Electroencephalographic, behavioral, and single-unit effects produced by stimulation of forebrain inhibitory structures in cats

Sleep-related erections: Clinical perspectives and neural mechanisms

Involuntary sleep-related erections (SREs) occur naturally during REM sleep in sexually potent men and other mammals. The regularity of their pattern and non-volitional nature made SREs useful clinically for differentiating psychogenic and organic erectile dysfunction (ED) in candidates for surgical intervention. Normative data available for different age groups added to the attractiveness of SRE measurement for clinical decision-making. Clinical SRE testing is less commonly applied today with the advent of minimally invasive medical therapies for ED. Nonetheless, as an objective measure of erectile function, SRE recording for research provides a precise technique for examining the mechanisms of erection and is still conducted to resolve legal disputes. SRE alterations provoked hormonally and pharmacologically are discussed. Different SRE patterns are associated with comorbid factors and some of these are illustrated, described, or both. Recording techniques developed for rats have proved extremely valuable for furthering our understanding of brain centers mediating erectile response. Data from lesion and stimulation studies are examined in the present review, moving us a step closer to understanding the underpinnings of erectile function.

The neurophysiological validation of the hyperpolarization theory of internal inhibition

The experiments in conscious non-immobilized rabbits showed that cessation of the reactions without reinforcement (elaboration of the internal inhibition) is accompanied by an enhanced phasic state, by alternation of activation and inhibition of neuron firing, and by the corresponding slow potential oscillation (SPO). These changes can be either localized, predominantly in the structures of conditioned stimulus, or, under enhancement of the inhibitory state, generalized in the brain structures. On the basis of our experience and published data, it is concluded that the above event results from relative enhancement of the inhibitory hyperpolarizing processes due to increase in reactivity of the inhibitory systems to stimulus, which acquires inhibitory properties during learning. Changes in the excitability and reactivity of neuron populations appearing during enhancement of the hyperpolarizing inhibition, and differing in the various brain structures, play an active role in the execution of the main function of the internal inhibition: limitation of excitation transmission to the effectors. An inhibitory mediator gamma aminobutyric acid (GABA) is of great importance in inhibiting the excitation in response to the stimulus which lost its biological significance. These experimental data and their interpretation in the light of published data give the basis for the development of the hyperpolarization theory of internal inhibition.

Extracellular serotonin variations during vigilance states in the preoptic area of rats: a microdialysis study

Numerous studies have shown that serotonergic transmission decreases from waking (W) to slow wave sleep (SWS) to paradoxical sleep (PS), suggesting an active role of serotonin (5-HT) in W but not in sleep. Conversely, the inhibition of 5-HT activity produces insomnia. This insomnia can be reversed by injections of 5-hydroxytryptophan in the preoptic area (POA), suggesting that 5-HT is necessary in this cerebral structure for sleep. Using microdialysis, we studied, 5-HT variations in the POA of rats in relation to vigilance states. 5-HT levels were higher during W than during during SWS and PS. 5-HT increased just before the rats fell asleep and then decreased during sleep. A decreased 5-HT transmission was also observed from SWS to PS. These data document a positive correlation between 5-HT levels in POA and wakefulness. Moreover, these observations are in favour of a permissive role of 5-HT in the POA during PS. A comparison between the POA and the prefrontal cortex in the sleep-wake cycle is discussed.

Electrophysiological signs of reduced prefrontal response control in schizophrenic patients

The prefrontal cortex is considered as a brain region important in the etiopathogenesis of schizophrenic disorders. Based on converging results from different research areas, the prefrontal cortex is regarded as the anatomical and functional representation of response control under physiological conditions. In previous studies, a robust electrophysiological marker for the investigation of response control in healthy control subjects was validated. This parameter was termed NoGo anteriorisation and consists of a more anterior peak of the event-related potentials during the inhibition of a prepared motor response (NoGo condition within the Continuous Performance Test) than during its execution (Go condition). The present study investigated these brain electrical correlates of response control in 19 schizophrenic patients and 19 age- and sex-matched healthy subjects. Compared to control subjects, the event-related potentials in schizophrenic patients were located more anterior in the Go condition and, as a trend, more posterior in the NoGo condition. The NoGo anteriorisation was strongly reduced in the schizophrenic group. On a qualitative level, the NoGo anteriorisation was present in all control subjects, but not in eight of the 19 patients. The results were interpreted as an indication of a disturbed prefrontal response control in schizophrenic patients. Further studies will clarify whether this method may be useful as a global test of hypofrontality in different groups of chronic schizophrenias, or as a quantifiable measure of an affected response control system, especially in catatonic subgroups.

Role of the lateral preoptic area in sleep-related erectile mechanisms and sleep generation in the rat

Penile erections are a characteristic phenomenon of paradoxical sleep (PS), or rapid eye movement sleep. Although the neural mechanisms of PS-related erections are unknown, the forebrain likely plays a critical role (Schmidt et al., 1999). The preoptic area is implicated in both sleep generation and copulatory mechanisms, suggesting it may be a primary candidate in PS erectile control. Continuous recordings of penile erections, body temperature, and sleep-wake states were performed before and up to 3 weeks after ibotenic acid lesions of the preoptic forebrain in three groups of rats. Neurotoxic lesions involving the medial preoptic area (MPOA) and anterior hypothalamus (n = 5) had no significant effects on either erectile activity or sleep-wake architecture. In contrast, bilateral lesions of the lateral preoptic region, with (n = 4) or without (n = 5) MPOA involvement, resulted in a significant decrease in the number of erections per hour of PS, number of PS-related erections, and PS phases exhibiting an erection. Lesion analysis revealed that the candidate structures for PS erectile control include both the lateral preoptic area (LPOA) and ventral division of the bed nucleus of the stria terminalis; however, lesions of the LPOA were the most effective in disrupting PS erectile activity. LPOA lesioning also resulted in a long-lasting insomnia, characterized by the significant increase in wakefulness and decrease in slow wave sleep (SWS). PS architecture and waking-state erections remained unchanged after lesion in all groups. These data identify an essential role of the LPOA in both PS-related erectile mechanisms and SWS generation. Moreover, higher erectile mechanisms appear to be context-specific because LPOA lesioning selectively disrupted PS-related erections while leaving waking-state erections intact.

Functional neuroimaging of normal human sleep by positron emission tomography

Functional neuroimaging using positron emission tomography has recently yielded original data on the functional neuroanatomy of human sleep. This paper attempts to describe the possibilities and limitations of the technique and clarify its usefulness in sleep research. A short overview of the methods of acquisition and statistical analysis (statistical parametric mapping, SPM) is presented before the results of PET sleep studies are reviewed. The discussion attempts to integrate the functional neuroimaging data into the body of knowledge already acquired on sleep in animals and humans using various other techniques (intracellular recordings, in situ neurophysiology, lesional and pharmacological trials, scalp EEG recordings, behavioural or psychological description). The published PET data describe a very reproducible functional neuroanatomy in sleep. The core characteristics of this 'canonical' sleep may be summarized as follows. In slow-wave sleep, most deactivated areas are located in the dorsal pons and mesencephalon, cerebellum, thalami, basal ganglia, basal forebrain/hypothalamus, prefrontal cortex, anterior cingulate cortex, precuneus and in the mesial aspect of the temporal lobe. During rapid-eye movement sleep, significant activations were found in the pontine tegmentum, thalamic nuclei, limbic areas (amygdaloid complexes, hippocampal formation, anterior cingulate cortex) and in the posterior cortices (temporo-occipital areas). In contrast, the dorso-lateral prefrontal cortex, parietal cortex, as well as the posterior cingulate cortex and precuneus, were the least active brain regions. These preliminary studies open up a whole field in sleep research. More detailed explorations of sleep in humans are now accessible to experimental challenges using PET and other neuroimaging techniques. These new methods will contribute to a better understanding of sleep functions.

Daily rhythms in Fos activity in the rat ventrolateral preoptic area and midline thalamic nuclei

The present experiment investigated the expression of the nuclear phosphoprotein Fos over the 24-h light-dark cycle in regions of the rat brain related to sleep and vigilance, including the ventrolateral preoptic area (VLPO), the paraventricular thalamic nucleus (PVT), and the central medial thalamic nucleus (CMT). Immunocytochemistry for Fos, an immediate-early gene product used as an index of neuronal activity, was carried out on brain sections from rats perfused at zeitgeber time (ZT) 1, ZT 5, ZT 12.5, and ZT 17 (lights on ZT 0-ZT 12). The number of Fos-immunopositive (Fos+) cells in the VLPO was elevated at ZT 5 and 12.5 (i.e., during or just after the rest phase of the cycle). Fos+ cell number increased at ZT 17 and ZT 1 in the PVT and CMT, 180 degrees out of phase with the VLPO. A positive correlation was found between the numbers of Fos+ cells in the PVT and CMT, and Fos expression in each thalamic nucleus was negatively correlated with VLPO Fos+ cell number. The VLPO, PVT, and CMT may integrate circadian and homeostatic influences to regulate the sleep-wake cycle.

Direct activating effect of the lateral preoptic region of the hypothalamus on the synchronizing system of the thalamus

Chronic studies on cats were used to analyze rearrangements of total bioelectrical activity and neuron responses in the median center of the thalamus to electrical stimulation of the lateral preoptic nucleus of the hypothalamus. These electrophysiological studies established the existence of ipsi- and contralateral projections from the preoptic region to the median center. The preoptic region was shown to have an activating effect on the thalamic mechanisms generating spindle activity. It is suggested that the preoptic region with the nonspecific thalamus, acting via direct hypothalamo-thalamic connections, is one of the mechanisms involving the preoptic somnogenic system in the initiation of sleep and in the formation of the slow-wave phase of sleep.

Unit activity of rat basal forebrain neurons: relationship to cortical activity

Unit activity in the magnocellular basal forebrain nucleus was examined to characterize discharge patterns during synchronized and desynchronized electroencephalogram. Two types of basal forebrain neurons were identified by their firing pattern under urethane anaesthesia: bursting and tonic neurons. Bursting neurons (62.9%) were characterized by a spontaneous firing that consisted of periodic bursts of two to six spikes that occurred at 0.3 to 2 Hz and were phase-locked with the electroencephalogram slow waves. Tonic neurons (37.1%) displayed spontaneous single spike firing at 12.1 + or - 1.6Hz. The firing of most of them was not related to the slow waves. Both neuronal types changed their firing patterns during the electroencephalogram desynchronization elicited by either electrical stimulation of the pedunculopontine tegmentum or pinching the rat's tail. Bursting neurons changed from the bursting mode to a tonic mode of discharge pattern, increasing their firing rate, while tonic cells were inhibited during electroencephalogram desynchronization. Multiunit recordings revealed that bursting cells discharged synchronously during periods of electroencephalogram slow waves, but that synchronization disappeared during electroencephalogram desynchronization. No correlation was found between the spike discharges of different tonic cells nor between bursting and tonic cells. However, bursting neurons, but not tonic neurons, were correlated with the spike firings of neocortical neurons during electroencephalogram slow waves. The rhythmic activity of neither neocortical nor bursting basal forebrain cells was found under pentobarbital anaesthesia. The characteristics of the discharge pattern shown by bursting basal forebrain neurons suggest that this type of cell could be cholinergic. Thus, bursting basal forebrain neurons may release acetylcholine in the cortex rhythmically, enhancing the rhythmic activity of cortical neurons during slow-wave sleep. It is concluded that basal forebrain neurons may contribute to the generation of the electroencephalogram slow waves.

Hypothalamo-preoptic histaminergic projections in sleep-wake control in the cat

Cats were chronically implanted with electrodes for polygraphic recordings and cannulae for intracerebral microinjections in order to study the functional role of histaminergic innervation of the preoptic-anterior hypothalamus in sleep-wake control. alpha-Fluoromethylhistidine (alpha FMH, 50 micrograms in 1 microliter), a specific inhibitor of the histamine-synthesizing enzyme, when injected bilaterally into the preoptic area, where numerous histaminergic fibres and terminal-like structures are present, caused a significant increase in deep slow wave sleep (S2) and paradoxical sleep (PS) and a decrease in wakefulness. In contrast, microinjections of histamine (5 or 30 micrograms in 1 microliter) in the same area dose-relatedly increased wakefulness and decreased both slow wave sleep and paradoxical sleep. The effects of histamine were reduced by pretreatment with mepyramine (1 mg/kg i.p.), a well known histamine H1 receptor antagonist, and were mimicked by a local injection of impromidine (1 microgram in 1 microliter), a potent histamine H2 receptor agonist. Microinjections of mepyramine alone (120 micrograms in 1 microliter) caused an increase in slow wave sleep. These results suggest that preoptic histaminergic innervation is involved in sleep-wake control and that the action might be mediated via both H1 and H2 receptors.

Exposure to heat restores sleep in cats with preoptic/anterior hypothalamic cell loss

Evidence suggests that thermosensitive neurons of the preoptic/anterior hypothalamus (POAH) influence sleep- and arousal-regulating mechanisms. We examined the effects of POAH cell loss, produced by microinjection of neurotoxin (N-methyl-DL-aspartic acid), on sleep and thermoregulation in cats. Cats with bilateral POAH cell loss did not defend their body temperatures in the heat as effectively as normals, and did not initiate panting until brain temperatures rose to abnormally high levels. During 14 h polygraphic recordings of sleep-waking state conducted at an ambient temperature (Ta) of 23 degrees C, POAH-damaged cats exhibited reduced sleep. Amounts of deep slow-wave sleep (SWS2) were significantly less than prelesion values through 7 weeks postlesion; significant REM sleep deficits persisted for 5 weeks. However, these sleep disturbances were dramatically attenuated when cats were exposed to high Tas. During 6 h recordings at Tas of 13, 23, or 33 degrees C, total sleep time was greatest at 33 degrees C at both 2 and 4 weeks postlesion. At 4 weeks, amounts of SWS2 at 33 degrees C were similar to maximal prelesion values. Increased sleep at 33 degrees C was associated with elevated brain temperatures. The finding that, after POAH damage, abnormally high brain temperatures were required to elicit both panting and normal amounts of SWS suggests that impaired hypothalamic sensitivity to heat was responsible for both deficits. These results support the hypothesis that thermosensitive neurons participate in the tonic regulation of sleep and arousal.

Sleep-waking discharge of basal forebrain projection neurons in cats

We have previously described a population of neurons in the magnocellular basal forebrain which have selectively elevated discharge rates during slow-wave sleep compared to waking; we postulate that these sleep-active neurons are a component of a basal forebrain sleep-promoting system. The purpose of the present experiment was to determine if sleep-active neurons contribute axons to recently described basal forebrain projection pathways. In cats prepared for chronic single unit and EEG-sleep recordings, stimulating electrodes were placed in the mesencephalic reticular formation, and the external capsule and anterior cingulate bundle, fiber bundles known to contain axons of basal forebrain projection neurons. Fifty-nine neurons were antidromically driven; differences in antidromic response latencies were related to sleep-waking discharge profiles. Of the cells with short antidromic latencies (less than 5 msec), the majority (9 of 12) had high discharge rates during waking and low rates during slow-wave sleep. Cells with long antidromic latencies had either very low discharge rates (less than 1 spike/sec) across all states, or had elevated discharge rates in slow-wave sleep. Sleep-active neurons were antidromically driven from external capsule (n = 9), anterior cingulate bundle (n = 9), or mesencephalic reticular formation (n = 5). Projection sleep-active neurons were recorded in the substantia innominata, ventral to the globus pallidus and medial to the central nucleus of the amygdala. Our study found that identified basal forebrain projection neurons in cats exhibit a variety of sleep-waking discharge patterns and conduction velocities. Sleep-active neurons were found to have slowly conducting axons, and to be a source of both ascending and descending projections.

Long-lasting insomnia induced by preoptic neuron lesions and its transient reversal by muscimol injection into the posterior hypothalamus in the cat

In order to analyse the role of the anterior hypothalamus in the regulation of the sleep-waking cycle we made bilateral neuronal lesions at different levels of the anterior hypothalamus in cats, by means of microinjections of a cell-specific neurotoxin:ibotenic acid. These lesions resulted in severe insomnia in eight cats. This insomnia was characterized by a large decrease or even disappearance of paradoxical sleep and deep slow wave sleep and, to a lesser extent, by a decrease of light slow wave sleep, for 2-3 weeks. In the other five animals, we observed a large reduction of deep slow wave sleep (0-40% of control level), but a less intensive decrease of time spent in paradoxical sleep (50-75% of control level) and no marked effect on light slow wave sleep. During the first 3-6 postoperative days we also noticed hyperthermia in all cats; thereafter, the animals presented only a slight increase in brain temperature which did not appear to trigger the sleep impairment. Histological analysis of the different lesions revealed that the insomnia could be attributed to neuronal cell body destruction in the mediobasal part of the anterior hypothalamus covering; the medial preoptic area and a narrow portion of the lateral preoptic area as well as a restricted part of the anterior hypothalamic nucleus. In order to investigate the putative role of the posterior hypothalamic structures in the mechanism of insomnia after lesion of the mediobasal preoptic area neurons we injected an agonist of GABA into the ventrolateral part of the posterior hypothalamus to locally depress the neuronal activity. The bilateral intracerebral microinjection of muscimol (0.5-5 micrograms) induced a transient intensive hypersomnia (slow wave sleep and paradoxical sleep). These findings indicate that neuronal cell loss in the mediobasal preoptic area induced a long lasting insomnia. Thus, it may be hypothesized that the integrity of this structure is necessary for sleep appearance. Finally, our data are in keeping with an intrahypothalamic regulation of the sleep-waking cycle.

Sleep-related neuronal discharge in the basal forebrain of cats

Although evidence suggests that the basal forebrain contains a hypnogenic mechanism, putative sleep-promoting neural elements within this area have not been identified. We examined basal forebrain neuronal activity during waking, non-rapid-eye-movement (NREM) sleep, REM sleep and various transition states. Based on state-related discharge rates. 3 cell types were defined. Thirty-nine of 83 cells were classified as waking-active, i.e. waking discharge rates were greater than 2 times NREM sleep rates. Twenty-three of 82 cells were classified as state-indifferent (waking and NREM rates differed by a factor of less than 2). NREM sleep discharge rates of the remaining 20 cells were greater than 2 times waking rates. These were labeled sleep-active cells. Discharge rates of these cells during epochs of alert waking were low, averaging less than 1 spike/s. Maximal discharge rates occurred during NREM sleep, averaging 9.44 spikes/s. Increased discharge of sleep-active cells anticipated sleep onset; cells had an average discharge rate of 6.60 spikes/s during transitions between waking and NREM sleep. Sleep-active cells were confined to the ventral basal forebrain, in the horizontal limb of the diagonal bands of Broca, substantia innominata, entopeduncular nucleus and ventral globus pallidus. These areas overlap, in part, with those where chemical, thermal and electrical stimulations evoke sleep, and where lesions suppress sleep. Based on location and discharge pattern we consider sleep-active cells candidates for mediating some of the sleep-promoting functions of the basal forebrain.

Aversive-CS-specific alterations of evoked potentials in limbic and related areas of rats

Averaged evoked potentials (EP) to a CS (flash) were recorded sequentially in classical appetitive conditioning, satiated state after appetitive conditioning, highly alert state by noncontingent shocks, and classical aversive conditioning from a rat. The EPs were obtained from the central gray matter, superior colliculus, perifornical hypothalamic area, dorsal frontal cortex, and occipital cortex. Alterations unique to aversive conditioning were found in the dorsal frontal cortex (40-60 msec in latency) and in the perifornical hypothalamus (80-120 msec) but not in the central gray or occipital cortex. The frontal cortex might start processing information related to aversive or defensive emotion before the perifornical hypothalamic area might do it.

A [14C]2-deoxyglucose analysis of the functional neural pathways of the limbic forebrain in the rat. IV. A pathway from the prefrontal cortical-medial thalamic system to the hypothalamus

The present study utilized the [14C]2-deoxyglucose (2-DG) cell labeling procedure to characterize a functional pathway from the prefrontal cortex (Pfc) and mediodorsal thalamic nucleus (MD) to the hypothalamus. Rats were injected with 2-DG prior to a 45 min experimental paradigm consisting of alternating 30 s on-off periods of electrical brain stimulation. Standard procedures were utilized for the removal and processing of brain tissue for X-ray autoradiography. In the first phase of this study, stimulation applied to the prefrontal cortex generally yielded a pattern of 2-DG distribution consistent with the findings of classical anatomical studies. Stimulation of the dorsomedial and ventromedial prefrontal cortex or the infralimbic cortex produced the most effective activation of the diencephalon. This activation was primarily limited to MD, with no involvement of any region of the hypothalamus. In the second phase of this study, brain regions activated following stimulation of sites along the rostro-caudal axis of MD were examined. Stimulation of MD resulted in the activation of the nucleus reuniens and other midline and non-specific thalamic nuclei. Stimulation of this nucleus also activated the ventromedial thalamic nucleus, medial aspects of the nucleus accumbens and the medial and sulcal prefrontal cortices. Again, in each of these cases, labeling within any region of the hypothalamus could not be detected. Since MD stimulation activated the midline thalamus, and the nucleus reuniens in particular, the last phase of this experiment involved stimulation of the nucleus reuniens in order to determine the source of medial thalamic inputs to the hypothalamus. Stimulation of the nucleus reuniens activated fibers which were distributed to both the medial and lateral hypothalamus. In addition, stimulation also activated the descending periventricular system, which could be followed to the level of the midbrain central gray and such limbic structures as the hippocampal formation, septal area, amygdala and prefrontal cortex. These findings indicate that Pfc-MD activation of the hypothalamus is achieved indirectly via interneurons within the nucleus reuniens.

Prefrontal cortex and bulbar reticular formation and behavioral inhibition in the rat

Electrical stimulation in the bulbar reticular formation will produce response suppression that is observably the same as that produced by stimulation in the prefrontal cortex. This includes suppression of bar-pressing for food and running in an activity wheel, but no suppression of approach and eating of food or general activity. These results, together with previous research, support the hypothesis that this inhibitory influence of the prefrontal cortex is mediated through the bulbar reticular formation. This hypothesis is not incompatible with the concept that the prefrontal cortex serves to suppress the activating influence of the rostral reticular formation.

Loss of neurons in the nucleus basalis of Meynert in Alzheimer's disease, paralysis agitans and Korsakoff's Disease

The nucleus basalis of Meynert, the major source of cholinergic innervation of the cerebral cortex, was morphometrically investigated in 58 cases of neuropsychiatric disorders and compared to 14 controls. The results demonstrate a loss of neurons in the nucleus basalis of Meynert in Alzheimer's disease (70%), paralysis agitans (77%), and Korsakoff's disease (47%) but no marked reduction of neurons in postencephalitic parkinsonism, Huntington's disease, chronic alcoholism without dementia, schizophrenia and infantile brain damage. Neurons of the three subdivisions of the nucleus basalis of Meynert (the nucleus septi medialis, the nucleus of the diagonal band of Broca and the nucleus basalis Meynert neurons in the substantia innominata) may be affected in a different manner in different patients within a single group homogeneous with respect to the usual clinical and neuropathological diagnostic criteria. Cell loss in the basal forebrain is restricted to the large neurons of the nucleus basalis, the immediately adjacent neurons of the globus pallidus externus not being affected. The selective degeneration of these neurons provides the morphological correlate of the cortical cholinergic deficiency in these neuropathological conditions. The degeneration of this discrete cholinergic neuronal population in several disorders of higher cortical function is probably directly related to the progressive deterioration of memory and cognitive processes in affected patients.

Neurophysiologic mechanisms of internal inhibition

The experimental results obtained in the authors' laboratory as a result of multiple recording of slow biopotentials, the recording of neuronal activity and of mathematical modeling, are reviewed. The authors conclude that the elaboration of internal inhibition is followed, and determined to a great extent, by the restriction in conduction of excitations due to the increase of inhibitory hyperpolarization and discordance in the periodicity of slow potentials, reflecting oscillations in excitability of neuronal populations in the cortex and other brain structures.

Pericruciate cortex unit activity during intentional movement. Effect of subcortical electrical stimulation

Extracellular unitary activity of pericruciate cortex neurons (CPCns) was recorded in cats performing a learned flexion--extension movement of the contralateral forearm. The present report concerns solely those cells showing firing changes on electrical stimulation of nucleus medialis dorsalis thalami (DM). These CPCns responding to DM stimulation (CPCdmns) were classified as either pyramidal tract or non-pyramidal tract neurons (CPCdm PTns, CPCdm non-PTns) by antidromic activation of the medullar pyramid. In addition, convergence of DM and other subcortical structures (lateral hypothalamus HL, basal amygdala AB, and dorsal amygdala AD) on CPCdmns was tested by means of single and paired electrical stimulation. On the bases of the obtained data, CPCdmns had been grouped in the following different types. Type I: thirty-two neurons activated by stimulation of all the studied subcortical structures. All these cells are PT neurons and 20 of them (62.5%) are task-related, showing firing frequency increase before movement onset. Type II: forty-six neurons also activated by stimulation of all subcortical structures. All are non-PT cells and 17 of them (36.9%) are task-related, showing firing decrease or firing arrest at movement onset. Type III: twenty-one neurons activated exclusively by DM stimulation (and therefore non-PT cells). Four of them (19%) being task-related, and showing firing increase after movement onset. Type IV: twenty neurons responding exclusively to DM stimulation with firing frequency increase frequency decrease. None of them was movement-related. It is concluded that the cat's CPC agranular cortex receives effective inputs from such subcortical structures as DM, AB, AD and HL and that these subcortical structures play an important role in the regulation of motorcortical cell activity.

Subcortical influences upon prefrontal cortex of the cat

Extracellular unit recordings were obtained from the prefrontal cortex (CPF) of free-moving cats with the head fixed. The prevailing effect produced by electrical stimulation of dorsal amygdala (AD) and N. medialis dorsalis thalami (DM) was a decrease in the spontaneous activity of CPF neurons, while lateral hypothalamus (HL) stimulation produced an increase. Concurrent electrical stimulation of HL and DM, and HL and AD produces suppression of the effect induced by HL single stimulation. Basal amygdala (AB) and DM simultaneous stimulation produces suppression of DM single stimulation.

Reciprocal connections between the lateral hypothalamus and the frontal complex in the rat: electrophysiological and anatomical observations

Inputs to rat lateral hypothalamus (LHA) from prefrontal cortex (FC), and vice versa, were studied by intracellular recording, and by retrograde horseradish peroxidase (HRP) method. Stimulation of the FC evoked 3 types of responses: a polysynaptic EPSP-IPSP sequence, IPSPs alone, or antidromic response in LHA neurons. Forty-five per cent of IPSPs were considered to be monosynaptic since the latencies were constant when stimulus intensity was changed. The neurons labeled in the FC following electrophoretic injections of HRP into LHA were located in the medial and sulcal FC. In these cortical areas, not only pyramidal neurons in layer V, but also non-pyramidal neurons in layer VI were labeled. Stimulation of the LHA evoked an EPSP-IPSP sequence, or antidromic response in FC neurons. Some of the fast EPSPs were considered to be monosynaptic. The neurons labeled in the LHA following HRP injection into the FC were either relatively large spherical neurons or small ovoid-shaped neurons. These were distributed diffusely throughout the LHA.

Cholinergic projections from magnocellular nuclei of the basal forebrain to cortical areas in rats

Acetylcholinesterase (AChE) and choline acetyltransferase (CHAc) activities were studied by quantitative histochemical (AChE) as well as biochemical methods (AChE, ChAc) in certain cortical brain areas in rats after stereotaxic lesions had been placed in several structures of the basal forebrain. After lesioning the magnocellular nuclei of the substantia innominata (nuc. basalis Meynert, NBM) the activities of AChE and ChAc decreased to moderate or low residual values in the ipsilateral cortical areas. This indicated that cholinergic pathways were directly linked to frontal, sensory-motor, auditory and visual cortex. After lesions of the globus pallidus the decrease in cortical AChE activity was less pronounced. Lesions of the caudate, accumbens or entopeduncular nucleus did not influence the cortical AChE activities. The results are discussed with respect to the similarity of the organization of the cholinergic projection to the cortex arising from NBM cells and the monoaminergic system which innervates the cortex. It is suggested that both neurotransmitter systems by their interaction might modulate and control cortical information processing and behavior in a manner analogous to the control of peripheral activity by the sympathetic and parasympathetic system.

Elevation of pain threshold to tooth shock by brain stimulation in primates

Electrical stimulation of the brain (ESB) for modulation of pain has been previously demonstrated in primates, but many of the sites which yield stimulation-produced analgesia (SPA) also elicit aversive side effects. In order to examine the aversive as well as analgesic effects of brain stimulation, nine rhesus monkeys (Macaca mulatta) were first trained to press a lever to escape or titrate noxious tooth shock. Stimulating electrodes were placed under the frontal cortex in 4 monkeys and were implanted in the diencephalon, brain stem, and cerebellum of five remaining monkeys. Diencephalic stimulation sites resulted in marked elevations of tooth shock threshold at ESB intensities which did not elicit aversive behaviors. The analgesic effects lasted up to 2 h past ESB offset. Moderate elevations of tooth shock threshold were also observed with orbital cortex stimulation. The midbrain central gray and the nucleus raphe magnus, however, did not greatly alter tooth shock level and typically resulted in aversive reactions. The diencephalic sites which elicited SPA also led to self-stimulation behavior, whereas stimulation of the brain stem or cerebellum usually resulted in escape responses. These findings thus indicate that, in primates, more effective relief of pain can be achieved with electrical activation of the medial diencephalon than with brain stem stimulation.

Suppression of attack behavior in cats by stimulation of ventral tegmental area and nucleus accumbens

Low frequency (6 pps) stimulation of ventral tegmental area (VTA) and nucleus accumbens (NA) produced EEG synchronization and suppressed attack behavior elicited by hypothalamic stimulation. Both quiet biting and affective attack with rage were suppressed. Autonomic and non-directed somatic motor components of the attack reaction were unaffected. High frequency (60 pps) stimulation of VTA failed to suppress any components of the attack reaction; high frequency stimulation of NA, however, did produce suppression of attack. Low frequency (6 pps) sensory stimulation, delivered by photic or lateral geniculate stimulation, produced EEG synchronization but failed to cause suppression of attack. These results indicate that low frequency stimulation per se does not cause suppression of ongoing behavior. This study demonstrates that VTA and NA, components of the mesolimbic dopamine system, are involved in the inhibition of emotional-type behaviors.

Effect of amphetamine and pentobarbital on sleep-wake patterns of cats with basal forebrain lesions

The effects of amphetamine and pentobarbital upon electrographic state were studied in naive cats and cats with forebrain lesions that induce insomnia. Amphetamine increased alertness and decreased both slow wave sleep (SWS) and rapid eye movement (REM) sleep states for up to 12 h in both intact animals and cats with lesions. Pentobarbital inhibited REM sleep and alert states while increasing SWS and drowsy states in naive cats. The effect was mainly restricted to the first 8 h. In cats with forebrain lesions, the effects were similar except that the amount of REM sleep was significantly elevated. During a portion of the first 8 h, the tracing cannot be distinguished from a normal control sample. It is hypothesized that pentobarbital mimics the normal inhibitory influence of the intact forebrain and either induces or facilitates 'normal' sleep patterns in cats with forebrain lesions.

Monosynaptic facilitatory pathway from the hypothalamic ventromedial nucleus to the frontal cortex in the rat

Stimulation of the ventromedial nucleus (VMH) evoked a short latency negative wave with two peaks (cN1 and cN2) followed by a small positive wave (cP) at the ipsilateral dorsal frontal cortex (area 10) in the rat. The maximum response was observed from the lateral edge of the frontal pole. From the depth profiles of recordings, cN1 changed polarity at a depth of about 4 mm and the cN1-cN2 changed into a large compound action potential at the medioventral part of the frontal pole at a depth of about 6 mm. Since the surface evoked potential and the compound action potential followed high frequency stimulation, these respective potentials are concluded to be due to antidromic and monosynaptic activation of the cortical neurons. This was verified by unit recording experiments. The cP was concluded to be produced by the initial rise of the monosynaptic EPSP.

Inhibitory pathway from the frontal cortex to the hypothalamic ventromedial nucleus in the rat

Stimulation of the dorsal frontal cortex (area 10, FCtx) evoked two negative waves with short latencies (N1 and N2) followed by a large, longlasting positive wave (P) in the ventromedial nucleus (VMH) as well as in the more dorsal structures in the hypothalamus and the ventral thalamus. Since the N1 followed high frequency stimulation, it was concluded to be due to antidromic activity. Double or triple pulse stimulation summated the P, and reduced the amplitude of the negative waves of the second and the third responses. VMH neuronal discharges were also decreased during the time course of the P. Therefore, the P was concluded to be composed of the IPSPs. VMH neuronal discharges were frequently superimposed on the N2, indicating the origin of this wave to be EPSPs. Strychnine reduced or blocked the inhibition of the VMH neurons caused by not only FCtx stimulation but also glycine application. The results indicate that the VMH receives both excitatory and inhibitory projections from the FCtx, and the inhibition may be transmitted by glycine.

Afferent and efferent subcortical projections of behaviorally defined sectors of prefrontal granular cortex

Although the functional significance of the midprincipalis region is well known, the afferent and efferent connections of this zone, in comparison to the anterior and posterior portions of the cortex lining the principal sulcus, are poorly understood. In 3 animals the retrograde tracer HRP and the anterograde tracers, tritiated proline, lysine and leucine, were injected into the sulcal cortex lining the principal sulcus. The cortex forming the banks of the principal sulcus was divided into anterior, middle and posterior sectors with one animal used for each zone. As expected from previous studies, the heaviest afferents to the cortex forming the principal sulcus were from the parvocellular portions of the medical dorsal nucleus. The medial pulvinar nucleus and the nucleus limitans projected to only the anterior and posterior portions of the cortex lining the principal sulcus. Projections were seen to all 3 sectors from the anterior, midline, intralaminar and lateral thalamic nuclei. Although cells were seen in the hypothalamus following injections in all 3 sectors of the cortex lining the principal sulcus, the heaviest hypothalamic projections were noted after injections into the mid-sector of the cortex. These HRP-positive cells were in the dorsal and lateral hypothalamic area, dorsal medial nucleus and in the lateral mammillary nucleus. These findings link the midprincipalis region with the prefrontolimbic circuit, and suggest that the midprincipalis region, n. medialis dorsalis, the mammillary bodies and perhaps the cingulate gyrus constitute part of an anatomical circuit concerned with memory processes.

Does the brain actively maintain itself?

All living systems have special mechanisms for combatting entropy; however, the brain has dimensions of organized complexity beyong those manifest in the anatomical structure and physiology of the rest of the body. Reasons are given in support of the notion that the brain therefore must have a special, intrinsic "homeostatic" system for its information bearing structures, and, further, that slow electroencephalographic activity has properties which might make it useful for such an order-maintaining function. Recovery from brain damage is hypothesized to be a byproduct of this process, which may involve a cruder sort of information processing than occurs with such functions as perception and learning. Synchronized EEG activity may be adequate to handle this sort of information processing. Speculations are offered about possible mechanics, on the neuronal level, of slow wave participation in plasticity; for example, one such suggestion is based on findings that electrical fields can influence cellular orientation. The methodology of discovering the distribution within the brain of the hypothetical maintenance system is discussed briefly.

A neural systems theory of schizophrenia and tardive dyskinesia

Some systems ideas applied to individual persons are used to try to explain symptoms of schizophrenia and a syndrome of uncontrolled fragments of movement which sometimes occurs as a side effect of chronic, antipsychotic drug therapy. The behavior of normal organisms may be conceptualized in three echelons of control, with each successively higher echelon organizing, by selective disinhibition, semiautonomous, spontaneous fragments of activity which comprise the next lower echelon. It is hypothesized that schizophrenia involves a deficiency of inhibition by the frontal cortex, first echelon, on the corpus striatum, second echelon. This results first in insufficiently integrated fragments of behavior, and second in premature associative linkages among active elements. First echelon control develops as a normal person matures and gradually loses some of the playful activities of childhood. It is hypothesized that by disrupting certain aspects of activity in the corpus striatum, neuroleptic drugs reduce schizophrenic symptoms but also reduce the capacity of the second echelon to inhibit and integrate the smaller behavioral fragments wired into lower parts of the brain, third echelon. This results in uncontrolled movements. Though many researchers already favor the hypothesis that neuroleptic drugs act on the corpus striatum, the broader theory presented here is new and depends in large part on general living systems considerations. Emphasis is on conceptual decomposition of the integrated behavior of a whole organism into less complex subsystems. Individually, these have neither too much nor too little complexity to yield a plausible model. Some experimental predictions and predictions about possible therapies are made from the theory.

Hypothalmic influences on the electrical activity of the olfactory pathway

By means of evoked potentials a direct efferent connection was found to run from the posterior hypothalmus and medial forebrain bundle to primary olfactory structures (olfactory bulb, olfactory tubercle and prepyriform cortex). The pathway from the hypothalmus to the olfactory bulb follows in the lateral olfactory tract at a conduction velocity 5-10 m/sec. The olfactory tubercle functions as a relay station for the efferent fibers from various sources, running to the olfactory bulb. In animals with electrodes chronically implanted in the olfactory structures, hypothalamic stimulation gives rise to a prolonged train of hypersynchronous bursts of activity (40-50 Hz), which resemble the arousal reaction. This response is modified by transecting the cervical sympathetic trunk. By pathways still to be defined, potentials are evoked in the olfactory bulb by stimulation of the cervical sympathetic trunk and the termination of these sympathetic fibers shows a common postsynaptic neuronal pool with axons of hyopothalmic origin. Epinephrine topically applied to the olfactory mucosa induced hypersynchronous activity in olfactory structures, quite similar to that consequent to hypothalmic stimulation. These results suggest a multichanneled hypothalmic modulation of olfactory input.

Attenuation of pain reactivity by caudate nucleus stimulation in monkeys

The effect of caudate nucleus stimulation on reactivity to painful stimuli was investigated in Macaca speciosa monkeys chronically implanted with electrodes in the right caudate nucleus. The force with which subjects escaped from electrocutaneous leg shock was used as a measure of pain reactivity and was decreased by caudate stimulation. Escape threshold and latencies were not influenced by the brain stimulation. Decreased escape force was obtained only when 50 msec trains of caudate stimulation preceded 20 msec trains of leg shock by 0-100 msec. Pain reactivity was not affected if brain stimulation followed leg shock or if leg shock followed brain stimulation by more than 100 msec. Intershock response distributions indcated that direct motor inhibition was not responsible for the depression of escape force, and the effectiveness of a restricted range of caudate-leg stimulation intervals ruled out generalized effects on arousal. The results indicate that the effect of caudate stimulation is to reduce the affective components of pain elicited by noxious electrocutaneous stimuli. The time course of this caudate effect parallels that previously reported for the caudate-induced depression of evoked activity in the non-specific somatosensory projections of the reticular formation and thalamus.

Effects of electrical stimulation of the lateral aspect of the prefrontal cortex upon attack behavior in cats

An experiment was performed to determine the role of the lateral aspect of the prefrontal cortex upon quiet biting attack behavior elicited from the hypothalamus in the cat. The results of this experiment indicate that stimulation of 19 of 28 electrode sites sampled in the lateral prefrontal cortex produced a statistically significant inhibition of attack behavior elicited from the hypothalamus of the ipsilateral side. Stimulation of sites in the prefrontal cortex on the side contralateral to the hypothalamus from which attack was elicited had no effect upon this response. No systematic effect of prefrontal stimulation upon flight behavior was observed. Anatomical studies suggest that the lateral prefrontal cortex may inhibit attack behavior by modulating neurons in either the mediodorsal thalamic nucleus or ventral tegmental area.

Magnocellular nuclei of the basal forebrain project to neocortex, brain stem, and olfactory bulb. Review of some functional correlates

Horseradish peroxidase was injected into the neocortex of squirrel monkeys, rats, tree shrews and one opossum, in the brain stem of one squirrel monkey and rats, and in the olfactory bulb, the corpus vitreum or the vascular system of rats. Following the cortical, brain stem and bulbar injections labeled cells were found (predominatly ipsilaterally) in the magnocellular nuclei of the basal forebrain: nucleus of the diagonal band, the magnocellular preoptic nucleus and nucleus basalis. These nuclei may, therefore, be classified together hodologically as well as cytologically and histochemically. The number of labeled cells was proportional to the size of the injected region. It is uncertain whether the same cells project to all target regions. Large labeled cells were found scattered among pallidal and entopeduncular neurons in rats with cortical or brain stem injections. These neurons may be the equivalent to the nucleus basalis in other species.

Basal forebrain and hypothalamic connection to frontal and parietal cortex in the Rhesus monkey

Horseradish peroxidase was injected in different parts of the frontal and parietal cortex in 17 rhesus monkeys. In all cases the enzyme was transported retrogradely to neurons in the substantia innominata and hypothalamus as well as in the thalamus. These new findings demonstrate that these cortical areas receive direct afferent fibers from limbic basal forebrain areas concerned with emotion and motivation.