Effects of pontine reticular formation lesions on optokinetic head nystagmus in rats

Electrolytic lesions were produced in the pontine reticular formation (PRF) of adult hooded rats. Unilateral lesions abolished quick phases of optokinetic head nystagmus to the side of the lesion. Some lesions also had temporary effects on slow phases of optokinetic head nystagmus. Effects of bilateral lesions were similar, except that they affected head movements in both directions. A class of "fast" head movements abolished by PRF lesions thus emerges that is analogous to the class of rapid eye movements abolished by similar lesions in other species, a finding that can be related to the coupling which has been observed between "fast" head and eye movements.

[Participation of angiotensin II in the establishment of negative emotional reactions]

In waking rats and rabbits systemically injected angiotensin II was shown to participate predominantly in the mechanisms of negative emotional reactions. The effects of angiotensin II were observed at the behavioural level as well as at the neuronal one. Depending on the dose and the time of injection of angiotensin II and its specific antagonist saralasin they inhibited or facilitated elaboration and extinction of automatized conditioned active avoidance independently of arterial, pressure changes, the pain threshold being altered. Injection of angiotensin II abolished individual behavioural reactions of the animals in response to stress factors and increased their resistability to emotional stress. The negative emotional reactions were found to induce changes of chemosensitivity of neurones of the parafascicular complex of the medial thalamus and the midbrain reticular formation during microionophoretic application of angiotensin II. A supposition is made about the increase of angiotensin II brain synthesis under conditions of emotional stress.

Paresis of lateral gaze alternating with so-called posterior internuclear ophthalmoplegia. A partial paramedian pontine reticular formation-abducens nucleus syndrome

A patient with multiple myeloma developed gaze paresis to the left with slowed saccades and gaze-paretic nystagmus, which alternated with abduction palsy in the left eye (with preserved oculocephalic deviation) and dissociated adducting nystagmus in the right eye, suggesting so-called posterior internuclear ophthalmoplegia. At autopsy multiple small infarcts were found with partial destruction of the left paramedian pontine reticula formation (PPRF) extending towards the abducens nucleus, which was involved only in its inferior pole. The medial longitudinal fasciculus and other oculomotor structures were spared. It is suggested that slowing of all ipsilateral saccades with gaze-paretic nystagmus corresponded to partial destruction of the PPRF, and that intermitted abduction palsy in the ipsilateral eye with adduction nystagmus in the fellow eye was due to intermittant dysfunction of the abducens nucleus. Involvement of voluntary saccades, pursuit movements and vestibulo-ocular responses may be dissociated in partial lesions of the abducens nucleus.

Thalamic nociceptive systems

A role for thalamic structures in the processing of signals of nociception and pain has been suggested on the basis of clinical data since the turn of the century. Searches for a 'pain centre' by lesion or stimulation were often disappointing and the electrophysiological data were rare and usually contradictory. However, recent electrophysiological anatomical and neuropharmacological studies, made in various species (mainly rat and monkey) appear now progressively to give some clues in the understanding of pain process at the thalamic level. These studies have been mainly concerned with the areas receiving projections from ascending spinal pathways conveying noxious inputs, either directly by the spinothalamic tract or indirectly by the spinoreticulothalamic pathway. The eventual respective roles of these thalamic structures are considered. Electrophysiological recordings from thalamic structures in a model of experimental pain, arthritic rats, are also presented.

Muscarinic cholinergic receptors in area postrema and brainstem areas regulating emesis

Central cholinergic pathways modulate both the perception of excessive motion stimuli and the expression of motion sickness symptoms, such as nausea and vomiting. Specific brainstem areas which mediate motion-induced emesis include the area postrema (AP), vagal nuclear complex (VNC), reticular formation (RF) at the site of the vomiting center, and the vestibular complex (VC). In this report, histological studies indicated the cellular organization of brainstem structures mediating emesis was similar in bovine and squirrel monkey brain. The objective of this study was to characterize biochemical and pharmacological properties of muscarinic cholinergic receptors assayed by 3H-QNB binding in these regions of bovine brainstem. Scatchard analyses of specific 3H-QNB binding showed an uneven distribution of muscarinic receptors, with high densities of sites in VNC and AP, intermediate levels in RF and lowest receptor concentrations in VC. Dissociation constants for 3H-QNB, measured in saturation and kinetic experiments, were similar in all brainstem regions. The pharmacological potency of cholinergic agonists and antagonists was the same as reported for muscarinic receptors labeled in other brain areas or peripheral organs. Several drugs which potently inhibited 3H-QNB binding in bovine brainstem also exhibited antiemetic activity in a squirrel monkey model of motion-induced emesis. The antimotion sickness effects of these drugs may be due, in part, to their antagonism of muscarinic receptors in brainstem areas regulating emesis.

The neuronal basis of compulsive behaviour in anorexia nervosa

The relationship between arousal and efficiency of the brain is shown by the inverted U of the Yerkes-Dodson curve. Measuring arousal has been difficult because the three types of arousal (EEG, behaviour and autonomic) do not change in unison. From Magoun's work, arousal can be stimulated via the reticular formation or from parts of the cortex. Kyotorphin (Tyr-Arg) causes widespread excitation when applied to the cortex and may represent this mechanism: it is then inhibited only by noradrenaline. The hippocampus causes stimulation of arousal to persist after the exciting stimulus stops and can itself be stimulated into long term potentiation. The latter may be related to the onset of compulsive behaviour which appears to occur only with excessive stimulation of arousal. The opioid dynorphin is the main stimulator of the hippocampus and can cause long term potentiation. Inhibition of opioid activity by continuous naloxone infusion facilitates weight gain in anorexia and in some will abolish the compulsive drive. Other opioid antagonists need to be found for the more severe compulsive behaviour patients.

Dorsal midbrain syndrome: clinical and oculographic findings

We report clinical and oculographic findings in seven patients with the dorsal midbrain syndrome (Parinaud's syndrome). All presented with limited upward voluntary gaze and convergence nystagmus with attempted upward voluntary gaze. Quantitative analysis of vertical eye movements documented characteristic abnormalities of saccades with relative preservation of reflex eye movements (ie, vestibular, optokinetic, and visual-vestibular). Vertical saccade velocity was only slightly decreased in five patients with tumors, indicating that the vertical burst neurons in the mesencephalic reticular formation and their efferent pathways to the oculomotor neurons were minimally damaged. On the other hand, two patients with probable brainstem encephalitis exhibited marked slowing of vertical saccades, indicating that the burst neurons, or their efferent pathways to the oculomotor neurons, were severely damaged.

The neurobiology of the narcoleptic syndrome

Relevant electroencephalographic, psychopharmacologic, and genetic research reports are described in support of a neurobiological explanation of the narcoleptic syndrome. Despite increased support in this realm, no single neurobiological theory has won unanimous approval among sleep researchers, which has led toward speculation that the condition may be heterogeneous in nature. A multifactorial perspective, including psychological as well as neurobiological influences, appears to be the most productive model for research. Future investigation of sleep disorders utilizing such a model may enhance the understanding of neurobiological correlates of behavioural disorders.

Midbrain paresis of horizontal gaze

Unilateral paramedian involvement of the midbrain tegmentum causes monocular paralysis of adduction in the ipsilateral eye, paresis of contralateral saccades in the opposite eye, and conjugate paresis of ipsilateral smooth pursuit. The adduction paralysis can be nuclear, or internuclear from a lesion in the medial longitudinal fasciculus. This distinctive midbrain syndrome of horizontal gaze paresis is exemplified by means of quantitative infrared oculographic, radiological, and neuropathological correlation in two patients with predominantly paramedian midbrain tumors involving the mesencephalic reticular formation and the oculomotor nucleus. Binocular paralysis of elevation provided evidence that one human oculomotor nucleus contains axons to both superior rectus muscles, as does the simian oculomotor nucleus. The midbrain tectum was spared. These pathophysiological correlations indicate that the mesencephalic reticular formation contains pathways that control contralateral saccades and ipsilateral smooth pursuit.

Effects of acute hypoxia on the EEG and impulse activity of the neurons of various brain structures in rats

The EEG and impulse activity of the neurons of the cerebral cortex and other structures of the brain were studied in the dynamics of hypoxic influence. In the initial phase of hypoxia (2000-6000 m), activation of the EEG and impulse discharge of neurons set in; in this case EEG activation arose earlier and was more pronounced. In the second phase of hypoxia (7500-10,000 m), the EEG changed in the direction of a reorganization of the frequency spectrum from one rhythm to another - from fast to slow activity of the type of delta waves. At this time the impulse activity was gradually suppressed, and the cortical neurons exhibited higher sensitivity to hypoxia and were inhibited earlier than the cells of the hypothalamus and medulla oblongata.

Characterization of inhibition of a spinal nociceptive reflex by stimulation medially and laterally in the midbrain and medulla in the pentobarbital-anesthetized rat

Inhibition of the spinal nociceptive tail flick (TF) reflex by electrical stimulation throughout the midbrain and medulla was examined and characterized in pentobarbital-anesthetized rats. The TF reflex in the lightly anesthetized state is of significantly shorter latency (1.63 s vs 2.36 s) and of greater amplitude than in the unanesthetized state. Systematic mapping studies revealed that inhibition of the TF reflex could be produced from widespread areas in the midbrain and medulla. Midbrain areas having the lowest thresholds for inhibition of the TF reflex were found lateral and ventrolateral to the periaqueductal gray matter, including nucleus cuneiformis, the lateral reticular formation, and extending into the central tegmental area. In the rostral medulla, the lowest thresholds for inhibition of the TF were distributed mediolaterally across the dorsal one-third of the nucleus raphe magnus and into the adjacent nucleus reticularis gigantocellularis. Thresholds for inhibition of the TF reflex were slightly higher in the ventral nucleus raphe magnus and adjacent nucleus reticularis paragigantocellularis. Chronaxies of stimulation in the midbrain and medulla were virtually the same, indicating that the same neural elements were affected by stimulation in both brainstem areas. The thresholds of stimulation for inhibition of the TF reflex in the lightly anesthetized state were not significantly different from the thresholds of stimulation at the same midbrain sites in the awake state in the same animals. These findings contribute to a growing body of literature establishing (1) the utility of the lightly pentobarbital-anesthetized rat model for investigations of antinociceptive mechanisms and (2) the presence of multiple loci and pathways in the brainstem capable of modulating spinal nociceptive processes.

Relative contributions of the nucleus raphe magnus and adjacent medullary reticular formation to the inhibition by stimulation in the periaqueductal gray of a spinal nociceptive reflex in the pentobarbital-anesthetized rat

The organization in the brainstem of descending pathways of spinal inhibition was examined in the lightly pentobarbital-anesthetized rat. Thresholds for focal electrical stimulation-produced inhibition of the spinal nociceptive tail flick (TF) reflex were determined at one stimulation site in the midbrain periaqueductal gray and three sites in the rostral medulla: nucleus raphe magnus, and the adjacent medullary reticular formation contralateral and ipsilateral to the stimulating electrode in the periaqueductal gray. Lidocaine (0.5 microliter, 4%) was subsequently microinjected in the same and other medullary loci in the same coronal plane to produce a time-limited, reversible functional neural block. The functional block produced by 0.5 microliter of lidocaine microinjected in the medulla was determined to have a radius of 0.5 mm and was maximally efficacious during the first 30 min after its intramedullary microinjection. The stimulation threshold in the periaqueductal gray for inhibition of the TF reflex was not increased significantly when either the nucleus raphe magnus was fully blocked by lidocaine microinjected in three dorsoventral positions 1.0 mm apart or when the medullary reticular formation ipsilateral and contralateral were simultaneously fully blocked. Not until the nucleus raphe magnus and medullary reticular formation ipsilateral were simultaneously blocked by lidocaine was the stimulation threshold in the periaqueductal gray for inhibition of the TF reflex significantly increased. An increase in the periaqueductal gray stimulation threshold twice as great resulted when the nucleus raphe magnus and both the ipsilateral and contralateral medullary reticular formations were all simultaneously blocked by lidocaine. These results indicate that: (1) the nucleus raphe magnus is not a necessary bulbar relay in a descending antinociceptive pathway activated by stimulation in the midbrain periaqueductal gray; and (2) descending inhibitory pathways activated in the periaqueductal gray course medially as well as laterally in the rat ventral medulla.

Role of mesencephalic reticular formation in cholinergic-induced catalepsy and anticholinergic reversal of neuroleptic-induced catalepsy

The present experiments investigate the brain sites involved in the elicitation of catalepsy by cholinergic agonists and neuroleptics. Microinjection of acetylcholine chloride (50 micrograms) in combination with eserine (2.5 micrograms) into the ventral mesencephalic reticular formation (MRF) elicited catalepsy. Microinjection of atropine sulfate (5 micrograms) into the same sites reversed the catalepsy of rats treated with haloperidol (1.5 mg/kg) 2 h earlier, but did not reverse morphine-induced (30 mg/kg, 1 h) catalepsy. Haloperidol (25 micrograms) injected into the nucleus accumbens septi (NAS) resulted in catalepsy as severe as that caused by an identical injection into the caudate nucleus. Catalepsy caused by intraNAS haloperidol occurred with a shorter latency than that resulting from intracaudate haloperidol, and was reversed by systemic scopolamine (0.4 mg/kg). On the basis of these results it is suggested that the ventral MRF is a site for the elicitation of catalepsy by cholinergic agonists and for the reversal of neuroleptic-induced catalepsy by anticholinergics, and that neuroleptic-induced catalepsy involves blockade of dopamine receptors in both the NAS and caudate nucleus.

[Opioid mechanisms for modulating pain: descending pathways. Critical review]

This paper presents an extensive review of contributions on opiate controlled descending projections modulating analgesia. While there is a quite definite agreement on the organisation and structure of these projections, their true physiological role remains quite dubious. The hypothesis so far formulated on the modalities of activation of these circuits apparently don't hold a critical re-examination.

Experimental gaze palsies in monkeys and their relation to human pathology

Lesions were placed in the paramedian pontine reticular formation ( PPRF ) of monkeys and the resulting gaze palsies studied. Brainstem regions were identified by single cell recordings before kainic acid was injected to selectively destroy neuronal cell bodies in the vicinity. Unilateral PPRF lesions led to a loss of all rapid eye movements towards the ipsilateral side. Deficits were identical to those after experimental electrolytic lesions in monkeys, or structural lesions in humans. Bilateral PPRF lesions produced two different syndromes. Rostral PPRF lesions led to a selective loss of horizontal rapid eye movements leaving vertical movements intact. Caudal PPRF lesions led in addition to a severe disruption of vertical rapid eye movements.

The effect of experimental concussion on somatosensory evoked potentials

Cortical somatosensory evoked potentials (SEPs) were recorded following experimental acceleration concussion in the rat. Immediately after head injury there was a general reduction in the amplitude of the SEP, and all its components were either temporarily abolished or increased in latency. The early components of the SEP recovered much more rapidly than did the amplitude and latencies of the later potentials. The purpose of the study was to investigate the relative effects of concussion on the lemniscal system (whose activity is reflected by the discrete early components of the SEP) and the reticular activating system (whose activity is reflected by the diffuse high amplitude late component of the SEP). Contrary to a widely accepted theory, there was a delay in transmission of somatosensory information through the lemniscal pathways as well as through the reticular system following head injury. Such an observation is consistent with recent studies of SEPs recorded from humans comatose after head trauma. As the changes in the morphology of the waveform of the SEP following concussion can be simulated by simply recording evoked potentials at high rates of stimulation, this suggests that the delays are caused by a failure or malfunction of synaptic transmission, but the level at which this is occurring remains to be determined.

[Characteristics of memory and the functional organization of the hippocampo-reticulo-neocortical complex of the brain in the acute postoperative period]

In tests on dogs, rabbits and rats, it has been established that in acute postoperative period, the time of memorizing of conditioned signals (light, tone and metronome) is reduced, the time of realization of conditioned reactions increases, the excitability and the bloodflow of the midbrain reticular formation and Mg-AtPhase activity of pons Varolii raise. In the hippocampus the excitability and local bloodflow lower and the activity of Ca-Mg-ATPhase is enhanced. In the frontal cortex these processes do not change. Functional interrelations of the brain structures in the acute postoperative period are characterized by the weakening of the activating influence of the reticular formation on the frontal cortex and an increase of its suppressive action on the dorsal hippocampus. It is suggested, that the discovered damages in the higher nervous activity are stipulated by the changes in neurochemical organization of the brain.

Responses of thoracic spinothalamic and spinoreticular cells to coronary artery occlusion

Spinothalamic and spinoreticular neurons in the C8-T5 spinal segments were examined for responsiveness to occlusion of the left main, left circumflex (CX), or left anterior descending (LAD) coronary artery in monkeys and cats. Four types of cell response to occlusion were observed, as follows: 1) cell activity increased (6 responses) or decreased (1 response) to myocardial ischemia produced by the occlusion; 2) cell activity increased at the onset of occlusion, adapted, and then increased again as ischemia developed (6 responses); 3) cell activity increased at the onset or release of occlusion, and rapidly adapted (13 responses) or remained elevated throughout the occlusion (2 responses); and 4) no response to occlusion (14 tests). Among the types of responses to occlusion, both the magnitude of increased cell activity as well as the spontaneous discharge rates were similar. There were no differences in types of response according to coronary artery ligated. Fourteen cells were tested for responses to separate occlusions of the LAD and CX. Ten cells responded differently to the two occlusions, and four cells exhibited similar responses. C-fiber input onto a neuron was significantly related to whether a cell exhibited a response to cardiac ischemia. Since every cell with C-fiber input did not respond to ischemia, however, this input was not sufficient to predict whether a cell would respond to ischemia. All cells had somatic fields, and all cells responded to noxious stimulation of the somatic field. Some cells also received input from hair movement. The modality of the effective somatic stimulus was not related to type of response to coronary artery occlusion. Spinothalamic and spinoreticular neurons responded similarly to occlusion. Type of response was neither related to cell location in spinal cord nor to projection site in brain. We conclude that spinothalamic and spinoreticular neurons respond to coronary artery occlusion. Different neurons may receive input from different regions of the heart as well as from different types of visceral afferents, resulting in various responses to occlusion. The population of cells excited from ischemia of a given portion of myocardium may determine how the brain interprets the noxious information and refers pain to different somatic structures.

Alumina cream-induced focal motor seizures in cats. V. Unilateral lesions of the brain-stem reticular formation

The effect of unilateral mesencephalic (MRF) and pontine (PRF) lesions on EEG-EMG patterns of type B and C alumina cream induced focal motor seizures was studied on cats with chronically implanted electrode and cannula lesion systems. EEG patterns included number, amplitude and contralateral propagation of type B spikes and occurrence and duration of type C tonic-clonic discharges. EMG patterns included changes in muscular multiple unit activity (EMG-MUA) time locked to the onset of type B spikes and to the onset (tonic OTCD) and the end (clonic ETCD) of type C tonic-clonic EEG paroxysmal discharges. (1) MRF lesions ipsilateral to the cortical epileptogenic focus significantly increased number, amplitude and propagation of type B EEG spikes and the occurrence, but not the duration, of type C EEG tonic-clonic discharges. They also reduced amplitude of type B muscular jerks and blocked type C tonic contradversion with a significant decrease in EMG-MUA time locked to the onset of type B spikes and type C paroxysmal EEG discharges. (2) PRF lesions contralateral to the cortical epileptogenic focus produced an effect on muscular contractions of type B and C seizures similar to that produced by ipsilateral MRF lesions. PRF lesions, however, did not significantly change the EEG patterns of type B and C seizures. (3) Neither MRF lesions contralateral nor PRF lesions ipsilateral to the cortical epileptogenic focus produced significant changes on EEG and EMG patterns of types B and C epileptic seizures.

Effect of the oral administration of branched chain amino acids on hepatic encephalopathy in the rat

The aim of this study was to investigate the effect of oral administration of branched-chain amino acid (BCAA)-enriched diets after portacaval shunt (PCS) in rats. Fifty-one Sprague-Dawley male rats (200 gm) underwent PCS and 55 a sham operation. Half of the animals received BCAA 142 mg per day through a gastric tube; the other half underwent a sham procedure. Sleep disturbances were evaluated at 7, 14, and 28 days postoperatively by measurement of the excitability of the reticular brain-stem formation during the slow-wave sleep and paradoxical sleep. Animals were killed at the same intervals and liver/body weight ratio, plasma, and brain amino acids, brain norepinephrine, brain serotonin, 5-hydroxyindolacetic acid and histamine were measured. Each group of animals was matched with a similar group of sham-operated rats, i.e., receiving or not receiving BCAA. After PCS (as compared to sham-operated animals) a significant hyperexcitability of the reticular brain-stem formation was found during the slow-wave sleep. The liver/body weight ratio was significantly lower. Tryptophan (free tryptophan in the plasma), phenylalanine, tyrosine, and histidine increased in the plasma and the brain. Leucine and isoleucine were decreased in the plasma. After PCS, an initial decrease at 7 days postoperatively of brain norepinephrine and blockade of the intracerebral metabolism of tryptophan were observed. These changes were transient and progressively disappeared at 14 and 28 days postoperatively. Brain histamine remained at a very high level through the experiment. A good correlation was demonstrated between modification of the sleep disturbance and tryptophan (or 5- hydroxyindolacetic acid) and histamine brain levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct projection of pause neurons to nystagmus-related excitatory burst neurons in the cat pontine reticular formation

Brain-stem pause neurons (PNs) are inhibitory neurons which cease their tonic firing about 20 ms prior to the quick phase of horizontal vestibular nystagmus in either direction. One group of nystagmus-related burst neurons just rostral to the abducens nucleus exhibits a burst of spikes before and during the quick phase to the ipsilateral side--excitatory burst neurons (EBNs). The present study supported the conclusion that PNs project to, and tonically inhibit EBNs during the slow phase and that the burst of activity of EBNs at the quick phase is partly caused by the abrupt release from pauser inhibition. The evidence leading to this conclusion is: simultaneous recording of PNs and EBNs showed close alternation of firing; PNs were antidromically activated from the EBN region; systematic microstimulation tracks within the EBN region showed an antidromic activation pattern of low threshold sites separated by high threshold sites consistent with PN axonal branching in the EBN region; during the nystagmus slow phase there were positive field potentials in the EBN region, followed by an abrupt negative deflection whose onset was synchronous with the last pauser spike; when single PN spikes were used to trigger averages of extracellular field potentials in the EBN region (postspike averaging), a consistent short-latency positivity was observed. This study shows an additional connection in the premotor neural network responsible for the generation of the quick phase of horizontal vestibular nystagmus.

[An acute syndrome of opsoclonus and body tremulousness. A case report of benign encephalitis]

A 30-year-old woman was admitted to our hospital in May 1977, suffering from oscillation, body tremulousness and astasia-abasia. Two months prior to admission she had caught a common cold and felt paresthesia on the right arm. Three days before admission, she had photophobia, tremulousness of the trunk and head, and astasia-abasia. A neurological examination revealed difficulty in standing, and jerky movement of the body and right arm, her limbs were well coordinated. An ocular examination resulted in normal findings except for intermittent oscillation of the eyeballs. As the pupils and fundi were normal, so were the routine laboratory tests. The cerebrospinal fluid was clear and colorless under normal pressure, and showed no more than 6 mononuclear cells in any of the three examinations. CSF protein was registered 20 mg/dl, glucose 75 mg/dl, and no virus titers were elevated. Electroencephalogram was slightly abnormal due to a slowing of the Alpha wave in the background activity. Both computerized tomography and vertebral-angiography were normal. A slow and steady abatement of all symptoms started while she was taking steroid treatment in hospital. Electrooculogram showed irregular disconjugation of the eyes rotating or moving in horizontal and vertical direction. There movements conjugated or disconjugated in both eyes with 5-7 Hz of frequency and 10-20 degrees of amplitude. They decreased when the eyelids were closed or staying in a dark room. These ocular movements were regarded as opsoclonus. Then opsoclonus changed to flutter-like oscillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of ventral medullary lesions on systemic and microinjection morphine analgesia

The effects of electrolytic lesions of the nucleus raphe magnus (NRM), nucleus reticularis paragigantocellularis (PGC) and nucleus raphe alatus (NRA) on analgesia elicited in the rat from systemic morphine and morphine microinjection into the periaqueductal gray (PAG) were evaluated using the tail flick test. No consistent change in baseline pain sensitivity was observed following lesions of the NRM, PGC or NRA. To determine the effect of ventral medullary lesions on systemic morphine analgesia, pain sensitivity was assessed prior to and 40 min after 6 mg/kg morphine administration (i.p.) at 2 days preceding lesioning and 5, 12 and 19 days post-lesion. NRM and PGC lesions produced only slight reductions in analgesia at 5 days after surgery. It was observed that large NRM, large PGC, and NRA lesions significantly attenuated analgesia evaluated at 12 days post-lesion. Smaller lesions confined within the NRM or PGC were reliably less effective than the larger lesions in reducing analgesia. In a subsequent study, 5 micrograms morphine in 0.5 microliter saline was microinjected into the ventral PAG at the level of the dorsal raphe. Identical testing procedures were used and the analgesia was assessed at 2 days before lesioning and 5 and 12 days post-lesion. In contrast to the previous study, large NRM lesions abolished analgesia as early as 5 days following lesioning. Small NRM lesions were less effective and PGC lesions were generally ineffective in attenuating analgesia induced by morphine microinjection. We conclude that the NRA may act as a functional unit in the mediation of systemic morphine analgesia. In contrast, analgesia elicited from intracerebral (PAG) morphine microinjection is mediated via the NRM.

Neuropsychological concepts of somatoform disorders

Clinical descriptions of somatoform disorders tend to fall largely into the two main categories of conversion disorder and hypochondriasis. These disorders frequently occur in the context of other psychopathology and also tend to have a significant association with CNS disease. Evidence implicating alterations in brainstem reticular arousal and attentional mechanisms in the etiology of these disorders is reviewed. Relevant studies investigating cerebral asymmetry of function have tended to associate right hemisphere information processing style with the sensory, attentional and affective changes that characterize conversion disorders. It is suggested that brain research in the field of somatoform disorders look to the second somatosensory area (SII), which appears to be especially suited to the types of neurophysiological and neuropsychological dynamics that are generally presumed to underlie this class of maladies. Finally, it is argued that a biopsychosocial approach to the understanding of somatoform disorders requires the incorporation of neuropsychological data into a multidimensional conceptual framework.