzyme into the mesencephalic locomotor region. Apart from the endopeduncular nucleus, different hypothalamic structures, and the substantia nigra, labeled neurons were discovered in the central tegmental region, the central gray, raphe and vestibular nuclei, the solitary tract nucleus, and the brain stem reticular formation. Neurons accumulating horseradish peroxidase were also discovered in nuclei where ascending sensory tracts originate. This fact serves to bring out the structural inhomogeneity of the midbrain locomotor region; electrical stimulation of this area is an effect which may be attributed to excitation of neurons found within it and activation of accompanying fiber tracts.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 763–773, November–December, 1986.     

The effect of electric stimulation of different regions of the cerebral cortex on the alimentary reaction in rabbits]

The influences of different parts of the neocortex on the rabbit alimentary behaviour produced by stimulation of the hypothalamic "alimentary centre" were studied in chronic experiments on rabbits with electrodes implanted in different formations of the limbic system and the midbrain. It has been found that electrical stimulation of the frontal and anterior parietal cortical areas raised the threshold of the evoked alimentary reaction. Inhibitory influences of the frontal areas proved to be stronger and more prolonged than those of the anterior parietal area. Electrical stimulation of the posterior parietal and occipital cortical areas decreased the threshold of the evoked alimentary reaction. Coagulation of the dorsal hippocampus eliminated the inhibitory influences of the neocortex, while coagulation of the mesencephalic reticular formation discontinued the facilitating influences of the neocortex on the alimentary reaction.     

Role of sensory signals in the development of cortical influences on hypothalamic structures]

Neuron discharges of the hypothalamic ventro-medial and posterior nuclei were registered in immobilized cats during electrical stimulation of the ipsi- and contralateral nerves of the brachial plexus, the 1st and the 2nd somatosensory regions (SI and SII) and the visual regions of the cortex and the reticular formation (RF) of the mesencephalon. A reversible cold block of the SI and SII failed to change the effect of the nerve stimulation. Stimulation of the postero-ventral thalamic nucleus did not change the initial activity of the hypothalamic neurons and gave rise to no neuron activity that appeared on stimulation of the SII. A conclusion was drawn that cortico-hypothalamic influences that appeared on stimulation of the nerves and the postero-ventral nucleus of the thalamus were pronounced weakly.     

Function of the superior colliculi of the corpora quadrigemina during creation of a local focus of increased excitability in the mesencephalic reticular formation and sensomotor cortex

In chronic experiments on waking rabbits, the foci of heightened excitability in the sensorimotor cortex and mesencephalic reticular formation affected in a similar way the background neuronal activity in the superior colliculi and that evoked by light stimuli. The effect was manifested in elimination of inhibitory pauses in the neuronal response to light stimulus and in a general increase of discharge frequency. Similarity of the cortical and reticular influences is due to their possible mediation by the same collicular interneurones participating in inhibitory pauses formation in the process of backward inhibition. Increased neuronal activity in the superior colliculi under the action of local foci in the sensorimotor cortex and mesencephalic reticular formation correlated with appearance of forelimb motor reaction to isolated light stimulus testifying to a formation of a functional connection between the visual and motor analyzers. Possible role of the superior colliculi in this process and their participation in the formation of a visually controlled reaction is discussed.     

Effects of thyroid hormone deficiency and replacement on rat hypothalamic growth hormone (GH)-releasing hormone gene expression in vivo are mediated by GH

The role of thyroid hormone and GH in the regulation of hypothalamic GH-releasing hormone (GRH) gene expression in the rat was examined after the induction of thyroid hormone deficiency by thyroidectomy. Thyroidectomy resulted in a time-dependent decrease in hypothalamic GRH content, which was significant by 2 weeks postoperatively, and a reduction in pituitary GH content to 1% of the control level by 4 weeks. In contrast, GRH secretion by incubated hypothalami under both basal and K(+)-stimulated conditions was increased after thyroidectomy. Hypothalamic GRH mRNA levels also exhibited a time-dependent increase, which was significant at 1 week and maximal by 2 weeks after thyroidectomy. Administration of antirat GH serum to thyroidectomized rats resulted in a further increase in GRH mRNA levels. T4 treatment of thyroidectomized rats for 5 days, which also partially restored pituitary GH content, lowered the elevated GRH mRNA levels. However, comparable effects on GRH mRNA levels were observed by rat GH treatment alone. These results suggest that the changes in hypothalamic GRH gene expression after thyroidectomy in the rat are due to the GH deficiency caused by thyroidectomy, rather than a direct effect of thyroid hormone on the hypothalamus, since the changes were reversible by GH alone despite persistent thyroid hormone deficiency. In addition, they further support the role of GH as a physiological negative feedback regulator of GRH gene expression.     

Changes of sex hormone-binding globulin/SHBG expression in the hypothalamo-hypophyseal system of rats during pregnancy, parturition and lactation.

Sex hormone-binding globulin (SHBG) is expressed in hypothalamic magnocellular neurons. High co-localization rates of SHBG with oxytocin have been observed in the hypothalamus, indicating that SHBG plays a role in pregnancy, parturition and lactation. Further studies have shown that hypothalamic SHBG expression is malleable to changing steroid conditions. In this study, we have examined SHBG levels in the supraoptic and paraventricular hypothalamic nuclei and in the posterior pituitary lobe of late pregnant, parturient and early lactating rats by IN SITU hybridization, immunocytochemistry, and ELISA. Immunocytochemical and biochemical analysis showed that the SHBG levels increased during late pregnancy in hypothalamic nuclei. During parturition, SHBG levels fell in the magnocellular nuclei but increased in the posterior pituitary lobe. SHBG levels increase again during lactation. At day six of lactation, there was no significant difference in SHBG levels compared to normal cycling female rats, which served as control in this study. IN SITU hybridization showed increased SHBG mRNA signal during late pregnancy. The highest SHBG expression was observed during parturition. Our data indicate that hypothalamic SHBG expression changes during pregnancy, parturition and lactation, parallel to ovarian steroid and co-localized OT levels. This may in part be linked to known steroid actions on synthesis and secretion of magnocellular hypothalamic peptide hormones, important for the control of parturition and lactation.     

The effect of thyroid hormone and glucocorticoids on carp growth hormone-releasing factor (GRF)-induced growth hormone (GH) release in rainbow trout (Oncorhynchus mykiss).

1. The effect of thyroid hormone and glucocorticoids on carp growth hormone-releasing factor (GRF)-induced growth hormone (GH) secretion was studied on rainbow trout using a dispersed pituitary cell culture system. 2. A combined administration of lower doses (0.01 microM) of 3,5,3'-triiodo-L-thyronine (T3) and dexamethasone (Dex) significantly increased spontaneous as well as carp GRF-induced GH release. 3. Lower doses of Dex alone had no effect, and T3 had a marginal effect on GH release. Higher doses of either Dex or T3 potentially reduced GH release. 4. This study indicates an important role of thyroid hormone and/or glucocorticoids in the hypothalamic regulation of GH secretion in fish.     

Afferent connections to the abducent nucleus in the cat.

The afferent connections to the abducent nucleus in the cat were studied by means of retrograde transport of WGA-HRP after implantations of the tracer in crystalline form. Retrogradely labelled cells were found bilaterally in the medial and descending vestibular nuclei, mainly in their ventral and medial portions, in the rostral part of the ipsilateral gigantocellular reticular nucleus, in the medial part of the contralateral caudal pontine reticular nucleus and bilaterally in the oculomotor nucleus, mainly in its dorsolateral division. Some labelled cells were also found bilaterally in the mesencephalic reticular formation, the periaqueductal grey and the nucleus of the trapezoid body.     

Nature of the distribution of synapses in the neurons of the reticular formation and some afferent nuclei]

Under study was the morphology of synaptic terminations of the brain reticular formation in cats and dogs as well as that of the afferent nuclei of the cat's posterior columns. The neurons of the Goll's and Burdach's nuclei have a richly ramified dendritic network. In this connection the main mass of synapses is disposed on the dendrites and their different branchings. The dendrites of the multipolar cells of the reticular formation have the main type of branching, but the cells are distributed from the nerve cell body at a considerable distance (up to 50 mu and more). The synapses are observed at the total length of the dendrite, so the axo-dendritic contacts quantitatively prevail over axo-somatic ones. The morphological data are compared with physiological axo-somatic and axo-dendritic concepts of the role of synapses in conducting the nerve impulse.     

Brainstem pathways of the initiation of locomotion

Conclusion This overview of the brainstem pathways of the initiation of locomotion can be summarized as follows. There are locomotor regions (hypothalamic and mesencephalic) whose stimulation leads to the appearance of rhythmic stepping movements. These regions are nonuniform in composition: transient fibers as well as cells are found. The locomotor effects of electrical stimulation of these regions can largely be explained on the basis of the presence of efferent projections of the neurons to the medial reticular formation, as well as the activation of the transient fibers of other brain systems. The ventromedial parts of the reticular formation of the medulla oblongata, including areas of the macrocellular and (to a lesser extent) gigantocellular nuclei, form the final element in the suprasegmental system of locomotion initiation. The inconclusive data of different scientists who have used chemical microinjections into the locomotor regions make it impossible at present to specify precisely the neurochemical mechanisms underlying the initiation of locomotion. NMDA has been found to play an important role. The activation of the reticular formation during the triggering of stepping movements can take place either from the locomotor regions or by means of signals coming from the collaterals of the ascending sensory tracts. The wide spectrum of possible pathways of the initiation of locomotion apparently affords the organism a choice of ways by which to realize this process and is an important factor in its adaptation to its environment.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 488–505, July–August, 1991.     

Gamma-aminobutyric acid-immunoreactive neurons in the rat trigeminal nuclei

The distribution of GABAergic neurons in the rat trigeminal nuclei was studied using a highly specific monoclonal antibody (mAb3A12) to gamma-aminobutyric acid (GABA). Immunopositive cells were relatively abundant in the marginal and gelatinosa beds of the caudal part of the trigeminal spinal tract nucleus, and in the dorsomedial areas of the oral subnucleus and the principal nucleus. A high density of GABA-immunoreactive somata was also found in the rostral part of the oral subnucleus and in the adjacent parvicellular reticular formation as well as in the supratrigeminal and intertrigeminal regions. Thus, the distribution of the GABAergic cells showed a relatively high density in areas related to the convergence of sensory stimuli, and in zones that contain interneurons inhibiting masticatory motorneurons. The results suggest, therefore, that GABA might play an important role both in discriminative sensory processing and in reflex modulation of the orofacial region.Abbreviations RF reticular formation - FRp parvicellular reticular formation - Vc trigeminal nucleus of the spinal tract, subnucleus caudalis - Vmes mesencephalic nucleus - Vmo trigeminal motor nucleus - Vo trigeminal nucleus of the spinal tract, subnucleus oralis - Vp principal trigeminal nucleus - Vsp spinal trigeminal nucleus - Vsup supratrigeminal nucleus     

Connections linking the mamillary complex and hypothalamo-tegmental area of the brain with the brainstem in lizards

Connections between the hypothalamus and brainstem formations were investigated inOphisaurus apodus by locally injecting horseradish peroxidase (HP) or lectin-HP into the mamillary complex and the hypothalamo-tegmental area of the brain. Direct reciprocal connections were found linking mamillary complex nuclei and posterior and lateral hypothalamic structures with the following brainstem formations: central gray matter, parabrachial nucleus, raphe nuclei and the lateral loop, reticular formation of the caudal mesencephalon, pons, and medulla. It was concluded that direct bilateral hypothalamo-brainstem connections were already in place in reptiles, serving as the basis for sympatho-emotional nociceptive, and antinociceptive response.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 114–123, January–February, 1990.     

Neurophysiological analysis of the development of endocrine and hypertensive reactions in long-term emotional stress

A study was made of the effect of chronic emotional stress on the formation of hypertension in animals. This was shown to be related to dynamic changes in the function of the CNS, particularly in the hypothalamic apparatus of the neuroendocrine control. The above changes played a role in the formation of hypertensive vascular reactions accompanied by a high hormonal secretion of the adrenal cortex and thyroid. During stabilization of high arterial blood pressure at the late stages of the "after-effect", the hormonal secretion returns to normal.     

Localization of alcohol and aldehyde dehydrogenases in the human spinal cord and brain

Location of aldehyde dehydrogenase (AldDG) and alcohol dehydrogenase (ADG) has been studied in 38 nuclei of the human brain. Neurons with a high AldDG activity predominate in the nucleus of the descending root of the trigeminal nerve, motor nuclei of the craniocerebral nerves (trigeminal, facial, abducent, blocking, sublingual, supraspinal), motor nuclei of the anterior horns of the spinal cord, lateral vestibular nucleus, posterior nucleus of the vagus nerve, pedunculopontine nucleus, superior salivary nucleus, and in the nucleus of Westphal-Edinger-Jacobovich. Neurons with a moderate AldDG activity predominate in the superior olivary complex, nucleus of the lateral loop, parabrachial (pigmented) mesencephalic nucleus and reticular lateral nucleus. A low enzymatic activity is specific for neurons of the pons proper, inferior vestibular nucleus, trapezoid body of the inferior olivary complex, dentate nucleus of the cerebellum, reticular nucleus of the tegmen of Bekhterev's pons and posterior nucleus of Gudden's suture. A high ADG activity is revealed in piriform neurons of the cerebellar cortex. Functional importance of ADG and AldDG activity in the brain is discussed.