Levels of nerve growth factor and its mRNA in the central nervous system of the rat correlate with cholinergic innervation.

The levels of nerve growth factor (NGF) and its mRNA in the rat central nervous system were determined by two-site enzyme immunoassay and quantitative Northern blots, respectively. Relatively high NGF levels (0.4-1.4 ng NGF/g wet weight) were found both in the regions innervated by the magnocellular cholinergic neurons of the basal forebrain (hippocampus, olfactory bulb, neocortex) and in the regions containing the cell bodies of these neurons (septum, nucleus of the diagonal band of Broca, nucleus basalis of Meynert). Comparatively low, but significant NGF levels (0.07-0.21 ng NGF/g wet weight) were found in various other brain regions. mRNANGF was found in the hippocampus and cortex but not in the septum. This suggests that magnocellular cholinergic neurons of the basal forebrain are supplied with NGF via retrograde axonal transport from their fields of innervation. These results, taken together with those of previous studies showing that these neurons are responsive to NGF, support the concept that NGF acts as trophic factor for magnocellular cholinergic neurons.     

Differential co-expression of AMPA receptor subunits in substance P receptor-containing neurons of basal forebrain regions of C57/BL mice

We are interested in cellular co-expression patterns of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptor subunits 1-4 (GluR1-4) in substance P receptor (SPR)-containing neurons of the basal forebrain, which may act as a morphological basis for interaction between neurokinins and glutamate-driven neuronal signaling and excitotoxicity. Immunohistochemistry and laser scanning confocal microscopy in adult C57/BL mice revealed that distribution of SPR-positive neurons overlapped with that of GluR1-4-containing ones in most basal forebrain regions, i.e. the medial septal nucleus, nucleus of diagonal band of Broca, magnocellular preoptic nucleus and substantia innominata. Neurons showing both SPR and GluR1-4-immunoreactivities were found in above cholinergic neurons-rich containing basal forebrain regions. Semi-quantification analysis indicated that about 57-95% of SPR-positive neurons displayed GluR1-4-immunoreactivity. The percentages of AMPA receptor subunits co-localizing in SPR-positive neurons were GluR4 (48%), GluR1 (47%), GluR2 (26%) and GluR3 (20%), respectively. However, the neurons co-expressing SPR and GluR1-4 were hardly detected in the basal nucleus of Meynert of the basal forebrain. The co-localization of SPR and AMPA receptors has provided a molecular basis for functional interaction between neurokinins and AMPA receptors-mediated signaling in basal forebrain neurons. This study has also implied that glutamate-driven neuronal transmission and excitotoxicity can be modulated by neurokinin peptides in most basal forebrain regions but not in the basal nucleus of Meynert, suggesting that neurokinins or SP may play certain roles in determining neuronal functional properties or excitotoxic susceptibility in the various basal forebrain regions of mammals.     

Activity of neurons in the pedunculopontine nucleus during defensive instrumental conditioning

The activity of 109 neurons in the compact and diffuse parts of the pedunculopontine tegmental nucleus (PPTg) was recorded in freely moving rabbits during the acquisition and actualization of the defensive instrumental conditioned reflex. It was found that 47% of the recorded neurons responded to a conditioned stimulus (CS). This finding suggests the involvement of the PPTg in the instrumental conditioning. A significant prevalence of the excitatory conditioned responses to the CS suggests the predominantly activating influence of the PPTg on its projection structures during conditioning. The neuronal responses to the CS were classified into several basic patterns reflecting stimulus effects, the structure of the behavioral act, and the nature of the reinforcement. They indicated the involvement of the PPTg in attention, motor learning, and reinforcement. A significant decrease in the reactivity of the CS of the PPTg neurons as a result of learning specialization was shown. The revealed differences in the associative and reactive properties (with respect to CS) between the neurons of the compact and diffuse PPTg parts testify to the functional heterogeneity of this structure and suggest the leading role of the cholinergic compact part of the PPTg in the instrumental defensive conditioning. Thus, the obtained evidence suggests the involvement of the PPTg in the mechanisms of attention and acquisition of the active defensive motor conditioning.     

Effects of acetylcholine and cholinergic transmission blockers on neuronal spike activity in the cat motor cortex associated with conditioned reflex

The effects of direct application of acetylcholine (ACh) and m- and n-cholinoreceptor blockers on test cells were investigated in waking cats having developed instrumental lever-pressing conditioned reflex. Changes were recorded in both spontaneous and invoked firing activity in a functionally homogeneous group of motor cortex cells, in which increased discharge rate usually preceded the start of conditioned reflex movements. It was found, however, that ACh increased spontaneous activity considerably in some of the neurons tested and reduced it moderately in others. Atropine sharply reduced background activity in cortical neurons while preserving spike response to presentation of a conditioned stimulus and n-cholino-blockers such as hexonium and (occasionally) tubocurarine inhibited spike response produced by conditioned stimuli; background activity was slightly inhibited by hexonium and reinforced by tubocurarine. It was concluded that ACh put out by cholinergic fibers helps to maintain background firing activity level in cortical neurons under naturally occurring conditions, acting via m-cholinoreceptors, whereas factors influencing generation of spike discharges associated with performance of conditioned reflex movements are mediated by n-cholinoreceptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 579–589, September–October, 1989.     

Activity of neurons in the pedunculopontine nucleus in conditioned instrumental appetitive reflex

Activity of 91 neurons in the compact and diffuse parts of the pedunculopontine tegmental nucleus (PPTg) was recorded in freely moving rabbits during execution of instrumental appetitive conditioning. Of the recorded neurons, 37.4% changed their activity in response to a conditioned stimulus, which is the evidence for the PPTg involvement in instrumental conditioning. Excitatory conditioned neuronal responses to the conditioned stimulus and food reinforcement significantly prevailed over inhibitory reactions. Neuronal responses to the conditioned stimulus were classified in several basic patterns reflecting stimulus effects, structure of the behavioral act, and reinforcement properties. These reactions indicate the involvement of the PPTg in attention, motor learning, and reinforcement. The revealed differences in associative reactive properties of the compact and diffuse parts of the PPTg to the conditioned stimulus and reinforcement point to the functional heterogeneity of this structure and suggest the leading role of the cholinergic part of the PPTg in instrumental appetitive conditioning and reinforcement as well as the essential contribution of the diffuse part into classical appetitive conditioning.     

Acetylcholinesterase in central vocal control nuclei of the zebra finch (<Emphasis Type="Italic">Taeniopygia guttata</Emphasis>)

The distribution of acetylcholinesterase (AChE) in the central vocal control nuclei of the zebra finch was studied using enzyme histochemistry. AChE fibres and cells are intensely labelled in the forebrain nucleus area X, strongly labelled in high vocal centre (HVC) perikarya, and moderately to lightly labelled in the somata and neuropil of vocal control nuclei robust nucleus of arcopallium (RA), medial magnocellular nucleus of the anterior nidopallium (MMAN) and lateral magnocellular nucleus of the anterior nidopallium (LMAN). The identified sites of cholinergic and/or cholinoceptive neurons are similar to the cholinergic presence in vocal control regions of other songbirds such as the song sparrow, starling and another genus of the zebra finch (Poephila guttata), and to a certain extent in parallel vocal control regions in vocalizing birds such as the budgerigar. AChE presence in the vocal control system suggests innervation by either afferent projecting cholinergic systems and/or local circuit cholinergic neurons. Co-occurrence with choline acetyltransferase (ChAT) indicates efferent cholinergic projections. The cholinergic presence in parts of the zebra finch vocal control system, such as the area X, that is also intricately wired with parts of the basal ganglia, the descending fibre tracts and brain stem nuclei could underlie this circuitry’s involvement in sensory processing and motor control of song.     

Configuration of the magnocellular nuclei in the basal forebrain of the human adult

With the use of gapless series of thick sections (800 microns) stained for lipofuscin pigment as a stable intraneuronal characteristic, it was found in the human brain that the three magnocellular nuclei in the basal forebrain-the medial septal nucleus, the nucleus of the diagonal band (vertical and horizontal limb) and the basal nucleus of Meynert located within the substantia innominata-were tightly connected with each other. A band-like anteromedial subnucleus and a semilunar posterolateral subnucleus could be delineated in the basal nucleus and were found to be embedded in a zone of low cell density, the substantia innominata, which medially blends into the horizontal limb of the diagonal band nucleus. A three-dimensional reconstruction was made to demonstrate the complex shape of the magnocellular basal forebrain nuclei.     

Tonotopic organization and functional characterization of the auditory thalamus in a songbird,the European starling

1. The diencephalic auditory nucleus of the European starling, the nucleus ovoidalis, shows rostrocaudal and dorsoventral diameters of 500-800 microns and a mediolateral diameter of 800-1000 microns. This small and sharply delimited nucleus is composed of densely packed neurons. 2. Its tonotopic organization consists of evenly spaced isofrequency contours, with best frequencies decreasing ventrally. The frequency range was found to be 150 Hz to 7030 Hz. 3. Apart from tonotopic organization, other characteristics of single units demonstrate the uniformity of the neuronal population. Units have high spontaneous activities (mean 61 pps; Fig. 4a), and show mainly stimulus correlated tonic discharge patterns. In most cases, excitatory frequency bands are enclosed by inhibitory frequency bands. 4. Single units were tested, applying various stimulus classes differing in time structure (BPN, sine, FM up, FM down, SFM, SAM) but sharing a common frequency band. All neurons tested responded to all classes. Evaluation of stimulus class preference, however, revealed that BPN and SFM caused the strongest responses, whereas FM and SAM were less effective. 5. Comparison of the single unit responses in the ovoid nucleus with those known for avian auditory forebrain and midbrain centres strongly suggests a relay function for the diencephalic nucleus.     

大鼠基底前脑NGF-R及CHAT免疫反应阳性神经元的分布:免疫双标法

本文用免疫组化双标法观察了神经生长因子受体(NGF-R)及胆碱乙酰转移酶(ChAT)免疫反应阳性神经元在成鼠基底前脑内的分布,结果发现嗅结节、隔内侧核、斜角带核、腹侧苍白球及基底大细胞核均有NGF-R及ChAT免疫反应阳性神经元.免疫组化双标染色发现,大部分免疫反应阳性神经元的NGF-R与ChAT共存,部分神经元呈单纯NGF-R或ChAT阳性,但这种NGF-R和ChAT的共存情况在不同区域不完全相同.在隔内侧核和斜角带核,大多数的NGF-R阳性神经元和ChAT阳性神经元共存,但在腹侧仓白球和基底大细胞核,两者共存的神经元较前两区为少.此外ChAT阳性神经元在尾壳核中分布较均匀,而NGF-R阳性神经元较少见.研究结果表明,大多数胆碱能神经元有NGF-R,提示NGF对胆碱能神经元的保护和激活作用,部分可能是通过直接与NGF受体的结合而发生作用.     

Effects of estrogens on cholinergic neurons in the rat basal nucleus

Estrogen replacement in postmenopausal women may help prevent or delay development of Alzheimer's disease. Because loss of basal forebrain cholinergic neurons with reductions in choline acetyltransferase (ChAT) concentration are associated with Alzheimer's disease, we investigated the effect of estradiol (E(2)) and J 861, a non-feminizing estrogen, on cholinergic neurons in the basal forebrain. Ovariectomized rats received E(2), J 861 or vehicle, and basal forebrain sections through the substantia innominata, medial septum, and nucleus of the diagonal band were immunostained for ChAT. ChAT-immunoreactive cells in the basal forebrain were significantly reduced in the ovariectomized rats compared to intact rats, but those ovariectomized rats receiving estrogen replacement with E(2) and J 861 had near normal levels of ChAT-positive neurons. While retrograde tracing experiments with fluorogold injected into the prefrontal cortex showed no significant differences in the number of fluorogold-labeled cells among the groups, ChAT-immunoreactive cells and double-labeled cells were significantly lower in OVX rats than in intact and E(2) rats. Some substantia innominata cells in the J 861 rats were ChAT/estrogen receptor alpha-positive. These results suggest that E(2) and J 861 have positive effects on cholinergic neurons that project from the basal nucleus to the forebrain cortex.     

The reactions of the cat motor cortex neurons to electrical stimulation of the base of the forebrain as a conditioned signal for the reflex of placing the forelimb on a support]

Electrical stimulation of the globus pallidus (500 ms, 300 Hz) in the area restricted by the stereotaxic coordinates AP 14-AP 16, L5-L8 at the level of the anterior commissura (HO) evoked food reactions in the form of mouth opening, chewing, and licking in the absence of food. There were no visible motor effects in the case of electrical stimulation of the subcommissural area (H-2-H-4) corresponding to the ventral pallidum and substantia innominata. The conditioned forepaw placing reaction was elaborated with the basal forebrain stimulation used as a conditioned stimulus. After conditioning, the short (3-5 pulses) conditioned basal forebrain stimulation evoked a prolonged (up to 500-1000 ms) activation of neurons in the motor cortex. This activation did not change in the absence of the movement, i.e., after acute extinction of the contralateral forepaw placing or transfer of placing reaction to the ipsilateral forepaw.     

Topography of oxytocinergic estradiol target neurons in the mouse hypothalamus

Combined (3H) estradiol autoradiography and oxytocin immunocytochemistry were used in order to study co-localization of cytoplasmic oxytocin immunoreactivity and nuclear uptake of (3H) estradiol in the forebrain of adult ovariectomized mice. Labelling with (3H) estradiol was found in subpopulations of neurons that constitute between 10 to 40% of the oxytocinergic cells in the paraventricular nucleus, the supraoptic nucleus and the intersupraoptico-paraventricular islands. Oxytocinergic neurons in the septohypothalamic nucleus, the anterior commissural nucleus, the periventricular nucleus and the zona incerta only occasionally showed nuclear uptake of (3H) estradiol. The results indicate that oxytocinergic cell groups within the classical magnocellular nuclei have much higher numbers of estrogen receptors than the so called accessory oxytocin neurons. Oxytocinergic neuronal systems seem to constitute functionally heterogenous populations of cells, differently influenced by estradiol.     

Neuronal spike response produced in the feline thalamic reticular nucleus by instrumental conditioned reflex

Spike response was investigated in 156 units of the thalamic reticular nucleus (RN) during performance of the instrumental feeding reflex of lever-pressing. This response consisted of lead and lag phases. Latency of the lead phase of response varied between 10 and 100 msec and total duration of response between 50 and 250 msec; minimum latency of the lag phase: 100–300 msec. Initial response to a conditioning clicking sound was found in 27 units, of which 26 showed excitation and the remaining single unit an inhibitory-excitatory pattern. The lag stage of response associated with performance of conditioned lever-pressing was found in 134 neurons, of which 115 showed an excitatory pattern, 19 displayed inhibition and the remaining 22 units failed to respond. The lag phase of response preceded the onset of conditioned reflex movement (CRM) in 30 neurons. A total of 118 neurons responded between the onset of CRM and the point of lever-pressing. It was concluded that the RN plays a part in perception of the conditioned signal as well as producing and controlling performance of CRM.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 8–18, January–February, 1991.     

Stimulus-Response-Outcome Coding in the Pigeon Nidopallium Caudolaterale

A prerequisite for adaptive goal-directed behavior is that animals constantly evaluate action outcomes and relate them to both their antecedent behavior and to stimuli predictive of reward or non-reward. Here, we investigate whether single neurons in the avian nidopallium caudolaterale (NCL), a multimodal associative forebrain structure and a presumed analogue of mammalian prefrontal cortex, represent information useful for goal-directed behavior. We subjected pigeons to a go-nogo task, in which responding to one visual stimulus (S+) was partially reinforced, responding to another stimulus (S–) was punished, and responding to test stimuli from the same physical dimension (spatial frequency) was inconsequential. The birds responded most intensely to S+, and their response rates decreased monotonically as stimuli became progressively dissimilar to S+; thereby, response rates provided a behavioral index of reward expectancy. We found that many NCL neurons'' responses were modulated in the stimulus discrimination phase, the outcome phase, or both. A substantial fraction of neurons increased firing for cues predicting non-reward or decreased firing for cues predicting reward. Interestingly, the same neurons also responded when reward was expected but not delivered, and could thus provide a negative reward prediction error or, alternatively, signal negative value. In addition, many cells showed motor-related response modulation. In summary, NCL neurons represent information about the reward value of specific stimuli, instrumental actions as well as action outcomes, and therefore provide signals useful for adaptive behavior in dynamically changing environments.     

Role of the midbrain periaqueductal gray matter in conditioned reflexes

Unit activity in the midbrain periaqueductal gray matter (PGM) during an instrumental placing reflex, its extinction, differentiation, and conditioned inhibition, was studied in chronic experiments on cats. Spike responses 1–2 sec in duration in 69 (36.7%) of 182 neurons preceded by 400–800 msec the beginning of conditioned-reflex and voluntary intertrial movements. These advanced responses appeared 200 msec before the corresponding advance responses of motor cortical neurons. Fifty-eight neurons (30.9%) responded directly to acoustic stimulation with a latent period of 10–50 msec for 2–6 sec, 19 neurons (10.1%) generated double responses, linked with both the acoustic stimulus and subsequent conditioned-reflex movement, and 42 neurons (22.3%) did not respond to acoustic stimulation, although individual neurons of this group changed the level of their spontaneous activity in response to repeated conditioned stimulation, and this change was maintained for some tens of minutes. Extinction, differentiation, and conditioned inhibition all abolished conditioned-reflex movements, but each type of internal inhibition was accompanied by its own characteristic changes in the firing pattern of PGM neurons. Functional independence of neurons of the first and second groups was demonstrated during extinction and recovery of the conditioned-reflex. The results indicate the important role of PGM not only in the mechanism of the conditioned reflex, but also in the development of its internal inhibition.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 403–419, May–June, 1984.     

Time disparity sensitive behavior and its neural substrates of a pulse-type gymnotiform electric fish, Brachyhypopomus gauderio

Roles of the time coding electrosensory system in the novelty responses of a pulse-type gymnotiform electric fish, Brachyhypopomus, were examined behaviorally, physiologically, and anatomically. Brachyhypopomus responded with the novelty responses to small changes (100 μs) in time difference between electrosensory stimulus pulses applied to different parts of the body, as long as these pulses were given within a time period of ~500 μs. Physiological recording revealed neurons in the hindbrain and midbrain that fire action potentials time-locked to stimulus pulses with short latency (500–900 μs). These time-locked neurons, along with other types of neurons, were labeled with intracellular and extracellular marker injection techniques. Light and electron microscopy of the labeled materials revealed neural connectivity within the time coding system. Two types of time-locked neurons, the pear-shaped cells and the large cells converge onto the small cells in a hypertrophied structure, the mesencephalic magnocellular nucleus. The small cells receive a calyx synapse from a large cell at their somata and an input from a pear-shaped cell at the tip of their dendrites via synaptic islands. The small cells project to the torus semicircularis. We hypothesized that the time-locked neural signals conveyed by the pear-shaped cells and the large cells are decoded by the small cells for detection of time shifts occurring across body areas.     

Response of recticular and dorsal thalamic nuclei neurons during extinction of conditioned implementation in the cat

Unit activity in 66 neurons of the reticular (R) nucleus and 31 neurons of the ventropostrolateral nuclei of the thalamus, and 14 neurons of the posterolateral nuclear complex, the pulvinar, were studied during extinction of the conditioned food implementation reflex. The number of R neurons that had responded to initial excitation in the first 300 msec after the conditional stimulus (CS) decreased with the extinction. Simultaneous disappearance of conditioned-reflex placement movements and late excitatory and inhibitory responses of R and dorsal thalamic nuclei neurons with latent periods exceeding 300 msec was also observed. Extinction of the conditioned reflex (CR) led to a significant lowering of background activity in two-thirds of investigated R and other thalamic nuclear neurons. This suggests that efferent effects from the reticular nucleus are decreased during Cr extinction.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 3–8, January–February, 1991.     

Does the magnocellular octaval nucleus process auditory information in the toadfish, Opsanus tau?

Previous work on auditory processing in Opsanus tau has focused on the descending octaval nucleus; however, the magnocellular octaval nucleus receives similar inputs from the otolithic endorgans. The purpose of this study was to assess whether cells in any of the three subdivisions of the magnocellular nucleus respond to auditory frequencies and encode sound source direction. Extracellular recording sites were chosen based on anatomical landmarks, and neurobiotin injections confirmed the location of auditory sites in subdivisions of the magnocellular nucleus. In general, the auditory cells in M2 and M3 responded best to frequencies at or below 100 Hz. Most auditory cells responded well to directional stimuli presented along axes in the horizontal plane. Cells in M3 (not M2) also responded to lateral line stimulation, consistent with otolithic endorgan and lateral line inputs to M3. The convergence of auditory and lateral line inputs in M3, the lack of Mauthner cells in this species, and previous evidence that the magnocellular nucleus does not contribute to ascending auditory pathways suggest to us that the large cells of M3 may play a role in rapid behavioral responses to particle motion stimuli in oyster toadfish.     

Neuronal response in the cat parietal association cerebral cortex (area 5) during performance of conditioned reflex motion

Responses in 160 neurons of the cat parietal cortex were investigated during the performance of instrumental food reflex (lever pressing) during experiments involving presentation of a conditioned acoustic stimulus. Discharge rate changed in 49% of neurons during the period preceding the conditioned reflex movement. Three basic types of cell with an excitatory response pattern were discovered apart from a small group showing suppression of activity, each differently involved in the process of conditioned reflex movement performance. Excitation arose in neurons of the first type 200±52.9 msec (average) before the onset of the conditioned reflex movement, reaching its peak discharge rate as the animal placed its paw on the lever. The former parameter was 605±54.2 msec for the second type of neuron, with firing rate peaking between the start of electromyographic response and the completion of lever pressing. The same parameter measured 1,000–2,000 msec in the third type and activation took the form of a diffuse increase in discharge rate without a clear-cut peak occurring during performance of the instrumental reflex. Findings would suggest the involvement of the parietal cortex neuronal system in the triggering as well as the follow-through of conditioned reflex motion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 223–231, March–April, 1987.