Lecture 7 Nov 23 2018 PDF

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NEUROLOGICAL FOUNDATION A quick recap of the nervous system; A look into the neurological significance for a stress response

• Neuron: the basic anatomical unit of the nervous system is the neuron = smallest functional unit

Remember…

For clinicians: Neural Transmission is extremely important because it serves as the basis for electrophysiological events such as electromyography, electrocardiography, and electroencephalography. ECG: recording the electrical activity of the heart

postsynaptic • Neural transmission begins at the _____________ membranes of the dendrites

• Chemical or electrical processes are initiated, which cause the neuron to conduct the incoming signal through the dendrites and the cell body, down the axon, until it reaches the presynaptic membranes • Neurons do not touch one another – there exists a space postsynaptic cleft between neurones called the _________________

Neural transmission

• These are the key to crossing the synaptic cleft storage vesicules • They are present in __________________ in the axon

• The chemical compounds await the proper cues to migrate toward the presynaptic membrane • Once there, they are ultimately discharged into the synaptic cleft to stimulate (or inhibit) the postsynaptic membrane of the next neuron

Neurotransmitters

Examples of neurotransmitters: • Noradrenalin/Norepinephrine (NE): a major excitatory neurotransmitter • Serotonin (5-HT): found in the brain stem and the limbic system • Acetylcholine (Ach): neuromuscular junctions, preganglionic sympathetic and parasympathetic NS and postganglionic PSNS • Gamma amino butyric acid (GABA): a major inhibitory neurotransmitter • Dopamine (DA): mesolimbic system

The central nervous system (CNS)

The peripheral nervous system (PNS)

PNS: i. Sensory division: Sensory & visceral fibres ii. Motor division: i. Somatic ii. Autonomic: i. Sympathetic ii. Parasympathetic

Two fundamental neural systems

• Cortex • Limbic system

need for social stressors

• Brain stem • Spinal cord

link cns to pns

The CNS

• Consists of two parts: 1. Somatic/motor nervous system: sensory and motor signals to and from the CNS 2. Autonomic nervous system (ANS): concerned with the regulation of the body’s internal environment and the maintenance of homeostasis (____________)

The PNS

• Sympathetic nervous system (SNS): concerned with preparing the body action for _________ • Parasympathetic nervous system (PSNS): concerned with restorative functions and relaxation of the body

The ANS is subdivided into

Stressor event (Psychosocial Stimuli)

Physiological response

Target organ activation

Cognitive appraisal and integration

Neurological triggering (i.e. limbic nuclei, hypothalamic nuclei)

_______ behaviour

coping

The stress response

Psychosocial stressors

Biogenic stressors

what is the difference between a psychosocial stressor and a biogenic stressor

Stressor event

• Cognitive appraisal: refers to the process of cognitive interpretation; i.e. the meanings that are assigned to the world as it unfolds affective integration • _______________________: refers to the blending and colouring of felt emotion into the cognitive interpretation • The resultant cognitive-affective complex represents how the stressors are ultimately perceived

Cognitive- affective processes

• Anatomical epicenters are: • Locus coeruleus (noradrenalin dominated) in the pons/part of the brainstem • _________________ (emotional control center limbic system of the brain) consisting of numeral neural structures: the hypothalamus, hippocampus, septum, cingulate gyrus and amygdala always has something to do with emotion

Neurological triggering

• Neural axes: stress response via neural innervation of target organs • Neuroendocrine axis: flight-or-fight response endocrine • ___________ axis: most chronic aspects of the stress response, greater intensity to activate

3 Physiological pathways

• The sympathetic nervous system: generalized arousal within end organs – most common form of neural stress responsiveness – Noradrenalin is responsible fastest response • The parasympathetic nervous system: inhibition, slowing – Acetylcholine is responsible slows heart rate for ex, brings back to normal • The neuromuscular system: a prime target for immediate activation – BUT limited to ability to release neurotransmitter under chronically high stimulation – “fight or flight response axis” skeletal, helps u run away

Three neural axes

• Amygdala is the highest point of fight or flight origination • There is a downward flow of neural impulses to the hypothalamus. • Descend through the thoracic spinal cord • Innervating the adrenal gland – more specifically the adrenal medulla. • Resulting in a hormonal output of catecholamines noradrenalin adrenalin (______________, ___________)

Pivotal organs: Fight-or-flight response (Walter Cannon 1953)

Limbic System, Neocortex

important lol

Fight-orFlight Response Catecholamines Noradrenalin is secreted by not only the adrenal medulla but also the adrenergic neurons of the CNS/SNS

• The most chronic and prolonged response to stress events are the result of the endocrine axes (Mason, 1968) • Four main axes: 1. 2. 3. 4.

Adrenal cortical axis Somatotropic axis thyroid _________ axis Posterior pituitary axis

Endocrine axes

HORMONES OF STRESS Specific stress effects of some of the key hormones that are involved

Hypothalamus

• CRF (corticotropinreleasing factor)

Anterior pituitary

• ACTH (adrenocorticotropic hormone) • Endorphins • Glucocorticoids Adrenal cortex

(Cortisol, Corticosterone)

• Mineralocorticoids (Aldosterone)

Adrenal cortical axis

CRF- corticotropin releasing factor

HPAC Axis Catecholamine

Hypothalamus

• SRF (somatotropin releasing factor)

anterior _________ pituitary

• GH (growth hormone)

• Increase in free fatty Effect of GH acids and glucose in blood

Somatotropic axis

Hypothalamus

• TRF (thyrotropinreleasing factor)

Anterior pituitary

• TSH (thyroid stimulating hormone)

Thyroid gland

• T3 and T4

Result: increase in general metabolism, heart rate, heart contractility, peripheral vascular resistance and sensitivity of some tissues to catecholamines

Thyroid axis

Figure 29.4E shows control of thyroxine secretion from the anterior pituitary

• Receives neural impulses from the supraoptic nuclei of the hypothalamus • Releases hormones: • ADH (antidiuretic hormone) – leads to water retention • Oxytocin – role in stress response is unclear but may birth be involved in

Posterior pituitary axis

DISTRESS: DOES IT MATTER?

• Stress and distress are dissociable concepts, distinguished by an animal’s ability or inability to cope or adapt to changes in its immediate environment and experience. • Stress responses are normal reactions to environmental or internal perturbations and can be considered adaptive in nature. Distress occurs when stress is severe, prolonged, or both. • The concepts of stress and distress can be distinguished from that of welfare, in that an adaptive and beneficial stress response may occur against a backdrop of a transient negative emotional state.

Stress-Distress

Recognition and Alleviation of Distress in Laboratory Animals, 2008

Relationship of stress, distress, adaptive capacity, and animal welfare

Moberg, 1999

Distress depletes bodily reserves and affects normal functions

• Depends on stressor: duration & _________ intensity _______ • For example: • Short-term restraint – no marked problems in adaptation • Long-term restraint – distress sometimes expressed by vocalization and gastric ulcers (Ushijima et al., 1985)

The transition

Controllability

Predictability

Animals that can predict the onset of a stressful stimulus or control its duration, the behavioural and physiological impacts of stressor exposure are reduced (Mayer and Watkins, 2005)

Oesophago-gastric ulcers are welfare problem in pigs. Mild or severe ulceration was observed in 20.7% of pigs, of which 13% had scar tissue.

“Gastric ulceration is observed in horses in hard training – 86% of 345 selected racehorses (with performance problems in Begg and O’Sullivan, 2003), 93% of 30 high-level endurance horses during the competition season (Tamzali et al., 2011) , and in horses used for leisure riding (53% of 201 horses in Luthersson et al., 2009)”.

A survey on mortality in veal calves in Belgium, perforating abomasal ulcerations, accounted for 3 % mortality (Pardon et al. 2012).

Gastric ulcers in animals kept in human managed systems

ANIMAL WELFARE IMPLICATIONS

• The absence of pain, fear and hunger – that induce negative affective states • Enables biological functioning (e.g. normal growth, freedom from disease) – physically healthy • Enables experience of positive emotional states such as comfort • Enables species-specific behaviour

Good animal welfare See Duncan, 2005; Fraser et al., 2007

• Briefly: • • •

E.g. during handling, injection or exposure to a predator Affects welfare on a moment-to-moment emotional state Do not impair its adaptive capacity & do NOT cause distress

• Over longer term: • • •

E.g. kept in a barren environment or major homeostatic disruption Impair adaptive capacity Distressful and indicative of poor welfare

• However, onset of distress can be difficult to measure!

Poor animal welfare

• Regrouping unfamiliar & familiar piglets • Social isolation for some species (e.g. pigs, cattle) • Exposure to extremes of temperature • Failure to provide analgesics for pain • Over crowding • Maternal deprivation • Poor conditions during transport

Examples of poor welfare situations

• Species, gender and age-specific behaviour • Consider maternal environment, rearing and postnatal separation, housing • Unclear whether any or all abnormal behaviour qualify as indicators of distress • (abnormal behaviours could also calm down the animal & serve to avoid distress – see Mason,1991)

Assessment of Distress: Behaviour

• Should be examined in an undisturbed environment with gentle handling • Parameters to observe: • • • • • • •

Appearance Posture Behaviour Respiratory rate Body weight Temperature Dehydration, etc.

Clinical signs

• Glucocorticosteroids: • CAVE – venipuncture & handling, capture-stressful procedure • Can be assessed in hair, feces, saliva • The circadian rhythm is crucial for correct collection of samples

• Prolactin and oxytocin: • Increased during distress

• Growth hormone and luteinizing hormone: • Also released in response to other stimuli – suckling, circadian variations

Assessment of Distress: Endocrinological parameters

• Neurological parameters: neurotransmitter • Immunological parameters: relationship between stress, distress and the immune system is very complex

Assessment of Distress: Other parameters

• The animal’s choice to continue or stop feeding while in a stressful situation • Demand studies that titrate the extent of the animal’s attraction or aversion to a stressor • Complemented by physiological measures: elevated HPA axis, sympatho-adrenomedullary system activity, elevated hormone levels, increased activity in target organs (e.g. heart rate, blood pressure, glucose levels) • =multiple measures to obtain a comprehensive picture (Rushen 1991)

Useful indicators include

• A stress response per se is a normal response to internal or environmental disturbance and is adaptive • Distress occurs when stress is severe and/or prolonged • Stress and Distress are distinguished by an animal’s ability to cope or adapt to changes in its environment and experience

Summary: Stress response...