Quantitative microchemical changes reflecting functional activity in supraoptic nerve cells of the rat

1. Neurones and nuclei, isolated from the supraoptic regions of the rat's hypothalamus, have been examined by phase contrast and interference microscopy and by ultraviolet absorption microspectrography, in a quantitative study of their metabolic response to stimulation. 2. Vhen isolated from rats dehydrated for up to five days, fresh supraoptic nuclei were larger and more likely to contain marginated nucleoli. The dry mass of fixed nuclei did not change. The mean dry mass and nucleic acid content of supra¬ optic nucleoli and cell bodies increased significantly with progressive osmotic stimulation. Nucleolar changes preceded those in the cell body by 24 to 48 hours. 3. The significance of these changes is discussed in relation to published data concerning neuronal responses to injury and prolonged stimulation. 4. The distribution of dry mass among supraoptic nucleol may be bimodal after moderate osmotic stress, but the presence of two populations of neurones within the supraoptic nucleus could not be confirmed. 5. The increases in dry mass and nucleic acid content of supraoptic nucleoli and cell bodies were both greater and faster during five days dehydration at a raised environmental temperature (24°C). Thus the metabolic response can be graded according to the functional load placed on the neurone. 6. Neurohypophyses which have been partially depleted of their "stores" of neurohormone contained some factor which, when injected into the lateral cerebral ventricle of normal rats, resulted in an increase in the mean dry mass and nucleic acid content of supraoptic nucleoli. These nucleolar changes seemed independent of neurohormone secretion or serum osmolality in the recipient animals. 7. Extracts of normal ("non-depleted") neurohypophyses significantly inhibited the dry mass response of supraoptic nucleoli to osmotic stress. 8. "Hormone-depleted" posterior lobe extracts did not alter the mean dry mass or nucleic acid content of nucleoli from the posterior part of the arcuate nucleus. 9. Extracts of tissue from the parietal cortex had no demonstrable effect on supraoptic nucleoli. 10. The possibility is discussed that "active" substances derived from the neurohypophysis may serve to match synthetic activity to secretory losses in supraoptic neurones. 11. The mean dry mass of pituicytes increases rapidly during the first 48 hours of dehydration. This response is as fast as any supraoptic changes detected in this investigation

The role of melatonin and the pineal gland in the photoperiodic control of reproduction and smoltification in Salmonid fish

The timing of seasonal events in salmonids is thought to be controlled by endogenous circannual rhythm(s) which are entrained by the seasonally-changing daylength. This thesis investigates the role of the pineal gland in the perception of the photoperiodic zeitgeber and the subsequent transmission of this information to the brain through neural or hormonal pathways. Melatonin biosynthesis by isolated rainbow trout pineal glands was shown to exhibit a differential response to graded photic or thermal stimuli. In vitro experiments were carried out at 10±0.50 C as this provided optimum melatonin levels for radioimmunoassay analysis together with a pineal longevity of up to 14 days. By incorporating a variety of light intensities into the light/dark cycle, the salmonid pineal gland was shown to synthesise significantly different levels of melatonin even when light levels varied by only 0.5 lux. Early work on the salmonid pineal suggested it was unresponsive to red light, having a spectral sensitivity which peaks between 500 and 550 nm, this study has revealed that the pineal is also capable of responding to wavelengths between 660 to 800 nm, at which pineal reception was previously thought to be severely limited. No endogenous rhythm of melatonin secretion was observed within the isolated rainbow' trout pineal gland. Both Atlantic salmon and Atlantic halibut pineals exhibited elevated levels- of melatonin in response to the dark phase, however, they also appeared capable of maintaining this rhythm in the absence of external stimuli. This provides the first evidence that the daily rhythm of melatonin production in these species is controlled by an endogenous circadian oscillator located within the pineal II gland. The pinealectomy technique developed during the course of this thesis successfully abolished the diel rhythm of melatonin secretion and, together with an enucleation procedure, enabled the pineal to be identified as the predominant source of the dark phase melatonin in Atlantic salmon and rainbow trout. However, the lateral eyes did contribute significantly to plasma melatonin levels in both species. Long term experiments, involving pinealectomy and/or implantation of melatonin, were used to investigate the role of the pineal gland in the timing of rainbow trout maturation and smoltification in Atlantic salmon. Pineal removal at the summer or winter solstices did not significantly alter the timing of smoltification. However, significantly higher blood serum osmolarities following seawater challenge tests were observed in smolts implanted with melatonin. This, together with a significant growth increase shown by salmon parr within 1 month of implantation, indicates that melatonin may directly affect the development of salmonids through either a physiological response or by influencing the entrainment of endogenous rhythms. The increased growth observed in the implanted parr is also thought to be responsible for the unimodal population distribution and high percentage of S1 smolts within this group. Investigations into the role of the pineal gland in the timing of spawning in rainbow trout found that pineal removal at the summer solstice caused a 6 week delay in spawning time compared to intact fish. However, no clear effects on spawning time were observed when pineal removal, with or without melatonin implantation, was performed to coincide with the change from long to short daylengths which is known to advance spawning times. Although no significant effect in spawning times was observed between groups, the 4 month spawning period of the pinealectomised group compared to 1 month in the shampinealectomised fish also suggested that pineal removal may have caused a desynchronisation in spawning time. Pinealectomy and/or implantation did not alter egg size or fecundity, but plasma calcium levels were shown to be significantly lower in the pinealectomised trout over the spawning period. To summarise, the pineal gland and melatonin play a significant role in salmonid development. It is suggested that melatonin can influence biological systems through a direct physiological action while the pineal gland may synchronise . circannual events through the photoneuroendocrine transduction of seasonal environmental information

Some electrophysiological and biochemical effects of denervation on the central nervous system of the cockroach, Periplaneta Americana L.

The effect of denervation on the excitability of cockroach central neurones has been investigated using both extracellular and Intracellular recording techniques. Stimulation of the anterior connectives produced a response in the flexor tibiae muscle 143b of the metathoracic segment. This muscle response could be correlated with action potentials in the anterior connective and fifth nerve trunk innervating the leg. The ganglionic delay for this pathway was 1,42 +/- 0.07 ms (n=6) suggesting the presence of a single synapse. This was reduced to 0.86 +/- 0.10 ms (n=10) 19-96 hours after cutting the contralateral fifth nerve trunk. It is suggested that this reduction in ganglionic delay could result from an increase in the excitability of the postsynatpic cell caused by differentiation. Intracellular recording were made from the cell body of the fast coxal depressor motoneurone (Df) in the me metathoracic ganglion. Acetylcholine (ACh) applied to the soma either topically or by iontophoresis caused dopolarisation of the cell membrane and if repeated in large doses resulted in rapid desensitisation and depression of the response. Some Df motoneurones were axotomised by cutting the ipsilateral fifth nerve trunk 4-118 days before the experiment. The sensitivity to ACh increased approximately three fold following axotomy. However there was no change in the mean resting potential, input resistance or membrane time constant. The change in sensitivity to ACh produced by axotomy was apparently not a result of a redistribution of cholinoceptors on the soma membrane since the rise Lime of the ACh responses were similar in control and axotomised preparations. Analysis also showed that there was no difference between control and axotomised cells in the number of ACh molecules needed to combine with individual cholinoceptors to produce a response. Similarly there was no significant difference in the mean values of the ACh reversal potential in control and axotomised neurones (as determined by extrapolation). It is suggested that the supersensitivity to ACh is due to a decreased inactivation of ACh by acetylcholinesterase since (i) the anticholinesterases physostigmine and neostigmine produced a greater potentiation of the ACh response in normal than in axotomised neurones and (ii) there was no significant difference in the sensitivity of control and axotomised cells to carbamylcholine. This suggestion is supported by the results obtained from a biochemical study in which the cholinesterase activity of normal and denervated metathoracic ganglia was determined. Denervation was produced by transection of both fifth nerve trunks 5-8 days before the assay. Denervated ganglia showed an approximately 33% reduction in their capacity to hydrolyse AThCh

Senescence

The book "Senescence" is aimed to describe all the phenomena related to aging and senescence of all forms of life on Earth, i.e. plants, animals and the human beings. The book contains 36 carefully reviewed chapters written by different authors, aiming to describe the aging and senescent changes of living creatures, i.e. plants and animals