Sensory projections to the nucleus basalis prosencephali of the pigeon

Summary The afferent pathways to the nucleus basalis prosencephali of the pigeon were studied by use of the horseradish peroxidase (HRP) technique. It was confirmed that this nucleus receives a direct pathway from the nucleus sensorius principalis nervi trigemini and that, as in the starling, it receives a direct input from the nucleus lemnisci lateralis, pars ventralis, an auditory relay. Totally novel is the finding that the nucleus basalis prosencephali is the target of a direct pathway originating in the medullary nucleus vestibularis superior. All three pathways bypass the thalamus. From within the telencephalon the nucleus basalis prosencephali also receives fibres from the tuberculum olfactorium and the peri-ectostriatal belt, suggestive of olfactory and visual input. Marked cell bodies were also found in the neostriatum frontolaterale. It is assumed that these arose from HRP uptake by axons of the tractus fronto-archistriatalis that course through the nucleus basalis prosencephali to the anterodorsal archistriatum. Marked fibres and bouton-like formations were observed in the latter structure. The afferents to the nucleus basalis prosencephali are discussed in conjunction with the probable role of the nucleus as a sensorimotor coordinator of the pecking/feeding behaviour of the pigeon.     

Identification of penile inputs to the rat gracile nucleus

Neurons in the medullary reticular formation (MRF) of the rat receive a vast array of urogenital inputs. Using select acute and chronic spinal cord lesions to identify the location of the ascending neural circuitries providing either direct or indirect inputs to MRF from the penis, our previous studies demonstrated that the dorsal columns and dorsal half of the lateral funiculus convey low- and high-threshold inputs, respectively. In the present study, the gracile nucleus was targeted as one of the likely sources of low-threshold information from the penis to MRF. Both electrophysiological recordings and neuroanatomical tracing [injection of cholera toxin B subunit (CTB) into a dorsal nerve of the penis] were used. After discrimination of a single neuron responding to penile stimulation, testing for somatovisceral convergence was done (mechanical stimulation of the distal colon and the skin over the entire hindquarters). In 12 rats, a limited number of neurons (43 in total) responded to penile stimulation. Many of these neurons also responded to scrotal stimulation (53.5%, dorsal and/or ventral scrotum) and/or prepuce stimulation (46.5%). Histological reconstruction of the electrode tracks showed that the majority of neurons responding to penile stimulation were located ventrally within the medial one-third of the gracile nucleus surrounding obex. This location corresponded to sparse innervation by CTB-immunoreactive primary afferent terminals. These results indicate that neurons in the gracile nucleus are likely part of the pathway that provides low-threshold penile inputs to MRF, a region known to play an important role in mating processes.     

Subthreshold aortic nerve inputs to neurons in nucleus of the solitary tract

Subthreshold aortic nerve (AN) inputs to neurons receiving a monosynaptic AN-evoked input (MSNs: respond to each of two AN stimuli separated by 5 ms) and neurons receiving a polysynaptic AN input (PSNs) in the nucleus of the solitary tract (NTS) were identified in anesthetized rats. In extracellular recordings from 24 MSNs and 49 PSNs, 12% of MSNs and 29% of PSNs only responded to AN stimulation during the application of excitatory amino acids. In intracellular recordings from 24 MSNs and 22 PSNs, 12% of MSNs and 14% of PSNs responded to AN stimulation with excitatory postsynaptic potentials that did not evoke action potential discharge. Reductions in arterial pressure produced minimal changes in the spontaneous discharge of suprathreshold AN-evoked neurons, suggesting that these neurons receive excitatory inputs from nonbaroreceptor sources. The results suggest that some baroreflex-related NTS neurons exist in a "reserve state and can be changed to an active state or vice versa. This will change the number of neurons involved in baroreflex circuits and provides a novel mechanism for regulating baroreflex function independently of alterations in peripheral afferent input.     

Neuronal activity in the nucleus basalis magnocellularis during performance of an instrumental task

Spike activity of 95 neurons in the rabbit basal forebrain forebrain magnocellular nucleus was recorded during spontaneous behavior and instrumental conditioned performance. Almost half of the neurons (48.4%) displayed a significant (p > 0.05) negative correlation between their spontaneous discharge rate and the power of the delta rhythm in the EEG of the frontal cortex; most of these cells can be classified as projection cholinergic neurons. During instrumental conditioned performance, neurons of this subgroup responded with excitation to the conditioned stimulus, whereas presumably noncholinergic nonprojection neurons responded to the conditioned stimulus with inhibition. Excitatory response of cells in the basal forebrain magnocellular nucleus was significantly more intense as compared to trials without the conditioned reaction. On the whole, our data testify that the basal forebrain magnocellular nucleus maintains the level of arousal and attention required for the instrumental conditioned performance.     

Sensory inputs stimulate progenitor cell proliferation in an adult insect brain

Although most brain neurons are produced during embryonic and early postnatal development, recent studies clearly demonstrated in a wide range of species from invertebrates to humans that new neurons are added to specific brain structures throughout adult life. Hormones, neurotransmitters, and growth factors as well as environmental conditions modulate this neurogenesis. In this study, we address the role of sensory inputs in the regulation of adult neural progenitor cell proliferation in an insect model. In some insect species, adult neurogenesis occurs in the mushroom bodies, the main sensory integrative centers of the brain, receiving multimodal information and often considered as the analog of the vertebrate hippocampus. We recently showed that rearing adult crickets in enriched sensory and social conditions enhanced neuroblast proliferation in the mushroom bodies. Here, by manipulating hormonal levels and affecting olfactory and/or visual inputs, we show that environmental regulation of neurogenesis is in direct response to olfactory and visual stimuli rather than being mediated via hormonal control. Experiments of unilateral sensory deprivation reveal that neuroblast proliferation can be inhibited in one brain hemisphere only. These results, obtained in a relatively simple brain, emphasize the role of sensory inputs on stem cell division.     

The spectral sensitivity of single units in the nucleus rotundus of pigeon, Columba livia

Responses to diffuse monochromatic light were recorded from single units in the diencephalon of pigeon. Units were both excited and inhibited by light stimulation. Intensity-response functions based on latency measures to the first spike after stimulation were used to generate action spectra. One class of spectral sensitivity functions presumably from rods, showed peak sensitivities near 500 nm: these functions were unaffected by changing criterion values used to generate the functions. A second class of cone functions showed multiple peak sensitivities at 540 nm and 600–620 nm. These units shifted their peak sensitivities with a change in criterion values. Unit response types tended to be localized differentially in the nucleus rotundus. Excitatory units were located in the dorsal half of the nucleus, while inhibitory units were located in the ventral half, with a few exceptions. An attempt was made to integrate the present findings with previous behavioral, electrophysiological, photochemical, and anatomical data in the pigeon.     

Auditory centre projection of the lower brainstem to the dorsal cochlear nucleus in the rabbit

Afferent projection to dCN from SOC and the periolivary regions was studied in the rabbit by retrograde transport of WGA-HRP. The projection originates primarily from the bilateral TrV and TrL with a very clear contralateral and ipsilateral predominance, respectively. A clear-cut topographical relationship was disclosed between location of neurons in these nuclei and projection sites in dCN. Thus, the medial region of dCN is target of projection arising from the medial regions of TrV and TrL, whereas the lateral region of dCN is supplied by projection from their lateral regions. Although participation in the projection of the ipsilateral TrV is smaller and the contralateral TrL is very weak, the pattern of these preferential connections is also apparent. Minute connections were traced from the other principal olivary nuclei, i.e. MSO, LSO and TrM, mainly from neurons located in their peripheral regions. In the periolivary region the cells of origin of the projection were found in VLPO and VMPO, and in lesser extent in DPO, DMPO, DLPO, RPO and CPO. The present results are discussed in comparison with those of earlier studies and with reference to other inputs to CN.     

Excitotoxin lesion of nucleus basalis causes a specific decrease in Go mRNA in cerebral cortex. Sensitivity to MK-801

Lesions of the ascending cholinergic pathway from nucleus basalis are known to have profound effects on cortical function. In particular, a substantial potentiation of carbachol-stimulated polyphosphoinositide turnover is detected from 1 day after lesion and is maintained for several days before returning to normal by 1 month. In this study the effect of this lesion was investigated on levels of three G-protein alpha-subunit mRNAs. Excitotoxin lesion of the nucleus basalis caused a selective reduction in the levels of Go alpha mRNA in cerebral cortex ipsilateral to the lesion, Gs alpha and Gi alpha mRNA being unaffected. The maximal effect was obtained at 3 days after lesion where levels of Go alpha mRNA were decreased by 40% compared to sham-operated animals. Levels of Go alpha mRNA returned to normal values by 28 days. Treatment with MK-801 caused a significant attenuation of the decrease in Go alpha mRNA, indicating the involvement of NMDA receptors in this response.     

Pallial origin of basal forebrain cholinergic neurons in the nucleus basalis of Meynert and horizontal limb of the diagonal band nucleus

The majority of the cortical cholinergic innervation implicated in attention and memory originates in the nucleus basalis of Meynert and in the horizontal limb of the diagonal band nucleus of the basal prosencephalon. Functional alterations in this system give rise to neuropsychiatric disorders as well as to the cognitive alterations described in Parkinson and Alzheimer's diseases. Despite the functional importance of these basal forebrain cholinergic neurons very little is known about their origin and development. Previous studies suggest that they originate in the medial ganglionic eminence of the telencephalic subpallium; however, our results identified Tbr1-expressing, reelin-positive neurons migrating from the ventral pallium to the subpallium that differentiate into cholinergic neurons in the basal forebrain nuclei projecting to the cortex. Experiments with Tbr1 knockout mice, which lack ventropallial structures, confirmed the pallial origin of cholinergic neurons in Meynert and horizontal diagonal band nuclei. Also, we demonstrate that Fgf8 signaling in the telencephalic midline attracts these neurons from the pallium to follow a tangential migratory route towards the basal forebrain.     

The behavioral effects of the destruction of the nucleus basalis magnocellularis in the cat forebrain]

Behavioural experiments were carried out on cats by the method modelling complicatedly organized non-automatized behaviour with elements of generalization and abstraction. By the results of fulfillment of test tasks by animals with partial destruction of the macrocellular basal nucleus the conclusion is made on the participation of this formation in the structural-functional ensuring of complex integrative forms of activity-thinking and learning. The suggested mechanism of drawing of the basal nucleus in gnostic and cognitive processes in the non-specific ensuring of the system of structures directly participated in thinking and learning.     

Roles of oxytocin in spatial learning and memory in the nucleus basalis of Meynert in rats

The present study was performed to explore the role of oxytocin (OT) in spatial learning and memory in the nucleus basalis of Meynert (NBM) of rats. The latency, distance and swimming path to find the platform were tested by Morris water maze and recorded by a video camera connected to a computer. Intra-NBM injections of 2 or 10 nmol of OT, but not 0.2 nmol of OT, induced significant increase on the latency of spatial learning. Rats receiving intra-NBM administrations of 2 or 10 nmol of OT showed a more random search pattern. There were no significant changes in the swimming speed in Morris water maze test after the injection of OT. Furthermore, the impaired effect of OT on the latency of spatial learning was blocked by intra-NBM injection of the selective OT antagonist Atosiban, indicating that the effect of OT was mediated by OT receptor in the NBM of rats. Moreover, there were no influences of OT or Atosiban on the retention performance in rats. The results suggest that OT plays an inhibitory role in spatial learning in the NBM; the effect is mediated by OT receptor.     

大鼠中脑、内脏和躯体传入在旁巨细胞外侧核神经元的聚合

用细胞外记录的方法观察大鼠巨细胞旁外侧核（ＰＧＬ）对刺激中脑导水管周围背侧部（ｄＰＡＧ）及腹外侧部（ｖＰＡＧ）、腓深神经（ＤＰＮ）、正中神经（ＭＮ）和内脏大神经（ＧＳＰＬ）的反应。这些神经元不仅对某一处刺激部位起反应,而且倾向于对其它任一刺激部位也起反应。８９％（７３／８２）的神经元接受两处或两处以上来源的汇聚投射。６０％（２１／３５）的神经元由于具有压力敏感性,并且其下行投射到脊髓的轴突具有慢的     

Pharmacological evaluation of GABAergic and glutamatergic inputs to the nucleus basalis--cortical and the septal-hippocampal cholinergic projections

The presence of different receptor populations within a given brain area can be effectively evaluated via the local injections of defined receptor agonists and antagonists. Using this approach, it has become evident that the nucleus basalis - cortical cholinergic pathway possesses an inhibitory GABAergic input to the nucleus basalis from the nucleus accumbens as well as a positive glutamatergic feedback from the cortex. The septal-hippocampal cholinergic pathway also possesses an inhibitory GABAergic regulation which consists of a large GABAergic interneuron population in the septum. A glutamatergic feedback from the hippocampus is also present. These regulatory inputs to cholinergic cells are not tonically active but appear to function as phasic modulators of cholinergic transmission in both pathways.