Mothers determine sexual preferences.
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Animals↗
Biomedical subjects
M R Hinton
Publications and source records attributed to M R Hinton.
Formation of olfactory memories mediated by nitric oxide.
Sheep learn to recognize the odours of their lambs within two hours of giving birth, and this learning involves synaptic changes within the olfactory bulb. Specifically, mitral cells become increasingly responsive to the learned odour, which stimulates release of both glutamate and GABA (gamma-aminobutyric acid) neurotransmitters from the reciprocal synapses between the excitatory mitral cells and inhibitory granule cells. Nitric oxide (NO) has been implicated in synaptic plasticity in other regions of the brain as a result of its modulation of cyclic GMP levels. Here we investigate the possible role of NO in olfactory learning. We find that the neuronal enzyme nitric oxide synthase (nNOS) is expressed in both mitral and granule cells, whereas the guanylyl cyclase subunits that are required for NO stimulation of cGMP formation are expressed only in mitral cells. Immediately after birth, glutamate levels rise, inducing formation of NO and cGMP, which potentiate glutamate release at the mitral-to-granule cell synapses. Inhibition of nNOS or guanylyl cyclase activity prevents both the potentiation of glutamate release and formation of the olfactory memory. The effects of nNOS inhibition can be reversed by infusion of NO into the olfactory bulb. Once memory has formed, however, inhibition of nNOS or guanylyl cyclase activity cannot impair either its recall or the neurochemical release evoked by the learned lamb odour. Nitric oxide therefore seems to act as a retrograde and/or intracellular messenger, being released from both mitral and granule cells to potentiate glutamate release from mitral cells by modulating cGMP concentrations. We propose that the resulting changes in the functional circuitry of the olfactory bulb underlie the formation of olfactory memories.
Animals↗
Microdialysis measurement of neurochemical changes in the mediobasal hypothalamus of ovariectomized ewes during oestrus.
Oestrus behaviour and the luteinizing hormone (LH) surge are induced in ovariectomized ewes by oestradiol (E2) after a period of progesterone priming with a low level of E2 (Pge2) and we have previously shown that these effects are primarily mediated through their action on the mediobasal hypothalamus (MBH). The aim of the present study was to assess what neurochemical changes in the MBH are induced by these steroids that might mediate their action on oestrus behaviour and LH release. Eight ovariectomized ewes were implanted with microdialysis probes in the MBH and submitted to three artificial cycles, so that they exhibited either both oestrus behaviour and an LH surge (Pge2 + E2), an LH surge alone (E2 alone) or neither oestrus behaviour nor an LH surge (Pge2 alone). Microdialysis and blood samples were collected every 30 min from 4 h before the end of Pge2 treatment until the end of oestrus. Behavioural tests with a ram were made to assess receptivity. Dopamine (DA) levels were found to increase significantly at the termination of Pge2 treatment after both Pge2 + E2 and Pge2 treatments. When the ewes received E2 after a Pge2 + low estradiol priming (Pge2 + E2), DA levels decreased 16 h later (4 h after E2) whereas they did not change after E2 or Pge2 alone. By contrast, serotonin (5HT) levels did not change significantly during the first 24 h but then increased when ewes received E2 alone and decreased when they were treated with Pge2 + E2. gamma-Aminobutyric acid (GABA) concentrations decreased significantly at the beginning of the sampling period after all treatments but this decrease lasted longer after Pge2 + E2 and was most pronounced at the beginning of receptivity. No significant long term effects of these steroid treatments were found on noradrenaline (NA), aspartate, glutamate, glycine and taurine levels. However, E2 administration was followed during the next few hours by a significant increase in glycine and to a smaller extent in glutamate and GABA. More importantly, when ewes were treated with Pge2 + E2, NA levels increased significantly following the behavioural interactions with a ram when the ewes were sexually receptive. In contrast to this, DA levels only increased during interactions with the ram when the ewes were not receptive. 5HT levels increased after tests where the ewe was either receptive or unreceptive to the male. GABA, aspartate and glycine levels increased in the sample just preceding the test and then decreased during it.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Effects of parturition and maternal experience on noradrenaline and acetylcholine release in the olfactory bulb of sheep.
Acetylcholine (ACh) and noradrenaline (NA) release in the olfactory bulb (OB) of ewes was monitored using microdialysis. Both ACh and NA release increased at parturition in multiparous but not in primiparous ewes. However, vaginocervical stimulation performed 6 hr postpartum induced an increase of ACh and NA release in both primiparous and multiparous ewes, indicating that a maturation process had occurred. Finally, pharmacological challenges to the ACh and NA inputs revealed differential responsiveness between nulliparous and multiparous nongestant ewes. These results suggest that the first parturition induces changes in neural circuitry involving ACh and NA inputs to the OB.
Acetylcholine↗
Oxytocin, amino acid and monoamine release in the region of the medial preoptic area and bed nucleus of the stria terminalis of the sheep during parturition and suckling.
Microdialysis sampling was used to measure the release of oxytocin (OXY) and monoamine and amino acid transmitters from the region of the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST) during parturition and suckling in sheep. Results showed that OXY and gamma-aminobutyric acid release increased in both the MPOA and BNST during parturition and suckling. Noradrenaline (NA) release increased in both structures during parturition but not during suckling. Dopamine (DA) release increased in the MPOA and decreased in the BNST during both parturition and suckling. Aspartate release increased in the MPOA during parturition, and the BNST during suckling, and glutamate release increased in the MPOA and BNST at parturition and only in the BNST during suckling. No changes in the release of serotonin or taurine occurred in these structures during parturition or suckling. In a further experiment on 6 estrogen-primed sheep, OXY (10 micrograms/ml) was infused into the MPOA via bilaterally placed microdialysis probes. This treatment inhibited rejection behavior towards lambs, but did not activate positive maternal responses. These OXY infusions also stimulated release of NA. These results show that complex patterns of neurochemical release occur in two closely related areas of the brain, the BNST and MPOA, during parturition when maternal behavior is stimulated. However, while these patterns of release are similar in the two structures, particularly at birth when maternal behavior is stimulated, they are not identical during labor contractions and suckling. The release of oxytocin within the MPOA during parturition may be important for stimulating a reduction in aggression towards lambs, although this action might be mediated via the effect of OXY on NA release.
Amino Acids↗
GABA release in the zona incerta of the sheep in response to the sight and ingestion of food and salt.
In order to establish which neurotransmitters may influence the activity of zona incerta neurones in the sheep which respond selectively to the sight or ingestion of food, we have measured the release of amino acid and monoamine neurotransmitters from this region using microdialysis sampling. Co-ordinates for the placement of microdialysis probes in regions of the zona incerta where cells respond to the sight or ingestion of food were first established by making single-unit extracellular recordings. When animals were food-deprived results showed that release of gamma-aminobutyric acid (GABA) was increased in response to the sight and ingestion of food but not of aspartate, glutamate, taurine, noradrenaline, dopamine or serotonin. This release of GABA was absent when the animals were shown non-food objects or saw or ingested salt solutions. When the same animals were physiologically sodium-depleted GABA release was evoked by the sight and ingestion of salt solutions and release following the sight and ingestion of food was significantly reduced. These results provide further evidence that GABA is an important neurotransmitter in neural circuits controlling the regulation of food intake.
Analysis of Variance↗
Cerebrospinal fluid and plasma concentrations of oxytocin and vasopressin during parturition and vaginocervical stimulation in the sheep.
Simultaneous blood and cerebrospinal fluid (CSF) samples were taken from conscious sheep before, during and after parturition. Concentrations of plasma and CSF oxytocin were significantly elevated during contractions and particularly at birth. Mean prepartum CSF concentrations of oxytocin were around 55% of those found in plasma but postpartum they were up to 2-fold higher than those in plasma. Plasma concentrations of oxytocin were only significantly elevated, compared to prepartum levels, for 15 min postpartum whereas those in CSF were increased for the whole of the 120 min postpartum sampling period. Plasma, but not CSF, concentrations of arginine-vasopressin (AVP) were significantly raised during contractions and birth, and for 15 min postpartum. During the prepartum period CSF AVP concentrations were 67% of those found in plasma whereas at birth plasma levels were 10-fold higher than in CSF. In a separate experiment it was shown that 5 min of mechanical vaginocervical stimulation also stimulated significant increases in CSF and plasma oxytocin concentrations and in plasma vasopressin. Results support previous work suggesting an important role for central oxytocin release in the postpartum induction of maternal behavior and demonstrate that elevated concentrations of oxytocin in the CSF are present for a greater period than in blood. Elevated plasma AVP concentrations during contractions, birth or vaginocervical stimulation may be stimulated by stress associated with these stimuli.
Animals↗
Controlled formaldehyde fumigation system.
A comparative study of formaldehyde (HCHO) fumigation was carried out by controlled vaporization, using an electric vapor generator, and by the Formalin-permanganate method. Determination of vapor levels as well as bactericidal action showed the generator to be more effective. Maximum achievable fumigant levels were temperature dependent and related to the equilibrium vapor concentration of HCHO. At a room temperature of 21 degrees C, vaporization of more than 2,000 micrograms of HCHO per liter resulted in conversion of HCHO to paraformaldehyde, which condensed on surfaces and contributed to prolonged residual vapor levels. An electronic monitor is described which is capable of detecting HCHO levels as low as 10 microgram/liter and can be used to monitor the complete fumigation process.
Bacillus subtilis↗
Plasma fractionation in Australia.
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Australia↗