Central antiaversive and antinociceptive effects of anterior pretectal nucleus stimulation: attenuation of autonomic and aversive effects of medial hypothalamic stimulation

Previous studies have shown that stimulation of the rat anterior pretectal nucleus (APtN) strongly depresses a spinal reflex to noxious heat without causing significant aversion or depression of other motor responses. It is not known if APtN stimulation can similarly reduce the aversiveness of electrical stimulation of the brain, nor is it known if APtN stimulation is itself rewarding or aversive. This study used a simple switch-off paradigm to examine the rewarding properties of APtN stimulation at different sites throughout the nucleus and also used the tail-flick test to determine if the stimulation produced antinociception. The effects of APtN stimulation on the behavioural and autonomic responses to electrical stimulation of the medial hypothalamus (MH) and the nucleus raphe magnus (NRM) were also examined. The results show that electrical stimulation of dorsal APtN was rewarding and also caused antinociception which lasted for 50 min. However, sites which gave the strongest reward were not necessarily those which gave the greatest antinociception, as these effects were not correlated. Electrical stimulation of ventral APtN induced only aversive effects. The aversive and autonomic effects of MH stimulation were significantly reduced by conditioning stimulation of dorsal APtN. However, the very similar escape and autonomic effects of NRM stimulation were unaffected by APtN stimulation. These results suggest that electrical stimulation of the dorsal parts of the APtN has positive rewarding properties as well as the well-known antinociceptive effects. The antiaversive effects of dorsal APtN stimulation may be due in part to the inhibition of central substrates of aversion as well as inhibition of sensory neurones.

The antinociceptive effects of anterior pretectal stimulation in tests using thermal, mechanical and chemical noxious stimuli

Four behavioural tests have been used to study the antinociceptive effects of electrical stimulation of the anterior pretectal nucleus (APtN) in the rat. The antinociceptive effects of stimulating this nucleus, which lies dorsally in the posterior diencephalon, have recently been studied extensively but always using briefly applied heat stimuli. It is reported here that APtN stimulation effectively inhibited responses to briefly applied noxious pressure and longer-lasting noxious chemical (formalin) stimuli. Although the tail-flick reflex to noxious heat was very potently depressed by APtN stimulation, responses to noxious heat in the hot-plate test were not. Three doses of morphine were also studied with each test and it was concluded that 15 sec of 35 microA r.m.s. current into the APtN was as effective as 3-5 mg/kg morphine s.c. in the rat.

Gastric enterochromaffin-like (ECL) cells in hypergastrinaemic duodenal ulcer disease

Patients with hypergastrinaemic duodenal ulcer disease were studied to determine whether chronic moderate hypergastrinaemia produces hyperplasia of gastric enterochromaffin-like cells in man. Eight patients had peak postprandial plasma gastrin concentrations greater than 200 pmol/l, which is the 92nd percentile for patients with duodenal ulcer disease in this laboratory. The control group was eight patients with duodenal ulcers whose peak postprandial gastrin concentrations were less than 200 pmol/l. Basal and peak postprandial plasma gastrin concentrations were 107 (37) and 306 (66) pmol/l (mean (SEM] respectively in the hypergastrinaemic patients compared with 26 (4) and 137 (14) pmol/l respectively in the controls. There was no significant difference in the density of gastrin enterochromaffin-like cells between the two groups. The number of enterochromaffin-like cells per high power field was 53 (8) in the hypergastrinaemic patients compared with 50 (8) in the controls. We conclude that chronic moderate hypergastrinaemia does not produce hyperplasia of enterochromaffin-like cells in man. Our hypergastrinaemic group had plasma gastrin concentrations similar to, or greater than those reported during treatment with drugs such as omeprazole and histamine H2 receptor blockers.

Activation of cells in the anterior pretectal nucleus by dorsal column stimulation in the rat

1. The responses of neurones in the anterior pretectal nucleus (APTN) to electrical stimulation of the dorsal columns at twice the threshold for A fibres were studied in the rat anaesthetized with urethane. 2. APTN cells were excited by dorsal column stimulation. Forty-six discharged phasically in response to a single stimulus. Sixteen cells did not respond phasically but slowly increased the discharge rate with repeated stimulation. 3. Electrical stimulation of the contralateral gracile fasciculus caused neurones in the APTN to discharge with a variable latency of 2-22 ms. Stimulations of the ipsilateral gracile and contralateral cuneate fasciculi had weaker effects. 4. Microinjection of DL-homocysteic acid into the contralateral gracile nucleus increased the discharge rate of APTN neurones. Microinjection of gamma-aminobutyric acid into the contralateral gracile nucleus blocked the gracile fasciculus evoked excitation of APTN neurones. 5. On thirteen occasions cells in the gracile nucleus were driven antidromically by electrical stimulation of the APTN. 6. It is concluded that electrical stimulation of the gracile fasciculus activates a monosynaptic excitatory input to the APTN.

Antinociceptive effects of dorsal column stimulation in the rat: involvement of the anterior pretectal nucleus

1. The effects of stimulating A fibres in the dorsal columns on the responses of dorsal horn neurones to intense cutaneous stimuli were studied in the rat anaesthetized with urethane. 2. Multireceptive cells deep in the lumbar dorsal horn were excited for 5-10 ms by dorsal column stimulation and subsequently responses to noxiously hot water placed on the cutaneous receptive field were reduced for the following 4-5 min. Seven of the cells studied projected to the brain via the contralateral anterolateral funiculus. 3. If the discharge of the multireceptive neurones was raised by ionophoretic application of DL-homocysteic acid, a brief period of inhibition lasting for 100-150 ms was seen following a single stimulus to the dorsal columns. Studies were conducted to determine if this brief inhibition could account for the long-lasting inhibition of responses to high-threshold stimuli. 4. Dorsal columns were transected at cervical levels. Stimulation caudal to the transection evoked only the brief excitation and subsequent inhibition for 100-150 ms. No long-lasting inhibition of high-threshold cutaneous afferent input was seen. 5. Stimulation of the dorsal columns rostral to transection did not evoke the brief excitation or inhibition of multireceptive dorsal horn neurones. However, the 4-5 min inhibition of responses to high-threshold cutaneous stimuli was present. 6. The long-lasting inhibition of responses to high-threshold stimuli by dorsal column stimulation was blocked by microinjection of gamma-aminobutyric acid into the anterior pretectal nucleus (APTN) but not by microinjections into adjacent areas of the brain. 7. Ipsilateral lesions of the dorsolateral funiculus at the cervical level also blocked the long-lasting inhibitory effects of dorsal column stimulation. 8. It is concluded that the brief excitation and inhibition of multireceptive dorsal horn neurones is due to antidromic action potentials passing caudally in the dorsal columns to activate spinal segmental mechanisms. The longer-lasting inhibition of responses to high-threshold cutaneous stimuli is due to action potentials ascending in the dorsal columns to activate cells in the APTN which in turn activate a descending inhibition mediated by the dorsolateral funiculus.

Afferent projections to the rostral anterior pretectal nucleus of the rat: a possible role in the processing of noxious stimuli

The afferent inputs to the rostral pole of the anterior pretectal nucleus have been examined by utilizing the retrograde axonal transport of a fluorescent dye, Fast Blue. After unilateral injection of the dye into the rostral anterior prectectal nucleus, large numbers of labelled neuronal somata were found in the somatosensory cortex, the ventrolateral geniculate nucleus, the zona incerta, the superior colliculus, the deep mesencephalic nuclei, the pedunculopontine tegmental nucleus and the medial vestibular nucleus. In addition, the contralateral parabigeminal nucleus provided a major input to the rostral part of the anterior pretectal nucleus. Smaller and sparser collections of stained cell bodies could be found in the ventromedial hypothalamus, the posterior pretectal nucleus, the nucleus of the posterior commissure, the peripeduncular nucleus, the periaqueductal central gray, the contralateral anterior pretectal nucleus, and the locus coeruleus. Many of the inputs originated in areas associated with nociceptive pathways. The regional distribution of neurons projecting to the rostral pole of the anterior pretectal nucleus differs substantially from that of the cells innervating the anterior pretectal nucleus proper, i.e. its more caudal parts. It is concluded from this that the rostral pole constitutes a separate nucleus, anatomically distinct from the rest of the anterior pretectal nucleus and other cell groups in the pretectal complex. The demonstration that many of the afferents to the rostral anterior pretectal nucleus arise in regions involved in nociception supports recent electrophysiological and behavioural evidence that this brain area plays a role in the processing of noxious stimuli, rather than as a component in the pretectal control of visual system reflexes.

The effects of intraperitoneal administration of antagonists and development of morphine tolerance on the antinociception induced by stimulating the anterior pretectal nucleus of the rat

1 The effects of intraperitoneal administration of antagonists to morphine, 5-hydroxytryptamine (5-HT), noradrenaline and dopamine have been studied on the antinociceptive effects of electrical stimulation of the anterior pretectal nucleus (APtN) of the rat. 2 A 15 s period of 35 microA sine wave stimulation of APtN significantly increased the latency of the tail flick reflex to noxious heat for periods up to 1 h. 3 Naloxone (0.25-1.0 mg kg-1) attenuated the effects of APtN stimulation in a dose-dependent manner. In rats made tolerant to morphine by daily administration of morphine, the antinociceptive effects of APtN stimulation were significantly reduced. 4 The 5-HT receptor antagonists methysergide (5 mg kg-1) and ketanserin (1 mg kg-1), the dopamine receptor antagonist haloperidol (1 mg kg-1) and the beta-adrenoceptor antagonist propranolol (1 mg kg-1) had little effect on the antinociceptive effects of stimulating the APtN. 5 alpha-Adrenoceptor antagonists caused a dose-dependent antagonism of the response. The order of potency was; idazoxan greater than prazosin greater than phenoxybenzamine, the respective ED50 for each drug being 0.08: 0.45: 1.5 mg kg-1. 6 It is concluded that antagonism at opioid receptors and alpha-adrenoceptors but not beta-adrenoceptors, dopamine or 5-HT receptors reduces the antinociceptive effects of APtN stimulation. This differs from the reported effects of these antagonists on the antinociception caused by stimulating other sites in the brain.

Anterior pretectal stimulation alters the responses of spinal dorsal horn neurones to cutaneous stimulation in the rat

1. The behavioural effects of stimulating sites in the anterior pretectal nucleus (a.p.t.n.) were studied in unanaesthetized rats; 1-2 weeks later these rats were anaesthetized with Fluothane and the effects of similar electrical stimulation determined on the responses of spinal neurones to cutaneous stimuli. 2. Stimulation of the a.p.t.n. for 15 s with 35 microA r.m.s. sine-wave current inhibited the tail-flick response to noxious heat of unanaesthetized animals for up to 1 h. 3. Stimulation of the same sites in anaesthetized rats inhibited the responses to noxious heat of forty-two multireceptive and two high-threshold neurones located deep in the spinal dorsal horn. 4. The high-threshold responses of seven cells were unaffected or slightly potentiated by pretectal stimulation. These seven cells were all recorded from the dorsal margin of the dorsal horn, were not multireceptive neurones and could be made to discharge only by water above 50 degrees C. 5. The responses of twelve multireceptive cells to low-threshold stimulation were not affected by pretectal stimulation. All these cells were recorded from deep within the dorsal horn. 6. On ten occasions, cells deep in the dorsal horn were identified as projection neurones which were driven antidromically by high-frequency (300 Hz) stimulation of the contralateral anterolateral tract at cervical levels. The high-threshold responses of all these cells were reduced by pretectal stimulation. No cells were driven antidromically by pretectal stimulation. 7. Ipsilateral lesions of the dorsolateral funiculus abolished the inhibitory effects of prectectal stimulation. Lesions of the dorsal columns were without effect. 8. It is concluded that stimulation of the a.p.t.n. inhibits the tail-flick reflex of unanaesthetized rats and inhibits the high-threshold discharge of deep dorsal horn cells to cutaneous stimuli in anaesthetized rats. Cells recorded from the dorsal margin of the dorsal horn are not affected. The inhibition is mediated via the dorsolateral funiculus and affects cells which project rostrally in the contralateral anterolateral funiculus.

Recombination and genome size

Within complements the chiasma frequency per chromosome, which directly reflects the amount of recombination, is generally closely correlated with chromosome length, i.e. the chromosomal DNA content. The correlation does not apply when comparisons are made between the complements of different species. Analyses of results from three Angiosperm genera show a progressive decrease in the chiasma frequency per picogram of DNA with increase in nuclear DNA amount.

Indium 111-granulocyte scanning in the assessment of disease extent and disease activity in inflammatory bowel disease. A comparison with colonoscopy, histology, and fecal indium 111-granulocyte excretion

Indium 111-leukocyte scanning has recently been introduced as a new method for imaging inflammatory bowel disease. The technique has recently been made more specific for acute inflammation by labeling a pure granulocyte fraction rather than the conventional mixed leukocyte preparation. We now report a prospective study comparing 111In-granulocyte scanning with endoscopy, histology, and fecal 111In-granulocyte excretion for the assessment of disease extent and severity in colonic inflammatory bowel disease. In 52 patients with Crohn's disease or ulcerative colitis, disease extent and severity were assessed macroscopically, histologically, or by scanning using a numerical grading system. Excellent correlations were found between both endoscopy and histology and 111In scans [r = 0.90 (endoscopy) and r = 0.90 (histology) for extent; r = 0.86 and r = 0.91 for disease activity]. Severity graded by scanning also showed a close correlation with fecal 111In-granulocyte excretion (r = 0.90). Indium 111-granulocyte scans are a rapid, accurate, noninvasive means of assessing both disease extent and severity of colonic involvement in inflammatory bowel disease.

The antinociceptive effects of stimulating the pretectal nucleus of the rat

Changes in the tail-flick latency to noxious heat were studied following electrical stimulation of the dorso-medial thalamus of the rat. Brief (15 sec), low intensity (35 microA) stimulation of the anterior pretectal nucleus caused no escape behavior or motor deficits but increased tail-flick latency for more than 45 min. Responses to non-noxious stimuli were enhanced but the animals were not hyperactive. The anterior pretectal nucleus does not receive retinal or accessory visual inputs like other parts of the pretectal complex but is known to receive axons from somatosensory cortex and project to the perirubral mesencephalic reticular formation and the periaqueductal gray (PAG). The antinociceptive effects of anterior pretectal stimulation were much longer lasting than those of PAG, less disrupting to motor performance and the stimulation was not aversive.

Iron deficiency anaemia, gastritis and antral vascular malformation

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111Indium autologous granulocytes in the detection of inflammatory bowel disease

Indium leucocyte scanning and measurement of faecal Indium leucocyte excretion are techniques which have recently been introduced for assessing patients with inflammatory bowel disease. The methodology has recently been made more specific for acute inflammation by labelling pure granulocytes rather than the mixed leucocyte preparation. To determine the accuracy of this modified technique in detecting inflammatory bowel disease, we have prospectively compared Indium granulocyte scanning and faecal In granulocyte excretion with rectal histology and contrast bowel radiology as screening procedures in 100 patients with suspected inflammatory bowel disease. Thirty three patients were shown to have inflammatory bowel disease - 24 with Crohn's disease and nine with ulcerative colitis or indeterminate colitis. Overall the respective sensitivities for detecting inflammatory bowel disease were 97% for faecal Indium granulocyte excretion, 94% for Indium granulocyte scanning, 79% for radiology and 70% for rectal histology. The superiority of In granulocytes over radiology and rectal histology in detecting inflammatory bowel disease was, in the main, due to the difficulty in diagnosing Crohn's with conventional techniques. Although three of the patients with ulcerative colitis and indeterminate colitis had normal sigmoidoscopic appearances - all had abnormal rectal histology. No patient with a non-inflammatory bowel disorder had a positive In granulocyte scan or a raised faecal excretion. These results show that investigations using In granulocytes are accurate in identifying inflammatory bowel disease and offer important advantages over conventional procedures for detecting Crohn's disease.

Chromosome size variation during pollen grain development in Scilla sibirica

The first pollen grain mitosis in Scilla sibirica takes place within three weeks after the completion of meiosis. Within one anther the duration of the first pollen grain mitotic cycle varies substantially. The duration of the mitotic cycle affects the length of chromosomes at metaphase of the first pollen grain mitosis. In grains which divide "early" the chromosomes at metaphase are longer, up to twice the length, of the chromosomes in grains dividing "late". The diminution in length with increase in the mitotic cycle is due to more intensive coiling which, in turn, is explained by a lengthening of G2 and of prophase. The relationship between the duration of the mitotic cycle and chromosome length at metaphase would account, at least largely, for the variation in chromosome length between different tissues within organisms. It explains also why the chromosome at metaphase of mitosis are shorter in polyploids than in their diploid ancestors.

Quantitative DNA variation and chromosome homology

In many genera, of both plants and animals, divergence and speciation is often accompanied by massive changes in the amount of nuclear DNA. These changes, in turn, result from amplification or repetition of base sequences within the chromosomal DNA. The chromosomes of different species are consequently of different size and structure. Observations in hybrids between species differing in nuclear DNA amount show that, despite large differences in DNA content, homoeologous chromosomes pair effectively at pachytene and form chiasmata. Only when the DNA differences are very large, of the order of 60% or more, is pairing at pachytene and chiasma formation impaired. The conclusion is that large scale chromosome structural change due to the repetition of DNA base sequences has surprisingly little effect upon the homology of chromosomes, i.e. their ability to pair effectively and form chiasmata at meiosis. Similar repetitive sequences are frequently distributed widely among non-homologous chromosomes within complements. The question then arises as to what prevents chiasma formation between the non-homologous chromosomes which have in common DNA segments of similar sequences? Evidence is presented which indicates that prevention is under the control of the genotype. The control is effected in one of two ways, either by the suppression of pairing at zygotene or pachytene or by suppression of chiasma formation subsequent to pairing.

Constraints upon the composition of supplementary DNA

Speciation in eukaryotes is often accompanied by massive changes in nuclear DNA amount resulting from the accumulation or deletion of DNA base sequences within chromosomes. Our evidence shows that, among related species, the DNA lost or gained during divergence is of a remarkably consistent and restricted composition in respect of the ratio of repetitive to non-repetitive base sequences. It is argued that the restriction may in part at least be imposed by natural selection, in the sense that the only changes tolerable are confined to DNA fractions of particular composition and organisation.