Behavioral Neuroscience, lecture on Leech and its behavior
Sensitization - Leech
III. Sensory Stimulation of Shortening back to Leeches and Behavior
A. Sensory Neurons - all Somatosensory
1. Respond specifically and selectively to mechanical stimuli
a. clearly defined receptive fields
i. circumscribed region of skin responds only to stimuli
b. T/P/N - Touch, Pressure and Pain cells have similar morphological features
i. Single process arises from cell body
(1) large 1o branches pass through neuropil
(a) leave the ganglion in peripheral nerve roots
(1) 2o processes different among T/P/N
2. Touch = T cell
a. mechanosensory/stretch resceptors
i. T/P not activated by temperature, acidity, or osmotic pressure
b. responds to light or heavier touch
c. simplest branching pattern
i. short 2o branches
ii. don't cross midline of ganglion
d. small - brief action potential
e. glutamatergic = secrretes glutamate (Glu)
i. AMPA and NMDA receptors (ionotropic)
3. Pressure = P cell
a. mechanosensory/stretch resceptors
b. responds to heavier pressure
i. not light touch
c. intermediate branching
d. bigger - longer action potentials
i. than T
e. Glu
i. AMPA & NMDA
ii. metabotropic (mGluR)
4. Nociceptive (pain) neurons = N cell
a. noxious mechanical stimulation of the skin
i. require stronger mechanical stimuli
b. elaborate branching
i. several 2o branches
ii. extending on both sides of the ganglion
c. larger longer action potentials (than T)
i. large after hyperpolarization (undershoot)
d. Glu
B. Sensory pathway to Shortening Reflex
1. Mechanosensory stimuli activates T/P/N
a. graded responses: T < P < N
2. T/P/N à S-cell
a. T/P/N release à Glu
i. Glu binds to S-cell AMPA and NMDA receptors
b. S cell = interneuron
c. + 2nd (unknown) intersegmental neural pathway
d. these 2 intersegmental neural pathways extend
from head ganglion along entire nerve
3. S ó R
a. R = Retzius cells are serotonergic cells
i. serotonin = 5-HT
(1) monoamine transmitter
ii. R = largest neurons in leech NS
4. S-cells à motor neurons (e.g. L-cells)