G.J. Ter Horst

Ascending projections from the solitary tract nucleus to the hypothalamus. A Phaseolus vulgaris lectin tracing study in the rat

The course of the ascending pathways originating from the anterior gustatory and posterior visceral sensory part of the solitary tract nucleus and the topographic organization of the projections to the hypothalamus in the rat were studied with anterogradely transported Phaseolus vulgaris lectin. In general, the posterior visceral sensory part of the solitary tract nucleus has ascending projections as far as the septum-diagonal band complex and gives rise to heavy input to the bed nucleus of the stria terminals, and to the dorsomedial and paraventricular hypothalamic nuclei. A more moderate projection is aimed at a variety of other hypothalamic nuclei, to the medial and central amygdaloid nuclei and to the paraventricular nucleus of the thalamus. The ventromedial hypothalamic nucleus is strikingly missing an afferent input from the nucleus of the solitary tract. Furthermore, it was shown that whereas the caudal solitary tract nucleus has predominant long ascending connections, the projections from the anterior taste related region of the nucleus of the solitary tract have only limited forebrain projections which do not reach beyond the level of the anterior dorsal hypothalamic nucleus.

The projections of the dorsomedial hypothalamic nucleus in the rat.

The dorsomedial hypothalamic nucleus (DMH) output pathways are revealed by using autoradiographic tracing of tritium labeled Leucine and by the recently introduced Phaseolus vulgaris leuco-agglutinin immunocytochemical method. Terminal labeling appears in the dorsal motor nucleus of the vagus, nucleus ambiguus and in the parvocellular reticular formation at the lower medullary level. Mesencephalic labeling is found in the periaqueductal gray at the level of the oculomotor nucleus. In the hypothalamus labeled terminal boutons are identified in the lateral and ventromedial hypothalamic nuclei but also in the parvocellular paraventricular nucleus. Furthermore, the circumventricular organs are found to receive a dense DMH input, particularly the organum vasculosum of the lamina terminalis and the subfornical organ. These findings are discussed in relation to the dorsomedial nucleus involvement in the control of feeding and pancreatic hormone release. It appears that the DMH participates in this control via descending pathways to the preganglionic pancreas innervating neurons but also via a neuroendocrine route. The latter connection is indicated by terminal labeling in the parvocellular paraventricular nucleus in the area that contains the corticotropin-releasing factor positive cells.

Anatomical demonstration of the suprachiasmatic nucleus-pineal pathway.

A polysynaptic pathway is proposed to transmit light information from the retina through the suprachiasmatic nucleus of the hypothalamus (SCN) to the pineal. In the present study, the powerful transneuronal tracer, pseudorabies virus (PRV), was used to provide a detailed description of this pathway. PRV injected into the pineal subsequently labeled the superior cervical ganglion, the intermediolateral column of the upper thoracic cord, the autonomic division of the paraventricular nucleus of the hypothalamus (PVN), and the SCN. Neurons in the autonomic division of the PVN were the only PRV‐labeled neurons in the hypothalamus shown to receive input from the SCN as demonstrated by the presence of vasoactive intestinal polypeptide axonal contacts. This observation concurred with the presence of ventrally placed neurons in the SCN that could only be observed a day after the appearance of PVN‐labeled neurons. Nevertheless the majority of the neurons were found in the dorsomedial position of the SCN, associated with the vasopressin‐containing population of SCN neurons. Confocal laser scanning microscopy showed double‐labeled neurons containing PRV and vasopressin or PRV and vasoactive intestinal polypeptide. Specificity of tracing was also established by prior removal of the superior cervical ganglion, resulting in a complete absence of the tracer but in the pineal. Thus, the present study provides the anatomical basis for circadian control of melatonin secretion. J. Comp. Neurol. 406:171–182, 1999.

Selective chronic stress-induced in vivo ERK1/2 hyperphosphorylation in medial prefrontocortical dendrites : implications for stress-related cortical pathology?

Stress has been shown to affect brain structural plasticity, promote long‐term changes in multiple neurotransmitter systems and cause neuronal atrophy. However, the mechanisms involved in these stress‐related neural alterations are still poorly understood. Mitogen‐activated protein kinase (MAPK) cascades play a crucial role in the transduction of neurotrophic signal from the cell surface to the nucleus and are implicated in the modulation of synaptic plasticity and neuronal survival. An intriguing possibility is that stress might influence brain plasticity through its effects on selective members of such intracellular signalling cascades responsible for the transduction of neurotrophin signals. Here, we have investigated the effects of stress on the expression of three members of the MAPK/extracellular‐regulated kinase (ERK) pathway such as phospho‐ERK1, phospho‐ERK2 and phospho‐cAMP/calcium‐responsive element‐binding protein (CREB) in the adult rat brain. Male rats were subjected to mild footshocks and the patterns of protein expression were analysed after 21 consecutive days of stress. We found that chronic stress induced a pronounced and persistent ERK1/2 hyperphosphorylation in dendrites of the higher prefrontocortical layers (II and III) and a reduction of phospho‐CREB expression in several cortical and subcortical regions. We hypothesized that defects in ERK signalling regulation combined with a reduced phospho‐CREB activity may be a crucial mechanism by which sustained stress may induce atrophy of selective subpopulations of vulnerable cortical neurons and/or distal dendrites. Thus, ERK‐mediated cortical abnormalities may represent a specific path by which chronic stress affects the functioning of cortical structures and causes selective neural network defects.

Projections from the rostral parvocellular reticular formation to pontine and medullary nuclei in the rat: Involvement in autonomic regulation and orofacial motor control

The efferent connections of the rostral parvocellular reticular formation to pontine and medullary nuclei in the rat were studied with anterogradely transported Phaseolus vulgaris leucoagglutinin. Dense innervations from the rostral parvocellular reticular formation were found in the mesencephalic trigeminal nucleus, the supratrigeminal area, the motor trigeminal nucleus, the motor trigeminal nucleus, the facial, hypoglossal and parabrachial nuclei and specific parts of the caudal parvocellular reticular formation, including nucleus linearis and the dorsal reticular nucleus of the medulla. The raphe nuclei, nucleus of the solitary tract, inferior olive, dorsal principal sensory, spinal trigeminal nuclei and gigantocellular reticular nucleus and the ventral reticular nucleus of the medulla received moderate projections. In general, the projections from the rostral parvocellular reticular formation were bilateral with an ipsilateral dominance. The dorsal motor vagus and the ambiguus nuclei were not labeled. It is concluded that the rostral parvocellular reticular formation participates in regulation of orofacial motor control and in neural networks for limbic control of metabolic homeostasis.

CNS cell groups projecting to the submandibular parasympathetic preganglionic neurons in the rat: a retrograde transneuronal viral cell body labeling study.

The retrograde transneuronal viral tracing method was used to study the CNS nuclei that innervate the parasympathetic preganglionic neurons controlling the submandibular gland in the rat. A genetically engineered beta-galactosidase expressing Bartha strain of pseudorabies virus (PRV) was injected into the submandibular gland of rats. After 4 days, PRV infected tissues were reacted with the Bluo-Gal substrate (halogenated indolyl-beta-D-galactoside) and labeled cell bodies were identified throughout the brain. In the medulla oblongata, cell body labeling was seen in the superior salivatory nucleus, and throughout the medullary reticular formation as well as in the nucleus of the solitary tract, spinal trigeminal nucleus, and deep cerebellar nuclei. In the pons, PRV labeled neurons were found bilaterally in the locus ceruleus, subceruleus region, and parabrachial complex. In the mesencephalon, labeled cells were found in the Edinger-Westphal nucleus, deep mesencephalic nucleus, and central grey matter. Several hypothalamic regions were labeled including the lateral, perifornical and paraventricular hypothalamic nuclei. In the telencephalon, PRV-positive cell bodies were observed in the substantia innominata, bed nucleus of the stria terminalis and central nucleus of the amygdala. The results suggest that widespread areas of the CNS are involved in control of salivation.

Phaseolus vulgaris leuco-agglutinin immunohistochemistry. A comparison between autoradiographic and lectin tracing of neuronal efferents

The autoradiographic pattern of anterograde labeling as a result from injections with tritiated amino acids is compared to the labeling of efferents with Phaseolus vulgaris leuco-agglutinin after lectin injections in the same nucleus visualized by immunohistochemical methods. This comparison is made for efferents from the ventromedial hypothalamic nucleus to the amygdaloid body.

Methylazoxymethanol acetate-induced abnormalities in the entorhinal cortex of the rat; parallels with morphological findings in schizophrenia.

It has been suggested repeatedly that the non-heritable factors in the pathogenesis of schizophrenia involve abnormalities of prenatal neurodevelopment. Furthermore, post-mortem studies show neuropathology of apparently developmental origin in the entorhinal cortex and other brain regions of schizophrenic subjects. In an attempt to model a developmental defect of the entorhinal region in the rat, cerebrocortical proliferation was briefly interrupted during its earliest stages, when the entorhinal area is thought to undergo major cell division. Specifically, the experimental set-up involved the administration of methylazoxymethanol acetate (MAM) on 1 of 4 consecutive days of embryonal development, from E9 to E12. Analysis of the forebrain in adult animals shows reduction of the entorhinal cortex in rats treated on each of these days. This effect shifts from lateral to medial divisions of the entorhinal cortex with later administration of MAM, following a known developmental gradient. Morphological consequences of MAM administration appear to be largely confined to the entorhinal cortex in the groups treated on E9 to E11, although slight reductions of the frontal and occipital neocortex were also observed in these animals. MAM treatment on E12 produces relatively more widespread damage, as reflected among other in a small reduction of brain weight. The described brain abnormalities are not accompanied by obvious phenotypical changes in any, but the E12-treated group. They, moreover, involve cortical thinning, disorganised cortical layering, and abnormal temporal asymmetries. These finding bare some similarity to observations in brains of schizophrenic subjects. The possible relevance of this approach in modeling neurodevelopmental aspects of schizophrenia is discussed.

Neurotransmitters and neuropeptides within the mesencephalic trigeminal nucleus of the rat: An immunohistochemical analysis

In order to determine which neurotransmitters and neuropeptides are utilized by the neurons of the mesencephalic trigeminal nucleus and by the fibres making synaptic contact with these primary sensory cells, we have set up an immunohistochemical study using antibodies against 17 major neurotransmitters and neuropeptides in the rat. Apart from some intracellular immunostaining for glutamate, no immunoreactivity to any of the tested neurotransmitters and neuropeptides could be detected inside mesencephalic nucleus of the trigeminal nerve neurons. Our immunohistochemical observations indicate that mesencephalic nucleus of the trigeminal nerve neurons receive input from various nerve fibres that appear to utilize serotonin, GABA, dopamine, noradrenaline (and likely glutamate) as transmitters. The innervation appeared randomly distributed over all mesencephalic nucleus of the trigeminal nerve neurons. The presence of substance P, cholecystokinin, vasoactive intestinal polypeptide, bombesin/gastrin releasing peptide, [Leu]enkephalin and neuropeptide Y observed in some fibres that contact with mesencephalic nucleus of the trigeminal nerve neurons, presumably reflect the co-existence of these peptides with one of the neurotransmitters.

Trigeminal nociception-induced, cerebral Fos expression in the conscious rat

Little is known about trigeminal nociception-induced cerebral activity and involvement of cerebral structures in pathogenesis of trigeminovascular headaches such as migraine. Neuroimaging has demonstrated cortical, hypothalamic and brainstem activation during the attack and after abolition with sumatriptan. This has led to the conclusion that the dorsal raphe and locus coeruleus may initiate events that generate migraneous headache. Using a conscious rat model of trigeminal nociception and cerebral Fos expression as histochemical markers of neuronal activity, we characterized the pattern of brain activity after noxious trigeminal stimulation with capsaicin (250 and 1000 nm). A significantly increased Fos immunoreactivity was found in the trigeminal nucleus caudalis (layers I and II), the area postrema, the nucleus of the solitary tract, the parvicellular reticular nucleus, the locus coeruleus, the parabrachial nucleus and the raphe nuclei. In addition, the ventrolateral periaqueductal grey, the intralaminar thalamic and various hypothalamic areas, showed an enhanced Fos expression after the intracisternal administration of capsaicin. Other responding areas were the amygdala, the upper lip and forelimb regions of the primary somatosensory cortex, and the insula. Many of these areas participate in (anti)-nociception, although we cannot exclude the possibility that in conscious animals the pain-associated physiological and behavioural responses that are an intrinsic and necessary part of coping with pain have generated the increased Fos expression. Trigeminal stimulation-induced locus coeruleus, dorsal raphe and hypothalamic activation are opposed to a suggested pathogenic role of these nuclei in migraine and cluster headache, respectively.