Behavioral Neuroscience Summers

Leech Shortening Sensory Stimulation of Shortening S&R Sensitization

Glu 5-HT Leech figures Shortening Neurocircuitry end     Acronyms/Abbreviations

Sensitization - Leech
I. Leeches 			back to  Syllabus

	A. Hirudinea  
	
		1. a subclass of the segmented worms (phylum Annelida)
		
			a. related to earthworms and polychaete worms
			
			b. Adult leeches weigh 2-3 g 
		
			c. segments confer functional advantage
			
				i. potent substrates for evolutionary adaptation
				
				ii. fixed number: most species = 32 segments
	
		2.  5 groups (orders)
					
			a. Rhynchobdellida - leeches with a proboscis 
			
				i. proboscis = protrusible and retractile anterior intestine
			
			Arhynchobdellida
			b. Gnathobdellida - jawed with strong cuticular teeth
			
				i. Hirudo medicinalis
			
			c. Pharyngobdellida - lack both proboscis and jaws
			
				i. "worm leeches"
			
			d. Acanthobdellida (retained chaetae or small bristles for locomotion)
			
				i. true leeches lack bristles or hairs
				
				ii. 29 segments
			
			e. Branchiobdellida - leech-like appearance (oligochaeta)
	
	B. Distribution is worldwide (except for Antarctica)
	
		1. Aquatic Ecosystems
		
			a. Marine
			
			b. Estuarine 
			
			b. Freshwater
			
				i. lentic - ponds, lakes
				
				ii. lotic - streams and rivers
				
					(1) even in mountains in Nepal
			
		2. Moist Terrestrial ecosystems
		
			a. Australia, SE Asia
			
		3. often found on the underside of rocks, vegetation, logs, 
		   and other submerged substrates
	
	
	C. Carnivorous - Entirely
	
		1. Feed on both vertebrate and invertebrate animals
		
		2. Predacious leeches are benthic (bottom) and camouflaged
		
			a. sit and wait predators
			
			b. feed on invertebrates
			
				i. gnats, mosquitos, blood worms, amphipods, snails
			
			c. some species actively seek prey
			
				i. using chemo- and mechanoreception
					
		2. Sanguivorous leeches feed on vertebrate blood
		
			a. fish, amphibians, reptiles, water birds, and mammals (including humans)
			
				i. ingest 5-10 ml of blood in one feeding
			
			b. occasionally pelagic (water column)
			
		3. also prey for dragonflies, damselfly nymphes, fish, amphibians, waterfowl
	
			
	D. Medical uses Sanguivorous leeches
	
		1. Important source for pharmacological products 
		
			a. anticoagulants and vasodilators for heart disease treatment
			
			b. extractions from leech salivary glands
		
		2. Treatment of Circulatory diseases
		
		3. Used in surgery 
		
			a. prevent bruising 
			
			b. reconstructive plastic surgery 
		
			c. re-attachment of amputated limbs.
		
		
	E. Segments - Functional Design
		
		1. Sexual organ = gonopore locations: body segments 5 and 6
								11 and 12?
			a. Hermaphroditic 
			                                
			b. Prostate and penis sheath in Segment 5
				
				i. 9-10 pairs of testes in body segments 7-15/16
				
			c. Female pore in Segment 6
				
				ii. Ovaries, oviduct gland, and vagina are caudal 
					cross anterior to the nerve cord
	
						
		2. Neural tissue - 34 ganglia - segmentally organized
			
			a. Ganglia form a chain 
				
				i. 6: main head segment à 21: body length à 7: main tail segment
				
				ii. Each segmental ganglion contains 400 neural cell bodies
				
					(1) non-polar neurons 10 - 60 mm diameter
				
					(2) similar cell appearance/relationships in all ganglia
					
					(3) central neuropil
					
						(a) contains passing axonal processes and neuritic trees
				
				iii. Nerve roots arise from each side of body ganglia
				
					(1) branch to innervate segmental structures of that region
			
				
			b. Connective nerves
			
				i. 2 large lateral fiber bundles 
				
				ii. thin medial connective - Faivre's nerve
				
				iii. covered by fibrous sheath - contains muscle fibers
					
			c. Entire nerve cord covered by ventral blood sinus (the "sock")
			
				i. Materials move freely and rapidly through the ganglion
				
				ii. ventral to alimentary canal

	
II. Leech Locomotory Behavior

	A. Benthic Leech Movements - Shortening
	
		1. Shortening  is a leech defensive behavior
		
			a. protecting anterior regions
			   including feeding area
			
			b. triggered by photic or mechanosensory stimuli
			
				i. in response to noxious stimuli
		
			
		2. Contraction of all body segments simultaneously
		
			a. Body wall contains 3 layers of muscle
		
				i. outermost layer: circumferential muscle fibers 
			
				ii. middle layer: oblique muscle fibers 
			
				iii. innermost: longitudinal layer 
			
					(1) thickest
					
					(2) discrete bands of fibers separated by connective tissue
					
					(3) contract to cause shortening
					
		3. Benthic Movement includes shortening and lengthening
	
		
	B. Pelagic movement - Swimming

		1. longitudinal muscle layer also are necessary for swimming