Postnatal development of thalamic reticular nucleus projections to the anterior thalamic nuclei in rats

The thalamic reticular nucleus (TRN) projects inhibitory signals to the thalamus, thereby controlling thalamocortical connections. Few studies have examined the development of TRN projections to the anterior thalamic nuclei with regard to axon course and the axon terminal distributions. In the present study, we used parvalbumin (PV) immunostaining to investigate inhibitory projections from the TRN to the thalamus in postnatal (P) 2- to 5-week-old rats (P14–35). The distribution of PV-positive (+) nerve fibers and nerve terminals markedly differed among the anterior thalamic nuclei at P14. Small, beaded nerve terminals were more distributed throughout the anterodorsal nucleus (AD) than in the anteroventral nucleus (AV) and anteromedial nucleus (AM). PV+ fibers traveling from the TRN to the AD were observed in the AV and AM. Nodular nerve terminals, spindle or en passant terminals, were identified on the axons passing through the AV and AM. At P21, axon bundles traveling without nodular terminals were observed, and nerve terminals were distributed throughout the AV and AM similar to the AD. At P28 and P35, the nerve terminals were evenly distributed throughout each nucleus. In addition, DiI tracer injections into the retrosplenial cortex revealed retrogradely-labeled projection neurons in the 3 nuclei at P14. At P14, the AD received abundant projections from the TRN and then projected to the retrosplenial cortex. The AV and AM seem to receive projections with distinct nodular nerve terminals from the TRN and project to the retrosplenial cortex. The projections from TRN to the AV and AM with nodular nerve terminals at P14 are probably developmental-period specific. In comparison, the TRN projections to the AD at P14 might be related to the development of spatial navigation as part of the head orientation system.Key words: Thalamic reticular nucleus, parvalbumin, axon terminal, development, anterior thalamic nucleus, rat     

Unit responses in area 5b of the suprasylvian gyrus to stimulation of the ventral posterolateral thalamic nucleus

Unanesthetized cats were immobilized with D-tubocurarine. Single unit responses in area 5b of the suprasylvian gyrus to stimulation of the ventral posterolateral thalamic nucleus were recorded extracellularly. Of the total number of neurons tested, 32% were excited and 3% inhibited. In 65% of neurons the responses were mixed, most of them being predominantly excitatory. Repetitive stimulation of the ventral posterolateral nucleus (6–9/sec) frequently intensified the excitatory component of the responses. Sometimes inhibition, present in the response to a single stimulus, was replaced by increased excitation. However, the same response as to a single stimulus frequently appeared in response to each consecutive stimulus of a series. Stimulation of the ventral posterolateral nucleus had a mainly excitatory effect on neurons in area 5b. Stimulation of the dorsal lateral nucleus, on the other hand, inhibited their activity. This antagonism could also be observed on the same neuron. It was concluded from the short latent periods of the orthodromic responses (3–6 msec) and from the antidromic responses of the cortical neurons to stimulation of the ventral posterolateral nucleus that this nucleus has direct two-way connections with the cortex of area 5b.     

Proposed pathways for vocal self-stimulation: Met-enkephalinergic projections linking the mibrain vocal nucleus,auditory-responsive thalamic vocal nucleus,auditory-responsive thalamic regions and neurosecretory hypothalamus

In this study, we have investigated the neuroanatomical pathways that may underlie the influence of a female bird's vocal behavior upon her own reproductive endocrine response. We traced the ascending efferent projections of the midbrain vocal control nucleus, the intercollicularis (ICo), using an anterograde tracer, PHAL, delivered by iontophoretic application. We found labelled terminal fields in the anterior regions of the hypothalamus that contained luteinizing hormone releasing hormone- (LHRH) immunoreactive neurons. We injected into the LHRH-rich anterior medial hypothalamus (AM) the retrograde tracer, fluorogold, to verify the results of PHAL anterograde tracing and exmine whether retrogradely labelled neurons in the ICo can be stained with met-enkephalin antiserum by the immunohistochemical method. Of the retrogradely labelled neurons in the medial division of ICo (mICo), between 5% and 15% were found to be met-enkephalin-immunoreactive positive perikarya. Our data suggest that axonal projections into the anterior medial hypothalamus may arise in part from enkephalin-immunoreactive neurons in the medial ICo. The mICo neurons distributed along the medial border of the midbrain auditory nucleus give rise to projections into the posterior medial hypothalamus (PMH) via synapses within the shell region of thalamic auditory nucleus, ovoidalis (Ov). We conclude that in the ring dove, the medial division of the vocal control nucleus, by virtue of its connection with the auditory thalamus and neurosecretory hypothalamus, is in a position to exert influence on endocrine response partly through enkephalinergic systems. Implications of similar connections in other species are discussed. 1994 John Wiley & Sons, Inc.     

Synaptic changes in the feline association cortex (area 5b) following lesion of the thalamic posterolateral nucleus

Numbers of intact and degenerating axonal terminals (AT) were determined in area 5b of the cat association cortex two, four, and 30 days after electrolytic destruction of the posterolateral thalamic nucleus (PL). The proportion of degenerating AT in area 5b two and four days after PL lesion was found to be 7.4 and 7.3%, respectively. Intact AT in the same field accounted for 83.6% of the total in intact animals four days after PL lesion. A 16.4% reduction occurred, consisting of AT with round vesicles and asymmetrical synaptic contacts (i.e., primarily excitatory AT); 40% of the damaged AT formed synapses on dendrites and 60% on spines. It follows that neurons of cortical association area 5b receive direct excitatory and mainly axonospinal afferents from the thalamic PL. Degenerating AT accounted for 4.6% 30 days after PL lesion, as compared with a decline of 31.2% and a rise of 7.0% in axospinal and axodendritic AT, respectively. No change occurred in axosomatic AT. The total number of AT had declined by 10.0%. Aspects of reinnervation of area 5b neurons following degeneration of the neuronal synapses induced by PL lesion are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 661–667, September–October, 1989.     

Dorsal thalamic connections of the ventral lateral geniculate nucleus of rats

In order to understand better the organisation of the ventral lateral geniculate nucleus of the ventral thalamus, this paper has examined the patterns of connections that this nucleus has with various nuclei of the dorsal thalamus in rats. Injections of biotinylated dextran or cholera toxin subunit B were made into the parafascicular, central lateral, posterior thalamic, medial dorsal, lateral dorsal, lateral posterior, dorsal lateral geniculate, anterior, ventral lateral, ventrobasal and medial geniculate nuclei of Sprague-Dawley rats and their brains were processed using standard tracer detection methods. Three general patterns of ventral lateral geniculate connectivity were seen. First, the parafascicular, central lateral, medial dorsal, posterior thalamic and lateral dorsal nuclei had heavy connections with the parvocellular (internal) lamina of the ventral lateral geniculate nucleus. This geniculate lamina has been shown previously to receive heavy inputs from many functionally diverse brainstem nuclei. Second, the visually related dorsal lateral geniculate and lateral posterior nuclei had heavy connections with the magnocellular (external) lamina of the ventral lateral geniculate nucleus. This geniculate lamina has been shown by previous studies to receive heavy inputs from the visual cortex and the retina. Finally, the anterior, ventral lateral, ventrobasal and medial geniculate nuclei had very sparse, if any, connections with the ventral lateral geniculate nucleus. Overall, our results strengthen the notion that one can package the ventral lateral geniculate nucleus into distinct visual (magnocellular) and non-visual (parvocellular) components.     

Ultrastructural characteristics of the reticular thalamic nucleus neurons in WAG/Rij rats

The aim of this study was to investigate the ultrastructure of the reticular thalamic nucleus (RTN) in rats of WAG/Rij strain, an established model for human absence epilepsy. Most RTN neurons are medium-to large-sized and have either dark or light appearance, depending on their functional state. Moreover, small-sized neurons with short axons are present, their characteristics being described for the first time.     

Nonolfactory afferent telencephalic projections in frogs

The degree of modal specificity of neurons of the tectum, dorsal thalamus, and primordial hippocampus relative to visual (photic) and somatic (tactile) stimulation was investigated in experiments on frogs (Rana temporaria) immobilized with tubocurarine. The specificity of sensory information arriving at the successive levels of the frog's thalamo-telencephalic afferent system diminishes in an ascending direction. Evoked potentials arising in the telencephalon in response to electrical stimulation of the sciatic nerve and to flashes are found not only in the primordial hippocampus, but also bilaterally in the septum and striatum. It is concluded on the basis of discharges recorded in the fibers of the thalamo-telencephalic tracts during somatic and visual stimulation that fibers carrying nonolfactory information into the telencephalon run in the medial and lateral forebrain bundles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. International Brain Research Laboratory, Kotor, Yugoslavia. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 537–544, September–October, 1973.     

Morphological and physiological evidence of a synaptic connection between the lateral parabrachial nucleus and neurons in the A7 catecholamine cell group in rats

Background

The descending noradrenergic (NAergic) system is one of the important endogenous analgesia systems. It has been suggested that noxious stimuli could activate descending NAergic system; nevertheless, the underlying neuronal circuit remains unclear. As NAergic neurons in the A7 catecholamine cell group (A7) are a part of the descending NAergic system and the lateral parabrachial nucleus (LPB) is an important brainstem structure that relays ascending nociceptive signal, we aimed to test whether LPB neurons have direct synaptic contact with NAergic A7 neurons.

Results

Stereotaxic injections of an anterograde tracer, biotinylated dextran-amine (BDA), were administered to LPB in rats. The BDA-labeled axonal terminals that have physical contacts with tyrosine hydroxylase-positive (presumed noadrenergic) neurons were identified in A7. Consistent with these morphological observations, the excitatory synaptic currents (EPSCs) were readily evoked in NAergic A7 neurons by extracellular stimulation of LPB. The EPSCs evoked by LPB stimulation were blocked by CNQX, a non-NMDA receptor blocker, and AP5, a selective NMDA receptor blocker, showing that LPB-A7 synaptic transmission is glutamatergic. Moreover, the amplitude of LPB-A7 EPSCs was significantly attenuated by DAMGO, a selective μ-opioid receptor agonist, which was associated with an increase in paired-pulse ratio.

Conclusions

Taken together, the above results showed direct synaptic connections between LPB and A7 catecholamine cell group, the function of which is subject to presynaptic modulation by μ-opioid receptors.     

Acquisition of an olfactory learning-set in rats with lesions of the mediodorsal thalamic nucleus

Rats with lesions of the mediodorsal thalamic nucleus had goodretention of a preoperatively leamed odor detection task butmade more errors than controls in the acquisition of a seriesof two-odor discrimination problems. While controls showed rapidacquisition of a learning-set, the performance of experimentalrats was highly variable. Deficits in acquisition occurred ondifferent problem for different rats and appeared unrelatedto problem difficulty or serial position of the discrimination.Experimental rats also had a significant deficit in the acquisitionof an odor reversal task. Error scores in both the learing-setand reversal task were related to lesion size. Small lesionsconfined to the rostral third of the nucleus or asymmetricallesions which spared the central (olfactory) division of mediodorsalnucleus on one side were without effect. The results suggestthat the deficit in olfactory learning produced by destructionof the mediodorsal thalamic nucleus is complex and is not adequatelyaccounted for by stimulus novelty, problem difficulty or bypoor interproblem transfer of learning.     

后连合核及其形态学和电生理学研究进展

后连合核位于腰骶尾髓的脊髓灰质后连合 ,含丰富的神经活性物质 ,并表达多种神经递质受体 ,与中枢及外周联系广泛 ,在功能上与内脏感觉的中继、内脏和躯体初级传入信息的整合、镇痛及内脏反射活动等密切相关。一些内源性物质可能通过对兴奋性及抑制性神经递质的作用 ,参与对后连合核信息传递的调控。本文对后连合核及其形态学和电生理学研究进展作一综述